Activation of Latent HIV-1 T Cell Reservoirs with a Combination of Innate Immune and Epigenetic Regulators

Abstract

The presence of T cell reservoirs in which human immunodeficiency virus (HIV) establishes latency by integrating into the host genome represents a major obstacle to an HIV cure and has prompted the development of strategies aimed at the eradication of HIV from latently infected cells. The "shock-and-kill" strategy is one of the most pursued approaches to the elimination of viral reservoirs. Although several latency-reversing agents (LRAs) have shown promising reactivation activity, they have failed to eliminate the cellular reservoir. In this study, we evaluated a novel immune system-mediated approach to clearing the HIV reservoir, based on a combination of innate immune stimulation and epigenetic reprogramming. The combination of the STING agonist cGAMP (cyclic GMP-AMP) and the FDA-approved histone deacetylase inhibitor resminostat resulted in a significant increase in HIV proviral reactivation and specific apoptosis in HIV-infected cells in vitro Reductions in the proportion of HIV-harboring cells and the total amount of HIV DNA were also observed in CD4⁺ central memory T (T_CM) cells, a primary cell model of latency, where resminostat alone or together with cGAMP induced high levels of selective cell death. Finally, high levels of cell-associated HIV RNA were detected ex vivo in peripheral blood mononuclear cells (PBMCs) and CD4⁺ T cells from individuals on suppressive antiretroviral therapy (ART). Although synergism was not detected in PBMCs with the combination, viral RNA expression was significantly increased in CD4⁺ T cells. Collectively, these results represent a promising step toward HIV eradication by demonstrating the potential of innate immune activation and epigenetic modulation for reducing the viral reservoir and inducing specific death of HIV-infected cells.IMPORTANCE One of the challenges associated with HIV-1 infection is that despite antiretroviral therapies that reduce HIV-1 loads to undetectable levels, proviral DNA remains dormant in a subpopulation of T lymphocytes. Numerous strategies to clear residual virus by reactivating latent virus and eliminating the reservoir of HIV-1 (so-called "shock-and-kill" strategies) have been proposed. In the present study, we use a combination of small molecules that activate the cGAS-STING antiviral innate immune response (the di-cyclic nucleotide cGAMP) and epigenetic modulators (histone deacetylase inhibitors) that induce reactivation and HIV-infected T cell killing in cell lines, primary T lymphocytes, and patient samples. These studies represent a novel strategy for HIV eradication by reducing the viral reservoir and inducing specific death of HIV-infected cells.

Keywords: HDAC inhibitors; HIV latency; apoptosis; cGAS-STING; shock and kill.