Definition

A recombinant fusion protein comprising a single chain B-domain deleted (BDD) analog of human antihemophilic factor (coagulation factor VIII; FVIII) covalently fused to the Fc domain of human immunoglobulin G1 (IgG1), the FVIII-binding D’D3 domain of human von Willebrand factor (VWF), and two XTEN polypeptides, that can be used to treat and control bleeding episodes in hemophilia A (congenital factor VIII deficiency). Upon administration, efanesoctocog alfa temporarily replaces the missing coagulation factor VIII, which binds factor IXa. Factor X is then converted to factor Xa. This facilitates the clotting cascade by converting prothrombin to thrombin, and leads to the conversion of fibrinogen to fibrin, and thus clot formation. This normalizes the activated partial thromboplastin time (aPTT) that is needed for effective hemostasis. Patients with hemophilia A lack factor VIII, a protein needed for normal clotting of the blood. B-domain has no known biological function. The FVIII-binding D’D3 domain of human VWF component of the fusion protein prevents FVIII interaction with endogenous VWF. The Fc region of human IgG1 binds to the neonatal Fc receptor (FcRn). The two XTEN polypeptides alter the hydrodynamic radius of the fusion protein. Altogether, they extend the half-life of the fusion protein.