The Depsipeptide Romidepsin Reverses HIV-1 Latency In Vivo

Advances in Developing CAR T-Cell Therapy for HIV Cure

Acquired immune deficiency syndrome (AIDS), which is caused by HIV infection, is an epidemic disease that has killed millions of people in the last several decades. Although combination antiretroviral therapy (cART) has enabled tremendous progress in suppressing HIV replication, it fails to eliminate HIV latently infected cells, and infected individuals remain HIV positive for life. Lifelong antiretroviral therapy is required to maintain control of virus replication, which may result in significant problems, including long-term toxicity, high cost, and stigma. Therefore, novel therapeutic strategies are urgently needed to eliminate the viral reservoir in the host for HIV cure. In this review, we compare several potential strategies regarding HIV cure and focus on how we might utilize chimeric antigen receptor-modified T cells (CAR T) as a therapy to cure HIV infection.

Transcriptional profiling indicates cAMP-driven reversal of HIV latency in monocytes occurs via transcription factor SP-1

Latent HIV reservoir is a major barrier to absolute HIV cure. Studies on latency reversal agents (LRA) have by far focused mainly on CD4+ T-lymphocytes, while myeloid reservoirs remain under-represented despite their persistence and key contribution to HIV pathogenesis. cAMP has been shown to increase HIV-1 transcription in latently-infected monocytes/macrophages. In this communication, we explored the potential of commercially available pharmacological drugs and phosphodiesterase inhibitors to reactivate HIV in latently-infected monocytic cell-line, U1. We showed that increased levels of intracellular cAMP reverse HIV latency in vitro, which is specific to cells of the myeloid lineage. High throughput RNA-seq analysis revealed that cAMP modulates transcriptional profile of latently HIV-infected cells and provides favourable cellular environment for HIV to produce viral proteins. This reactivation of latent HIV was inhibited by Mithramycin A, a selective Sp1 inhibitor, indicating that the reversal of HIV latency in monocytes is driven by transcription factor Sp1.

Underestimated effect of intragenic HIV-1 DNA methylation on viral transcription in infected individuals

Background

The HIV-1 proviral genome harbors multiple CpG islands (CpGIs), both in the promoter and intragenic regions. DNA methylation in the promoter region has been shown to be heavily involved in HIV-1 latency regulation in cultured cells. However, its exact role in proviral transcriptional regulation in infected individuals is poorly understood or characterized. Moreover, methylation at intragenic CpGIs has never been studied in depth.

Results

A large, well-characterized HIV-1 patient cohort (n = 72), consisting of 17 long-term non-progressors and 8 recent seroconverters (SRCV) without combination antiretroviral therapy (cART), 15 early cART-treated, and 32 late cART-treated patients, was analyzed using a next-generation bisulfite sequencing DNA methylation method. In general, we observed low level of promoter methylation and higher levels of intragenic methylation. Additionally, SRCV showed increased promoter methylation and decreased intragenic methylation compared with the other patient groups. This data indicates that increased intragenic methylation could be involved in proviral transcriptional regulation.

Conclusions

Contrasting in vitro studies, our results indicate that intragenic hypermethylation of HIV-1 proviral DNA is an underestimated factor in viral control in HIV-1-infected individuals, showing the importance of analyzing the complete proviral genome in future DNA methylation studies.

Nicotinamide activates latent HIV-1 ex vivo in ART suppressed individuals, revealing higher potency than the association of two methyltransferase inhibitors, chaetocin and BIX01294

Background

Latent HIV-1 is a major hurdle in obtaining HIV-1 sustained virological remission (SVR). Here we explored histone deacetylation inhibition property of nicotinamide (NAM; n = 17) for the first time in comparison to a combination of methyltransferase inhibitors (MTIs; Chaetocin and BIX01294; n = 25) to reactivate latent HIV ex vivo in CD8-depleted PBMCs from antiretroviral treated aviremic individuals.

Results

NAM reactivated HIV-1 from 13/17 (76.4%) samples compared to 20/25 (80.0%) using MTIs with mean viral load (VLs) of 4.32 and 3.22 log₁₀ RNA copies/mL, respectively (p = 0.004). Mean purging time after NAM and MTIs stimulation was 5.1 and 6.75 days, respectively (p = 0.73). Viral purging in autologous cultures exhibited blunted HIV recovery with fluctuating VLs followed by a complete viral extinction when expanded in allogenic system. Electron microscopy from five supernatants revealed anomalous viral particles, with lack of complete viral genomes when characterized by ultradeep sequencing through metagenomics approach (n = 4).

Conclusion

NAM alone was more potent HIV-1 activator than combination of MTIs, with potential of clinical use.

Impact of Myeloid Reservoirs in HIV Cure Trials

PURPOSE OF REVIEW

Gallant efforts are ongoing to achieve sustained antiretroviral therapy (ART)-free HIV remission in the HIV-infected person; however, most, if not all, current human clinical studies have primarily focused these efforts on targeting viral persistence in CD4 T cells in blood and tissue sanctuaries. The lack of myeloid centered HIV clinical trials, either as primary or secondary end points, has hindered our understanding of the contribution of myeloid cells in unsuccessful trials but may also guide successes in future HIV eradication clinical strategies.

RECENT FINDINGS

Recent advances have highlighted the importance of myeloid reservoirs as sanctuaries of HIV persistence and therefore may partially be responsible for viral recrudescence following ART treatment interruption in several clinical trials where HIV was not detectable or recovered from CD4 T cells. Given these findings, novel innovative therapeutic approaches specifically focused on HIV clearance in myeloid cell populations need to be vigorously pursued if we are to achieve additional cases of sustained ART-free remission. This review will highlight new research efforts defining myeloid persistence and recent advances in HIV remission and cure trials that would be relevant in targeting this compartment and make an argument as to their clinical relevancy as we progress towards sustained ART-free HIV remission in all HIV-infected persons.

Systemic HIV and SIV latency reversal via non-canonical NF-κB signalling in vivo

Long-lasting, latently infected resting CD4+ T cells are the greatest obstacle to obtaining a cure for HIV infection, as these cells can persist despite decades of treatment with antiretroviral therapy (ART). Estimates indicate that more than 70 years of continuous, fully suppressive ART are needed to eliminate the HIV reservoir1. Alternatively, induction of HIV from its latent state could accelerate the decrease in the reservoir, thus reducing the time to eradication. Previous attempts to reactivate latent HIV in preclinical animal models and in clinical trials have measured HIV induction in the peripheral blood with minimal focus on tissue reservoirs and have had limited effect2-9. Here we show that activation of the non-canonical NF-κB signalling pathway by AZD5582 results in the induction of HIV and SIV RNA expression in the blood and tissues of ART-suppressed bone-marrow-liver-thymus (BLT) humanized mice and rhesus macaques infected with HIV and SIV, respectively. Analysis of resting CD4+ T cells from tissues after AZD5582 treatment revealed increased SIV RNA expression in the lymph nodes of macaques and robust induction of HIV in almost all tissues analysed in humanized mice, including the lymph nodes, thymus, bone marrow, liver and lung. This promising approach to latency reversal-in combination with appropriate tools for systemic clearance of persistent HIV infection-greatly increases opportunities for HIV eradication.

Robust and persistent reactivation of SIV and HIV by N-803 and depletion of CD8+ cells

Human immunodeficiency virus (HIV) persists indefinitely in individuals with HIV who receive antiretroviral therapy (ART) owing to a reservoir of latently infected cells that contain replication-competent virus1-4. Here, to better understand the mechanisms responsible for latency persistence and reversal, we used the interleukin-15 superagonist N-803 in conjunction with the depletion of CD8+ lymphocytes in ART-treated macaques infected with simian immunodeficiency virus (SIV). Although N-803 alone did not reactivate virus production, its administration after the depletion of CD8+ lymphocytes in conjunction with ART treatment induced robust and persistent reactivation of the virus in vivo. We found viraemia of more than 60 copies per ml in all macaques (n = 14; 100%) and in 41 out of a total of 56 samples (73.2%) that were collected each week after N-803 administration. Notably, concordant results were obtained in ART-treated HIV-infected humanized mice. In addition, we observed that co-culture with CD8+ T cells blocked the in vitro latency-reversing effect of N-803 on primary human CD4+ T cells that were latently infected with HIV. These results advance our understanding of the mechanisms responsible for latency reversal and lentivirus reactivation during ART-suppressed infection.

Immune checkpoint inhibitors in people living with HIV: what about anti-HIV effects?

: Immune checkpoint inhibitors (ICPi) have shown major therapeutic successes when used in various cancers. In the HIV field a double benefit of such ICPi should result from their dual ability to restore in-vitro HIV-specific CD8 T-cell functions and to enhance HIV production from reservoir cells, thus fulfilling the goals of the 'shock and kill' concept proposed as an HIV cure therapeutic strategy. We conducted a systematic review to identify studies reporting the tolerance profile of ICPi and their effects on HIV plasma loads (pVL), CD4 cell count, HIV reservoirs (cell-associated HIV-DNA) and/or HIV-specific CD8 T cells in PLWH. Thirty-one articles were included for a total 176 participants. Twelve percent of the participants experienced severe adverse events and 49% nonsevere adverse events. pVL remained stable in 91.9% participant, showed increases in 5.8% participant, and decreases in 2.3%. CD4 cell count remained stable in 60.7% participants, showed increases in 24.6%, and decreases in 14.7%. Regarding ICPi effects on HIV-DNA and HIV-specific immunity, we identified three distinct profiles: profile I, transient pVL increases followed by a boost in HIV-specific CD8 T cells concomitant to a decrease in HIV-DNA, reported in one participant. Profile II: increase in HIV-specific CD8 T cells without changes in pVL or HIV-DNA, reported in three participants. III: no effect, reported in five participants. In conclusion, the clinical, virological and immunological safety profiles of ICPi reported in about 200 PLWH appear to be favorable but there are still modest results in terms of HIV cure strategy.

Combination Immune Checkpoint Blockade to Reverse HIV Latency

In people living with HIV on antiretroviral therapy, HIV latency is the major barrier to a cure. HIV persists preferentially in CD4⁺ T cells expressing multiple immune checkpoint (IC) molecules, including programmed death (PD)-1, T cell Ig and mucin domain-containing protein 3 (TIM-3), lymphocyte associated gene 3 (LAG-3), and T cell immunoreceptor with Ig and ITIM domains (TIGIT). We aimed to determine whether these and other IC molecules have a functional role in maintaining HIV latency and whether blocking IC molecules with Abs reverses HIV latency. Using an in vitro model that establishes latency in both nonproliferating and proliferating human CD4⁺ T cells, we show that proliferating cells express multiple IC molecules at high levels. Latent infection was enriched in proliferating cells expressing PD-1. In contrast, nonproliferating cells expressed IC molecules at significantly lower levels, but latent infection was enriched in cells expressing PD-1, TIM-3, CTL-associated protein 4 (CTLA-4), or B and T lymphocyte attenuator (BTLA). In the presence of an additional T cell-activating stimulus, staphylococcal enterotoxin B, Abs to CTLA-4 and PD-1 reversed HIV latency in proliferating and nonproliferating CD4⁺ T cells, respectively. In the absence of staphylococcal enterotoxin B, only the combination of Abs to PD-1, CTLA-4, TIM-3, and TIGIT reversed latency. The potency of latency reversal was significantly higher following combination IC blockade compared with other latency-reversing agents, including vorinostat and bryostatin. Combination IC blockade should be further explored as a strategy to reverse HIV latency.

Current Status of Latency Reversing Agents Facing the Heterogeneity of HIV-1 Cellular and Tissue Reservoirs

One of the most explored therapeutic approaches aimed at eradicating HIV-1 reservoirs is the "shock and kill" strategy which is based on HIV-1 reactivation in latently-infected cells ("shock" phase) while maintaining antiretroviral therapy (ART) in order to prevent spreading of the infection by the neosynthesized virus. This kind of strategy allows for the "kill" phase, during which latently-infected cells die from viral cytopathic effects or from host cytolytic effector mechanisms following viral reactivation. Several latency reversing agents (LRAs) with distinct mechanistic classes have been characterized to reactivate HIV-1 viral gene expression. Some LRAs have been tested in terms of their potential to purge latent HIV-1 in vivo in clinical trials, showing that reversing HIV-1 latency is possible. However, LRAs alone have failed to reduce the size of the viral reservoirs. Together with the inability of the immune system to clear the LRA-activated reservoirs and the lack of specificity of these LRAs, the heterogeneity of the reservoirs largely contributes to the limited success of clinical trials using LRAs. Indeed, HIV-1 latency is established in numerous cell types that are characterized by distinct phenotypes and metabolic properties, and these are influenced by patient history. Hence, the silencing mechanisms of HIV-1 gene expression in these cellular and tissue reservoirs need to be better understood to rationally improve this cure strategy and hopefully reach clinical success.

[HIV and cancer: Update 2020]

The HIV infection remains a serious public health concern in France and around the world. Cancers are frequent among people living with HIV (PLWH) and have become the leading cause of mortality among this population in France. Certain non-AIDS-defining cancers are much more common among PLWH, such as anal carcinoma, Hodgkin lymphoma, hepatocellular carcinoma and lung cancer. The incidence of cancer among PLWH depending on various factors, virological control under combined antiretrovial therapies (cART), exposure prevention to oncogenic virus and toxics are of utmost importance, such as the implementation of specific screening programmes. Drug interactions between cART and oncologic treatments can lead to serious adverse effects or to a reduction in the therapeutic effects, therefore they require a close monitoring. The PLWH have been excluded from the oncologic clinical trials assessing the efficacy and toxicity profile of the immune checkpoints inhibitors (ICPi) because of an increased theoretical risk of inducing adverse events and a feared lack of efficacy in the immunocompromised population. However, the mostly retrospective clinical data reporting the use of ICPi among PLWH are somewhat reassuring with a safety and efficacy profile similar to what observed in HIV-negative patients. Regarding the "shock and kill" anti-HIV effects of ICPi, the preliminary clinical data available are still modest and relatively disappointing despite encouraging results obtained in vitro. HIV-associated cancers represent a particular care challenge due to the multiple comorbidities in the population and the high risk of drug interactions, thus the CANCERVIH national network is of particular interest within this context.

HIV-1 CRF01_AE subtype and HIV-1 DNA level among patients with chronic HIV-1 infection: a correlation study

Background

The impact of HIV-1 subtype (CRF01_AE and non-CRF01_AE) on HIV-1 DNA levels in HIV-1 chronically infected patients with suppressive antiretroviral therapy (ART) remains poorly understood. To evaluate the correlation of HIV-1 subtype with DNA level, and identify baseline predictors of HIV-1 DNA decay.

Methods

ART-naïve HIV-1-infected patients from two large multi-center studies in China were classified into CRF01_AE and non-CRF01_AE subtype groups. Peripheral blood samples were collected at baseline and week 12, 24, 48 and 96 after ART initiation and total HIV-1 DNA levels were quantified by real-time PCR. HIV-1 DNA levels at week 96 were categorized into high, moderate, and low levels, reflecting HIV-1 DNA ≥ 3, 2–3, ≤ 2 log₁₀ copies/10⁶ PBMCs, respectively, and the corresponding proportion of CRF01_AE and non-CRF01_AE subtype were compared. The baseline predictors of low HIV-1 total DNA levels (≤ 2 log₁₀ copies/10⁶ PBMCs) at week 96 were evaluated using a logistic regression model.

Results

Compared to the non-CRF01_AE subtypes (n = 185), patients with CRF01_AE subtype (n = 188) harboured a higher level of HIV-1 DNA (median: 3.19 vs. 2.95 log₁₀ copies/10⁶ PBMCs, P < 0.001) prior to treatment. After 96 weeks of ART, HIV-1 DNA levels remained higher in the CRF01_AE subtype group (median: 2.63 vs. 2.39 log₁₀ copies/10⁶ PBMCs, P = 0.002). There was no significant difference in the proportion of patients achieving high (22.3% vs. 14.6%, P = 0.054), moderate (59.6% vs. 60.5%, P = 0.849) and low levels (18.1% vs 24.9%, P = 0.111) between CRF01_AE and non-CRF01_AE groups. In the multivariable analysis, baseline HIV-1 DNA level and CD4⁺ T cell count but not the subtype were independent risk factors for achieving HIV-1 DNA level ≤ 2 log₁₀ copies/10⁶ PBMCs.

Conclusion

HIV-1 CRF01_AE subtype is neither correlated with HIV-1 DNA reservoir decline nor a prognostic factor for achieving lower HIV-1 DNA levels (≤ 2 log₁₀ copies/10⁶ PBMCs) after ART. However, higher HIV-1 DNA level in HIV-1 CRF01_AE patients should be aroused much attention and strengthen surveillance during ART.

Block-And-Lock Strategies to Cure HIV Infection

Today HIV infection cannot be cured due to the presence of a reservoir of latently infected cells inducing a viral rebound upon treatment interruption. Hence, the latent reservoir is considered as the major barrier for an HIV cure. So far, efforts to completely eradicate the reservoir via a shock-and-kill approach have proven difficult and unsuccessful. Therefore, more research has been done recently on an alternative block-and-lock functional cure strategy. In contrast to the shock-and-kill strategy that aims to eradicate the entire reservoir, block-and-lock aims to permanently silence all proviruses, even after treatment interruption. HIV silencing can be achieved by targeting different factors of the transcription machinery. In this review, we first describe the underlying mechanisms of HIV transcription and silencing. Next, we give an overview of the different block-and-lock strategies under investigation.

Single-Cell Analysis of Quiescent HIV Infection Reveals Host Transcriptional Profiles that Regulate Proviral Latency

A detailed understanding of the mechanisms that establish or maintain the latent reservoir of HIV will guide approaches to eliminate persistent infection. We used a cell line and primary cell models of HIV latency to investigate viral RNA (vRNA) expression and the role of the host transcriptome using single-cell approaches. Single-cell vRNA quantitation identified distinct populations of cells expressing various levels of vRNA, including completely silent populations. Strikingly, single-cell RNA-seq of latently infected primary cells demonstrated that HIV downregulation occurred in diverse transcriptomic environments but was significantly associated with expression of a specific set of cellular genes. In particular, latency was more frequent in cells expressing a transcriptional signature that included markers of naive and central memory T cells. These data reveal that expression of HIV proviruses within the latent reservoir are influenced by the host cell transcriptional program. Therapeutic modulation of these programs may reverse or enforce HIV latency.

Targeting histone epigenetics to control viral infections

During the past decades, many studies have significantly broadened our understanding of complex virus-host interactions to control chromatin structure and dynamics.1, 2 However, the role and impact of such modifications during viral infections is not fully revealed. Indeed, this type of regulation is bidirectional between the virus and the host. While viral replication and gene expression are significantly impacted by histone modifications on the viral chromatin,³ studies have shown that some viral pathogens dynamically manipulate cellular epigenetic factors to enhance their own survival and pathogenesis, as well as escape the immune system defense lines.⁴ In this dynamic, histone posttranslational modifications (PTMs) appear to play fundamental roles in the regulation of chromatin structure and recruitment of other factors.⁵ Genuinely, those PTMs play a vital role in lytic infection, latency reinforcement, or, conversely, viral reactivation.⁶ In this chapter, we will examine and review the involvement of histone modifications as well as their potential manipulation to control infections during various viral life cycle stages, highlighting their prospective implications in the clinical management of human immunodeficiency virus (HIV), herpes simplex virus (HSV), human cytomegalovirus (HCMV), hepatitis B and C viruses (HBV and HCV, respectively), Epstein–Barr virus (EBV), and other viral diseases. Targeting histone modifications is critical in setting the treatment of chronic viral infections with both lytic and latent stages (HIV, HCMV, HSV, RSV), virus-induced cancers (HBV, HCV, EBV, KSHV, HPV), and epidemic/emerging viruses (e.g. influenza virus, arboviruses).

Role of Dendritic Cells in Exposing Latent HIV-1 for the Kill

The development of effective yet nontoxic strategies to target the latent human immunodeficiency virus-1 (HIV-1) reservoir in antiretroviral therapy (ART)-suppressed individuals poses a critical barrier to a functional cure. The ‘kick and kill’ approach to HIV eradication entails proviral reactivation during ART, coupled with generation of cytotoxic T lymphocytes (CTLs) or other immune effectors equipped to eliminate exposed infected cells. Pharmacological latency reversal agents (LRAs) that have produced modest reductions in the latent reservoir ex vivo have not impacted levels of proviral DNA in HIV-infected individuals. An optimal cure strategy incorporates methods that facilitate sufficient antigen exposure on reactivated cells following the induction of proviral gene expression, as well as the elimination of infected targets by either polyfunctional HIV-specific CTLs or other immune-based strategies. Although conventional dendritic cells (DCs) have been used extensively for the purpose of inducing antigen-specific CTL responses in HIV-1 clinical trials, their immunotherapeutic potential as cellular LRAs has been largely ignored. In this review, we discuss the challenges associated with current HIV-1 eradication strategies, as well as the unharnessed potential of ex vivo-programmed DCs for both the ‘kick and kill’ of latent HIV-1.

Why and where an HIV cure is needed and how it might be achieved

Despite considerable global investment, only 60% of people who live with HIV currently receive antiretroviral therapy. The sustainability of current programmes remains unknown and key incidence rates are declining only modestly. Given the complexities and expenses associated with lifelong medication, developing an effective curative intervention is now a global priority. Here we review why and where a cure is needed, and how it might be achieved. We argue for expanding these efforts from resource-rich regions to sub-Saharan Africa and elsewhere: for any intervention to have an effect, region-specific biological, therapeutic and implementation issues must be addressed.

Heterogeneous HIV-1 Reactivation Patterns of Disulfiram and Combined Disulfiram+Romidepsin Treatments

OBJECTIVES

Few single latency-reversing agents (LRAs) have been tested in vivo, and only some of them have demonstrated an effect, albeit weak, on the decrease of latent reservoir. Therefore, other LRAs and combinations of LRAs need to be assessed. Here, we evaluated the potential of combined treatments of therapeutically promising LRAs, disulfiram and romidepsin.

SETTING AND METHODS

We assessed the reactivation potential of individual disulfiram or simultaneous or sequential combined treatments with romidepsin in vitro in latently infected cell lines of T-lymphoid and myeloid origins and in ex vivo cultures of CD8-depleted peripheral blood mononuclear cells isolated from 18 HIV-1 combination antiretroviral therapy-treated individuals.

RESULTS

We demonstrated heterogeneous reactivation effects of disulfiram in vitro in various cell lines of myeloid origin and no latency reversal neither in vitro in T-lymphoid cells nor ex vivo, even if doses corresponding to maximal plasmatic concentration or higher were tested. Disulfiram+romidepsin combined treatments produced distinct reactivation patterns in vitro. Ex vivo, the combined treatments showed a modest reactivation effect when used simultaneously as opposed to no viral reactivation for the corresponding sequential treatment.

CONCLUSIONS

Exclusive reactivation effects of disulfiram in myeloid latency cell lines suggest that disulfiram could be a potential LRA for this neglected reservoir. Moreover, distinct reactivation profiles pinpoint heterogeneity of the latent reservoir and confirm that the mechanisms that contribute to HIV latency are diverse. Importantly, disulfiram+romidepsin treatments are not potent ex vivo and most likely do not represent an effective drug combination to achieve high levels of latency reversal in vivo.

Nuclear Transit and HIV LTR Binding of NF-κB Subunits Held by IκB Proteins: Implications for HIV-1 Activation

No effective therapy to eliminate the HIV latently infected cell reservoir has been developed. One approach, “shock and kill”, employs agents that activate HIV, subsequently killing the activated infected cells and/or virus. Shock and kill requires agents that safely and effectively activate HIV. One class of activation agents works through classical NF-κB pathways, but global NF-κB activators are non-specific and toxic. There exist two major IκBs: IκBα, and IκBε, which hold activating NF-κB subunits in the cytoplasm, releasing them for nuclear transit upon cell stimulation. IκBα was considered the main IκB responsible for gene expression regulation, including HIV activation. IκBε is expressed in cells constituting much of the latent HIV reservoir, and IκBε knockout mice have a minimal phenotype, suggesting that IκBε could be a valuable target for HIV activation and reservoir depletion. We previously showed that targeting IκBε yields substantial increases in HIV expression. Here, we show that IκBε holds c-Rel and p65 activating NF-κB subunits in the cytoplasm, and that targeting IκBε with siRNA produces a strong increase in HIV expression associated with enhanced c-Rel and p65 transit to the nucleus and binding to the HIV LTR of the activating NF-κBs, demonstrating a mechanism through which targeting IκBε increases HIV expression. The findings suggest that it may be helpful to develop HIV activation approaches, acting specifically to target IκBε and its interactions with the NF-κBs.

Functional cure of HIV: the scale of the challenge

A variety of interventions to induce a functional cure of HIV are being explored, with the aim being to allow patients to cease antiretroviral therapy (ART) for prolonged periods of time or for life. These interventions share the goal of inducing ART-free remission from HIV pathogenesis and disease progression but achieve this in quite different ways, by reducing the size of the latent reservoir (for example, small-molecule stimulation of latently infected cells), reducing the number of target cells available for the virus (for example, gene therapy) or improving immune responses (for example, active or passive immunotherapy). Here, we consider a number of these alternative strategies for inducing post-treatment control of HIV and use mathematical modelling to predict the scale of the challenge inherent in these different approaches. For many approaches, over 99.9% efficacy will likely be required to induce durable ART-free remissions. The efficacy of individual approaches is currently far below what we predict will be necessary, and new technologies to achieve lifelong functional cure are needed.

Discovery and Development of Anti-HIV Therapeutic Agents: Progress Towards Improved HIV Medication

The history of the human immunodeficiency virus (HIV)/AIDS therapy, which spans over 30 years, is one of the most dramatic stories of science and medicine leading to the treatment of a disease. Since the advent of the first AIDS drug, AZT or zidovudine, a number of agents acting on different drug targets, such as HIV enzymes (e.g. reverse transcriptase, protease, and integrase) and host cell factors critical for HIV infection (e.g. CD4 and CCR5), have been added to our armamentarium to combat HIV/AIDS. In this review article, we first discuss the history of the development of anti-HIV drugs, during which several problems such as drug-induced side effects and the emergence of drug-resistant viruses became apparent and had to be overcome. Nowadays, the success of Combination Antiretroviral Therapy (cART), combined with recently-developed powerful but nonetheless less toxic drugs has transformed HIV/AIDS from an inevitably fatal disease into a manageable chronic infection. However, even with such potent cART, it is impossible to eradicate HIV because none of the currently available HIV drugs are effective in eliminating occult “dormant” HIV cell reservoirs. A number of novel unique treatment approaches that should drastically improve the quality of life (QOL) of patients or might actually be able to eliminate HIV altogether have also been discussed later in the review.

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.

Predictors of SIV recrudescence following antiretroviral treatment interruption

There is currently a need for proxy measures of the HIV rebound competent reservoir (RCR) that can predict viral rebound after combined antiretroviral treatment (cART) interruption. In this study, macaques infected with a barcoded SIVmac239 virus received cART beginning between 4- and 27 days post-infection, leading to the establishment of different levels of viral dissemination and persistence. Later treatment initiation led to higher SIV DNA levels maintained during treatment, which was significantly associated with an increased frequency of SIV reactivation and production of progeny capable of causing rebound viremia following treatment interruption. However, a 100-fold increase in SIV DNA in PBMCs was associated with only a 2-fold increase in the frequency of reactivation. These data suggest that the RCR can be established soon after infection, and that a large fraction of persistent viral DNA that accumulates after this time makes relatively little contribution to viral rebound.

Targeting Cellular and Tissue HIV Reservoirs With Toll-Like Receptor Agonists

The elimination of both cellular and tissue latent reservoirs is a challenge toward a successful HIV cure. "Shock and Kill" are among the therapeutic strategies that have been more extensively studied to target these reservoirs. These strategies are aimed toward the reactivation of the latent reservoir using a latency-reversal agent (LRA) with the subsequent killing of the reactivated cell either by the cytotoxic arm of the immune system, including NK and CD8 T cells, or by viral cytopathic mechanisms. Numerous LRAs are currently being investigated in vitro, ex vivo as well as in vivo for their ability to reactivate and reduce latent reservoirs. Among those, several toll-like receptor (TLR) agonists have been shown to reactivate latent HIV. In humans, there are 10 TLRs that recognize different pathogen-associated molecular patterns. TLRs are present in several cell types, including CD4 T cells, the cell compartment that harbors the majority of the latent reservoir. Besides their ability to reactivate latent HIV, TLR agonists also increase immune activation and promote an antiviral response. These combined properties make TLR agonists unique among the different LRAs characterized to date. Additionally, some of these agonists have shown promise toward finding an HIV cure in animal models. When in combination with broadly neutralizing antibodies, TLR-7 agonists have shown to impact the SIV latent reservoir and delay viral rebound. Moreover, there are FDA-approved TLR agonists that are currently being investigated for cancer therapy and other diseases. All these has prompted clinical trials using TLR agonists either alone or in combination toward HIV eradication approaches. In this review, we provide an extensive characterization of the state-of-the-art of the use of TLR agonists toward HIV eradication strategies and the mechanism behind how TLR agonists target both cellular and tissue HIV reservoirs.

HIV latency in isolated patient CD4+ T cells may be due to blocks in HIV transcriptional elongation, completion, and splicing

Latently infected CD4⁺ T cells are the main barrier to complete clearance of HIV infection, but it is unclear what mechanisms govern latent HIV infection in vivo. To address this question, we developed a new panel of reverse transcription droplet digital polymerase chain reaction (RT-ddPCR) assays specific for different HIV transcripts that define distinct blocks to transcription. We applied this panel of assays to CD4⁺ T cells freshly isolated from HIV-infected patients on suppressive antiretroviral therapy (ART) to quantify the degree to which different mechanisms inhibit HIV transcription. In addition, we measured the degree to which these transcriptional blocks could be reversed ex vivo by T cell activation (using anti-CD3/CD28 antibodies) or latency-reversing agents. We found that the main reversible block to HIV RNA transcription was not inhibition of transcriptional initiation but rather a series of blocks to proximal elongation, distal transcription/polyadenylation (completion), and multiple splicing. Cell dilution experiments suggested that these mechanisms operated in most of the HIV-infected CD4⁺ T cells examined. Latency-reversing agents exerted differential effects on the three blocks to HIV transcription, suggesting that these blocks may be governed by different mechanisms.

Statistical analysis of single-copy assays when some observations are zero

Observational and interventional studies for HIV cure research often use single-copy assays to quantify rare entities in blood or tissue samples. Statistical analysis of such measurements presents challenges due to tissue sampling variability and frequent findings of 0 copies in the sample analysed. We examined four approaches to analysing such studies, reflecting different ways of handling observations of 0 copies: (A) replace observations of 0 copies with 1 copy; (B) add 1 to all observed numbers of copies; (C) treat observations of 0 copies as left-censored at 1 copy; and (D) leave the data unaltered and apply a method for count data, negative binomial regression. Because research seeks to estimate general patterns rather than individuals' values, we argue that unaltered use of 0 copies is suitable for research purposes and that altering those observations can introduce bias. When applied to a simulated study comparing preintervention to postintervention measurements within 12 participants, methods A-C showed more attenuation than method D in the estimated intervention effect, less chance of finding P < 0.05 for the intervention effect and a lower chance of including the true intervention effect within the 95% confidence interval. Application of the methods to actual data from a study comparing multiply-spliced HIV RNA among men and women estimated smaller differences by methods A-C than by method D. We recommend that negative binomial regression, which is readily available in many statistical software packages, be considered for analysis of studies of rare entities that are measured by single-copy assays.

Fimepinostat, a novel dual inhibitor of HDAC and PI3K, effectively reverses HIV-1 latency ex vivo without T cell activation

OBJECTIVES

To test the potential of fimepinostat (CUDC-907), a dual inhibitor of histone deacetylases (HDAC) and phosphatidylinositol-3-kinases (PI3K), to reverse human immunodeficiency virus type 1 (HIV-1) latency in infected cell lines and in CD4+ T cells from HIV-1-infected donors on long-term combination antiretroviral therapy (cART).

METHODS

Latently HIV-1-infected J-lat Tat-GFP and ACH-2 cell lines were stimulated with clinically relevant concentrations of fimepinostat using the HDAC inhibitors (HDACi) panobinostat and romidepsin for comparison. Next, CD4+ T cells from donors living with HIV-1 on long-term cART were stimulated ex vivo and cell-associated unspliced HIV-1 RNA was measured to quantify changes in HIV-1 transcription. Finally, the impact of fimepinostat on T cell activation (CD69 expression) and proliferation (Ki67 expression) was determined using peripheral blood mononuclear cells from uninfected donors.

RESULTS

We found fimepinostat to be a potent latency-reversing agent. This was true in two latently infected cell lines as well as ex vivo in CD4+ T cells isolated from donors living with HIV-1. Relative to therapeutic dosing levels, fimepinostat showed latency-reversing potential comparable to romidepsin, which is the most potent HDACi tested in HIV-1 cure-related trials. Interestingly, in contrast to romidepsin, fimepinostat stimulation resulted in decreased T cell activation and had no negative impact on T cell proliferation.

CONCLUSIONS

At therapeutic concentration, the dual HDAC and PI3K inhibitor fimepinostat was a potent HIV-1 latency-reversing agent and it did not induce T cell activation and proliferation. The potential of fimepinostat as a latency-reversing agent warrants further investigation.

CAR T cells for infection, autoimmunity and allotransplantation

Chimeric antigen receptors (CARs) have shown remarkable ability to re-direct T cells to target CD19-expressing tumours, resulting in remission rates of up to 90% in individuals with paediatric acute lymphoblastic lymphoma. Lessons learned from these clinical trials of adoptive T cell therapy for cancer, as well as investments made in manufacturing T cells at commercial scale, have inspired researchers to develop CARs for additional applications. Here, we explore the challenges and opportunities of using this technology to target infectious diseases such as with HIV and undesired immune responses such as autoimmunity and transplant rejection. Despite substantial obstacles, the potential of CAR T cells to enable cures for a wide array of disease settings could be transformational for the medical field.

Blocking Formation of the Stable HIV Reservoir: A New Perspective for HIV-1 Cure

Recent studies demonstrate that the stable HIV-1 reservoir in resting CD4+ T cells is mostly formed from viruses circulating when combination antiretroviral therapy (ART) is initiated. Here we explore the immunological basis for these observations. Untreated HIV-1 infection is characterized by a progressive depletion of memory CD4+ T cells which mostly express CD127, the α chain of the IL-7 receptor (IL-7R). Depletion results from both direct infection and bystander loss of memory CD4+ T cells in part attributed to dysregulated IL-7/IL-7R signaling. While IL-7/IL7R signaling is not essential for the generation of effector CD4+ T cells from naïve cells, it is essential for the further transition of effectors to memory CD4+ T cells and their subsequent homeostatic maintenance. HIV-1 infection therefore limits the transition of CD4+ T cells from an effector to long-lived memory state. With the onset of ART, virus load (VL) levels rapidly decrease and the frequency of CD127+ CD4+ memory T cells increases, indicating restoration of effector to memory transition in CD4+ T cells. Collectively these data suggest that following ART initiation, HIV-1 infected effector CD4+ T cells transition to long-lived, CD127+ CD4+ T cells forming the majority of the stable HIV-1 reservoir. We propose that combining ART initiation with inhibition of IL-7/IL-7R signaling to block CD4+ T cell memory formation will limit the generation of long-lived HIV-infected CD4+ T cells and reduce the overall size of the stable HIV-1 reservoir.

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.

Have Cells Harboring the HIV Reservoir Been Immunoedited?

Immunoediting is an important concept in oncology, delineating the mechanisms through which tumors are selected for resistance to immune-mediated elimination. The recent emergence of immunotherapies, such as checkpoint inhibitors, as pillars of cancer therapy has intensified interest in immunoediting as a constraint limiting the efficacy of these approaches. Immunoediting manifests at a number of levels for different cancers, for example through the establishment of immunosuppressive microenvironments within solid tumors. Of particular interest to the current review, selection also occurs at the cellular level; and recent studies have revealed novel mechanisms by which tumor cells acquire intrinsic resistance to immune recognition and elimination. While the selection of escape mutations in viral epitopes by HIV-specific T cells, which is a hallmark of chronic HIV infection, can be considered a form of immunoediting, few studies have considered the possibility that HIV-infected cells themselves may parallel tumors in having differential intrinsic susceptibilities to immune-mediated elimination. Such selection, on the level of an infected cell, may not play a significant role in untreated HIV, where infection is propagated by high levels of cell-free virus produced by cells that quickly succumb to viral cytopathicity. However, it may play an unappreciated role in individuals treated with effective antiretroviral therapy where viral replication is abrogated. In this context, an "HIV reservoir" persists, comprising long-lived infected cells which undergo extensive and dynamic clonal expansion. The ability of these cells to persist in infected individuals has generally been attributed to viral latency, thought to render them invisible to immune recognition, and/or to their compartmentalization in anatomical sites that are poorly accessible to immune effectors. Recent data from ex vivo studies have led us to propose that reservoir-harboring cells may additionally have been selected for intrinsic resistance to CD8+ T cells, limiting their elimination even in the context of antigen expression. Here, we draw on knowledge from tumor immunoediting to discuss potential mechanisms by which clones of HIV reservoir-harboring cells may resist elimination by CD8+ T cells. The establishment of such parallels may provide a premise for testing therapeutics designed to sensitize tumor cells to immune-mediated elimination as novel approaches aimed at curing HIV infection.

Latency reversal agents affect differently the latent reservoir present in distinct CD4+ T subpopulations

Latency reversal agents (LRAs) have proven to induce HIV-1 transcription in vivo but are ineffective at decreasing the size of the latent reservoir in antiretroviral treated patients. The capacity of the LRAs to perturb the viral reservoir present in distinct subpopulations of cells is currently unknown. Here, using a new RNA FISH/flow ex vivo viral reactivation assay, we performed a comprehensive assessment of the viral reactivation capacity of different families of LRAs, and their combinations, in different CD4+ T cell subsets. We observed that a median of 16.28% of the whole HIV-reservoir induced HIV-1 transcripts after viral reactivation, but only 10.10% of these HIV-1 RNA+ cells produced the viral protein p24. Moreover, none of the LRAs were powerful enough to reactivate HIV-1 transcription in all CD4+ T cell subpopulations. For instance, the combination of Romidepsin and Ingenol was identified as the best combination of drugs at increasing the proportion of HIV-1 RNA+ cells, in most, but not all, CD4+ T cell subsets. Importantly, memory stem cells were identified as highly resistant to HIV-1 reactivation, and only the combination of Panobinostat and Bryostatin-1 significantly increased the number of cells transcribing HIV within this subset. Overall, our results validate the use of the RNA FISH/flow technique to assess the potency of LRAs among different CD4+ T cell subsets, manifest the intrinsic differences between cells that encompass the latent HIV reservoir, and highlight the difficulty to significantly impact the latent infection with the currently available drugs. Thus, our results have important implications for the rational design of therapies aimed at reversing HIV latency from diverse cellular reservoirs.

HDAC inhibitors as antifibrotic drugs in cardiac and pulmonary fibrosis

Fibrosis usually results from dysregulated wound repair and is characterized by excessive scar tissue. It is a complex process with unclear mechanisms. Accumulating evidence indicates that epigenetic alterations, including histone acetylation, play a pivotal role in this process. Histone acetylation is governed by histone acetyltransferases (HATs) and histone deacetylases (HDACs). HDACs are enzymes that remove the acetyl groups from both histone and nonhistone proteins. Aberrant HDAC activities are observed in fibrotic diseases, including cardiac and pulmonary fibrosis. HDAC inhibitors (HDACIs) are molecules that block HDAC functions. HDACIs have been studied extensively in a variety of tumors. Currently, there are four HDACIs approved by the US Food and Drug Administration for cancer treatment yet none for fibrotic diseases. Emerging evidence from in vitro and in vivo preclinical studies has presented beneficial effects of HDACIs in preventing or reversing fibrogenesis. In this review, we summarize the latest findings of the roles of HDACs in the pathogenesis of cardiac and pulmonary fibrosis and highlight the potential applications of HDACIs in these two fibrotic diseases.

Effects of 24-week Toll-like receptor 9 agonist treatment in HIV type 1+ individuals

DESIGN

This was an exploratory, single-arm clinical trial that tested the immune enhancement effects of 24-weeks of Toll-like receptor 9 (TLR9) agonist (MGN1703; Lefitolimod; 60 mg × 2 weekly) therapy.

METHODS

We enrolled HIV-1-infected individuals on suppressive combination antiretroviral therapy. Safety was assessed throughout the study. The primary outcome was reduction in total CD4 T-cell viral DNA levels. Secondary outcomes included safety, detailed immunological and virological analyses, and time to viral rebound (viral load > 5000 copies/ml) after randomization into an analytical treatment interruption (ATI).

RESULTS

A total of 12 individuals completed the treatment phase and nine completed the ATI. Adverse events were limited and consistent with previous reports for MGN1703. Although the dosing regimen led to potent T-cell activation and increased HIV-1-specific T-cell responses, there were no cohort-wide changes in persistent virus (total CD4 T cells viral DNA; P = 0.34). No difference in time to rebound was observed between the ATI arms (log rank P = 0.25). One of nine ATI participants, despite harboring a large replication-competent reservoir, controlled viremia for 150 days via both HIV-1-specific cellular and antibody-mediated immune responses.

CONCLUSION

A period of 24 weeks of MGN1703 treatment was safe and improved innate as well as HIV-1-specific adaptive immunity in HIV-1+ individuals. These findings support the incorporation of TLR9 agonism into combination HIV-1 cure strategies.

TRIAL NAME AND REGISTRATION

TLR9 Enhancement of antiviral immunity in chronic HIV-1 infection: a phase 1B/2A trial; ClinicalTrials.gov NCT02443935.

The HIV Reservoir in Monocytes and Macrophages

In people living with HIV (PLWH) who are failing or unable to access combination antiretroviral therapy (cART), monocytes and macrophages are important drivers of pathogenesis and progression to AIDS. The relevance of the monocyte/macrophage reservoir in PLWH receiving cART is debatable as in vivo evidence for infected cells is limited and suggests the reservoir is small. Macrophages were assumed to have a moderate life span and lack self-renewing potential, but recent discoveries challenge this dogma and suggest a potentially important role of these cells as long-lived HIV reservoirs. This, combined with new HIV infection animal models, has led to a resurgence of interest in monocyte/macrophage reservoirs. Infection of non-human primates with myeloid-tropic SIV implicates monocyte/macrophage activation and infection in the brain with neurocognitive disorders, and infection of myeloid-only humanized mouse models are consistent with the potential of the monocyte/macrophage reservoir to sustain infection and be a source of rebound viremia following cART cessation. An increased resistance to HIV-induced cytopathic effects and a reduced susceptibility to some antiretroviral drugs implies macrophages may be relevant to residual replication under cART and to rebound viremia. With a reappraisal of monocyte circulation dynamics, and the development of techniques to differentiate between self-renewing tissue-resident, and monocyte-derived macrophages in different tissues, a new framework exists to contextualize and evaluate the significance and relevance of the monocyte/macrophage HIV reservoir. In this review, we discuss recent developments in monocyte and macrophage biology and appraise current and emerging techniques to quantify the reservoir. We discuss how this knowledge influences our evaluation of the myeloid HIV reservoir, the implications for HIV pathogenesis in both viremic and virologically-suppressed PLWH and the need to address the myeloid reservoir in future treatment and cure strategies.

Progress in achieving long-term HIV remission

PURPOSE OF REVIEW

The purpose of the present review is to describe the major barriers to HIV eradication and assess the most promising cure strategies under investigation.

RECENT FINDINGS

There are significant challenges to achieve HIV eradication. These include the establishment of persistent latently infected cells, systemic chronic immune activation, and immune dysfunction. Since the announcement of the first HIV cure involving the Berlin patient, several attempts to reproduce these results have failed. Thus, it is widely accepted that long-term HIV remission would be a more feasible approach. Optimization of ART, immune-based therapies, therapeutic vaccinations, and gene editing, amongst others, are strategies aimed at controlling HIV in the absence of ART. These new strategies alone or in combination are being developed in preclinical studies and clinical trials and will provide further insight into whether long-term HIV remission is possible.

SUMMARY

The present review discusses several mechanisms that mediate the persistence of the HIV reservoir, clinical cases that provide hope in finding a functional cure of HIV, and promising interventional strategies being tested in preclinical studies and clinical trials that attempt to reduce the HIV reservoirs and/or boost the immune responses to control HIV in the absence of ART.

Therapeutic vaccination for HIV: hopes and challenges

PURPOSE OF REVIEW

This review summarizes the recent landscape of HIV therapeutic vaccine research, emphasizing the results of randomized controlled trials that included analytical treatment interruption (ATI) to assess efficacy.

RECENT FINDINGS

Therapeutic vaccines for HIV are designed to re-educate the host immune response in HIV-infected individuals to better control viral replication in the absence of antiretroviral therapy. No therapeutic vaccine has yet to induce long-term HIV remission following ATI in a randomized controlled trial. This is likely because the vaccines have not elicited a broad enough immune response to suppress the diverse escape variants that emerge during viral rebound, and have not been used with effective agents to reduce the HIV reservoir. Recent studies in nonhuman primates using combination approaches are showing significant successes, with several candidates eliciting significant antiviral activity following ATI. Future studies pairing these vaccines with effective reservoir reduction hold great promise.

SUMMARY

Therapeutic vaccines aim to modulate the immune system of HIV-infected individuals to elicit sustained virologic control in the absence of antiretroviral therapy. Therapeutic vaccines that elicit broad immune responses have recently shown promise in randomized controlled trials and nonhuman primate studies.

Interferon-inducible TRIM22 contributes to maintenance of HIV-1 proviral latency in T cell lines

The human immunodeficiency virus type-1 (HIV-1) establishes a state of latent infection in a small number of CD4⁺ T lymphocytes that, nonetheless, represent a major obstacle to viral eradication. We here show that Tripartite Motif-containing protein 22 (TRIM22), an epigenetic inhibitor of Specificity protein 1 (Sp1)-dependent HIV-1 transcription, is a relevant factor in maintaining a state of repressed HIV-1 expression at least in CD4⁺ T cell lines. By knocking-down (KD) TRIM22 expression, we observed an accelerated reactivation of a doxycycline (Dox)-controlled HIV-1 replication in the T lymphocytic SupT1 cell line. Furthermore, we here report for the first time that TRIM22 is a crucial factor for maintaining a state of HIV-1 quiescence in chronically infected ACH2 -T cell line while its KD potentiated HIV-1 expression in both ACH-2 and J-Lat 10.6 cell lines upon cell stimulation with either tumor necrosis factor-α (TNF-α) or histone deacetylase inhibitors (HDACi). In conclusion, TRIM22 is a novel determinant of HIV-1 latency, at least in T cell lines, thus representing a potential pharmacological target for strategies aiming at curtailing or silencing the pool of latently infected CD4⁺ T lymphocytes constituting the HIV-1 reservoir in individuals receiving combination antiretroviral therapy.

Development of CAR-T cells for long-term eradication and surveillance of HIV-1 reservoir

Human immunodeficiency virus type 1 (HIV-1) reservoir is a pool of latently infected cells harboring replication-competent proviral DNA that limits antiretroviral therapy. Suppression of HIV-1 by combination antiretroviral therapy (cART) delays progression of the disease but does not eliminate the viral reservoir, necessitating lifetime daily administration of antiretroviral drugs. To achieve durable suppression of viremia without daily therapy, various strategies have been developed, including long-acting antiretroviral drugs (LA-ARVs), broadly neutralizing antibodies (bNAbs), and chimeric antigen receptor T (CAR-T) cells. Here, we summarize and discuss recent breakthroughs in CAR-T cell therapies toward the eradication of HIV-1 reservoir. Although substantial challenges exist, CAR-T cell technology may serve as a promising strategy toward HIV-1 functional cure.

Humanized Mouse Model of HIV-1 Latency with Enrichment of Latent Virus in PD-1+ and TIGIT+ CD4 T Cells

Combination anti-retroviral drug therapy (ART) potently suppresses HIV-1 replication but does not result in virus eradication or a cure. A major contributing factor is the long-term persistence of a reservoir of latently infected cells. To study this reservoir, we established a humanized mouse model of HIV-1 infection and ART suppression based on an oral ART regimen. Similar to humans, HIV-1 levels in the blood of ART-treated animals were frequently suppressed below the limits of detection. However, the limited timeframe of the mouse model and the small volume of available samples makes it a challenging model with which to achieve full viral suppression and to investigate the latent reservoir. We therefore used an ex vivo latency reactivation assay that allows a semiquantitative measure of the latent reservoir that establishes in individual animals, regardless of whether they are treated with ART. Using this assay, we found that latently infected human CD4 T cells can be readily detected in mouse lymphoid tissues and that latent HIV-1 was enriched in populations expressing markers of T cell exhaustion, PD-1 and TIGIT. In addition, we were able to use the ex vivo latency reactivation assay to demonstrate that HIV-specific TALENs can reduce the fraction of reactivatable virus in the latently infected cell population that establishes in vivo, supporting the use of targeted nuclease-based approaches for an HIV-1 cure.IMPORTANCE HIV-1 can establish latent infections that are not cleared by current antiretroviral drugs or the body's immune responses and therefore represent a major barrier to curing HIV-infected individuals. However, the lack of expression of viral antigens on latently infected cells makes them difficult to identify or study. Here, we describe a humanized mouse model that can be used to detect latent but reactivatable HIV-1 in both untreated mice and those on ART and therefore provides a simple system with which to study the latent HIV-1 reservoir and the impact of interventions aimed at reducing it.

Therapeutic Vaccination Refocuses T-cell Responses Towards Conserved Regions of HIV-1 in Early Treated Individuals (BCN 01 study)

BACKGROUND

Strong and broad antiviral T-cell responses targeting vulnerable sites of HIV-1 will likely be a critical component for any effective cure strategy.

METHODS

BCN01 trial was a phase I, open-label, non-randomized, multicenter study in HIV-1-positive individuals diagnosed and treated during early HIV-1 infection to evaluate two vaccination regimen arms, which differed in the time (8 versus 24 week) between the ChAdV63.HIVconsv prime and MVA.HIVconsv boost vaccinations. The primary outcome was safety. Secondary endpoints included frequencies of vaccine-induced IFN-γ⁺ CD8⁺ T cells, in vitro virus-inhibitory capacity, plasma HIV-1 RNA and total CD4⁺ T-cells associated HIV-1 DNA. (NCT01712425).

FINDINGS

No differences in safety, peak magnitude or durability of vaccine-induced responses were observed between long and short interval vaccination arms. Grade 1/2 local and systemic post-vaccination events occurred in 22/24 individuals and resolved within 3 days. Weak responses to conserved HIV-1 regions were detected in 50% of the individuals before cART initiation, representing median of less than 10% of their total HIV-1-specific T cells. All participants significantly elevated these subdominant T-cell responses, which after MVA.HIVconsv peaked at median (range) of 938 (73-6,805) IFN-γ SFU/10⁶ PBMC, representing on average 58% of their total anti-HIV-1 T cells. The decay in the size of the HIV-1 reservoir was consistent with the first year of early cART initiation in both arms.

INTERPRETATION

Heterologous prime-boost vaccination with ChAdV63-MVA/HIVconsv was well-tolerated and refocused pre-cART T-cell responses towards more protective epitopes, in which immune escape is frequently associated with reduced HIV-1 replicative fitness and which are common to most global HIV-1 variants.

FUNDING

HIVACAT Catalan research program for an HIV vaccine and Fundació Gloria Soler. Vaccine manufacture was jointly funded by the Medical Research Council (MRC) UK and the UK Department for International Development (DFID) under the MRC/DFID Concordat agreements (G0701669.

RESEARCH IN CONTEXT

Evidence Before this Study: T cells play an important role in the control of HIV infection and may be particularly useful for HIV-1 cure by killing cells with reactivated HIV-1. Evidence is emerging that not all T-cell responses are protective and mainly only those targeting conserved regions of HIV-1 proteins are effective, but typically immunologically subdominant, while those recognizing hypervariable, easy-to-escape immunodominant 'decoys' do not control viremia and do not protect from a loss of CD4 T cells. We pioneered a vaccine strategy focusing T-cell responses on the most conserved regions of the HIV-1 proteome using an immunogen designated HIVconsv. T cells elicited by the HIVconsv vaccines in HIV-uninfected UK and Kenyan adults inhibited in vitro replication of HIV-1 isolates from 4 major global clades A, B, C and D.Added Value of this Study: The present study demonstrated the concept that epitopes subdominant in natural infection, when taken out of the context of the whole HIV-1 proteome and presented to the immune system by a potent simian adenovirus prime-poxvirus MVA boost regimen, can induce strong responses in patients on antiretroviral treatment and efficiently refocus HIV-1-specific T-cells to the protective epitopes delivered by the vaccine.Implications of all the Available Evidence: Nearly all HIV-1 vaccine strategies currently emphasize induction of broadly neutralizing Abs. The HIVconsv vaccine is one of a very few approaches focussing exclusively on elicitation of T cells and, therefore, can complement antibody induction for better prevention and cure. Given the cross-clade reach on the HIVconsv immunogen design, if efficient, the HIVconsv vaccines could be deployed globally. Effective vaccines will likely be a necessary component in combination with other available preventive measures for halting the HIV-1/AIDS epidemic.

Nanotechnology approaches to eradicating HIV reservoirs

The advent of combination antiretroviral therapy (cART) has transformed HIV-1 infection into a controllable chronic disease, but these therapies are incapable of eradicating the virus to bring about an HIV cure. Multiple strategies have been proposed and investigated to eradicate latent viral reservoirs from various biological sanctuaries. However, due to the complexity of HIV infection and latency maintenance, a single drug is unlikely to eliminate all HIV reservoirs and novel strategies may be needed to achieve better efficacy while limiting systemic toxicity. In this review, we describe HIV latency in cellular and anatomical reservoirs, and present an overview of current strategies for HIV cure with a focus on their challenges for clinical translation. Then we provide a summary of nanotechnology solutions that have been used to address challenges in HIV cure by delivering physicochemically diverse agents for combination therapy or targeting HIV reservoir sites. We also review nanocarrier-based gene delivery and immunotherapy used in cancer treatment but may have potential applications in HIV cure.

Barriers and strategies to achieve a cure for HIV

9 years since the report of a cure for HIV after C-C chemokine receptor type 5 Δ32 stem cell transplantation, no other case of HIV cure has been reported, despite much research. However, substantial progress has been made in understanding the biology of the latent HIV reservoir, and in measuring the amount of virus that persists after antiretroviral therapy (ART) with increasingly sophisticated approaches. This knowledge is being translated into a long pipeline of clinical trials seeking to reduce viral persistence in participants on suppressive treatment and ultimately to allow safe cessation of ART. In this Review, we discuss the main barriers preventing the development of an HIV cure, methods used to measure HIV persistence in individuals on ART, clinical strategies that aim to cure HIV, and future directions for studies in the field of HIV cure research.

Tat inhibition by didehydro-Cortistatin A promotes heterochromatin formation at the HIV-1 long terminal repeat

BACKGROUND

Transcription from the integrated HIV-1 promoter is directly governed by its chromatin environment, and the nucleosome-1 downstream from the transcription start site directly impedes transcription from the HIV-1 promoter. The HIV-1 Tat protein regulates the passage from viral latency to active transcription by binding to the viral mRNA hairpin (TAR) and recruiting transcriptional factors to promote transcriptional elongation. The Tat inhibitor didehydro-Cortistatin A (dCA) inhibits transcription and overtime, the lack of low-grade transcriptional events, triggers epigenetic changes at the latent loci that "lock" HIV transcription in a latent state.

RESULTS

Here we investigated those epigenetic changes using multiple cell line models of HIV-1 latency and active transcription. We demonstrated that dCA treatment does not alter the classic nucleosome positioning at the HIV-1 promoter, but promotes tighter nucleosome/DNA association correlating with increased deacetylated H3 occupancy at nucleosome-1. Recruitment of the SWI/SNF chromatin remodeling complex PBAF, necessary for Tat-mediated transactivation, is also inhibited, while recruitment of the repressive BAF complex is enhanced. These results were supported by loss of RNA polymerase II recruitment on the HIV genome, even during strong stimulation with latency-reversing agents. No epigenetic changes were detected in cell line models of latency with Tat-TAR incompetent proviruses confirming the specificity of dCA for Tat.

CONCLUSIONS

We characterized the dCA-mediated epigenetic signature on the HIV genome, which translates into potent blocking effects on HIV expression, further strengthening the potential of Tat inhibitors in "block-and-lock" functional cure approaches.

STING agonists activate latently infected cells and enhance SIV-specific responses ex vivo in naturally SIV controlled cynomolgus macaques

To achieve a functional cure for HIV, treatment regimens that eradicate latently HIV-infected cells must be established. For this, many groups have attempted to reactivate latently-infected cells to induce cytopathic effects and/or elicit cytotoxic T lymphocyte (CTL)/NK cell-mediated immune responses to kill these cells. We believe that not only the reactivation of latently-infected cells, but also the induction of strong CTL responses, would be required for this. Here, we used typical immune activators that target pattern recognition receptors (PRRs). For our experimental model, we identified eight SIV-infected cynomolgus monkeys that became natural controllers of viremia. Although plasma viral loads were undetectable, we could measure SIV-DNA by qPCR in peripheral blood mononuclear cells (PBMCs). Using these PBMCs, we screened 10 distinct PRR ligands to measure IFN-α and IFN-γ production. Among these, STING ligands, cGAMP and c-di-AMP, and the TLR7/8 agonist R848 markedly increased cytokine levels. Both R848 and STING ligands could reactivate latently-infected cells in both cynomolgus monkeys and human PBMCs in vitro. Furthermore, c-di-AMP increased the frequency of SIV Gag-specific CD8⁺ T cells including polyfunctional CD8⁺ T cells, as compared to that in untreated control or R848-treated cells. Together, STING ligands might be candidates for HIV treatment.

Histone deacetylase inhibitors induce complex host responses that contribute to differential potencies of these compounds in HIV reactivation

Histone deacetylase (HDAC) inhibitors (HDACis) have been widely tested in clinical trials for their ability to reverse HIV latency but have yielded only limited success. One HDACi, suberoylanilide hydroxamic acid (SAHA), exhibits off-target effects on host gene expression predicted to interfere with induction of HIV transcription. Romidepsin (RMD) has higher potency and specificity for class I HDACs implicated in maintaining HIV provirus in the latent state. More robust HIV reactivation has indeed been achieved with RMD use ex vivo than with SAHA; however, reduction of viral reservoir size has not been observed in clinical trials. Therefore, using RNA-Seq, we sought to compare the effects of SAHA and RMD on gene expression in primary CD4+ T cells. Among the genes whose expression was modulated by both HDACi agents, we identified genes previously implicated in HIV latency. Two genes, SMARCB1 and PARP1, whose modulation by SAHA and RMD is predicted to inhibit HIV reactivation, were evaluated in the major maturation subsets of CD4+ T cells and were consistently either up- or down-regulated by both HDACi compounds. Our results indicate that despite having different potencies and HDAC specificities, SAHA and RMD modulate an overlapping set of genes, implicated in HIV latency regulation. Some of these genes merit exploration as additional targets to improve the therapeutic outcomes of "shock and kill" strategies. The overall complexity of HDACi-induced responses among host genes with predicted stimulatory or inhibitory effects on HIV expression likely contributes to differential HDACi potencies and dictates the outcome of HIV reactivation.

Identification of isoform-selective hydroxamic acid derivatives that potently reactivate HIV from latency

OBJECTIVES

Current antiretroviral therapy can suppress HIV replication, increase CD4 count and result in increased lifespan. However, it cannot eradicate the virus due to the presence of latent provirus in cellular reservoirs, such as resting CD4+ T cells. Using combination latency-reversing agents to shock the virus out of latency for elimination through immune clearance or viral cytopathic effect is one of the most promising strategies for HIV eradication. Specifically, recent evidence shows that isoform-selective histone deacetylase inhibitors may be more effective than their non-selective counterparts. Therefore, identification and characterisation of new isoform-selective compounds are of prime importance. Here, we sought to determine the ability of two new isoform-targeted hydroxamic acid derivatives to reactivate HIV from latency.

METHODS

We used cell lines and infected primary resting CD4+ T cells. These were treated with these compounds with HIV reactivation measured using fluorescence-activated cell sorting, Western blots and luciferase luminescence. Isoform selectivity and acetylation of the HIV promoter were measured by Western blotting and chromatic immunoprecipitation.

RESULTS AND CONCLUSIONS

The two new hydroxamic acid derivatives, MC2625 and MC1742, potently reactivate HIV from latency. These compounds are isoform-selective histone deacetylate inhibitors that increase the levels of histone acetylation at the HIV promoter. In addition, they synergise effectively with the protein kinase C modulators bryostatin-1 and INDY, an inhibitor of the dual-specificity tyrosine phosphorylation regulated kinase 1A. We conclude that the combinations of new hydroxamic acid derivatives and bryostatin-1 or INDY could be a new tool for HIV reactivation in the cure efforts.