BIVV001: The First Investigational Factor VIII Therapy to Break Through the VWF Ceiling in Hemophilia A, with Potential for Extended Protection for One Week or Longer

Introduction: The standard of care for patients with severe hemophilia A is prophylactic factor VIII (FVIII) replacement. Conventional recombinant FVIII products are efficacious but require frequent administration because of their short half-life, which reflects the dependence of FVIII on von Willebrand factor (VWF). Recombinant FVIII Fc fusion protein (rFVIIIFc) provides an extended dosing interval, as well as joint protection and improved quality of life (Oldenburg et al, Haemophilia, 2018; Wang et al, Blood, 2016), with a well-characterized safety profile. While rFVIIIFc reduces the required administration frequency, longer prophylactic dosing intervals that also offer maximum overall protection are still an unmet need for patients with severe hemophilia A. Increasing the half-life of rFVIII is ultimately dependent upon decoupling FVIII and endogenous VWF.

BIVV001 (rFVIII-VWF-XTEN) is a novel investigational rFVIII therapy with single-chain FVIII, the Fc domain of human immunoglobulin G1, 2 XTEN polypeptides, and the FVIII-binding D′D3 domain of VWF, designed to circulate in plasma independently of VWF, thereby breaking the VWF half-life ceiling. Here, we present the low-dose cohort results of EXTEN-A, a Phase 1/2a study assessing the safety and tolerability of a single dose of BIVV001, and the pharmacokinetic (PK) characteristics of a single dose of BIVV001 compared with rFVIII.

Methods: EXTEN-A (NCT03205163) is an open-label, dose-escalation, multicenter study. Previously treated adult males with severe hemophilia A (<1 IU/dL [<1%] endogenous FVIII activity) with ≥150 exposure days to FVIII products were included. Patients were assigned to either the low-dose cohort (25 IU/kg of rFVIII and 25 IU/kg of BIVV001; n≥6) or the high-dose cohort (65 IU/kg of rFVIII and 65 IU/kg of BIVV001; n≥8). Escalation from the low-dose cohort, and enrolment of patients to the high-dose cohort was undertaken after assessment of available data from the low-dose cohort.

After a screening and washout period of up to 28 days, patients received a single dose (25 or 65 IU/kg) of rFVIII. After a 3- to 4-day washout period, patients received a single dose of BIVV001 at the same dose level as rFVIII. Blood samples for PK analysis were collected for 3 days after dosing of rFVIII and up to 14 days after dosing of BIVV001. Inhibitor testing was performed 14 and 28 days following BIVV001 administration. Adverse events, clinical abnormalities in laboratory tests (including inhibitor development), and PK parameters were assessed. An interim analysis is planned, including the first 2 patients of the high-dose cohort.

Results: Out of 7 patients enrolled in the low-dose cohort (25 IU/kg), 6 patients were dosed with BIVV001. Patients in this group were primarily white, with 1 patient of Asian descent, and 1 of Hispanic/Latino ethnicity. Patient ages ranged from 19 to 60 years. Low-dose BIVV001 was well tolerated and no inhibitors were detected through 28 days after BIVV001 dosing. Low-dose BIVV001 demonstrated an extended half-life of 37.6 hours, compared with a 12.1-hour half-life for rFVIII. Average FVIII activity post-infusion of BIVV001 was 12.2% at 5 days and 5.3% at 7 days.

At least 8 patients will be enrolled in the high-dose cohort (65 IU/kg); preliminary data for the first 2 patients will be reported.

Conclusions: BIVV001 was well tolerated in 6 patients with severe hemophilia A who were treated with a single low dose (25 IU/kg). No patient developed an inhibitor to FVIII. Low-dose cohort data demonstrated a breakthrough in the half-life of rFVIII therapy, with BIVV001 providing sustained FVIII levels that could potentially allow for more optimal, extended protection for patients.