F8 and hemophilia A: However, therapeutic AAV-FVIII gene transfer in animal models has required substantially higher vector doses and the risk of inhibitor formation is generally greater for hemophilia A. We previously demonstrated tolerance induction to FIX by AAV gene transfer to the liver of hemophilic animals, which was particularly effective when using AAV8-a serotype that is highly effective in transducing murine hepatocytes [9], [15].