Structure of blood coagulation factor VIII in complex with an anti-C1 domain pathogenic antibody inhibitor.

Antibody inhibitor development in hemophilia A represents the most significant complication resulting from factor VIII (fVIII) replacement therapy. Recent studies have demonstrated that epitopes present in the C1 domain contribute to a pathogenic inhibitor response. In this study, we report the structure of a group A anti-C1 domain inhibitor, termed 2A9, in complex with a B domain-deleted, bioengineered fVIII construct (ET3i).