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Background Despite much work, safe and effective approaches to attack and deplete the long-lived reservoir of cells latently infected with HIV-1 remain an elusive goal. Patients infected with HIV-1 treated with cytotoxic agents or bone marrow transplantation can experience decreases in the reservoir of HIV-1 latently infected cells. Other viruses capable of long-term latency, such as herpesviruses, can sense host cell apoptosis and respond by initiating replication. These observations suggest that other viruses capable of long-term latency, like HIV-1, might also sense when its host cell is about to undergo apoptosis and respond by initiating replication. Results Pro-monocytic (U1) and lymphoid (ACH-2) HIV-1 persistently infected cell lines were treated with cytotoxic drugs – doxorubicin, etoposide, fludarabine phosphate, or vincristine – and activation of latent HIV-1 was evaluated using assays for HIV-1 RNA and p24 production. Both cell lines showed dose-dependent increases in apoptosis and associated HIV-1 activation following exposure to the cytotoxic agents. Pretreatment of the cells with the pan-caspase inhibitor Z-VAD-FMK prior to exposure to the cytotoxic agents inhibited apoptosis and viral activation. Direct exposure of the latently infected cell lines to activated caspases also induced viral replication. HIV-1 virions produced in association with host cell apoptosis were infectious. Conclusions The results indicate that latent HIV-1 can sense when its host cell is undergoing apoptosis and responds by completing its replication cycle. The results may help explain why patients treated with cytotoxic regimens for bone marrow transplantation showed reductions in the reservoir of latently infected cells. The results also suggest that the mechanisms that HIV-1 uses to sense and respond to host cell apoptosis signals may represent helpful new targets for approaches to attack and deplete the long-lived reservoir of cells latently infected with HIV-1.

Long-lived reservoirs of Human Immunodeficiency Virus (HIV) latently infected cells present the main barrier to a cure for HIV infection. Much interest has focused on identifying strategies to activate HIV, which would be used together with antiretrovirals to attack reservoirs. Several HIV activating agents, including Tumor Necrosis Factor alpha (TNFα) and other agents that activate via NF-kB are not fully effective in all latent infection models due to epigenetic restrictions, such as DNA methylation and the state of histone acetylation. DNA methyltransferases (DNMT) inhibitors like 5-aza-2'deoxycytidine (Aza-CdR) and histone deacetylase (HDAC) inhibitors like Trichostatin A (TSA) have been proposed as agents to enhance reactivation and have shown activity in model systems. However, it is not clear how the activities of DNMT and HDAC inhibitors range across different latently infected cell lines, potential models for the many different latently infected cells within an HIV patient. We determined HIV activation following treatment with TNFα, TSA and Aza-CdR across a range of well known latently infected cell lines. We assessed the activity of these compounds in four different Jurkat T cell-derived J-Lat cell lines (6.3, 8.4, 9.2 and 10.6), which have a latent HIV provirus in which GFP replaces Nef coding sequence, and ACH-2 and J1.1 (T cell-derived), and U1 (promonocyte-derived) cell lines with full-length provirus. We found that Aza-CdR plus TNFα activated HIV at least twice as well as TNFα alone for almost all J-Lat cells, as previously described, but not for J-Lat 10.6, in which TNFα plus Aza-CdR moderately decreased activation compared to TNFα alone. Surprisingly, a much greater reduction of TNFα-stimulated activation with Aza-CdR was detected for ACH-2, J1.1 and U1 cells. Reaching the highest reduction in U1 cells with a 75% reduction. Interestingly, Aza-CdR not only decreased TNFα induction of HIV expression in certain cell lines, but also decreased activation by TSA. Since DNMT inhibitors reduce the activity of provirus activators in some HIV latently infected cell lines the use of epigenetic modifying agents may need to be carefully optimized if they are to find clinical utility in therapies aimed at attacking latent HIV reservoirs.