Ex vivo liver-directed gene therapy for the treatment of metabolic diseases: advances in hepatocyte transplantation and retroviral vectors.

Transplantation of hepatocytes, whether genetically modified or not, has become an alternative to orthotopic liver transplantation for the treatment of patients with metabolic disease. However, more than ten years after the first clinical trial of ex vivo gene therapy to treat patients with Familial Hypercholesterolemia, there are still a number of impediments to these approaches. Numerous animal models are still being developed on the one hand to improve hepatocyte integration within hepatic parenchyma and function, and on the other hand to develop vectors that drive long-term transgene expression in situ. These include large animal models such as non-human primates, which have recently led to significant progress in hepatocyte transplantation. Simultaneous development of lentiviral vectors from different lentivirus species has permitted the transfer of genes into mitotically-quiescent primary cells including differentiated hepatocytes. Particularly third generation vectors derived from HIV-1 lentivirus are the most widely used and have significantly improved the safety and efficiency of these vectors. Given the shortage of organs and problems related to immunosuppression on one hand, and recent progresses in hepatocyte transduction and transplantation on the other hand, ex vivo approach is becoming a real alternative to allogeneic hepatocyte transplantation. We review the present progresses and limits of the ex vivo liver gene therapy approach in different animal models, emphasizing clinically relevant procedures.