Nonviral gene therapy approaches to hemophilia.

The goal of hemophilia gene therapy is to obtain long-term therapeutic levels of factor VIII (FVIII) or factor IX (FIX) without stimulating an immune response against the transgene product or the vector. The success of gene therapy is largely dependent on the development of appropriate gene delivery vectors. Both viral vectors and nonviral vectors have been considered for the development of hemophilia gene therapy. In general, viral vectors are far more efficient than nonviral gene delivery approaches and resulted in long-term therapeutic levels of FVIII or FIX in preclinical animal models. However, there are several reasons why a nonviral treatment would still be desirable, particularly because some viral vectors are associated with inflammatory reactions, that render transgene expression transient, or with an increased risk of insertional oncogenesis when random integrating vectors are used. Nonviral vectors may obviate some of these concerns. Since nonviral vectors are typically assembled in cell-free systems from well-defined components, they have significant manufacturing advantages over viral vectors. The continued development of improved nonviral gene delivery approaches offers new perspectives for gene therapy of chronic diseases including hemophilia.