The FVIII-mimetic activity of our bispecific antibodies measured by an enzymatic assay shows a good correlation with a thrombin generation assay using commercial FVIII-deficient human plasma that was derived from a severe hemophilia A patient,6,7 and the activity shown by that assay also correlates with the in vivo efficacy in a cynomolgus monkey acquired hemophilia model.6,8. This evidence concerns the gene F8 and hemophilia A.