HIV-1 Vpr- and Reverse Transcription-Induced Apoptosis in Resting Peripheral Blood CD4 T Cells and Protection by Common Gamma-Chain Cytokines

Abstract

HIV-1 infection leads to the progressive depletion of the CD4 T cell compartment by various known and unknown mechanisms.In vivo, HIV-1 infects both activated and resting CD4 T cells, but in vitro, in the absence of any stimuli, resting CD4 T cells from peripheral blood are resistant to infection. This resistance is generally attributed to an intracellular environment that does not efficiently support processes such as reverse transcription (RT), resulting in abortive infection. Here, we show that in vitro HIV-1 infection of resting CD4 T cells induces substantial cell death, leading to abortive infection. In vivo, however, various microenvironmental stimuli in lymphoid and mucosal tissues provide support for HIV-1 replication. For example, common gamma-chain cytokines (CGCC), such as interleukin-7 (IL-7), render resting CD4 T cells permissible to HIV-1 infection without inducing T cell activation. Here, we find that CGCC primarily allow productive infection by preventing HIV-1 triggering of apoptosis, as evidenced by early release of cytochrome c and caspase 3/7 activation. Cell death is triggered both by products of reverse transcription and by virion-borne Vpr protein, and CGCC block both mechanisms. When HIV-1 RT efficiency was enhanced by SIVmac239 Vpx protein, cell death was still observed, indicating that the speed of reverse transcription and the efficiency of its completion contributed little to HIV-1-induced cell death in this system. These results show that a major restriction on HIV-1 infection in resting CD4 T cells resides in the capacity of these cells to survive the early steps of HIV-1 infection. IMPORTANCE A major consequence of HIV-1 infection is the destruction of CD4 T cells.Here, we show that delivery of virion-associated Vpr protein and the process of reverse transcription are each sufficient to trigger apoptosis of resting CD4 T cells isolated from peripheral blood. While these 2 mechanisms have been previously described in various cell types, we show for the first time their concerted effect in inducing resting CD4 T cell depletion. Importantly, we found that cytokines such as IL-7 and IL-4, which are particularly active in sites of HIV-1 replication, protect resting CD4 T cells from these cytopathic effects and, primarily through this protection, rather than through enhancement of specific replicative steps, they promote productive infection. This study provides important new insights for the understanding of the early steps of HIV-1 infection and T cell depletion. E arly human immunodeficiency virus type 1 (HIV-1) infection is characterized by rapid and substantial depletion of both activated and resting CD4 T cells (1). The acute phase of both human HIV-1 infection and simian immunodeficiency virus (SIV) infection of macaques is characterized by Ն90% of viral RNA ϩ cells displaying a resting phenotype (2). It is during this stage that the main HIV-1 reservoir and source of virus rebound in vivo is established in resting memory T cells. Latency can be directly established upon...

Potent Inhibition of HIV-1 Replication in Resting CD4 T Cells by Resveratrol and Pterostilbene

“…Resting T cells are less permissive to productive HIV-1 infection, owing to several blocks, including the lack of transcription factors and the presence of restriction factors, such as SAMHD1 (45,46); nevertheless, both in vivo and in vitro abundant productive infection in resting CD4 T cells is observed (29,39,(47)(48)(49). Importantly, resting T cells contain dNTPs at levels 2 orders of magnitude lower than those in activated T cells (50), which slows the kinetics of reverse transcription (51) but does not prevent its eventual completion, resulting in productive infection and virus spread (49,52). We thus revisited resveratrol and examined pterostilbene in the context of resting T cells.…”

“…Next, we tested the effects of resveratrol in peripheral blood resting CD4 T cells. To improve the survival of the cells following infection, thus increasing the overall infection frequency (49), we treated the cells with interleukin-4 (IL-4), which, our prior studies indicated, maintains the resting phenotype, including small cell size, a lack of proliferation, and low levels of to no expression of activation markers, including CD25, CD38, CD62L, and CD69 (48,57,58). In contrast to the inability of resveratrol to inhibit productive HIV-1 infection of activated and transformed T cells, resveratrol completely prevented productive infection of resting CD4 T cells in a dose-dependent manner (Fig.…”

“…In this study, we treated the purified resting CD4 T cells with IL-4, which increases the yield of infected cells without inducing T cell activation (48,63). Apart from IL-4, other cytokines, such as IL-6 and IL-7, have been shown to support the infection of resting CD4 T cells in vitro (48,49,63,64). We have previously demonstrated that common gamma-chain cytokines, such as IL-4 and IL-7, increase HIV-1 infection of resting CD4 T cells by preventing the apoptosis that infection triggers rather than increasing the activation status of the cells (48,57,58) or the efficiency of infection itself (49).…”

“…Apart from IL-4, other cytokines, such as IL-6 and IL-7, have been shown to support the infection of resting CD4 T cells in vitro (48,49,63,64). We have previously demonstrated that common gamma-chain cytokines, such as IL-4 and IL-7, increase HIV-1 infection of resting CD4 T cells by preventing the apoptosis that infection triggers rather than increasing the activation status of the cells (48,57,58) or the efficiency of infection itself (49). IL-4 enhances HIV-1 infection in lymphoid tissues and thus likely contributes to HIV-1 replication of resting T cells in vivo (65).…”

“…1 to 5B, or 1 or 2 days after infection. Virus entry was complete prior to the day 1 dosing, while reverse transcription in resting CD4 T cells requires Ն2 days for completion (49), significantly slower than that in activated T cells and cell lines. We analyzed viral DNA 3 days after infection and GFP expression 5 days after infection ( Fig.…”