| Hepatitis C can be viewed as an acquired genetic disease and represents a major potential application of gene therapy. The development of successful gene therapy protocols requires a therapeutic gene capable of blocking viral gene expression or function, vectors that confer safe, efficient, and stable recombinant gene expression, as well as, animal models to test the toxicity and in vivo efficacy of anti-viral agents. To develop a primate model for liver directed gene therapy, we studied several gene transfer vehicles and routes in 8 rhesus monkeys. Adenovirus-mediated gene transfer to primate livers via the portal vein or saphenous vein was efficient, but resulted in transient expression and was accompanied by an immune response to both vector and transgene products and acute hepatitis, while lipofectamine-mediated transfer was inefficient. Immunosuppression prior to administration of adenovirus prolonged transgene expression and prevented hepatitis. Selective gene ablation with intracellular single-chain immunoglobulin (sFv) represents a novel approach to treatment of viral infection. For this purpose, recombinant variable regions of the human monoclonal antibodies CM3.B6 and DIO.E6 that react with the NS3 and NS4A proteins of HCV respectively, were introduced into adenoviral vectors. The sFv's were efficiently and stably expressed in hepatocytes and bound to their cognate antigens within cells. Significantly, expression of sFv to NS3 resulted in a decrease in HCV RNA in primary hepatocytes isolated from explanted livers of three patients with chronic HCV when measured by quantitative, competitive RT-PCR. In an attempt to establish a convenient animal model of HCV infection, we produced transgenic mice by introducing the polyprotein coding region of HCV genotype lb genome under transcriptional control of the liver-specific mouse albumin enhancer/promoter. One mouse expressed the transgene in the liver, however he failed to reproduce. Interestingly, this mouse developed hepatocellular carcinoma (HCC). More data is needed to make a connection between HCV transgene expression and HCC. This study demonstrates the therapeutic potential of adenovirus mediated expression of sFv's to HCV proteins. However, improved vectors or immunomodulatory adjunct therapy will be required to make this therapy feasible in humans. HCV transgenic mice may be a good model to test this antiviral approach. |
