We have recently reported a recombinant humanized bispecific antibody to FIXa and FX, termed hBS23, which exerted coagulation activity in FVIII-deficient plasma, even in the presence of FVIII inhibitors, and showed invivo hemostatic activity in a cynomolgus monkey model of acquired hemophilia A, and had high subcutaneous bioavailability and a 2-week half-life in cynomolgus monkey [23]. This evidence concerns the gene F8 and hemophilia A.