Preclinical Study for Hemophilia Gene and Cell Therapy in Model Mice and in Non-human Primates

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Hemophilia is an X-linked inherited bleeding disorder caused by mutations in the factor VIII (FVIII) gene or the factor IX (FIX) gene which in turn create deficiency of FVIII or FIX. Gene therapy for hemophilia is studied in mice and in macaques. High and long term expression of canine FVIII without immune suppression was achieved with the AAV8 vector carrying the canine FVIII gene under the control of the liver specific HCR/α1-antitrypsin enhancer/promoter complex in hemophilia A mice, suggesting that immune tolerance to FVIII can be achieved with specific expression of FVIII in the liver. Because of the short half-life of human FVIII in the mouse circulation and neutralizing antibody formation to human FVIII, it had been difficult to express human FVIII at the therapeutic level in hemophilia A mice. We could express human FVIII at the therapeutic level in hemophilia A mice with administration of the AAV8 vector carrying the human FVIII gene under control of the liver specific HCR/α1- … More antitrypsin enhancer/promoter complex. Transplantation of hematpoietic stem cells transduced with the SIV vector carrying the FVIII gene under control of the GPIbα promoter in hemophilia A mice resulted in platelet-specific expression of FVIII that rescued hemophilia A mice from bleeding upon tail clipping. The similar approach to express FVII in the activated form (FVIIa) could also rescue hemophilia A mice from bleeding upon tail clipping even in the presence of neutralizing antibody to FVIII, suggesting that the platelet-specific expression of coagulation factors can be a genetic therapy for bleeding disorders. AAV vectors serotypes 1, 8, and 9 had been shown to express FIX at the therapeutic levels and even at the super normal levels in mice. A preclinical study of gene therapy for hemophilia B was conducted using macaques. The AAV vector serotypes 1, 8, and 9 carrying the macaque FIX gene that could express mutant macaque FIX T262A, which could be quantified by the human FIX specific monoclonal antibody, were administered into macaques and expression of mutant FIX T262A was studied. The therapeutic levels of FIX persisted in all AAV1 vector-injected macaques, one macaque of serotype AAV8 vector-injected group, and one macaque of AAV9 vector-injected group for one year without adverse effect. However, expression of macaque FIX T262A in other macaques with AAV8 or AAV9 vector injection did not reach the therapeutic levels. Presence of pre-existing neutralizing antibody against wild-type AAV was thought to function inhibitory to AAV vector-mediated gene transfer. These data suggested that AAV vector-mediated gene transfer to the muscle and to the liver is a safe and promising genetic therapy for hemophilia. Less