Clinical Interventions in HIV Cure Research

Bifurcation analysis of multistability and hysteresis in a model of HIV infection

The infectious disease caused by human immunodeficiency virus type 1 (HIV-1) remains a serious threat to hu- man health. The current approach to HIV-1 treatment is based on the use of highly active antiretroviral therapy, which has side effects and is costly. For clinical practice, it is highly important to create functional cures that can enhance immune control of viral growth and infection of target cells with a subsequent reduction in viral load and restoration of the immune status. HIV-1 control efforts with reliance on immunotherapy remain at a conceptual stage due to the complexity of a set of processes that regulate the dynamics of infection and immune response. For this reason, it is extremely important to use methods of mathematical modeling of HIV-1 infection dynamics for theoretical analysis of possibilities of reducing the viral load by affecting the immune system without the usage of antiviral therapy. The aim of our study is to examine the existence of bi-, multistability and hysteresis properties with a meaningful mathematical model of HIV-1 infection. The model describes the most important blocks of the processes of interaction between viruses and the human body, namely, the spread of infection in productively and latently infected cells, the appearance of viral mutants and the develop- ment of the T cell immune response. Furthermore, our analysis aims to study the possibilities of transferring the clinical pattern of the disease from a more severe state to a milder one. We analyze numerically the conditions for the existence of steady states of the mathematical model of HIV-1 infection for the numerical values of model parameters correspond- ing to phenotypically different variants of the infectious disease course. To this end, original computational methods of bifurcation analysis of mathematical models formulated with systems of ordinary differential equations and delay differ- ential equations are used. The macrophage activation rate constant is considered as a bifurcation parameter. The regions in the model parameter space, in particular, for the rate of activation of innate immune cells (macrophages), in which the properties of bi-, multistability and hysteresis are expressed, have been identified, and the features characterizing transi- tion kinetics between stable equilibrium states have been explored. Overall, the results of bifurcation analysis of the HIV-1 infection model form a theoretical basis for the development of combination immune-based therapeutic approaches to HIV-1 treatment. In particular, the results of the study of the HIV-1 infection model for parameter sets corresponding to different phenotypes of disease dynamics (typical, long-term non-progressing and rapidly progressing courses) indicate that an effective functional treatment (cure) of HIV-1-infected patients requires the development of a personalized ap- proach that takes into account both the properties of the HIV-1 quasispecies population and the patient's immune status.

Clinical trials aimed at HIV cure or remission: new pathways and lessons learned

INTRODUCTION

The main barrier to finding a cure against HIV is the latent HIV reservoir, which persists in people living with HIV (PLWH) despite antiretroviral treatment (ART). Here, we discuss recent findings from interventional studies using mono- and combination therapies aimed at enhancing immune-mediated killing of the virus with or without activating HIV from latency.

AREAS COVERED

We discuss latency reversal agents (LRAs), broadly neutralizing antibodies, immunomodulatory therapies, and studies aimed at inducing apoptosis.

EXPERT OPINION

The landscape of clinical trials for HIV cure and remission has evolved considerably over the past 10 years. Several novel interventions such as immune checkpoint inhibitors, therapeutic vaccines, and broadly neutralizing antibodies have been tested either alone or in combination with LRAs but studies have so far not shown a meaningful impact on the frequency of latently infected cells. Immunomodulatory therapies could work differently in the setting of antigen expression, that is, during active viremia, and timing of interventions could therefore, be key to future therapeutic success. Lessons learned from clinical trials aimed at HIV cure indicate that while we are still far from reaching a complete eradication cure of HIV, clinical interventions capable of inducing enhanced control of HIV replication in the absence of ART might be a more feasible goal.

Latency Reversal and Clearance of Persistent HIV Infection

Efforts to prevent and treat human immunodeficiency virus type 1 (HIV) infection have begun to blunt the spread of HIV infection. Potent, safe, and well-tolerated antiretroviral therapy (ART) allows those infected with HIV to attain a life expectancy similar to that of HIV-uninfected individuals. But the persistence of the quiescent retroviral genome, enforced by the natural proliferative responses of the immune system itself, and a delicate balance of regulators viral expression, mandates lifelong ART suppression to prevent rebound viremia and the return of disease.The approach to HIV eradication that has been studied the most extensively envisions adding therapies to induce the expression of quiescent HIV-1 genomes following the control of viremia by ART, paired with immunotherapies to clear persistent infection. Paired testing of latency reversal and clearance strategies has begun, but the field is still in its infancy and additional obstacles to HIV eradication may emerge. However, there is reason for optimism that together with advances in ART delivery and HIV prevention strategies, efforts in HIV cure research will markedly diminish the effect of the HIV pandemic on society.

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.

VIP-SPOT: an Innovative Assay To Quantify the Productive HIV-1 Reservoir in the Monitoring of Cure Strategies

Improved assays are critical to the successful implementation of novel HIV-1 cure strategies, given the limited ability of currently available assays to quantify true effects on the viral reservoir. As interventions based on immune clearance target infected cells producing viral antigens, irrespective of whether the viruses generated are infectious or not, we developed a novel assay to identify viral protein production at the single-cell level. The novel viral protein spot (VIP-SPOT) assay, based on the enzyme-linked ImmunoSpot (ELISpot) approach, quantifies the frequency of CD4⁺ T cells that produce HIV antigen upon stimulation. The performance of the VIP-SPOT assay was validated in samples from viremic (n = 18) and antiretroviral therapy (ART)-treated subjects (n = 35), and the results were compared with total and intact proviral DNA and plasma viremia. The size of the functional reservoir, measured by VIP-SPOT, correlates with total HIV-1 DNA and, more strongly, with intact proviruses. However, the frequency of HIV antigen-producing cells is 100-fold lower than that of intact proviruses, thus suggesting that most latently infected cells harboring full-length proviruses are not prone to reactivation. Furthermore, VIP-SPOT was useful for evaluating the efficacy of latency reversing agents (LRAs) in primary cells. VIP-SPOT is a novel tool for measuring the size of the functional HIV-1 reservoir in a rapid, sensitive, and precise manner. It might benefit the evaluation of cure strategies based on immune clearance, as these will specifically target this minor fraction of the viral reservoir, and might assist in the identification of novel therapeutic candidates that modulate viral latency.

Gliotoxin, identified from a screen of fungal metabolites, disrupts 7SK snRNP, releases P-TEFb, and reverses HIV-1 latency

A leading pharmacological strategy toward HIV cure requires "shock" or activation of HIV gene expression in latently infected cells with latency reversal agents (LRAs) followed by their subsequent clearance. In a screen for novel LRAs, we used fungal secondary metabolites as a source of bioactive molecules. Using orthogonal mass spectrometry (MS) coupled to latency reversal bioassays, we identified gliotoxin (GTX) as a novel LRA. GTX significantly induced HIV-1 gene expression in latent ex vivo infected primary cells and in CD4⁺ T cells from all aviremic HIV-1⁺ participants. RNA sequencing identified 7SK RNA, the scaffold of the positive transcription elongation factor b (P-TEFb) inhibitory 7SK small nuclear ribonucleoprotein (snRNP) complex, to be significantly reduced upon GTX treatment of CD4⁺ T cells. GTX directly disrupted 7SK snRNP by targeting La-related protein 7 (LARP7), releasing active P-TEFb, which phosphorylated RNA polymerase II (Pol II) C-terminal domain (CTD), inducing HIV transcription.

Novel Approaches Towards a Functional Cure of HIV/AIDS

Therapeutic approaches towards a functional cure or eradication of HIV have gained renewed momentum upon encouraging data emerging from studies in SIV monkey models and recent results from human clinical studies. However, a multitude of questions remain to be addressed, including how to deal with the latent viral reservoir, how to boost the host immune response to the virus and what the hurdles are to reach relevant viral compartments in the body. Advances have been made especially with regard to identifying agents that can reactivate the latent virus in vivo and boost the cellular and humoral immunity, but it remains largely unclear whether any of these strategies can awaken a sufficiently large fraction of the viral reservoir and whether the boosted immunity can prevent rapid viral replication once antiretroviral treatments are stopped.

Curing HIV: Seeking to Target and Clear Persistent Infection

Human immunodeficiency virus type 1 (HIV-1) infection persists despite years of antiretroviral therapy (ART). To remove the stigma and burden of chronic infection, approaches to eradicate or cure HIV infection are desired. Attempts to augment ART with therapies that reverse viral latency, paired with immunotherapies to clear infection, have advanced into the clinic, but the field is still in its infancy. We review foundational studies and highlight new insights in HIV cure research. Together with advances in ART delivery and HIV prevention strategies, future therapies that clear HIV infection may relieve society of the affliction of the HIV pandemic.

Repurposing Disulfiram as an Anti-Obesity Drug: Treating and Preventing Obesity in High-Fat-Fed Rats

BACKGROUND AND OBJECTIVES

A drug repurposing strategy is an approach for identifying new therapeutic uses for approved or investigational drugs. Thanks to the moderate cost of repurposing a drug compared to bringing new chemical entity to the market, drug repurposing is rapidly gaining ground. The aim of this work is to study the anti-obesity effect of disulfiram (DSF), an irreversible aldehyde dehydrogenase inhibitor approved by the Food and Drug Administration (FDA) to treat chronic alcoholism since 1951.

METHODS

Thirty male Albino rats were randomly assigned to six groups. G1, the control group, was given a standard diet. G2, the positive control group, was given a high-fat diet (HFD). G3 was given an HFD, and DSF 50 mg/kg/day was administered orally from day one for six weeks. G4 was given an HFD, and DSF 200 mg/kg/day was administered orally from day one for six weeks. G5 was given an HFD for six weeks; then treatment started with 50 mg/kg/day DSF orally. G6 was given an HFD for six weeks; then treatment started with 200 mg/kg/day DSF orally for three weeks. The body weight, food consumption and blood glucose levels were monitored over the given time interval.

RESULTS

Both doses of DSF significantly limited the body weight gain caused by an HFD for the treated animals. HF-fed rats received 50 and 200 mg/kg/day of DSF had their body weight increased by 51.93 ± 7.89% and 20.88 ± 15.05% respectively, whereas the body weight of control animals increased by 93.1 ± 20.04%. DSF also significantly decreased the body weight of obese animals. At 50 and 200 mg/kg/day of DSF, HF-fed rats lost 16.74 ± 8.61% and 23.9 ± 3.93% respectively, as their untreated counterparts had their body weight increased by 11.85 ± 3.79% after three weeks of treatment, thus restoring a body weight matching those who received a standard diet.

CONCLUSION

FDA-approved disulfiram has a strong anti-obesity effect on HFD-fed rats.

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

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 (TCM) 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.

HIV-2 as a model to identify a functional HIV cure

Two HIV virus types exist: HIV-1 is pandemic and aggressive, whereas HIV-2 is confined mainly to West Africa and less pathogenic. Despite the fact that it has been almost 40 years since the discovery of AIDS, there is still no cure or vaccine against HIV. Consequently, the concepts of functional vaccines and cures that aim to limit HIV disease progression and spread by persistent control of viral replication without life-long treatment have been suggested as more feasible options to control the HIV pandemic. To identify virus-host mechanisms that could be targeted for functional cure development, researchers have focused on a small fraction of HIV-1 infected individuals that control their infection spontaneously, so-called elite controllers. However, these efforts have not been able to unravel the key mechanisms of the infection control. This is partly due to lack in statistical power since only 0.15% of HIV-1 infected individuals are natural elite controllers. The proportion of long-term viral control is larger in HIV-2 infection compared with HIV-1 infection. We therefore present the idea of using HIV-2 as a model for finding a functional cure against HIV. Understanding the key differences between HIV-1 and HIV-2 infections, and the cross-reactive effects in HIV-1/HIV-2 dual-infection could provide novel insights in developing functional HIV cures and vaccines.

Impacts of HIV Cure Interventions on Viral Reservoirs in Tissues

HIV reservoirs persist in infected individuals despite combination antiretroviral therapy and can be identified in secondary lymphoid tissues, in intestinal tissues, in the central nervous system as well as in blood. Clinical trials have begun to explore effects of small molecule interventions to perturb the latent viral infection, but only limited information is available regarding the impacts of HIV cure-related clinical interventions on viral reservoirs found in tissues. Of the 14 HIV cure-related clinical trials since 2012 that have evaluated the effects of small molecule interventions in vivo, four trials have examined the impacts of the interventions in peripheral blood as well as other tissues that harbor persistent HIV. The additional tissues examined include cerebral spinal fluid, intestines and lymph nodes. We provide a comparison contrast analyses of the data across anatomical compartments tested in these studies to reveal where peripheral blood analyses reflect outcomes in other tissues as well as where the data reveal differences between tissue outcomes. We also summarize the current knowledge on these topics and highlight key open questions that need to be addressed experimentally to move the HIV cure research field closer to the development of an intervention strategy capable of eliciting long-term antiretroviral free remission of HIV disease.

A broad drug arsenal to attack a strenuous latent HIV reservoir

HIV cure is impeded by the persistence of a strenuous reservoir of latent but replication competent infected cells, which remain unsusceptible to c-ART and unrecognized by the immune system for elimination. Ongoing progress in understanding the molecular mechanisms that control HIV transcription and latency has led to the development of strategies to either permanently inactivate the latent HIV infected reservoir of cells or to stimulate the virus to emerge out of latency, coupled to either induction of death in the infected reactivated cell or its clearance by the immune system. This review focuses on the currently explored and non-exclusive pharmacological strategies and their molecular targets that 1. stimulate reversal of HIV latency in infected cells by targeting distinct steps in the HIV-1 gene expression cycle, 2. exploit mechanisms that promote cell death and apoptosis to render the infected cell harboring reactivated virus more susceptible to death and/or elimination by the immune system, and 3. permanently inactivate any remaining latently infected cells such that c-ART can be safely discontinued.

Long-term remission despite clonal expansion of replication-competent HIV-1 isolates

Clonal expansion of T cells harboring replication-competent virus has recently been demonstrated in patients on suppressive antiretroviral therapy (ART) regimens. However, there has not been direct evidence of this phenomenon in settings of natural control, including in posttreatment controllers who maintain control of viral replication after treatment when ART is discontinued. We present a case of an individual who has had undetectable viral loads for more than 15 years following the cessation of ART. Using near-full-genome sequence analysis, we demonstrate that 9 of 12 replication-competent isolates cultured from this subject were identical and that this identity was maintained 6 months later. A similar pattern of replication-competent virus clonality was seen in a treatment-naive HLA-B*57 elite controller. In both cases, we show that CD8+ T cells are capable of suppressing the replication of the clonally expanded viruses in vitro. Our data suggest that, while clonal expansion of replication-competent virus can present a barrier to viral eradication, these viral isolates remain susceptible to HIV-specific immune responses and can be controlled in patients with long-term suppression of viral replication.