DEFECTIVE HERPES-SIMPLEX VIRUS TYPE-1 VECTORS HARBORING GAG, POL, ANDENV GENES CAN BE USED TO RESCUE DEFECTIVE RETROVIRUS VECTORS

A retroviral packaging transcription unit was constructed in which the Moloney murine leukemia virus (MoMLV) gag-pol and env genes are expre ssed under the control of herpesvirus regulatory sequences, This trans cription unit, lacking long terminal repeats, primer binding sites, an d most of the retrovirus packaging signal but retaining both retrovira l donor and acceptor splice sites, was cloned into a herpes simplex vi rus type 1 (HSV-1) amplicon plasmid, and amplicon vectors (the gag-pol -env [GPE] vectors) were generated by using a defective HSV-1 vector a s helper virus, The GPE vector population was used to infect human TE6 71 cells (ATCC CRL 8805), harboring a lacZ provirus (TE-lac2 cells), a nd supernatants of infected cells were collected and filtered at diffe rent times after infection, These supernatants were found to contain i nfectious ecotropic lacZ retroviral particles, as shown both by revers e transcription-PCR and by their ability to transduce a P-galactosidas e activity to murine NIH 3T3 cells but not to human TE671 cells, The t iter of retroviral vectors released by GPE vector-infected TE-lac2 cel ls increased with the dose of infectious amplicon particles, Retroviru s vector production was inhibited by superinfection with helper virus, indicating that helper virus coinfection negatively interfered with r etrovirus production, Induction of retrovirus vectors by GPE vectors w as neutralized by anti-HSV-1 but not by anti-MoMLV antiserum, while tr ansduction of P-galactosidase activity to NIH 3T3 cells by supernatant s of GPE vector-infected TE-lac2 cells was neutralized by anti-MoMLV a ntiserum, These results demonstrate that HSV-1 GPE amplicon vectors ca n rescue defective lacZ retrovirus vectors and suggest that they could be used as a sort of launching ramp to fire defective retrovirus vect ors from within virtually any in vitro or in vivo cell type containing defective retroviral vectors.