Clinical Outcomes in Children with Hemophilia B Treated Long Term with Rfixfc: Interim Results of the B-Yond Extension Study

Background: Early prophylactic replacement of coagulation factor IX (FIX) improves clinical outcomes in children with hemophilia B; however, frequent intravenous infusions (2-3 times/week) are often required due to the short half-life of conventional FIX products. Recombinant FIX Fc fusion protein (rFIXFc), 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 FIX.The phase 3 Kids B-LONG study (NCT01425723) demonstrated the safety, efficacy and prolonged half-life of once weekly recombinant factor IX Fc fusion protein (rFIXFc) in children aged <12 years with hemophilia B (endogenous FIX ≤2 IU/dL). Here, we report interim safety and efficacy data for children enrolled in the ongoing rFIXFc extension study, B-YOND (NCT01425723).