Replacement of posttranscriptional regulation in SIVmac239 generated a Rev-independent infectious virus able to propagate in rhesus peripheral blood mononuclear cells.

Lentiviruses control virion production via posttranscriptional regulation mediated by the viral Rev protein. In this study, we demonstrate that the Rev regulation of SIVmac239 can be replaced by the presence of the cis-acting transport element (CTE) of the type D simian retroviruses 1 (SRV-1). To avoid the possibility of generating revertants, the Rev-Independent SIV clones have both rev and the Rev responsive element (RRE) destroyed by multiple point mutations that do not affect the overlapping tat and env open reading frames. Virus stocks generated from these Rev-independent SIV molecular clones can infect and can be propagated in rhesus peripheral blood mononuclear cells (PBMCs). Therefore, the Rev/RRE system of SIVmac239 can be replaced by the SRV-1 CTE as previously shown for HIV-1. In both rhesus and human primary cells, the replicative capacity of the Rev-independent SIV is 10- to 20-fold lower than that of the wild-type virus. Rhesus PBMC-derived virus stocks of the Rev-independent SIV have lower infectivity. Interestingly, in CEM x 174 cells, no difference in replicative capacity between wild-type and Rev-independent SIV has been observed. The Rev-independent SIV has a stable genotype after several passages in primary cells. The availability of such Rev-Independent viruses will allow the study of the role of Rev in pathogenesis and the potential generation of attenuated SIV strains.