RESUMEN
We replaced capsid genes by reporter genes and assessed expression in different types of human cancer cells and their normal counterparts, either at the level of whole cell population (CAT ELISA) or at the single cell level [FACS analysis of green fluorescent protein (GFP)]. CAT expression was substantial (up to 10,000 times background) in all infected tumor cells, despite variations according to the cell types. In contrast, no gene expression was detected in similarly infected normal cells (with t he exception of an expression slightly above background in fibroblasts). FACS analysis of GFP expression revealed that most tumor cells expressed high level of GFP while no GFP-positive normal cells could be detected with the exception of very few (less than 0.1%) human fibroblast cells expressing high level of GFP. We also replace capsid genes by genes coding for the costimulatory molecules B7-1 and B7-2 and show that, upon infection with B7 recombinant virions, only tumor cells display the costimulatory molecules and their immunogenicity was increased without any effect on normal cells. Using a recombinant minute virus of mice (MVM) containing the herpes simplex thymidine kinase gene, we could get efficient killing of most tumor cell types in the presence of ganciclovir. without affecting normal proliferating cells. The prospects and limitations of these different strategies are discussed.