WO2025171279A9 - Treatment of hemophilia with fitusiran - Google Patents

Abstract

The present disclosure provides methods for using fitusiran to treat patients with hemophilia A or hemophilia B.

Description

TREATMENT OF HEMOPHILIA WITH FITUSIRAN

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the priority benefit of U.S. Provisional Application No. 63/552,026, filed February 9, 2024, U.S. Provisional Application No. 63/663,043, filed June 21, 2024, U.S. Provisional Application No. 63/678,006, filed July 31, 2024, U.S. Provisional Application No. 63/679,419, filed August 5, 2024, and U.S. Provisional Application No. 63/709,161, filed October 18, 2024, the content of each of which are incorporated herein by reference in their entireties.

REFERENCE TO AN ELECTRONIC SEQUENCE LISTING

[0002] The content of the electronic sequence listing (159792020540seqlist.xml; Size: 45,389 bytes; and Date of Creation: February 4, 2025) is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

[0003] Hemophilia A and hemophilia B are X-linked recessive inherited bleeding disorders, characterized by deficiency of coagulation Factor VIII (FVIII) or Factor IX (FIX), leading to a profound defect of thrombin generation with impaired hemostasis and increased risk of bleeding. Hemophilia A is found in approximately 1 in 4,000 males whereas hemophilia B is five times less common and seen in approximately 1 in 20,000 males. The disease phenotype presents similarly in hemophilia A and B.

[0004] Hemophilia is classified as mild (factor levels 6% to 30%), moderate (factor levels 1% to 5%), or severe (factor levels <1%) based on clotting factor activity relative to normal (healthy, non-hemophiliac plasma levels of factor are 50% to 150%). Patients with mild hemophilia typically experience bleeding after a serious injury or surgery. Patients with moderate hemophilia experience bleeding episodes associated with injuries, and may have spontaneous bleeding episodes. Severe hemophilia patients experience substantial bleeding with injury and may have frequent spontaneous bleeding episodes resulting in debilitating musculoskeletal damage that can markedly impair a patient’s mobility and quality of life (QoL).

[0005] The hemostatic system aims to maintain the integrity of the vasculature by protecting against bleeding from vessel lesions combined with multiple options to prevent thrombosis. This hemostatic balance is achieved through an orchestrated regulation of both procoagulant (e.g., Factor V (FV), Factor VII (FVII), FVIII, FIX, Factor X (FX)) and anticoagulant (e.g., antithrombin, protein C/protein S and tissue factor pathway inhibitor) factors. Recent studies have suggested that coinheritance of a deficiency in natural anticoagulants may contribute to a milder phenotype in patients with hemophilia.

[0006] Antithrombin (AT) is a liver-expressed natural anticoagulant that plays a key role in inhibiting thrombin. AT acts as an inhibitor of FVIIa and FXa, which are typically at normal levels in patients with hemophilia A or B. Extensive preclinical in vitro and in vivo studies have described reduction of AT as a potential safe and effective way to correct thrombin generation in both hemophilia A and B and control against microvascular and macrovascular traumatic bleeding episodes. Therefore, suppression of AT production is being investigated as a potential hemophilia treatment.

[0007] While the current standard of care with clotting factor substitution therapy, administered either episodically or as routine prophylaxis, is well established, safe, and efficacious, it is associated with high treatment burden due to requiring intravenous (IV) administration on a frequent schedule (two to three times per week or more) to prophylactically maintain hemostasis. Factor concentrates also can be of limited availability in developing nations. In addition, patients receiving factor concentrates may develop an inhibitory antibody to factor, a result that carries a poorer prognosis and requires a change in treatment regimen to infusion with bypassing agents (BPAs).

[0008] Hemophilia patients who develop inhibitory antibodies to factor concentrates represent a distinct subset of the population; these patients typically experience more difficult-to-treat bleeding episodes, leading to increased morbidity and increased mortality. Development of inhibitors to infused factor occurs mainly in severe hemophilia, and more frequently in hemophilia A (up to 39% of patients) than in hemophilia B (1% to 3.5% of patients) with the greatest risk of development in the early exposure days. These “inhibitor” patients, may be eligible for immune tolerance therapy; however, in most cases bleeding episodes require hemostatic intervention with intravenously (IV)-administered BPAs, i.e., recombinant Factor Vila (rVIIa), or activated prothrombin complex concentrates (aPCC), either as prophylaxis or as on-demand episodic treatment of bleeding episodes.

[0009] There remains a need for alternative treatments for patients having hemophilia, to prevent or reduce the frequency of bleeding episodes, while reducing treatment burden, improving clinical outcomes, and enhancing quality of life. SUMMARY OF THE INVENTION

[0010] The present disclosure provides a method of reducing the risk of a hepatobiliary event in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising: (a) subcutaneously administering to the patient in need thereof fitusiran at a starting dose amount at a selected dosing frequency; (b) obtaining a measurement of an antithrombin (AT) level in the patient; and (c) performing one of the following steps: (i) if the AT level is 15-35%, repeating step (a), (ii) if the AT level is >35%, subcutaneously administering to the patient fitusiran at a higher dose amount at the selected dosing frequency, or at the starting dose amount at a higher dosing frequency, or (iii) if the AT level is <15%, discontinuing or pausing fitusiran treatment. The present disclosure also provides a method of reducing the risk of a hepatobiliary event in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising subcutaneously administering to the patient in need thereof fitusiran at a dose of: about 50 mg about once a month or about every four weeks, about 20 mg about once a month or about every four weeks, about 50 mg about once every other month or about once every eight weeks, or about 20 mg about once every other month or about once every eight weeks. In some embodiments, the hepatobiliary event is alanine transaminase (ALT) elevation more than three times the upper limit of normal (ULN), aspartate aminotransferase (AST) elevation more than three times the ULN, severe liver toxicity, liver failure, cholecystitis, cholelithiasis, or a need for cholecystectomy. In some embodiments, the method further comprises administering an effective amount of a replacement factor or bypassing agent (BPA) to treat a bleeding episode, wherein the effective amount of the replacement factor or BPA is reduced as compared to the recommended effective amount of the replacement factor or BPA for patients who are not on fitusiran therapy.

[0011] The present disclosure also provides a method of reducing thrombotic risk in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising: (a) subcutaneously administering to the patient in need thereof fitusiran at a starting dose amount at a selected dosing frequency; (b) obtaining a measurement of an antithrombin (AT) level in the patient; and (c) performing one of the following steps: (i) if the AT level is 15-35%, repeating step (a), (ii) if the AT level is >35%, subcutaneously administering to the patient fitusiran at a higher dose amount at the selected dosing frequency, or at the starting dose amount at a higher dosing frequency, or (iii) if the AT level is <15%, discontinuing or pausing fitusiran treatment; wherein the patient is further administered an effective amount of replacement factor or bypassing agent (BPA) to treat a bleeding episode, wherein the effective amount of the replacement factor or BPA is reduced as compared to the recommended effective amount of the replacement factor or BPA for patients who are not on fitusiran therapy. Also provided is a method of routine prophylaxis to prevent or reduce the frequency of bleeding episodes in a human patient having hemophilia A or B with or without factor VIII or factor IX inhibitors, comprising: (a) subcutaneously administering to the patient in need thereof fitusiran at a starting dose amount at a selected dosing frequency; (b) obtaining a measurement of an antithrombin (AT) level in the patient; and (c) performing one of the following steps: (i) if the AT level is 15-35%, repeating step

(a), (ii) if the AT level is >35%, subcutaneously administering to the patient fitusiran at a higher dose amount at the selected dosing frequency, or at the starting dose amount at a higher dosing frequency, or (iii) if the AT level is <15%, discontinuing or pausing fitusiran treatment; wherein the patient is further administered an effective amount of replacement factor or bypassing agent (BPA) to treat a bleeding episode, wherein the effective amount of the replacement factor or BPA is reduced as compared to the recommended effective amount of the replacement factor or BPA for patients who are not on fitusiran therapy.

[0012] The present disclosure also provides a method of improving patient-reported outcome (PRO) or quality of life (QoL) in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising: (a) subcutaneously administering to the patient in need thereof fitusiran at a starting dose amount at a selected dosing frequency;

(b) obtaining a measurement of an antithrombin (AT) level in the patient; and (c) performing one of the following steps: (i) if the AT level is 15-35%, repeating step (a), (ii) if the AT level is >35%, subcutaneously administering to the patient fitusiran at a higher dose amount at the selected dosing frequency, or at the starting dose amount at a higher dosing frequency, or (iii) if the AT level is <15%, discontinuing or pausing fitusiran treatment. In some embodiments, the one or more QoL domains are domains in a QoL questionnaire, optionally wherein the QoL questionnaire is Haemophilia Quality of Life Questionnaire for Adults (Haem-A-QoL). The administering may result in a clinically meaningful improvement indicated by a reduction of 7.1 or more units (optionally 8 or more, 9 or more, 10 or more, or 11 or more units) in the Total Score or a reduction of 10 or more units (optionally 11 or more, 12 or more, 13 or more, or 14 or more units) in the Physical Health domain score of the questionnaire.

[0013] In some embodiments, the bleeding episode is a major surgery, optionally wherein the patient is a patient not being treated with AT replacement therapy before, during, or after surgery. The major surgery may be an opening into a major body cavity (e.g., abdomen, thorax, or skull), operation on a joint, removal of an organ, operative alteration of normal anatomy, crossing of a mesenchymal barrier (e.g., pleura, peritoneum, or dura), dental extraction of molar teeth or >3 nonmolar teeth, or tooth implantation.

[0014] In some embodiments, the patient is a hemophilia A patient without factor VIII inhibitors. In some embodiments, the replacement factor is factor VIII (FVIII) and a single dose of FVIII is no more than 20 lU/kg and optionally is 10 lU/kg, optionally wherein the FVIII administration is repeated, if needed, in no less than 24 hours.

[0015] In some embodiments, the human patient is a hemophilia B patient without factor IX inhibitors. In some embodiments, the replacement factor is factor IX (FIX) and a single dose of FIX is no more than 30 lU/kg and optionally is 20 lU/kg, optionally wherein the Factor IX administration is repeated, if needed, in no less than 24 hours for standard half-life FIX or in no less than 5-7 days for extended half-life FIX.

[0016] In some embodiments, the human patient is a hemophilia A patient with factor VIII inhibitors. The human patient may be a hemophilia B patient with factor IX inhibitors. In some embodiments, the BPA is activated prothrombin complex concentrate (aPCC) and a single dose of aPCC is no more than 50 U/kg and optionally is 30 U/kg, optionally wherein the aPCC administration is repeated, if needed, in no less than 24 hours. In some embodiments, the BPA is recombinant factor Vila (rFVIIa) and a single dose of rFVIIa is no more than 45 pg/kg, optionally wherein the rFVIIa administration is repeated, if needed, in no less than two hours.

[0017] In some embodiments, the patient has been on prophylactic treatment with a replacement factor or a bypassing agent (BPA), and wherein the method comprises terminating the prophylactic replacement factor or BPA treatment in the human patient within about two weeks or about 14 days or about one week or about seven days of the first dose of fitusiran.

[0018] In some embodiments, the dose of fitusiran is administered to the human patient about once a month or about every four weeks or about once every other month or about once every eight weeks. In some embodiments, the dose of fitusiran is administered to the human patient at a dose of about 10 to about 100 mg, optionally about 80 mg, about 50 mg, or about 20 mg. [0019] In some embodiments, the starting dose amount of fitusiran is about 50 mg. In some embodiments, the selected dosing frequency is every two months (Q2M) or every eight weeks (Q8W), optionally wherein the higher dosing frequency is every month (QM) or every four weeks (Q4W). In some embodiments, the starting dose amount is 50 mg and the selected dosing frequency is Q2M or Q8W, optionally wherein step (c)(ii) is performed if two measurements of the AT level are >35% or if the AT level is >35% six months after the prior dose, or step (c)(iii) is performed if more than one measurement, optionally two measurements, of the AT level is <15%. In some embodiments, step (c)(ii) comprises subcutaneously administering to the patient fitusiran at 50 mg QM. In some embodiments, the method comprises, after step (c)(ii), subcutaneously administering to the patient fitusiran at 80 mg QM if the AT level in the patient after step (c)(ii) is >35%, optionally according to two measurements. In some embodiments the method comprises, after step (c)(iii): (A) subcutaneously administering fitusiran to the patient at 20 mg Q2M, optionally wherein the 20 mg dose is administered three months after the prior dose; (B) if the AT level of the patient after step (A) is <15%, optionally according to more than measurement, discontinuing fitusiran treatment, 15-35%, repeating step (A), or >35%, optionally according to two measurements, subcutaneously administering to the patient fitusiran at 20 mg QM.

[0020] In some embodiments, each AT level measurement is obtained after the patient has received at least two doses of fitusiran at a given dose amount.

In some embodiments, the method comprises obtaining a measurement of AT level in the patient every four weeks, every eight weeks, every month, every two months, every four months, every six months, or every 12 months. In some embodiments, the method comprises obtaining a measurement of AT level in the human patient at four weeks or one month, twelve weeks or three months, 20 weeks or five months, and 24 weeks or six months following administration of the starting dose or following administration of a modified dose as compared to the prior dose. In some embodiments, obtaining a measurement of the AT level in the human patient comprises use of a kinetic or chromogenic assay. In some embodiments, obtaining a measurement of the AT level in the human patient comprises use of a chromogenic assay that quantifies functionally active AT in human citrated plasma based on the inhibition of an excess of factor Xa by AT. In some embodiments, obtaining a measurement of the AT level in the human patient comprises use of an INNO VANCE™ Antithrombin assay.

[0021] In some embodiments, the method further comprises subcutaneously administering fitusiran to the patient at a dose amount and a dosing frequency sufficient to maintain the AT level in the patient at 15-35%, optionally comprising subcutaneously administering fitusiran at: 10 mg QM or Q4W, 20 mg QM or Q4W, 20 mg Q2M or Q8W, 50 mg QM or Q4W, 50 mg Q2M or Q8W, or80 mg QM or Q4W.

[0022] In some embodiments, the method further comprises obtaining a liver function test in the human patient every two months following initiation of fitusiran treatment, optionally wherein the liver function test is an aspartate transaminase or alanine aminotransferase test, further optionally wherein the liver function test is obtained every two months for the first six months following initiation of fitusiran treatment.

[0023] In some embodiments, the method further comprises obtaining a liver function test in the human patient (i) prior to administering the starting dose of fitusiran to determine a baseline level of liver function; and (ii) every month following initiation of fitusiran treatment, optionally wherein the liver function test is an aspartate transaminase or alanine aminotransferase test, further optionally wherein the liver function test is obtained every month for the first six months following initiation of fitusiran treatment.

[0024] In some embodiments, the method further comprises discontinuing or pausing fitusiran treatment if the aspartate transaminase or alanine aminotransferase test shows aspartate transaminase or alanine aminotransferase levels that are progressing or are persistent and five times the upper limit of normal, optionally wherein fitusiran treatment is resumed if the aspartate transaminase or alanine aminotransferase test shows aspartate transaminase or alanine aminotransferase levels have returned to baseline level.

[0025] In some embodiments, the method further comprises discontinuing or pausing fitusiran treatment if the human patient is diagnosed with gallbladder disease, optionally wherein the gallbladder disease comprises cholecystitis, cholelithiasis, or a need for cholecy stectomy .

[0026] In some embodiments, the patient does not have (i) clinically significant liver disease, (ii) ALT >1.5x upper limit of normal reference range (ULN), (iii) AST >1.5x upper limit of normal reference range (ULN), (iv) hepatitis C, (v) hepatitis A, (vi) hepatitis E, and/or (vii) hepatitis B. In some embodiments, the patient is an adult or adolescent patient twelve years or older.

[0027] In some embodiments, the disclosure provides a method of reducing the risk of a hepatobiliary event in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising (a) subcutaneously administering to the human patient in need thereof fitusiran at a starting dose of 50 mg every two months; (b) obtaining a measurement of an antithrombin (AT) level in the human patient; and (c) performing one of the following steps: (i) if the AT level is 15-35%, repeating step (a),

(ii) if the AT level is >35% after six months, subcutaneously administering to the human patient fitusiran at 50 mg every month, or (iii) if the AT level is <15%, subcutaneously administering to the human patient fitusiran at 20 mg every two months.

[0028] In some embodiments, the disclosure provides a method of reducing the risk of a hepatobiliary event in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising (a) subcutaneously administering to the human patient in need thereof fitusiran at a modified dose of 20 mg every two months; (b) obtaining a measurement of an antithrombin (AT) level in the human patient; and (c) performing one of the following steps: (i) if the AT level is 15-35%, repeating step (a),

(ii) if the AT level is >35% after six months, subcutaneously administering to the human patient fitusiran at 20 mg every month, or (iii) if the AT level is <15%, pausing or discontinuing fitusiran treatment.

[0029] In some embodiments, the disclosure provides a method of improving PRO or QoL in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising (a) subcutaneously administering to the human patient in need thereof fitusiran at a starting dose of 50 mg every two months; (b) obtaining a measurement of an antithrombin (AT) level in the human patient; and (c) performing one of the following steps:

(i) if the AT level is 15-35%, repeating step (a),

(ii) if the AT level is >35% after six months, subcutaneously administering to the human patient fitusiran at 50 mg every month, or (iii) if the AT level is <15%, subcutaneously administering to the human patient fitusiran at 20 mg every two months.

[0030] In some embodiments, the disclosure provides a method of improving PRO or QoL in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising (a) subcutaneously administering to the human patient in need thereof fitusiran at a modified dose of 20 mg every two months; (b) obtaining a measurement of an antithrombin (AT) level in the human patient; and (c) performing one of the following steps: (i) if the AT level is 15-35%, repeating step (a), (ii) if the AT level is >35% after six months, subcutaneously administering to the human patient fitusiran at 20 mg every month, or (iii) if the AT level is <15%, pausing or discontinuing fitusiran treatment.

[0031] In some embodiments, the disclosure provides a method of reducing thrombotic risk in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising (a) subcutaneously administering to the human patient in need thereof fitusiran at a starting dose of 50 mg every two months; (b) obtaining a measurement of an antithrombin (AT) level in the human patient; and (c) performing one of the following steps:

(i) if the AT level is 15-35%, repeating step (a),

(ii) if the AT level is >35% after six months, subcutaneously administering to the human patient fitusiran at 50 mg every month, or (iii) if the AT level is <15%, subcutaneously administering to the human patient fitusiran at 20 mg every two months, wherein the human patient is further administered an effective amount of replacement factor or bypassing agent (BPA) to treat a bleeding episode that occurs eight or more days after the first fitusiran dose, wherein the effective amount of the replacement factor or BPA is reduced as compared to the recommended effective amount of the replacement factor or BPA for human patients who are not on fitusiran therapy.

[0032] In some embodiments, the disclosure provides a method of reducing thrombotic risk in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising (a) subcutaneously administering to the human patient in need thereof fitusiran at a modified dose of 20 mg every two months; (b) obtaining a measurement of an antithrombin (AT) level in the human patient; and (c) performing one of the following steps:

(i) if the AT level is 15-35%, repeating step (a),

(ii) if the AT level is >35% after six months, subcutaneously administering to the human patient fitusiran at 20 mg every month, or (iii) if the AT level is <15%, pausing or discontinuing fitusiran treatment, wherein the human patient is further administered an effective amount of replacement factor or bypassing agent (BPA) to treat a bleeding episode that occurs eight or more days after the first fitusiran dose, wherein the effective amount of the replacement factor or BPA is reduced as compared to the recommended effective amount of the replacement factor or BPA for human patients who are not on fitusiran therapy.

[0033] In some embodiments, the disclosure provides a method of routine prophylaxis to prevent or reduce the frequency of bleeding episodes in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising (a) subcutaneously administering to the human patient in need thereof fitusiran at a starting dose of 50 mg every two months; (b) obtaining a measurement of an antithrombin (AT) level in the human patient; and (c) performing one of the following steps: (i) if the AT level is 15- 35%, repeating step (a),

(ii) if the AT level is >35% after six months, subcutaneously administering to the human patient fitusiran at 50 mg every month, or (iii) if the AT level is <15%, subcutaneously administering to the human patient fitusiran at 20 mg every two months, wherein the human patient is further administered an effective amount of replacement factor or bypassing agent (BPA) to treat a bleeding episode that occurs eight or more days after the first fitusiran dose, wherein the effective amount of the replacement factor or BPA is reduced as compared to the recommended effective amount of the replacement factor or BPA for human patients who are not on fitusiran therapy.

[0034] In some embodiments, the disclosure provides a method of routine prophylaxis to prevent or reduce the frequency of bleeding episodes in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising (a) subcutaneously administering to the human patient in need thereof fitusiran at a modified dose of 20 mg every two months; (b) obtaining a measurement of an antithrombin (AT) level in the human patient; and (c) performing one of the following steps: (i) if the AT level is 15- 35%, repeating step (a),

(ii) if the AT level is >35% after six months, subcutaneously administering to the human patient fitusiran at 20 mg every month, or (iii) if the AT level is <15%, pausing or discontinuing fitusiran treatment, wherein the human patient is further administered an effective amount of replacement factor or bypassing agent (BPA) to treat a bleeding episode that occurs eight or more days after the first fitusiran dose, wherein the effective amount of the replacement factor or BPA is reduced as compared to the recommended effective amount of the replacement factor or BPA for human patients who are not on fitusiran therapy.

[0035] In some embodiments, the disclosure provides a method of reducing thrombotic risk in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising (a) subcutaneously administering to the human patient in need thereof fitusiran at a starting dose of 50 mg every two months; (b) obtaining a measurement of an antithrombin (AT) level in the human patient; and (c) performing one of the following steps:

(i) if the AT level is 15-35%, repeating step (a),

(ii) if the AT level is >35% after six months, subcutaneously administering to the human patient fitusiran at 50 mg every month, or (iii) if the AT level is <15%, subcutaneously administering to the human patient fitusiran at 20 mg every two months, wherein the human patient is further administered an effective amount of replacement factor or bypassing agent (BPA) to treat a bleeding episode that occurs seven or fewer days after the first fitusiran dose, wherein the effective amount of the replacement factor or BPA is administered according to the human patient’s prior dosing regimen of replacement factor or BPA.

[0036] In some embodiments, the disclosure provides a method of reducing thrombotic risk in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising (a) subcutaneously administering to the human patient in need thereof fitusiran at a modified dose of 20 mg every two months; (b) obtaining a measurement of an antithrombin (AT) level in the human patient; and (c) performing one of the following steps:

(i) if the AT level is 15-35%, repeating step (a),

(ii) if the AT level is >35% after six months, subcutaneously administering to the human patient fitusiran at 20 mg every month, or (iii) if the AT level is <15%, pausing or discontinuing fitusiran treatment, wherein the human patient is further administered an effective amount of replacement factor or bypassing agent (BPA) to treat a bleeding episode that occurs seven or fewer days after the first fitusiran dose, wherein the effective amount of the replacement factor or BPA is administered according to the human patient’s prior dosing regimen of replacement factor or BPA.

[0037] In some embodiments, the disclosure provides a method of routine prophylaxis to prevent or reduce the frequency of bleeding episodes in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising (a) subcutaneously administering to the human patient in need thereof fitusiran at a starting dose of 50 mg every two months; (b) obtaining a measurement of an antithrombin (AT) level in the human patient; and (c) performing one of the following steps: (i) if the AT level is 15- 35%, repeating step (a),

(ii) if the AT level is >35% after six months, subcutaneously administering to the human patient fitusiran at 50 mg every month, or (iii) if the AT level is <15%, subcutaneously administering to the human patient fitusiran at 20 mg every two months, wherein the human patient is further administered an effective amount of replacement factor or bypassing agent (BPA) to treat a bleeding episode that occurs seven or fewer days after the first fitusiran dose, wherein the effective amount of the replacement factor or BPA is administered according to the human patient’s prior dosing regimen of replacement factor or BPA.

[0038] In some embodiments, the disclosure provides a method of routine prophylaxis to prevent or reduce the frequency of bleeding episodes in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising (a) subcutaneously administering to the human patient in need thereof fitusiran at a modified dose of 20 mg every two months; (b) obtaining a measurement of an antithrombin (AT) level in the human patient; and (c) performing one of the following steps: (i) if the AT level is 15- 35%, repeating step (a),

(ii) if the AT level is >35% after six months, subcutaneously administering to the human patient fitusiran at 20 mg every month, or (iii) if the AT level is <15%, pausing or discontinuing fitusiran treatment, wherein the human patient is further administered an effective amount of replacement factor or bypassing agent (BPA) to treat a bleeding episode that occurs seven or fewer days after the first fitusiran dose, wherein the effective amount of the replacement factor or BPA is administered according to the human patient’s prior dosing regimen of replacement factor or BPA.

[0039] Fitusiran may be provided in a phosphate-buffered saline (PBS) at 50-200 mg/mL, optionally 100 mg/mL, and optionally wherein the PBS has a pH of 7.

[0040] The present disclosure also provides fitusiran for use in any one of the present methods, as well as use of fitusiran in the manufacture of a medicament for use in any one of the present methods. A pharmaceutical composition comprising fitusiran for use in any one of the present methods is also provided.

[0041] The present disclosure also provides an article of manufacture for use in any one of the present methods. In some embodiment the article of manufacture is a kit. In some embodiments, the article of manufacture is a container containing one or more doses of fitusiran, each dose being 80 mg, 50 mg, 20 mg, or 10 mg, optionally wherein the 80 mg of fitusiran is in 0.8 mL of a phosphate-buffered saline (PBS), the 50 mg of fitusiran is in 0.5 mL of a PBS, the 20 mg of fitusiran is in 0.2 mL of a PBS, or the 10 mg of fitusiran is in 0.1 mL of a PBS, and optionally wherein the PBS has a pH of 7. In some embodiments, the article of manufacture is a single-use, single-dose prefilled syringe. In some embodiments, the article of manufacture is a single-use glass vial. [0042] Other features, objectives, and advantages of the invention are apparent in the detailed description that follows. It should be understood, however, that the detailed description, while indicating embodiments and aspects of the invention, is given by way of illustration only, not limitation. Various changes and modification within the scope of the invention will become apparent to those skilled in the art from the detailed description.

BRIEF DESRIPTION OF THE FIGURES

[0043] FIG. 1 shows the expanded structural formula, chemical formula, and molecular mass of fitusiran sodium, including SEQ ID NOS: 1 and 2.

[0044] FIG. 2 is a flow chart showing the risk mitigation strategy for vascular thrombotic events. “AT”: antithrombin activity; “QM”: once monthly; “Q2M”: every second month;

“ss”: steady state. After discontinuing fitusiran due to AT levels <15% at a dose of 50 mg Q2M, patients are eligible to resume treatment with 20 mg Q2M fitusiran, optionally if their AT level is 22%. There is no requirement to measure AT levels monthly after a dose change unless it is a change from 50 mg Q2M to 20 mg Q2M in which case the measurements restart for a year. ^aFor participants eligible for cohort, start of dosing after de- escalation from higher dose to occur only after centrally measured AT activity levels %22%’. ^bClinical criteria for dose escalation at AT activity levels <35% may also be considered.

Tarticipants receiving fitusiran at a dose of 20 mg Q2M who experience 1 AT level <15% (as per central laboratory) within a 12-month period must permanently discontinue fitusiran treatment. AT, antithrombin; AT-DR, AT-based dose regimen; QM, once monthly; Q2M, once every other month; SS, steady state.

[0045] FIG. 3 is a diagram showing the design for the study of patients with inhibitors. Abbreviations are as follows: BPA, bypassing agent; HA, hemophilia type A; HB, hemophilia type B; R, randomized. In the on-demand arm, patients are treated with on- demand factor concentrates as routinely prescribed by physician per local standard practice. [0046] FIG. 4 is a diagram showing the design for the study of patients without inhibitors. Abbreviations are as described in FIG. 3.

[0047] FIG. 5 is a diagram showing the participant disposition of patients enrolled in the Phase 3 clinical trial of fitusiran in Hemophilia A and B patients with inhibitors.

[0048] FIG. 6 shows the clinical trial study design for patients who are treated prophylactically with replacement factor or BPA before beginning fitusiran treatment. For subgroup of Cohort A patients enrolling directly into the fitusiran treatment period, see FIG. 7. “a”: patients will continue to receive prescribed factor or BPA prophylaxis for the first 7 days of the onset period. “ZJ”: following final fitusiran dose, AT activity level will be monitored at monthly intervals following the final fitusiran dose until activity levels return to approximately 60% (per the central laboratory) or per Investigator discretion in consultation with the study Medical Monitor.

[0049] FIG. 7 shows the clinical trial study design for hemophilia B patients with inhibitory antibodies to Factor IX who are also not responding adequately to BPA prophylaxis treatment (historical annualized bleeding rate (ABR) >20), and are therefore not currently undergoing prophylactic treatment with BPA. These patients directly begin fitusiran treatment without participating in the six-month factor/BPA period described in FIG. 6. “a”: patients will receive prescribed factor or BPA prophylaxis for the first 7 days of the onset period. “Z?”: same meaning as in FIG. 6.

[0050] FIG. 8 shows the antithrombin-driven dose escalation process. Abbreviations: BL, baseline; D, Day; M, Month; PR, post-restart. If any of the prior doses are missed, or if any of the relevant central AT values are not available, then the decision-making for escalation must be shifted accordingly.

[0051] FIG. 9 shows the antithrombin-driven dose escalation process for lower dose cohort participants. If any of the prior doses are missed or relevant central AT values are not available, then the decision-making for escalation must be shifted accordingly.

[0052] FIG. 10A shows the safety analyses performed in the Phase 1 and 1/2 OLE studies of fitusiran and the breakthrough bleed management guidelines (BMG) introduced to mitigate the risk of thrombotic events during the Phase 2 study. Tour healthy volunteers are not counted; ^bFor situations requiring higher doses, more frequent administration, or multiple repeat doses, clinical judgment should be used. Adjunctive management of bleeding episodes and cases of thrombosis should be carried out per standard of care. aPCC, activated prothrombin complex concentrate; BMG, breakthrough bleed management guidelines; BPA, bypassing agent; CFC, clotting factor concentrate; EHL, extended half-life; ODR, original dose regimen; OLE, open-label extension; PK, pharmacokinetics; PD, pharmacodynamics; QM, once monthly; rFVIIa, recombinant activated factor; SHL, standard half-life. FIG. 10B shows the incidence of thrombotic events in the phase 3 studies and the resulting revision of dosing strategy, ^rivastava A, et al. Lancet Haematol (2023) 10:e322-32; ²Young G, et al. Lancet (2023) 401:1427-37; ³Kenet G, et al. Blood. (2024) blood.2023021864.

[0053] FIG. 11 shows the incidence of thrombotic events in patients treated with the original dose regimen compared to patients treated with the AT-based dose regimen. Safety analyses included all participants exposed to fitusiran. Exposure adjusted incidence rate = # of participants with events/participant year of exposure *per 100 participant-years. AT, antithrombin; AT-DR, AT-based dose regimen; PY, participant-years; TEAE, treatment- emergent adverse event.

[0054] FIG. 12 shows incidents of thrombosis in patients treated with the original dosing regimen. ^aAs reported by the investigator; verbatim: thrombophlebitis superficial; ^bRisk factors include CV risk factors, CVAD-related risk factors, and non-compliance with BMG. AT, antithrombin; BMG, bleed management guidelines; CV, cardiovascular; CVAD, central venous access device; DVT, deep vein thrombosis; F, factor; HCV, hepatitis C virus; HIV, human immunodeficiency virus; MoA, mechanism of action; rFVIIa, recombinant activated factor VII; TE, thrombotic event.

[0055] FIG. 13 shows thrombotic events observed in patients treated with the AT-based dosing regimen. All thrombotic events with the fitusiran AT-DR had multiple risk factors. Antithrombin concentrate (ATIIIIc) has not been used for any of the thrombotic events. ^aNo thrombolytic treatment. aPCC, activated prothrombin complex concentrate; AT, antithrombin; AT-DR, AT-based dose regimen; BID, twice daily; BMG bleed management guidelines; CV, cardiovascular; CVAD, central venous access device; DVT, deep vein thrombosis; F, factor; IU, International units; MRI, magnetic resonance imaging; PIV, peripheral intravenous; PwH, people with hemophilia.

[0056] FIGS. 14A and 14B show the venous thromboembolism incidence rate per 100 participant-years (FIG. 14A) and the arterial thrombosis incident rate per 100 participant- years (FIG. 14B). CI, confidence interval; HA/HB, hemophilia A/B; IR, incidence rate; PwH, people with hemophilia; PY, participant-years; VTE, venous thromboembolism.

[0057] FIG. 15A shows hemostatic outcomes of major surgeries conducted while on fitusiran prophylaxis in participants with inhibitors. FIG. 15B shows hemostatic outcomes of major surgeries conducted while on fitusiran prophylaxis in participants without inhibitors. FIG. 15C shows hemostatic control, mean perioperative consumption of factor/BPA, and postoperative thrombosis in major surgeries conducted in patients treated with fitusiran. FIG. 15D shows the hemostatic outcomes of major surgeries in patients with and without inhibitors, including three surgeries that were conducted without additional CFC/BPA; ^bIncluding one surgery that was conducted without additional CFC/BPA; ^cHemostatic assessment not performed in eight participants; ^dHemostatic assessment not performed in one participant; ^eHemostatic assessment not performed in six participants; ^fHemostatic assessment not performed in one participant. FIG. 15E compares the hemostatic outcomes of major surgeries in participants receiving the original dose regimen compared to the AT-based dose regimen, including three surgeries that were conducted without additional CFC/BPA; ^bIncluding one surgery that was conducted without additional CFC/BPA; ^cHemostatic assessment not done for four participants; ^dHemostatic assessment not done for one participant; ^eHemostatic assessment not done for ten participants; ^fHemostatic assessment not done for one participant.

[0058] FIG. 16 shows the liver function trajectories in two participants treated with fitusiran.

[0059] FIG. 17 shows the study design for the ATLAS-OLE study. ^aUp to 60 days (under certain circumstances, screening may have been extended beyond 60 days following consultation with the Sponsor). Screening period after voluntary pause included participants that first started fitusiran dosing in this study after the dosing pause; ^bAn open-label treatment period that varies depending on the timing of participant’s restart after the dosing pause in October 2020 - participants that first started fitusiran dosing in this study after the dosing pause were planned to have a maximum treatment duration of up to 48 months; participants that had started fitusiran before the 2020 dosing pause were planned to have a maximum treatment duration of up to 76 months; ^c10 participants were fitusiran naive; AT-DR, revised antithrombin-based dose regimen; ODR, original dose regimen; SC, subcutaneous.

[0060] FIG. 18 shows participant disposition in the ATLAS-OLE trial.

[0061] FIG. 19 shows the baseline characteristics were balanced across the ATLAS-OLE study population.

[0062] FIG. 20 shows the AT value by visit during the primary efficacy period in the ATLAS-OLE trial.

[0063] FIG. 21 shows exposure to fitusiran in the ATLAS-OLE trial.

[0064] FIG. 22 shows the overall safety profile in the ATLAS-OLE trial.

[0065] FIG. 23 shows a summary of TEAEs in the AT-DR treatment period.

[0066] FIG. 24 shows the incidence of thrombotic events in the ATLAS-OLE trail.

[0067] FIG. 25 shows the characteristics of thrombotic events observed in patients treated with the fitusiran AT-DR.

[0068] FIG. 26 shows TEAESIs in the AT-DR treatment period.

[0069] FIG. 27 shows the observed median ABR in patients treated with the fitusiran AT-DR.

[0070] FIG. 28 shows the observed median ABR during the primary treatment period.

[0071] FIG. 29 shows the observed median AsBR in patients treated with the fitusiran AT-DR.

[0072] FIG. 30 shows the observed median AjBR in patients treated with the fitusiran AT-DR.

[0073] FIG. 31 shows three pools each representing a subset of participants from the ATLAS-OLE study. ^apatients treated with antithrombin-based dose regimen (AT-DR). ^bNo formal statistical testing; family-wise error rate is controlled at 0.05 by hierarchical test procedure. BPA, bypassing agent; CFC, clotting factor concentrates; FAS, full analysis set; ITT, intention-to-treat.

[0074] FIG. 32 shows the estimated mean ABR for treated bleeds in patients with hemophilia A or B with inhibitors

[0075] FIG. 33 shows the estimated mean ABR for treated bleeds in patients with hemophilia A or B without inhibitors

[0076] FIG. 34 shows ABR for treated bleeds in patients with hemophilia A or B with inhibitors.

[0077] FIG. 35 shows ABR for treated bleeds in patients with hemophilia A or B without inhibitors.

[0078] FIG. 36 shows the estimated mean ABR for treated bleeds in patients with hemophilia A or B with inhibitors.

[0079] FIG. 37 shows the estimated mean ABR for treated bleeds in patients with hemophilia A or B without inhibitors.

[0080] FIG. 38 shows ABR for treated bleeds in patients with hemophilia A or B with inhibitors.

[0081] FIG. 39 shows ABR for treated bleeds in patients with hemophilia A or B without inhibitors.

[0082] FIG. 40 shows annualized spontaneous bleeding rate (AsBR) for treated bleeds in patients with hemophilia A or B with inhibitors.

[0083] FIG. 41 shows AsBR for treated bleeds in patients with hemophilia A or B without inhibitors.

[0084] FIG. 42 shows AsBR for treated bleeds in patients with hemophilia A or B with inhibitors.

[0085] FIG. 43 shows AsBR for treated bleeds in patients with hemophilia A or B without inhibitors.

[0086] FIG. 44 shows annualized joint bleeding rate (AjBR) for treated bleeds in patients with hemophilia A or B with inhibitors.

[0087] FIG. 45 shows AjBR for treated bleeds in patients with hemophilia A or B without inhibitors.

[0088] FIG. 46 shows AjBR for treated bleeds in patients with hemophilia A or B with inhibitors.

[0089] FIG. 47 shows AjBR for treated bleeds in patients with hemophilia A or B without inhibitors.

[0090] FIG. 48 shows AsBR for treated bleeds in patients with hemophilia A or B with or without inhibitors.

[0091] FIG. 49 shows AjBR for treated bleeds in patients with hemophilia A or B with or without inhibitors.

[0092] FIG. 50 shows AsBR for treated bleeds in patients with hemophilia A or B with or without inhibitors.

[0093] FIG. 51 shows AjBR for treated bleeds in patients with hemophilia A or B with or without inhibitors.

[0094] FIG. 52 shows Haem-A-QoL physical health scores.

[0095] FIG. 53 show Haem-A-QoL physical health scores.

[0096] FIG. 54 shows treatment of breakthrough bleeds in patients on the AT-DR regimen vs. BPA/CFC prophylaxis

[0097] FIG. 55 shows the relationship between median ABR and AT levels.

[0098] FIG. 56 shows a summary of the completed Phase 3 trials of fitusiran (original dose regimen). ^bPrimary efficacy endpoint was ABR. Information presented here is intended as a summary of these trials only - direct comparisons cannot be made between trials. ABR, annualized bleeding rate; AsBR, annualized spontaneous bleeding rate; AjBR, annualized joint bleeding rate; AT, antithrombin; BPA, bypassing agent; CFC, clotting factor concentrate; OD, on demand; PPX, prophylaxis; PwH, people with hemophilia; SD, standard deviation. 'Young G, et al. Lancet (2023) 401:1427-37; ²Srivastava A, et al. Lancet Haematol (2023) 10:e322-32; ³Kenet G, et al. Blood (2024) blood.2023021864.

[0099] FIG. 57 shows a summary of the completed and ongoing Phase 3 trials. Abbreviations are as in FIG. 51. ^b Additionally, 54 de-novo participants from China were enrolled; interim ATLAS-OLE study results focus on participants who previously completed a Phase 3 study; Trimary efficacy endpoint was ABR. Information presented here is intended as a summary of these trials only - direct comparisons cannot be made between trials. 'Young G, et al. Lancet (2023) 401:1427-1437; ²Srivastava A, et al. Lancet Haematol (2023) 10:e322-e332; ³Kenet G, et al. Blood (2024) blood.2023021864; ⁴Young G, et al. Presented at EAHAD 2024. Oral presentation.

[0100] FIG. 58 shows the design of the fitusiran phase 2 open-label extension (OLE) study. *Phase 1, NCT02035605; Phase 2 OLE, NCT02554773; ⁺A total of five subjects in Part C previously participated in Part B. *A total of three subjects started the Phase 2 OLE at their original phase 1 dose; later they were converted to 50 mg or 80 mg. Patients were eligible for Phase 2 if they completed and tolerated fitusiran treatment in Phase 1. ^§ A change in the fitusiran dosing regimen was introduced as a risk mitigation measure for vascular thrombotic events. ABR, annualized bleed rate; AT, antithrombin; HA, hemophilia A; HB, hemophilia B; OLE, open-label extension; PK, pharmacokinetics; QM, monthly; Q2M, every other month; QOL, quality of life; SC, subcutaneous.

[0101] FIG. 59 shows the dose modification rules for patients in the phase 2 OLE study treated on the antithrombin [AT]-based dose-regimen. *Patients currently on a dose of 50 mg or 80 mg QM, with no more than one AT level <15% based on ^3 months of AT data, may remain on their current 50 or 80 mg QM dose. AT, antithrombin; QM, once monthly; Q2M, every second month; SS, steady state. Note: Restart following dosing pause to occur only once centrally measured AT activity levels %22%’.

[0102] FIG. 60 shows the patient disposition in the phase 2 OLE trial. *One participant required dose escalation to 50 mg QM as per investigator decision, not due to antithrombin activity levels >35%. AE, adverse event; AT, antithrombin; SAE, serious adverse event; QM, once monthly; Q2M, every second month; SC, subcutaneous.

[0103] FIG. 61 shows the annualized bleed rate (ABR) during efficacy periods 1 and 2 in the phase 2 OLE trial.

[0104] FIG. 62 shows the spontaneous annualized bleed rate in the phase 2 OLE trial.

[0105] FIG. 63 shows the joint annualized bleed rate in the phase 2 OLE trial.

[0106] FIGS. 64A and 64B are spaghetti plots showing antithrombin (AT) (%) activity level over time (FIG. 64A) and peak thrombin (nM) over time (FIG. 64B) in the phase 2 OLE trial.

[0107] FIGS. 65A and 65B show the mean change in antithrombin (AT) (%) level from baseline under the original dose regimen (FIG. 65A) and mean change in AT (%) level from baseline under the AT-based dose regimen (FIG. 65B) in all patients in the phase 2 OLE trial.

[0108] FIGS. 66A and 66B show the mean change in peak thrombin (nmol/L) level from baseline under the original dose regimen (FIG. 66A) and mean change in peak thrombin (nmol/L) level from baseline under the AT-based dose regimen (FIG. 66B) in all patients in the phase 2 OLE trial.

[0109] FIG. 67 shows the change from baseline in Haem-A-QoL domains in the phase 2 OLE trial. *A reduction of 7.1 points in ‘Total Score’ is regarded as a clinically meaningful improvement and is depicted by the dashed line, f A reduction of 10 points in ‘Physical Health’ is regarded as a clinically meaningful improvement and is depicted by the dashed line. Baseline was defined as last non-missing assessment on or before the first significant dose. Under the original dose regimen the mean change in baseline was through 24 months (n=14). Under the AT-based dose regimen the mean change from baseline was through 12 months (n=9). AT, antithrombin; QoL, quality of life; SD, standard deviation.

[0110] FIG. 68 shows the Haem-A-QoL five-point Likert scale and the Haem-A-QoL quality of life domain scores.

[0111] FIG. 69 shows the meaningful change thresholds for physical health and total scores in the Haem-A-QoL.

[0112] FIG. 70 shows the severity thresholds for physical health and total scores in the Haem-A-QoL.

[0113] FIG. 71 shows the distribution of Haem-A-QoL physical health score according to EQ-5D-5L (A) pain/discomfort and (B) usual activity. Data was from the pooled ATLAS- OLE study. EQ-5D-5L: EuroQol-5 Dimensions-5 Levels Questionnaire; Haem-A-QoL: Hemophilia Quality of Life Questionnaire for Adults. No categories were classified as “very severe”. In the shaded boxes, “o” represents the mean, while the horizontal line indicates the median. The horizontal line spanning the length of the graph indicates severity threshold. The bottom and top edges of the box denote lower and upper quartiles, respectively. The whiskers extending from the box show variability beyond the lower and upper quartiles. The outliers, denoted by “o”, are data points lying outside the whiskers and were plotted individually, suggesting data characteristics.

[0114] FIG. 72 shows the cumulative distribution function of change from baseline in the primary treatment period in Haem-A-QoL transformed physical health score (Panel A) and total score (Panel B) by indication for participants 17 years of age. The primary treatment period is from the dose restart day 169. The analysis is based on while on-treatment strategy which excluded the related measurements in the period of intercurrent events. The scores are presented as the Transformed Scale Score (TSS) ranging from 0 - 100, with lower scores indicating a better quality of life. A score can be calculated when at least 50% of questions are answered (non-missing and not N/A, not applicable). Baseline is defined as the last nonmissing value before the first ever dose of fitusiran in either a parent study or this study. The last visit means the last measurement on or prior to data end date.

[0115] FIG. 73 shows the cumulative distribution function of change from baseline in Haem-A-QoL physical health scores to the end of primary treatment period for fitusiran prophylaxis, and to the end of control period for BPA on-demand (Panel A) and CFC on- demand (Panel B). The scores are presented as the Transformed Scale Score (TSS) ranging from 0-100, with lower scores indicating a better quality of life. A score can be calculated when at least 50% of questions are answered (non-missing and not N/A, not applicable). Baseline is defined as the last non-missing value before the first ever dose of fitusiran in parent study. BPA: bypassing agent; ITT: intent to treat.

DETAILED DESCRIPTION OF THE INVENTION

[0116] The present disclosure provides methods of using fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes in patients with hemophilia A (congenital factor VIII deficiency) or hemophilia B (congenital factor IX deficiency), with or without factor VIII or factor IX inhibitors. In some embodiments, the patient is an adult or adolescent > 12 years old. In some embodiments, the present methods reduce the risk of a hepatobiliary event, or the thrombotic risk, in a human patient receiving fitusiran.

[0117] The present disclosure also provide a method of routine prophylaxis to prevent or reduce the frequency of bleeding episodes in a human patient having hemophilia A or B with or without factor VIII or factor IX inhibitors, wherein the patient is further administered an effective amount of replacement factor (clotting factor concentrates or CFC) or bypassing agent (BPA) to treat a bleeding episode (e.g., breakthrough bleeding or bleeding associated with surgery), wherein the effective amount of the replacement factor or BPA is reduced as compared to the recommended (i.e., standard) effective amount of the replacement factor or BPA used on patients not receiving fitusiran therapy.

[0118] A hemophilia A or B patient with inhibitors refers to a patient who has developed alloantibodies to the factor he/she has previously received (e.g., factor VIII for hemophilia A patients or factor IX for hemophilia B patients). A hemophilia A or B patient with inhibitors may become refractory to replacement coagulation factor therapies. A patient without factor VIII or factor IX inhibitors refers to a patient who does not have such alloantibodies. The present treatment methods are beneficial for hemophilia A patients with or without factor VIII inhibitors, as well as for hemophilia B patients with or without factor IX inhibitors.

I. Fitusiran Pharmaceutical Compositions

[0119] Hemophilia results in a profound defect in thrombin generation, and further, hemophilia severity is correlated with the inability to generate thrombin. Without being bound by theory, it is believed that fitusiran-mediated lowering of antithrombin (AT) levels will increase thrombin generation and thus improve hemostasis in patients with hemophilia. Antithrombin is encoded by the SERPINC1 gene.

[0120] Fitusiran, whose structure is described herein, is a synthetic, chemically modified double-stranded small interfering RNA (siRNA) oligonucleotide covalently linked to a tri- antennary N-acetyl-galactosamine (GalNAc) ligand targeting the AT3 mRNA in the liver, thereby suppressing the synthesis of antithrombin. The nucleosides in each strand of fitusiran are connected through either 3’-5’ phosphodiester or phosphorothioate linkages, thus forming the sugar-phosphate backbone of the oligonucleotide.

[0121] Fitusiran is a double- stranded small interfering ribonucleic acid that targets AT mRNA which has been conjugated to a triantennary N-acetyl galactosamine ligand for directed delivery to the liver. The molecular formula of fitusiran sodium is Cs2oH636F2iNi75Na430309P43S6 and the molecular weight is 17,193 Da.

[0122] The sense strand and the antisense strand of fitusiran contain 21 and 23 nucleotides, respectively. The 3’-end of the sense strand is conjugated to the GalNAc containing moiety (referred to as L96) through a phosphodiester linkage. The sense strand contains two consecutive phosphorothioate linkages at its 5’ end. The antisense strand contains four phosphorothioate linkages, two at the 3’ end and two at the 5’ end. The 21 nucleotides of the sense strand hybridize with the complementary 21 nucleotides of the antisense strand, thus forming 21 nucleotide base pairs and a two-base overhang at the 3 ’-end of the antisense strand. See also U.S. Pat. 9,127,274, U.S. Pat. 11,091,759, and WO 2019/014187.

[0123] The two nucleotide strands of fitusiran are shown below: sense strand: 5’Gf-ps-Gm-ps-Uf-Um-Af-Am-Cf-Am-Cf-Cf-Af-Um-Uf-Um-Af-Cm-Uf- Um-Cf-Am-Af-L96 3’ (SEQ ID NO: 1), and antisense strand: 5’ Um-ps-Uf-ps-Gm-Af-Am-Gf-Um-Af-Am-Af-Um-Gm-Gm-Uf-Gm- Uf-Um-Af-Am-Cf-Cm-ps-Am-ps-Gm 3’ (SEQ ID NO: 2), wherein Af = 2’ -fluoroadenosine (i.e., 2’ -deoxy-2’ -fluoroadenosine)

Cf = 2 ’-fluorocytidine (i.e., 2 ’-deoxy-2 ’-fluorocytidine)

Gf = 2’ -fluoroguanosine (i.e., 2’-deoxy-2’-fluoroguanosine)

Uf = 2’ -fluorouridine (i.e., 2’ -deoxy-2’ -fluorouridine)

Am = 2’-O-methyladenosine

Cm = 2’-O-methylcytidine

Gm = 2’-O-methylguanosine

Um = 2’-O-methyluridine

(hyphen) = 3 ’-5’ phosphodiester linkage sodium salt

“-ps-” = 3 ’-5’ phosphorothioate linkage sodium salt and wherein L96 has the following formula:

[0124] The expanded structural formula, molecular formula, and molecular weight of fitusiran (sodium form) are shown in FIG. 1. As used herein, the term 2’ -fluoroadenosine is used interchangeably with the term 2’-deoxy-2’-fluoroadenosine; the term 2 ’-fluorocytidine is used interchangeably with the term 2 ’-deoxy-2 ’-fluorocytidine; the term 2’- fluoroguanosine is used interchangeably with the term 2’-deoxy-2’-fluoroguanosine, and the term 2 ’-fluorouridine is used interchangeably with the term 2’ -deoxy-2’ -fluorouridine.

[0125] The structure of fitusiran can also be described using the following diagram, wherein the X is O: [0126] For use in the present treatment methods, fitusiran may be provided in a pharmaceutical composition comprising it and a pharmaceutically acceptable excipient. In certain embodiments, fitusiran is in sodium salt form.

[0127] In some embodiments, fitusiran is provided in an aqueous solution at a concentration of about 1 to about 200 mg/mL (e.g., about 50 to about 150 mg/mL, about 80 to about 110 mg/mL, or about 90 to about 110 mg/mL). As used herein, values intermediate to recited ranges and values are also intended to be part of this disclosure. In addition, ranges of values using a combination of any of recited values as upper and/or lower limits are intended to be included. In further embodiments, the pharmaceutical composition comprises fitusiran at a concentration of about 6.25, about 12.5, about 25, about 50, about 75, about 100, about 125, about 150, or about 200 mg/mL.

[0128] Unless otherwise indicated, a fitusiran weight recited in the present disclosure is the weight of fitusiran free acid (the active moiety), even though fitusiran is injected to patients subcutaneously in its sodium form (in an aqueous solution). For example, 100 mg/mL fitusiran means 100 mg of fitusiran free acid (equivalent to 106 mg fitusiran sodium, the drug substance) per mL.

[0129] In some embodiments, the pharmaceutical compositions comprise fitusiran in a phosphate-buffered saline. The phosphate concentration in the solution may be about 1 to 10 mM (e.g., 2, 3, 4, 5, 6, 7, 8, or 9 mM), with a pH of 6.0-8.0. The pharmaceutical compositions herein may include a preservative such as EDTA. Alternatively, the pharmaceutical compositions are preservative-free. In particular embodiments, the fitusiran pharmaceutical composition is preservative-free and comprises, consists of, or consists essentially of about 100 mg of fitusiran per mL of a 5 mM phosphate buffered saline (PBS) solution. The PBS solution is composed of sodium chloride, dibasic sodium phosphate (heptahydrate), and monobasic sodium phosphate (monohydrate). Sodium hydroxide solution and diluted phosphoric acid may be used to adjust the pH of the composition to 7.0.

[0130] The pharmaceutical composition may be provided in a container (e.g., a vial or a syringe). The container may contain single or multiple doses. In some embodiments, the container is a single-use container (e.g., a single-use ampule or a single-use syringe such as a single-use pre-filled syringe), with each container containing about 10 to about 100 mg fitusiran (e.g., about 10 mg, about 20 mg, about 25 mg, about 40 mg, about 50 mg, or about 80 mg). In some embodiments, a Luer Lock syringe is used to withdraw the pharmaceutical composition from the single-use container. The fitusiran may be provided in a solid form in the container and reconstituted in an aqueous solution (e.g., PBS) prior to use, with the reconstituted solution containing about 1 to about 150 mg/mL (e.g., 100 mg/mL) fitusiran. In some embodiments, fitusiran is provided in sodium salt form in a single-use glass vial or a single-use prefilled syringe (e.g., one with a safety system). In further embodiments, each vial or syringe contains about 80 mg of fitusiran in about 0.8 mL (or about 50 mg of fitusiran in about 0.5 mL, about 20 mg of fitusiran in about 0.2 mL, or about 10 mg of fitusiran in about 0.1 mL) of 5 mM phosphate buffered saline solution (pH 7.0); and the solution is administered to patients through subcutaneous injection. The solution can be stored at 2 to 30°C (e.g., 2 to 8°C).

[0131] In particular embodiments, the fitusiran composition for subcutaneous injection contains fitusiran in a 5 mM phosphate buffered saline having 0.64 mM NaH2PO4, 4.36 mM Na2HPO4, and 84 mM NaCl at pH 7.0. In certain embodiments, the composition of fitusiran solution for subcutaneous injection is shown in Table 1A.

Table 1A. Exemplary Formulation q.s.: quantum satis.

[0132] In some embodiments, fitusiran is packaged in a pre-filled pen containing 50 mg of fitusiran (equivalent to 53 mg fitusiran sodium). In some embodiments, each single-use pre-filled pen contains 50 mg of fitusiran in 0.5 mL solution at a concentration of 100 mg/mL. In some embodiments, each pre-filled pen is designed to deliver 50 mg fitusiran in 0.5 mL which also contains: sodium chloride (2.455 mg), dibasic sodium phosphate (0.585 mg), monobasic sodium phosphate (0.044 mg), phosphoric acid (q.s. pH 7.0), sodium hydroxide (q.s. pH 7.0), and water for injection (q.s. 0.5 mL). Fitusiran may be supplied as a sterile, clear solution for subcutaneous injection in the 50 mg PFP. In some embodiments, the PFP contains a single dose of fitusiran and comprises a prefilled syringe (PFS) assembled with an automated injection system (pen). The PFS is a 1 mL colorless type 1 glass syringe with a 29 gauge, (¥2 inch) stainless steel staked needle covered with a rigid needle shield. The syringe is closed with a rubber coated (bromobutyl gray) plunger stopper.

[0133] In some embodiments, fitusiran is packaged in a vial containing 20 mg of fitusiran (equivalent to 21 mg fitusiran sodium). In these embodiments, tach single-use vial contains 20 mg of fitusiran in 0.2 mL solution at a concentration of 100 mg/mL. In some embodiments, each vial contains 20 mg fitusiran in 0.2 mL which also contains: sodium chloride (0.982 mg), dibasic sodium phosphate (0.234 mg), monobasic sodium phosphate (0.018 mg), phosphoric acid (q.s. pH 7), sodium hydroxide (q.s. pH 7.0), and water for injection (q.s. 0.2 mL). Fitusiran may be supplied as a sterile, clear solution for subcutaneous injection in the vial. The vial comprises a single dose of fitusiran in a 2 mL colorless Type-1 glass vial with a bromobutyl rubber stopper and an aluminum polypropylene colored crimping cap. In certain embodiments, the composition of fitusiran solution for subcutaneous injection is shown in Table IB below.

Table IB. Fitusiran Formulations

[0134] While the fitusiran dosage weight described herein refers to the weight of fitusiran free acid (active moiety), administration of fitusiran to patients herein refers to administration of fitusiran sodium (drug substance) provided in a pharmaceutically suitable aqueous solution (e.g., a phosphate-buffered saline at a physiological pH).

II. Therapeutic Use of Fitusiran

[0135] Fitusiran is an antithrombin-directed small interfering ribonucleic acid and can suppress liver production of antithrombin (AT). In its role as an anti-coagulant, AT regulates hemostasis by directly targeting thrombin production or by inactivating uncomplexed FXa, which in turn reduces thrombin production (Quinsey et al., Int J Biochem Cell Biol. (2004) 36(3):386-9). Fitusiran may be used to treat those who have impaired hemostasis. For example, fitusiran can be used to treat patients with hemophilia A or B with or without inhibitors for routine prophylaxis to prevent or reduce the frequency of bleeding episodes. In particular embodiments, fitusiran is used to treat adult and adolescent patients (at least twelve years of age) with hemophilia A (congenital factor VIII deficiency) or hemophilia B (congenital factor IX deficiency) with or without inhibitors. The present methods include administering to the hemophilia patient (e.g., a hemophilia A or B patient) in need thereof a therapeutically effective amount of fitusiran. “Therapeutically effective amount” refers to the amount of fitusiran that helps the patient to achieve a desired clinical endpoint.

[0136] In some embodiments, fitusiran may be used for routine prophylaxis to prevent or reduce the frequency of bleeding episodes in adult and adolescent patients aged 12 years and older with hemophilia A or B with or without factor VIII or IX inhibitors. In certain embodiments, a fitusiran-containing pharmaceutical composition is administered by subcutaneous injection at a dose strength of, for example, about 10 to about 100 mg (e.g., about 10 to about 95 mg, about 40 to about 90 mg, about 50 to about 100 mg, about 50 to about 90 mg, about 50 to about 85 mg, or about 50 to about 80 mg) per dose. In particular embodiments, fitusiran is administered subcutaneously at about 10, about 20, about 50, or about 80 mg (weight of active moiety) per dose in a PBS solution as described above. In some embodiments, fitusiran is for subcutaneous use only.

[0137] A plurality of fitusiran doses may be administered to a patient at an interval of about one, about two, about three, about four, about five, about six, about seven, or about eight weeks, or of about one, about two, or about three months. In particular embodiments, a fixed dose of fitusiran (e.g., about 50 or about 80 mg subcutaneous injection) is administered to a hemophilia patient (e.g., a hemophilia A or hemophilia B patient who is twelve years or older and who has or has not developed inhibitors) about once every four weeks or about once a month or about once every eight weeks or about once every other month.

[0138] In some embodiments, the present methods involve measurement of AT levels in a patient. In some embodiments, the present methods involve obtaining a measurement of AT level in the human patient at four weeks or one month following administration of the starting dose or following administration of a modified dose as compared to the prior dose. In some embodiments, the present methods involve obtaining a measurement of AT level in the human patient at twelve weeks or three months following administration of the starting dose or following administration of a modified dose as compared to the prior dose. In some 1 embodiments, the present methods involve obtaining a measurement of AT level in the human patient at 20 weeks or five months following administration of the starting dose or following administration of a modified dose as compared to the prior dose. In some embodiments, the present methods involve obtaining a measurement of AT level in the human patient at 24 weeks or six months following administration of the starting dose or following administration of a modified dose as compared to the prior dose.

[0139] AT measurements can be performed by well-established methods, including both kinetic and/or chromogenic assays. One commonly used method is the INNOVANCE™ Antithrombin assay (Siemens Healthineers, Malvern, PA; U.S. FDA 510(k) # K081769). INNOVANCE™ is a chromogenic assay that quantifies functionally active AT in human citrated plasma based on the inhibition of an excess of factor Xa by AT. The assay may be performed by using an automated coagulation instrument (e.g., Siemens BCS® XP, Sysmex® CA-600 and CS Systems, or Atellica® COAG 360 System), and may be calibrated using Siemens standard human plasma (SHP) with a defined value of AT activity calibrated against World Health Organization (WHO) reference plasma. An equivalent assay is the Dade Behring Berichrom™ Antithrombin III assay (Dade Behring Marburg GmbH, Marburg, Germany; U.S. FDA 510(k) # K933125). Each measurement may be controlled by two independent controls (low and normal value) also calibrated against the WHO standard. The AT activity (%) in a plasma sample is calculated against the WHO reference plasma. 100% AT level is defined as 1 unit of antithrombin activity in 1 mF of reference plasma sample. The limit of detection of the INNOVANCE™ assay is 6.0% based on the assay’s U.S. FDA 510(k) decision summary. AT levels range from about 80% to about 120% in the general population.

[0140] In some embodiments, AT activity may be measured using a validated or approved AT activity assay or device. For example, to monitor AT activity, a specific FDA- cleared human factor Xa based chromogenic activity assay is used. Bovine factor Ila based chromogenic assays, if used, may be validated at low AT activity (< 15%). Bovine factor Xa based chromogenic assay may be avoided if the AT levels are below 35%. If an FDA-cleared human factor Xa based chromogenic activity assay is not locally available, a reference laboratory may be utilized.

[0141] In some embodiments, the starting dose of fitusiran is 50 mg once every two months (Q2M) for patients 12 years of age and older. In some embodiments, the starting dose of fitusiran is 50 mg once every two months (Q2M). In some embodiments, the dose is adjusted if needed, to maintain antithrombin (AT) activity between 15-35%. In some embodiments, the modified doses include 50 mg once every month (QM), 20 mg Q2M, or 20 mg QM.

[0142] It has been observed that the risk of arterial thrombotic events among patients receiving fitusiran may increase with AT levels <10%. To mitigate the risk of vascular thrombotic events while maintaining a favorable benefit-risk balance for patients on fitusiran, a patient, for example an adult patient (>18 years of age) or an adolescent patient (12 to 17 years of age, inclusive), may start on a fitusiran therapy by subcutaneous injection of 50 mg fitusiran every two months (or every eight weeks). The patient’s AT level is monitored periodically (e.g., every one, two, three, four, five, six, seven, or eight weeks, or every one, two, three, four, five, or six months). If the patient has two AT measures of <15% (e.g., <10%), the patient will pause fitusiran treatment, or discontinue fitusiran treatment. In some embodiments, upon the first AT level <15%, the patient has another AT activity level sample drawn within a month (e.g., within one or two weeks). If this result is <15%, this will be considered the second AT <15%. Patients receiving fitusiran at a dose of 50 mg Q2M with more than 1 (e.g., 2) AT activity levels <15% will pause fitusiran, or discontinue treatment. [0143] However, if the 50 mg/Q2M (or Q8W) patient has two AT measures of >35%), the patient will escalate the dosing regimen as illustrated in FIG. 2. In the approach of FIG.

2, the patient may receive fitusiran at 50 mg every month (or every four weeks); if the patient has two AT measurements of >35%) under the 50 mg/QM (Q4W) regimen, the patient may receive fitusiran at 80 mg every month (or every four weeks).

[0144] Patients who have discontinued fitusiran after having more than one (e.g., 2) AT activity levels <15% when receiving fitusiran at a dose of 50 mg Q2M may receive fitusiran at a dose of 20 mg Q2M, optionally once their AT levels have returned to >22% (FIG. 2). Patients receiving fitusiran at a dose of 20 mg Q2M with more than one (e.g., two) AT activity level <15% will discontinue fitusiran treatment. If a patient receiving fitusiran at a dose of 20 mg/Q2M (or Q8W) has two AT measures of >35%, the patient may receive fitusiran at 20 mg QM or Q4W.

[0145] In the above dose finding regimens, AT measurements for dosing determination are those taken during steady state (SS) of AT activity, i.e., once the patient’s AT levels have been stabilized (at low AT activity range) after fitusiran treatment. The SS is typically reached after two or three doses of fitusiran. AT measurements for dosing determination are taken at an appropriate interval (e.g., every four weeks or every eight weeks).

[0146] In the above dose finding regimens, the starting dose of 50 mg fitusiran Q2M is included as an illustrative example. For example, a starting dose of fitusiran may be 50 mg Q2M, 20 mg Q2M, 20 mg QM, or 10 mg QM. Dose escalation and de-escalation can then be carried out accordingly from each starting dose. For example, a starting dose of 20 mg Q2M fitusiran can be escalated to 20 mg QM, 50 mg Q2M, 50 mg QM, or 80 mg QM, optionally sequentially in that order, or de-escalated to 10 mg QM.

[0147] An AT level of 10-35% (e.g., 10-25%, 15-35%, or 15-25%) is targeted to mitigate the risk of vascular thrombotic events while maintaining a favorable benefit-risk balance for patients on fitusiran. Thus, so long as the patient reaches this targeted AT level, there is no need for the patient to receive a higher fitusiran dosage or more frequent dosing. That is, he remains on the current treatment regimen (i.e., maintenance regimen). For example, once the desired AT level is reached, the patient may be treated with a subcutaneous dose of fitusiran (e.g., 40-90 mg per dose) at an interval of, e.g., every one, two, three, four, five, six, seven, or eight weeks, or every one, two, three, four, five, or six months. In some embodiments, if the patient has two AT measurements of no greater than 35% while receiving 50 mg Q2M, he will maintain this dosing regimen, with no need to further escalate the dosage or dosing frequency. As another example, if the patient has two AT measurements of no greater than 35% while receiving 80 mg Q2M or 50 mg QM, he will remain on this dosing regimen, with no need to further escalate the dosage or dosing frequency (to, e.g., 80 mg QM). However, fitusiran treatment should be discontinued if a patient has more than 1 (e.g., 2) AT measurements < 15% (e.g., < 10%) as a risk mitigation measure for vascular thrombotic events. Alternatively, the patient may resume treatment with a lower dose of fitusiran, optionally after their AT levels have returned to above 15%, e.g., >22%.

[0148] In some embodiments, if AT activity is consistently <15% and a dose reduction is required, the lower dose should be initiated three months after the prior dose. In some embodiments, AT activity should be measured prior to initiation of fitusiran treatment and then every other month prior to the next dose for six months. After a dose modification, AT measurements may be restarted.

• If AT activity is consistently <15% and a dose reduction is required, the lower dose may be initiated three months after the prior dose.

• If AT activity is >35% after six months, or if the patient has not achieved satisfactory bleed control, dose modification may be considered.

• After the initial AT monitoring period, AT activity may be measured annually. [0149] Recommended dose modification based on AT activity levels is shown in Table

2.

Table 2. Recommended Dose Modification Based on AT Activity

[0150] In some embodiments of maintenance regimens, a patient with hemophilia A or B with or without inhibitors is treated with a subcutaneous dose of fitusiran at 50 mg per dose every two months (or every eight weeks). In other embodiments, a patient with hemophilia A or B with or without inhibitors is treated with a subcutaneous dose of fitusiran at 50 mg every month (or every four weeks). In yet other embodiments, a patient with hemophilia A or B with or without inhibitors is treated with a subcutaneous dose of fitusiran at 80 mg every two months (or every eight weeks). In yet other embodiments, a patient with hemophilia A or B with or without inhibitors is treated with a subcutaneous dose of fitusiran at 80 mg every month (or every four weeks). In yet other embodiments, a patient with hemophilia A or B with or without inhibitors is treated with a subcutaneous dose of fitusiran at 20 mg every two months (or every eight weeks). In yet other embodiments, a patient with hemophilia A or B with or without inhibitors is treated with a subcutaneous dose of fitusiran at 20 mg every month (or every four weeks). In yet other embodiments, a patient with hemophilia A or B with or without inhibitors is treated with a subcutaneous dose of fitusiran at 10 mg every month (or every four weeks).

[0151] In some embodiments, patients may receive periodic (e.g., monthly or every four weeks) AT monitoring for 12 months following a change in fitusiran dosing regimen.

[0152] In some embodiments, once a patient stays on a maintenance regimen (e.g., 10 mg QM or Q4W, 20 mg Q2M or Q8W, 20 mg QM or Q4W, 50 mg Q2M or Q8W, 50 mg QM or Q4W, 80 mg QM or Q4W, or 80 mg Q2M or Q8W), the patient may receive less frequent AT monitoring. For example, his AT level may be monitored every month, every two months, every three months, every four months, semi-annually, annually, or every two years.

[0153] In some embodiments, the starting dose of fitusiran is 50 mg Q2M and this dose is adjusted, if needed, to maintain antithrombin (AT) activity between 15-35% (Table 2 above); the modified doses include 50 mg QM, 20 mg Q2M, or 20 mg QM; and the AT activity is measured using an FDA-specific validated AT activity assay, where AT monitoring is initiated prior to the first dose of fitusiran treatment as shown in Table 2. After cessation of fitusiran dosing, routine AT monitoring may not be needed unless the patient is bleeding and treatment with CFC/BPA is required. Based on data from the clinical studies, the majority of patients have an AT activity >60% by 6 months after the last dose, after which normal doses of CFC/BPA may be used.

[0154] In some embodiments, if a dose of fitusiran is missed, fitusiran is administered as soon as possible; thereafter, the dosing schedule is resumed either once every month or once every two months, as applicable, from the last dose.

[0155] In some embodiments, the patient receiving fitusiran therapy has been on routine prophylactic use of replacement factor or bypassing agent (BPA). Patients undergoing prophylactic treatment with replacement factor or BPA are typically treated as described in Table 3, wherein factor and bypassing agents are administered intravenously.

Table 3. Factor or bypassing agent prophylaxis requirements

[0156] After fitusiran therapy is initiated, these patients may continue their prior replacement factor or bypassing agent (BPA) prophylaxis for the first seven days of treatment, and after the first seven days of fitusiran treatment, the factor or BPA prophylaxis is discontinued. Subsequent to day seven of the fitusiran treatment period, factor concentrates or BPAs are administered only for bleeding episodes or if needed in advance of invasive medical procedures. [0157] In some embodiments, fitusiran is administered subcutaneously into the thigh or abdomen. In some embodiments, a caregiver injects fitusiran in the outer area of the patient’s upper arm. In some embodiments, fitusiran is not inject into a vein.

III. Bleed Management

[0158] Patients receiving fitusiran prophylactic therapy herein may have breakthrough bleed episodes or may have surgery -related bleed episodes. The factor or BPA dose necessary to safely and effectively treat bleed episodes in patients receiving fitusiran during the fitusiran treatment period will be lower than standardly prescribed. Clinical experience suggests that pharmacodynamic (PD) drug interactions between fitusiran and concomitantly administered clotting factor concentrates (CFC) or BPA may occur when higher or more frequent doses of CFC or BPA than recommended in the breakthrough bleed management guidance (Table 4) are used.

[0159] In some embodiments, for patients using on-demand treatment with CFC or BPA after fitusiran initiation, the prior dosing regimen of CFC or BPA therapy may be used to treat breakthrough bleeding episodes only for the first seven days.

[0160] If breakthrough bleeding occurs after seven days of the first fitusiran dose, bleeds may be managed with a reduced dose and frequency of CFC/BPA to minimize the risk of thrombotic events. Initially, the weight-based dose of a CFC/BPA may be halved, and the dosing interval doubled compared to the routine dose (Table 4). If adequate hemostatic control is not achieved, higher doses may be used per clinical judgement. In some embodiments, antifibrinolytics with CFC or BPA are not used in combination.

Table 4. Bleed Management for Breakthrough Bleeding Occurring Eight or More Days After the First Fitusiran Dose

Adjunctive management of bleeding episodes and cases of thrombosis should be carried out per standard of care. aPCC = activated prothrombin complex concentrate. *For situations requiring higher doses, more frequent administration, or multiple repeat doses, use clinical judgment. [0161] Under the above management guidelines, after the first seven days of the first fitusiran dose, when a patient experiences a symptom that may be consistent with bleeding episodes, the following steps are followed:

A single dose is administered according to the guidelines in Table 4.

The patient is instructed to re-evaluate symptoms in 24 hours for bleeds treated with FVIII, FIX or aPCC and in 2-3 hours for bleeds treated with rFVIIa.

Administration of FIX Extended half-life is not to be more frequent than every 5-7 days.

Doses are not administered at less than 24-hour intervals (except rFVIIa as indicated in Table 4).

Doses do not exceed the protocol maximum recommended dose indicated in Table 4.

[0162] In some embodiments, the bleeding episode is a minor bleeding episode. In some embodiments, the bleeding episode is a moderate bleeding episode. In some embodiments, the bleeding episode is a severe bleeding episode.

[0163] In some embodiments, the bleed management guidelines maintain hemostasis in a patient undergoing a major surgery. As used herein, a “major surgery” includes, for example, opening into a major body cavity (e.g., abdomen, thorax, or skull), operation on a joint, removal of an organ, operative alteration of normal anatomy, crossing of a mesenchymal barrier (e.g., pleura, peritoneum, or dura), dental extraction of molar teeth or >3 non-molar teeth, or tooth implantation. In some embodiments, major orthopedic surgery is an operation on a joint or bone and associated soft tissue. In some embodiments, the peri-operative hemostatic control is assessed based on the ISTH 4-point response scale (excellent/good/moderate/poor). In some embodiments, the patient is not being treated with AT replacement therapy before surgery. In some embodiments, the patient is not being treated with AT replacement therapy during surgery. In some embodiments, the patient is not being treated with AT replacement therapy after surgery.

[0164] In some embodiments, reduced doses of replacement factor or bypassing agent are used as perioperative prophylaxis. In some embodiments, no replacement factor or bypassing agent is used as perioperative prophylaxis. In some embodiments, hemostatic control on the day of the surgery is rated excellent or good. In some embodiments, ATIII concentrate is used to reverse the pharmacodynamic effect of fitusiran in surgeries with an excellent/good hemostatic outcome.

IV. Selection of Patients [0165] The present treatments may be used to prophylactically treat patients with hemophilia A or hemophilia B with or without inhibitors. In some embodiments, the patient is a male aged >12 years with severe hemophilia A or B with or without inhibitors. A diagnosis of severe hemophilia is based on Factor VIII level of <1% (for hemophilia A) or a Factor IX level of <2% (for hemophilia B). In some embodiments, the patient is a male aged >18 years with moderate or severe hemophilia A or B with or without inhibitors. A diagnosis of moderate or severe hemophilia is based on FVIII or FIX level V5%’.

[0166] In some embodiments, the patient has used replacement factors or bypassing agents prophylactically to manage bleeding episodes for at least six months prior to the start of treatment. In some embodiments, these patients have inhibitory antibodies to factor VIII or factor IX, and have experienced a minimum of two bleeding episodes requiring BPA treatment within the last six months prior to treatment. In some embodiments, these patients are without inhibitory antibodies to factor VIII or factor IX, and have experienced a minimum of one bleeding episode requiring factor treatment within the last twelve months prior to treatment.

[0167] In some embodiments, the patient has not used replacement factors or bypassing agents prophylactically to manage bleeding episodes for at least six months prior to the start of treatment. In some embodiments, these patients have experienced a minimum of six bleeding episodes requiring BPA (inhibitor participants) or factor (non-inhibitor participants) treatment within the last six months prior to treatment.

[0168] In some embodiments, the patient has inhibitory antibodies to Factor VIII or Factor IX (i.e., is a patient with inhibitors). A patient is defined as a patient with inhibitors if they meet at least one of the following Nijmegen-modified Bethesda assay results criteria: a. inhibitor tier of >0.6 BU/mL prior to treatment, or b. inhibitor titer of <0.6 BU/mL prior to treatment with medical record evidence of two consecutive titers >0.6 BU/mL, or c. inhibitor titer of <0.6 BU/mL prior to treatment with medical record evidence of anamnestic response.

[0169] In some embodiments, the patient does not have inhibitory antibodies to Factor VIII or Factor IX (i.e., is a patient without inhibitors). A patient is defined as a patient without inhibitors if they meet at least one of the following Nijmegen-modified Bethesda assay results criteria: a. Nijmegen-modified Bethesda assay inhibitor titer of <0.6 BU/mL prior to treatment, b. no use of bypassing agents to treat bleeding episodes for at least the last six months prior to treatment, and c. no history of immune tolerance induction therapy within the past three years prior to treatment.

[0170] In some embodiments, the patient does not have a known co-existing bleeding disorder other than hemophilia A or B, e.g., Von Willebrand’s disease, additional factor deficiencies, or platelet disorders. The patient may not have a co-existing thrombophilic disorder, as determined by presence of any of the below: a. FV Leiden mutation (homozygous or heterozygous), b. protein S deficiency, c. protein C deficiency, or d. prothrombin mutation (G20210A; homozygous and heterozygous).

[0171] In some embodiments, the patient does not have a history of antiphospholipid antibody syndrome or arterial or venous thromboembolism, atrial fibrillation, significant valvular disease, myocardial infarction, angina, transient ischemic attack, or stroke. Patients who have experienced thrombosis associated with indwelling venous access may be treated with the present methods.

[0172] In some embodiments, the patient has not had a malignancy within two years, except for basal or squamous cell carcinoma of the skin that has been successfully treated. [0173] In some embodiments, the patient is not currently participating in immune tolerance induction therapy (ITI).

[0174] In some embodiments, the patient has not used compounds, other than factor concentrates or BPAs for hemophilia treatment (including emicizumab (Hemlibra®)) within six months prior to treatment.

[0175] In some embodiments, the patient does not have an ALT and/or AST measurement >1.5x upper limit of normal reference range (ULN). In some embodiments, the patient does not have an ALT and/or AST measurement >5x ULN. The patient may not have an AT activity <60% prior to treatment. In some embodiments, the patient does not have a clinically significant liver disease, as indicated by (i) history of portal hypertension, esophageal varices, or hepatic encephalopathy; or (ii) presence of ascites by physical exam. In some embodiments, the patient does not have total bilirubin levels > 1.5 x ULN, or >2.0 x ULN in participants with Gilbert's Syndrome. In some embodiments, the patient does not have uncontrolled hypertension defined as systolic blood pressure 160 mmHg and diastolic blood pressure 100 mmHg.

[0176] In some embodiments, fitusiran is not used in patients with underlying hepatic diseases or moderate to severe hepatic impairment.

[0177] In some embodiments, baseline liver function tests (LFTs), including AST and ALT, are obtained in all patients initiating fitusiran prophylaxis and then be monitored every two months for a period of at least six months. In some embodiments, if AST or ALT remain elevated above baseline, LFT monitoring is continued periodically thereafter.

[0178] In some embodiments, if new or worsening liver dysfunction is observed, appropriate diagnostic evaluations are performed. In some embodiments, medical management is initiated as appropriate and laboratory parameters are monitored until normalization to baseline. In some embodiments, if transaminase levels show evidence of progression, particularly if they rise to greater than five times ULN and are persistent, or if they are associated with symptoms, the present treatment methods are interrupted. In some embodiments, the benefits and risks of resuming fitusiran prophylaxis following resolution of transaminase elevations are considered.

[0179] In some embodiments, the patient is not Hepatitis C virus antibody positive. A patient who is Hepatitis C virus antibody positive may be treated with the present methods only if they have: a. completed curative treatment at least 12 weeks prior to enrollment and attained sustained virologic response as documented by a negative HCV RNA prior to treatment, or they have spontaneously cleared infection as documented by negative HCV RNA prior to treatment, and b. no evidence of cirrhosis according to FibroScan < 12.5 kPa (where available), or FibroTest score <0.75 and APRI <2 (if FibroScan unavailable).

[0180] In some embodiments, the patient does not have acute hepatitis, i.e., hepatitis A or hepatitis E. In some embodiments, the patient does not have acute or chronic hepatitis B infection (IgM anti-HBc antibody positive or HBsAg positive).

[0181] In some embodiments, the patient does not have (i) a platelet count <100,000/pL, (ii) is not HIV positive with CD4 count <200 cells/pL, and/or (iii) does not have an estimated glomerular filtration rate <45 mL/min/1.73 m² (using the Modification of Diet in Renal Disease [MDRD] formula). [0182] In some embodiments, the patient is not a pregnant woman. In some embodiments, fitusiran is used during pregnancy only if the potential benefit justifies the potential risks, including those to the fetus.

[0183] In some embodiments, the patient is not breastfeeding. In some embodiments, the developmental and health benefits of breastfeeding is considered along with the mother's clinical need for fitusiran and any potential adverse effects on the breastfed infant from fitusiran or from the underlying maternal condition.

[0184] In some embodiments, women of childbearing potential use non-hormonal contraception prior to starting treatment with and while receiving fitusiran.

[0185] In some embodiments, the patient is 65 years old.

[0186] In some embodiments, the patient has mild renal impairment (eGFR 60 to < 90 mL/min/1.73m²). In some embodiments, the patient has moderate renal impairment (eGFR 30 mL/min/1.73 m² to <60 mL/min/1.73m²).

[0187] In some embodiments, the patient does not have a corrected QT(QTc) interval 450 ms. The patient may not have an international normalized ratio (INR) of >1.5.

[0188] In some embodiments, the patient meets one or more of the inclusion criteria and one or more of the exclusion criteria detailed in any one of Examples 1-4 and 14 below.

V. Treatment Outcomes and Evaluation

[0189] In some embodiments, the present treatment methods reduce the frequency of bleeding episodes in a patient. A bleeding episode is defined as any occurrence of hemorrhage that requires replacement factor or BPA infusion, e.g., hemarthrosis, muscle, or mucosal bleeding. The definition of bleeding episode types described below is based on consensus opinion of International Society on Thrombosis and Haemostasis (ISTH) (Blanchette et al., J Thromb Haemost. (2014) 12(11): 1935-9).

[0190] The start time of a bleeding episode is defined as the time at which symptoms of a bleeding episode first develop. Bleeding or any symptoms of bleeding at the same location that occurs within 72 hours of the last injection used to treat a bleeding episode at that location is considered a part of the original bleeding event, and will count as one bleeding episode towards the ABR. Any bleeding symptoms that begin more than 72 hours from the last injection used to treat a bleeding episode at that location will constitute a new bleeding event.

[0191] A spontaneous bleeding episode refers to a bleeding event that occurs for no apparent or known reason, particularly into the joints, muscles, and soft tissues. A joint bleeding episode is characterized by an unusual sensation in the joint (“aura”) in combination with 1) increasing swelling or warmth over the skin over the joint, 2) increasing pain, or 3) progressive loss of range of motion or difficulty in using the limb as compared with baseline. A muscle bleed may be characterized by pain, swelling and loss of movement over the affected muscle group. A target joint is defined as a joint where three or more spontaneous bleeding episodes in a single joint within a consecutive six-month period has occurred; where there have been less than or equal to two bleeding episodes in the joint within a consecutive 12-month period the joint is no longer considered a target joint. A traumatic bleeding episode is one that is caused by a known injury or trauma. Bleeding episodes sustained during sports and recreation is counted as traumatic bleeding episodes.

[0192] In some embodiments, the present treatment methods result in reduction in the annualized bleed rate (ABR), and/or the annualized spontaneous bleeding rate (AsBR) in the treated population compared to a population treated prophylactically with compared to another prophylaxis treatment (e.g., replacement factor, BPA, or emicizumab).

[0193] In some embodiments, the present treatment methods result in improved patient- reported outcomes (PROs) or an improvement in quality of life (QoL) as further described below. Hemophilia, through its associated symptoms, functional limitations and treatment burden, directly impacts the health-related quality of life (HRQoL) of patients. Improving HRQoL is a critical aspect of hemophilia disease management. The present methods improve HRQoL of patients as determined by well-designed, detailed questionnaires.

[0194] In some embodiments, the treatment efficacy can be measured by a reduction in the severity of disease as evaluated by the patient based on a valid and reliable hemophiliaspecific PRO instrument, for example, the Haemophilia Quality of Life Questionnaire for Adults (“Haem-A-QoL”; von Mackensen et al., Haematologica (2005) 90(s2): 115-6, Abstract 0290; Wyrwich et al., Haemophilia (2015) 21 (5):578-84). Any positive change resulting in, for example, lessening of severity of disease measured using the appropriate scale, represents adequate treatment using the pharmaceutical compositions as described herein.

[0195] Hemophilia, through its associated symptoms, functional limitations and treatment burden, directly impacts the health-related quality of life (HRQoL) of patients. Improving HRQoL is a critical aspect of hemophilia disease management. The present methods improve HRQoL of patients as determined by well-designed, detailed questionnaires. For examples, HRQoL in adult patients (17 years or older, e.g., 18 years or older) can be measured by the Haem-A-QoL questionnaire. In particular embodiments, HRQoL of adult patients may be measured by scores in Haem-A-QoL. See, e.g., von Mackensen et al., Value in Health. (2005) 8(6):A127; von Mackensen et al., J Thrombosis and Haemostasis. (2005) 3(Supl):P0813; von Mackensen and Gringeri, “Quality of Life in Hemophilia” In: Handbook of Disease Burdens and Quality of Life Measures. Heidelberg: Springer; 2009, pp.1910-1; and Bullinger et al., Value in Health. (2009) 12(5):808-20; Wyrwich, supra. The Haem-A-QoL questionnaire includes 46 items contributing to 10 domains, including Physical Health (5 items), Feeling (4 items), View of Self (5 items), Sports and Leisure (5 items), Work and School (4 items), Dealing with Hemophilia (3 items), Treatment (8 items), Future (5 items), Family Planning (4 items), and Partnership and Sexuality (3 items).

[0196] All Haem-A-QoL items are measured based on a 5-point frequency scale (1 = never, 2 = rarely, 3 = sometimes, 4 = often, and 5 = all the time). A “Not Applicable” response option is also available for the domains of “Sports & Leisure,” “Work & School,” and “Family Planning” when the question does not apply to the participant. A

“Total Score” is also used to represent the average of all 10 domains of the Haem-A-QoL questionnaire. Haem-A-QoL domain scores and the Total Score are transformed to a scale of 0 - 100 with higher scores representing greater impairment. A decrease in score relative to the corresponding baseline score (score before the treatment being evaluated) indicates an improvement in the patient’s quality of life. The questionnaire may be taken before treatment and after treatment with one or more (e.g., two or more, three or more, four or more, five or more, or six or more) doses of fitusiran (e.g., administered subcutaneously at about 50 mg or about 80 mg about once every four weeks or about once a month). For example, the questionnaire may be taken at week 8, 12, 16, 20, 24, 25, 26, or 27 after commencement of fitusiran treatment.

[0197] In some embodiments, the present treatment improves the quality of life of patients in one or more of QoL domains (e.g., hemophilia- specific QoL domains). These QoL domains include, for example, domains related to Physical Health, Feeling, View of Self, Sports and Leisure, Work and School, Dealing with Hemophilia, Treatment, Future, Family Planning, and/or Partnership and Sexuality. Improvement in these domains may be evaluated by patient-reported outcome (PRO) and may be aided by questionnaires. For example, improvement in these domains may be reported by a patient to his/her physician, and/or may be scored by a QoL questionnaire.

[0198] In some embodiments, the present therapy improves the score in at least one of the Haem-A-QoL domains (e.g., Physical Health, Feeling, View of Self, Sports and Leisure, Work and School, Dealing with Hemophilia, Treatment, Future, Family Planning, and/or Partnership and Sexuality) from baseline, and/or improves the Haem-A-QoL Total Score compared to the score in patients prophylactically treated with replacement factor or BPA. In particular, the present methods may improve the quality of life of hemophilia patients, including improvement (e.g., alleviation and disappearance) of patient-reported hemophilia- related symptoms (e.g., painful swellings and joint pain) and physical functioning (e.g., pain with movement and difficulty walking far) as determined by the Physical Health score and/or the Total Score of Haem-A-QoL.

[0199] In some embodiments, the present treatment methods result in an improvement in a patient-reported outcome (PRO) or an improvement in quality of life (QoL). In some embodiments, the improvement is measured using the Haemophilia Quality of Life Questionnaire for Adults (Haem-A-QoL) questionnaire. In some embodiments, the present treatment methods decrease the Haem-A-QoL questionnaire total or physical health domain score, with a decrease of at least 2 units in the fitusiran prophylaxis patient compared to the prophylactically treated BPA or factor patient (e.g., a decrease of at least 3 at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, at least 10, at least 11, at least 12, at least 13, at least 14, at least 15, or at least 16 units).

[0200] In some embodiments, HRQoL is measured by the Patient-Reported Outcomes Measurement Information System v2.0 Pain Intensity 3a (PROMIS v2.0 Pain Intensity 3a). The PROMIS v2.0 Pain Intensity 3a is a system of reliable and precise measures of adolescent and adult (age at least twelve years) participant-reported health status (Celia et al., Med Care. (2007) 45(5 Suppl 1): S3-S11). The PROMIS v2.0 Pain Intensity 3a is a psychometrically and clinically tested instrument assessing how much a person hurts. The instrument consists of three items measuring the worst, average, and current intensity of pain with a recall period of 7 days. Each question has five response options ranging from one (“no pain”) to five (“very severe”). Raw scores are translated into a T-score (an item-level calibration adjustment). A higher PROMIS T-score represents more of the concept being measured (Pain Intensity). The questionnaire may be taken after treatment with one or more (e.g., two or more, three or more, four or more, five or more, or six or more) doses of fitusiran (e.g., administered subcutaneously at 50 mg once every four weeks or once a month). For example, the questionnaire may be taken at about month 6, 12, or 18 after commencement of fitusiran treatment. In some embodiments, the present treatment methods decrease the PROMIS T-score compared to another prophylaxis treatment. [0201] In some embodiments, the improvement in PRO or in QoL is measured using the Treatment Satisfaction Questionnaire for Medication-9 Items (TSQM-9). The TSQM-9 assesses participants’ satisfaction with treatment. The TSQM-9 is a psychometrically validated tool that provides a general measure of participants’ satisfaction with medication (Atkinson et al., Health Qual Life Outcomes. (2004) 2:12). The questionnaire consists of nine items directed to the overall patient satisfaction or dissatisfaction with the medication administered in the clinical trial, as measured by the patient evaluation of the effectiveness, side effects, and convenience of the medication over the preceding two to three weeks. Each question has seven response options ranging from one (“extremely dissatisfied”) to seven (“extremely satisfied”). Higher scores indicate better health status. The questionnaire may be taken after treatment with one or more (e.g., two or more, three or more, four or more, five or more, or six or more) doses of fitusiran (e.g., administered subcutaneously at about 50 mg once about every four weeks or about once a month). For example, the questionnaire may be taken at about month 6, 12, or 18 after commencement of fitusiran treatment. In some embodiments, the present treatment methods increase the TSQM-9 score compared to another prophylaxis treatment.

[0202] In some embodiments, the improvement in PRO or in QoL is measured using the Preference Questionnaire. The Preference Questionnaire is a three-item questionnaire measuring participants’ preferences for fitusiran compared to standard of care. The Preference Questionnaire evaluates the respondent’ s preferred treatment, reasons for preference, and willingness to continue treatment. The questionnaire consists of three items directed to the patient preference for fitusiran versus standard of care, the main reasons for the indicated preference, and the respondent’s willingness to continue their preferred treatment method. Respondents indicate preference for either standard of care (prior to fitusiran treatment), the fitusiran treatment administered during the clinical trial, or no preference for either treatment. Respondents rank the three main reasons for their preferred treatment selected from the following: less time required to receive the treatment, less frequent administration, easier to use, more flexibility in treatment administration, better quality of life, or less worry about having a bleed. The respondent’s willingness to continue their preferred treatment is indicated by a range of five response options from “extremely unwilling” to “extremely willing.” The questionnaire may be taken twelve months after commencement of fitusiran treatment. In some embodiments, the present treatment methods increase the reported preference for fitusiran prophylaxis compared to another prophylaxis treatment. [0203] In some embodiments, the improvement in PRO or in QoL is measured using the International Physical Activity Questionnaire (IPAQ). The IPAQ measures levels of physical activity in adult participants (>18 years) by collecting information on household and yard work activities, occupational activity, self-powered transport, and leisure time physical activity as well as sedentary activity (Craig et al., Med Sci Sports Exerc. (2003) 35(8): 1381- 95). The questionnaire consists of 27 items directed to the number of days and amount of time spent sitting, walking, and engaging in moderate and vigorous physical activities in the last seven days or the last usual week. Global and domain scores can be calculated with higher scores denoting higher physical activity. The questionnaire may be taken after treatment with one or more (e.g., two or more, three or more, four or more, five or more, or six or more) doses of fitusiran (e.g., administered subcutaneously at 50 mg about once every four weeks or about once a month). For example, the questionnaire may be taken at about month 6, 12, or 18 after commencement of fitusiran treatment. In some embodiments, the present treatment methods increase the IPAQ score compared to another prophylaxis treatment.

[0204] In some embodiments, the improvement in PRO or in QoL is measured using participant qualitative interviews. Patient qualitative interviews document the experience of treatment and trial participation from the patient perspective. Specifically, the interviews capture 1) experience of living with hemophilia, 2) experience with treatments prior to the trial participation, and 3) expectations for the trial and experiences during the trial. The interview may be conducted within two weeks after participant screening and within two weeks of the end of the study. Dominant trends can be identified in each interview and compared across the results of the other interviews to generate themes or patterns in the way participants describe their disease, treatment, and clinical trial experiences. In some embodiments, the present treatment methods produce a favorable experience with fitusiran prophylaxis compared to another prophylaxis treatment

[0205] In some embodiments, the present treatment methods improve the joint health of patients with hemophilia. The efficacy of fitusiran in improving joint health is measured using the Hemophilia Joint Health Score (HJHS). The HJHS is a clinician-reported outcome tool for the evaluation of joint health in participants with hemophilia. The HJHS assesses impairment in six joints (right and left elbows, knees, and ankles) and includes a global gait score assessed by a trained physician or trained healthcare professional using an 1 l-item score (swelling, duration of swelling, axial alignment, muscle atrophy, crepitus, flexion loss, extension loss, joint pain, instability, gait, and strength). Total scores range from 0 to 148, with lower scores denoting less functional limitations (reduced impairment). The HJHS assessment may be administered at the time of the first dose of fitusiran prophylaxis, and after treatment with one or more (e.g., two or more, three or more, four or more, five or more, or six or more) doses of fitusiran (e.g., administered subcutaneously at 50 mg administered about once every four weeks or about once a month). In some embodiments, the present treatment methods reduce the HJHS score of patients treated with fitusiran prophylaxis compared to another prophylaxis treatment.

[0206] According to the International Conference on Harmonisation (ICH) E2A guideline Definitions and Standards for Expedited Reporting, and 21 Code of Federal Regulations (CFR) 312.32, IND Safety Reporting, an adverse event (AE) is any untoward medical occurrence in a patient or clinical investigational patient administered a medicinal product and which does not necessarily have a causal relationship with this treatment. Since bleeding episodes are recorded as an efficacy assessment of fitusiran, these will not be treated as AEs unless they meet any of the severe adverse event (SAE) criteria listed below.

[0207] An SAE is any untoward medical occurrence that at any dose: a. results in death, b. is life-threatening (an event which places the patient at immediate risk of death from the event as it occurred. It does not include an event that had it occurred in a more severe form might have caused death), c. requires in-patient hospitalization or prolongation of existing hospitalization, d. results in persistent or significant disability or incapacity, e. is a congenital anomaly or birth defect, or f. is an important medical event that may not be immediately life-threatening or result in death or hospitalization but may jeopardize the patient and may require intervention to prevent one of the other outcomes listed in the definition above (e.g., events include allergic bronchospasm requiring intensive treatment in an emergency room or at home, blood dyscrasias, convulsions, or the development of drug dependency or abuse).

[0208] In some embodiments, the present treatment methods reduce the risk of a hepatobiliary event in a human patient receiving fitusiran for prophylactic treatment of hemophilia A or B with or without factor VIII or factor IX inhibitors. These methods use lower dosage of fitusiran, or allow AT-based downward titration of fitusiran dosage to a level that is appropriate for individual patients, such that hepatobiliary adverse events are reduced (e.g., fitusiran dosage at 50 mg Q2M, 20 mg QM, or 20 Q2M). In some embodiments, the hepatobiliary event is ALT elevation >3x upper limit of normal (ULN), AST elevation >3x upper limit of normal (ULN), severe liver toxicity, liver failure, cholecystitis, cholelithiasis, or need for cholecystectomy. In some embodiments, the risk of a hepatobiliary event is reduced as compared to the risk of a hepatobiliary event in a patient treated with the original dose regimen (e.g., a regimen of 80 mg QM or Q4W). In some embodiments, the exposure adjusted incidence rate (per 100 patient years) of cholecystitis/cholelithiasis is about 2.26 in patients treated with the AT-based dose regimen, compared to about 14.67 in patients treated with the original dose regimen. In some embodiments, the exposure adjusted incidence rate (per 100 patient years) of ALT/AST elevations > 3xULN is about 2.06 in patients treated with the AT-based dose regimen, compared to about 18.25 in patients treated with the original dose regimen. In some embodiments, ALT and AST elevations observed in patients treated with the AT-based dose regimen are transient.

[0209] In some embodiments, the method further comprises obtaining a liver function test in the human patient every month following initiation of fitusiran treatment. In some embodiments, the liver function test is an aspartate transaminase test. In some embodiments, the liver function test is an alanine aminotransferase test. In some embodiments, the method further comprises obtaining a liver function test every month for the first six months following initiation of fitusiran treatment.

[0210] In some embodiments, the method further comprises discontinuing or pausing fitusiran treatment if the human patient is diagnosed with gallbladder disease. In some embodiments, the gallbladder disease comprises cholecystitis, cholelithiasis, or a need for cholecy stectomy .

[0211] The risk of thrombosis is multifactorial and may be greater in patients with AT activity levels <10% and/or existent comorbidities. AT levels are monitored to reduce the potential risk of thrombosis. Fitusiran is used with caution in patients with underlying conditions that may predispose them to a higher risk of thrombosis. In some embodiments, patients do not have established thrombophilic conditions or a prior history of thrombosis. [0212] In some embodiments, the present treatment methods reduce the risk of a thrombotic event in a human patient receiving fitusiran for prophylactic treatment of hemophilia A or B with or without factor VIII or factor IX inhibitors. In some embodiments, the risk of a thrombotic event is reduced as compared to the risk of a thrombotic event in a patient treated with the original dose regimen (e.g., a regimen of 80 mg QM or Q4W). In some embodiments, the exposure adjusted incidence rate (per 100 patient years) of thrombotic events is about 0.82 in patients treated with the AT-based dose regimen, compared to about 2.28 in patients treated with the original dose regimen.

[0213] The present treatment methods may also reduce the consumption of factor or BPA in a human patient receiving fitusiran for prophylactic treatment of hemophilia A or B with or without factor VIII or factor IX inhibitors. The reduction may be in, e.g., the annualized consumption of factor or BPA or the weight-adjusted dose of factor of BPA needed to treat a bleeding episode in the patient.

VI. Articles of Manufacture and kits

[0214] The present invention also provides kits comprising a pharmaceutical composition for use in the present treatment methods. Such kits include one or more vials or one or more pre-filled syringes or injectors (e.g., pre-filled pens such as pre-filled single-use pens) comprising a pharmaceutical composition of the invention and instructions for use, e.g., instructions for administering a therapeutically effective amount of fitusiran.

[0215] In some embodiments, fitusiran is packaged in a drug delivery device. In some embodiments, a drug delivery device may involve a needle -based injection system as described in Table 1 of section 5.2 of ISO 11608-l:2014(E). As described in ISO 11608- l:2014(E), needle -based injection systems may be broadly distinguished into multi-dose container systems and single-dose (with partial or full evacuation) container systems. The container may be a replaceable container or an integrated non-replaceable container.

[0216] As further described in ISO 11608-l:2014(E), a multi-dose container system may involve a needle-based injection device with a replaceable container. In such a system, each container holds multiple doses, the size of which may be fixed or variable (pre-set by the user). Another multi-dose container system may involve a needle-based injection device with an integrated non-replaceable container. In such a system, each container holds multiple doses, the size of which may be fixed or variable (pre-set by the user).

[0217] As further described in ISO 11608-l:2014(E), a single-dose container system may involve a needle-based injection device with a replaceable container. As also described in ISO 11608-l:2014(E), a single-dose container system may involve a needle-based injection device with an integrated non-replaceable container. In some embodiments, each container holds a single dose, whereby the entire deliverable volume is expelled (full evacuation). In other embodiments, each container holds a single dose, whereby a portion of the deliverable volume is expelled (partial evacuation).

[0218] An exemplary sleeve-triggered auto-injector with manual needle insertion is described in W02015/004052. Exemplary audible end-of-dose feedback mechanisms are described in WO2016/193346 and WO2016/193348. An exemplary needle-safety mechanism after using an auto-injector is described in WO2016/193352. An exemplary needle sheath remover mechanism for a syringe auto-injector is described in WO2016/193353. An exemplary support mechanism for supporting an axial position of a syringe is described in WO2016/193355.

[0219] Fitusiran may be supplied in a single-use vial containing 20 mg fitusiran (equivalent to 21 mg fitusiran sodium) in 0.2 mL of solution at a concentration of 100 mg/mL. Fitusiran may also be supplied in a single-dose pre-filled pen containing 50 mg of fitusiran (equivalent to 53 mg fitusiran sodium) in 0.5 mL solution at a concentration of 100 mg/mL. In some embodiments, fitusiran is provided as a solution for injection as 50 mg/0.5 mL (100 mg/mL) in a single-dose prefilled pen or 20 mg/0.2 mL (100 mg/mL) in a singledose vial.

[0220] In some embodiments, the vial or pre-filled pen is supplied in a carton. In some embodiments, fitusiran is available in cartons containing one prefilled pen or one vial.

[0221] In some embodiments, fitusiran is a clear, colorless to pale yellow solution supplied in a single-dose pre-filled pen or a single-dose vial. In some embodiments, each prefilled pen is designed to deliver 50 mg of fitusiran in 0.5 mL. In some embodiments, each vial is designed to deliver 20 mg of fitusiran in 0.2 mL.

[0222] In some embodiments, fitusiran is stored at 2°C to 30°C (36°F to 86°F) in the original carton to protect from light. In some embodiments, fitusiran is not shaken, heated, frozen, or put into direct sunlight at any time.

[0223] Unless otherwise defined herein, scientific and technical terms used in connection with the present disclosure shall have the meanings that are commonly understood by those of ordinary skill in the art. Exemplary methods and materials are described below, although methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present disclosure. In case of conflict, the present specification, including definitions, will control. Generally, nomenclature used in connection with, and techniques of hematology, medicine, medicinal and pharmaceutical chemistry, and cell biology described herein are those well-known and commonly used in the art. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular. All publications and other references mentioned herein are incorporated by reference in their entirety. Although a number of documents are cited herein, this citation does not constitute an admission that any of these documents forms part of the common general knowledge in the art. As used herein, the term “approximately” or “about” as applied to one or more values of interest refers to a value that is similar to a stated reference value. In certain aspects, the term refers to a range of values that fall within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less in either direction (greater than or less than) of the stated reference value unless otherwise stated or otherwise evident from the context.

[0224] According to the present disclosure, back-references in the dependent claims are meant as short-hand writing for a direct and unambiguous disclosure of each and every combination of claims that is indicated by the back-reference. Further, headers herein are created for ease of organization and are not intended to limit the scope of the claimed invention in any manner.

[0225] In order that this invention may be better understood, the following examples are set forth. These examples are for purposes of illustration only and are not to be construed as limiting the scope of the invention in any manner.

EXAMPLES

Example 1: Phase I/II OLE (NCT02554773) Clinical Study Design and Patient Population

[0226] In a Phase II OLE study of AD-57213 (Sense (5’ to 3’):

GfsgsUfuAfaCfaCfCfAfuUfuAfcUfuCfaAfL96 (SEQ ID NO:3); Antisense (5’ to 3’): usUfsgAfaGfuAfaAfuggUfgUfuAfaCfcsasg (SEQ ID NO: 4)), patients without inhibitors previously administered AD-57213 in the Phase I Part B and C clinical trials described above, were eligible to be enrolled into a Phase II open-label extension (OLE) study. Twelve patients from the Phase I Part B study having Hemophilia A or B that had been subcutaneously administered 0.015 mg/kg weekly for three weeks (15 micrograms/kg qw x 3; 15 mcg/kg) of AD-57213; or had been subcutaneously administered 0.045 mg/kg weekly for three weeks (45 micrograms/kg qw x 3; 45 mcg/kg) of AD-57213; or had been subcutaneously administered 0.075 mg/kg weekly for three weeks (75 micrograms/kg qw x 3; 75 mcg/kg) of AD-57213; and 18 patients from the Phase I Part C study having Hemophilia A or B that had been subcutaneously administered a monthly 0.225 mg/kg dose of AD-57213 for three months (225 micrograms/kg qm x 3; 225 mcg/kg); or had been subcutaneously administered a monthly 0.450 mg/kg dose of AD-57213 for three months (450 micrograms/kg qm x 3; 450 mcg/kg); or had been subcutaneously administered a monthly 0.900 mg/kg dose of AD-57213 for three months (900 micrograms/kg qm x 3; 900 mcg/kg); or had been subcutaneously administered a monthly 1.800 mg/kg dose of AD-57213 for three months (1800 micrograms/kg qm x 3; 1800 mcg/kg); or had been subcutaneously administered a monthly fixed dose of 80 mg of AD-57213 for three months (80 mg qM x 3) were eligible to be enrolled into this study.

[0227] Sixteen patients were enrolled. Eight patients having Hemophilia A (n=6) or Hemophilia B (n=2) were subcutaneously administered a fixed dose of 50 mg of AD-57213 monthly for three months (50 mg qM x 3); and 8 patients having Hemophilia A (n=7) or Hemophilia B (n=l) were subcutaneously administered a fixed dose of 80 mg of AD-57213 monthly for three months (50 mg qM x 3). The demographics and baseline characteristics of the patients enrolled in this study are shown in Table 5 below.

Table 5. Demographics and Baseline Characteristics of Study Participants

Example 2: ATLAS-INH and ATLAS-A/B Clinical Study Design and Patient Population

[0228] This Example describes two Phase 3 clinical trials protocols used in studies of fitusiran administered subcutaneously to male patients having severe hemophilia A or B with or without inhibitors.

Study Assessments

[0229] Patient-reported outcomes were utilized to assess health-related quality of life (HRQOL), physical activity, and treatment satisfaction and health utility. The Haem-A-QoL was provided to patients >17 years of age. The Haemo-QoL (children’s and adolescent’s short version for age groups II/III [8-16 years of age]) was provided to patients <17 years of age. The Treatment Satisfaction Questionnaire for Medication (TSQM) was used to assess patient satisfaction with treatment in patients >18 years of age. The HAL was assessed in patients >18 years of age, and the pedHAL will be assessed in patients <18 years of age. The EQ-5D-5L was used as a measure of QOL outcome in patients >18 years of age. Study Design

[0230] The clinical trials described herein are open-label Phase 3 studies designed to evaluate the efficacy and safety of fitusiran in male patients aged >12 years with hemophilia A or B, with or without inhibitory antibodies to FVIII or FIX, who are not receiving prophylactic therapy. The study designs are described in FIG. 3 (patients with inhibitors) and FIG. 4 (patients without inhibitors). FIG. 5 describes the participant disposition of patients enrolled in the Phase 3 clinical trial of fitusiran in Hemophilia A and B patients with inhibitors.

[0231] Eligible patients were randomized in a 2: 1 ratio to the following arms: i. Fitusiran treatment arm', fitusiran 80 mg administered SC as prophylaxis once monthly, with use of on-demand BPA or factor concentrate for treatment of breakthrough bleeding episodes, and ii. On-demand arm', on-demand (OD) use of BPA or factor concentrate for treatment of breakthrough bleeding episodes.

[0232] On-demand use of BPA or factor concentrate is defined as the use of these agents, as needed, for episodic bleeding episodes, and not on a regular regimen intended to prevent spontaneous bleeding. Throughout the study, patients in the fitusiran treatment arm received on-demand treatment for breakthrough bleeding episodes with BPA or factor concentrate, as appropriate. In the clinical trials, factor concentrate is also referred to as clotting factor concentrate (CFC).

[0233] All patients were treated for a total of nine months; patients randomized to the fitusiran treatment arm received a total of nine subcutaneous injections of fitusiran. Because the full PD effect of fitusiran is not achieved until approximately 28 days after receiving the first dose, efficacy was assessed during the final eight months on study (Day 29 to Month 9). Therefore, the overall fitusiran treatment period was defined as the onset period (Day 1 to Day 28 after receipt of the first dose, during which the AT lowering capacity of fitusiran is increasing but has not yet reached therapeutic levels) plus the efficacy period (Day 29 and after, when the AT lowering capacity of fitusiran has achieved therapeutic target range).

Study population

[0234] The inclusion criteria were as follows: i. males >12 years of age, ii. severe hemophilia A or B with or without inhibitors evidenced by a central laboratory measurement or documented medical record evidence of FVIII < 1% or FIX level <2% prior to treatment, and iii. a minimum of six bleeding episodes requiring BPA or factor concentrate treatment within the last six months prior to treatment.

[0235] A patient with severe hemophilia A or B with inhibitors is evidenced by on- demand use of BPAs to manage bleeding episodes for at least the last six months prior to treatment, and must meet at least one of the following Nijmegen-modified Bethesda assay results criteria:

- inhibitor titer of >0.6 BU/mL prior to treatment, or

- inhibitor titer of <0.6 BU/mL prior to treatment with medical record evidence of two consecutive titers >0.6 BU/mL, or

- inhibitor titer of <0.6 BU/mL prior to treatment with medical record evidence of anamnestic response.

[0236] A patient with severe hemophilia A or B without inhibitors is evidenced by on- demand use of factor concentrate to manage bleeding episodes for at least the last six months prior to treatment, and must meet each of the following criterion: i. Nijmegen modified Bethesda assay inhibitor titer of <0.6 BU/mL, ii. no use of BPAs to treat bleeding episodes for at least the last six months, and iii. no history of immune tolerance induction therapy within the last six months.

[0237] The key exclusion criteria were as follows: i. known co-existing bleeding disorders other than hemophilia A or B, i.e., Von Willebrand’s disease, additional factor deficiencies, or platelet disorders, ii. current use of BPA (for patients with inhibitors) or factor concentrates (for patients without inhibitors) as regularly administered prophylaxis designed to prevent spontaneous bleeding episodes, iii. AT activity <60% prior to treatment, iv. presence of clinically significant liver disease, as indicated by any of the conditions below:

1. INR >1.2,

2. ALT and/or AST > 1.5x upper limit of normal reference range (ULN),

3. total bilirubin >ULN (>1.5x ULN in patients with Gilbert’s Syndrome), 4. history of portal hypertension, esophageal varices, or hepatic encephalopathy, and/or

5. presence of ascites by physical exam, v. hepatitis C virus antibody positive, except patients with a history of HCV infection who both:

1. completed curative treatment at least 12 weeks prior to enrollment and attained sustained virologic response as documented by a negative HCV RNA at screening, or they have spontaneously cleared infection as documented by negative HCV RNA at Screening, and

2. have no evidence of cirrhosis according to one of the following assessments: a. FibroScan <12.5 kPa (where available), or b. FibroTest score <0.75 and APRI <2 (if FibroScan unavailable), vi. presence of acute hepatitis, i.e., hepatitis A or hepatitis E, vii. presence of acute or chronic hepatitis B infection (IgM anti-HBc antibody positive or HBs Ag positive), viii. platelet count <100, 000/pL, ix. presence of acute infection prior to treatment, x. known to be HIV positive with CD4 count <200 cells/pL, xi. estimated glomerular filtration rate <45 mL/min/1.73 m² (using the Modification of Diet in Renal Disease [MDRD] formula), xii. co-existing thrombophilic disorder, as determined by presence of any of:

1. FV Leiden mutation (homozygous or heterozygous),

2. protein S deficiency,

3. protein C deficiency, or

4. prothrombin mutation (G20210A; homozygous or heterozygous), xiii. history of antiphospholipid antibody syndrome, xiv. history of arterial or venous thromboembolism, atrial fibrillation, significant valvular disease, myocardial infarction, angina, transient ischemic attack, or stroke (except patients who have experienced thrombosis associated with indwelling venous access), xv. malignancy within two years prior to treatment, except for basal or squamous cell carcinoma of the skin that has been successfully treated, xvi. significant active and poorly controlled (unstable) cardiovascular, neurologic, gastrointestinal, endocrine, renal or psychiatric disorders unrelated to hemophilia identified by key laboratory abnormalities or medical history, xvii. anticipated need of surgery during the study or planned surgery scheduled to occur during the study, xviii. completion of a surgical procedure within 14 days prior to treatment, or currently receiving additional BPA infusion for postoperative hemostasis, xix. history of multiple drug allergies or history of allergic reaction to an oligonucleotide or GalNAc, xx. inadequate venous access to allow the blood draws required by the study protocol, xxi. history of intolerance to SC injection(s), xxii. current or future participation in another clinical study, scheduled to occur during this study, involving an investigational product other than fitusiran or an investigational device; in order to participate in this study, patient must discontinue the investigational product or investigational device at least 30 days (or 5x the investigational product half-life, whichever is longer) prior to dosing (Day 1), xxiii. current or prior participation in a gene therapy trial, and xxiv. history of alcohol abuse within the 12 months prior to treatment.

Alcohol abuse is defined as regular weekly intake of more than 14 units (unit: 1 glass of wine [approximately 125 mL] = 1 measure of spirits (approximately 1 fluid ounce) = * pint of beer [approximately 284 mL]).

[0238] The baseline demographics of patients treated in each study are shown in Table 6. The baseline demographics are for the intent-to-treat (ITT) analysis set (i.e., all randomized patients). Overall, baseline patient characteristics where similar across groups.

Table 6. Mean Baseline Patient Demographics by Study (ITT Set)

Dosing regimens and formulation

[0239] Fitusiran (SAR439774) solution for injection (SC use) was supplied as a sterile solution. Patients randomized to the fitusiran treatment arm received open-label 80 mg fitusiran as an SC injection once monthly, for a total of nine months.

Example 3: Clinical Trial Protocol for an Open-Label, Switching Study to Describe the Efficacy and Safety of Fitusiran Prophylaxis in Patients with Hemophilia A and B Previously Receiving Factor or Bypassing Agent Prophylaxis (ATLAS-PPX)

[0240] The Example describes an open-label, Phase 3 switching study designed to demonstrate the efficacy and safety of fitusiran in patients with hemophilia A or B, who are currently treated with prophylactic regimens of factor concentrates or BPAs. The switching design allows for an intra-patient control to enable examination of the effect of the two treatment methods through comparison of the median ABR during the factor or BPA prophylaxis period and the median ABR of the same patient group when receiving fitusiran, while limiting confounding effects of different patient bleeding phenotypes and prophylaxis therapy variability. Inhibitor patients with hemophilia B may have a high unmet need despite prophylactic BPA therapy, with limited other treatment options. Therefore, a limited number of inhibitor patients with hemophilia B who are not adequately responding to prophylactic BPA therapy could enroll directly into the fitusiran treatment period, thereby skipping the 6- month BPA prophylaxis period. The onset period duration reflects modeling data that estimates it takes approximately 28 days to reach the therapeutic target range in the majority of patients. Given that the study design employed is a single treatment arm, with a switch from prophylaxis to fitusiran for each patient, the study is not blinded. [0241] The primary endpoint of the study is ABR in the fitusiran efficacy period and the factor or BPA prophylaxis period. ABR is a well-established endpoint that has been used as the primary endpoint in global approvals of factor replacement and BPA products. Secondary endpoints characterize annualized spontaneous and joint bleeding rates, change in Haem-A- QoL physical health score and total score in patients 17 years of age, ABR in the onset period, overall safety profile and the consumption of factor/BPA.

[0242] Characterization of bleeding episodes is clinically relevant to assess overall bleeding episode protection. Joint bleeding episodes result in pain and hemarthrosis, leading to progressive joint destruction, and hence are important to assess. The Haem-A-QOL is a hemophilia- specific HRQOL survey instrument, has been used in other hemophilia clinical trials, has been validated, reviewed by clinicians, and is considered the most appropriate HRQOL tool available for use in the study.

[0243] The study population will be comprised of males ^ 12 years of age; it is appropriate to study fitusiran in adolescents (patients to <18 years of age) because the pathophysiology of disease progression and bleeding episode management is the same as adults and self-management of hemophilia typically begins at 12 years of age.

[0244] In the event of a breakthrough bleeding episode, on-demand use of factors or BPAs will be permitted throughout the entire study duration.

Duration of Treatment

[0245] The duration of treatment with fitusiran is 7 months. The estimated total time on the study, inclusive of screening, for each patient is up to 15 months for all patients who enroll in the extension study, except for patients in the subgroup of Cohort A, which is up to 9 months. The estimated total time on study may be up to 21 months (up to 15 months for patients in the subgroup of Cohort A) for patients who do not enroll in the extension study due to the requirement for an additional six months of follow-up for monitoring of AT levels.

Study Objectives and Endpoints

[0246] The primary objective of this study is to characterize the frequency of bleeding episodes while receiving fitusiran treatment, relative to the frequency of bleeding episodes while receiving factor or bypassing agent (BPA) prophylaxis.

[0247] The secondary objectives of this study are: to characterize the following while receiving fitusiran treatment, relative to receiving factor or BPA prophylaxis: the frequency of spontaneous bleeding episodes, the frequency of joint bleeding episodes, and health related quality of life (HRQOL) in patients years of age; to characterize the frequency of bleeding episodes during the onset and treatment periods in patients receiving fitusiran; to characterize the safety and tolerability of fitusiran; and to characterize the annualized weight-adjusted consumption of factor/BPA while receiving fitusiran treatment, relative to receiving factor or BPA prophylaxis.

[0248] The exploratory objectives are: to characterize the effects of fitusiran on the following patient-reported outcomes while receiving fitusiran treatment, relative to receiving factor or BPA prophylaxis: patient satisfaction with fitusiran, patient activity, and

HRQOL in adolescents 12 to <17 years of age); to characterize the pharmacodynamic (PD) effect, pharmacokinetics (PK), and immunogenicity of fitusiran; to characterize the effects of fitusiran on joint status while receiving fitusiran treatment, relative to receiving factor or BPA prophylaxis; and to characterize the effects of fitusiran on patient resource use, relative to receiving factor or BPA prophylaxis.

[0249] The primary endpoint of this study is to evaluate the Annualized Bleeding Rate (ABR) in the fitusiran efficacy period and the factor or BPA prophylaxis period.

[0250] The secondary endpoints are to evaluate: annualized spontaneous bleeding rate in the fitusiran efficacy period and the factor or BPA prophylaxis period; annualized joint bleeding rate (AJBR) in the fitusiran efficacy period and the factor or BPA prophylaxis period; and change in Haem-A-QOL physical health score and total score in the fitusiran treatment period and the factor or BPA prophylaxis period.

[0251] The exploratory endpoints are:

Change in the following in the fitusiran treatment period: treatment Satisfaction Questionnaire for Medication (TSQM) domain scores, Haemophilia Activities List (HAL) score, paediatric HAL (pedHAL) score, euroQol-5 Dimensions (EQ-5D) score, Haemo-QOL score, and/or Hemophilia Joint Health Score (HJHS); number of target joint bleeding episodes; incidence and titer of antidrug antibodies to fitusiran in the fitusiran treatment period; antithrombin (AT) activity level over time; thrombin generation over time; fitusiran plasma levels; and change in patient resource use (e.g., work/school attendance, visits to doctor/hospital).

[0252] The safety endpoint was to evaluate the incidence, severity, seriousness, and relatedness of adverse events.

Study Design

[0253] The study evaluates male patients, aged 2= 12 years, with hemophilia A or B, who have switched from prior bypassing agent (BPA, Cohort A) or factor (Cohort B) prophylaxis. Cohort A patients have inhibitory antibodies to Factor VIII or Factor IX, whereas Cohort B patients do not have inhibitor antibodies to Factor VIII or Factor IX.

[0254] A subgroup of Cohort A patients includes hemophilia B patients with inhibitory antibodies to Factor IX who are not responding adequately to BPA prophylaxis treatment (historical ABR 2== 20) .

[0255] The study has three periods defined by type of prophylaxis regimen (FIG. 6): Six-month factor or BPA prophylaxis period in which patients continued their pre-study, regularly scheduled prophylaxis regimen with factors or BPAs, 1 -month onset period in which patients receive first dose of fitusiran while continuing their factor or BPA prophylaxis for up to 7 days, and 6-month fitusiran efficacy period in which patients receive fitusiran as prophylaxis.

[0256] The subgroup of Cohort A patients who are not responding adequately to BPA prophylaxis treatment will not participate in the six-month BPA prophylaxis period and will start to directly receive fitusiran (in the one-month onset period) after the screening period (FIG. 7). [0257] Together, the one-month onset period and the six-month fitusiran efficacy period constitute the fitusiran treatment period.

[0258] On-demand use of factor concentrates or BPAs is defined as the use of these agents, as needed, for episodic bleeding, and not on a regular regimen intended to prevent spontaneous bleeding. Throughout the study, patients in the fitusiran treatment period received on-demand treatment for breakthrough bleeding episodes with factors or BPAs, as appropriate. For patients in the fitusiran treatment period who have received at least 1 dose of fitusiran and are being treated for breakthrough bleeding episodes, it is recommended to follow the guidelines provided in Table 4.

[0259] Following the screening and prophylaxis periods (or following the screening period for the subgroup of Cohort A enrolling directly into the fitusiran treatment period) all patients were treated with fitusiran for a total of seven months. Therefore, the overall fitusiran treatment period was defined as the onset period (day 1-28 after receipt of the first dose, during which the AT lowering capacity of fitusiran is increasing but has not yet reached therapeutic levels) plus the efficacy period (day 29 and after, when the AT lowering capacity of fitusiran has achieved therapeutic target range).

Study Population

[0260] This study will include males with severe hemophilia A or B with or without inhibitors, aged 12 years, who have been prescribed prophylactic treatment with factor concentrates or BPAs for at least 6 months prior to screening. Diagnosis of severe hemophilia A or B will be based on a central laboratory measurement or documented medical record evidence of FVIII level < 1% or FIX level ^-2%. Patients with inhibitors must have used BPAs for prophylaxis for at least the last 6 months prior to screening and must meet one of the following Nijmegen-modified Bethesda assay results criteria: 1) inhibitor titer of ^0.6 BU/mL at screening; 2) inhibitor titer of <0.6 BU/mL at screening with medical record evidence of 2 consecutive titers ^0.6 BU/mL; or 3) inhibitor titer of <0.6 BU/mL at screening with medical record evidence of anamnestic response.

[0261] The subgroup of patients in Cohort A patients must additionally meet the following criteria to be eligible to start treatment with fitusiran directly after the screening period: 1) hemophilia B with inhibitory antibody to Factor IX as defined above; 2) Not responding adequately to BPA treatment (historical ABR 2== 20) prior to enrollment; and 3) 6- month BPA prophylaxis period should be omitted as deemed appropriate. A minimum of 2 bleeding episodes requiring BPA treatment within the last 6 months prior to screening is required.

[0262] Patients without inhibitors must have used factor concentrates for prophylaxis for at least the last 6 months prior to Screening and must meet each of the following criteria: 1) Nijmegen-modified Bethesda assay inhibitor titer of <0.6 BU/mL at screening; 2) no use of bypassing agents to treat bleeding episodes for at least the last 6 months prior to screening; and 3) no history of immune tolerance induction therapy within the last 3 years prior to Screening. A minimum of 1 bleeding episode requiring factor treatment within the last 12 months prior to Screening is required.

[0263] The inclusion criteria are further described as follows:

101. males years of age;

102. severe hemophilia A or B, as evidenced by a measurement at screening or documented medical record evidence of FVIII <1% or FIX level ^-2%;

103. a minimum of two bleeding episodes requiring BPA treatment within the last six months prior to screening for patients with inhibitory antibodies to Factor VIII or Factor IX (Cohort A); or a minimum of one bleeding episode requiring factor treatment within the last 12 months prior to screening for patients without inhibitory antibodies to Factor VIII or Factor IX (Cohort B);

104. must meet either the definition of inhibitor or non-inhibitor patient as below:

Inhibitor (Cohort A): use of BPAs for prophylaxis and for any bleeding episodes for at least the last six months prior to Screening, and meet one of the following Nijmegen-modified Bethesda assay results criteria: o inhibitor titer of ^0.6 BU/mL at Screening, or o inhibitor titer of <0.6 BU/mL at Screening with medical record evidence of 2 consecutive titers ^0.6 BU/mL, or o inhibitor titer of <0.6 BU/mL at Screening with medical record evidence of anamnestic response; o the subgroup of Cohort A patients must additionally meet the following criteria to be eligible to start treatment with fitusiran directly after the screening period:

■ hemophilia B with inhibitory antibody to Factor IX as defined above, and ■ not responding adequately to BPA treatment (historical ABR 2== 20) prior to treatment; non-inhibitor: use of factor concentrates for prophylaxis and for any bleeding episodes for at least the last six months prior to Screening, and meet each of the following criterion: o Nijmegen-modified Bethesda assay inhibitor titer of <0.6 BU/mL at Screening, o no use of bypassing agents to treat bleeding episodes for at least the last 6 months prior to Screening and, o no history of immune tolerance induction therapy within the past three years prior to Screening; and

105. prescribed (and adhered to) prophylactic treatment (documented in the medical or pharmacy records) of hemophilia with factor concentrates or BPAs for at least six months prior to Screening; the regimen must be consistent with the approved prescribing information for the product or local recommendations, allowing for adjustment to individual patient response, and designed to decrease spontaneous bleeding; and

106. Adherent to the prescribed prophylactic therapy for at least 6 months prior to Screening per Investigator assessment.

[0264] The exclusion criteria are further described as follows:

E 01. known co-existing bleeding disorders other than hemophilia A or B, i.e., Von Willebrand’s disease, additional factor deficiencies, or platelet disorders;

E 02. current participation in immune tolerance induction therapy (ITI);

E 03. AT activity <60% at Screening, as determined by central laboratory measurement.

E 04. presence of clinically significant liver disease, or as indicated by any of the conditions below:

- INR >1.2;

ALT and/or AST > 1.5x upper limit of normal reference range (ULN);

Total bilirubin >ULN (>1.5x ULN in patients with Gilbert’s Syndrome); History of portal hypertension, esophageal varices, or hepatic encephalopathy; or presence of ascites by physical exam;

E 05. Hepatitis C virus antibody positive, except patients with a history of HCV infection who meet both of the following conditions: completed curative treatment at least 12 weeks prior to enrollment and attained sustained virologic response as documented by a negative HCV RNA at screening, or they have spontaneously cleared infection as documented by negative HCV RNA at Screening. no evidence of cirrhosis according to one of the following assessments: o FibroScan <12.5 kPa (where available), or o FibroTest score <0.75 and APRI <2 (if FibroScan unavailable) E 06.

E 06. presence of acute hepatitis, i.e., hepatitis A, hepatitis E;

E 07. presence of acute or chronic hepatitis B infection (IgM anti-HBc antibody positive or HBsAg positive);

E 08. platelet count V 100,000/ U L;

E 09. presence of acute infection at Screening;

E 010. known to be HIV positive with CD4 count <200 cells/pL;

E 011. inadequate renal function, as evidenced by estimated glomerular filtration rate V45 mL/min/1.73 m2 (using the Modification of Diet in Renal Disease [MDRD] formula);

E 012. co-existing thrombophilic disorder, as determined by presence of any of the below as identified at central laboratory (or via historical results, where available):

FV Leiden mutation (homozygous or heterozygous), Protein S deficiency, or Protein C deficiency; prothrombin mutation (G20210A; homozygous and heterozygous);

E 013. history of antiphospholipid antibody syndrome; E 014. history of arterial or venous thromboembolism, atrial fibrillation, significant valvular disease, myocardial infarction, angina, transient ischemic attack, or stroke; Patients who have experienced thrombosis associated with indwelling venous access may be enrolled; or

E 015. had a malignancy within two years, except for basal or squamous cell carcinoma of the skin that has been successfully treated.

Dosing Regimens and Formulation

[0265] Fitusiran solution for injection (SC use) is supplied as a sterile solution. Patients receive 80 mg fitusiran as an SC injection once monthly (or 50 mg fitusiran every two months), for a total of seven months.

Antithrombin Level Criteria for a Dose Adjustment

[0266] Upon the first AT level <15%, the patient in this study has another AT activity level sample drawn within 1 week of site receipt of the result. If this result is <15%, this will be considered the second AT activity level <15%. In this study, patients receiving fitusiran at a dose of 50 mg Q2M with more than 1 AT activity level <15% at any time during the study discontinue fitusiran.

Routine Use of Factor or Bypassing Agent Prophylaxis in the Factor or Bypassing Agent Prophylaxis Period

[0267] During the factor or BPA prophylaxis period, patients will continue to receive prophylaxis with their usual products on a regimen consistent with recommendations in the approved prescribing information, allowing for adjustment to individual patient response, and designed to decrease spontaneous bleeding. The regimen used during the factor or BPA prophylaxis period must have a minimum frequency of administration as presented in Table 3 (supra).

[0268] The subgroup of Cohort A patients who are not responding adequately to BPA prophylaxis treatment will not participate in this BPA prophylaxis period and will directly start the fitusiran treatment period after the screening period.

Management of Factor or Bypassing Agent Prophylaxis During the Transition to the Fitusiran Treatment Period

[0269] The first 28 days of fitusiran treatment is referred to as the onset period. During the onset period AT lowering will be progressing toward therapeutic levels. Patients will continue factor or BPA prophylaxis with minimum frequency as in Table 3, for the first 7 days of the fitusiran onset period. Subsequent to Day 7 of the fitusiran treatment period, factor concentrates or BPAs should be administered only for bleeding episodes or if needed in advance of invasive medical procedures.

Bleeding Episode Management Recommendations for Patients During the Fitusiran Treatment Period

[0270] See Section III of the detailed description above.

Study Assessments

[0271] A bleeding episode is defined as any occurrence of hemorrhage that requires BPA or replacement factor infusion, e.g., hemarthrosis, muscle, or mucosal bleeding. The definition of bleeding episode types described below is based on consensus opinion of International Society on Thrombosis and Haemostasis (ISTH) (Blanchette et al., J Thromb Haemost. (2014) 12(11): 1935-9).

[0272] The start time of a bleeding episode was considered the time at which symptoms of a bleeding episode first develop. Bleeding or any symptoms of bleeding at the same location that occurs within 72 hours of the last injection used to treat a bleeding episode at that location was considered a part of the original bleeding event, and will count as one bleeding episode towards the ABR. Any bleeding symptoms that begin more than 72 hours from the last injection used to treat a bleeding episode at that location will constitute a new bleeding event.

[0273] A spontaneous bleeding episode is a bleeding event that occurs for no apparent or known reason, particularly into the joints, muscles, and soft tissues.

[0274] A joint bleeding episode is characterized by an unusual sensation in the joint (“aura”) in combination with 1) increasing swelling or warmth over the skin over the joint, 2) increasing pain, or 3) progressive loss of range of motion or difficulty in using the limb as compared with baseline.

[0275] A muscle bleed may be characterized by pain, swelling and loss of movement over the affected muscle group.

[0276] A target joint is defined as a joint where three or more spontaneous bleeding episodes in a single joint within a consecutive six-month period has occurred; where there have been less than or equal to two bleeding episodes in the joint within a consecutive 12- month period the joint is no longer considered a target joint.

[0277] A traumatic bleeding episode is one that is caused by a known injury or trauma. Bleeding episodes sustained during sports and recreation was counted as traumatic bleeding episodes. [0278] Patient-reported outcomes are utilized to assess health-related quality of life (HRQOL), physical activity, and treatment satisfaction and health utility. The Hemophilia Quality of Life Questionnaire for adults (Haem-A-QOL) is a psychometrically tested QOL assessment instruments for patients with hemophilia. The Haem-A-QOL is provided to patients 17 years of age, and includes 46 items contributing to 10 QOL domains (physical health, feelings, view of yourself, sports and leisure, work and school, dealing with hemophilia, treatment, future, family planning, partnership and sexuality). Scoring for each item is based on a 5-point Likert scale (never, rarely, sometimes, often, and all the time), and higher scores represent greater impairment.

Antithrombin Activity

[0279] AT activity level will be assessed twice a month (about every two weeks) for the first two months and then monthly (about every four weeks) thereafter. On dosing days, samples will be collected within 4 hours prior to dosing. Antithrombin protein may be measured in a subset of plasma samples for correlation.

Statistical Methodology

[0280] The primary analysis will be performed on the EAS and will include all bleeding episodes occurring in the factor or BPA prophylaxis period (Day -162 to Day -1) and the fitusiran efficacy period (Day 29 to Day 190). If a patient does not have bleeding episode data collected after Day 28 (e.g., due to early study discontinuation), the available bleeding episode data starting from Day 1 will be used in the primary analysis. To avoid confounding the treatment effect, bleeding episode data during and after major surgery, antithrombin administration, major trauma, or initiation of prophylaxis treatment with factors or BPAs during the fitusiran treatment period will be excluded from the primary analysis.

[0281] The number of bleeding episodes will be analyzed using a repeated measures negative binomial model with fixed effect of treatment period. The logarithm number of days that each patient spends in the efficacy period matching the bleeding episode data being analyzed will be included as an offset variable to account for unequal follow-up time due to early withdrawal or surgery. The ratio of bleeding rates in the fitusiran efficacy period to the factor or BPA prophylaxis period and its 95% CI and p-value will be presented.

[0282] In addition, as a contrast Bayesian analyses will be performed to summarize the point estimates of the posterior probability of a clinically significant treatment effect, along with associated measures of uncertainty. The estimated mean ABRs in these 2 periods along with their 95% Cis will be presented from this model. In addition, summary statistics for ABR, including the median and interquartile range, will be presented for each treatment arm, where ABR is defined as:

(total number of qualifying bleeding episodes / total number of days in the respective period) x 365.25

[0283] Spontaneous bleeding episodes and joint bleeding episodes will be analyzed using the same method as primary analysis of ABR. Summary statistics, including the median and interquartile range, for annualized spontaneous bleeding rate and annualized joint bleeding rate will be reported.

[0284] Change in Haem-A-QOL physical health score and total score (in patients 17 years of age) in the factor or BPA prophylaxis period and fitusiran treatment period will be summarized descriptively. A mixed model for repeated measures analysis may be performed as deemed appropriate.

[0285] The bleeding episodes in the fitusiran onset period and in the fitusiran treatment period will be analyzed using a negative binomial model with logarithm of follow-up time in the period as an offset parameter. Summary statistics, including the median and interquartile range, for the ABR in 2 periods will be reported.

[0286] The secondary endpoint of annualized weight- adjusted consumption of factor/BPA injections will be summarized using descriptive statistics.

[0287] The fitusiran efficacy period (fitusiran prophylaxis) was defined as starting on Day 29 after the first dose of fitusiran up to Day 190, or the last day of bleeding follow up, whichever is the earliest. The factor/BPA prophylaxis period was defined as starting on Day - 168 to Day -1, or the last day of bleeding follow up, whichever is the earliest. The factor/BPA prophylaxis period is defined as starting on day -168 to day -1, or the last day of bleeding follow up, whichever is the earliest.

Example 4: Clinical Trial Protocol for an Open-label, Long-term Safety and Efficacy Study of Fitusiran in Patients with Hemophilia A or B, with or without Inhibitory Antibodies to Factor VIII or IX (ATLAS-OLE)

[0288] The Example describes a multicenter, multinational, open-label extension study of the long-term safety and efficacy of fitusiran in males at least twelve years of age with hemophilia A or B with or without inhibitory antibodies to factor VIII (FVIII) or factor IX (FIX). The primary endpoint of this study is the incidence, severity, relatedness, and seriousness of AEs and laboratory assessments.

Justification for Dose [0289] The study initiated with a fixed 80 mg fitusiran dose investigated in the Phase 3 trials. Data from Phase 1 and Phase 1/2 studies in participants with hemophilia A and B, with or without inhibitors, and PK/PD modeled data supported the selection of a fixed dose of 80 mg for the Phase 3 studies, as SC administered once monthly. The 80 mg fitusiran dose was generally well tolerated by participants in the Phase 1 and Phase 1/2 studies, and this dose was associated with substantial increases in peak thrombin generation, which approached the lower end of the normal range, but did not exceed the normal range.

[0290] As the risk of vascular thrombotic events is thought to be increased in the setting of low AT activity levels, a reduced dose of 50 mg administered SC once every 2 months was selected to minimize the occurrence of AT activity levels below 10%. At a reduced dose of 50 mg every 2 months, if a participant has more than 1 AT activity level <15% during a 12- month period, the participant will be required to discontinue fitusiran and may have the option to enroll in the lower dose cohort to receive fitusiran at 20 mg Q2M. Participants previously exposed to fitusiran at a dose of 80 mg monthly with no more than 1 AT activity level <15% at any time during fitusiran treatment (based on at least 3 months of prior AT measurements) may have the option to remain on that dose.

[0291] The AT activity window to mitigate the risk of vascular thrombosis while maintaining efficacy is between 15%-35%. The objective of any selected dosing regimen is to maintain participant’s AT activity levels within this window.

[0292] All PK/PD modeling described below was conducted with the objective of finding dosing regimens that could maintain AT activity level between 15% and 35%.

[0293] A population pharmacokinetic/pharmacodynamic (popPK/PD) model that describes the dynamics of AT activity level for participants treated with fitusiran was developed and characterized on AT activity data from Phase 1, Phase 2 and Phase 3 studies. The model with the estimated parameters was used to simulate AT activity level at steady state for different dosing scenarios in a virtual population of 1000 participants.

[0294] The results of the simulations are shown in Table 7. Every 2 months (Q2M) and every month (QM) refer to fitusiran dosing every 8 weeks and every 4 weeks respectively; Trough AT and PeakAT are trough and peak AT activities; 5th, Median and 95th referring to 5th percentile, median and 95th percentile.

Table 7. Simulated AT Activity Percentiles for Various Doses of Fitusiran

[0295] Based on the simulation results from Table 7, at the 50 mg Q2M regimen, approximately 45.7% of the virtual participants are expected to have AT activity <15% and therefore may require a de-escalation in dose.

[0296] The simulations for lower dosing regimens in 1000 de-novo virtual participants, namely 20 mg Q2M and 20 mg QM, predict that 3.8% and 23.4% of the participants would have AT activity level <15%. Thus, based on the simulations, 20 mg Q2M was considered an appropriate de-escalation regimen for the 45.7% participants who may have AT activity level <15% at 50 mg Q2M. On de-escalation to 20 mg Q2M, approximately 8% of the de-escalated participants may have AT activity level <15% and approximately 7% of the de-escalated participants may have AT activity level >35%, while the rest, 84%-85%, of de-escalated participants are predicted to have AT activity level within the target AT window of 15%-35%. [0297] Additionally, the current data and modeling that took into consideration these data suggest that some participants are very sensitive to fitusiran and have low AT activity levels (< 15%) even at the 50 mg Q2M dosing regimen. With the objective to maintain potential fitusiran treatment benefits for these specific participants, while adequately mitigating risk, an additional lower dosing cohort has been implemented for these participants.

[0298] The participants who start on 50 mg Q2M and have AT activity level >35%, will have the option of escalating the dose to 50 mg QM. If 50 mg QM also results in AT activity level >35%, then the participant can escalate to 80 mg QM. Clinical criteria for dose escalation are also included with a goal to achieve adequate efficacy while maintaining AT levels above 15%.

Duration of Treatment

[0299] The estimated total time on the study for a participant that started fitusiran treatment before the 2020 dosing pause is of up to 90 months and up to 62 months for a participant that started fitusiran treatment after the lifting of the pause (including the up to two-month Screening Period, the maximum treatment durations as stated below, and up to two six-month AT Follow-up Periods). The fitusiran treatment duration for each individual participant is to be up to 48 months post initiation of modified IMP dose/frequency following the 2020 Q4 dosing pause or until fitusiran becomes commercially available, whichever comes first. Thus, the maximum treatment duration will vary depending on the timing of the dose re-start relative to the initial dose start in this study. For a participant starting the study directly on new dosing regimens, total study treatment duration would be around 48 months but the longest duration for a participant that started fitusiran dosing before the dosing pause could be 76 months.

Study Objectives and Endpoints

[0300] The primary objective of this study is to characterize the long-term safety and tolerability of fitusiran.

[0301] The secondary objectives of this study are: to characterize efficacy and long-term efficacy of fitusiran as assessed by the frequency of: bleeding episodes, spontaneous bleeding episodes, and joint bleeding episodes; and to characterize the effects of fitusiran on health-related quality of life measures in participants 17 years of age.

[0302] The exploratory objectives are: to characterize the pharmacodynamic (PD) effect of fitusiran; to characterize the pharmacokinetics (PK) of fitusiran; to characterize immunogenicity of fitusiran; to characterize the long-term effects of fitusiran on the following patient- reported outcomes: participant satisfaction with fitusiran, participant activity, health-related quality of life in adolescents (^ 12 to <17 years of age); to characterize the long-term effects of fitusiran on the weight-adjusted consumption of factor concentrates and BPAs; to characterize the long-term effects of fitusiran on consumption of analgesic medications; to characterize the long-term effects of fitusiran on joint health; and to characterize the long-term effects of fitusiran on participant resource use. [0303] The primary endpoint of this study is to evaluate the incidence, severity, relatedness, and seriousness of AEs, and laboratory assessments.

[0304] The secondary endpoints are to evaluate: annualized bleeding rate in the fitusiran treatment period; annualized spontaneous bleeding rater in the fitusiran treatment period; annualized joint bleeding rate (AJBR) in the fitusiran treatment period; and change in haemophilia quality of life for adults (Haem-A-QoL) physical health score in the fitusiran treatment period (in participants ^ 17 years of age).

[0305] The exploratory endpoints are: antithrombin (AT) activity level over time; thrombin generation over time; plasma concentrations of fitusiran and derived PK parameters in: (1) subset of East Asian and non-East Asian participants, (2) subset of participants before and after transition from vial/syringe to pre-filled pen; incidence and titer of antidrug antibodies to fitusiran in the treatment period; incidence of new inhibitors with corresponding inhibitor titer levels in the treatment period; change in the following in the fitusiran treatment period:

Hemophilia quality of life questionnaire for adults (Haem-A-QoL) total score;

Treatment Satisfaction Questionnaire for Medication domain (TSQM09) scores;

Haemophilia Activities List (HAL) scores;

Paediatric HAL (pedHAL) scores;

Pediatric hemophilia quality of life questionnaire (Haemo-QoL) score (in participants 12 to <17 years of age);

EuroQoL-5 Dimension-5 Level questionnaire (EQ-5D-5L) scores; annualized weight-adjusted consumption of factor concentrates and BPAs; reported use of analgesic medications; change in Hemophilia Joint Health Score (HJHS) in the treatment period; number of target joint bleeds, and number of target joints; change in patient resource use (e.g., school/work attendance, visits to doctor/hospital). Study Design

[0306] The study evaluates the long term safety and efficacy of fitusiran in males years of age with hemophilia A or B with or without inhibitory antibodies to FVIII or FIX. Participants from 3 parent studies - ALN AT3SC-003, ALN-AT3SC-004, and ALN AT3SC 009) - may be considered for enrollment. ALN-AT3SC-003 (ATLAS-INH) is a Phase 3 study to evaluate the efficacy and safety of fitusiran in participants with hemophilia A or B, with inhibitory antibodies to factor VIII or IX. ALN-AT3SC-004 (ATLAS-A/B) is a Phase 3 study to evaluate the efficacy and safety of fitusiran in participants with hemophilia A or B, without inhibitory antibodies to factor VIII or IX. ALN AT3SC 009 (ATLAS-PPX) is an open-label, multinational, switching study to describe the efficacy and safety of fitusiran prophylaxis in participants with hemophilia A and B previously receiving factor or bypassing agent prophylaxis.

[0307] The study will consist of the following:

A screening period of up to 60 days.

An open-label treatment period that will vary depending on the timing of participant’s re-start post lifting of the dosing pause implemented in Q42020 (i.e., participants are to be dosed up to 48 months after the re-start):

Participants that started fitusiran dosing in this study after lifting of the dosing pause are planned to have a maximum treatment duration of 48 months.

Participants that have started fitusiran before the 2020 dosing pause are planned to have a maximum treatment duration of 76 months.

An approximately 6-month AT follow-up period after the last dose of fitusiran (note that some participants may undergo two six-month AT follow-up periods, one at the end of the core study, i.e., before starting in the low dose cohort, and one at the completion of the whole study).

[0308] Regarding transition from the parent study:

For participants transitioning directly from the parent studies, the ICF will be signed by the participant at the end of the End of Study (EOS) visit of the parent study, after all the tests and assessments of this visit are performed. The EOS visit tests and assessments in the parent study will be utilized as baseline results. Baseline assessments that are not a part of the EOS visit in the parent study (inhibitor status, ADA, factor VIII/IX levels and pre-dose PK) will be performed after the ICF in this study is signed. Additionally, LFTs must also be performed within seven days prior to dosing and the results must be available before the first injection.

For participants who cannot transition directly from the parent studies or within 10 weeks after the EOT visit of the parent study, a complete screening visit will be performed and it is recommended that this screening visit occurs within 6 months after the EOS visit of the parent study.

[0309] AT assessment must be considered for each participant from the fitusiran arm in a parent study and bleeding management should be planned according to AT activity level.

Study Population

[0310] This study will include males with hemophilia A or B with or without inhibitors, aged >12 years, who have completed a Phase 3 clinical parent study of fitusiran. Participants who have not received fitusiran prior to enrollment will have additional screening requirements similar to the screening assessments of the parent study they have completed.

[0311] Participants will be excluded from this study if they are: currently receiving immune tolerance induction (ITI) therapy; had an operative procedure within 14 days prior to screening or are receiving additional factor/BPA infusion for postoperative hemostasis; or received an investigational drug or device other than fitusiran within 30 days of dosing (Day 1) or five half-lives of the investigational product, whichever is longer.

[0312] Participants are eligible to be included in the study if all of the following criteria apply:

107. Participant must be at least twelve years of age inclusive, at the time of signing the informed consent.

108. Participants with severe hemophilia A or B who have completed a Phase 3 fitusiran clinical trial.

109. Male.

There are no contraceptive requirements for this study except where required by local regulations.

[0313] The exclusion criteria are further described as follows:

E 016. Completion of a surgical procedure within 14 days prior to screening, or currently receiving additional factor concentrate or BPA infusion for postoperative hemostasis.

E 017. current participation in immune tolerance induction therapy (ITI). E 018. Current use of factor concentrates or BPAs as regularly administered prophylaxis designed to prevent spontaneous bleeding episodes. However, participants requiring factor concentrates of BPAs prophylaxis during the study dosing pause period, per Investigator’s judgment in agreement with the study Medical Monitor may be permitted to be enrolled.

E 019. Use of compounds other than factor concentrates or BPAs for hemophilia treatment, including use of emicizumab (Hemlibra®) within six months prior to screening.

E 020. Received an investigational drug or device, other than fitusiran, within 30 days of anticipated IMP administration or five half-lives of the IMP, whichever is longer.

E 021. Current or prior participation in a gene therapy trial.

E 022. ALT and/or AST > 1.5x upper limit of normal reference range (ULN) for participants who are naive to fitusiran at study start; ALT and/or AST >5x ULN for participants who were in the fitusiran arm in the parent study.

Dosing Regimens and Formulation

[0314] Fitusiran solution for injection (SC use) is supplied as a sterile solution for injection. At the start of the trial, patients receive 50 mg fitusiran as an SC injection every two months, for a total of up to 48 months. A lower dose cohort will receive 20 mg fitusiran as an SC injection every two months, for a total of up to 48 months.

Antithrombin Level Criteria for a Dose Adjustment

[0315] At each dose level, upon the first AT level <15%, the patient in this study has another AT activity level sample drawn within 1 week of site receipt of the result. If this result is <15%, this will be considered the second AT activity level <15%. In this study, patients receiving fitusiran at a dose of 50 mg Q2M with more than 1 AT activity level <15% at any time during the study discontinue fitusiran.

Bleeding Episode Management Recommendations for Patients During the Fitusiran Treatment Period

[0316] See Section III of the detailed description above.

Study Assessments

[0317] A bleeding episode is defined as any occurrence of hemorrhage that requires BPA or replacement factor infusion, e.g., hemarthrosis, muscle, or mucosal bleeding. The definition of bleeding episode types described below is based on consensus opinion of International Society on Thrombosis and Haemostasis (ISTH) (Blanchette et al., J Thromb Haemost. (2014) 12(11): 1935-9).

[0318] The start time of a bleeding episode was considered the time at which symptoms of a bleeding episode first develop. Bleeding or any symptoms of bleeding at the same location that occurs within 72 hours of the last injection used to treat a bleeding episode at that location was considered a part of the original bleeding event, and will count as one bleeding episode towards the ABR. Any bleeding symptoms that begin more than 72 hours from the last injection used to treat a bleeding episode at that location will constitute a new bleeding event.

[0319] A spontaneous bleeding episode is a bleeding event that occurs for no apparent or known reason, particularly into the joints, muscles, and soft tissues.

[0320] A joint bleeding episode is characterized by an unusual sensation in the joint

(“aura”) in combination with 1) increasing swelling or warmth over the skin over the joint, 2) increasing pain, or 3) progressive loss of range of motion or difficulty in using the limb as compared with baseline.

[0321] A muscle bleed may be characterized by pain, swelling and loss of movement over the affected muscle group.

[0322] A target joint is defined as a joint where three or more spontaneous bleeding episodes in a single joint within a consecutive six-month period has occurred; where there have been less than or equal to two bleeding episodes in the joint within a consecutive 12- month period the joint is no longer considered a target joint.

[0323] A traumatic bleeding episode is one that is caused by a known injury or trauma. Bleeding episodes sustained during sports and recreation was counted as traumatic bleeding episodes.

[0324] Patient-reported outcomes are utilized to assess health-related quality of life (HRQOL), physical activity, treatment satisfaction, patient resource utilization, and health utility. The Hemophilia Quality of Life Questionnaire for adults (Haem-A-QOL) is a psychometrically tested QOL assessment instruments for patients with hemophilia. The Haem-A-QOL is provided to patients ^ 17 years of age, and includes 46 items contributing to 10 QOL domains (physical health, feelings, view of yourself, sports and leisure, work and school, dealing with hemophilia, treatment, future, family planning, partnership and sexuality). Scoring for each item is based on a 5-point Likert scale (never, rarely, sometimes, often, and all the time), and higher scores represent greater impairment. The Haemo-QoL (Children’s short version for age groups II/III [8-16 years of age]) is provided to participants <17 years of age at baseline.

[0325] The Treatment Satisfaction Questionnaire for Medication -9 items (TSQM-9) will assess participant satisfaction with treatment. The TSQM is a validated psychometric tool that provides a general measure of participant satisfaction with medication (see, e.g., Atkinson et al., Health Qual Life Outcomes. (2004) 2:12). Higher scores indicate better health status.

[0326] The Haemophilia Activities List (HAL) and paediatric HAL (pedHAL) questionnaires will assess subjective functional ability to perform activities of daily living (20). The HAL will be assessed in participants ^ 18 years of age at baseline, and the pedHAL will be assessed in participants <18 years of age at baseline. Higher scores indicate better health status.

[0327] The EuroQoL-5 dimension-5 level questionnaire (EQ-5D-5L) is a standardized instrument for use as a measure of QOL outcome (21). It consists of a questionnaire pertaining to five dimensions (mobility, self-care, usual activities, pain/discomfort, and anxiety /depression and a visual analog scale). Scoring of the questionnaire is based on five degrees of disability (none, slight, moderate, severe, or extreme). Scoring of the visual analog scale is based on a visual scale ranging from 0 (worst imaginable health state) to 100 (best imaginable health state). Higher scores indicate better health status.

[0328] The Hemophilia Joint Health Score (HJHS) is a tool for assessment of joint health in participants with hemophilia. Joint health status will be assessed via the HJHS, as administered by a healthcare professional trained in the use of anthropometric measures, as specified in the So As. Completed HJHS score forms will be collected and archived.

[0329] Information regarding health resource use will be collected, including days missed from work/school (as appropriate) and days not able to perform normal activities outside of work/school due to hemophilia, physician office visits, hemophilia treatment site visits, emergency room visits (reason and number), hospitalizations (reason, dates of hospitalization and associated length of stay).

[0330] Qualitative semi-structured interviews with participants or their caregivers that meet the eligibility criteria of the standalone interview study will be conducted at least one month following the second fitusiran dose injection. The interviews will evaluate participants or caregiver experiences with hemophilia and previous treatments prior to the trial participation, their expectations, and experiences during the trial, specifically any perceived benefit and the importance of these improvements.

Antithrombin Activity

[0331] AT activity level will be assessed twice a month (about every two weeks) for the first month and then monthly (about every four weeks) for the following two months. Thereafter, AT activity level will be assessed every three months until the end of two years, and every six months thereafter. On dosing days, samples will be collected within 4 hours prior to dosing. Antithrombin protein may be measured in a subset of plasma samples for correlation. Following final fitusiran dose, AT activity level will be monitored at approximately monthly intervals for about six months, or as necessary, until AT activity levels return to at least 60%.

Antithrombin Level Criteria for a Dose Adjustment

[0332] With the introduction of the new dose and regimen, participants will receive fitusiran treatment according to the below antithrombin level scenarios and criteria. The dose escalation/de-escalation scheme is described in FIG. 2. The schedule of AT measurements and dose escalation process are shown in FIGS. 8 and 9.

[0333] At each dose level, upon the first AT activity level <15%, the participant must have another AT measurement within one week of site receipt of the results. If the result is <15%, this will be considered the second AT activity level <15%. Participants with one AT activity level <15% must not receive fitusiran at the current regimen until the AT activity level from the second measurement is available. If any of the prior doses are missed or if any of the relevant central AT activity levels are not available, then the decision-making for escalation must be shifted accordingly. In the circumstance that a participant does not meet the criteria for escalation at the timepoints above and later meets criteria, the Investigator may use any of the central AT measurements available once the participant is at steady state but will consult with the study Medical Monitor prior to dose escalation. Antithrombin (AT) activity levels and additional clinical data, as applicable, will be considered in the dose escalation of individual participants.

[0334] Antithrombin activity level will be assessed according to the SoAs. Samples will be collected within 4 hours prior to dosing. Antithrombin protein may be measured in a subset of plasma samples for correlation. Antithrombin levels will be determined by validated assay. Results will be collected and interpreted centrally. Following final fitusiran dose, AT activity level will be monitored at approximately monthly intervals for about 6 months, or as necessary, until AT activity levels return to at least 60% (per the central laboratory). [0335] For participants rolling into this study from the ALN-AT3SC-009 study after being treated under the reduced dosing, their experience at the lower dose in the prior study will be taken into account for dose adjustments in this study.

1. Dose restart a) Restart at 50 mg Q2M participants that reach AT activity levels > 22% (per central laboratory) participants previously exposed to fitusiran at 80 mg QM with more than one AT activity level <15% (per central laboratory) at any time during fitusiran treatment participants with fewer than three AT measurements or received fewer than three doses of fitusiran at 80 mg QM participants naive to fitusiran (no earlier fitusiran dose ever received). Note: these participants are starting fitusiran for the first time but are included in this section because they must follow the 50 mg Q2M regimen.

Participant will start/resume dosing at 50 mg Q2M. b) Restart at 80 mg QM participants that reach AT activity levels > 22% (per central laboratory), and participants previously exposed to fitusiran at 80 mg QM with no more than one AT activity level <15% (per central laboratory) at any time during fitusiran treatment (based on at least three months AT measurements and received at least three doses of fitusiran at 80 mg QM).

2. Dose escalation a) Dose escalation to 50 mg QM after a period of dosing at 50 mg Q2M, and based on two steady state AT activity level >35% at 50 mg Q2M. Specifically, at least two of the three AT measurements at Month 4, Month 5 and Month 6 must be >35% to meet the escalation rule.

If escalation rules are met, participant will receive the 50 mg dose at Month 7 (this will be considered the Month 1 of 50 mg QM, i.e., the second 50 mg QM dose) The Investigator may request permission from the study Medical Monitor to escalate the study participant to 50 mg QM at AT activity levels <35% if: at least two doses of fitusiran at 50 mg Q2M have been administered, and the Investigator judges suboptimal control at 50 mg Q2M, defined as two or more treated bleeds within a 12-week period starting with Month 3. b) Dose escalation to 80 mg QM after a prior escalation to the 50 mg QM, and based on 2 steady state AT activity level >35% at 50 mg QM. The AT measurements at Month 2 and Month 3 of 50 mg QM will be used for assessment. Participants who previously had more than one AT activity level <15% at 80 mg QM are not eligible to re-escalate to this dose level.

If escalation rules are met, participant will receive the 80 mg dose at Month 4 (this will be considered the Day 1 of 80 mg QM)

The Investigator may request permission from the study Medical Monitor to escalate the participant to 80 mg QM at AT activity levels <35% if: at least two doses of fitusiran at 50 mg QM have been administered, and the Investigator judges suboptimal control at 50 mg QM regimen, defined as two or more treated bleeds within a 12-week period starting with Month 2. Dose de-escalation a) Participant at 50 mg Q2M with more than one AT activity level <15% within a 12-month period must discontinue fitusiran 50 mg Q2M dosing and may have the option to enroll into the lower dose cohort, if deemed beneficial for the study participant and study participant is eligible. b) Participants escalated to 50 mg QM or 80 mg QM based on more than one AT activity level >35% who subsequently experience more than one AT activity level <15% within a 12-month period may have the possibility to de-escalate to the previous regimen in consultation with the study Medical Monitor. c) Participants escalated to 50 mg QM or 80 mg QM before the AT activity level of 35% threshold has been reached who subsequently experience more than one AT activity level <15% within a 12-month period cannot be de-escalated and will have to discontinue fitusiran administration. d) Participant having restarted at 80 mg QM subsequently having more than 1 AT activity level <15% within a 12-month period must be de-escalated to 50 mg Q2M.

When the participant is de-escalated, the first fitusiran dose should be administered only after the participant's AT activity level reaches again >22 %. Dose restart at 20 mg Q2M

Participants that have been deemed qualified for this cohort will re-start fitusiran at 20 mg Q2M. 5. Dose escalation

After a period of dosing at 20 mg Q2M, and based on two steady state AT activity level >35% at 20 mg Q2M. Specifically, at least 2 of the 3 AT measurements at Month 4, Month 5 and Month 6 must be >35% to meet the escalation rule.

The investigator may request permission from the study Medical Monitor to escalate the participant to 20 mg QM at AT activity levels <35% if:

At least two doses of fitusiran at 20 mg Q2M have been administered, and

The investigator judges suboptimal control at 20 mg Q2M, defined as two or more treated bleeds within a 12-week period starting with Month 3.

Participants that have been escalated to 20 mg QM cannot be further escalated to 50 mg Q2M.

6. Dose de-escalation a) Participant at 20 mg Q2M with more than one AT activity level <15% within a 12-month period must permanently discontinue fitusiran administration and start the AT follow-up period. b) Participants escalated to 20 mg QM based on more than one AT activity level >35% who subsequently experience more than 1 AT activity level <15% within a 12-month period may have the possibility to de-escalate to the previous regimen. c) Participants escalated to 20 mg QM before the AT activity level of 35% threshold has been reached who subsequently experience more than one AT activity level <15% within a 12-month period cannot be de-escalated to 20 mg Q2M and will have to permanently discontinue fitusiran administration.

Example 5: Incidence of Thrombotic Events in the Fitusiran Clinical Development Program

[0336] AT levels were evaluated as a potential modifiable target for risk mitigation.

Based on the MoA of fitusiran and observation of AT levels <10% for prolonged periods of time in participants with reported vascular thrombotic events, AT levels were evaluated as a potential modifiable target for risk mitigation (see, e.g., Pipe SW et al., Presented at ISTH 2022. Oral presentation). An AT level of between 15-35% was chosen for risk mitigation. Given that data suggest that the risk of serious vascular thrombotic events may be greater with prolonged AT levels <10%, a lower AT threshold of 15% was selected to minimize the occurrence of AT levels <10%. Given that AT levels <25% may lead to a desirable ABR, an upper AT threshold of 35% was chosen based on fitusiran efficacy data. A simulation based on PK/PD modeling was conducted to identify a dose and regimen that would target AT levels between 15% and 35%. See, e.g., FIG. 2. This example describes thrombotic events in the fitusiran clinical program that occurred on the revised AT-based dose regimen (AT-DR) compared to the original dose regimen (ODR).

[0337] Revised breakthrough bleed management guidelines (BMG) were also introduced as a risk mitigation for thrombotic events during the Phase 2 study (FIGS. 10A and 10B) (see, e.g., Young G, et al., RPTH (2023) 7(4): 100179; Nogami K, et al., Blood (2019) 133:399-406). The revised BMG included a reduced dose and frequency of CFC/BPA to enable treatment of breakthrough bleeds during fitusiran prophylaxis (see, e.g., Ragni M, et al. Presented at: EAHAD 2021. Oral presentation).

[0338] The analysis of the incidence of thrombotic events included males aged 12 years with moderate or severe hemophilia A or B, with or without inhibitors who participated in fitusiran studies ATLAS-INH (NCT03417102), ATLAS-A/B (NCT03417245), ATLAS- PPX (NCT03549871), ATLAS-OLE (NCT03754790), and Phase VII OLE (NCT02035605; NCT02554773). The integrated safety analysis compared the exposure-adjusted incidence rate (EAIR) of thrombotic events in participants exposed to the fitusiran AT-DR versus the ODR. Safety analyses included all participants exposed to fitusiran. The exposure adjusted incidence rate was defined as the number of participants with events/participant year of exposure *per 100 participant-years.

[0339] Overall, 286 participants were exposed to fitusiran AT-DR (n=221 hemophilia A; n=65 hemophilia B) and 270 were exposed to ODR (n=211 HA; n=59 HB). Three participants had moderate hemophilia; all other participants had severe hemophilia. Total patient-years of exposure were 486.0 (^ 12 months exposure n=237) with the AT-DR and 306.8 (^ 12 months exposure n=101) with the ODR. There were nine thrombotic events reported in seven participants with the ODR (Table 8), and four events in four participants with the AT-DR (Table 9). The incidence of thrombotic events is summarized in FIG. 11.

Table 8. Thrombotic Events with the Original Fitusiran Dose Regimen

[0340] The above events are also summarized in FIG. 12.

Table 9. Thrombotic Events with the Revised Antithrombin-Based Dose Regimen

[0341] The above events are also summarized in FIG. 13.

[0342] Based on recent reports (see, e.g., Optum Ciinformatics Data Mart™, a US claim database; events occurring from July 2007 to May 2023), observed IRs of VTE were generally higher in PwHA (excluding individuals who had venous thromboembolism within the 6-month pre-index period) than the matched general population. IRs of arterial thrombosis (excluding individuals with a diagnosis of arterial thrombosis within the 6-month pre- index period) for PwHA/B were similar to the matched population (see, e.g., Young G, et al. Abstract presented at WFH 2024). Additional exclusion criteria for the matched populations were individuals with a record of hemophilia or other coagulation defects at any time within the database (ICD-9 codes: 286.xx; ICD-10 codes: D65-D68.xxx) and individuals with one or more prescriptions for hemophilia drug products.

[0343] The incidence rates of VTE may be higher in PwHA compared to the general population (FIGS. 14A and 14B). The incidence rate of thrombotic events with the fitusiran revised AT-based dose regimen was comparable with the general hemophilia population, as found in a real- world Optum database analysis.

[0344] Overall, only one thrombotic event, with the ODR, did not have any provoking or significant predisposing risk factors. The EAIR of thrombotic events per 100 patient-years was numerically lower with the AT-DR (0.82) versus the ODR (2.28). The fitusiran AT-DR mitigated the risk of thrombotic events in people with hemophilia A or B, irrespective of inhibitor status, compared with the ODR.

[0345] In conclusion, the AT-DR targeting AT activity levels of 15-35% optimized the benefit-risk profile of fitusiran and the BMG and AT-DR were successful in mitigating the risk of thrombotic events. Prolonged AT levels below 10% have been identified as a potential risk factor for thrombotic events. Fitusiran AT-DR prophylaxis led to a reduction in thrombotic events versus the original dose regimen despite substantially longer exposure on the AT-DR, and all thrombotic events with the fitusiran AT-DR had multiple risk factors and/or deviated from the BMG. The investigators reported that three of the four thrombotic events with the AT-DR were not related to fitusiran. In addition, in recent reports, higher or similar incidence of thrombotic events were observed in PwH compared with the general population.

Example 6: Surgical Experience in People with Hemophilia A or B With and Without Inhibitors Receiving Fitusiran

[0346] For the management of perioperative hemostasis, bleed management guidelines with reduced dose and/or frequency of clotting factor concentrates (CFC) or bypassing agents (BPA) were implemented (Table 10). Given the 20-40% factor equivalency of fitusiran, the bleed management guidelines recommend reduced dose and frequency of CFC/BPA. No dose adjustments to fitusiran are required for perioperative management, and pre-operative AT activity level assessment is not necessary as AT levels remain stable.

Table 10. Bleed and Perioperative Hemostasis Management Guidelines While on Fitusiran

[0347] This Example describes hemostatic outcomes of major surgeries conducted while on fitusiran prophylaxis in people with hemophilia A or B aged >12 years, regardless of inhibitor status.

[0348] All major surgeries in the fitusiran clinical development program until June 2023 were evaluated, including participants on the 80 mg QM and revised antithrombin-based dose regimen. Participants may have been part of the Phase 1/2 OLE trial (NCT02554773), the Phase 3 ATLAS-INH (NCT03417102), ATLAS-A/B (NCT03417245), or ATLAS-PPX (NCT03549871) trials, or the Phase 3 OLE (ATLAS-OLE; NCT03754790). Procedures conducted during fitusiran prophylaxis and AT activity <60% were included. Major surgeries included: opening into a major body cavity (e.g., abdomen, thorax, skull), operation on a joint, removal of an organ, operative alteration of normal anatomy, crossing of a mesenchymal barrier (e.g., pleura, peritoneum, dura), dental extraction of molar teeth or >3 nonmolar teeth, or tooth implantation. Major orthopedic surgery was defined as an operation on a joint or bone and associated soft tissue. Investigators/surgeon assessed peri-operative hemostatic control based on the ISTH 4-point response scale (excellent/good/moderate/poor). [0349] A total 121 surgeries were performed in participants receiving fitusiran prophylaxis during the clinical development program. 61 of these were minor surgeries. Sixty major surgeries (24 in inhibitor patients) were performed. In 47 (78.3%) major surgeries, the bleed management guidelines were followed, and reduced doses were used as perioperative prophylaxis. Of the major surgeries, 15 were abdominal surgeries, 3 were soft tissue surgeries, 19 were orthopedic surgeries, 4 were plastic/reconstructive surgeries, and 19 were dental surgeries. Orthopedic and dental surgeries were performed in 8 and 5 participants with inhibitors, respectively. A summary of the major surgeries is provided in Table 11.

Table 11. Summary of Major Surgeries Performed in Participants Receiving Fitusiran Prophylaxis in Clinical Development Program

[0350] Four major surgeries were conducted without additional CFC/BPA. In addition, perioperative hemostatic control was rated excellent/good in 95% (39/41) of major surgeries in which hemostatic assessment was conducted. Investigators/surgeon assessed peri-operative hemostatic control based on the ISTH 4-point response scale (excellent/good/moderate/poor). Analysis was provided for the day of the surgery (Day 0). Perioperative hemostatic assessments were not available for 19 cases.

[0351] BMG were followed in the majority (78.3%) of major surgeries. Hemostatic control on the day of the surgery was rated excellent/good in 30/31 (97%) cases following the bleed management guidelines and 9/10 (90%) cases not following the bleed management guidelines (FIGS. 15A and 15B).

[0352] ATIII concentrate was used to reverse the pharmacodynamic effect of fitusiran in seven surgeries with an excellent/good hemostatic outcome. No major treatment-related safety concerns were identified perioperatively. Postoperative thrombosis occurred only when dosing exceeded the bleed management guidelines recommendations in two participants (FIG. 15C). The consumption values of BPA/factor were only 15-25% of what would be usually used in major surgeries otherwise (FIG. 15C). The majority of major surgeries had excellent/good hemostatic control irrespective of inhibitor status (FIG. 15D). In participants without inhibitors, hemostatic control was rated excellent/good in 89% cases with BMG and 100% cases without BMG (i.e., not following recommended reduced doses and frequency of CFCs/BPAs). In participants with inhibitors, hemostatic control was rated excellent/good in 100% of cases with and without BMG (i.e., not following recommended reduced doses and frequency of CFCs/BPAs). [0353] Hemostatic control was similar in patients treated with the fitusiran original dose regimen and the AT-based dose regimen (FIG. 15E). In patients receiving the original dose regimen, hemostatic control was rated excellent/good in 100% cases with and without BMG. In Participants receiving AT-based dose regimen, hemostatic control was rated excellent/good in 88% cases with BMG and 100% cases without BMG.

[0354] Hemostatic control was similar in participants who underwent major surgery with and without AT reversal. If the clinical circumstance was such that the recommended doses and/or dose intervals outlined in the bleed management guidelines were deemed insufficient for hemostasis, AT replacement was considered and thrombotic risk managed as per investigator practice for a hemophilia participant undergoing that particular surgery. Perioperative monitoring guidelines were followed. ATIII was used to reverse the pharmacodynamic effect of fitusiran in seven surgeries (six major; one minor) with an excellent/good hemostatic outcome. The seven surgeries were: renal artery branch embolization; laparoscopic cholecystectomy; excision of hemophilia pseudotumor in hip & re-exploration of pseudotumor; splenectomy; knee arthroplasty; patella & femoral fracture surgery; and multiple dental extractions. Reversal of the effect of fitusiran by ATIII was not considered necessary as a risk mitigation, but could be used per physician discretion. There were no safety findings or complications with or without ATIII usage in the setting of surgeries. The mean perioperative consumption of BPA/factor per major surgery is shown in Table 12.

Table 12. Mean Perioperative^b Consumption of BPA/CFC Per Major Surgery

[0355] These data show that major surgeries can be safely and effectively conducted during fitusiran prophylaxis when the bleed management guidelines are followed, irrespective of inhibitor status. Reversal of lowered AT is not necessary.

[0356] With regard to orthopedic and dental surgeries, of the participants with hemostatic assessment available on the day of the surgery (n=15 for orthopedic; n=l 1 for dental), hemostatic control was good/excellent in 87% (n=13) and moderate in 13% (n=2) of orthopedic surgeries and good/excellent in 100% (n=l 1) of dental surgeries. Adherence to BMG was 78.9% for both orthopedic and dental surgeries (n=15 each). Postoperative thrombosis occurred in only one participant who underwent knee arthroplasty in the setting of pre-existing risk factors, including morbid obesity, and dosing exceeding BMG recommendations. AT concentrate was used per investigator discretion in 2 participants who underwent orthopedic surgery and one participant who underwent dental surgery. Hemostatic control was comparable to participants who did not receive AT concentrate and no postoperative safety findings or complications were reported related to AT usage. This data suggests that major orthopedic and dental surgeries can be safely and effectively performed in patients with hemophilia A or B with or without inhibitors receiving fitusiran prophylaxis when the bleed management guidelines are followed. Reversal of fitusiran effect with administration of AT concentrate is not necessary.

[0357] In sum, 60 major surgeries, including 24 in PwH with inhibitors, have been conducted in the fitusiran clinical development program. In the majority of major surgeries, reduced doses of CFC/BPA were used for perioperative management. Four major surgeries were conducted without additional CFC/BPA. Compliance with BMG and hemostatic outcomes were similar for surgeries conducted with the AT-based and original dose regimens. No major treatment-related safety concerns were identified. Postoperative thrombosis was reported in two participants when dosing factor or BPA dosing exceeded the bleed management guidelines, and no incidents of postoperative thrombosis were reported when the bleed management guidelines were followed. Reversal of the effect of fitusiran by ATIII is not considered clinically necessary for management of surgery.

Example 7: Hepatobiliary Events in the Fitusiran Clinical Development Program with the Revised AT-Based Dose Regimen

[0358] This Example describes hepatobiliary events in patients who received the fitusiran AT-DR.

[0359] Integrated safety analysis included all males aged 12 years with moderate or severe hemophilia A or B, with or without inhibitors who received the fitusiran AT-DR in the following studies: ATLAS-PPX (NCT03549871), ATLAS-OLE (NCT03754790), ATLAS- INH (NCT03417102), ATLAS-A/B (NCT03417245), and a Phase Eli OLE (NCT02035605, NCT02554773). Eitusiran dose was individually adjusted to achieve target AT levels of 15- 35%. Participants with significant liver disease were ineligible. ALT/AST elevations > 3xULN were identified by central lab. This Example excludes events reported during major surgery periods. The exposure adjusted incidence rate is equal to the # of participants with events/participant year of exposure *100 participant years.

[0360] Overall, 286 participants were included in the analysis, with total patient-years of exposure of 486.0 (^ 12 months exposure n=237) with the AT-DR. The incidence of ALT/AST elevations >3x ULN was substantially reduced with the AT-DR (Table 13). A total of 8/286 (2.8%) and 6/286 (2.1%) participants experienced ALT or AST elevations >3x upper limit of normal (ULN) with the AT-DR, respectively. The mean (SD) time to elevation was 241 (204.6), and 255 (240.6) days, respectively. All initial ALT/AST elevations >3xULN resolved spontaneously; mean (SD) time to resolution was 55 (26.3) and 45 (11.2) days. One event of asymptomatic transaminase elevation resulted in fitusiran discontinuation at physician discretion. There were no cases of severe liver toxicity or liver failure. Overall, 11/286 (3.8%) participants experienced events of cholecystitis/cholelithiasis, and one participant underwent cholecystectomy. No events of cholecystitis/cholelithiasis resulted in discontinuation of fitusiran.

Table 13. Incidence of ALT/AST Elevations >3x ULN in Participants Treated with ODR and AT-DR

[0361] With the AT-DR, there were no cases of severe liver toxicity or liver failure, and two (2/14 [14%]) events of ALT or AST elevations >3xULN were classified as SAEs. These were assessed by the Investigator as related to study drug. No SAE had a fatal outcome or resulted in study drug discontinuation.

[0362] The majority of ALT/AST elevations >3xULN observed in participants treated with the AT-DR resolved spontaneously. ALT/AST elevations >3xULN were asymptomatic, transient, and resolved without any therapeutic intervention. The majority (12/14 [86%]) of ALT/AST elevations >3xULN in participants treated with the AT-DR were reported as recovered/resolved without dose change or interruption. Recurrent ALT and AST >3xULN elevations occurred in one participant each (among participants who experienced an ALT/AST elevation of >3xULN while on the revised AT-DR) in the setting of repeated fitusiran exposure. In one participant, fitusiran treatment was discontinued due to asymptomatic transaminase elevations. At the physician’s discretion, this event was considered related to fitusiran and was not serious. The participant recovered from the event. [0363] Liver function trajectories demonstrate alternate etiologies and the transient nature of ALT/AST elevations (FIG. 16). Both participants met criteria of ALT/AST>3x ULN after dose resumption, had no HCV history or antibody, and did not have inhibitors.

[0364] The incidence of cholecystitis/cholelithiasis was substantially reduced with the AT-DR (Table 14). One participant with the AT-DR underwent cholecystectomy. A total of three (1.0%) participants treated with the AT-DR experienced an SAE of cholecystitis/cholelithiasis (cholecystitis [2 [0.7%] participants] and cholangitis [1 [0.3%] participant]).

Table 14. Incidence of Cholecystitis/Cholelithiasis in Patients on the Original Dose and AT-Based Dose Regimens

[0365] Liver transaminase elevations were infrequent and transient with the fitusiran AT- DR. Events of cholecystitis/cholelithiasis resolved without clinical sequalae and participants continued dosing with fitusiran.

[0366] In sum, the AT-DR targeting AT activity levels of 15-35% optimized the benefitrisk profile of fitusiran. Fitusiran AT-DR prophylaxis led to reductions in ALT/AST elevations and cholecystitis/cholelithiasis events versus the original dose regimen despite substantially longer exposure on the AT-DR. ALT or AST elevations >3xULN with the AT- DR were asymptomatic and transient, and the majority were reported as recovered/resolved spontaneously. The median time to onset for ALT or AST elevations >3xULN was about six months. The majority of events of cholecystitis/cholelithiasis resolved without clinical sequalae and participants continued dosing with fitusiran, and one participant underwent cholecy stectomy . Example 8: Safety and Efficacy of the Fitusiran Revised Antithrombin-Based Dose Regimen (AT-DR) in the ATLAS-OLE Trial

[0367] The ATLAS-OLE (NCT03754790) trial is a multicenter, multinational, open-label extension study (FIG. 17). The participant distribution in the ATLAS-OLE trial is shown in FIG. 18.

[0368] The primary objective is to characterize the long-term safety and tolerability of fitusiran. The secondary objective is to characterize the long-term efficacy of fitusiran. The results described below were generated using a data cutoff (DCO) date of June 14, 2023. Baseline characteristics in the trial were balanced across the study population (FIG. 19) [0369] The AT-DR achieved its aim of maintaining AT levels between 15-35% (FIG. 20). The mean (SD) AT level was 23.5% (4.6) with the AT-DR. In total, 78% (n=167) patients were on a Q2M regimen at final dose. 94% (n=199) of patients required zero or one dose adjustment to achieve AT 15-35%. In particular, 80 participants (38%) required zero dose adjustments, and 119 (56%) required one dose adjustment to achieve AT range 15-35%. 54% (n=l 14) were on 50 mg Q2M or QM, and 44% (n=94) were on 20 mg Q2M or QM at final dose. 11.7% (n=25) discontinued 20 mg Q2M due to low AT levels (<15% more than once).

[0370] Participants’ exposure to fitusiran was greater on the revised AT-DR vs. the ODR (FIG. 21). The safety of all participants exposed to the AT-DR was compared with all participants exposed to the ODR across all fitusiran studies (ATLAS-INH, ATLAS-A/B, ATLAS-PPX, ATLAS-OLE). For the original dose regimen period, the exposure is calculated starting from the first significant dose (>20 mg).

[0371] Of the 227 enrolled patients, 78 patients had inhibitors (Hemophilia A=59 and Hemophilia B=19) and 149 patients did not have inhibitors (Hemophilia A=115 and Hemophilia B=34). All patients in the study were male. The mean age of patients was 30.7 years, and 39 (17.2%) patients were 12-17 years of age. The majority of patients were Asian (52.9%) or White (41%). Generally, the demographic and patient characteristics at baseline were comparable between the patients with or without inhibitors, as well as between patients with hemophilia A and B.

[0372] Efficacy of fitusiran was evaluated for a duration of seven months (primary efficacy period) following a six-month dose adjustment period. Median observed ABR (IQR) was 3.7 (0.0;7.5) overall, 1.9 (0.0; 5.6) in inhibitor patients and 3.8 (0.0; 11.2) in noninhibitor patients (Table 15). Table 15. Efficacy of Fitusiran in OLE Trial

[0373] The overall safety profile of the AT-DR was favorable, with greater exposure compared with the ODR (FIG. 22). The safety analyses included all participants exposed to fitusiran. For the original dose regimen, the exposure was calculated starting from the first significant dose (^20 mg), excluding events reported during major surgery periods. The most common TEAEs (>5%) reported with the AT-DR were: COVID- 19, upper respiratory tract infection, arthralgia, nasopharyngitis, alanine aminotransferase increased, pyrexia, pain in extremity, prothrombin fragment 1+2 increased, diarrhea, cough, hemophilic arthropathy, headache, and influenza.

[0374] FIG. 23 shows a summary of TEAEs in the AT-DR Period. During the Revised AT-DR Treatment Period, TESAEs were reported in 38 (17.8%) participants. The majority of TESAEs were assessed by the Investigator as mild to moderate in severity.

[0375] Ten TESAEs in six (2.8%) participants were assessed by the Investigator as related to fitusiran and included cholecystitis and hematuria reported in two participants each, and large intestine infection, pancreatitis, cholangitis, limb mass, ALT increased, and AST increased reported in one participant each. No TESAE has a fatal outcome. No TESAEs resulted in fitusiran discontinuation during the Revised AT-DR Treatment Period.

[0376] During the Revised AT-DR Treatment Period, three (1.4%) participants reported at least one TEAE leading to treatment discontinuation and included cerebral infarction, pruritus, and deep vein thrombosis postoperative. The TEAE of cerebral infarction was assessed by the investigator as non-serious, mild, and not related to fitusiran. The TEAE of pruritus was assessed by the Investigator as non-serious, moderate, and related to fitusiran. The TEAE of deep vein thrombosis postoperative was assessed by the Investigator as non- serious, moderate, and related to fitusiran.

[0377] Mean values for coagulation parameters at baseline were generally similar for participants with the ODR and the revised AT-DR. There was a trend toward increased values for D-dimer and decreased values for fibrinogen for participants with the ODR and the revised AT-DR. Overall, the majority of elevations were not considered clinically meaningful. The values for prothrombin fragments 1+2 were limited to a small number of participants and were inconclusive.

[0378] With the ODR, there was a trend towards increased alkaline phosphatase and gamma glutamyl transferase levels. With the revised AT-DR, this trend was less apparent. There were no clinically meaningful trends observed in bilirubin levels for both regimens. [0379] The incidence of thrombotic events was reduced in patients treated with the AT- DR as compared to patients treated with the ODR (Table 16, FIG. 24). The exposure adjusted incidence rate is equal to the number of participants with events/participant year of exposure * per 100 patient-years. Table 16. Incidence of Thrombotic Events

[0380] Based on a recently submitted abstract on Optum claims database analysis (events occurring from July 2007 to September 2021), the rate of TEs with the AT-DR were similar to the general hemophilia population.

[0381] All thrombotic events observed with the fitusiran AT-DR had multiple risk factors

(FIG. 25).

[0382] The incidence of ALT/AST elevations 3x ULN and cholecystitis/cholelithiasis was substantially reduced in patients treated with the AT-DR compared to patients treated with the ODR (Tables 17 and 18; FIG. 26). The majority of ALT or AST elevations 3x ULN with the AT-DR were transient and reported as recovered/resolved, with a median of 212 and 186 days to onset and median time to normalization of 88 and 49 days, respectively.

Table 17. Incidence of Cholecystitis/Cholelithiasis

Table 18. Incidence of ALT/AST Elevations 3x ULN

[0383] Recurrent ALT >3 x ULN elevation occurred in one (12.5%) participant in the setting of repeated fitusiran exposure; the time from recovery to recurrence in this participant was 30.0 days. Recurrent AST >3 x ULN elevation occurred in one (16.7%) participant; the time from recovery to recurrence in this participant was 28.0 days (Table 19). Is used herein, recurrent means another ALT/AST elevation >3xULN after recovery from the first episode.

Table 19. Median Times to ALT/AST Elevations Onset, Recovery and Normalization

[0384] The Fitusiran AT-DR provided clinically meaningful bleed control in participants with hemophilia A and B with and without inhibitors during the primary efficacy period (FIG. 27). The observed median ABR in the primary treatment period is shown in FIG. 28. [0385] The observed median AsBR during the primary efficacy period (FIG. 29) and the observed median AjBR during primary efficacy period (FIG. 30) were also determined. [0386] 55% of participants on the AT-DR experienced a meaningful change in quality of life as per the Haem-A-QoL physical health score in the treatment period (Table 20).

Participants ^ 17 years of age filled in the Haem-A-QoL questionnaire which is a validated tool to assess quality of life in adult patients with hemophilia. The Haem-A-QoL includes 46 items contributing to ten QoL domains (physical health, feelings, view of yourself, sports and leisure, work and school, dealing with hemophilia, treatment, future, family planning, partnership and sexuality). Scoring for each item is based on a 5-point Likert scale (never, rarely, sometimes, often, and all the time), and transformed scores range from 0 to 100. Higher scores represent greater impairment, and a clinically meaningful change in the physical health score (transformed) is defined as an improvement greater or equal to 10 (change in score % -10).

Table 20. Haem-A-QoL Physical Health Score in the Treatment Period

[0387] Joint health was evaluated using the HJHS version 2.1, a validated tool developed for the assessment of joint health in people with hemophilia. This questionnaire consists of eight item scores (swelling, duration of swelling, muscle atrophy, crepitus on motion, flexion loss, extension loss, joint pain and strength) for each joint and a global gait score. Scores range from 0 to 20 per joint and the global gait score ranges from 0 to 4, resulting in a HJHS total score of 0 to 124, lower scores representing less functional limitations (Table 21).

Table 21. HJHS in the Treatment Period

Pooled Analyses

[0388] The integrated efficacy analyses were conducted according to intent to treat (ITT) principle preserving the randomization in the parent studies. The efficacy of fitusiran was evaluated in 177 patients comparing fitusiran prophylaxis under the AT-based dose regimen in ATLAS-OLE and BPA/CFC on- demand in the parent studies. In addition, 69 patients were evaluated comparing fitusiran prophylaxis under the AT-based dose regimen in ATLAS-OLE to BPA/CFC prophylaxis in the parent studies. Each pool (FIG. 31) represents a subset of participants enrolled in the ATLAS-OLE study. Missing data were imputed using multiple imputation methods maintaining the ITT/FAS analysis principle.

[0389] In patients with inhibitors, the estimated ABR (95% CI) 5.139 (2.775, 9.516) in patients treated with fitusiran prophylaxis was reduced by 73% compared to 19.123 (11.804, 30.982) in the BPA on- demand arm (p=0.0006). The proportion of patients with % 1 bleeds increased from 5.3% in the on- demand BPA group to 54.8% in the fitusiran group. In patients without inhibitors, the estimated ABR (95% CI) 9.011 (5.587, 14.535) in patients treated with fitusiran prophylaxis was reduced by 71% compared to 31.424 (20.484, 48.208) in the CFC on-demand arm (p<0.0001). The proportion of patients with 1 bleeds increased from 2.5% in the on-demand CFC group to 41.3% in the fitusiran group.

[0390] In patients with inhibitors, there was a significant 82% reduction in the estimated annualized spontaneous bleeding rate (AsBR) (95% CI) in patients treated with fitusiran (3.106 [1.778, 5.426] compared to those treated with BPA on-demand in the control period (17.087 [9.866, 29.595], p-value <0.0001). The proportion of patients with % 1 spontaneous bleeds increased from 15.8% in the on- demand BPA group to 83.9% in the fitusiran group.80 In patients without inhibitors, there was a significant 74% reduction in the estimated AsBR (95% CI) in patients treated with fitusiran (5.395 [3.652, 7.969]) compared to those treated with CFC on-demand in the control period (20.991 [13.947, 31.592], p-value <0.0001). The proportion of patients with % 1 spontaneous bleeds increased from 15.0% in the on-demand CFC group to 52.4% in the fitusiran group.

[0391] In patients with inhibitors, there was a significant 73% reduction in the estimated annualized joint bleeding rate (AjBR) (95% CI) in patients treated with fitusiran (3.950 [2.500, 6.24]) compared to those treated with BPA on-demand in the control period (14.414 [8.976, 23.146], p-value =0.0001). The proportion of patients with % 1 joint bleeds increased from 10.5% in the on-demand BPA group to 61.3% in the fitusiran group. In patients without inhibitors, there was a significant 71% reduction in the estimated AjBR (95% CI) in patients treated with fitusiran (6.182 [4.175, 9.152]) compared to those treated with CFC on-demand in the control period (21.561 [14.561, 31.925], p-value <0.0001). The proportion of patients with %onc joint bleed increased from 12.5% in the on-demand BPA group to 47.6% in the fitusiran group.

[0392] Patient-reported symptoms and physical functioning (pain with movement, difficulty walking far, and increased time to get ready) were evaluated using the Physical Health Score of the Haemophilia- specific Quality of Life (Haem-A-QoL) questionnaire for patients 17 years of age. Compared to on-demand CFC during the control period, fitusiran prophylaxis improves physical health of patients with hemophilia as shown by the clinically meaningful and statistically significant improvements in the Haem-A-QoL physical health score during the primary efficacy period. The Haem-A-QoL transformed Physical Health Score LS Mean difference (95% CI) vs control period was -8.17 (-15.28, -1.05), p=0.0246 in non-inhibitor patients. [0393] Patients receiving fitusiran prophylaxis had a clinically meaningful reduction in risk of having a bleed compared to BPA by 78.8% and CFC by 81.4% (p<0.0001) during the efficacy period.

[0394] In patients on prior CFC or BPA prophylaxis, the estimated ABR (95% CI) in patients treated with fitusiran prophylaxis was reduced by 25% compared to the SOC prophylaxis (5.651 [3.878, 8.235] and 7.543 [5.621, 10.122], respectively). In a subgroup analysis in patients with inhibitors, the estimated ABR (95% CI) in patients treated with fitusiran prophylaxis was reduced by 70% compared to the BPA prophylaxis arm (3.413 [1.910, 6.099] and 11.287 [7.540, 16.896], respectively). The proportion of patients with ^ 1 bleeds increased from 28.6% in the BPA prophylaxis group to 57.9% in the fitusiran group. In patients without inhibitors, the estimated ABR in the fitusiran prophylaxis arm was comparable to the CFC prophylaxis arm (6.932 [4.486, 10.713] and 5.961 [4.024, 8.829], respectively). Patients receiving fitusiran prophylaxis had a clinically meaningful reduction in risk of having a bleed compared to BPA or CFC prophylaxis by 36.2% during the efficacy period. On fitusiran prophylaxis, mean (SD) annualized weight-adjusted consumption of CFC was reduced from 365.6 (375.6) lU/kg to 131.0 (131.4) lU/kg for FVIII and from 412.3 (428.9) lU/kg to 126.7 (89.3) lU/kg for FIX. Mean (SD) annualized weight-adjusted consumption of BPA was reduced from 2403.2 (4175.4) U/kg to 147.9 (95.5) U/kg for aPCC and 5585.1 (5697.7) ug/kg to 1996.5 (3810.0) ug/kg for rFVIIa.

[0395] Treatment of breakthrough bleeds that occurred while on fitusiran prophylaxis required fewer CFC or BPA injections compared to those while on CFC or BPA prophylaxis. The percentage of bleeds requiring two or less injections of FVIII or FIX was 99.1% and 100%, respectively, compared to 91.7% and 77.8%, respectively while on CFC prophylaxis. While on fitusiran prophylaxis, the percentage of bleeds requiring two injections or less of activated prothrombin complex concentrate (aPCC) or recombinant activated factor VII (rFVIIa) was 90.9% and 85.7%, respectively, compared to 62.9% and 50.0%, respectively while on BPA prophylaxis.

[0396] The fitusiran AT-DR demonstrated superiority over on-demand regimens for both inhibitor and non-inhibitor participants. In particular, the estimated mean ABR for treated bleeds in patients with hemophilia A or B with inhibitors was reduced (FIG. 32), as was the estimated mean ABR for treated bleeds in patients with hemophilia A or B without inhibitors (FIG. 33). [0397] With regard to the observed median ABR in patients treated with AT-DR vs. BPA/CFC on-demand treatment, ABR for treated bleeds in patients with hemophilia A or B with inhibitors is shown in FIG. 34. The proportion of participants with zero bleeds was 5.3% for BPA on-demand patients vs. 35.5% in fitusiran AT-DR patients. ABR for treated bleeds in patients with hemophilia A or B without inhibitors is shown in FIG. 35. The proportion of participants with zero bleeds was 2.5% in patients treated with CFC on-demand vs. 27.0% in patients treated with AT-DR.

[0398] In addition, fitusiran AT-DR showed substantial improvement over BPA prophylaxis and comparable efficacy to CFC prophylaxis. In particular, the estimated mean ABR for treated bleeds in patients with hemophilia A or B with inhibitors was reduced (FIG. 36), and the estimated mean ABR for treated bleeds in patients with hemophilia A or B without inhibitors was comparable (FIG. 37).

[0399] With regard to the observed median ABR in patients treated with the AT-DR vs. BPA/CFC Prophylaxis, the ABR for treated bleeds in patients with hemophilia A or B with inhibitors is shown in FIG. 38, and the ABR for treated bleeds in patients with hemophilia A or B without inhibitors is shown in FIG. 39. The proportion of participants with zero bleeds was 16.4% in patients treated with BPA/CFC prophylaxis vs 29.6% in patients treated with fitusiran AT-DR.

[0400] With regard to the estimated mean AsBR in patients treated with the AT-DR vs. BPA/CFC on-demand treatment, AsBR for treated bleeds in patients with hemophilia A or B with inhibitors is shown in FIG. 40 and AsBR for treated bleeds in patients with hemophilia A or B without inhibitors is shown in FIG. 41.

[0401] With regard to the observed median AsBR in patients treated with the AT-DR vs. BPA/CFC on-demand treatment, AsBR for treated bleeds in patients with hemophilia A or B with inhibitors is shown in FIG. 42 and AsBR for treated bleeds in patients with hemophilia A or B without inhibitors is shown in FIG. 43.

[0402] With regard to the estimated mean AjBR in patients treated with the AT-DR vs. BPA/CFC on-demand treatment, AjBR for treated bleeds in patients with hemophilia A or B with inhibitors is shown in FIG. 44 and AjBR for treated bleeds in patients with hemophilia A or B without inhibitors is shown in FIG. 45.

[0403] With regard to the observed median AjBR in patients treated with the AT-DR vs. BPA/CFC on-demand treatment, AjBR for treated bleeds in patients with hemophilia A or B with inhibitors is shown in FIG. 46 and AjBR for treated bleeds in patients with hemophilia A or B without inhibitors is shown in FIG. 47. [0404] With regard to the estimated Mean AsBR and AjBR in patients treated with the AT-DR vs. BPA/CFC prophylaxis, AsBR for treated bleeds in patients with hemophilia A or B with or without inhibitors is shown in FIG. 48 and AjBR for treated bleeds in patients with hemophilia A or B with or without inhibitors is shown in FIG. 49.

[0405] With regard to the observed median AsBR and AjBR in patients treated with the AT-DR vs. BPA/CFC prophylaxis, AsBR for treated bleeds in patients with hemophilia A or B with or without inhibitors is shown in FIG. 50 and AjBR for treated bleeds in patients with hemophilia A or B with or without inhibitors is shown in FIG. 51.

[0406] Participants ^ 17 years of age filled in the Haem-A-QoL questionnaire which is a validated tool to assess quality of life in adult patients with hemophilia. The Haem-A-QoL includes 46 items contributing to ten QoL domains (physical health, feelings, view of yourself, sports and leisure, work and school, dealing with hemophilia, treatment, future, family planning, partnership and sexuality). Scoring for each item is based on a 5-point Likert scale (never, rarely, sometimes, often, and all the time), and transformed scores range from 0 to 100. Higher scores represent greater impairment, and a clinically meaningful change in the physical health score (transformed) is defined as an improvement greater or equal to 10 (change in score % -10). The LS mean and mean difference (95% CI) are estimated by mixed-effect model with repeated measures (MMRM) with robust sandwich covariance matrix, and fixed effects of study arm, the randomization strata of number of bleeding episodes in the 6 months prior to parent study and baseline score.

[0407] The Haem-A-QoL physical health score comprises the following components: In the past four weeks ....: ...my swellings hurt, ...1 had pain in my joints, ...it was painful for me to move, ...1 had difficulty walking as far as I wanted to, and ...1 needed more time to prepare myself because of my condition.

[0408] With regard to the change in QoL in patients treated with the AT-DR vs. BPA/CFC on-demand treatment, the Haem-A-QoL physical health scores are shown in FIG. 52. With regard to the change in QoL in patients treated with the AT-DR vs. BPA/CFC prophylaxis, the Haem-A-QoL physical health score is shown in FIG. 53.

[0409] Treatment of breakthrough bleeds in patients treated with the AT-DR vs. BPA/CFC prophylaxis is shown in FIG. 54. It was also observed that there is a direct correlation between AT activity and ABR (FIG. 55; Table 22). An Andersen Gill model with frailty was fitted to investigate the relation between a linear function of AT and mean ABR. Lower AT levels corresponded to decreased bleeding rates. Table 22. Relationship Between Median ABR and AT levels

[0410] In conclusion, the AT-based dose regimen targeting AT levels of 15-35% substantially improved the safety profile compared with the original dose regimen. AT-based dose regimen maintained clinically meaningful bleed protection in people with hemophilia A or B, with or without inhibitors, and lower AT activity levels corresponded to decreased bleeding rates. Most participants received six injections per year, highlighting the potential for a reduced treatment burden with fitusiran.

[0411] The AT-based dose regimen targeting AT levels of 15-35% substantially improved the safety profile compared with the original dose regimen. The AT-DR resulted in a substantially lower exposure-adjusted incidence rate of thrombotic events vs. the ODR. The AT-based dose regimen maintained clinically meaningful bleed protection in people with hemophilia A or B, with or without inhibitors. Lower AT activity levels corresponded to decreased bleeding rates.

Example 9: Revised AT-Based Dose Regimen

[0412] The Revised AT-DR was Designed to Optimize the Benefit-risk Profile of fitusiran by targeting an AT level of 15-35%. Regular AT monitoring was used to guide dosing. Based on the mechanism of action of fitusiran and observation of AT levels <10% for prolonged periods of time in participants with reported vascular thrombotic events in the fitusiran clinical development program, AT levels were evaluated as a potential modifiable target for risk mitigation.

[0413] Data suggest that the risk of serious vascular thrombotic events may be greater with AT levels <10% (Table 23). A lower AT threshold of 15% was selected to minimize the occurrence of AT levels <10%. AT levels <25% may lead to a desirable ABR. An upper AT threshold of 35% was chosen based on fitusiran efficacy data.

[0414] A simulation based on PK/PD modeling was conducted to identify a dose and regimen that would target AT levels between 15% and 35%. Table 23. Incidence Rate for Vascular Thrombotic Events by AT Category in Patient- Years

[0415] Participants with AT levels <10% had arterial (or suspected arterial) thrombosis events. Participants with AT levels 10-20% had venous events that occurred when participants were also receiving CFC/BPA in excess of the revised breakthrough bleed management guidelines.

[0416] For all adult and adolescent participants exposed to at least one dose of fitusiran, the total patient-years for each of three AT categories was calculated: <10%, 10-20%, and >20%. The participants with vascular thrombotic events were then included in the AT category representative of their level for the greatest amount of time during fitusiran exposure and an incident rate per 100 patient years was derived.

[0417] An AT level of approximately <25% may lead to a desirable ABR (Table 24). An analysis was conducted to understand the distribution of ABR by AT level above and below 20% for participants who had received fitusiran. A median ABR of 1 was found for all <20% AT subgroups. This analysis reinforced prior data that AT levels <25% maintained efficacy.

Table 24. Observed ABR by AT Level Across all Fitusiran Trials

[0418] The above table excludes participants from the ALN-AT3SC-001 (TDR14767) dose finding study, the pediatric study, and participants enrolled in these studies who did not receive any fitusiran.

[0419] A median ABR of 1 was found for all <20% AT subgroups. This analysis reinforced prior data that AT levels <25% maintained efficacy. Example 10: Fitusiran Pharmacodynamics

[0420] In clinical studies with fitusiran in hemophilia patients, the primary pharmacodynamic measure assessed was plasma antithrombin AT activity measurements. [0421] Hemophilia A or B is a bleeding disorder characterized by a deficiency of functional coagulation factor VIII or FIX, respectively. Administration of fitusiran decreases plasma level of antithrombin resulting in increased thrombin generation and therefore reducing bleeding in hemophilia A or B patients, irrespective of inhibitor status. Reduction in AT level result in increased thrombin generation and improved hemostasis that were associated with a reduced bleed risk in patients with hemophilia A or B, with and without inhibitors. Lower AT activity levels are associated with lower annualized bleeding rates (ABR); the monotonic increasing relationship between AT and ABR was confirmed by modeling and simulation.

[0422] In study LTE15174 mean (SD) AT level on the revised AT-based dose regimen was 23.48 (4.64). In the parent studies on the fixed 80 mg dose mean (SD) AT level was 10.73(2.92) in ATLAS-INH, 11.76 (3.96) in ATLAS-A/B and 11.00 (2.54) in ATLAS-PPX, respectively. Simulations performed using a population pharmacokinetic-pharmacodynamic (PopK-PD) model indicate that with the recommended AT-based dose regimen (50 mg or 20 mg Q2M or QM), 48% of patients are predicted to reach AT target level 15-35% on the starting dose of 50 mg Q2M and will not require any dose adjustments. A single dose adjustment is predicted to be needed in 40% of patients. These predictions are consistent with observed clinical study data, as shown in Table 25 below.

Table 25. Distribution of Patients Across Recommended Fitusiran Dose Regimens at Which Individual Patient AT Activity is Maintained Between 15-35% [0423] Simulations to estimate time for AT activity to reach steady state found that regardless of the dose regimen, more than 99% of participants reached steady state AT levels (defined as <10% variability among consecutive measures) within 23 weeks following initiation of fitusiran dosing or following dose escalation or de-escalation. The persistence of AT activity <60% (negligible impact of fitusiran on coagulation) following fitusiran treatment discontinuation was estimated to be approximately 20 weeks, after which standard doses of CFC/BPA may be administered. The time required for AT activity recovery prior to initiation of lower dose was estimated to be 12 weeks. AT reduction did not differ between patients with hemophilia A or B, with or without inhibitors.

Example 11: Fitusiran Pharmacokinetics

[0424] The pharmacokinetic (PK) properties of fitusiran were evaluated following administration of fitusiran in patients with hemophilia A and B, with or without inhibitors as summarized in Table 26. Fitusiran PD is driven by liver PK rather than plasma PK. Fitusiran dosing strategy is based on maintaining plasma AT activity levels at 15 to 35% with Q2M or QM dosing at 20 or 50 mg.

Table 26. Pharmacokinetic Parameters of Fitusiran

Example 12: Fitusiran Clinical Studies

[0425] The efficacy and safety of fitusiran in adults and adolescents with hemophilia A or

B with or without inhibitors was evaluated in four pivotal studies: Hemophilia A or B with Inhibitory Antibodies: ATLAS-INH (NCT03417102),

Hemophilia A or B without Inhibitory Antibodies: ATLAS-A/B (NCT03417245), and

• Hemophilia A or B previously receiving CFC or BPA prophylaxis: ATLAS-PPX (NCT03549871).

Patients in the above parent studies rolled over into the long-term extension study:

• Hemophilia A or B with or without inhibitory antibodies: ATLAS -OLE (NCT03754790)

[0426] Dosing in the pivotal studies was initiated with fitusiran at 80 mg QM. To mitigate the risk of thrombotic events, an AT-based dose regimen with the target AT activity range of 15-35% was implemented in ATLAS-OLE.

[0427] ATLAS-INH was a randomized, multicenter, open-label clinical study in 57 adult and adolescent males (aged 12 years) with hemophilia A or B with inhibitory antibodies to factor VIII (FVIII) or factor IX (FIX), who previously received on-demand (episodic) treatment with BPAs for bleeding. Eligible patients were randomized in a 2: 1 ratio to receive fitusiran prophylaxis 80 mg SC once-monthly (N=38) or BPA on-demand for treatment of breakthrough bleeding episodes (N=19) for 9 months.

[0428] ATLAS A/B was a randomized, multicenter, open-label clinical study in 120 adult and adolescent males (aged 12 years) with hemophilia A or B without inhibitory antibodies to FVIII or FIX, who previously received on-demand (episodic) treatment with CFC for bleeding. Eligible patients were randomized in a 2:1 ratio to receive fitusiran prophylaxis 80 mg SC once-monthly (N=80) or CFCs on-demand to treat breakthrough bleeding episodes (N=40) for 9 months.

[0429] ATLAS-PPX was a multicenter, open-label crossover study in 80 adult and adolescent males (aged % 12 years) with Hemophilia A or B with or without inhibitory antibodies to FVIII or FIX, previously receiving CFC or BPA prophylaxis. The study consisted of a 6-month CFC or BPA prophylaxis period, a one-month treatment onset period where patients received an initial dose of fitusiran 80 mg SC while continuing their CFC or BPA prophylaxis for up to seven days, and a six-month treatment efficacy period in which patients received fitusiran 80 mg SC as once-monthly prophylaxis. Of the 78 patients who entered the CFC/BPA prophylaxis period, 67 patients entered the fitusiran treatment period on fitusiran 80 mg SC QM and two patients on the AT-based dose regimen starting at fitusiran 50 mg Q2M. [0430] A total of 246 patients enrolled in one of three parent studies mentioned above, of which 227 patients rolled over and were enrolled and treated with fitusiran in a multicenter study which was initiated as an open-label extension study to evaluate the long-term safety and efficacy of fitusiran in adult and adolescent males aged % 12 years with hemophilia A or B, with or without inhibitory antibodies to FVIII or FIX. Eligible patients initially received fitusiran 80 mg SC QM. The study was amended to evaluate the efficacy and safety of the AT-based dose regimen. Patients were subsequently transitioned to an AT-based dose regimen with the target AT activity range of 15-35%.

[0431] In the AT-based dose regimen, the fitusiran starting dose was 50mg Q2M, and dosing was individually adjusted based on AT activity level. The dose could be increased to 50mg QM or 80 mg QM, or decreased to 20mg Q2M or 20mg QM, or treatment discontinued if AT activity <15% at the lowest dose. No patients required escalation to 80 mg QM to achieve the target AT range.

[0432] Patients with known co-existing coagulation disorders other than hemophilia A or B, increased risk of thrombosis as assessed by history of arterial or venous thromboembolism, significant valvular disease or atrial fibrillation, or co-existing thrombophilic disorder (e.g., Factor V Leiden mutation), AT activity <60% at screening, platelet count % 100,000/pL, eGFR %45 mL/min (using the MDRD), or clinically significant liver disease were not eligible for enrollment.

[0433] In the pivotal studies, higher rates of transaminase elevations were observed on fitusiran 80 mg QM dose regimen compared to the AT-based dose regimen. On the AT-based dose regimen, a total of 8 (2.8%) patients exposed to fitusiran were observed to have at least one alanine aminotransferase (ALT) value three or more times the upper limit of normal (ULN), of which 5 (1.8%) had at least one ALT value five or more times the ULN. None of these events were associated with symptoms of jaundice and all were asymptomatic. Initial ALT elevations exceeding 3 times the ULN on the AT- based dose regimen had a median duration of 54.5 days (maximum: 85 days). All transaminase elevations returned to normal. One of the patients receiving fitusiran prophylaxis on the AT-based dose regimen discontinued treatment due to transaminase elevations.

[0434] Serious thrombotic events have been reported in clinical studies of fitusiran including one fatal event of cerebral venous sinus thrombosis. To mitigate the risk of thrombotic events, an AT-based dose regimen was implemented. Thrombotic events were reported in seven patients (2.6%, n=9 events) receiving fitusiran 80 mg QM prophylaxis and four patients (1.4%, n=4 events) receiving fitusiran prophylaxis under the AT-based dose regimen. The exposure-adjusted incidence rate (EAIRF) for thrombotic events on fitusiran 80 mg QM was 2.28 compared to 0.82 on the AT-based dose regimen per 100 person years.

[0435] A summary of the completed phase 3 trials (original dose regimen) is provided in FIG. 56. Fitusiran has been studied in the largest pre-approval hemophilia cohort to date, with 373 participants exposed from 24 countries as of a data cut-off date of November 19, 2023. Data on PwHA/B, with or without inhibitors are from ongoing/completed unblinded/open label studies, including Phase 1, Phase 1/2 OLE, ATLAS-INH, ATLAS- A/B, ATLAS-PPX, and ATLAS-OLE. Participants in both Phase 1 and the extension study, and in both ATLAS-INH (or ATLAS-A/B or ATLAS-PPX) and the extension study, ATLAS-OLE, were counted only once. A summary of the completed and ongoing phase 3 trials is provided in FIG. 57.

Example 13: Physical Health and Overall Health-Related Quality of Life in Adults With Hemophilia A or B With or Without Inhibitors on Fitusiran Prophylaxis

[0436] This analysis included people with hemophilia A or B aged 17 years with or without inhibitors, who participated in the ATLAS-OLE trial and received fitusiran prophylaxis at the AT-based dose regimen (AT-DR). Eitusiran dosing was individually adjusted to achieve target AT levels of 15-35%. Endpoints assessed the change in hemophilia QoL (Haem-A-QoL) questionnaire physical health (PH) and total scores (TS) during the primary treatment period.

[0437] Integrated analyses were conducted on pooled data to compare fitusiran AT-DR prophylaxis with clotting factor concentrate/bypassing agent (CLC/BPA) regimen from the parent studies. Each pool included participants from ATLAS-OLE and the control arm of the parent study.

[0438] The total score of Haem-A-QoL consists of 46-items covering ten domains comprising physical health. Mean (SD) change from baseline (i.e., last non-missing value before the first ever dose of fitusiran in either the parent study or this study) to last visit on AT-DR was calculated for physical health and total score (transformed score range: 0-100; higher scores indicate greater impairment). Clinically meaningful within-patient change in physical health and total score was defined as an improvement of 10 and ^7.1 points, respectively.

[0439] Total score of the Haem-A-QoL was good at baseline while physical health showed mild impairment. The mean (SD) change from baseline was -8.06 (22.18) for physical health score and -6.10 (12.85) for total score, indicating an improvement in physical health and overall HRQoL with fitusiran. These improvements were clinically meaningful in people with hemophilia A or B with inhibitors (Table 27). Of all participants overall, 54.9% achieved meaningful within-patient change in both physical health and total score.

Table 27. Mean (SD) Change from Baseline in Haem-A-QoL Physical Health (PH) and Total Score (TS)* in ATLAS-OLE Study

[0440] Comparisons between participants (i.e., inter-patient comparisons) showed that fitusiran prophylaxis led to a clinically meaningful and substantially higher improvement in the transformed physical health score from baseline to end of primary treatment period compared with CFC on-demand, while the difference was numerically in favor of fitusiran versus BPA on-demand (Table 28). Fitusiran prophylaxis maintained the physical health score of participants previously treated with CFC/BPA prophylaxis.

Table 28. Inter-Patient and Intra-Patient Comparison in Adult People with Hemophilia A or B With or Without Inhibitors in the Physical Health Score (Transformed) from Baseline to End of Primary Treatment Period

[0441] Intra-patient sensitivity analyses yielded complementary findings. AT-DR showed clinically meaningful improvement among participants previously treated with clotting factor concentration or bypassing agent on-demand: least square (LS) mean change in the fitusiran arm [95% confidence interval (CI)] from baseline was -12.70 [-23.02 to -2.38] and -16.87 [- 29.81 to -3.94], respectively (Table 28).

[0442] In conclusion, beyond the sustained and clinically meaningful bleed control provided by fitusiran prophylaxis on AT-DR, fitusiran prophylaxis also improved the physical health and overall hemophilia-related quality of life of adult people with hemophilia A or B, as measured by Haem-A-QoL physical health and total scores.

Example 14: Long-Term Safety and Efficacy of Fitusiran Prophylaxis, and Perioperative Management in People with Hemophilia A or B

[0443] This Example describes the results of the completed Phase 2 open-label extension study, which evaluated the long-term safety and efficacy of fitusiran in participants with moderate or severe hemophilia A or B with or without inhibitors.

[0444] Male participants who had completed the Phase 1 study (NCT02035605) were enrolled. Participants received monthly subcutaneous fitusiran (50 mg or 80 mg) under the original dose regimen until a voluntary dosing pause in 2020, following which the AT-based dose regimen was introduced, targeting the recommended AT activity levels of 15-35%.

[0445] Thirty-four participants (hemophilia A [n=27]; hemophilia B [n=7]) were enrolled in the Phase 2 study and treated with fitusiran for a median exposure of 4.1 years. Adverse events reported on the original and the AT-based dose regimen were generally consistent with the identified risks of fitusiran. Following implementation of the AT-based dose regimen, no thrombotic events, and a reduction in the incidence of elevated transaminases and biliary events, were reported. The observed median annualized bleeding rate (ABR) on the AT-based dose regimen (0.87) was comparable to ABR under the original dose regimen (0.70). Furthermore, fitusiran prophylaxis was associated with improved health-related quality of life compared to baseline and provided successful hemostatic control during surgical procedures.

[0446] Overall, fitusiran was well tolerated with an improved safety profile on the AT- based dose regimen and effective bleeding control was maintained. This trial was registered with the FDA as NCT02554773.

Methods

[0447] Study design and patient population: This Phase 1/2 multicenter, multinational, non-randomized, long-term, OLE study (NCT02554773), was initiated in September 2015 and completed in March 2023. The study was conducted in accordance with the protocol and consensus ethical principles derived from international guidelines, including the Declaration of Helsinki, and the International Council for Harmonisation guidelines for Good Clinical Practice, all applicable laws, rules, and regulations. Participants were informed that their participation was voluntary and written informed consent was obtained from all participants or their legally authorized representative before enrollment in the study.

[0448] Participants who had previously completed the Phase 1 multiple ascending dose study and received /Sone SC dose of fitusiran, ranging from 0.225 mg/kg to 1.8 mg/kg, or 50 mg or 80 mg fixed doses, were enrolled (FIG. 58). All participants were transitioned to either 50 mg or 80 mg monthly SC fitusiran after no more than four monthly doses in this study.

[0449] The study was placed on hold on September 1, 2017 following a fatal event confirmed as an intracranial hemorrhage due to a cerebral venous sinus thrombosis (CVST), adjudicated by an independent neuroradiologic review of imaging. The event was initially misdiagnosed as a subarachnoid (primary cerebral) hemorrhage and treated with high doses (i.e., >30 lU/kg) of FVIII concentrate, which exceeded the “capped” dose of ' AO lU/kg FVIII that was recommended per protocol at the time. As a result of this event, risk mitigation measures were introduced including recommendations for management of thrombotic events, revised recommendations for management of sepsis, and additional exploratory laboratory assessments. Furthermore, the breakthrough bleed management guidelines were updated with recommendations for use of a lower dose and frequency of CFCs/BPAs than previously allowed (Table 4). The study was restarted in December 2017 and dosing subsequently resumed.

[0450] A voluntary dosing pause was implemented on October 30, 2020 due to non-fatal thrombotic events observed in other clinical studies within the fitusiran clinical program (Negrier et al., “Fitusiran, an siRNA therapeutic targeting antithrombin for the treatment of haemophilia: proposed revisions to dose and regimen as a risk mitigation for vascular thrombosis.” (2021) Abstract presented at The European Association for Haemophilia and Allied Disorders Virtual Meeting). A thorough evaluation of the thrombotic events was conducted, which showed the incident rate of vascular thrombotic events per 100 patient- years in AT categories < 10%, 10-20%, and >20% was 5.9, 1.5, and 0, respectively, suggesting that very low (<10%) AT activity levels were associated with an increased risk of thrombotic events. This led to the introduction of a modified dose regimen, on November 25, 2020, as a risk mitigation measure for thrombotic events, which targeted the recommended AT activity levels of 15-35%. A reduced dose of 50 mg administered SC every second month (Q2M) was selected to minimize the occurrence of AT activity levels <10%. At a reduced dose of 50 mg Q2M, if a participant had >1 AT activity level <15%, the participant was required to permanently discontinue fitusiran. Participants previously exposed to fitusiran at a monthly dose of 50 mg or 80 mg with no more than 1 AT activity level <15% at any time during fitusiran treatment had the option to remain on either dose, respectively (FIG. 59). This modified dose regimen is hereafter referred to as the “AT-based dose regimen”.

[0451] Eligible participants were males aged % 18 years with moderate or severe clinically stable hemophilia A or B as evidenced by a laboratory FVIII or FIX level %5%’ at screening, or based on a historic laboratory report, who had tolerated fitusiran dosing, and completed the Phase 1 study NCT02035605. Exclusion criteria included liver disease, known HIV, and history of venous thromboembolism. Full inclusion and exclusion criteria are provided below.

[0452] Inclusion criteria included:

Completed and tolerated study drug dosing in study ALN-AT3SC-001.

Male aged % 18 years.

Moderate or severe, clinically stable hemophilia A or B as evidenced by a laboratory FVIII or FIX level %5%’ at screening. Patients with a FVIII or FIX level >5% at screening will be eligible on provision of a historic laboratory report indicating a trough level %5%’. Willing and able to comply with the study requirements and provide written informed consent.

[0453] Exclusion criteria included:

Liver disease defined as any of the following:

- Clinically significant cirrhosis as determined by the investigator

- INR >1.5 at Screening.

- ALT or AST >3x upper limit of normal (ULN) of the reference range at Screening.

- Platelet count 120,000/ U L and/or other complete blood count test results that are considered clinically significant and unacceptable by the investigator.

- Known hepatitis C virus (HCV) infection currently requiring treatment with ribavirin or interferon.

Known to be human immunodeficiency virus seropositive and have a CD4 count <200 cells/pL at screening (a CD4 result from the previous 6 months may be used to confirm eligibility).

History of venous thromboembolism, except for those patients who have a medical history of previous thrombotic event related to permanent indwelling venous access.

Current serious mental illness that, in the judgment of the Investigator, may compromise patient safety, ability to participate in all study assessments, or study integrity.

Uncontrolled hypertension (defined as systolic blood pressure 160 mmHg and diastolic blood pressure S? 100 mmHg).

Corrected QT(QTc) interval ^450 ms and/or concomitant use of drugs known to prolong the QT/QTc interval at screening.

Estimated glomerular filtration rate ^45 mL/min (using the Modification of Diet in Renal Disease formula).

Clinically relevant history or presence of cardiovascular, respiratory, gastrointestinal, renal, neurological, inflammatory, or other diseases that, in the judgment of the Investigator, precludes study participation.

I l l If using nonsteroidal anti-inflammatory drugs intermittently or chronically, must tolerate them with no previous side effects (e.g., gastric distress or bleeding).

Clinically significant alcohol consumption, as assessed by the investigator. Any condition(s) that, in the opinion of the Investigator, would make the patient unsuitable for enrollment or could interfere with patient participation in or completion of the study.

[0454] Study assessments and measurements: Baseline demographic characteristics were assessed at the time of enrollment date in the parent study. The primary objective was to evaluate the long-term safety and tolerability of fitusiran in male participants with moderate or severe hemophilia A or B, with or without inhibitors. Safety assessments included reported adverse events (AEs), serious adverse events (SAEs), and adverse events of special interest (AESIs) including thromboembolic events, transaminase elevations (alanine aminotransferase [ALT] and/or aspartate transaminase [AST] >3 times upper limit of normal [ULN]), and cholelithiasis/cholestasis; and clinical laboratory evaluations including antidrug antibodies.

[0455] Secondary objectives were to investigate the long-term efficacy of fitusiran by assessing annualized bleed rate (ABR), spontaneous ABR, and joint ABR during the efficacy period; to characterize AT reduction and TG increase by measuring AT activity levels and TG over time; to characterize the pharmacokinetics of fitusiran (using plasma and urine samples); and to assess changes in health-related QoL (HRQoL) over time using EQ-5D-5L and Haem-A-QoL total score and domain scores. HRQoL scores range from 0-100, with lower scores indicating improvements in QoL.

[0456] The Haem-A-QoL questionnaire is a psychometrically validated QoL assessment instrument for adult participants with hemophilia (Wyrwich et al., Haemophilia (2015) 21 (5) :578-84) . Haem-A-QoL Physical Health and Total transformed scores range from 0 to 100, where a lower score denotes improvement in QoL. Reductions of 7.1 points in “Total score” and 10 points in “Physical Health score” are regarded as practical thresholds for identifying notable improvements in HRQoL (Young et al., Lancet (2023). 401(10386): 1427- 37).

[0457] The EQ-5D-5L is a standardized and disease-generic instrument for use as a measure of QoL outcome. It consists of a questionnaire pertaining to five dimensions (mobility, self-care, usual activities, pain/discomfort, and anxiety/depression) and a visual analog scale (VAS). Scoring of the visual analog scale is based on a visual scale ranging from 0 (worst imaginable health state) to 100 (best imaginable health state). [0458] The exploratory objective of this study was to assess the safety and hemostatic efficacy rating for operative procedures performed while on study, based on the hemostatic rating scale adapted from ISTH Scientific and Standardization Committee definitions. Major surgery was defined as any invasive operative procedure that requires any of the following: opening into a major body cavity (e.g., abdomen, thorax, skull), operation on a joint, removal of an organ, dental extraction of any molar teeth or ^3 non-molar teeth or any tooth implantation, or operative alteration of normal anatomy or crossing of a mesenchymal barrier (e.g., pleura, peritoneum, dura).

[0459] Statistical analysis: All measures of safety and efficacy included in the analysis were summarized using descriptive statistics. Estimates of ABR were calculated as the number of bleed events occurring after the first significant dose (defined as a single dose of fitusiran that is ^20 mg), in the parent study or this study and until the end of study visit. [0460] The following analysis periods were defined for the purpose of ABR calculation:

The “onset period” was the first 28 days after the first significant dose of fitusiran (defined as a single dose of fitusiran that is ^20 mg), during which the target pharmacodynamic effect was reached.

The “adjustment period” was the dose restart Day 1 to the earlier of dose restart Day 168 or the end of study under the AT-based dose regimen.

The “efficacy period” started on treatment Day 29 in the original dose regimen period and on Day 169 in the AT-based dose regimen period.

The “treatment period in the original dose regimen” was the period of treatment including the onset and efficacy periods.

The “treatment period in the AT-based dose regimen” was the period of treatment including the dose adjustment and efficacy periods.

[0461] Both efficacy and safety analyses under the original and AT-based dose regimens were performed separately, unless otherwise specified. Before the voluntary dosing pause, the analysis period for efficacy endpoints started from the date of first significant dose up to the earlier of the 2020 voluntary dosing pause date or the last day of study follow-up. For participants under the AT-based dose regimen, both efficacy and safety data were analyzed from the dose restart Day 1 up until the last day of study follow-up.

[0462] Safety analysis set 1 (50 or 80 mg once monthly dose regimen period, referred to as the “original dose regimen”) and safety analysis set 2 (the modified dose regimen period referred to as “AT-based dose regimen”, which included doses of 50 mg once monthly, 80 mg once monthly, or 50 mg every other month) were the primary sets for safety assessments. The primary sets for efficacy assessments were full analysis set 1, which includes 34 participants under the original dose regimen, and full analysis set 2, which includes 18 participants who resumed fitusiran under the AT-based dose regimen. Similarly, the operative procedure analysis set 1 and operative procedure analysis set 2, i.e., all participants who received 1 dose of study drug and underwent 1 operative procedure during the study under the original dose regimen or under the AT-based dose regimen, respectively.

Results

[0463] Baseline demographics and patient disposition: All (100%) participants were male (Table 29). For participants under the original dose regimen, safety analysis set 1, the median age was 36.5 years, and all were under 65 years of age. For participants under the AT-based dosing regimen, safety analysis set 2, the median age was 36.0 years of age. The majority of participants in safety analysis set 1 and safety analysis set 2 were white (97.1% and 100% of participants, respectively) and were from Europe (94.1% and 88.9% of participants, respectively).

Table 29. Demographics and clinical characteristics at baseline

[0464] In safety analysis set 1 (original dose regimen), 31 participants (91.2%) had severe hemophilia at study entry, 26 (76.5%) had a history of hepatitis C, and the median historical ABR was 20. In safety analysis set 2 (AT-based dose regimen), 15 participants (83.3%) had severe hemophilia at study entry, the 13 participants (72.2%) had a history of hepatitis C, and the median historical ABR was 18.

[0465] Of the 34 participants enrolled in the study (FIG. 60), 34 received 1 (50 mg or 80 mg) fitusiran dose since the first dose in the treatment period under the original dose regimen, with a median duration of fitusiran treatment exposure of 1135.0 days (3.1 years) (Table 29). Eighteen participants received 1 dose under the AT-based dose regimen (FIG. 60), with a median duration of fitusiran treatment exposure of 568.0 days (1.6 years) (Table 29). Overall, 34 participants initiated the original dose regimen, 18 restarted the study with the AT-based dose regimen, and 12 completed the study, with an overall median duration of fitusiran treatment exposure of 1584.0 days (4.1 years) from first significant dose in the treatment period until the end of the study. [0466] Safety: In safety analysis set 1 (original dose regimen), 33/34 (97.1%) participants experienced 1 treatment-emergent adverse event (TEAE) (Table 30). The most common TEAEs included ALT increase (10 [29.4%] participants), headache (9 [26.5%] participants), arthralgia (8 [23.5%] participants), injection site erythema (7 [20.6%] participants), and nasopharyngitis (7 [20.6%] participants). Treatment-emergent serious adverse events (TESAEs) were reported in 13 (38.2%) participants in safety analysis set 1. The most common TESAE was cholecystitis in two (5.9%) participants. Cholecystitis and cholelithiasis were regarded as treatment-emergent AESIs and overall, in the original dose regimen period, 4 (11.8%) participants reported cholecystitis and cholelithiasis (each 2 [5.9%] participants).

Table 30. Adverse Events

[0467] Five TEAEs in five (14.7%) participants were reported to result in discontinuation of study drug and included dyspnea, transaminases increased, atrial thrombosis, and CVST (initially misdiagnosed as subarachnoid hemorrhage) (Table 30). The events of dyspnea, transaminases increased, and CVST, led to study withdrawal in three (8.8%) participants. [0468] The TEAEs of atrial thrombosis and transaminases increased were assessed by the investigator as serious and related to fitusiran; the TEAEs of dyspnea and ALT increased were categorized as non-serious but related to fitusiran. The TEAE of CVST initially misdiagnosed as subarachnoid hemorrhage was confirmed to be a CVST by an independent adjudication committee, which included three who reviewed the participant’s computed tomography imaging results. The CVST that was misdiagnosed and treated as a subarachnoid hemorrhage neuroradiologists resulted in death, and the event was recategorized from not related to fitusiran to possibly related to fitusiran. A summary of thrombotic events is provided below:

Hemophilia A patient without inhibitor, treated with the original dose regimen. Received other treatments of concomitant use of factor concentrate in excess of the current bleed management guidelines. Last AT activity level prior to the event was 15.9%. The patient’s medical history was as follows:

- Hepatitis C positive, cholecystitis, and smoking history (10 cigarettes a day).

- No history of drug or alcohol abuse.

- The family history included a fatal ICH in a male sibling with hemophilia at the age of 2 months.

CVST occurred in 2017 (As assessed by an independent adjudication committee including review of the patient’s CT scans by three independent neuroradiologists, who all confirmed that the initiating event was a CSVT, and not a subarachnoid hemorrhage). The participant was initially suspected of having viral meningitis but was subsequently diagnosed with subarachnoid hemorrhage on the basis of CT imaging. The participant’s clinical course deteriorated despite the administration of FVIII concentrate 2-3 times a day and the participant died secondary to cerebral edema. Following this event, the participant’ s CT scans were reviewed, and it was confirmed that the initiating event was a CVST, not a subarachnoid hemorrhage.

Hemophilia B patient with inhibitor, treated with the original dose regimen. Received other treatment of concomitant use of BPA (rFVIIa) in excess of the current bleed management guidelines in fitusiran clinical studies. The last AT activity level prior to the event was 11.7%. The medical history was as follows:

- The participant developed an inhibitor to FIX as an infant with the first few exposures to FIX concentrates.

- Coincident with the development of the FIX inhibitor the participant manifested with anaphylaxis. He had a prolonged attempt of desensitization to FIX along with immunosuppression, but this culminated in the development of nephrotic syndrome, so this was abandoned.

- Prior to initiation of fitusiran, the participant had almost continuous bleeding into his left elbow and most of the bleeds occurred with the use of an arm sling or splint over weeks at a time despite attempts at intensified dosing and prophylaxis

Atrial thrombosis was detected in 2019. The participant was evaluated by general surgery due to right lower quadrant discomfort. A CT scan confirmed a right atrial mass. Fitusiran dosing was interrupted, and the patient was started on FXa inhibitors. The mass did not change in size during treatment with anticoagulation and the participant began to bleed again under FXa inhibitors. The participant resumed fitusiran and continued to be dosed at 80 mg QM until the program- wide hold in 2020, and restarted under 50 mg Q2M with the AT-based dose regimen. A follow-up echocardiogram showed enlargement of the right atrial mass and fitusiran was subsequently permanently discontinued.

[0469] In the safety analysis set 2 (AT-based dose regimen), 14/18 (77.8%) participants experienced 1 TEAE (Table 30). The most common TEAEs were CO VID- 19 and viral upper respiratory tract infection (both reported in 2 [11.1%] participants). There were no “suspected or confirmed thromboembolic events” and there were no events of cholecystitis or cholelithiasis reported during the AT-based dose regimen. There was one drug discontinuation/withdrawal due to a TESAE of hepatocellular carcinoma (in a participant who was hepatitis C positive), which was assessed by the investigator as not related to fitusiran.

[0470] Six (17.6%) participants with hemophilia A were reported to have “ALT or AST elevations >3 x ULN” in safety analysis set 1 (original dose regimen) (Table 31), which were classified by the investigator as non-serious, and the majority were rated as mild or moderate in severity; 4/6 participants reported a history of alcohol consumption before ALT/AST elevations occurred.

[0471] One (5.6%) participant was reported to have “ALT or AST elevations >3 x ULN” in safety analysis set 2 (AT-based dose regimen) (Table 31). The participant had increased transaminases which led to study drug discontinuation due to withdrawal of consent. The participant reported a history of alcohol consumption prior to the occurrence of ALT/AST elevations.

Table 31. Liver Function

[0472] Overall, 2 participants in the original dose regimen period developed antidrug antibodies (ADAs). One participant was ADA-positive at Month 10 (titer, 200 and ADAnegative at subsequent timepoints (months 13 and 16); the ADA response in this participant was considered transient. The second participant was ADA-positive at Month 48 in the original dose regimen period (titer, 400) and at Month 60 and 72 (titer, 100) in the AT-based dose regimen period but was ADA-negative at the end of treatment (Month 84). No other participants were ADA-positive in the AT-based dose regimen period.

[0473] Bleeding episodes: Eitusiran prophylaxis maintained effective bleed protection over a 6-year period. The observed median ABR (QI; Q3) during the efficacy period was 0.70 (0.00; 3.97) in the original dose regimen and 0.87 (0.00; 5.36) in the AT-based dose regimen period (FIG. 61).

[0474] Overall, the spontaneous ABR and joint ABR in the original dose regimen and in the AT-based dose regimen were similar. The median observed spontaneous ABR (QI; Q3) in the original dose regimen period was 0.33 (0.00; 1.68) and 0.00 (0.00; 3.84) in the AT- based dose regimen period (FIG. 62). The median observed joint ABR (QI; Q3) in the original dose regimen period was 0.55 (0.00; 2.83) and 0.87 (0.00; 3.84) in the AT-based dose regimen period (FIG. 63).

[0475] Assessment of AT activity levels and TG: In the original dose regimen period, monthly dosing with fitusiran resulted in a sustained lowering of AT activity levels with a 96.41% (11.82) mean (standard deviation [SD]) reduction from baseline to endpoint (i.e., last available assessment before end of study) and a mean AT percentage change from baseline to endpoint of -85.59% (4.25) starting at Month 1 and persisting over several months. In the AT-based dose regimen, the mean (SD) reduction and mean (SD) AT percentage change from baseline to endpoint (i.e., last available assessment before end of study) were 82.28% (14.98) and -76.69% (8.64). There were three participants who discontinued the study in the AT-based dose regimen period due to > one AT activity level <15%. The AT activity levels of the remainder of the participants were maintained between 15-35% (FIG. 64A, FIG. 65A, and FIG. 65B).

[0476] Consistent with the mechanism of action of fitusiran, TG increased with AT lowering (FIG. 64B, FIG. 66A, and FIG. 66B), from a mean (SD) at baseline of 17.42 (9.69) nM to a peak mean (SD) of 74.42 (26.95) nM by endpoint evaluation (i.e., last available assessment of each participant) that remained elevated during the course of fitusiran treatment for the overall participants in the original dose regimen period (i.e., 66 months). In the AT-based dose regimen period, TG increased from mean (SD) at baseline of 15.01 (5.88) nM to a peak mean (SD) of 88.08 (28.72) nM by endpoint evaluation (i.e., last available assessment of each participant) for the overall participants, although TG assessments were only included for the first six months under the AT-based dose regimen. This was due to an issue with a batch of trigger reagent used for the TG assay, which meant that samples from 17 participants in the AT-based dose regimen analysis set were excluded from the data analysis. Antithrombin lowering correlated with TG peak increase until the point where the samples had to be excluded and no further conclusions could be made.

[0477] During the clinical hold in 2017, AT activity levels in patients previously receiving fitusiran progressively increased. The mean AT recovery was >60% at five months after dosing interruption (mean 69.07%, SD [16.76]), with a mean AT recovery of 7% per month over 11 months. Consequently, TG gradually decreased, with a peak mean (SD) of 23.81 (12.57) nM by Month 5 of the clinical hold.

[0478] Patient-reported outcomes: Reductions in Haem-A-QoL “Total” and “Physical Health” scores were observed in 14/34 participants in the original dose regimen period and 9/18 participants in the AT-based dosing period (FIG. 67). Reductions of 7.1 points in “Total” score and 10 points in “Physical Health” score are regarded as practical thresholds for identifying notable improvements in HRQoL. Thus, observed reductions in both the “Total” and “Physical Health” scores under both dose regimens are indicative of HRQoL benefits, with meaningful improvements observed under the AT-based dose regimen.

[0479] Perioperative management: Six participants receiving the original dose regimen underwent a total of nine major surgical procedures, and 1 participant receiving the AT-based dose regimen underwent one major surgical procedure (Table 32). Fitusiran treatment was paused for 2/9 procedures (surgery 1 and 3) under the original dose regimen but was continued for the majority of procedures (7/9 [77.8%] procedures under the original dose regimen and 1/1 [100%] procedure under the AT-based dose regimen). Following major surgery, excellent hemostatic efficacy was reported by the investigator for 5/9 procedures (surgeries 1, 2, 6, 7, and 9) in the original dose regimen period and 1/1 procedure (surgery 10) in the AT-based dosing period. Hemostatic efficacy was not rated/reported by the investigator for 4/9 procedures (surgeries 3-5, and 8) under the original dose regimen, although hemostatic management was successful. No blood components or AT concentrate were given during any of the procedures (although AT concentrate was given 1 day before surgery 10, which was a tooth extraction under the AT-based dose regimen), and blood loss was minimal.

Table 32. Summary of Surgical Procedures Performed During Trial [0480] Further details for each of these surgeries are provided below.

[0481] Surgery number 1 :

Participant Characteristics: Hemophilia A without inhibitors.

Fitusiran Dosing Regimen: Fitusiran dosing discontinued prior to surgery due to dosing hold.

AT Activity Level: 51.0% (1 day prior to surgery); 54.2% (at the time of the procedure).

Type of Procedure: Laparoscopic cholecystectomy.

Perioperative Hemostatic Treatment: Participant received reduced doses and frequency of FVIII as follows: Procedure day: 1000 IU (11.8 lU/kg) OD. 1 day post-surgery: 500 IU (5.9 lU/kg) OD and 1500 IU (17.7 lU/kg) OD. 2 days post-surgery: 1500 IU (17.7 lU/kg) OD. 3 days post-surgery: 1500 IU (17.7 lU/kg) OD and 1000 IU (11.8 lU/kg) OD. 4 days post-surgery: 1500 IU (17.7 lU/kg) OD and 1000 IU (11.8 lU/kg) OD.

Outcome: Hemostasis rated as excellent. No blood components were given for the surgery. No estimated blood loss during surgery was reported. AT concentrate was not used for the surgery. No chemical thrombo-prophylaxis was used.

Adverse events in perioperative period: CRP increased, LDH increased. [0482] Surgery number 2:

Participant Characteristics: Hemophilia B with inhibitors.

Fitusiran Dosing Regimen: Fitusiran dosing (original dose regimen) was ongoing.

AT Activity Level: 14.3% (2 days prior to surgery); 12.3% (on the day of surgery).

Type of Procedure: Right ankle fusion and Achilles tendon lengthening. Perioperative Hemostatic Treatment: Participant received reduced doses and frequency of rFVIIa as follows: Procedure day: 4 mg (50.1 pg/kg) 3 times/day. 1 day post-surgery: 4 mg (50.1 pg/kg) 5 times/day.

Outcome: Hemostasis rated as excellent. No blood components were given for the surgery. Estimated blood loss during surgery was 15 ml. AT concentrate was not used for the surgery. No bleeds were reported in the perioperative period. No chemical thrombo-prophylaxis was used.

Adverse events in perioperative period: None. / [0483] Surgery number 3:

Participant Characteristics: Hemophilia A with inhibitors. Fitusiran Dosing Regimen: Fitusiran treatment was paused due to surgery. AT Activity Level: 17.7% (62 days prior to surgery). Type of Procedure: Left knee total replacement.

Perioperative Hemostatic Treatment: Prior to surgery the participant received reduced doses and frequency of aPCC as follows: 4 days prior to the surgery: 1000 IU (18.1 lU/kg) and 1500 IU (27.1 lU/kg) OD; 3 days prior to the surgery: 2500 IU (45.1 lU/kg) OD; 2 days prior to the surgery and 1 day prior to the surgery: 1500 IU (27.1 lU/kg) each OD. On the day of surgery and postsurgery the participant received reduced doses and frequency of aPCC as follows: Procedure day: 2500 IU (45.1 lU/kg) OD and 500 IU (9 lU/kg) OD; 1 day post-surgery: 2500 IU (45.1 lU/kg) OD; 2 days post-surgery to 8 days post-surgery: 3000 IU (54.2 lU/kg) each OD; 9 days post-surgery to 14 days post-surgery: 2000 IU (36.1 lU/kg) each OD and 1000 IU (18.1 lU/kg) each OD.

Outcome: Hemostasis was not reported. No blood components were given for the surgery. Estimated blood loss during surgery was 500 ml. AT concentrate was not used for the surgery. No chemical thrombo-prophylaxis was used. Adverse events in perioperative period: Anemia postoperative, blood loss anemia, and post procedural oedema.

[0484] Surgery number 4:

Participant Characteristics: Hemophilia A with inhibitors.

Fitusiran Dosing Regimen: Fitusiran dosing (original dose regimen) was ongoing.

AT Activity Level: 13% (1 day prior to surgery); 14.1% (1 day after surgery). Type of Procedure: Metal plate removal and right hip total replacement. Perioperative Hemostatic Treatment: The participant received 2 injections of reduced doses and frequency of aPCC 1000 IU (12.1 lU/kg) each OD as presurgery loading dose 5 days before surgery and 1 day before surgery. On the day of surgery and post-surgery the participant received reduced doses and frequency of aPCC as follows: Procedure day: 1000 IU (12.1 lU/kg) OD; 1 day post-surgery to 6 days post-surgery: 1000 IU (12.1 lU/kg) each OD; 7 days post-surgery to 9 days post-surgery: 1000 IU (12.1 lU/kg) OD. Outcome: Hemostasis was not reported. The removal of the plate was carried out with minimal blood loss, and blood loss during endoprosthesis was comparable to that in the study participants without hemostasis pathology. No blood components were given for the surgery. Estimated blood loss during surgery was 500 ml. AT concentrate was not used for the surgery. No chemical thrombo-prophylaxis was used.

Adverse events in perioperative period: Mild post operative hematoma reported on Day 976, which required no treatment; postoperative anemia.

[0485] Surgery number 5:

Participant Characteristics: Hemophilia A with inhibitors.

Fitusiran Dosing Regimen: Fitusiran dosing (original dose regimen) was ongoing.

AT Activity Eevel: 12.6% (1 day prior to surgery).

Type of Procedure: Eeft knee total replacement.

Perioperative Hemostatic Treatment: On the day of surgery, the participant received the loading dose aPCC 2000 IU OD. On the day of surgery and postsurgery the participant received reduced doses and frequency of aPCC as follows: Procedure day: 1000 IU (12.1 lU/kg) OD; 1 day post-surgery to 5 days post-surgery: 3000 IU (36.2 lU/kg) each OD; 6 days post-surgery to 9 days post- surgery: 2000 IU (24.1 lU/kg) OD.

Outcome: Hemostasis was not reported. Blood loss was as expected for any non-hemophilia study participant or even less. AT concentrate was not used for the surgery. No chemical thrombo-prophylaxis was used.

Adverse events in perioperative period: None.

[0486] Surgery number 6:

Participant Characteristics: Hemophilia A without inhibitors.

Fitusiran Dosing Regimen: Fitusiran dosing (original dose regimen) was ongoing.

AT Activity Eevel: 15.0% (1 day prior to surgery); 12.9% (2 days postsurgery).

Type of Procedure: Nasal septoplasty.

Perioperative Hemostatic Treatment: On the day of surgery, the study participant received FVIII 2000 IU (28.2 lU/kg) OD as preoperative dose. On the day of surgery and post-surgery the participant received reduced doses and frequency of FVIII as follows: Procedure day, 2 days post-surgery), 3 days post-surgery, and 7 days post-surgery: 14.1 lU/kg once/day.

Outcome: Hemostasis rated as excellent. No blood components were given for the surgery. Estimated blood loss during surgery was 50 ml. AT concentrate was not used for the surgery. No chemical thrombo-prophylaxis was used. Adverse events in perioperative period: None.

[0487] Surgery number 7 :

Participant Characteristics: Hemophilia A without inhibitors.

Fitusiran Dosing Regimen: Fitusiran dosing (original dose regimen) was ongoing.

AT Activity Eevel: 13.3% (21 days prior to surgery).

Type of Procedure: Endoscopic Cholecystectomy.

Perioperative Hemostatic Treatment: On the day of surgery and post-surgery the participant received reduced doses and frequency of FVIII as follows: Procedure day, 1 day post-surgery, and 2 days post-surgery: 1000 IU (14.1 lU/kg) twice/day; 3 days post-surgery, 4 days post-surgery, and 5 days postsurgery, 1000 IU (14.1 lU/kg) OD.

Outcome: Hemostasis rated as excellent. No blood components were given for the surgery. Estimated blood loss during surgery was 50 ml. AT concentrate was not used for the surgery. No chemical thrombo-prophylaxis was used. Adverse events in perioperative period: None.

[0488] Surgery number 8:

Participant Characteristics: Hemophilia A without inhibitors.

Fitusiran Dosing Regimen: Fitusiran dosing (original dose regimen) was ongoing.

AT Activity Eevel: 15.7% (18 days prior to surgery).

Type of Procedure: Extraction of two wisdom teeth.

Perioperative Hemostatic Treatment: None.

Outcome: Hemostasis was not rated. No complication was reported. Went as for a non-hemophilia study participant. No blood components were given for the surgery. Estimated blood loss during surgery was 5 ml. AT concentrate was not used for the surgery.

Adverse events in perioperative period: None.

[0489] Surgery number 9: Participant Characteristics: Hemophilia A without inhibitors.

Fitusiran Dosing Regimen: Fitusiran dosing (original dose regimen) was ongoing.

AT Activity Level: 13.2% (3 days prior to the surgery).

Type of Procedure: Bilateral knee replacement.

Perioperative Hemostatic Treatment: The participant received reduced doses and frequency of FVIII as follows: Procedure day: 2000 IU (24.9 lU/kg) OD;

1 day post-surgery to 3 days post-surgery: 800 IU (10 lU/kg) each OD; 3 days post-surgery to 7 days post-surgery: 820 IU (10.2 lU/kg) each OD; 8 days post-surgery to 14 days post-surgery: 1230 IU (15.3 lU/kg) each OD.

Outcome: Hemostasis rated as excellent. No blood components were given for the surgery. Estimated blood loss during surgery was not reported. AT concentrate was not used for the surgery. No chemical thrombo-prophylaxis was used.

Adverse events in perioperative period: None.

[0490] Surgery number 10:

Participant Characteristics: Hemophilia B without inhibitors.

Fitusiran Dosing Regimen: Fitusiran dosing (AT-based dose regimen) was ongoing.

AT Activity Level: 12.2% (2 days prior to surgery); 26.1% (2 days postsurgery).

Type of Procedure: Tooth extraction (teeth 24, 25, 28, and 37).

Perioperative Hemostatic Treatment: AT III (human) concentrate 2500 IU (43.1 lU/kg) was used for surgery (1 day prior to the surgery). The participant received reduced doses and frequency of tranexamic acid 500 mg (8.6 mg/kg)

2 times/day and FIX 3000 IU (51.7 lU/kg on the day of the procedure.

Outcome: Hemostasis rated as excellent. No blood components were given for the surgery. AT concentrate was not required during the surgery, and no excessive bleed occurred during the surgery.

Adverse events in perioperative period: None.

[0491] Discussion: Overall, participants were treated with fitusiran for a median exposure of 4.1 years during the study. Risk-mitigation measures including bleed management guidance (using reduced doses and frequency of CFCs/BPAs) as well as a revised dose regimen targeting AT activity levels of 15-35% were implemented successfully. Long-term safety and efficacy data are consistent with the findings of Part C and D of the Phase 1 study in which participants were exposed to similar doses and regimen of fitusiran as the present study with doses ranging from 0.225 mg/kg to 1.8 mg/kg, or 50 mg or 80 mg fixed monthly doses (Pasi et al., N Engl J Med (2017). 377(9):819-28; Pasi et al., J Thromb Haemost (2021) 19(6): 1436-46).

[0492] Participants with hemophilia treated with fitusiran maintained effective bleed control on the AT-based dose regimen, regardless of hemophilia type and inhibitor status. Fitusiran was well tolerated with an improved safety profile on the AT-based dose regimen relative to the original dose regimen. With the AT-based dose regimen, there were no thrombotic events, and the incidence of elevated transaminases and biliary events was reduced. In addition, ADA data indicate that fitusiran has low potential to elicit an immunogenic response.

[0493] Long-term safety assessments conducted during the original dose regimen period and the AT-based dose regimen period showed that the benefit-risk profile of fitusiran during long-term dosing was favorable, and the type and frequency of reported AEs were generally consistent with the identified risks of fitusiran including events of liver transaminase elevations, thrombosis, cholecystitis, and cholelithiasis.

[0494] Two cases of thrombosis occurred over the course of the study. Within the general population, the risk of thrombosis may be increased by exogenous factors such as surgery, or immobilization, or endogenous factors such as cancer, obesity, or disorders of hypercoagulation (Cushman, Semin Hematol (2007) 44(2):62-9). In the context of hemophilia treatment and restoring TG, the risk of thrombosis should be a consideration when non-factor therapies are used concomitantly with other hemostatic agents, such as CFCs/BPAs, to treat bleeding episodes (Arruda et al., FlOOORes (2018) 7). In the present study, both thrombotic events occurred under the original dose regimen, and in both cases the patients were given concomitant CFC/BPA in excess of the current bleed management guidelines, and had no other thrombotic risk factors. Following the introduction of the revised breakthrough bleed management guidelines for fitusiran and the AT-based dose regimen, no additional thrombotic events were reported in this study.

[0495] It has been suggested that it may be useful to evaluate hemophilia patients for thrombophilias prior to starting non-factor therapies, to help determine the risk of thrombotic events (Arruda et al., FlOOORes (2018) 7). Participants in the fitusiran trials were all screened for known major hereditary thrombophilias including Factor V Leiden, protein S deficiency, protein C deficiency, and prothrombin mutation (G20210A). Patients with a known coexisting thrombophilic disorder were excluded from the trial.

[0496] In the present study, the majority of elevations in liver enzymes ALT or AST >3 x ULN were classified as mild to moderate in severity, they were transient and resolved, and were less frequent on the AT-based dose regimen. Similarly, cholecystitis and cholelithiasis were reported in two (5.9%) participants each on the original dose regimen but not on the AT-based dose regimen. The mechanism of action of fitusiran relies on targeted delivery of the drug to the liver where AT is synthesized (Machin N et al., J Blood. Med (2018). 9:135- 40). Therefore, occurrence of hepatic AEs is also of particular interest, especially in a population highly exposed to hepatitis C. The underlying pathophysiology for the development of transaminase elevations, cholecystitis, and cholelithiasis is unknown and these risks remain under investigation in ongoing trials. Transaminase elevations have also been reported with approved siRNA therapies for other indications (Lorenzer et al., J Control Release (2015) 203:1-15; Padda et al., Treasure Island (FL): StatPearls Publishing; (Jan 2023)). Risk mitigation measures for hepatotoxicity are implemented in ongoing clinical studies and include transaminase monitoring and guidelines for the withholding and permanent discontinuation of fitusiran.

[0497] Treatment with fitusiran resulted in sustained lowering of AT activity levels and a substantial decrease in observed median ABRs, spontaneous ABRs, and joint ABRs over a 6- year period compared with baseline. Haem-A-QoL assessments taken during the study showed improvements, with both the original dose regimen and AT-based dose regimen compared with baseline. This included an improvement in the score for “Physical Health”, which evaluates painful swelling, joint pain, pain with movement, difficulty walking, and time to get ready, and is regarded as one of the domains that reflects key impairments in QoL (Wyrwich et al., Haemophilia (2015) 21 (5) :578-84). Further observations will be made to assess changes in Haem-A-QoL in ongoing studies.

[0498] Successful perioperative hemostatic control while receiving SC fitusiran was observed in 7/7 (100%) participants who underwent surgery.

[0499] Extensive long-term exposure to fitusiran was achieved on both original and AT- based dose regimens, with an average of 3 and 1.5 years, respectively. Despite two periods where fitusiran treatment was paused in 2017 and 2020, a substantial number of participants completed the entire study. Adequate bleed control was maintained on fitusiran prophylaxis, both at the original and AT-based dose regimens throughout six years of fitusiran exposure. [0500] Conclusion: Fitusiran, an investigational, SC prophylactic siRNA therapeutic, targets AT to rebalance hemostasis in people with hemophilia A or B, with or without inhibitors. Fitusiran was well tolerated with an improved safety profile on the AT-based dose regimen, relative to the original dose regimen, and maintained effective bleeding control on the AT-based dose regimen. Following implementation of the AT-based dose regimen, no thrombotic events, no cholecystitis/cholelithiasis, and a reduction in ALT/AST elevations were reported.

[0501] The results of this long-term study indicate that fitusiran prophylaxis was effective at reducing AT and restoring sufficient TG to achieve hemostasis and a reduction in bleeding episodes in patients with hemophilia A and B, with and without inhibitors under both the original and the AT-based dose regimens. HRQoL was improved with fitusiran in the study participants compared with baseline. Furthermore, it was demonstrated that fitusiran was effective in providing successful bleed control during surgical procedures.

Example 15: Use of Factor Concentrates and Bypassing Agents to Treat Breakthrough Bleeds in Patients with Hemophilia A and B on Fitusiran Antithrombin-Based Dosing Regimen in the ATLAS-OLE Trial

[0502] In the ATLAS-INH [NCT03417102], ATLAS-A/B [NCT03417245], and ATLAS-PPX [NCT03549871]) phase 3 trials of fitusiran, the majority of breakthrough bleeds were successfully managed with only one infusion of reduced dose CFC or BPA. This Example compares a subset of participants receiving the fitusiran antithrombin-based dosing regimen (AT-DR) in ATLAS-OLE (NCT03754790) to their previous CFC/BPA prophylaxis in the ATLAS-PPX study. This Example reports on CFC/BPA utilization in this subgroup. [0503] Methods: Analysis included males aged 12 years with severe hemophilia A or B, with or without inhibitors, who received one dose of fitusiran in ATLAS-PPX and then continued AT-DR in the ATLAS-OLE study. CFC/BPAs were used for the management of breakthrough bleeds during both periods and for standard of care prophylaxis during the CFC/BPA period, with BPAs (activated prothrombin complex concentrate (aPCC) or recombinant activated factor VII (rFVIIa)) used to treat patients with hemophilia with inhibitors, and FVIII and FIX clotting factor concentrates used for patients with hemophilia without inhibitors. Annualized weight-adjusted CFC/BPA consumption, number of treated bleeds, and infusions per bleed were assessed in the fitusiran efficacy period and in the CFC/BPA prophylaxis period. [0504] Results: Data from 67 participants (patients with hemophilia A, n=52; patients with hemophilia B, n=15) receiving CFC/BPA prophylaxis and 69 participants (patients with hemophilia A, n=52; patients with hemophilia B, n=17) receiving fitusiran prophylaxis were included in the analysis. Overall, 33.3% of participants with inhibitors (Cohort A) and 66.7% without inhibitors (Cohort B) were enrolled. The AT-DR demonstrated a substantial reduction in mean annualized bleeding rate (ABR) versus BPA prophylaxis (70% reduction, p=0.0002) and was comparable with CFC prophylaxis (p=0.61).

[0505] Compliance with BMG for the treatment of breakthrough bleeds was >90%. Annualized mean weight-adjusted consumption of CFCs and BPAs and number of infusions per breakthrough bleed were lower with fitusiran AT-DR versus CFC/BPA prophylaxis. The mean (SD) total weight-adjusted dose per bleed for participants without inhibitors and with inhibitors was reduced during fitusiran prophylaxis as compared to the CFC/BPA prophylaxis period (FVIII/FIX (45.3 [41.8] lU/kg and 73.6 [54.7] lU/kg, respectively, with CFC prophylaxis vs FVIII/FIX (12.0 [6.0] lU/kg and 22.3 [10.8] lU/kg, respectively, with fitusiran prophylaxis, and aPCC/rFVIIa (207.8 [373.5] U/kg and 637.3 [1090.8] ug/kg, respectively, during the BPA prophylaxis period versus 50.1 [32.2] U/kg and 86.5 [85.8] ug/kg, respectively, during fitusiran prophylaxis. On average, with fitusiran prophylaxis, 1.1 and 1.0 infusions of reduced dose FVIII and FIX were required to treat a bleed among those without inhibitors, and 1.5 and 1.9 infusions of reduced dose aPCC and rFVIIa were required to treat a bleed among those with inhibitors. A higher proportion of bleeds were successfully treated with 1-2 injections of CFC in participants without inhibitors who received fitusiran prophylaxis (99.2%) as compared with CFC prophylaxis (89.7%), and 1-2 injections of BPA in participants with inhibitors who received fitusiran prophylaxis (87.5%) as compared to BPA prophylaxis (59.6%) (Table 33).

Table 33. Integrated Efficacy Analysis of BPA/CFC Consumption for Treatment of Breakthrough Bleeds (Fitusiran AT-DR vs BPA/CFC Prophylaxis)

[0506] Overall, participants required fewer infusions for the management of breakthrough bleeds with fitusiran AT-DR (with inhibitors=57, without inhibitors=148) versus those who received CFC (total=189) or BPA (total=465) prophylaxis.

[0507] Conclusion: Fitusiran prophylaxis was associated with a meaningful reduction in the number of infusions and substantially lower doses of CFCs/BPAs required to treat breakthrough bleeds as compared to standard of care prophylaxis. Consumption was reduced in patients on the fitusiran AT-DR. These results support the modeled factor equivalency and hemostatic capacity of fitusiran prophylaxis which led to a reduction in the number of bleeds and the amount of CFC/BPA required for the management of breakthrough bleeding events. Example 16: Meaningful Change and Severity Thresholds of Haem-A-QoL in Patients with Hemophilia Based on Clinical Studies of Fitusiran

[0508] This Example assesses clinically meaningful change thresholds (MCTs) and severity thresholds as per Haem-A-QoL using data from fitusiran clinical trials in people with hemophilia A or B.

[0509] The Hemophilia Quality of Life questionnaire for Adults (Haem-A-QoL) is a validated instrument that was used to measure changes in health-related quality of life (HRQoL) among adult patients with hemophilia treated with fitusiran (see, e.g., von Mackensen et al., Haemophilia. (2020) 26(6): 1019-30 and Kenet et al., Blood. (2024) 143(22):2256-69). The Haem-A-QoL comprises 46 items scored on a 5-point Likert scale (FIG. 68). A total score (TS) and 10 quality of life (QoL) domains scores were calculated. [0510] The data from the open-label extension (OLE) trial (ATLAS-OLE [NCT03754790]) were utilized to derive within-patient and between-group MCTs for physical health (PH; N=129) and TS (N=105). The within-patient change score was defined as the amount of change an individual needed to report a meaningful treatment benefit. The between-group patient change score was defined as the difference in change from baseline between treatment groups that could be considered clinically relevant.

[0511] The pooled data (N=207 at baseline; N=206 at month 7/9) from parent phase 3 trials (ATLAS-INH [NCT03417102], ATLAS-A/B [NCT03417245], and ATLAS-PPX [NCT03549871]) were employed to assess interpretations of both scores in terms of severity thresholds, which were defined as the specific level of hemophilia severity at which the QoL changes significantly.

[0512] Anchor-based methods (i.e., methods relying on an external indicator) using patient-reported outcomes in the EuroQol-5 Dimensions-5 Levels Questionnaire (EQ-5D-5L) as anchors were implemented to determine MCTs and severity thresholds for PH score and TS. The EQ-5D-5L comprises the following five dimensions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression.

[0513] Results: The participants from the pooled studies were all male patients (N=242 [100.0%]), with the majority being between 18 to 64 years of age (194 [80.9%]). The OLE study included 180 participants. In the pooled studies, most participants were either Asian (53.7%) or White (42.6%). [0514] Change from baseline in EQ-5D-5L pain/discomfort and usual activities items were sufficiently correlated with change in physical health (PH) score (0.327 and 0.352, respectively). Similarly, change from baseline in EQ-5D-5L usual activities were sufficiently correlated with change in total score (TS) (0.440), suggesting these anchors are appropriate. [0515] Meaningful Change Thresholds: Based on the anchor-based estimates and supported by the distribution-based estimates, the suggested within-patient and between- group MCTs for PH score and TS are presented in FIG. 69. These findings are comparable with the previously published data (Wyrwich et al., Haemophilia (2015) 21(5): 578-84).

[0516] Severity Score Regions: For severity thresholds, PH score quartiles using the EQ- 5D-5L pain/discomfort groups were largely distinct, except for an overlap in the scores between patients reporting “moderate” or “severe” pain/discomfort. The recommended PH and TS severity thresholds are presented in FIG. 70. The distribution of Haem-A-QoL PH scores according to EQ-5D-5L (pain/discomfort and usual activities (pooled ATLAS-OLE study)) are presented in FIG. 71.

[0517] Conclusion: The analyses present clinically meaningful thresholds for within- patient change and between-group differences to provide interpretations for improvements in the Haem-A-QoL physical health and total scores. To help understand the patients’ experiences related to physical health and overall HRQoL, levels of severity were also derived. These results support the use of Haem-A-QoL in understanding patient experiences, and evaluating treatment benefits in people with hemophilia A or B.

Example 17: Physical Health and Overall Health-Related Quality of Life in Adults With Hemophilia A or B With or Without Inhibitors on Fitusiran Prophylaxis

[0518] People with hemophilia A or B experience frequent spontaneous bleeding episodes and major bleeding events resulting from injury, which result in debilitating musculoskeletal damage that can remarkably impair mobility and quality of life (Germanini et al., J Thromb Haemost. (2022) 20(6): 1364-75). This analysis assessed the effect of fitusiran on physical health (PH) and overall health-related quality of life (HRQoL) measures in adult people with hemophilia A or B included in the open-label extension trial (ATLAS- OLE [NCT03754790]).

[0519] Methods: This analysis included people with hemophilia A or B (aged 17 years) with or without inhibitors who participated in ATLAS-OLE, which recruited patients from the ATLAS-A/B, ATLAS-INH, and ATLAS-PPX parent phase 3 studies. Patients received fitusiran prophylaxis with an AT guided dose regimen (AT-DR). Fitusiran dosing was individually adjusted to achieve target AT levels of 15%— 35%. The AT-DR started at 50 mg once every two months (Q2M) with the option to increase to 50 mg or 80 mg once monthly (QM) based on AT levels, or decrease to 20 mg Q2M or 20 mg QM.

[0520] Endpoints: Change from baseline in PH and total scores (TS) of the hemophiliaspecific health-related QoL questionnaire (Haem-A-QoL) was assessed during the primary treatment period (dose re-start Day 169). The Haem-A-QoL questionnaire is scored on a 5- point Likert scale (never, rarely, sometimes, often, and all the time), range: 0-100, with higher scores indicating a greater impairment. The mean (standard deviation [SD]) change from baseline (last non-missing value before the first ever dose of fitusiran in either parent study or this study) to last visit on AT-DR was calculated for PH and TS.

[0521] For this analysis, a clinically meaningful within-patient change (MWPC) in PH and TS was defined as an improvement of 10, and ^7.1 points, respectively, and the clinically meaningful between-group change thresholds (MCT) were 7.0 points for PH and 7.7 points for TS. The within-patient change score was defined as the amount of change an individual needed to experience to report a meaningful treatment benefit, and the between- group patient change score was defined as the difference in change from baseline between treatment groups that could be considered clinically relevant.

[0522] For the inter-patient comparison, integrated analyses were conducted on pooled data to compare fitusiran AT-DR prophylaxis with the patient’s CFC/BPA regimen from the parent studies. Each pool included participants from ATLAS-OLE and the control arm of the parent study.

[0523] The intra-patient comparison included participants randomized to the control group of CFC/BPA on-demand during the parent studies who had received at least one dose of fitusiran under the revised AT-DR.

[0524] Results: TS of the Haem-A-QoL was good at baseline and PH showed mild impairment. Mean (SD) change from baseline was -8.06 (22.18) for PH score and -6.10 (12.85) for TS, indicating an improvement in PH and overall HRQoL with fitusiran. PH and TS improvements were found in people with hemophilia A or B with inhibitors with the mean (SD) change from baseline of -11.55 (23.63) and -9.35 (9.36), respectively. These improvements were clinically meaningful in people with hemophilia A or B with inhibitors (Table 34).

Table 34. Mean (SD) Change from Baseline in Haem-A-QoL Physical Health (PH) and Total Scores (TS)* in ATLAS-OLE Study

[0525] Of the participants, 48.0% (n = 83) and 39.3% (n = 68) achieved MWPC in PH and TS, respectively. Of those achieving MWPC in PH, 35 (60.3%) had hemophilia presented with inhibitors and 48 (41.7%) did not, 67 (49.6%) had hemophilia A, and 16 (42.1%) had hemophilia B. Of those achieving MWPC in TS, 31 (53.4%) had hemophilia with inhibitors and 37 (32.2%) without inhibitors, 54 (40%) had hemophilia A, and 14 (36.8%) had hemophilia B. The cumulative changes for the participants in Haem-A-QoL PH and TS during the primary treatment period is presented in FIG. 72.

[0526] Comparisons between participants (i.e., inter-patient comparison) showed that fitusiran prophylaxis led to a clinically meaningful and substantially higher improvement in the transformed PH score from baseline to end of primary treatment period compared with CFC on-demand, while the difference was numerically in favor of fitusiran compared to BPA on-demand (Table 35). Fitusiran prophylaxis maintained the PH score of participants previously treated with CFC/BPA prophylaxis.

[0527] The cumulative changes in the Haem-A-QoL PH score for participants from baseline to their last visit, categorized by treatment group (FIG. 73), evaluated the meaningfulness of the within-patient changes. Panel A of FIG. 73 depicts the patient responses across a wide range of thresholds up to the within-patient meaningful threshold of -10. The curves show higher levels of improvements with fitusiran prophylaxis. They also show that a higher proportion of responders showing the highest levels of improvement when treated with fitusiran prophylaxis versus BPA on-demand. Panel B of FIG. 73 shows that a greater percentage of respondents were treated with fitusiran prophylaxis compared to CFC on-demand. These respondents were separated across a wide range of thresholds (especially in the improvement area, including the threshold of 10 meaningful improvement in PH).

While none of the CFC on-demand patients attained improvements of %30, 20% of fitusiran prophylaxis patients had improvements in PH with change scores %30. Table 35: Inter-Patient and Intra-Patient Comparison in Adult People with Hemophilia A or B With or Without Inhibitors in the PH Score (Transformed) From Baseline to End of Primary Treatment Period

[0528] Intra-patient sensitivity analyses yielded complementary findings. AT-DR showed clinically meaningful improvement among participants previously treated with CFC/BPA on- demand: least square (LS) mean change (95% confidence interval [95% CI]) from baseline was -12.70 [-23.02 to -2.38] and -16.87 [-29.81 to -3.94] in the fitusiran arm, respectively (Table 35).

[0529] Conclusion: Beyond the sustained and clinically meaningful bleed control provided by fitusiran prophylaxis on antithrombin-based dose regimen, fitusiran prophylaxis also improved the physical health and overall health-related quality of life of adult people with hemophilia A or B, as measured by Hemophilia quality of life questionnaire for adults’ physical health and total scores. These improvements observed while receiving fitusiran prophylaxis were clinically meaningful in people with hemophilia A and B without inhibitors, specifically higher in hemophilia A participants compared to those receiving factor on-demand.

Claims

1. A method of reducing the risk of a hepatobiliary event in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising:

(a) subcutaneously administering to the human patient in need thereof fitusiran at a starting dose amount at a selected dosing frequency;

(b) obtaining a measurement of an antithrombin (AT) level in the human patient; and

(c) performing one of the following steps:

(i) if the AT level is 15-35%, repeating step (a),

(ii) if the AT level is >35%, subcutaneously administering to the human patient fitusiran at a higher dose amount at the selected dosing frequency, or at the starting dose amount at a higher dosing frequency, or

(iii) if the AT level is <15%, discontinuing or pausing fitusiran treatment.

2. A method of reducing the risk of a hepatobiliary event in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising subcutaneously administering to the human patient in need thereof fitusiran at a dose of: about 50 mg about once a month or about every four weeks, about 20 mg about once a month or about every four weeks, about 50 mg about once every other month or about once every eight weeks, or about 20 mg about once every other month or about once every eight weeks.

3. The method of claim 1 or claim 2, wherein the hepatobiliary event is alanine transaminase (ALT) elevation more than three times the upper limit of normal (ULN), aspartate aminotransferase (AST) elevation more than three times the ULN, severe liver toxicity, liver failure, cholecystitis, cholelithiasis, or a need for cholecystectomy.

4. A method of improving patient-reported outcome (PRO) or quality of life (QoL) in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising: (a) subcutaneously administering to the human patient in need thereof fitusiran at a starting dose amount at a selected dosing frequency;

(b) obtaining a measurement of an antithrombin (AT) level in the human patient; and

(c) performing one of the following steps:

(i) if the AT level is 15-35%, repeating step (a),

(ii) if the AT level is >35%, subcutaneously administering to the human patient fitusiran at a higher dose amount at the selected dosing frequency, or at the starting dose amount at a higher dosing frequency, or

(iii) if the AT level is <15%, discontinuing or pausing fitusiran treatment.

5. The method of claim 4, wherein the one or more QoL domains are domains in a QoL questionnaire, optionally wherein the QoL questionnaire is Haemophilia Quality of Life Questionnaire for Adults (Haem-A-QoL).

6. The method of claim 5, wherein the administering results in a clinically meaningful improvement indicated by a reduction of 7.1 or more units (optionally 8 or more, 9 or more, 10 or more, or 11 or more units) in the Total Score or a reduction of 10 or more units (optionally 11 or more, 12 or more, 13 or more, or 14 or more units) in the Physical Health domain score of the questionnaire.

7. The method of any one of claims 1-6, further comprising administering an effective amount of a replacement factor or bypassing agent (BPA) to treat a bleeding episode that occurs eight or more days after the first fitusiran dose, wherein the effective amount of the replacement factor or BPA is reduced as compared to the recommended effective amount of the replacement factor or BPA for human patients who are not on fitusiran therapy.

8. A method of reducing thrombotic risk in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising:

(a) subcutaneously administering to the human patient in need thereof fitusiran at a starting dose amount at a selected dosing frequency;

(b) obtaining a measurement of an antithrombin (AT) level in the human patient; and

(c) performing one of the following steps:

(i) if the AT level is 15-35%, repeating step (a), (ii) if the AT level is >35%, subcutaneously administering to the human patient fitusiran at a higher dose amount at the selected dosing frequency, or at the starting dose amount at a higher dosing frequency, or

(iii) if the AT level is <15%, discontinuing or pausing fitusiran treatment; wherein the human patient is further administered an effective amount of replacement factor or bypassing agent (BPA) to treat a bleeding episode that occurs eight or more days after the first fitusiran dose, wherein the effective amount of the replacement factor or BPA is reduced as compared to the recommended effective amount of the replacement factor or BPA for human patients who are not on fitusiran therapy.

9. A method of routine prophylaxis to prevent or reduce the frequency of bleeding episodes in a human patient having hemophilia A or B with or without factor VIII or factor IX inhibitors, comprising:

(a) subcutaneously administering to the patient in need thereof fitusiran at a starting dose amount at a selected dosing frequency;

(b) obtaining a measurement of an antithrombin (AT) level in the human patient; and

(c) performing one of the following steps:

(i) if the AT level is 15-35%, repeating step (a),

(ii) if the AT level is >35%, subcutaneously administering to the human patient fitusiran at a higher dose amount at the selected dosing frequency, or at the starting dose amount at a higher dosing frequency, or

(iii) if the AT level is <15%, discontinuing or pausing fitusiran treatment; wherein the human patient is further administered an effective amount of replacement factor or bypassing agent (BPA) to treat a bleeding episode that occurs eight or more days after the first fitusiran dose, wherein the effective amount of the replacement factor or BPA is reduced as compared to the recommended effective amount of the replacement factor or BPA for human patients who are not on fitusiran therapy.

10. The method of any one of claims 1-9, wherein the human patient is a hemophilia A patient without factor VIII inhibitors.

11. The method of claim 10, wherein the replacement factor is factor VIII (FVIII) and a single dose of FVIII is no more than 20 lU/kg and optionally is 10 lU/kg, optionally wherein the FVIII administration is repeated, if needed, in no less than 24 hours.

12. The method of any one of claims 1-9, wherein the human patient is a hemophilia B patient without factor IX inhibitors.

13. The method of claim 12, wherein the replacement factor is factor IX (FIX) and a single dose of FIX is no more than 30 lU/kg and optionally is 20 lU/kg, optionally wherein the Factor IX administration is repeated, if needed, in no less than 24 hours for standard halflife FIX or in no less than 5-7 days for extended half-life FIX.

14. The method of any one of claims 1-9, wherein the human patient is a hemophilia A patient with factor VIII inhibitors.

15. The method of any one of claims 1-9, wherein the human patient is a hemophilia B patient with factor IX inhibitors.

16. The method of claim 14 or claim 15, wherein the BPA is activated prothrombin complex concentrate (aPCC) and a single dose of aPCC is no more than 50 U/kg and optionally is 30 U/kg, optionally wherein the aPCC administration is repeated, if needed, in no less than 24 hours.

17. The method of claim 14 or claim 15, wherein the BPA is recombinant factor Vila (rFVIIa) and a single dose of rFVIIa is no more than 45 pg/kg, optionally wherein the rFVIIa administration is repeated, if needed, in no less than two hours.

18. The method of any one of claims 1-6, further comprising administering an effective amount of a replacement factor or bypassing agent (BPA) to treat a bleeding episode that occurs seven or fewer days after the first fitusiran dose, wherein the effective amount of the replacement factor or BPA is administered according to the human patient’s prior dosing regimen of replacement factor or BPA.

19. A method of reducing thrombotic risk in a human patient with hemophilia A or B with or without factor VIII or factor IX inhibitors who receives fitusiran for routine prophylaxis to prevent or reduce the frequency of bleeding episodes, comprising: (a) subcutaneously administering to the human patient in need thereof fitusiran at a starting dose amount at a selected dosing frequency;

(b) obtaining a measurement of an antithrombin (AT) level in the human patient; and

(c) performing one of the following steps:

(i) if the AT level is 15-35%, repeating step (a),

(ii) if the AT level is >35%, subcutaneously administering to the human patient fitusiran at a higher dose amount at the selected dosing frequency, or at the starting dose amount at a higher dosing frequency, or

(iii) if the AT level is <15%, discontinuing or pausing fitusiran treatment; wherein the human patient is further administered an effective amount of replacement factor or bypassing agent (BPA) to treat a bleeding episode that occurs seven or fewer days after the first fitusiran dose, wherein the effective amount of the replacement factor or BPA is administered according to the human patient’s prior dosing regimen of replacement factor or BPA.

20. A method of routine prophylaxis to prevent or reduce the frequency of bleeding episodes in a human patient having hemophilia A or B with or without factor VIII or factor IX inhibitors, comprising:

(a) subcutaneously administering to the human patient in need thereof fitusiran at a starting dose amount at a selected dosing frequency;

(b) obtaining a measurement of an antithrombin (AT) level in the human patient; and

(c) performing one of the following steps:

(i) if the AT level is 15-35%, repeating step (a),

(ii) if the AT level is >35%, subcutaneously administering to the human patient fitusiran at a higher dose amount at the selected dosing frequency, or at the starting dose amount at a higher dosing frequency, or

(iii) if the AT level is <15%, discontinuing or pausing fitusiran treatment; wherein the human patient is further administered an effective amount of replacement factor or bypassing agent (BPA) to treat a bleeding episode that occurs seven or fewer days after the first fitusiran dose, wherein the effective amount of the replacement factor or BPA is administered according to the human patient’s prior dosing regimen of replacement factor or BPA.

21. The method of any one of claims 18-20, wherein the human patient is a hemophilia A patient without factor VIII inhibitors.

22. The method of any one of claims 18-20, wherein the human patient is a hemophilia B patient without factor IX inhibitors.

23. The method of any one of claims 18-20, wherein the human patient is a hemophilia A patient with factor VIII inhibitors.

24. The method of any one of claims 18-20, wherein the human patient is a hemophilia B patient with factor IX inhibitors.

25. The method of any one of claims 7-24, wherein the bleeding episode is a major surgery, optionally wherein the human patient is a patient not being treated with AT replacement therapy before, during, or after surgery.

26. The method of claim 25, wherein the major surgery is an opening into a major body cavity, operation on a joint, removal of an organ, operative alteration of normal anatomy, crossing of a mesenchymal barrier, dental extraction of molar teeth or >3 nonmolar teeth, or tooth implantation.

27. The method of any one of claims 1-26, wherein the human patient has been on prophylactic treatment with a replacement factor or a bypassing agent (BPA), and wherein the method comprises terminating the prophylactic replacement factor or BPA treatment in the human patient within about two weeks or about 14 days or about one week or about seven days of the first dose of fitusiran.

28. The method of any one of claims 1 or 3-27, wherein the dose of fitusiran is administered to the human patient about once a month or about every four weeks or about once every other month or about once every eight weeks.

29. The method of any one of claims 1 or 3-28, wherein fitusiran is administered to the human patient at a dose of about 10 to about 100 mg, optionally about 80 mg, about 50 mg, or about 20 mg.

30. The method of any one of claims 1 or 3-28, wherein the starting dose amount of fitusiran is about 50 mg.

31. The method of claim 30, wherein the selected dosing frequency is every two months (Q2M) or every eight weeks (Q8W), optionally wherein the higher dosing frequency is every month (QM) or every four weeks (Q4W).

32. The method of any one of claims 1 or 3-27, wherein the starting dose amount is 50 mg and the selected dosing frequency is Q2M or Q8W, optionally wherein step (c)(ii) is performed if two measurements of the AT level are >35% or if the AT level is >35% six months after the prior dose, or step (c)(iii) is performed if more than one measurement, optionally two measurements, of the AT level is <15%.

33. The method of claim 32, wherein step (c)(ii) comprises subcutaneously administering to the human patient fitusiran at 50 mg QM.

34. The method of claim 32 or claim 33, comprising, after step (c)(iii):

(A) subcutaneously administering fitusiran to the human patient at 20 mg Q2M, optionally wherein the 20 mg dose is administered three months after the prior dose;

(B) if the AT level of the human patient after step (A) is

<15%, optionally according to more than measurement, discontinuing fitusiran treatment,

15-35%, repeating step (A), or

>35%, optionally according to two measurements, subcutaneously administering to the human patient fitusiran at 20 mg QM.

35. The method of any one of claims 1 or 3-34, wherein each AT level measurement is obtained after the human patient has received at least two doses of fitusiran at a given dose amount.

36. The method of any one of claims 1-35, comprising obtaining a measurement of AT level in the human patient every four weeks, every eight weeks, every month, every two months, every four months, every six months, or every 12 months.

37. The method of any one of claims 1-35, comprising obtaining a measurement of AT level in the human patient at four weeks or one month, twelve weeks or three months, 20 weeks or five months, and 24 weeks or six months following administration of the starting dose or following administration of a modified dose as compared to the prior dose.

38. The method of any one of claims 1 or 3-37, wherein the obtaining a measurement of the AT level in the human patient comprises use of a kinetic or chromogenic assay.

39. The method of claim 38, wherein obtaining a measurement of the AT level in the human patient comprises use of a chromogenic assay that quantifies functionally active AT in human citrated plasma based on the inhibition of an excess of factor Xa by AT.

40. The method of claim 38, wherein obtaining a measurement of the AT level in the human patient comprises use of an INNOVANCE™ Antithrombin assay.

41. The method of any one of claims 1 or 3-40, further comprising subcutaneously administering fitusiran to the human patient at a dose amount and a dosing frequency sufficient to maintain the AT level in the human patient at 15-35%, optionally comprising subcutaneously administering fitusiran at:

10 mg QM or Q4W,

20 mg QM or Q4W,

20 mg Q2M or Q8W,

50 mg QM or Q4W,

50 mg Q2M or Q8W, or

80 mg QM or Q4W.

42. The method of any one of claims 1-41, further comprising obtaining a liver function test in the human patient every two months following initiation of fitusiran treatment, optionally wherein the liver function test is an aspartate transaminase or alanine aminotransferase test, further optionally wherein the liver function test is obtained every two months for the first six months following initiation of fitusiran treatment.

43. The method of any one of claims 1-42, further comprising obtaining a liver function test in the human patient (i) prior to administering the starting dose of fitusiran to determine a baseline level of liver function; and (ii) every month following initiation of fitusiran treatment, optionally wherein the liver function test is an aspartate transaminase or alanine aminotransferase test, further optionally wherein the liver function test is obtained every month for the first six months following initiation of fitusiran treatment.

44. The method of claim 42 or claim 43, further comprising discontinuing or pausing fitusiran treatment if the aspartate transaminase or alanine aminotransferase test shows aspartate transaminase or alanine aminotransferase levels that are progressing or are persistent and five times the upper limit of normal, optionally wherein fitusiran treatment is resumed if the aspartate transaminase or alanine aminotransferase test shows aspartate transaminase or alanine aminotransferase levels have returned to baseline level.

45. The method of any one of claims 1-44, further comprising discontinuing or pausing fitusiran treatment if the human patient is diagnosed with gallbladder disease, optionally wherein the gallbladder disease comprises cholecystitis, cholelithiasis, or a need for cholecy stectomy .

46. The method of any one of claims 1-45, wherein the human patient does not have

(i) clinically significant liver disease,

(ii) ALT >1.5x upper limit of normal reference range (ULN),

(iii) AST >1.5x upper limit of normal reference range (ULN),

(iv) hepatitis C,

(v) hepatitis A,

(vi) hepatitis E, and/or

(vii) hepatitis B.

47. The method of any one of claims 1-46, wherein the human patient is an adult or adolescent patient twelve years or older.

48. The method of any one of claims 1-47, wherein fitusiran is provided in a phosphate- buffered saline (PBS) at 50-200 mg/mL, optionally 100 mg/mL, and optionally wherein the PBS has a pH of 7.

49. Fitusiran for use in a method of any one of claims 1-48.

50. Use of fitusiran in the manufacture of a medicament for use in a method of any one of claims 1-48.

51. A pharmaceutical composition comprising fitusiran for use in a method of any one of claims 1-48.

52. An article of manufacture for use in a method of any one of claims 1-48, optionally wherein the article of manufacture is a kit.

53. The article of manufacture for use of claim 52, wherein the article of manufacture is a container containing one or more doses of fitusiran, each dose being 80 mg, 50 mg, 20 mg, or 10 mg, optionally wherein the 80 mg of fitusiran is in 0.8 mL of a phosphate-buffered saline (PBS), the 50 mg of fitusiran is in 0.5 mL of a PBS, the 20 mg of fitusiran is in 0.2 mL of a PBS, or the 10 mg of fitusiran is in 0.1 mL of a PBS, and optionally wherein the PBS has a pH of 7.

54. The article of manufacture for use of claim 53, wherein the container is a single-use, single-dose prefilled syringe.

55. The article of manufacture for use of claim 53, wherein the container is a single-use glass vial.