Peripheral Vγ9Vδ2 T Cells Are a Novel Reservoir of Latent HIV Infection

Cell and gene therapy strategies to eradicate HIV reservoirs

PURPOSE OF REVIEW

Highly active antiretroviral treatment has dramatically improved the prognosis for people living with HIV by preventing AIDS-related morbidity and mortality through profound suppression of viral replication. However, a long-lived viral reservoir persists in latently infected cells that harbor replication-competent HIV genomes. If therapy is discontinued, latently infected memory cells inevitably reactivate and produce infectious virus, resulting in viral rebound. The reservoir is the biggest obstacle to a cure of HIV.

RECENT FINDINGS

This review summarizes significant advances of the past year in the development of cellular and gene therapies for HIV cure. In particular, we highlight work done on suppression or disruption of HIV coreceptors, vectored delivery of antibodies and antibody-like molecules, T-cell therapies and HIV genome disruption.

SUMMARY

Several recent advancements in cellular and gene therapies have emerged at the forefront of HIV cure research, potentially having broad implications for the future of HIV treatment.

SLDAssay: A software package and web tool for analyzing limiting dilution assays

Serial limiting dilution (SLD) assays are used in many areas of infectious disease related research. This paper presents SLDAssay, a free and publicly available R software package and web tool for analyzing data from SLD assays. SLDAssay computes the maximum likelihood estimate (MLE) for the concentration of target cells, with corresponding exact and asymptotic confidence intervals. Exact and asymptotic goodness of fit p-values, and a bias-corrected (BC) MLE are also provided. No other publicly available software currently implements the BC MLE or the exact methods. For validation of SLDAssay, results from Myers et al. (1994) are replicated. Simulations demonstrate the BC MLE is less biased than the MLE. Additionally, simulations demonstrate that exact methods tend to give better confidence interval coverage and goodness-of-fit tests with lower type I error than the asymptotic methods. Additional advantages of using exact methods are also discussed.

Assessment of the HIV-1 reservoir in CD4+ regulatory T cells by a Droplet Digital PCR based approach

The relative contribution of regulatory T cells (Treg) as reservoir of HIV-1 in patients on chronic antiretroviral therapy is unclear to date. The aim of the current study was to assess the total HIV DNA burden and replication competent viral reservoir in Treg in comparison to central and effector memory cells (Tcm and Tem). Peripheral blood mononuclear cells were obtained from 10 HIV patients treated with antiretroviral therapy. Droplet Digital PCR (ddPCR) was used to quantify total HIV DNA loads in FACS-sorted CD4+ Treg (CD25+CD127lo) as compared to Tcm (CD45RO+CCR7+) and Tem (CD45RO+CCR7-). In contrast to earlier reports, no significant difference was found in total HIV DNA burden associated with Treg when compared to Tem and Tcm cells. In a subset of patients, quantitative viral outgrowth assays were also performed, using novel ddPCR based readout to quantify frequencies of Treg harboring replication competent virus.

Adoptive transfer of aminobisphonate-expanded Vγ9Vδ2+ T cells does not control HIV replication in a humanized mouse model

AIM

Vγ9Vδ2 γδ T cells have effector potential against several cancers and infectious agents. Whether these cells control HIV replication was tested in humanized mouse model.

METHODS

NOD SCID gamma mice engrafted with human peripheral blood mononuclear cells (PBMCs) and infected with HIVBAL were treated with zoledronate-expanded Vγ9Vδ2 T cells either alone or in combination with an anti-HIV envelope antibody b12.

RESULTS

Severe depletion of CD4+CCR5+ T cells was observed in PBMCs of all infected mice. HIV plasma p24 levels were comparable in all infected groups with no decrease in plasma viremia achieved by adoptive transfer of cells.

CONCLUSION

Autologous transfer of ex vivo expanded Vγ9Vδ2 T cells may not be a successful treatment choice for controlling HIV replication in vivo.

Are T cells the only HIV-1 reservoir?

Current antiretroviral therapies have improved the duration and quality of life of people living with HIV-1. However, viral reservoirs impede complete eradication of the virus. Although there are many strategies to eliminate infectious virus, the most actively pursued are latency reversing agents in conjunction with immune modulation. This strategy, known as “shock and kill”, has been tested primarily against the most widely recognized HIV-1 latent reservoir found in resting memory CD4+ T cells. This is in part because of the dearth of conclusive evidence about the existence of non-T cell reservoirs. Studies of non-T cell reservoirs have been difficult to interpret because of technical and biological issues that have hampered a better understanding. This review considers the current knowledge of non-T cell reservoirs, the challenges encountered in a better understanding of these populations, and their implications for HIV-1 cure research.

Current views on HIV-1 latency, persistence, and cure

HIV-1 infection cannot be cured as it persists in latently infected cells that are targeted neither by the immune system nor by available therapeutic approaches. Consequently, a lifelong therapy suppressing only the actively replicating virus is necessary. The latent reservoir has been defined and characterized in various experimental models and in human patients, allowing research and development of approaches targeting individual steps critical for HIV-1 latency establishment, maintenance, and reactivation. However, additional mechanisms and processes driving the remaining low-level HIV-1 replication in the presence of the suppressive therapy still remain to be identified and targeted. Current approaches toward HIV-1 cure involve namely attempts to reactivate and purge HIV latently infected cells (so-called "shock and kill" strategy), as well as approaches involving gene therapy and/or gene editing and stem cell transplantation aiming at generation of cells resistant to HIV-1. This review summarizes current views and concepts underlying different approaches aiming at functional or sterilizing cure of HIV-1 infection.

Latency reversal and viral clearance to cure HIV-1

Research toward a cure for human immunodeficiency virus type 1 (HIV-1) infection has joined prevention and treatment efforts in the global public health agenda. A major approach to HIV eradication envisions antiretroviral suppression, paired with targeted therapies to enforce the expression of viral antigen from quiescent HIV-1 genomes, and immunotherapies to clear latent infection. These strategies are targeted to lead to viral eradication--a cure for AIDS. Paired testing of latency reversal and clearance strategies has begun, but additional obstacles to HIV eradication may emerge. Nevertheless, there is reason for optimism that advances in long-acting antiretroviral therapy and HIV prevention strategies will contribute to efforts in HIV cure research and that the implementation of these efforts will synergize to markedly blunt the effect of the HIV pandemic on society.

Ageing and inflammation in patients with HIV infection

Nowadays, HIV⁺ patients have an expected lifespan that is only slightly shorter than healthy individuals. For this reason, along with the fact that infection can be acquired at a relatively advanced age, the effects of ageing on HIV⁺ people have begun to be evident. Successful anti-viral treatment is, on one hand, responsible for the development of side effects related to drug toxicity; on the other hand, it is not able to inhibit the onset of several complications caused by persistent immune activation and chronic inflammation. Therefore, patients with a relatively advanced age, i.e. aged more than 50 years, can experience pathologies that affect much older citizens. HIV⁺ individuals with non-AIDS-related complications can thus come to the attention of clinicians because of the presence of neurocognitive disorders, cardiovascular diseases, metabolic syndrome, bone abnormalities and non-HIV-associated cancers. Chronic inflammation and immune activation, observed typically in elderly people and defined as 'inflammaging', can be present in HIV⁺ patients who experience a type of premature ageing, which affects the quality of life significantly. This relatively new condition is extremely complex, and important factors have been identified as well as the traditional behavioural risk factors, e.g. the toxicity of anti-retroviral treatments and the above-mentioned chronic inflammation leading to a functional decline and a vulnerability to injury or pathologies. Here, we discuss the role of inflammation and immune activation on the most important non-AIDS-related complications of chronic HIV infection, and the contribution of aging per se to this scenario.

HIV-1 Reservoirs During Suppressive Therapy

The introduction of antiretroviral therapy (ART) 20 years ago has dramatically reduced morbidity and mortality associated with HIV-1. Initially there was hope that ART would be curative, but it quickly became clear that even though ART was able to restore CD4(+) T cell counts and suppress viral loads below levels of detection, discontinuation of treatment resulted in a rapid rebound of infection. This is due to persistence of a small reservoir of latently infected cells with a long half-life, which necessitates life-long ART. Over the past few years, significant progress has been made in defining and characterizing the latent reservoir of HIV-1, and here we review how understanding the latent reservoir during suppressive therapy will lead to significant advances in curative approaches for HIV-1.

Measuring the latent reservoir in vivo

Current efforts toward achieving a cure for HIV are focused on developing strategies to eliminate latently infected CD4+ T cells, which represent the major barrier to virus eradication. Sensitive, precise, and practical assays that can reliably characterize and measure this HIV reservoir and can reliably measure the impact of a candidate treatment strategy are essential. PCR-based procedures for detecting integrated HIV DNA will overestimate the size of the reservoir by detecting replication-incompetent proviruses; however, viral outgrowth assays underestimate the size of the reservoir. Here, we describe the attributes and limitations of current procedures for measuring the HIV reservoir. Characterizing their relative merits will require rigorous evaluation of their performance characteristics (sensitivity, specificity, reproducibility, etc.) and their relationship to the results of clinical studies.

HIV reservoirs: what, where and how to target them

One of the main challenges in the fight against HIV infection is to develop strategies that are able to eliminate the persistent viral reservoir that harbours integrated, replication-competent provirus within host cellular DNA. This reservoir is resistant to antiretroviral therapy (ART) and to clearance by the immune system of the host; viruses originating from this reservoir lead to rebound viraemia once treatment is stopped, giving rise to new rounds of infection. Several studies have focused on elucidating the cells and tissues that harbour persistent virus, the true size of the reservoir and how best to target it, but these topics are the subject of ongoing debate. In this Viewpoint article, several experts in the field discuss the constitution of the viral reservoir, how best to measure it and the best ways to target this source of persistent infection.