Why the HIV Reservoir Never Runs Dry: Clonal Expansion and the Characteristics of HIV-Infected Cells Challenge Strategies to Cure and Control HIV Infection

Antiretroviral therapy (ART) effectively reduces cycles of viral replication but does not target proviral populations in cells that persist for prolonged periods and that can undergo clonal expansion. Consequently, chronic human immunodeficiency virus (HIV) infection is sustained during ART by a reservoir of long-lived latently infected cells and their progeny. This proviral landscape undergoes change over time on ART. One of the forces driving change in the landscape is the clonal expansion of infected CD4 T cells, which presents a key obstacle to HIV eradication. Potential mechanisms of clonal expansion include general immune activation, antigenic stimulation, homeostatic proliferation, and provirus-driven clonal expansion, each of which likely contributes in varying, and largely unmeasured, amounts to maintaining the reservoir. The role of clinical events, such as infections or neoplasms, in driving these mechanisms remains uncertain, but characterizing these forces may shed light on approaches to effectively eradicate HIV. A limited number of individuals have been cured of HIV infection in the setting of bone marrow transplant; information from these and other studies may identify the means to eradicate or control the virus without ART. In this review, we describe the mechanisms of HIV-1 persistence and clonal expansion, along with the attempts to modify these factors as part of reservoir reduction and cure strategies.

Hydrogen sulfide blocks HIV rebound by maintaining mitochondrial bioenergetics and redox homeostasis

A fundamental challenge in HIV eradication is to understand how the virus establishes latency, maintains stable cellular reservoirs, and promotes rebound upon interruption of antiretroviral treatment (ART). Here, we discovered an unexpected role of the ubiquitous gasotransmitter hydrogen sulfide (H2S) in HIV latency and reactivation. We show that reactivation of HIV-1 is associated with down-regulation of the key H2S producing enzyme cystathionine-g-lyase (CTH) and reduction in endogenous H2S. Genetic silencing of CTH disrupts redox homeostasis, impairs mitochondrial function, and remodels the transcriptome of latent cells to trigger HIV reactivation. Chemical complementation of CTH activity using a slow-releasing H2S donor, GYY4137, suppressed HIV reactivation and diminished virus replication. Mechanistically, GYY4137 blocked HIV reactivation by inducing the Keap1-Nrf2 pathway, inhibiting NF-kB, and recruiting the epigenetic silencer, YY1, to the HIV promoter. In latently infected CD4+ T cells from ART-suppressed human subjects, GYY4137 in combination with ART prevented viral rebound and improved mitochondrial bioenergetics. Moreover, prolonged exposure to GYY4137 exhibited no adverse influence on proviral content or CD4+ T cell subsets, indicating that diminished viral rebound is due to a loss of transcription rather than a selective loss of infected cells. In summary, this work provides mechanistic insight into H2S-mediated suppression of viral rebound and suggests exploration of H2S donors to maintain HIV in a latent form.

The HIV latency reversal agent HODHBt enhances NK Cell effector and memory-like functions by increasing IL-15 mediated-STAT activation

Elimination of latent HIV reservoirs is a critical endpoint to eradicate HIV. One therapeutic intervention against latent HIV is ‘shock and kill’. This strategy is based on the transcriptional activation of latent HIV with a Latency-Reversing Agent (LRA) with the consequent killing of the reactivated cell by either the cytopathic effect of HIV or the immune system. We have previously found that the small molecule 3-Hydroxy-1,2,3-benzotriazin-4(3H)-one (HODHBt) act as an LRA by increasing Signal Transducers and Activators of Transcription (STAT) activation mediated by IL-15 in cells isolated from aviremic participants. The IL-15 superagonist (N-803) is currently under clinical investigation to eliminate latent reservoirs. IL-15 and N-803 share similar mechanism of action by promoting the activation STATs and have shown some promise in pre-clinical models directed towards HIV eradication . In this work, we evaluated the ability of HODHBt to enhance IL-15 signaling in NK cells and the biological consequences associated with increased STAT activation in NK effector and memory-like functions. We showed that HODHBt increased IL-15-mediated STAT phosphorylation in NK cells, resulting in increased secretion of CXCL10 and IFN- g and expression of cytotoxic proteins including Granzyme B, Granzyme A, Perforin, Granulysin, FASL and TRAIL. This increased cytotoxic profile results in an increase cytotoxicity against different tumor cell lines and HIV-infected cells. HODHBt also improved the generation of cytokine-induced memory-like NK cells. Overall, our data demonstrate that enhancing the magnitude of IL-15 signaling with HODHBt favors NK cell cytotoxicity and memory-like generation, and targeting this pathway could be further explored for HIV cure interventions.

Hydrogen sulfide blocks HIV rebound by maintaining mitochondrial bioenergetics and redox homeostasis

A fundamental challenge in HIV eradication is to understand how the virus establishes latency, maintains stable cellular reservoirs, and promotes rebound upon interruption of antiretroviral treatment (ART). Here, we discovered an unexpected role of the ubiquitous gasotransmitter hydrogen sulfide (H2S) in HIV latency and reactivation. We show that reactivation of HIV-1 is associated with down-regulation of the key H2S producing enzyme cystathionine-g-lyase (CTH) and reduction in endogenous H2S. Genetic silencing of CTH disrupts redox homeostasis, impairs mitochondrial function, and remodels the transcriptome of latent cells to trigger HIV reactivation. Chemical complementation of CTH activity using a slow-releasing H2S donor, GYY4137, suppressed HIV reactivation and diminished virus replication. Mechanistically, GYY4137 blocked HIV reactivation by inducing the Keap1-Nrf2 pathway, inhibiting NF-kB, and recruiting the epigenetic silencer, YY1, to the HIV promoter. In latently infected CD4+ T cells from ART-suppressed human subjects, GYY4137 in combination with ART prevented viral rebound and improved mitochondrial bioenergetics. Moreover, prolonged exposure to GYY4137 exhibited no adverse influence on proviral content or CD4+ T cell subsets, indicating that diminished viral rebound is due to a loss of transcription rather than a selective loss of infected cells. In summary, this work provides mechanistic insight into H2S-mediated suppression of viral rebound and suggests the inclusion of an H2S donor in the current ART regimen to achieve a functional HIV-1 cure.

A universal CAR-NK cell approach for HIV eradication

<abstract> <p>No therapeutic drug has been able to completely eradicate HIV-infection so far, even after decades of research. A major challenge in HIV drug development is its immense diversity. NK cells are well-known for their anti-viral and anti-tumor functions. Since recently, NK cells have gained interest of researchers as they have paved the way for novel approaches in controlling HIV-infection supported by promising results observed in cancer immunotherapy trials. Here we report an anti-DNP CAR-NK cell approach introduced by Lim et al. capable of recognizing 2,4-dinitrophenyl tagged to anti-gp160 antibodies, which seemingly provides an effective solution to counteract HIV variability.</p> </abstract>

HIV-1C env and gag Variation in the Cerebrospinal Fluid and Plasma of Patients with HIV-Associated Cryptococcal Meningitis in Botswana

HIV-1 compartmentalization in reservoir sites remains a barrier to complete HIV eradication. It is unclear whether there is variation in HIV-1 env and gag between cerebrospinal fluid (CSF) and plasma of individuals with HIV-associated cryptococcal meningitis (CM). We compared HIV-1 env characteristics and the gag cytotoxic T-lymphocyte (CTL) escape mutations from CSF and plasma samples. Employing population-based Sanger sequencing, we sequenced HIV-1 env from CSF of 25 patients and plasma of 26 patients. For gag, 15 CSF and 21 plasma samples were successfully sequenced. Of these, 18 and 9 were paired env and gag CSF/plasma samples, respectively. There was no statistically significant difference in the proportion of CCR5-using strains in the CSF and plasma, (p = 0.50). Discordant CSF/plasma virus co-receptor use was found in 2/18 pairs (11.1%). The polymorphisms in the HIV-1 V3 loop were concordant between the two compartments. From the HIV-1 gag sequences, three pairs had discordant CTL escape mutations in three different epitopes of the nine analyzed. These findings suggest little variation in the HIV-1 env between plasma and CSF and that the CCR5-using strains predominate in both compartments. HIV-1 gag CTL escape mutations also displayed little variation in CSF and plasma suggesting similar CTL selective pressure.

Depicting HIV-1 Transcriptional Mechanisms: A Summary of What We Know

Despite the introduction of combinatory antiretroviral therapy (cART), HIV-1 infection cannot be cured and is still one of the major health issues worldwide. Indeed, as soon as cART is interrupted, a rapid rebound of viremia is observed. The establishment of viral latency and the persistence of the virus in cellular reservoirs constitute the main barrier to HIV eradication. For this reason, new therapeutic approaches have emerged to purge or restrain the HIV-1 reservoirs in order to cure infected patients. However, the viral latency is a multifactorial process that depends on various cellular mechanisms. Since these new therapies mainly target viral transcription, their development requires a detailed and precise understanding of the regulatory mechanism underlying HIV-1 transcription. In this review, we discuss the complex molecular transcriptional network regulating HIV-1 gene expression by focusing on the involvement of host cell factors that could be used as potential drug targets to design new therapeutic strategies and, to a larger extent, to reach an HIV-1 functional cure.

A review of current strategies towards the elimination of latent HIV-1 and subsequent HIV-1 cure

Background: During the past 35 years, highly effective ART has saved the lives of millions of people worldwide by suppressing viruses to undetectable levels. However, this does not translate to the absence of viruses in the body as HIV persists in latent reservoirs. Indeed, rebounded HIV has been recently observed in the Mississippi and California infants previously thought to have been cured. Hence, much remains to be learned about HIV latency, and the search for the best strategy to eliminate reservoir is the direction current research is taking. A systems-level approach that fully recapitulate the dynamics and complexity of HIV-1 latency in vivo and applicable in human therapy is prudent for HIV eradication to be more feasible. Objectives: The main barriers preventing the cure of HIV with antiretroviral therapy have been identified, progress has been made in the understanding of the therapeutic targets to which potentially eradicating drugs could be directed, integrative strategies have been proposed and clinical trials with various alternatives are underway. The aim of this review is to provide an update on the main advances in HIV eradication, with particular emphasis on the obstacles to HIV eradication and the different strategies proposed. We highlight the core challenges of each strategy and propose the most promising strategy and newresearch avenues in HIV eradication strategies. Methods: We conducted a systematic literature search of all English-language articles published between 2015 and 2019 using MEDLINE (PubMed) and Google scholar. Where available, medical subject headings (MeSH) were used as search terms and included: HIV, HIV latency, HIV reservoir, latency reactivation and HIV cure. Additional search terms consisted ofsuppression, persistence, establishment, generation, and formation. A total of 250 articles were found usingthe above search terms. Of these, 89 relevant articles related to HIV-1 latency establishment and eradication strategies were collected and reviewed, with no limitation of study design. Additional studies (commonly referenced and/or older and more recent articles of significance) were selected from bibliographies and references listed in the primary resources. Results : :In general, when exploring the literature, there are four main strategies heavily researched and provides promising strategies to the elimination of latent HIV: Haematopoietic Stem-Cell Transplantation, Shock and Kill Strategy, Gene-specific transcriptional activation using RNA-guided CRISPR-Cas9 system, and Block and Lock strategy. Most of these strategies studies are applicable in vitro, leaving many questions about the extent to which, or if any, these strategies are applicable to complex picture in vivo. However, the success of these strategies at least shows in part that HIV-1 can be cured, though some strategies are too invasive and expensive to become a standard of care for all HIV-infected patients. Conclusion: Recent advances hold promise for the ultimate cure of HIV infection. A systems-level approach that fully recapitulate the dynamics and complexity of HIV-1 latency in vivo and applicable in human therapy is prudent for HIV eradication to be more feasible. Future studies aimed at achieving a prolonged HIV remission state are more likely to be successful if they focus on a combination strategy including the block and kill, and stem cell approaches. These strategies propose a functional cure with minimal toxicity for patients. We believe that the cure of HIV infection will be attained in the short term if a strategy based on purging the reservoirs is complemented with an aggressive HAART strategy.

In vitro anti-HIV activity of ethanol extract from gandarusa (Justicia gendarussa Burm. f) leaves

Anti retroviral drugs for HIV has problems with uncomfortable side effects and that endanger the lives of HIV sufferers. Several herbs have been empirically proven to have an effect on HIV eradication through inhibition of reverse transcriptase. One of such antiviral herbs is Justicia gendarussa (J. gendarussa). The aim of research is to evaluate anti-HIV activity of 70% fractionated-ethanol extract (with releasing alkaloids) and 70% ethanol extract (without releasing alkaloids) of J. gendarussa leaves on in vitro HIV-infected of MOLT-4 cells. The effect of the extracts in inhibiting viral replication and fusion process on acute HIV infection was identi- fied through syncytia formation assay. Effect of the extracts on HIV p24 antigen was evaluated using HIV-1 p24 ELISA kit. It was found that 70% fractionated-ethanol extract and 70% ethanol extract of J. gendarussa leaves significantly inhibited of HIV replication by inhibition of syncytia formation, where the 50% effective concen- tration (EC50) values of the 70% fractionated-ethanol extract and 70% ethanol extract are 70.5 μg/mL and 228.7 μg/mL, respec- tively. Both of the extracts were also significantly inhibited HIV replication by decreasing HIV p24 antigen level where the EC 50 values of the 70% fractionated-ethanol extract and 70% ethanol extract are 88.8 μg/mL and 540.7 μg/mL, respectively. Moreover, it was found that 70% fractionated-ethanol extract of J. gendarussa leaves has anti-HIV activity since its EC50 values less than 100 μg/mL. It was concluded that J. gendarussa could be potentially developed into a phytopharmaceutical product due to its anti-HIV activity.