Homeostatic Proliferation Fails to Efficiently Reactivate HIV-1 Latently Infected Central Memory CD4+ T Cells

Abstract

Homeostatic proliferation ensures the longevity of central memory T-cells by inducing cell proliferation in the absence of cellular differentiation or activation. This process is governed mainly by IL-7. Central memory T-cells can also be stimulated via engagement of the T-cell receptor, leading to cell proliferation but also activation and differentiation. Using an in vitro model of HIV-1 latency, we have examined in detail the effects of homeostatic proliferation on latently infected central memory T cells. We have also used antigenic stimulation via anti-CD3/anti-CD28 antibodies and established a comparison with a homeostatic proliferation stimulus, to evaluate potential differences in how either treatment affects the dynamics of latent virus populations. First, we show that homeostatic proliferation, as induced by a combination of IL-2 plus IL-7, leads to partial reactivation of latent HIV-1 but is unable to reduce the size of the reservoir in vitro. Second, latently infected cells are able to homeostatically proliferate in the absence of viral reactivation or cell differentiation. These results indicate that IL-2 plus IL-7 may induce a detrimental effect by favoring the maintenance of the latent HIV-1 reservoir. On the other hand, antigenic stimulation efficiently reactivated latent HIV-1 in cultured central memory cells and led to depletion of the latently infected cells via virus-induced cell death.

Latent HIV reservoirs exhibit inherent resistance to elimination by CD8+ T cells

“…We observed that treatment with bryostatin alone led to significant decreases in both levels of HIV DNA and IUPM (Supplemental Figure 3, P < 0.0001 and P = 0.003, respectively). This is consistent with previous studies, which have indicated that potent LRAs alone are sufficient to drive some elimination of infected cells in this and other models of latency (5,32). As expected, substantially greater reductions in levels of both HIV DNA and IUPM were observed following combination treatment with bryostatin and ABT-199 (Supplemental Figure 3, P = 0.0009 and P < 0.0001, respectively, compared with bryostatin alone).…”

“…We therefore moved to the use of CD8 + T cell clones to define the potential roles of immune escape and effector function in our observations. Before applying this assay to ex vivo CD4 + T cells, we performed validation experiments on a primary cell model of postactivation latency (32,33) to determine whether it could reliably measure changes in levels of both HIV DNA and IUPM. Infected cells of this latency model were spiked into autologous ex vivo CD4 + T cells to generate target cell populations, approximating the infected cell frequencies found in patient samples.…”

Clonal expansion of genome-intact HIV-1 in functionally polarized Th1 CD4+ T cells

“…Whether the efficacy of viral reactivation in functionally polarized cells is influenced by signature transcription factors of polarized T cells is currently unknown; however, it is noteworthy that GATA-3 and c-Maf, two transcription factors involved in regulating Th2-polarization, can stimulate HIV-1 expression through direct interactions with the HIV-1 promoter (28,29); this may facilitate immune-mediated clearance of HIV-1-infected Th2 cells and correspond to the very low frequency of clonally-expanded Th2 cells encoding intact HIV-1 in our study. Interestingly, TCR-independent homeostatic proliferation can drive HIV-1-infected cell proliferation in the absence of viral reactivation (30), at least in in vitro experiments, but this mechanism may possibly account for a smaller proportion of clonal turnover in T cells, relative to antigen-driven T cell proliferation.…”

Cyclin T1 and CDK9 T-Loop Phosphorylation Are Downregulated during Establishment of HIV-1 Latency in Primary Resting Memory CD4+T Cells

“…There was a progressive decrease in p24 Gag staining at days 5 and 7 after infection. This decrease in productively infected cells was previously shown to be due to cellular apoptosis (39). Infected cultures were maintained in medium containing recombinant IL-2 (rIL-2) for 9 days postinfection, allowing the cells to naturally revert to a quiescent state and acquire a central-memory phenotype.…”