Retroviral vectors have provided a versatile, efficient method for transferring genes into many types of mammalian cells, in vitro. We are adapting this technology to develop methods for gene transfer in vivo, for the ultimate purpose of treating patients afflicted with genetically determined liver diseases. Our two basic approaches are virus delivery in vivo, and tissue engineering. Virus delivery involves injection of concentrated virus preparations directly into regenerating rat liver. This experimental model provides us with unique opportunities, both for the development of stable vector formulations and in vivo gene transfer strategies. Targeting of modified vector, specifically, to the hepatocytes' asialo-glycoprotein receptor, (ASG-R), and continuous-release virus delivery systems, represent two of our major ongoing efforts to improve the efficiency of gene transfer in vivo. Tissue engineering involves the creation of """"""""tissues"""""""" from biocompatible implant materials. These are made according to precise specifications, and together with growth factors, and purified extracellular matrix components, constitute an environment capable of inducing capillary development, and supporting genetically-modified transplanted cells. Sustained expression of the relevant proteins, in significant amounts, signifies both successful engraftment, and genetic reconstitution of hepatocytic functions. Finally, new retroviral packaging cell lines based on liver, bone marrow and thymic epithelial cells, are under development. These may have certain advantages over the current virus-producer cell lines which have been derived from 3T3 cells.
