TRANSCRIPTIONAL TARGETING OF HERPES-SIMPLEX VIRUS FOR CELL-SPECIFIC REPLICATION

Tissue- or cell-specific targeting of vectors is critical to the succe ss of gene therapy, We describe a novel approach to virus-mediated gen e therapy, where viral replication and associated cytotoxicity are lim ited to a specific cell type by the regulated expression of an essenti al immediate-early viral gene product. This is illustrated with a herp es simplex virus type 1 (HSV-1) vector (G92A) whose growth is restrict ed to albumin-expressing cells. G9ZA was constructed by inserting an a lbumin enhancer/promoter-ICP4 transgene into the thymidine kinase gene of mutant HSV-1 d120, deleted for both copies of the ICP4 gene, This vector also contains the Escherihia coli lacZ gene under control of th e thymidine kinase promoter, a viral early promoter, to permit easy de tection of infected cells containing replicating vector, In the adult, albumin is expressed uniquely in the liver and in hepatocellular carc inoma and is transcriptionally regulated. The plaquing efficiency of G 92A is > 10(3) times higher on human hepatoma cells than on non-albumi n-expressing human cells, The growth kinetics of G92A in albumin-expre ssing cells is delayed compared with that of wild-type HSV-1, likely d ue to aberrant expression of ICP4 protein. Cells undergoing a producti ve infection expressed detectable levels of ICP4 protein, as well as t he reporter gene product beta-galactosidase, Confining a productive, c ytotoxic viral infection to a specific cell type should be useful for tumor therapy and the ablation of specific cell types for the generati on of animal models of disease.