When hemophilia A mice were preconditioned with busulfan or busulfan plus cyclophosphamide followed by transplantation of MSCV-porcine fVIII-transduced Sca-1+ cells, transient FVIII expression was obtained in recipients on day 7, but dropped to undetectable on day 14 and afterward due to the development of anti-FVIII inhibitors. This evidence concerns the gene F8 and hemophilia.