Development of a clinical protocol for hepatic gene transfer: Lessons learned in preclinical studies

Strategies for hepatic gene therapy have been proposed that involve isolation of primary hepatocytes and introduction of recombinant genes into these cells in culture, followed by autologous hepatocellular transplantation (HCT). Consideration of clinical applications requires data suggesting that HCT can be performed safely in human subjects in addition to data indicating that recombinant gene expression can reverse a disease process, This report describes preclinical studies that underlie a clinical trial of HCT in which hepatocytes would be labeled with a marker gene to facilitate assessment of engraftment in the recipient, Human hepatocytes were harvested from liver segments preserved in Belzar's solution and transduced with an amphotropic retroviral vector carrying a recombinant marker gene (neomycin phosphotransferase II). Human hepatocytes were recovered from monolayer culture, stained with the fluorescent dye 1,1 '-dioctadecyl-3,3,3,3'-tetra-methy lindo-carbocyanine perchlorate (Dil) and transplanted into severe combined immunodeficient mice by splenic injection, Engrafted hepatocytes were identified in the liver and spleen of severe combined immunodeficient mice but not immunocompetent controls. Two large animal models of HCT are described, In a dog model, neomycin phosphotransferase II-containing hepatocytes were identified in the liver 7 wk after transplantation, In a baboon model, autologous HCT with Dil-stained cells demonstrated that transplanted cells assume a normal morphology and constitute up to 5% of hepatocytes. These data demonstrate transduction and transplantation of human hepatocytes and the feasibility of HCT in large animals, On the basis of these studies, the proposed clinical trial for gene transfer and transplantation in human subjects has been approved by the National Institutes of Health and the Food and Drug Administration, These studies illustrate the nature and extent of preclinical data required to gain approval for clinical trials involving gene transfer into human subjects, These data also illustrate the limitations of existing methods that may be used for hepatic gene therapy in the future.