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In this phase 1 study, a chemically modified RNA interference therapy designed to target antithrombin was administered to participants with hemophilia A or B. Antithrombin levels decreased and the generation of thrombin increased.

Fidanacogene elaparvovec, an adeno-associated virus (AAV) gene-therapy vector for hemophilia B containing a high-activity human factor IX variant (FIX-R338L/FIX-Padua), was associated with sustained factor IX activity in a phase 1-2a study. We conducted a phase 3 open-label study of fidanacogene elaparvovec at a dose of 5×10 vector genome copies per kilogram of body weight. Men 18 to 65 years of age with hemophilia B and a factor IX level of 2% or less were eligible for screening if they had received at least 6 months of therapy with prophylactic factor IX concentrate. The primary end point, tested for noninferiority, was the annualized bleeding rate (treated and untreated bleeding episodes) from week 12 to month 15 after treatment with fidanacogene elaparvovec as compared with the prophylaxis lead-in period. Superiority, additional efficacy end points, and safety were also assessed. Of 316 men who underwent screening for the lead-in study, 204 (64.6%) were not eligible; 188 (59.5%) of those were ineligible owing to the presence of anti-AAV neutralizing antibodies. Of the 45 participants who received fidanacogene elaparvovec, 44 completed at least 15 months of follow-up. The annualized rate of bleeding for all bleeding episodes decreased by 71%, from 4.42 (95% confidence interval [CI], 1.80 to 7.05) at baseline to 1.28 (95% CI, 0.57 to 1.98) after gene therapy, a treatment difference of -3.15 episodes (95% CI, -5.46 to -0.83; P = 0.008). This result shows the noninferiority and superiority of fidanacogene elaparvovec to prophylaxis. At 15 months, the mean factor IX activity was 26.9% (median, 22.9%; range, 1.9 to 119.0) by one-stage SynthASil assay. A total of 28 participants (62%) received glucocorticoids for increased aminotransferase levels or decreased factor IX levels (or both) starting between 11 and 123 days. No infusion-related serious adverse events, thrombotic events, development of factor IX inhibitors, or malignant conditions were observed. Fidanacogene elaparvovec was superior to prophylaxis for the treatment of participants with hemophilia B, leading to reduced bleeding and stable factor IX expression. (Funded by Pfizer; BENEGENE-2 ClinicalTrials.gov number, NCT03861273.).

Haemophilia A and B are congenital X-linked bleeding disorders resulting from deficiencies in clotting factors VIII (haemophilia A) and IX (haemophilia B). Patients with severe deficiency, defined as having less than 1% of normal plasma factor activivity, often have spontaneous bleeding within the first few years of life. Those with moderate and mild deficiencies typically present with post-traumatic or post-surgical bleeding later in life. A high index of suspicion and measurement of factor activity in plasma facilitates early diagnosis. In the 21st century, therapeutic advances and comprehensive care have substantially improved both mortality and morbidity associated with these conditions. Management strategies for haemophilia include on-demand treatment for bleeding episodes and all surgeries and regular treatment (ie, prophylaxis) aimed at reducing bleeds, morbidity, and mortality, thereby enhancing quality of life. Treatment options include factor replacement therapy, non-replacement therapies that increase thrombin generation, and gene therapies that facilitate in vivo clotting factor synthesis. The therapies differ in their use for prophylaxis and on-demand treatment, the mode and frequency of administration, duration of treatment effect, degree of haemostatic protection, and side-effects. Monitoring the effectiveness of these prophylactic therapies involves assessing annual bleeding rates and joint damage. Personalised management strategies, which align treatment with individual goals (eg, playing competitive sports), initiated at diagnosis and maintained throughout the lifespan, are crucial for optimal outcomes. These strategies are facilitated by a multidisciplinary team and supported by clinician-led education for both clinicians and patients.

Fitusiran, a subcutaneous investigational small interfering RNA therapeutic, targets antithrombin to rebalance haemostasis in people with haemophilia A or haemophilia B, irrespective of inhibitor status. We evaluated the efficacy and safety of fitusiran prophylaxis in people with haemophilia A or haemophilia B with inhibitors. This multicentre, randomised, open-label phase 3 study was done at 26 sites (primarily secondary or tertiary centres) in 12 countries. Men, boys, and young adults aged 12 years or older with severe haemophilia A or haemophilia B with inhibitors previously treated with on-demand bypassing agents were randomly assigned (2:1) to receive once-a-month 80 mg subcutaneous fitusiran prophylaxis (fitusiran prophylaxis group) or to continue with bypassing agents on-demand (bypassing agents on-demand group) for 9 months. The primary endpoint was mean annualised bleeding rate during the efficacy period in the intention-to-treat population estimated by negative binomial model. Safety was assessed as a secondary endpoint in the safety population. This trial is complete and is registered with ClinicalTrials.gov, NCT03417102. Between Feb 14, 2018, and June 23, 2021, 85 participants were screened for inclusion, of whom 57 (67%; 57 [100%] men; median age 27·0 years [IQR 19·5–33·5]) were randomly assigned: 19 (33%) participants to the bypassing agent on-demand group and 38 (67%) participants to the fitusiran prophylaxis. Negative binomial model-based mean annualised bleeding rate was significantly lower in the fitusiran prophylaxis group (1·7 [95% CI 1·0–2·7]) than in the bypassing agents on-demand group (18·1 [10·6–30·8]), corresponding to a 90·8% (95% CI 80·8–95·6) reduction in annualised bleeding rate in favour of fitusiran prophylaxis (p<0·0001). 25 (66%) participants had zero treated bleeds in the fitusiran prophylaxis group versus one (5%) in the bypassing agents on-demand group. The most frequent treatment-emergent adverse event in the fitusiran prophylaxis group was increased alanine aminotransferase in 13 (32%) of 41 participants in the safety population; there were no increased alanine aminotransferase treatment-emergent adverse events in the bypassing agents on-demand group. Suspected or confirmed thromboembolic events were reported in two (5%) participants in the fitusiran prophylaxis group. No deaths were reported. Subcutaneous fitusiran prophylaxis resulted in statistically significant reductions in annualised bleeding rate in participants with haemophilia A or haemophilia B with inhibitors, with two-thirds of participants having zero bleeds. Fitusiran prophylaxis might show haemostatic efficacy in participants with haemophilia A or haemophilia B with inhibitors; therefore, the therapeutic might have the potential to improve the management of people with haemophilia. Sanofi.

In contrast to the standard enzyme-replacement therapy, administered from once per 7–14 days to 2–3 times a week in patients with severe hemophilia B, as a result of a single injection, gene therapy can restore F9 gene expression and maintain it for a prolonged time. In clinical research, the approach of delivering a functional copy of a gene using adeno-associated viral (AAV) vectors is widely used. The scientific community is actively researching possible modifications to improve delivery efficiency and expression. In preclinical studies, the possibility of genome editing using CRISPR/Cas9 technology for the treatment of hemophilia B is also being actively studied.

The current standard of care treatment for severe hemophilia A and B (SHA and SHB) is the prophylactic intravenous replacement of coagulation factor VIII or IX (FVIII/FIX) to prevent spontaneous bleeding. Persons with hemophilia without prophylactic treatment receive therapy in case of bleeding, i.e., on demand. To assess treatment patterns, utilization of products, and bleeding outcomes in a real-world cohort of persons with SHA and SHB, defined as FVIII or FIX activity < 1%, data was retrospectively collected from hemophilia-specific patient diaries used for home treatment, medical records, and entries into the Austrian Hemophilia Registry from the year 2012 to 2017. Fifty-three male persons with SHA (n = 47) and SHB (n = 6) were included; 26 with SHA and 5 with SHB were on prophylaxis, 8 and 1 switched therapy regimen, and 13 and 0 received on-demand therapy. Persons on prophylaxis used a mean factor FVIII or FIX dose of 71.7 and 40.1 IU/kg/week. Median (IQR) annualized bleeding rates (ABR) in SHA were 28.0 (23.4–31.3) in the on-demand, 4.9 (1.6–13.5) in the prophylaxis group, and 3.0 (2.0–6.8) in the prophylactic group of SHB. Three persons with SHA had zero bleeds during the observation period. On-demand therapy and hepatitis B and C were associated with higher ABR but not age, weight, and HIV positivity. Bleeding rates and the proportion of on-demand therapy in persons with hemophilia were high in our real-world cohort. Further improvement is needed, which might be facilitated with the advent of factor products with extended half-life or non-factor therapies.

A fusion protein comprising factor IX and the dimeric Fc domain of IgG1 has a half-life that is five times as long as that of native factor IX, allowing prophylactic injections to be spaced as far as 2 weeks apart while maintaining levels of factor IX that are sufficient to prevent bleeding. In patients with severe hemophilia B, recurrent bleeding leads to painful hemarthroses, disabling hemophilic arthropathy, and other sequelae. 1 , 2 Prophylactic replacement of coagulation factor IX is associated with improved clinical outcomes 3 – 7 ; however, the relatively short half-lives of currently available factor IX products necessitate frequent intravenous injections (two or three times weekly) to maintain protective levels (at or above 1 IU per deciliter). 8 , 9 The frequency of injections is a considerable burden, cited by patients as a key deterrent to undertaking prophylactic treatment. 10 Various strategies to reduce this burden and improve the treatment of hemophilia B are under investigation, . . .

Haemophilia A and B are hereditary haemorrhagic disorders characterised by deficiency or dysfunction of coagulation protein factors VIII and IX, respectively. Recurrent joint and muscle bleeds lead to severe and progressive musculoskeletal damage. Existing treatment relies on replacement therapy with clotting factors, either at the time of bleeding (ie, on demand) or as part of a prophylactic schedule. The major complication of such therapy is the development of neutralising antibodies (ie, inhibitors), which is most frequent in haemophilia A. Treatment might improve considerably with the availability of new modified drugs, which might overcome existing prophylaxis limitations by reducing dosing frequency and thereby rendering therapy less distressing for the patient. Subcutaneous administration of some new therapies would also simplify prophylaxis in children with poor venous access. Gene therapy has the potential for a definitive cure, and important results have been obtained in haemophilia B. Despite improvements in haemophilia care, the availability of clotting factor concentrates for all affected individuals worldwide remains the biggest challenge.

An AAV5 vector containing the factor IX Padua allele was administered to 54 men with hemophilia B. Factor IX expression increased to approximately 39% of normal, and the annualized bleeding rate was decreased to 1.5.

An adeno-associated viral vector was used to introduce a FIX gene with enhanced biologic activity in 10 participants with hemophilia B. The annualized bleeding rate was 11.1 events per year before therapy versus 0.4 afterward. Steady-state factor IX levels were 33.7% of normal.