Engraftment of autologous retrovirally transduced hepatocytes after intraportal transplantation into nonhuman primates: Implication for ex vivo gene therapy

The main impediment to effective ex vivo liver gene therapy of metabolic di seases is the lack of experimental work on large animals to resolve such im portant issues as effective gene delivery, cell-processing techniques, and the development of appropriate vectors. We have used a nonhuman primate, as a preclinical model, to analyze the limiting steps of this approach using recombinant retroviruses. Seven monkeys (Macaca fascicularis) underwent the complete protocol: their left liver lobe was resected, a catheter was plac ed in the inferior mesenteric vein and connected to an infusion chamber, an d the hepatocytes were isolated, cultured, and transduced with a retroviral vector containing the beta -galactosidase gene. The hepatocytes mere harve sted and returned to the host via the infusion chamber. Biopsies mere taken 4-40 days later. No animal was killed in the course of the experiments, Th ey all tolerated the procedure well. We have developed and defined conditio ns that permit the proliferation and transduction of up to 90% of the plate d hepatocytes, A significant proportion of genetically modified cells, repr esenting up to 3% of the liver mass, were safely delivered to the liver via the chamber. Polymerase chain reaction analysis detected integrated viral DNA sequences and quantitative analysis of the in situ beta -Gal-expressing hepatocytes indicated that a significant amount of transduced hepatocytes, up to 2%, had become integrated into the Liver and were functional. These results represent substantial advances in the development of the ex vivo ap proach and suggest that this approach is of clinical relevance for liver-di rected gene therapy.