Hepatic repopulation with stably transduced conditionally immortalized hepatocytes in the Gunn rat

Background/Aims: Conditionally immortalized hepatocytes offer a renewable source of hepatocytes, but although preparative maneuvers have been developed for hepatic repopulation with primary hepatocytes, extensive proliferation of transplanted immortalized hepatocytes has not been accomplished heretofore. Our aim was to achieve ex vivo gene therapy of uridinediphosphoglucuronate glucuronosyltransferase-1A1 (UGT1A1)-deficient jaundiced Gunn rats (model of Crigler-Najjar syndrome type-1) by hepatic repopulation with genetically modified and conditionally immortalized hepatocytes. Methods: Gunn rat hepatocytes were conditionally immortalized by stable transduction with a thermolabile mutant simian virus 40 T-antigen (^tsTag^A58) and further transduced with UGT1A1. These hepatocytes proliferate at 33°C, but at 37°C the ^tsTag^A58 is degraded and the cells become quiescent. The cells were transplanted into Gunn rat livers after preparative hepatic irradiation (50 Gy) and 66% hepatectomy. Results: The engrafted UGT1A1-positive immortalized hepatocytes replaced ∼80% of the host hepatocytes in 20 weeks, leading to normalization of hyperbilirubinemia. Liver histology, and serum albumin and alanine aminotransferase levels remained normal. Conclusions: We achieved complete cure of hyperbilirubinemia in Gunn rats by ex vivo gene therapy via genetically modified and conditionally immortalized hepatocytes.