Observational study of recombinant factor VIII-Fc, rFVIIIFc, in hemophilia A

Introduction: rFVIIIFc (Eloctate) is an extended-half-life recombinant factor VIII-Fc fusion protein that may promote factor VIII (FVIII) tolerance through Fc immunoregulatory properties. Yet, little is known regarding its immunogenicity in patients with hemophilia A (HA) or in HA with inhibitors (HA-I), including tolerized, immune tolerance induction (ITI)-refractory, or ITI-naive. Methods: We reviewed medical records of 60 patients, including 2 previously-untreated patients (PUPs) and 58 previously-treated patients (PTPs), cared for between 01/01/06 and 06/01/17, on whom anti-FVIII antibody data were available before and after initiating rFVIIIFc. Continuous data were analyzed by student's t-test, and discrete data by chi square or Fisher's exact test. Results: After initiating rFVIIIFc, one of two HA PUPs developed a low-responding (LR) inhibitor after 10 exposures, which resolved (anti-VIII< 0.6 B.U.) within 8 additional exposures, while none of 41 HA PTPS developed an inhibitor. Among 19 HA-I PTPs with detectable inhibitors prior to rFVIIIFc, 5 developed an anamnestic response to rFVIIIFc, including 1 of 8 (12.5%) low-responding (LR), and 4 of 9 (44.9%) high-responding (HR), of whom 3 were ITI-naive and 1 ITI-refractory. Inhibitors resolved in 4 HR within 2 months of continuing rFVIIIFc (median) but persisted in 1 LR at low titer. The remaining 11 HA-I PTPs, including 4 HR and seven LR, had no detectable inhibitor at the time of or after initiating rFVIIIFc. Discussion: rFVIIIFc was immunogenic in HA PUPs and in HA-I PTPs persistently ITI-naive or ITI-refractory, with inhibitor resolution in the majority. rFVIIIFc immunogenicity appears to be similar to other FVIII products.