RAPID REGENERATION OF VIRUS FROM CELLS INFECTED WITH A RETROVIRAL VECTOR

Recombinant retroviral vectors usually encode the genes of interest in place of the viral structural genes, which must be provided in trans. These viruses are therefore defective for replication: infected cells cannot produce progeny virus. However in some cases it may be desirab le to generate virus from an infected cell clone displaying a phenotyp e of interest. We describe a rapid method for producing virus, which i nvolves fusing the infected cells to fresh packaging cells. Stable pro ducer lines are generated after fusion by co-selecting for the Ecogpt( +) marker in the packaging cells and the G418 resistance (neo(r)) mark er in the infected cells. We have used this method to develop cell lin es that produce retroviruses encoding a Leu 61-activated c-Ha-ras onco gene as well as a neo(r) gene. The viruses confer oncogenic transforma tion on 95%-100% of infected target cells as assayed by altered morpho logy, focus formation and soft agar growth.