Cross‐reacting Inhibitors Against Recombinant Porcine Factor VIII in Acquired Hemophilia A: Data from the GTH‐AH 01/2010 Study

BACKGROUND: Recombinant porcine factor VIII (rpFVIII, OBI-1, susoctocog alfa) is used for the treatment of acute bleeds in patients with acquired hemophilia A (AHA). Inhibitors in AHA can sometimes cross-react with rpFVIII. OBJECTIVES: To assess the frequency, strength, and determinants of cross-reactivity. PATIENTS/METHODS: Baseline samples from 70 patients of the prospective, observational cohort study GTH-AH 01/2010 were assessed for anti-human FVIII and anti-rpFVIII inhibitors using modified Nijmegen-Bethesda assays, as well as anti-human FVIII domain reactivity using enzyme-linked immunoassay (ELISA). RESULTS: Anti-human FVIII inhibitors were present in all samples ranging between 0.7 and 3891 Bethesda Units (BU)/mL. Inhibitors from 31 of 70 patients (44%) partially inhibited rpFVIII with anti-rpFVIII titers ranging between 0.5 and 471 BU/mL. Anti-rpFVIII titers were 100 BU/mL predicted cross-reactivity with 97% likelihood, whereas an anti-human FVIII titer of 100 BU/mL.