Fatal immunopathogenesis by SIV/HIV-1 (SHIV) containing a variant form of the HIV-1SF33 env gene in juvenile and newborn rhesus macaques

SIV/HIV-1 (SHIV) chimeric clones, constructed by substituting portions of the pathogenic molecular clone SIVmac239 with counterpart portions from HIV-1 clones, provide a means to analyze functions of selected HIV-1 genes in vivo in nonhuman primates. Our studies focused on SHIVSF33, which contains the vpu, tat, rev, and env genes of the cytopathic, T-cell line tropic clone HIV-1SF33 (subtype-B); this clone has a premature stop codon in the vpu gene. In three juvenile macaques inoculated intravenously with SHIVSF33, low-level persistent infection was established; no disease was observed for a period of >2 years. However, at ~ 16 months p.i., one of four SHIVSF33-infected juvenile macaques exhibited an increase in virus load, depletion of CD4⁺ T cells in peripheral blood and lymph nodes, and other symptoms of simian AIDS (SAIDS). Virus recovered from this animal in the symptomatic stage was designated SHIVSF33A (A, adapted); this virus displayed multiple amino acid sequence changes throughout the HIV-1 env gene compared with the input SHIVSF33 clone. Additionally, a mutation in all clones from SHIVSF33A restored the open reading frame for the vpu gene. In vitro evaluations in tissue-culture systems revealed that SHIVSF33A replicated to higher levels and exhibited greater cytopathicity than SHIVSF33. Furthermore cloned env genes for SHIVSF33A were more fusogenic in a cell-fusion assay compared with the env gene of the SHIVSF33. Intravenous inoculation of SHIVSF33A into juvenile and newborn macaques resulted in a rapid decline in CD4⁺ T cells to very low levels and development of a fatal AIDS-like disease. A cell-free preparation of this pathogenic chimeric virus also established persistent infection when applied to oral mucosal membranes of juvenile macaques and produced a fatal AIDS-like disease. These studies on pathogenic SHIVSF33A establish the basis for further investigations on the role of the HIV-1 env gene in virus adaptation and in mechanism(s) of immunodeficiency in primates; moreover, the chimeric virus SHIVSF33A can play a role in elucidating mucosal membrane transmission and development of antiviral vaccines in newborns as well as juvenile and adult macaques.