So Pathogenic or So What?—A Brief Overview of SIV Pathogenesis with an Emphasis on Cure Research

HIV infection requires lifelong antiretroviral therapy (ART) to control disease progression. Although ART has greatly extended the life expectancy of persons living with HIV (PWH), PWH nonetheless suffer from an increase in AIDS-related and non-AIDS related comorbidities resulting from HIV pathogenesis. Thus, an HIV cure is imperative to improve the quality of life of PWH. In this review, we discuss the origins of various SIV strains utilized in cure and comorbidity research as well as their respective animal species used. We briefly detail the life cycle of HIV and describe the pathogenesis of HIV/SIV and the integral role of chronic immune activation and inflammation on disease progression and comorbidities, with comparisons between pathogenic infections and nonpathogenic infections that occur in natural hosts of SIVs. We further discuss the various HIV cure strategies being explored with an emphasis on immunological therapies and “shock and kill”.

The Novel PKC Activator 10-Methyl-Aplog-1 Combined with JQ1 Induced Strong and Synergistic HIV Reactivation with Tolerable Global T Cell Activation

The presence of latent human immunodeficiency virus (HIV) reservoirs is a major obstacle to a cure. The “shock and kill” therapy is based on the concept that latent reservoirs in HIV carriers with antiretroviral therapy are reactivated by latency-reversing agents (LRAs), followed by elimination due to HIV-associated cell death or killing by virus-specific cytotoxic T lymphocytes. Protein kinase C (PKC) activators are considered robust LRAs as they efficiently reactivate latently infected HIV. However, various adverse events hamper the intervention trial of PKC activators as LRAs. We found in this study that a novel PKC activator, 10-Methyl-aplog-1 (10MA-1), combined with an inhibitor of bromodomain and extra-terminal domain motifs, JQ1, strongly and synergistically reactivated latently infected HIV. Notably, higher concentrations of 10MA-1 alone induced the predominant side effect, i.e., global T cell activation as defined by CD25 expression and pro-inflammatory cytokine production in primary CD4+ T lymphocytes; however, JQ1 efficiently suppressed the 10MA-1-induced side effect in a dose-dependent manner. Considering the reasonable accessibility and availability of 10MA-1 since the chemical synthesis of 10MA-1 requires fewer processes than that of bryostatin 1 or prostratin, our results suggest that the combination of 10MA-1 with JQ1 may be a promising pair of LRAs for the clinical application of the “shock and kill” therapy.

Therapeutic Potential of IL-15 and N-803 in HIV/SIV Infection

IL-15, a proinflammatory cytokine critical for the generation, maintenance, and homeostasis of T cell responses, is produced naturally in response to HIV/SIV infection, but has also demonstrated therapeutic potential. IL-15 can boost CD4+ and CD8+ T cell and NK cell proliferation, activation, and function. However, IL-15 treatment may cause aberrant immune activation and accelerated disease progression in certain circumstances. Moreover, the relationship between the timing of IL-15 administration and disease progression remains unclear. The IL-15 superagonist N-803 was developed to expand the therapeutic potential of IL-15 by maximizing its tissue distribution and half-life. N-803 has garnered enthusiasm recently as a way to enhance the innate and cellular immune responses to HIV/SIV by improving CD8+ T cell recognition and killing of virus-infected cells and directing immune cells to mucosal sites and lymph nodes, the primary sites of virus replication. N-803 has also been evaluated in “shock and kill” strategies due to its potential to reverse latency (shock) and enhance antiviral immunity (kill). This review examines the current literature about the effects of IL-15 and N-803 on innate and cellular immunity, viral burden, and latency reversal in the context of HIV/SIV, and their therapeutic potential both alone and combined with additional interventions such as antiretroviral therapy (ART) and vaccination.

New Latency Reversing Agents for HIV-1 Cure: Insights from Nonhuman Primate Models

Antiretroviral therapy (ART) controls human immunodeficiency virus 1 (HIV-1) replication and prevents disease progression but does not eradicate HIV-1. The persistence of a reservoir of latently infected cells represents the main barrier to a cure. “Shock and kill” is a promising strategy involving latency reversing agents (LRAs) to reactivate HIV-1 from latently infected cells, thus exposing the infected cells to killing by the immune system or clearance agents. Here, we review advances to the “shock and kill” strategy made through the nonhuman primate (NHP) model, highlighting recently identified latency reversing agents and approaches such as mimetics of the second mitochondrial activator of caspase (SMACm), experimental CD8+ T cell depletion, immune checkpoint blockade (ICI), and toll-like receptor (TLR) agonists. We also discuss the advantages and limits of the NHP model for HIV cure research and methods developed to evaluate the efficacy of in vivo treatment with LRAs in NHPs.

Potential Utility of Natural Killer Cells for Eliminating Cells Harboring Reactivated Latent HIV-1 Following the Removal of CD8+ T Cell-Mediated Pro-Latency Effect(s)

An impediment to curing HIV-1 infection is the persistence of latently infected cells in ART-treated people living with HIV (PLWH). A key strategy for curing HIV-1 infection is to activate transcription and translation of latent virus using latency reversing agents (LRAs) and eliminate cells harboring reactivated virus via viral cytopathic effect or immune clearance. In this review, we provide an overview of available LRAs and their use in clinical trials. Furthermore, we describe recent data suggesting that CD8+ T cells promote HIV-1 latency in the context of ART, even in the presence of LRAs, which might at least partially explain the clinical inefficiency of previous “shock and kill” trials. Here, we propose a novel cure strategy called “unlock, shock, disarm, and kill”. The general premise of this strategy is to shut down the pro-latency function(s) of CD8+ T cells, use LRAs to reverse HIV-1 latency, counteract anti-apoptotic molecules, and engage natural killer (NK) cells to mediate the killing of cells harboring reactivated latent HIV-1.

Alprazolam Prompts HIV-1 Transcriptional Reactivation and Enhances CTL Response Through RUNX1 Inhibition and STAT5 Activation

The HIV-1 pandemic is a significant challenge to the field of medicine. Despite advancements in antiretroviral (ART) development, 38 million people worldwide still live with this disease without a cure. A significant barrier to the eradication of HIV-1 lies in the persistently latent pool that establishes early in the infection. The “shock and kill” strategy relies on the discovery of a latency-reversing agent (LRA) that can robustly reactivate the latent pool and not limit immune clearance. We have found that a benzodiazepine (BDZ), that is commonly prescribed for panic and anxiety disorder, to be an ideal candidate for latency reversal. The BDZ Alprazolam functions as an inhibitor of the transcription factor RUNX1, which negatively regulates HIV-1 transcription. In addition to the displacement of RUNX1 from the HIV-1 5′LTR, Alprazolam potentiates the activation of STAT5 and its recruitment to the viral promoter. The activation of STAT5 in cytotoxic T cells may enable immune activation which is independent of the IL-2 receptor. These findings have significance for the potential use of Alprazolam in a curative strategy and to addressing the neuroinflammation associated with neuroHIV-1.

CPI-637 as a Potential Bifunctional Latency-Reversing Agent That Targets Both the BRD4 and TIP60 Proteins

The failure of highly active antiretroviral therapy (HAART) has been largely responsible for the existence of latent human immunodeficiency virus type 1 (HIV-1) reservoirs. The “shock and kill” strategy was confirmed to reactivate HIV-1 latent reservoirs by latency-reversing agents (LRAs) for accelerated HIV-1 clearance. However, a single LRA might be insufficient to induce HIV-1 reactivation from latency due to the complexity of the multiple signaling regulatory pathways that establish the HIV-1 latent reservoir. Therefore, combinations of LRAs or dual-mechanism LRAs are urgently needed to purge the latent reservoirs. We demonstrate here for the first time that a dual-target inhibitor with a specific suppressive effect on both BRD4 and TIP60, CPI-637, could reactivate latent HIV-1 in vitro by permitting Tat to bind positive transcription elongation factor b (P-TEFb) and assembling Tat-super-elongation complex (SEC) formation. In addition, CPI-637-mediated TIP60 downregulation further stimulated BRD4 dissociation from the HIV-1 long terminal repeat (LTR) promoter, allowing Tat to more effectively bind P-TEFb compared to BRD4 inhibition alone. Much more importantly, CPI-637 exerted a potent synergistic effect but alleviated global T cell activation and blocked viral spread to uninfected bystander CD4+ T cells with minimal cytotoxicity. Our results indicate that CPI-637 opens up the prospect of novel dual-target inhibitors for antagonizing HIV-1 latency and deserves further investigation for development as a promising LRA with a “shock and kill” strategy.

TLR1/2 Agonist Enhances Reversal of HIV-1 Latency and Promotes NK Cell-Induced Suppression of HIV-1-Infected Autologous CD4 + T Cells

The complete eradication of human immunodeficiency virus type 1 (HIV-1) is blocked by latent reservoirs in CD4 + T cells and myeloid lineage cells. Toll-like receptors (TLRs) can induce the reversal of HIV-1 latency and trigger the innate immune response. To the best of our knowledge, there is little evidence show the “killing” effect of TLR1/2 agonists but only with a small “shock” potential. To identify a new approach for eradicating the HIV latent reservoir, we evaluated the effectiveness of SMU-Z1, a novel TLR1/2 small molecule agonist, in the “shock and kill” strategy. The results showed that SMU-Z1 can not only enhance latent HIV-1 transcription in ex vivo peripheral blood mononuclear cells (PBMCs) from aviremic HIV-1-infected donors receiving combined antiretroviral therapy (cART) but also in cells of myeloid-monocytic origin in vitro targeting the nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) pathways. Interestingly, activation marker CD69 was significantly upregulated in NK cells, B cells, and monocytes 48 hours after SMU-Z1 treatment. Furthermore, SMU-Z1 was able to activate T cells without global T cell activation, as well as increase NK cell degranulation and interferon-gamma (IFN-γ) production which further block HIV-1-infected CD4 lymphocytes. In summary, the present study found that SMU-Z1 can both enhance HIV-1 transcription and promote NK cell-mediated inhibition of HIV-1-infected autologous CD4 + T cells. These findings indicate that novel TLR1/2 agonist SMU-Z1 is a promising latency-reversing agent (LRA) for eradication of HIV-1 reservoirs. IMPORTANCE Multiple in vivo studies have shown that many LRAs implemented in the “shock and kill” approach could activate viral transcription but could not induce “killing” effectively. Therefore, a dual function LRA is needed for elimination of HIV-1 reservoirs. We previously developed a small molecule TLR1/2 agonist, SMU-Z1, and demonstrated that it could upregulate NK cells and CD8 + T cells with immune adjuvant and anti-tumor properties in vivo . In the present study, SMU-Z1 can activate innate immune cells without global T cell activation, induce production of proinflammatory and antiviral cytokines, and enhance the cytotoxic function of NK cells. We showed that SMU-Z1 displayed dual potential ex vivo in the “shock” of exposure of HIV-1 latently infected cells and in the “kill” of clearance of infected cells, which is critical for effective use in combination with therapeutic vaccines or broadly neutralizing antibody treatments aimed at curing AIDS.

STING ligand-mediated priming of functional CD8 + T-cells specific for HIV-1 protective epitopes from naïve T-cells

Functional HIV-1-specific CD8 + T-cells primed from naïve T-cells are expected to act as effector T-cells in a ‘‘shock and kill’’ therapeutic strategy for an HIV-1 cure since less functional HIV-1-specific CD8 + T-cells are elicited from memory T-cells in HIV-1-infected individuals on cART. CD8 + T-cells specific for HIV-1 conserved and protective epitopes are candidates of such T-cells. We here investigated the priming with STING ligand of CD8 + T-cells specific for HLA-B*52:01 or HLA-C*12:02-restricted protective epitopes from naïve T-cells. STING ligand 3’3’-cGAMP effectively primed CD8 + T-cells specific for 3 of 4 HLA-B*52:01-restricted epitopes but failed to prime those specific for all 3 HLA-C*12:02-restricted epitopes from the naïve T-cells of HIV-1-uninfected individuals having an HLA-B*52:01-C*12:02 protective haplotype. These HLA-B*52:01-restricted CD8 + T-cells had a strong ability to suppress HIV-1 replication and expressed a high level of cytolytic effector molecules. The viral suppression ability of these T-cells was significantly correlated with the expression level of perforin and showed a trend for a positive correlation with the expression level of CD107a. The present study highlighted the priming with STING ligand of functional CD8 + T-cells specific for protective epitopes, which T-cells would contribute as effector T-cells to a ‘‘shock and kill’’ therapy. Importance Current therapeutic strategy ‘‘shock and kill’’ for HIV cure has been directed towards eliminating latent viral reservoirs by reactivation of latent reservoirs with latency-reversing agents followed by eradication of these cells by immune-mediated responses. Although HIV-1-specific T-cells are expected to eradicate viral reservoirs, the function of these T-cells is reduced in HIV-1-infected individuals with long-term cART. Therefore, priming of HIV-1-specific T-cells with high function from naïve T-cells are to be expected in these individuals. We here demonstrated the priming with STING ligand 3’3’-cGAMP of CD8 + T-cells specific for HIV-1 protective epitopes from naïve T cells. cGAMP primed CD8 + T-cells specific for 3 HLA-B*52:01-restricted protective epitopes, which cells expressed a high level of cytolytic effector molecules and effectively suppressed HIV-1 replication. The present study suggested that the priming with STING ligand of functional CD8 + T-cells specific for protective epitopes would be useful in a therapy for an HIV-1 cure.

Brain HIV-1 latently-infected reservoirs targeted by the suicide gene strategy

Reducing the pool of HIV-1 reservoirs in patients is a must to achieve functional cure. The most prominent HIV-1 cell reservoirs are resting CD4 + T cells and brain derived microglial cells. Infected microglial cells are believed to be the source of peripheral tissues reseedings and the emergence of drug resistance. Clearing infected cells from the brain is therefore crucial. However, many characteristics of microglial cells and the central nervous system make extremely difficult their eradication from brain reservoirs. Current methods, such as the “shock and kill”, the “block and lock” and gene editing strategies cannot override these difficulties. Therefore, new strategies have to be designed when considering the elimination of brain reservoirs. We set up an original gene suicide strategy using latently infected microglial cells as model cells. In this paper we provide proof of concept of this strategy.