Long-Term Safety and Efficacy of rFVIIIFc in Adults and Adolescents with Severe Hemophilia A: A Longitudinal Analysis of A-LONG and ASPIRE

Background: Prophylactic replacement of coagulation factor VIII (FVIII) is the standard of care for patients with hemophilia A; however, prophylactic treatment with conventional FVIII products usually requires frequent intravenous infusions (3-4 times/week). Recombinant FVIII Fc fusion protein (rFVIIIFc), which is produced in a human cell line, binds the neonatal Fc receptor and utilizes the natural IgG recycling pathway to prolong the half-life of FVIII. The safety, efficacy and prolonged half-life of rFVIIIFc in adults and adolescents with severe hemophilia A were demonstrated in the phase 3 A-LONG study (NCT01027377, completed) and ASPIRE extension study (NCT01454739, ongoing). Here, we report cumulative long-term data on the safety and efficacy of rFVIIIFc in participants in these studies.

Methods: This longitudinal analysis includes cumulative data from A-LONG and ASPIRE (as of the interim data cut, 6 January 2014) for subjects treated with ≥1 dose of rFVIIIFc (n=164). A-LONG evaluated 2 prophylaxis regimens—individualized (IP): 25 IU/kg on day 1 and 50 IU/kg on day 4 to start, then 25-65 IU/kg every 3-5 days, to target a 1-3 IU/dL FVIII trough level, and weekly (WP): 65 IU/kg dosed once weekly—as well as episodic (on-demand) treatment. Subjects completing A-LONG and meeting enrollment criteria for ASPIRE could participate in the IP, WP, or episodic treatment groups, or, if optimal dosing could not be achieved with IP or WP, in an additional modified prophylaxis (MP) treatment group. Subjects could change treatment groups at any point during ASPIRE. For efficacy analyses, data were summarized according to the treatment group in which each subject participated, for the time period they were in that treatment group; thus, subjects may be included in the analysis of more than one treatment group. Outcomes evaluated included: incidence of inhibitors (neutralizing antibody value ≥0.6 BU/mL as measured by the Nijmegen-modified Bethesda assay at a central laboratory, confirmed upon retesting within 2 to 4 weeks), adverse events (AEs), annualized bleeding rate (ABR), treatment of acute bleeds, and prophylactic dose and dosing interval.

Results: Of the 164 subjects dosed with rFVIIIFc during A-LONG, 153 completed the study and 150 enrolled in ASPIRE. At the time of the interim data cut, 140 subjects were ongoing in ASPIRE. Cumulatively, subjects had a median (IQR) of 25.5 (24.6, 26.7) months of rFVIIIFc treatment, and a median (IQR) of 183.0 (120.5, 232.5) rFVIIIFc exposure days (EDs). No inhibitors were reported. The estimated inhibitor incidence rate (95% CI) was 0.0% (0.0, 2.2) overall (N=164), and 0.0% (0.0, 2.7) in subjects with ≥100 rFVIIIFc EDs (n=136). The type and incidence of AEs observed were consistent with those expected for the general hemophilia population. 84.8% of subjects reported ≥1 AE on study, with the majority assessed by the investigator as mild and unrelated to rFVIIIFc treatment. 17.7% of subjects experienced at least 1 SAE; none were assessed by the investigator as related to rFVIIIFc. There were no reports of anaphylaxis or serious hypersensitivity events, and no serious vascular thrombotic events. Median ABRs for subjects on IP and WP (MP was not an option during A-LONG) were generally lower with rFVIIIFc treatment compared with prestudy FVIII (Figure). In the IP treatment group, the year 1 and year 2 median spontaneous ABRs were 0.0. Overall, 89.1% of bleeding episodes were controlled with 1 infusion; 97.3% with 1 or 2 infusions. Among subjects treated with FVIII prophylaxis prior to entering A-LONG (n=79), 86% were dosed at least 3 times/week. With rFVIIIFc, 96% of these subjects extended their dosing interval compared with their prestudy product, while the median (IQR) total weekly prophylactic dose was comparable (prestudy FVIII: 78.0 [60.0, 102.0] IU/kg; on-study rFVIIIFc: 75.0 [70.0, 113.2] IU/kg).

Conclusions: Longitudinal data from patients with severe hemophilia A treated with rFVIIIFc in A-LONG and ASPIRE demonstrate long-term safety, with no inhibitors observed in any subjects, and efficacy in the prevention and treatment of bleeding. Low median ABRs were maintained with extended prophylactic dosing intervals, without an increase in median prophylactic factor consumption.