HIV therapeutic vaccines: moving towards a functional cure

Decoupling HIV-1 antiretroviral drug inhibition from plasma antibody activity to evaluate broadly neutralizing antibody therapeutics and vaccines

The development of broadly neutralizing antibody (bnAb)-based therapeutic HIV-1 vaccines and cure concepts depends on monitoring bnAb plasma activity in people with HIV (PWH) on suppressive antiretroviral therapy (ART). To enable this, analytical strategies must be defined to reliably distinguish antibody-based neutralization from drug inhibition. Here, we explore strategies that either utilize drug-resistant viruses or remove drugs from plasma. We develop ART-DEX (ART dissociation and size exclusion), an approach which quantitatively separates drugs from plasma proteins following pH-triggered release allowing accurate definition of antibody-based neutralization. We demonstrate that ART-DEX, alone or combined with ART-resistant viruses, provides a highly effective and scalable means of assessing antibody neutralization during ART. Implementation of ART-DEX in standard neutralization protocols should be considered to enhance the analytical capabilities of studies evaluating bnAb therapeutics and therapeutic vaccines, furthering the development of advanced ART and HIV-1 cure strategies.

Engineered dendritic cells-derived exosomes harboring HIV-1 Nefmut-Tat fusion protein and heat shock protein 70: A promising HIV-1 safe vaccine candidate

Antigen presenting cells (APCs)-derived exosomes are nano-vesicles that can induce antigen-specific T cell responses, and possess therapeutic effects in clinical settings. Moreover, dendritic cells (DCs)-based vaccines have been developed to combat human immunodeficiency virus-1 (HIV-1) infection in preclinical and clinical trials. We investigated the immunostimulatory effects (B- and T-cells activities) of DCs- and exosomes-based vaccine constructs harboring HIV-1 Nefmut-Tat fusion protein as an antigen candidate and heat shock protein 70 (Hsp70) as an adjuvant in mice. The modified DCs and engineered exosomes harboring Nefmut-Tat protein or Hsp70 were prepared using lentiviral vectors compared to electroporation, characterized and evaluated by in vitro and in vivo immunological tests. Our data indicated that the engineered exosomes induced high levels of total IgG, IgG2a, IFN-γ, TNF-α and Granzyme B. Moreover, co-injection of exosomes harboring Hsp70 could significantly increase the secretion of antibodies, cytokines and Granzyme B. The highest levels of IFN-γ and TNF-α were observed in exosomes harboring Nefmut-Tat combined with exosomes harboring Hsp70 (Exo-Nefmut-Tat + Exo-Hsp70) regimen after single-cycle replicable (SCR) HIV-1 exposure. Generally, Exo-Nefmut-Tat + Exo-Hsp70 regimen can be considered as a promising safe vaccine candidate due to high T-cells (Th1 and CTL) activity and its maintenance against SCR HIV-1 exposure.

Effects of Anesthesia on Cerebral Blood Flow and Functional Connectivity of Nonhuman Primates

Nonhuman primates (NHPs) are the closest living relatives of humans and play a critical and unique role in neuroscience research and pharmaceutical development. General anesthesia is usually required in neuroimaging studies of NHPs to keep the animal from stress and motion. However, the adverse effects of anesthesia on cerebral physiology and neural activity are pronounced and can compromise the data collection and interpretation. Functional connectivity is frequently examined using resting-state functional MRI (rsfMRI) to assess the functional abnormality in the animal brain under anesthesia. The fMRI signal can be dramatically suppressed by most anesthetics in a dose-dependent manner. In addition, rsfMRI studies may be further compromised by inter-subject variations when the sample size is small (as seen in most neuroscience studies of NHPs). Therefore, proper use of anesthesia is strongly demanded to ensure steady and consistent physiology maintained during rsfMRI data collection of each subject. The aim of this review is to summarize typical anesthesia used in rsfMRI scans of NHPs and the effects of anesthetics on cerebral physiology and functional connectivity. Moreover, the protocols with optimal rsfMRI data acquisition and anesthesia procedures for functional connectivity study of macaque monkeys are introduced.

New Approaches to Dendritic Cell-Based Therapeutic Vaccines Against HIV-1 Infection

Due to the success of combined antiretroviral therapy (cART) in recent years, the pathological outcome of Human Immunodeficiency Virus type 1 (HIV-1) infection has improved substantially, achieving undetectable viral loads in most cases. Nevertheless, the presence of a viral reservoir formed by latently infected cells results in patients having to maintain treatment for life. In the absence of effective eradication strategies against HIV-1, research efforts are focused on obtaining a cure. One of these approaches is the creation of therapeutic vaccines. In this sense, the most promising one up to now is based on the establishing of the immunological synapse between dendritic cells (DCs) and T lymphocytes (TL). DCs are one of the first cells of the immune system to encounter HIV-1 by acting as antigen presenting cells, bringing about the interaction between innate and adaptive immune responses mediated by TL. Furthermore, TL are the end effector, and their response capacity is essential in the adaptive elimination of cells infected by pathogens. In this review, we summarize the knowledge of the interaction between DCs with TL, as well as the characterization of the specific T-cell response against HIV-1 infection. The use of nanotechnology in the design and improvement of vaccines based on DCs has been researched and presented here with a special emphasis.

Benefits of antiretroviral therapy initiation during acute HIV infection

Objectives: In the last decade, there has been increasing scientific and legislative focus on antiretroviral treatment (ART) for all people living with HIV. Especially early ART initiation, preferably during acute HIV infection, has been named as a promising strategy, both for the individual and for the society. This article will review the benefits and possible future applications of immediate ART initiation during acute HIV infection and explore the remaining hurdles towards this strategy.Results: On an individual level, initiation of ART during acute HIV infection limits the viral reservoir, preserves immune function, and decreases systemic inflammation. In addition, obtaining viral suppression soon after infection can be beneficial for the society by decreasing the chance of onward HIV transmission. Reducing the transmission will reduce HIV incidence and can curtail HIV-related health expenditure. Furthermore, the favorable immunological and virological profile obtained by treating during acute HIV infection will form an ideal starting point for several HIV cure strategies.Conclusions: Initiation of ART during acute HIV infection has shown distinct benefits for the individual, for the society, and for future research on HIV cure. In order to implement this strategy, equal focus should be placed on early diagnosis.

Protection against SIV in Rhesus Macaques Using Albumin and CD4-Based Vector-Mediated Gene Transfer

Antibody-like molecules were evaluated with potent simian immunodeficiency virus (SIV) neutralizing properties (immunoadhesins) that were delivered by a recombinant adeno-associated virus (rAAV) vector in the SIV-infected rhesus macaque model. When injected intramuscularly into the host, the vector directs in vivo production of the transgenes with antibody-like binding properties that lead to serum neutralizing activity against SIV. To extend the half-life of the immunoadhesins, rhesus cluster of differentiation 4 (CD4) and a single-chain antibody (4L6) were fused with albumin molecules, and these constructs were tested in our model of SIV infection. Antibody-based immunoadhesins provided high serum neutralizing titers against the original SIV strain. CD4-based immunoadhesins provided a wider spectrum of neutralization against different SIV strains in comparison to antibody-based therapeutics and had the potential to protect against high viral challenging doses. Although the albumin-antibody fusion immunoadhesin provided strong and prolonged protection of the immunized animals against SIV challenge, the albumin-CD4 fusion altered the specificity and decreased the overall protection effectiveness of the immunoadhesin in comparison to the antibody-based molecules. Albumin-based immunoadhesins increase in vivo longevity of the immune protection; however, they present challenges likely linked to the induction of anti-immunoadhesin antibodies.

Novel Approaches Towards a Functional Cure of HIV/AIDS

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

Measuring the Success of HIV-1 Cure Strategies

HIV-1 eradication strategies aim to achieve viral remission in the absence of antiretroviral therapy (ART). The development of an HIV-1 cure remains challenging due to the latent reservoir (LR): long-lived CD4 T cells that harbor transcriptionally silent HIV-1 provirus. The LR is stable despite years of suppressive ART and is the source of rebound viremia following therapy interruption. Cure strategies such as "shock and kill" aim to eliminate or reduce the LR by reversing latency, exposing the infected cells to clearance via the immune response or the viral cytopathic effect. Alternative strategies include therapeutic vaccination, which aims to prime the immune response to facilitate control of the virus in the absence of ART. Despite promising advances, these strategies have been unable to significantly reduce the LR or increase the time to viral rebound but have provided invaluable insight in the field of HIV-1 eradication. The development and assessment of an HIV-1 cure requires robust assays that can measure the LR with sufficient sensitivity to detect changes that may occur following treatment. The viral outgrowth assay (VOA) is considered the gold standard method for LR quantification due to its ability to distinguish intact and defective provirus. However, the VOA is time consuming and resource intensive, therefore several alternative assays have been developed to bridge the gap between practicality and accuracy. Whilst a cure for HIV-1 infection remains elusive, recent advances in our understanding of the LR and methods for its eradication have offered renewed hope regarding achieving ART free viral remission.

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.

HIV therapeutic vaccines aimed at intensifying combination antiretroviral therapy

Introduction: Although successful at suppressing HIV replication, combination antiretroviral therapy (cART) only partially restores immune functions and fails to reduce the latent HIV reservoir, thus requiring novel interventions for its intensification.Areas covered: Here are reviewed therapeutic vaccine candidates that are being developed to this goal. Among them, the Tat vaccine has been shown to promote immune restoration, including CD4+ T-cell recovery in low immunological responders, and to reduce the virus reservoirs well beyond what achieved with long-term suppressive cART.Expert opinion: The authors propose the Tat vaccine as a promising vaccine candidate for cART intensification toward HIV reservoirs depletion, functional cure, and eradication strategies, suggesting that targeting a key protein in the virus life cycle is pivotal to success.

PD-1 Expression in HIV-Specific CD8+ T cells Before Antiretroviral Therapy Is Associated With HIV Persistence

BACKGROUND

The persistence of latently infected T cells remains the principal barrier to HIV cure. Understanding how the early immune responses shape persistence of HIV on antiretroviral therapy (ART) will be fundamental for potential eradication. Here, we aimed to determine the relationship between CD8 T-cell function and phenotype before therapy and HIV persistence on ART.

METHODS

Blood samples from 29 individuals enrolled during primary HIV infection (at baseline and every 3 months up to 2 years post-ART initiation) were obtained. HIV-specific T-cell function and expression of the activation markers were evaluated before ART by flow cytometry. Cell-associated HIV DNA and unspliced (US)-RNA were quantified in purified CD4 T cells by real-time polymerase chain reaction. Data were analyzed using nonparametric statistics.

RESULTS

Elevated immune activation, dominance of monofunctional CD8 T cells, and skewed distribution of memory profile were observed before ART. After ART initiation, HIV DNA and US-RNA levels rapidly diminished, reaching a plateau by 30 weeks after ART. The proportion of baseline HIV-specific effector memory and terminal effector CD8 T cells directly correlated with HIV DNA levels at 1 year after ART. A strong positive correlation was observed between the proportion of bulk and HIV-specific PD-1 CD8 T cells measured before ART and HIV DNA at 1 year after ART.

CONCLUSIONS

A higher proportion of terminally differentiated CD8 T cells and increased PD1 expression were associated with HIV persistence on ART after treatment of primary infection. Thus, the quality of the early CD8 T-cell immune response may serve as a predictor of HIV persistence on ART.

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.

The Tat inhibitor didehydro-cortistatin A suppresses SIV replication and reactivation

The HIV-1 transactivation protein (Tat) binds the HIV mRNA transactivation responsive element (TAR), regulating transcription and reactivation from latency. Drugs against Tat are unfortunately not clinically available. We reported that didehydro-cortistatin A (dCA) inhibits HIV-1 Tat activity. In human CD4⁺ T cells isolated from aviremic individuals and in the humanized mouse model of latency, combining dCA with antiretroviral therapy accelerates HIV-1 suppression and delays viral rebound upon treatment interruption. This drug class is amenable to block-and-lock functional cure approaches, aimed at a durable state of latency. Simian immunodeficiency virus (SIV) infection of rhesus macaques (RhMs) is the best-characterized model for AIDS research. Here, we demonstrate, using in vitro and cell-based assays, that dCA directly binds to SIV Tat's basic domain. dCA specifically inhibits SIV Tat binding to TAR, but not a Tat-Rev fusion protein, which activates transcription when Rev binds to its cognate RNA binding site replacing the apical region of TAR. Tat-TAR inhibition results in loss of RNA polymerase II recruitment to the SIV promoter. Importantly, dCA potently inhibits SIV reactivation from latently infected Hut78 cells and from primary CD4⁺ T cells explanted from SIV_mac239-infected RhMs. In sum, dCA's remarkable breadth of activity encourages SIV-infected RhM use for dCA preclinical evaluation.-Mediouni, S., Kessing, C. F., Jablonski, J. A., Thenin-Houssier, S., Clementz, M., Kovach, M. D., Mousseau, G., de Vera, I.M.S., Li, C., Kojetin, D. J., Evans, D. T., Valente, S. T. The Tat inhibitor didehydro-cortistatin A suppresses SIV replication and reactivation.

Modeling the effect of tat inhibitors on HIV latency

Even in the presence of a successful combination therapy stalling the progress of AIDS, developing a cure for this disease is still an open question. One of the major steps towards a cure would be to be able to eradicate latent HIV reservoirs present in patients. During the last decade, multiple findings point to the dominant role of the viral protein Tat in the establishment of latency. Here we present a mathematical study to understand the potential role of Tat inhibitors as virus-suppressing agents. For this aim, we implemented a computational model that reproduces intracellular dynamics. Simulating an HIV-infected cell and its intracellular feedback we observed that removing Tat protein from the system via inhibitors resulted in a temporary and reversible viral suppression. In contrast, we observed that compounds that interact with Tat protein and disrupt the integrated viral genome produced a more permanent viral suppression.

Phenotype, Polyfunctionality, and Antiviral Activity of in vitro Stimulated CD8+ T-Cells From HIV+ Subjects Who Initiated cART at Different Time-Points After Acute Infection

Since anti-HIV treatment cannot cure the infection, many strategies have been proposed to eradicate the viral reservoir, which still remains as a major challenge. The success of some of these strategies will rely on the ability of HIV-specific CD8+ T-cells (CD8TC) to clear reactivated infected cells. Here, we aimed to investigate the phenotype and function of in vitro expanded CD8TC obtained from HIV+ subjects on combination antiretroviral therapy (cART), either initiated earlier (median = 3 months postinfection, ET: Early treatment) or later (median = 20 months postinfection, DT: Delayed treatment) after infection. Peripheral blood mononuclear cells from 12 DT and 13 ET subjects were obtained and stimulated with Nef and Gag peptide pools plus IL-2 for 14 days. ELISPOT was performed pre- and post-expansion. CD8TC memory/effector phenotype, PD-1 expression, polyfunctionality (CD107a/b, IFN-γ, IL-2, CCL4 (MIP-1β), and/or TNF-α production) and antiviral activity were evaluated post-expansion. Magnitude of ELISPOT responses increased after expansion by 103 times, in both groups. Expanded cells were highly polyfunctional, regardless of time of cART initiation. The memory/effector phenotype distribution was sharply skewed toward an effector phenotype after expansion in both groups although ET subjects showed significantly higher proportions of stem-cell and central memory CD8TCs. PD-1 expression was clustered in HIV-specific effector memory CD8TCs, subset that also showed the highest proportion of cytokine-producing cells. Moreover, PD-1 expression directly correlated with CD8TC functionality. Expanded CD8TCs from DT and ET subjects were highly capable of mediating antiviral activity, measured by two different assays. Antiviral function directly correlated with the proportion of fully differentiated effector cells (viral inhibition assay) as well as with CD8TC polyfunctionality and PD-1 expression (VITAL assay). In sum, we show that, despite being dampened in subjects on cART, the HIV-specific CD8TC response could be selectively stimulated and expanded in vitro, presenting a high proportion of cells able to carry-out multiple effector functions. Timing of cART initiation had an impact on the memory/effector differentiation phenotype, most likely reflecting how different periods of antigen persistence affected immune function. Overall, these results have important implications for the design and evaluation of strategies aimed at modulating CD8TCs to achieve the HIV functional cure.

Comparative analysis and generation of a robust HIV-1 DNA quantification assay

HIV-1 infection cannot be cured due to the presence of the latent reservoir (LR). Novel cure or treatment strategies, such as "shock and kill" or therapeutic vaccination, aim to reduce or eradicate the LR. Cure strategies utilise robust DNA quantification assays to measure the change in the LR in low copy scenarios. No standard assay exists, which impedes the reliable comparison of results from different therapy and vaccine trials and HIV-1 total DNA quantification methods have not been previously compared. The HIV-1 long terminal repeat (LTR) has been shown to be the best target for DNA quantification. We have analysed two HIV-1 quantification assays, both able to differentiate between the variant HIV-1 DNA forms via the use of pre-amplification and primers targeting LTR. We identify a strong correlation (r=0.9759, P<0.0001) between assays which is conserved in low copy samples (r=0.8220, P<0.0001) indicating that these assays may be used interchangeably. The RvS assay performed significantly (P=0.0021) better than the CV assay when quantifying HIV-1 total DNA in patient CD4+ T lymphocytes. Sequence analysis demonstrated that viral diversity can limit DNA quantification, however in silico analysis of the primers indicated that within the target region nucleotide miss-matches appear infrequently. Further in silico analysis using up to-date sequence information led to the improvement of primers and enabled us to establish a more broadly specific assay with significantly higher HIV-1 DNA quantification capacity in patient samples (p=0.0057, n=17).

TLR3 agonist and CD40-targeting vaccination induces immune responses and reduces HIV-1 reservoirs

Activation of HIV-1 reservoirs and induction of anti-HIV-1 T cells are critical to control HIV-1 rebound after combined antiretroviral therapy (cART). Here we evaluated in humanized mice (hu-mice) with persistent HIV-1 infection the therapeutic effect of TLR3 agonist and a CD40-targeting HIV-1 vaccine, which consists of a string of 5 highly conserved CD4+ and CD8+ T cell epitope-rich regions of HIV-1 Gag, Nef, and Pol fused to the C-terminus of a recombinant anti-human CD40 antibody (αCD40.HIV5pep). We show that αCD40.HIV5pep vaccination coadministered with poly(I:C) adjuvant induced HIV-1-specific human CD8+ and CD4+ T cell responses in hu-mice. Interestingly, poly(I:C) treatment also reactivated HIV-1 reservoirs. When administrated in therapeutic settings in HIV-1-infected hu-mice under effective cART, αCD40.HIV5pep with poly(I:C) vaccination induced HIV-1-specific CD8+ T cells and reduced the level of cell-associated HIV-1 DNA (or HIV-1 reservoirs) in lymphoid tissues. Most strikingly, the vaccination significantly delayed HIV-1 rebound after cART cessation. In summary, the αCD40.HIV5pep with poly(I:C) vaccination approach both activates replication of HIV-1 reservoirs and enhances the anti-HIV-1 T cell response, leading to a reduced level of cell-associated HIV-1 DNA or reservoirs. Our proof-of-concept study has significant implication for the development of CD40-targeting HIV-1 vaccine to enhance anti-HIV-1 immunity and reduce HIV-1 reservoirs in patients with suppressive cART.

Immune Checkpoints as the Immune System Regulators and Potential Biomarkers in HIV-1 Infection

Immune checkpoints are several co-stimulatory and inhibitory pathways that regulate T cell immune responses. Most of the discoveries about immune checkpoints were made in cancer research where inhibitory immune checkpoints cause immune exhaustion and down-regulate anti-tumor responses. In addition to cancer, immune checkpoints are exploited in chronic infectious diseases. In human immunodeficiency virus (HIV) infection, the immune checkpoint molecule called programmed cell death protein 1 (PD-1) has been determined as being a major regulatory factor for T cell exhaustion. Recent studies with antibodies blocking either PD-1 ligand 1 (PD-L1) or PD-1 show not only promising results in the enhancement of HIV-specific immune responses but even in reducing the latent HIV reservoir. Apart from the therapeutic target for a functional cure of HIV-1, immune checkpoint molecules might be used as biomarkers for monitoring disease progression and therapeutic response. In this review, we will summarize and discuss the inhibitory immune checkpoint molecules PD-1, cytotoxic T-lymphocyte-associated protein 4 (CTLA4), lymphocyte-activation gene 3 (LAG3), and T cell immunoglobulin and mucin-domain-containing-3 (TIM3) as well as the co-stimulatory molecules CD40L and CD70, including their role in immunity, with a particular focus on HIV infection, and being potential targets for a functional HIV cure.

Tackling HIV and AIDS: contributions by non-human primate models

During the past three decades, non-human primate (NHP) models have gained an increasing importance in HIV basic and translational research. In contrast to natural host models, infection of macaques with virulent simian or simian-human immunodeficiency viruses (SIV, SHIV) results in a disease that closely resembles HIV infection and AIDS. Although there is no perfect animal model, and each of the available models has its benefits and limitations, carefully designed NHP studies with selection of experimental variables have unraveled important questions of basic pathogenesis and have provided the tools to explore and screen intervention strategies. For example, NHP studies have advanced our understanding of the crucial events during early infection, and have provided proof-of-concept of antiretroviral drug treatment and prevention strategies such as pre-exposure prophylaxis (PrEP) regimes that are increasingly used worldwide, and upon overcoming further barriers of implementation, have the potential to make the next generation AIDS-free. Remaining goals include the pursuit of an effective HIV vaccine, and HIV cure strategies that would allow HIV-infected people to ultimately stop taking antiretroviral drugs. Through a reiterative process with feed-back from results of human studies, NHP models can be further validated and strengthened to advance our scientific knowledge and guide clinical trials.

Therapeutic conserved elements (CE) DNA vaccine induces strong T-cell responses against highly conserved viral sequences during simian-human immunodeficiency virus infection

HIV-specific T-cell responses play a key role in controlling HIV infection, and therapeutic vaccines for HIV that aim to improve viral control will likely need to improve on the T-cell responses induced by infection. However, in the setting of chronic infection, an effective therapeutic vaccine must overcome the enormous viral genetic diversity and the presence of pre-existing T-cell responses that are biased toward immunodominant T-cell epitopes that can readily mutate to evade host immunity and thus potentially provide inferior protection. To address these issues, we investigated a novel, epidermally administered DNA vaccine expressing SIV capsid (p27^Gag) homologues of highly conserved elements (CE) of the HIV proteome in macaques experiencing chronic but controlled SHIV infection. We assessed the ability to boost or induce de novo T-cell responses against the conserved but immunologically subdominant CE epitopes. Two groups of animals were immunized with either the CE DNA vaccine or a full-length SIV p57^gag DNA vaccine. Prior to vaccination, CE responses were similar in both groups. The full-length p57^gag DNA vaccine, which contains the CE, increased overall Gag-specific responses but did not increase CE responses in any animals (0/4). In contrast, the CE DNA vaccine increased CE responses in all (4/4) vaccinated macaques. In SIV infected but unvaccinated macaques, those that developed stronger CE-specific responses during acute infection exhibited lower viral loads. We conclude that CE DNA vaccination can re-direct the immunodominance hierarchy towards CE in the setting of attenuated chronic infection and that induction of these responses by therapeutic vaccination may improve immune control of HIV.

Postvaccination C-Reactive Protein and C5/gp41732-744 Antibody Level Fold-Changes Over Baseline Are Independent Predictors of Therapeutic HIV Vaccine Effect in a Phase 2 Clinical Study of Vacc-4x

Therapeutic vaccination has the potential to contribute to functional HIV cure strategies. However, to show functional HIV cure, study participants must be taken off combination antiretroviral therapy (cART). The availability of suitable biomarkers that can predict viral load (VL) or CD4 count outcomes following therapeutic HIV vaccination would reduce the risks associated with cART interruption in such studies. This report sought to determine baseline and postvaccination biomarker predictors of vaccine effect (VE) on VL and CD4 counts following cART interruption in a double-blind, randomized phase 2 study of the peptide-based therapeutic HIV vaccine, Vacc-4x (n = 93), versus placebo (n = 43). Antibody responses to a novel envelope glycoprotein antigen, C5/gp41^732-744, and three safety marker measurements [C-reactive protein (CRP), white blood cell, and lactate dehydrogenase] were considered. Interaction tests in univariate and multivariate linear regression models were used to estimate the effect of biomarkers on VE, defined as the VL or CD4 count difference in Vacc-4x versus placebo groups. The reported q-values (considered significant for hypothesis-generating purposes if ≤0.2) accounted for multiple comparisons using the false discovery rate method. Data were analyzed from all available 58 Vacc-4x and 25 placebo recipients before cART resumption. Lower postvaccination fold-change over baseline of CRP concentration (interaction p- (q-) value = 0.005 (0.11) for VL) and higher fold-change of anti-C5/gp41^732-744 antibody levels (0.005 (0.11) for VL and 0.009 (0.20) for CD4) were associated with Vacc-4x benefit. These findings suggest potential roles for inflammation and immune activation markers in predicting therapeutic HIV VE.

Perspectives for immunotherapy: which applications might achieve an HIV functional cure?

The major advances achieved in devising successful combined antiretroviral therapy (cART) have enabled the sustained control of HIV replication. However, this is associated with costly lifelong treatment, partial immune restoration, chronic inflammation and persistent viral reservoirs. In this context, new therapeutic strategies deserve investigation as adjuncts to cART so as to potentiate immune responses that are capable of completely containing HIV pathogenicity, particularly if cART is discontinued. This may seem a dauntingly high hurdle given the results to date. This review outlines the key research efforts that have recently resurrected immunotherapeutic options, and some of the approaches tested to date. These areas include promising cytokines or vaccine strategies, using different viral or non-viral vectors based on polyvalent “mosaic” antigens and highly conserved HIV envelope peptides, broadly neutralizing antibodies or new properties of antibodies to improve the control of immune system homeostasis. These novel immunotherapeutic strategies appear promising per se, or in combination with TLR-agonists in order to bypass the complexity of the interplay between immune activation, massive CD4⁺ T-cell loss and viral persistence.

Delayed differentiation of potent effector CD8+ T cells reducing viremia and reservoir seeding in acute HIV infection

CD8⁺ T cells play a critical role in controlling HIV viremia and could be important in reducing HIV-infected cells in approaches to eradicate HIV. The simian immunodeficiency virus model provided the proof of concept for a CD8⁺ T cell-mediated reservoir clearance but showed conflicting evidence on the role of these cells to eliminate HIV-infected cells. In humans, HIV-specific CD8⁺ T cell responses have not been associated with a reduction of the HIV-infected cell pool in vivo. We studied HIV-specific CD8⁺ T cells in the RV254 cohort of individuals initiating ART in the earliest stages of acute HIV infection (AHI). We showed that the HIV-specific CD8⁺ T cells generated as early as AHI stages 1 and 2 before peak viremia are delayed in expanding and acquiring effector functions but are endowed with higher memory potential. In contrast, the fully differentiated HIV-specific CD8⁺ T cells at peak viremia in AHI stage 3 were more prone to apoptosis but were associated with a steeper viral load decrease after ART initiation. Their capacity to persist in vivo after ART initiation correlated with a lower HIV DNA reservoir. These findings demonstrate that HIV-specific CD8⁺ T cell magnitude and differentiation are delayed in the earliest stages of infection. These results also demonstrate that potent HIV-specific CD8⁺ T cells contribute to the reduction of the pool of HIV-producing cells and the HIV reservoir seeding in vivo and provide the rationale to design interventions aiming at inducing these potent responses to cure HIV infection.

Novel Latency Reversal Agents for HIV-1 Cure

Antiretroviral therapy (ART) has rendered HIV-1 infection a treatable illness; however, ART is not curative owing to the persistence of replication-competent, latent proviruses in long-lived resting T cells. Strategies that target these latently infected cells and allow immune recognition and clearance of this reservoir will be necessary to eradicate HIV-1 in infected individuals. This review describes current pharmacologic approaches to reactivate the latent reservoir so that infected cells can be recognized and targeted, with the ultimate goal of achieving an HIV-1 cure.

Landscape review of current HIV 'kick and kill' cure research - some kicking, not enough killing

BACKGROUND

Current antiretroviral therapy (ART) used to treat human immunodeficiency virus (HIV) patients is life-long because it only suppresses de novo infections. Recent efforts to eliminate HIV have tested the ability of a number of agents to reactivate ('Kick') the well-known latent reservoir. This approach is rooted in the assumption that once these cells are reactivated the host's immune system itself will eliminate ('Kill') the virus. While many agents have been shown to reactivate large quantities of the latent reservoir, the impact on the size of the latent reservoir has been negligible. This suggests that the immune system is not sufficient to eliminate reactivated reservoirs. Thus, there is a need for more emphasis on 'kill' strategies in HIV cure research, and how these might work in combination with current or future kick strategies.

METHODS

We conducted a landscape review of HIV 'cure' clinical trials using 'kick and kill' approaches. We identified and reviewed current available clinical trial results in human participants as well as ongoing and planned clinical trials. We dichotomized trials by whether they did not include or include a 'kill' agent. We extracted potential reasons why the 'kill' is missing from current 'kick and kill' strategies. We subsequently summarized and reviewed current 'kill' strategies have entered the phase of clinical trial testing in human participants and highlighted those with the greatest promise.

RESULTS

The identified 'kick' trials only showed promise on surrogate measures activating latent T-cells, but did not show any positive effects on clinical 'cure' measures. Of the 'kill' agents currently being tested in clinical trials, early results have shown small but meaningful proportions of participants remaining off ART for several months with broadly neutralizing antibodies, as well as agents for regulating immune cell responses. A similar result was also recently observed in a trial combining a conventional 'kick' with a vaccine immune booster ('kill').

CONCLUSION

While an understanding of the efficacy of each individual component is crucial, no single 'kick' or 'kill' agent is likely to be a fully effective cure. Rather, the solution is likely found in a combination of multiple 'kick and kill' interventions.

Kill: boosting HIV-specific immune responses

PURPOSE OF REVIEW

Increasing evidence suggests that purging the latent HIV reservoir in virally suppressed individuals will require both the induction of viral replication from its latent state and the elimination of these reactivated HIV-infected cells ('Shock and Kill' strategy). Boosting potent HIV-specific CD8 T cells is a promising way to achieve an HIV cure.

RECENT FINDINGS

Recent studies provided the rationale for developing immune interventions to increase the numbers, function and location of HIV-specific CD8 T cells to purge HIV reservoirs. Multiple approaches are being evaluated including very early suppression of HIV replication in acute infection, adoptive cell transfer, therapeutic vaccination or use of immunomodulatory molecules. New assays to measure the killing and antiviral function of induced HIV-specific CD8 T cells have been developed to assess the efficacy of these new approaches. The strategies combining HIV reactivation and immunobased therapies to boost HIV-specific CD8 T cells can be tested in in-vivo and in-silico models to accelerate the design of new clinical trials.

SUMMARY

New immunobased strategies are explored to boost HIV-specific CD8 T cells able to purge the HIV-infected cells with the ultimate goal of achieving spontaneous control of viral replication without antiretroviral treatment.

Monocytes Phenotype and Cytokine Production in Human Immunodeficiency Virus-1 Infected Patients Receiving a Modified Vaccinia Ankara-Based HIV-1 Vaccine: Relationship to CD300 Molecules Expression

A modified vaccinia Ankara-based HIV-1 vaccine clade B (MVA-B) has been tested for safety and immunogenicity in low-risk human immunodeficiency virus (HIV)-uninfected individuals and as a therapeutic vaccine in HIV-1-infected individuals on combined antiretroviral therapy (cART). As a therapeutic vaccine, MVA-B was safe and broadly immunogenic; however, patients still showed a viral rebound upon treatment interruption. Monocytes are an important part of the viral reservoir and several studies suggest that they are partly responsible for the chronic inflammation observed in cART-treated HIV-infected people. The CD300 family of receptors has an important role in several diseases, including viral infections. Monocytes express CD300a, c, e, and f molecules and lipopolysaccharide (LPS) and other stimuli regulate their expression. However, the expression and function of CD300 receptors on monocytes in HIV infection is still unknown. In this work, we investigated for the first time the expression of CD300 molecules and the cytokine production in response to LPS on monocytes from HIV-1-infected patients before and after vaccination with MVA-B. Our results showed that CD300 receptors expression on monocytes from HIV-1-infected patients correlates with markers of HIV infection progression and immune inflammation. Specifically, we observed a positive correlation between the expression of CD300e and CD300f receptors on monocytes with the number of CD4+ T cells of HIV-1-infected patients before vaccination. We also saw a positive correlation between the expression of the inhibitory receptor CD300f and the expression of CD163 on monocytes from HIV-1-infected individuals before and after vaccination. In addition, monocytes exhibited a higher cytokine production in response to LPS after vaccination, almost at the same levels of monocytes from healthy donors. Furthermore, we also described a correlation in the expression of CD300e and CD300f receptors with TNF-α production in response to LPS, only in monocytes of HIV-1-infected patients before vaccination. Altogether, our results describe the impact of HIV-1 and of the MVA-B vaccine in cytokine production and monocytes phenotype.

On the way to find a cure: Purging latent HIV-1 reservoirs

Introduction of cART in 1996 has drastically increased the life expectancy of people living with HIV-1. However, this treatment has not allowed cure as cessation of cART is associated with a rapid viral rebound. The main barrier to the eradication of the virus is related to the persistence of latent HIV reservoirs. Evidence is now accumulating that purging the HIV-1 reservoir might lead to a cure or a remission. The most studied strategy is the so called "shock and kill" therapy. This strategy is based on reactivation of dormant viruses from the latently-infected reservoirs (the shock) followed by the eradication of the reservoirs (the kill). This review focuses mainly on the recent advances made in the "shock and kill" therapy. We believe that a cure or a remission will come from combinatorial approaches i.e. combination of drugs to reactivate the dormant virus from all the reservoirs including the one located in sanctuaries, and combination of strategies boosting the immune system. Alternative strategies based on cell and gene therapy or based in inducing deep latency, which are evoked in this review reinforce the idea that at least a remission is attainable.

HIV/AIDS infection: The beginning of the end for today's greatest pandemic?

Recently, there have been significant advances in the fight against human immunodeficiency virus, which have increased the hopes of definitively halting its dissemination and of starting the decline of the epidemic it has caused. Transmission of the infection was drastically reduced when infected patients were given antiretroviral treatments, which boosted the diffusion of treatments to middle- and low-income countries. Global therapy coverage has doubled in recent years; meanwhile the incidence of new infections has decreased. Various curative strategies are also actively being investigated, including those aiming to induce cell resistance to the infection through gene therapy and the elimination of latent virus reservoirs. This article reviews the current situation and future developments in terms of controlling the pandemic and, eventually, curing the infection.

Immune Interventions to Eliminate the HIV Reservoir

Inducing HIV remission is a monumental challenge. A potential strategy is the "kick and kill" approach where latently infected cells are first activated to express viral proteins and then eliminated through cytopathic effects of HIV or immune-mediated killing. However, pre-existing immune responses to HIV cannot eradicate HIV infection due to the presence of escape variants, inadequate magnitude, and breadth of responses as well as immune exhaustion. The two major approaches to boost immune-mediated elimination of infected cells include enhancing cytotoxic T lymphocyte mediated killing and harnessing antibodies to eliminate HIV. Specific strategies include increasing the magnitude and breadth of T cell responses through therapeutic vaccinations, reversing the effects of T cell exhaustion using immune checkpoint inhibition, employing bispecific T cell targeting immunomodulatory proteins or dual-affinity re-targeting molecules to direct cytotoxic T lymphocytes to virus-expressing cells and broadly neutralizing antibody infusions. Methods to steer immune responses to tissue sites where latently infected cells are located need to be further explored. Ultimately, strategies to induce HIV remission must be tolerable, safe, and scalable in order to make a global impact.

Clinical Use of DNA Vaccines

Owing to their unique advantages in simplicity, safety, scalability, and possibility of repeated administrations, DNA vaccines represent an appealing and competitive immunization approach for a wide array of conditions, including but not limited to infectious diseases and cancer immunotherapy. Despite the exciting efficacy observed in preclinical studies, DNA vaccines have faced challenges in inducing strong immune responses in humans. This unexpected poor immunogenicity has severely hampered the translation of DNA vaccines from investigational medications to licensed products. To overcome this obstacle, tremendous efforts have been made to improve antigen expression and enhance immunogenicity. Among these endeavors, in vivo DNA electroporation (EP) has proved to be a breakthrough technology capable of mediating efficient DNA uptake and resulting in enhanced antigen expression and vaccine immunogenicity. EP-mediated DNA delivery has become one of the major platforms used in clinical trials to evaluate DNA vaccines in humans. In this chapter, in addition to EP delivery, other progress made in DNA vaccine development including plasmid optimization, antigen design, and immunologic adjuvants is also reviewed. Finally, the use of DNA vaccines in the context of clinical trials for infectious diseases and cancer immunotherapy is summarized. Specifically, the strategies that allow DNA vaccines to overcome antigenic diversity for viral infection and break immune tolerance for cancer therapy are explored. Based on the advantages of DNA vaccines and the immense progress, led by the electroporation-mediated vaccine delivery, DNA vaccines appear to have the potential to fundamentally transform the vaccine field, providing important benefits for preventing and curing diseases.

Clinical challenges in HIV/AIDS: Hints for advancing prevention and patient management strategies

Acquired immune deficiency syndrome has been one of the most devastating epidemics of the last century. The current estimate for people living with the HIV is 36.9 million. Today, despite availability of potent and safe drugs for effective treatment, lifelong therapy is required for preventing HIV re-emergence from a pool of latently infected cells. However, recent evidence show the importance to expand HIV testing, to offer antiretroviral treatment to all infected individuals, and to ensure retention through all the cascade of care. In addition, circumcision, pre-exposure prophylaxis, and other biomedical tools are now available for included in a comprehensive preventive package. Use of all the available tools might allow cutting the HIV transmission in 2030. In this article, we review the status of the epidemic, the latest advances in prevention and treatment, the concept of treatment as prevention and the challenges and opportunities for the HIV cure agenda.

Antiretroviral Drugs for Treatment and Prevention of HIV Infection in Adults: 2016 Recommendations of the International Antiviral Society-USA Panel

IMPORTANCE

New data and therapeutic options warrant updated recommendations for the use of antiretroviral drugs (ARVs) to treat or to prevent HIV infection in adults.

OBJECTIVE

To provide updated recommendations for the use of antiretroviral therapy in adults (aged ≥18 years) with established HIV infection, including when to start treatment, initial regimens, and changing regimens, along with recommendations for using ARVs for preventing HIV among those at risk, including preexposure and postexposure prophylaxis.

EVIDENCE REVIEW

A panel of experts in HIV research and patient care convened by the International Antiviral Society-USA reviewed data published in peer-reviewed journals, presented by regulatory agencies, or presented as conference abstracts at peer-reviewed scientific conferences since the 2014 report, for new data or evidence that would change previous recommendations or their ratings. Comprehensive literature searches were conducted in the PubMed and EMBASE databases through April 2016. Recommendations were by consensus, and each recommendation was rated by strength and quality of the evidence.

FINDINGS

Newer data support the widely accepted recommendation that antiretroviral therapy should be started in all individuals with HIV infection with detectable viremia regardless of CD4 cell count. Recommended optimal initial regimens for most patients are 2 nucleoside reverse transcriptase inhibitors (NRTIs) plus an integrase strand transfer inhibitor (InSTI). Other effective regimens include nonnucleoside reverse transcriptase inhibitors or boosted protease inhibitors with 2 NRTIs. Recommendations for special populations and in the settings of opportunistic infections and concomitant conditions are provided. Reasons for switching therapy include convenience, tolerability, simplification, anticipation of potential new drug interactions, pregnancy or plans for pregnancy, elimination of food restrictions, virologic failure, or drug toxicities. Laboratory assessments are recommended before treatment, and monitoring during treatment is recommended to assess response, adverse effects, and adherence. Approaches are recommended to improve linkage to and retention in care are provided. Daily tenofovir disoproxil fumarate/emtricitabine is recommended for use as preexposure prophylaxis to prevent HIV infection in persons at high risk. When indicated, postexposure prophylaxis should be started as soon as possible after exposure.

CONCLUSIONS AND RELEVANCE

Antiretroviral agents remain the cornerstone of HIV treatment and prevention. All HIV-infected individuals with detectable plasma virus should receive treatment with recommended initial regimens consisting of an InSTI plus 2 NRTIs. Preexposure prophylaxis should be considered as part of an HIV prevention strategy for at-risk individuals. When used effectively, currently available ARVs can sustain HIV suppression and can prevent new HIV infection. With these treatment regimens, survival rates among HIV-infected adults who are retained in care can approach those of uninfected adults.

Challenges and strategies for the eradication of the HIV reservoir

Despite the success of highly active antiretroviral therapy (HAART) for inhibiting HIV replication and improving clinical outcomes, it fails to cure infection due to the existence of a stable latent proviral reservoir in memory CD4⁺ T cells. Because of the longevity of these cells harboring transcriptionally silent proviruses, devising strategies to induce viral gene expression so the host immune response can mediate clearance of the infected cells or the cells can undergo virus-induced cell death, has been of considerable recent interest. Here, we review current knowledge of latency, and the challenges to virus induction and eradication. Novel strategies to reactivate HIV reservoirs more effectively, in combination with immunotherapy, could lead to better clearance of the latent HIV reservoir.

Some vexations that challenge viral immunology

The field of viral immunology seeks to understand mechanisms of virus-host interaction with a view of applying this knowledge to the design of effective vaccines and immunomodulators that control viral infections. This brief review discusses several areas of the field that hold substantial promise for translation, but where further work is critically required to find solutions. We emphasize that our fundamental understanding of virus-host relationships is moving in leaps and bounds, but we lag behind in applying this knowledge to the successful control of many viral infections.

The clinical applications of genome editing in HIV

HIV/AIDS has long been at the forefront of the development of gene- and cell-based therapies. Although conventional gene therapy approaches typically involve the addition of anti-HIV genes to cells using semirandomly integrating viral vectors, newer genome editing technologies based on engineered nucleases are now allowing more precise genetic manipulations. The possible outcomes of genome editing include gene disruption, which has been most notably applied to the CCR5 coreceptor gene, or the introduction of small mutations or larger whole gene cassette insertions at a targeted locus. Disruption of CCR5 using zinc finger nucleases was the first-in-human application of genome editing and remains the most clinically advanced platform, with 7 completed or ongoing clinical trials in T cells and hematopoietic stem/progenitor cells (HSPCs). Here we review the laboratory and clinical findings of CCR5 editing in T cells and HSPCs for HIV therapy and summarize other promising genome editing approaches for future clinical development. In particular, recent advances in the delivery of genome editing reagents and the demonstration of highly efficient homology-directed editing in both T cells and HSPCs are expected to spur the development of even more sophisticated applications of this technology for HIV therapy.

Status of vaccine research and development of vaccines for HIV-1

Human immunodeficiency virus (HIV) is the cause of one of the most lethal pandemics in human history, although in recent years access to highly effective anti-retroviral therapy has provided new hope worldwide. Transmission of HIV by sexual contact, childbirth and injection drug use has been reduced, but 2 million are newly infected each year, and much of the transmission is from people who do not know their status. In addition to known methods, a preventive vaccine is needed to end the pandemic. The extraordinary mutability and genetic diversity of HIV is an enormous challenge, but vaccines are being designed for broad coverage. Computer-aided design of mosaic immunogens, incorporating many epitopes from the entire genome or from conserved regions aim to induce CD8+ T cells to kill virus-infected cells or inhibit virus replication, while trimeric envelope proteins or synthetic mimics aim to induce broadly reactive neutralizing antibodies similar to those cloned from some infected patients. Induction of more potent and durable responses may require new adjuvants or replicating chimeric vectors chimeras that bear HIV genes. Passive or genetic delivery of broadly neutralizing antibodies may provide broad protection and/or lead to insights for vaccine designers. Proof-of-concept trials in non-human primates and in one human efficacy trial have provided scientific clues for a vaccine that could provide broad and durable protection against HIV. The use of vaccines to destroy HIV reservoirs as part of therapy or cure is now also being explored.

The F4/AS01B HIV-1 Vaccine Candidate Is Safe and Immunogenic, But Does Not Show Viral Efficacy in Antiretroviral Therapy-Naive, HIV-1-Infected Adults: A Randomized Controlled Trial

The impact of the investigational human immunodeficiency virus type 1 (HIV-1) F4/AS01B vaccine on HIV-1 viral load (VL) was evaluated in antiretroviral therapy (ART)-naive HIV-1 infected adults.This phase IIb, observer-blind study (NCT01218113), included ART-naive HIV-1 infected adults aged 18 to 55 years. Participants were randomized to receive 2 (F4/AS01B_2 group, N = 64) or 3 (F4/AS01B_3 group, N = 62) doses of F4/AS01B or placebo (control group, N = 64) at weeks 0, 4, and 28. Efficacy (HIV-1 VL, CD4 T-cell count, ART initiation, and HIV-related clinical events), safety, and immunogenicity (antibody and T-cell responses) were evaluated during 48 weeks.At week 48, based on a mixed model, no statistically significant difference in HIV-1 VL change from baseline was demonstrated between F4/AS01B_2 and control group (0.073 log10 copies/mL [97.5% confidence interval (CI): -0.088; 0.235]), or F4/AS01B_3 and control group (-0.096 log10 copies/mL [97.5% CI: -0.257; 0.065]). No differences between groups were observed in HIV-1 VL change, CD4 T-cell count, ART initiation, or HIV-related clinical events at intermediate timepoints. Among F4/AS01B recipients, the most frequent solicited symptoms were pain at injection site (252/300 doses), fatigue (137/300 doses), myalgia (105/300 doses), and headache (90/300 doses). Twelve serious adverse events were reported in 6 participants; 1 was considered vaccine-related (F4/AS01B_2 group: angioedema). F4/AS01B induced polyfunctional F4-specific CD4 T-cells, but had no significant impact on F4-specific CD8 T-cell and anti-F4 antibody levels.F4/AS01B had a clinically acceptable safety profile, induced F4-specific CD4 T-cell responses, but did not reduce HIV-1 VL, impact CD4 T-cells count, delay ART initiation, or prevent HIV-1 related clinical events.

Might dolutegravir be part of a functional cure for HIV?

Antiretroviral therapy (ART) has greatly decreased HIV-related morbidity and mortality. However, HIV can establish viral reservoirs that evade both the immune system and ART. Dolutegravir (DTG) is a second-generation integrase strand transfer inhibitor (INSTI) related to the first-generation INSTIs raltegravir (RAL) and elvitegravir (EVG). DTG shows a higher genetic barrier to the development of HIV-1 resistance than RAL and EVG. More interestingly, clinical resistance mutations to DTG in treatment-naïve patients have not been observed to date. This review summarizes recent studies on strategies toward a cure for HIV, explores resistance profiles of DTG, and discusses how DTG might help in finding a functional cure for HIV.

An initial examination of the potential role of T-cell immunity in protection against feline immunodeficiency virus (FIV) infection

The importance of vaccine-induced T-cell immunity in conferring protection with prototype and commercial FIV vaccines is still unclear. Current studies performed adoptive transfer of T cells from prototype FIV-vaccinated cats to partial-to-complete feline leukocyte antigen (FLA)-matched cats a day before either homologous FIVPet or heterologous-subtype pathogenic FIVFC1 challenge. Adoptive-transfer (A-T) conferred a protection rate of 87% (13 of 15, p < 0.001) against FIVPet using the FLA-matched T cells, whereas all 12 control cats were unprotected. Furthermore, A-T conferred protection rate of 50% (6 of 12, p<0.023) against FIVFC1 using FLA-matched T cells, whereas all 8 control cats were unprotected. Transfer of FLA-matched T and B cells demonstrated that T cells are needed to confer A-T protection. In addition, complete FLA-matching and addition of T-cell numbers > 13 × 10(6) cells were required for A-T protection against FIVFC1 strain, reported to be a highly pathogenic virus resistant to vaccine-induced neutralizing-antibodies. The addition of FLA-matched B cells alone was not protective. The poor quality of the anti-FIV T-cell immunity induced by the vaccine likely contributed to the lack of protection in an FLA-matched recipient against FIVFC1. The quality of the immune response was determined by the presence of high mRNA levels of cytolysin (perforin) and cytotoxins (granzymes A, B, and H) and T helper-1 cytokines (interferon-γ [IFNγ] and IL2). Increased cytokine, cytolysin and cytotoxin production was detected in the donors which conferred protection in A-T studies. In addition, the CD4(+) and CD8(+) T-cell proliferation and/or IFNγ responses to FIV p24 and reverse transcriptase increased with each year in cats receiving 1X-3X vaccine boosts over 4 years. These studies demonstrate that anti-FIV T-cell immunity induced by vaccination with a dual-subtype FIV vaccine is essential for prophylactic protection against AIDS lentiviruses such as FIV and potentially HIV-1.

HIV-specific CD8⁺ T cells and HIV eradication

After the success of combination antiretroviral therapy (cART) to treat HIV infection, the next great frontier is to cure infected persons, a formidable challenge. HIV persists in a quiescent state in resting CD4+ T cells, where the replicative enzymes targeted by cART are not active. Although low levels of HIV transcripts are detectable in these resting cells, little to no viral protein is produced, rendering this reservoir difficult to detect by the host CD8+ T cell response. However, recent advances suggest that this state of latency might be pharmacologically reversed, resulting in viral protein expression without the adverse effects of massive cellular activation. Emerging data suggest that with this approach, infected cells will not die of viral cytopathic effects, but might be eliminated if HIV-specific CD8+ T cells can be effectively harnessed. Here, we address the antiviral properties of HIV-specific CD8+ T cells and how these cells might be harnessed to greater effect toward achieving viral eradication or a functional cure.

Didehydro-Cortistatin A: a new player in HIV-therapy?

Antiretroviral therapy can effectively suppress HIV-1 infection but is ineffective against integrated proviruses. A latent viral reservoir composed of latently infected CD4(+)T cells persists under suppressive therapy, and infected individuals must remain indefinitely on antiretroviral therapy to prevent viral reactivation and propagation. Despite therapy, some degree of low-level ongoing replication is detected and transient viral reactivation may replenish the latent reservoir. An analog of the natural compound, Cortistatin A, blocks HIV-1 transcription by specifically targeting the viral transactivator, Tat. Treatment of latently infected cells with this Tat inhibitor promotes a state of deep-latency from which HIV reactivation capacity is greatly diminished. Here we discuss the use of Tat inhibitors to limit the latent reservoir to achieve a functional cure.

Evaluating the efficacy of therapeutic HIV vaccines through analytical treatment interruptions

INTRODUCTION

The development of an effective therapeutic HIV vaccine that induces immunologic control of viral replication, thereby eliminating or reducing the need for antiretroviral therapy (ART), would be of great value. Besides the obvious challenges of developing a therapeutic vaccine that would generate effective, sustained anti-HIV immunity in infected individuals is the issue of how to best assess the efficacy of vaccine candidates.

DISCUSSION

This review discusses the various outcome measures assessed in therapeutic HIV vaccine clinical trials involving individuals receiving suppressive ART, with a particular focus on the role of analytical treatment interruption (ATI) as a way to assess the virologic control induced by an immunotherapy. This strategy is critical given that there are otherwise no readily available measures to determine the ability of a vaccine-induced immune response to effectively control HIV replication. The various outcome measures that have been used to assess vaccine efficacy in published therapeutic HIV vaccine clinical trials will also be discussed. Outcome measures have included the kinetics of viral rebound, the new viral set point and changes in the size of the viral reservoir. Clinically relevant outcomes such as the CD4 decline, the time to resume therapy or the time to meet the criterion to resume therapy, the proportion of participants who resume therapy and/or the development of clinical symptoms such as acute retroviral syndrome are also measures of vaccine efficacy.

CONCLUSIONS

Given the lack of consistency between therapeutic HIV vaccine trials in how efficacy is assessed, comparing vaccines has been difficult. It would, therefore, be beneficial to determine the most clinically relevant measure for use in future studies. Other recommendations for future clinical trials also include studying compartments in addition to blood and replacing ATIs with single-copy assays in situations in which the use of an ATI is not ideal.

Challenges and Opportunities for T-Cell-Mediated Strategies to Eliminate HIV Reservoirs

HIV's ability to establish latent reservoirs of reactivation-competent virus is the major barrier to cure. "Shock and kill" methods consisting of latency-reversing agents (LRAs) followed by elimination of reactivating cells through cytopathic effects are under active development. However, the clinical efficacy of LRAs remains to be established. Moreover, recent studies indicate that reservoirs may not be reduced efficiently by either viral cytopathic or CD8(+) T-cell-mediated mechanisms. In this perspective, we highlight challenges to T-cell-mediated elimination of HIV reservoirs, including characteristics of responding T cells, aspects of the cellular reservoirs, and properties of the latent virus itself. We also discuss potential strategies to overcome these challenges by targeting the antiviral activity of T cells toward appropriate viral antigens following latency.