Generation of deletion mutants of simian immunodeficiency virus incapable of proviral integration.

Deletion mutants of simian immunodeficiency virus (SIVmac) which were unable to integrate into host cells were generated by removing a portion of the integrase (IN) domain of the pol gene. The resulting plasmid was transfected into HUT-78 and human rhabdomyosarcoma cells. In comparison with the parental plasmid DNA transfected in parallel, the deletion mutant was found to direct efficient production of virus in both cell systems. Viruses derived from wild-type and mutant proviral DNAs were also tested for their relative replicative abilities in HUT-78 and U937 cells, and the kinetics of virus production was found to vary between these two cell systems. Analysis of DNA from infected cell nuclei showed that the deletion mutant lacked the ability to integrate despite being able to produce infectious virus. Using the sensitive polymerase chain reaction technique, we have clearly demonstrated the absence of the IN domain in the deletion mutant after infection and replication in HUT-78 cells. Such mutants might form the basis for the development of an experimental live attenuated vaccine.