F8 and hemophilia A: In this study, we utilized the exon-16 disrupted murine model of hemophilia A on predominantly a C57Bl/6 genetic background, which previously was shown to produce higher anti-fVIII inhibitory antibodies than the Balb/c model of hemophilia A.34 Using this model, two animals developed inhibitors to ET3, as evidenced by loss of fVIII activity and confirmed by ELISA and Bethesda assays.