Longitudinal Analysis of Long-Term Safety and Efficacy of Recombinant Factor VIII Fc Fusion Protein (rFVIIFc) in Adults/Adolescents with Severe Hemophilia a

Background: Prophylactic replacement of coagulation factor VIII (FVIII) is the standard of care for patients with hemophilia A; however, prophylaxis with conventional FVIII products usually requires frequent intravenous injections (3-4 times/week). The safety, efficacy, and prolonged half-life of rFVIIIFc in previously treated adults and adolescents (≥12 y) with severe hemophilia A were demonstrated in the phase 3 A-LONG study (NCT01181128, completed) and ASPIRE extension study (NCT01454739, ongoing). Here, we report cumulative long-term data on the safety and efficacy of rFVIIIFc in study participants as of the second interim data cut (8 Dec 2014).

Methods: This longitudinal analysis includes cumulative data from A-LONG and ASPIRE (as of the second interim data cut 8 Dec 2014) for subjects treated with ≥1 dose of rFVIIIFc. 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 (ET). Subjects completing A-LONG and meeting enrollment criteria for ASPIRE could participate in the IP, WP, or ET groups, or, if optimal dosing could not be achieved with IP or WP, in an additional modified prophylaxis (MP) group. Subjects could change treatment groups at any point during ASPIRE. Efficacy analyses were performed using data 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 group. Outcomes evaluated included: incidence of inhibitors (neutralizing antibody value ≥0.6 BU/mL identified and confirmed on 2 separate samples drawn approximately 2-4 weeks apart and performed by the central laboratory as measured by the Nijmegen-modified Bethesda assay), adverse events (AEs), annualized bleeding rate (ABR), treatment of acute bleeds, and prophylactic consumption and dosing interval compared to pre-A-LONG (prestudy).

Results: Of 164 subjects dosed with rFVIIIFc during A-LONG, 153 completed the study and 150 enrolled in ASPIRE; at the time of this second interim data cut, 97 subjects were ongoing in ASPIRE, 40 subjects had completed the study, and 13 subjects withdrew. Cumulatively, subjects had 38,662 rFVIIIFc exposure days (EDs), inclusive of surgery. As of this second interim data cut (8 Dec 2014), no inhibitors were observed; the type and incidence of adverse events (AEs) observed were typical of previous hemophilia A populations studied. 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 lower with rFVIIIFc compared with prestudy FVIII for subjects on prestudy prophylaxis or ET (Figure). In the IP group, the median (interquartile range [IQR]) spontaneous ABRs in Years 1, 2, and 3 on-study were 0.0 (0.0, 2.0), 0.0 (0.0, 1.0), and 0.0 (0.0, 1.0), respectively. In the WP treatment group, the median (IQR) spontaneous ABRs in Years 1, 2, and 3 on-study were 1.0 (0.5, 3.0), 0.5 (0.0, 2.1), and 0.0 (0.0, 1.0), respectively. Overall, 88.5% and 97.0% of bleeding episodes were controlled with 1 or ≤2 intervenous injections, respectively. Among subjects treated with FVIII prophylaxis prestudy (n = 79), 86% were dosed at least 3 times/week prestudy. Compared with prestudy dosing intervals, dosing intervals with rFVIIIFc were extended in 96.2% of subjects, were shortened in 2.5% of subjects, and were unchanged in 1.3% of subjects. The median (IQR) total weekly prophylactic consumption was comparable (prestudy FVIII: 78.0 [60.0, 102.0] IU/kg; on-study rFVIIIFc: 75.0 [70.0, 113.8] IU/kg).

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

This research was funded by Biogen and Sobi. Biogen and Sobi reviewed and provided feedback on the abstract. The authors had full editorial control of the abstract and provided their final approval of all content.

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