Effects of Keratinocyte and Hepatocyte Growth FactorIn Vivo:Implications for Retrovirus-Mediated Gene Transfer to Liver

Abstract

We have previously shown that intravenous administration of keratinocyte growth factor (KGF) induces hepatocyte proliferation, allowing for efficient and noninvasive in vivo gene transfer with high-titer retroviral vectors in mice. The distinctive periportal distribution of transduced cells led us to investigate the ability of virus-sized particles to perfuse the liver adequately after growth factor treatment. We found that perfusion was adequate, and that transduction was limited to the periportal region because only those cells were stimulated to divide. Cells in this region also showed increased expression of Ram-1, the receptor for the murine Moloney leukemia virus (MoMLV) amphotropic envelope, after KGF treatment. In further studies we found that recombinant hepatocyte growth factor (HGF) induces a different population of hepatocytes to divide and upregulate Ram-1. The differential pattern of induction suggested that combining KGF and HGF would improve gene transfer efficiency further. Indeed, simultaneous delivery of both growth factors leads to an overall increase in the number of proliferating cells. Importantly, when coupled with MoMLV delivery, efficiency of gene transfer increased. These results confirm the utility of growth factors for noninvasive hepatic gene transfer in mice, and demonstrate how experiments to define the mechanism of transduction can be taken advantage of to develop improved gene transfer protocols. Gene transfer with recombinant MoMLV-based retroviruses requires a proliferating environment for transduction. Previous studies showed that induction of cell division by intravenous growth factor delivery allowed for efficient gene transfer to mice hepatocytes. However, only periportal cells were transduced when keratinocyte growth factor was used. In this study we determined why transduction occurred in this manner, how it was different than when hepatocyte growth factor was used, and how this information could be taken advantage of to improve gene transfer efficiency.