We have developed an effective and optimally safe microculture method for rapid and convenient assay of the in vitro cytopathic effects of human immunodeficiency virus (HIV-1) on human lymphoblastoid or other suitable host cells. The assay procedure is applicable to the evaluation of drug effects on in vitro infections induced directly in cultured host cells by cell-free HIV-1 or by coculture with H9 cells chronically infected with HIV-1. The assay uses a newly developed tetrazolium reagent that is metabolically reduced by viable cells to yield a soluble, colored formazan product measurable by conventional colorimetric techniques. This simple microassay minimizes the number of plate manipulations typically required with other assay methods and, coupled with computerized data collection and analysis, facilitates large-scale screening of agents for potential antiviral activity. To support and enhance the discovery of new anti-HIV-1 agents, the National Cancer Institute is offering investigators worldwide the opportunity to submit new candidate agents for anti-HIV-1 screening with this method.

Transient antiretroviral treatment with tenofovir, (R)-9-(2-phosphonylmethoxypropyl)adenine, begun shortly after inoculation of rhesus macaques with the highly pathogenic simian immunodeficiency virus (SIV) isolateSIVsmE660, facilitated the development of SIV-specific lymphoproliferative responses and sustained effective control of the infection following drug discontinuation. Animals that controlled plasma viremia following transient postinoculation treatment showed substantial resistance to subsequent intravenous rechallenge with homologous (SIVsmE660) and highly heterologous (SIVmac239) SIV isolates, up to more than 1 year later, despite the absence of measurable neutralizing antibody. In some instances, resistance to rechallenge was observed despite the absence of detectable SIV-specific binding antibody and in the face of SIV lymphoproliferative responses that were low or undetectable at the time of challenge. In vivo monoclonal antibody depletion experiments demonstrated a critical role for CD8 ؉ lymphocytes in the control of viral replication; plasma viremia rose by as much as five log units after depletion of CD8 ؉ cells and returned to predepletion levels (as low as <100 copy Eq/ml) as circulating CD8؉ cells were restored. The extent of host control of replication of highly pathogenic SIV strains and the level of resistance to heterologous rechallenge achieved following transient postinoculation treatment compared favorably to the results seen after SIVsmE660 and SIVmac239 challenge with many vaccine strategies. This impressive control of viral replication was observed despite comparatively modest measured immune responses, less than those often achieved with vaccination regimens. The results help establish the underlying feasibility of efforts to develop vaccines for the prevention of AIDS, although the exact nature of the protective host responses involved remains to be elucidated.

The lack of a primate model that utilizes HIV-1 as the challenge virus is an impediment to AIDS research; existing models generally employ simian viruses that are divergent from HIV-1, reducing their usefulness in preclinical investigations. Based on an understanding of species-specific variation in primate TRIM5 and APOBEC3 antiretroviral genes, we constructed simian-tropic (st)HIV-1 strains that differ from HIV-1 only in the vif gene. We demonstrate that such minimally modified stHIV-1 strains are capable of high levels of replication in vitro in pig-tailed macaque (Macaca nemestrina) lymphocytes. Importantly, infection of pig-tailed macaques with stHIV-1 results in acute viremia, approaching the levels observed in HIV-1-infected humans, and an ensuing persistent infection for several months. stHIV-1 replication was controlled thereafter, at least in part, by CD8؉ T cells. We demonstrate the potential utility of this HIV-1-based animal model in a chemoprophylaxis experiment, by showing that a commonly used HIV-1 therapeutic regimen can provide apparently sterilizing protection from infection following a rigorous high-dose stHIV-1 challenge.