Gene therapy for hemophilia: clinical trials and technical tribulations.

As monogenic disorders, hemophilia A and B are compelling candidates for treatment with gene therapy. In hemophilia, a therapeutic benefit achieved by gene therapy should only require a modest increase in the endogenous factor level; response to treatment can be monitored easily; and there are relevant small and large animal models. The two main approaches aiming to restore factor VIII or factor IX production are based on genetically modified cells or direct in vivo gene delivery using viral or plasmid vectors. The progress toward gene therapy for hemophilia A and B in both preclinical and clinical models will be evaluated in this review. Various viral and nonviral vectors are discussed in the context of current hurdles arising from preclinical and clinical trials. Despite disappointing clinical results to date, there are favorable indications that the near future should deliver on the long-sought promise of a cure for hemophilia.