In vivo retrovirus-mediated gene transfer to the liver of dogs results in transient expression and induction of a cytotoxic immune response

Gene transfer in regenerating dog liver using high-titer recombinant retroviral vectors carrying the E. coli beta-galactosidase gene was studied, Supernatants containing amphotropic or gibbon ape pseudotyped recombinant retroviruses were infused into a peripheral vein in beagle dogs after partial hepatectomy. The kinetics of liver regeneration were determined in the animals and daily infusions were carried out for 4 or 5 days during the regeneration period. Up to 2.8% of hepatocytes were beta-galactosidase positive at the end of the procedure. However, the number of positive cells declined rapidly and few positive hepatocytes were detected after 3 weeks, PCR demonstrated the disappearance of the provirus, Histologically, inflammatory lesions were observed in the transduced livers, Finally, we demonstrated the presence of a cytotoxic T lymphocyte immune response directed against beta-galactosidase-expressing cells, which could explain the disappearance of the transgene, This work suggests that the efficiency of in vivo gene delivery using high-titer retroviral vectors directly infused into the circulation may be hampered by a cytotoxic immune response against the infected cells.