SIVagm does not induce disease in its African green monkey (AGM) host. In comparison, the hybrid simian-human immunodeficiency virus SHIV89.6P that carries the HIV env gene induces disease in rhesus macaques more rapidly than the SIVmac parent virus. To address the possibility that this enhancement of disease by HIV env would also occur when present in SIVagm, a full-length SIVagm/89.6Penv chimeric lentivirus genome (termed SHIV-MP) was constructed. SHIV-MP replicated similarly to SIVagm in simian peripheral blood mononuclear cells (PBMCs). In inoculated AGMs, rhesus macaques and pig-tailed (PT) macaques the absolute number of CD4(+) T lymphocytes remained at normal levels. The peak levels of productively infected cells in SHIV-MP-infected monkeys ranged from 10(1) to 10(2) per 10(6) PBMCs, while in SIVagm infected macaques the levels were 10-100-fold higher. The env gene of SHIV89.6P therefore appears insufficient to confer acute pathogenicity to a non-pathogenic primate lentivirus due to poor in vivo replication.
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