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Current antiretroviral therapy (ART) provides potent suppression of HIV-1 replication. However, ART does not target latent viral reservoirs, so persistent infection remains a challenge. Small molecules with pharmacological properties that allow them to reach and activate viral reservoirs could potentially be utilized to eliminate the latent arm of the infection when used in combination with ART. Here we describe a cellbased system modeling HIV-1 latency that was utilized in a high-throughput screen to identify small molecule antagonists of HIV-1 latency. A more detailed analysis is provided for one of the hit compounds, antiviral 6 (AV6), which required nuclear factor of activated T cells for early mRNA expression while exhibiting RNA-stabilizing activity. It was found that AV6 reproducibly activated latent provirus from different lymphocyte-based clonal cell lines as well as from latently infected primary resting CD4 ؉ T cells without causing general T cell proliferation or activation. Moreover, AV6 complemented the latency antagonist activity of a previously described histone deacetylase (HDAC) inhibitor. This is a proof of concept showing that a high-throughput screen employing a cell-based model of HIV-1 latency can be utilized to identify new classes of compounds that can be used in concert with other persistent antagonists with the aim of viral clearance.The ability of human immunodeficiency virus type 1 (HIV-1) to establish a latent infection results in life-long virus persistence even after long-term antiretroviral therapy (ART). 4 The role that latency plays in preventing sustained clearance of the virus infection has become evident in recent years. Patients that have been successfully treated with ART, having undetectable levels of viral RNA (below 50 copies/ml) in the plasma for years, experienced rapid virus rebound upon withdrawal of therapy (1, 2). Moreover, it was found that after T cell activation, virus could be isolated from CD4 ϩ T cells taken from these patients, underscoring the need to eliminate the latently infected cells to eradicate the virus (3-5).Activation of latent proviruses from infected cells in combination with ART is part of a therapeutic strategy that may lead to the complete elimination of HIV infection. Prior attempts to "flush out" the virus by activation of latently infected resting CD4 ϩ T cells with the administration of IL-2 and/or anti-CD3 monoclonal antibodies were ultimately unsuccessful, probably because of its inability to reach all of the latent viral reservoirs and the toxicity of the regimen (6 -10). A more promising approach to complete viral clearance is the use of small molecules with pharmacological properties that allow them to access the viral reservoirs and to specifically reactivate the latent proviruses. The concept of small molecule activation of latent HIV-1 has been tested in a clinical study using the histone deacetylase (HDAC) inhibitor valproic acid (VA) (11). However, it is questionable whether VA alone can be used as a supplement to ART for succe...

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Human immunodeficiency virus type 1 (HIV-1), the causative agent of AIDS in humans, exhibits a very high rate of recombination. Bearing in mind the significant epidemiological and clinical contrast between HIV-2 and HIV-1 as well as the critical role that recombination plays in viral evolution, we examined the nature of HIV-2 recombination. Towards this end, a strategy was devised to measure the rate of crossover of HIV-2 by evaluating recombinant progeny produced exclusively by heterodimeric virions. The results showed that HIV-2 exhibits a crossover rate similar to that of HIV-1 and murine leukemia virus, indicating that the extremely high rate of crossover is a common retroviral feature.Human immunodeficiency virus type 1 (HIV-1) exhibits significant genetic diversity, which allows it to constantly evade the host immune response, to circumvent antiretroviral therapy, and to erect barriers to the development of an effective vaccine (3, 23). The molecular basis for such diversity lies in the error-prone nature of the virally encoded reverse transcriptase (RT) (16) and the ability of RT to switch templates (27). Together, these mechanisms generate viral variants at a high rate and represent a major force in driving HIV-1 evolution in infected populations worldwide. Previous studies from our laboratory and others have shown that HIV-1 exhibits a high rate of recombination, averaging between three and four crossovers per cycle of replication (10,20,29). It has been reported to be significantly higher when macrophages were used as targets (14). This high rate of recombination is not surprising in the context of the 16 circulating recombinant forms that have been recorded so far from patient samples worldwide (13).It is hypothesized that, like HIV-1, HIV-2 arose by zoonotic transmission from simian immunodeficiency virus-infected primates to humans and while HIV-1 is responsible for the global AIDS epidemic, HIV-2 has remained largely restricted to West Africa, certain parts of Europe, and some parts of southwestern India (18, 26). Although they are very similar in the genomic organization and biological functions of their gene products, their sequences diverge by approximately 50% at the nucleotide level (8,15,22). Overall, HIV-2 differs from HIV-1 in having (i) lower rates of horizontal and vertical transmission (2, 11, 17), (ii) reduced pathogenicity (4), (iii) considerable CD4-independent tropism (19), and (iv) longer clinical latency periods (1, 5). In spite of its restricted geographical distribution, recombinant strains of HIV-2 have been reported in West Africa. These chimeric viruses include both intra-and intergroup (subtypes A and B) recombinants (7,21). In this study we aimed at measuring the crossover rate of HIV-2 by using a strategy that selectively scores for progeny of heterodimeric virions. Moreover, by using the same strategy, experiments with HIV-1 were conducted in parallel to further validate our findings. Also, the significance of a high crossover rate to the basic mechanism of retroviral reve...