Replication of the Rev-independent nef(-) SIV in juvenile macaques

All lentiviruses depend on the posttranscriptional regulation mediated by the viral Rev protein binding to the RRE located on a subset of viral mRNAs encoding the structural proteins. In contrast, type D retroviruses expression is mediated via cellular factor(s) interacting with the viral CTE, an RNA element with an extended stem-loop structure (1). In the presence of the positive acting factors, the RRE- and CTE-containing mRNAs are efficiently transported to the cytoplasm via distinct nuclear export pathways (2). To study the role of the Rev in virus propagation, we have generated Rev-independent clones of HIV and SIV and have demonstrated that the Rev/RRE system can be replaced by the CTE and generate infectious virus (3). The Rev-independent viruses have lower infectivity; lower replicative capacities in cultured PBMC; stable genotypes and stable in vitro attenuated growth properties. In SCID-hu mice, infection by these viruses results in reduced viral load and do not cause CD4 depletion (4). To test the in vivo properties, three juvenile macaques were injected intravenously with a Rev(-)RRE(-)Nef(-)CTE(+) SIVmac239. We show that this virus induced consistent, low-level infections. Analysis of cell-associated viral load and plasma RNA demonstrated that all monkeys are infected systemically. Starting 4 weeks post inoculation, they were also persistently Western blot positive. Upon propagation in monkeys, the genotype is stable and retained its in vitro characteristics. Since this virus variant lacks Nef, it is not expected to be pathogenic, and its ability to induce protection against wild type virus challenge will be tested The ability to express SIV independent of Rev may allow the generation of less pathogenic virus variants in vivo due to a change in the regulatory axis, which may result in an altered interaction with the host.

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