An HIVgp41 vaccine protects CD4 central memory T cells in SHIV-infected macaques

Antibody response against selected epitopes in the HIV-1 envelope gp41 ectodomain contributes to reduce viral burden in HIV-1 infected patients

The ectodomain of gp41 is the target of potent binding and neutralizing antibodies (NAbs) and is being explored in new strategies for antibody-based HIV vaccines. Previous studies have suggested that the W164A-3S (3S) and EC26-2A4 (EC26) peptides located in the gp41 ectodomain may be potential HIV vaccine candidates. We assessed 3S- and EC26-specific binding antibody responses and related neutralizing activity in a large panel of chronic HIV-1-infected Portuguese individuals on ART. A similar proportion of participants had antibodies binding to 3S (9.6%) and EC26 (9.9%) peptides but the level of reactivity against 3S was significantly higher compared to EC26, except in the rare patients with double peptide reactivity. The higher antigenicity of 3S was unrelated with disease stage, as assessed by CD4⁺ T cell counts, but it was directly related with plasma viral load. Most patients that were tested (89.9%, N = 268) showed tier 1 neutralizing activity, the potency being inversely associated with plasma viral load. In the subset of patients that were tested for neutralization of tier 2 isolates, neutralization breadth was inversely correlated with plasma viral load and directly correlated with CD4⁺ T cell counts. These results are consistent with a role for neutralizing antibodies in controlling viral replication and preventing the decline of CD4⁺ T lymphocytes. Importantly, in patients with 3S-specific antibodies, neutralizing titers were inversely correlated with viral RNA levels and proviral DNA levels. Moreover, patients with 3S and/or EC26-specific antibodies showed a 1.9-fold higher tier 2 neutralization score than patients without antibodies suggesting that 3S and/or EC26-specific antibodies contribute to neutralization breadth and potency in HIV-1 infected patients. Overall, these results suggest that antibodies targeting the S3 and EC26 epitopes may contribute to reduce viral burden and provide further support for the inclusion of 3S and EC26 epitopes in HIV-1 vaccine candidates.

Peptide-Based Vaccination for Antibody Responses Against HIV

HIV-1 is responsible for a global pandemic of 35 million people and continues to spread at a rate of >2 million new infections/year. It is widely acknowledged that a protective vaccine would be the most effective means to reduce HIV-1 spread and ultimately eliminate the pandemic, whereas a therapeutic vaccine might help to mitigate the clinical course of the disease and to contribute to virus eradication strategies. However, despite more than 30 years of research, we do not have a vaccine capable of protecting against HIV-1 infection or impacting on disease progression. This, in part, denotes the challenge of identifying immunogens and vaccine modalities with a reduced risk of failure in late stage development. However, progress has been made in epitope identification for the induction of broadly neutralizing antibodies. Thus, peptide-based vaccination has become one of the challenges of this decade. While some researchers reconstitute envelope protein conformation and stabilization to conserve the epitope targeted by neutralizing antibodies, others have developed strategies based on peptide-carrier vaccines with a similar goal. Here, we will review the major peptide-carrier based approaches in the vaccine field and their application and recent development in the HIV-1 field.

HIV therapeutic vaccine enhances non-exhausted CD4+ T cells in a randomised phase 2 trial

VAC-3S is a therapeutic vaccine comprising a highly conserved HIV-gp41 motif coupled with the CRM197 carrier protein. High levels of anti-3S antibodies (Abs) have been associated with improved protection of CD4⁺ T-cell survival. A previous phase 1 study demonstrated the safety of VAC-3S. This multicentre, randomised, double-blind, placebo-controlled phase 2 clinical trial enroled between January 2014 and March 2015 HIV-1-infected patients under ART with plasma HIV RNA levels below 50 copies/mL and CD4 counts between 200 and 500 cells/μL. Participants were immunised with 16, 32, or 64 μg of VAC-3S, and compared to placebo. The primary outcome was immunogenicity assessed by changes from baseline of anti-3S Abs levels at week 12. Secondary outcomes included adverse events and the course of plasma HIV RNA level, CD4 count, CD4/CD8 ratio, inflammation and immune checkpoints from week 0 to week 48. Vaccination was well tolerated with no serious adverse events and induced a significant increase in anti-3S Ab response in vaccinated patients (p < 0.0001), compared to placebo. In high responders, the robust increased of CD4 count was associated with a significant and sustained reduction of PD-1 expression on CD4⁺ T cells through week 48 (variance p = 0.0017). PD-1 expression was correlated with level of anti-3S Abs (p = 0.0092, r = −0.68) and expression of NKp44L (p < 0.0001; r = 0.54) in CD4⁺ T cells. Our findings regarding the increase of non-exhausted CD4⁺ T cells have potentially important application in personalised HIV vaccination for HIV-infected patients with high level of PD-1 to improve their T-cell immune function.

NK Cells Accumulate in Infected Tissues and Contribute to Pathogenicity of Ebola Virus in Mice

Ebola virus (EBOV) outbreaks can claim numerous lives and also devastate the local health infrastructure, as well as the economy, of affected countries. Lethal EBOV infection has been documented to decrease the levels of several immune cells in the blood that are necessary to defend the host. This decrease in immune cells is, however, not observed in individuals who survive EBOV infection. Having a better grasp of how these immune cells are lost is therefore of high importance to develop and improve new and existing therapeutics. The significance of our research is in identifying the mechanism responsible for the apparent loss of immune cells in lethal EBOV infection. This will allow therapeutic options aimed at preventing the loss of these immune cells, therefore allowing infected individuals to better fight the infection.

Understanding the immune parameters responsible for survival following Ebola virus (EBOV) infection is paramount for developing countermeasures. In lethal EBOV infections, levels of both NK and T cells decline drastically in the circulation and lymphoid tissues before death. However, the fate of these lymphocytes in viral replication sites remains unknown. In this study, reverse transcription-PCR (RT-PCR) and fluorescence-activated cell sorting (FACS) analysis were used to investigate lymphocyte frequencies in various infected mouse tissues after challenge with mouse-adapted EBOV (MA-EBOV). A decrease in NK cell numbers from systemic circulation was observed concomitant to an increase of these cells in tissues that are supporting active replication of EBOV. Unexpectedly, NK accumulation in virus replication sites correlated with enhanced EBOV disease progression in specific conditions; at a high challenge dose, NK-depleted mice displayed lower viremia and liver damage and higher hepatic T cell levels. Upregulation of UL16 binding protein 1 (ULBP-1) was detected in hepatic T cells, suggesting that NK cells participate in their elimination. Overall, this study supports the concept that NK cells accumulate in EBOV-infected tissues and can contribute to viral pathogenicity.

IMPORTANCE Ebola virus (EBOV) outbreaks can claim numerous lives and also devastate the local health infrastructure, as well as the economy, of affected countries. Lethal EBOV infection has been documented to decrease the levels of several immune cells in the blood that are necessary to defend the host. This decrease in immune cells is, however, not observed in individuals who survive EBOV infection. Having a better grasp of how these immune cells are lost is therefore of high importance to develop and improve new and existing therapeutics. The significance of our research is in identifying the mechanism responsible for the apparent loss of immune cells in lethal EBOV infection. This will allow therapeutic options aimed at preventing the loss of these immune cells, therefore allowing infected individuals to better fight the infection.

Reverse Immunology Approach to Define a New HIV-gp41-Neutralizing Epitope

The design of immunogens susceptible to elicit potent and broadly neutralizing antibodies against the human immunodeficiency virus type 1 (HIV-1) remains a veritable challenge in the course of vaccine development. Viral envelope proteins adopt different conformational states during the entry process, allowing the presentation of transient neutralizing epitopes. We focused on the highly conserved 3S motif of gp41, which is exposed to the surface envelope in its trimeric prefusion state. Vaccination with a W614A-modified 3S peptide induces in animals neutralizing anti-HIV-1 antibodies among which we selected clone F8. We used F8 as bait to select for W614A-3S phage-peptide mimics. Binding and molecular docking studies revealed that F8 interacts similarly with W614A-3S and a Mim_F8-1 mimotope, despite their lack of sequence homology, suggesting structural mimicry. Finally, vaccination of mice with the purified Mim_F8-1 phage elicited HIV-1-neutralizing antibodies that bound to the cognate W614A-3S motif. Collectively, our findings provide new insights into the molecular design of immunogens to elicit antibodies with neutralizing properties.

The Hard Way towards an Antibody-Based HIV-1 Env Vaccine: Lessons from Other Viruses

Although effective antibody-based vaccines have been developed against multiple viruses, such approaches have so far failed for the human immunodeficiency virus type 1 (HIV-1). Despite the success of anti-retroviral therapy (ART) that has turned HIV-1 infection into a chronic disease and has reduced the number of new infections worldwide, a vaccine against HIV-1 is still urgently needed. We discuss here the major reasons for the failure of “classical” vaccine approaches, which are mostly due to the biological properties of the virus itself. HIV-1 has developed multiple mechanisms of immune escape, which also account for vaccine failure. So far, no vaccine candidate has been able to induce broadly neutralizing antibodies (bnAbs) against primary patient viruses from different clades. However, such antibodies were identified in a subset of patients during chronic infection and were shown to protect from infection in animal models and to reduce viremia in first clinical trials. Their detailed characterization has guided structure-based reverse vaccinology approaches to design better HIV-1 envelope (Env) immunogens. Furthermore, conserved Env epitopes have been identified, which are promising candidates in view of clinical applications. Together with new vector-based technologies, considerable progress has been achieved in recent years towards the development of an effective antibody-based HIV-1 vaccine.

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.

Neutralizing Antibodies Against a Specific Human Immunodeficiency Virus gp41 Epitope are Associated With Long-term Non-progressor Status

Antibodies (Abs) play a central role in human immunodeficiency virus (HIV) protection due to their multiple functional inhibitory activities. W614A-3S Abs recognize a specific form of a highly conserved motif of the gp41 envelope protein and can elicit viral neutralization to protect CD4+ T cells. Here, we describe in detail the neutralizing profile of W614A-3S Abs in untreated long-term non-progressor (LTNP) HIV-infected patients. W614A-3S Abs were detected in 23.5% (16/68) of untreated LTNP patients compared with <5% (5/104) of HIV-1 progressor patients. The W614A-3S Abs had efficient neutralizing activity that inhibited transmitted founder primary viruses and exhibited Fc-mediated inhibitory functions at low concentrations in primary monocyte-derived macrophages. The neutralizing capacity of W614A-3S Abs was inversely correlated with viral load (r=-0.9013; p<0.0001), viral DNA (r=-0.7696; p=0.0005) and was associated the preservation of high CD4+ T-cell counts and T-cell responses. This study demonstrates that W614A-3S neutralizing Abs may confer a crucial advantage to LTNP patients. These results provide insights for both pathophysiological research and the development of vaccine strategies.

[Towards a vaccine against HIV: antibodies raised by a gp41 peptide neutralize the virus and inhibit pathogenesis]

In spite of numerous attempts, only one vaccine candidate showed a potentiality to prevent HIV infection. Such capacity, unfortunately partial, was due to the activity of specific antibodies, indicating the importance of humoral responses. However, the lack of a specific target did not allow to identify an epitope able to stimulate such a response. In addition, in view of a vaccine with preventive and therapeutic activities, it seems of interest to both be able to neutralize the virus and prevent its pathogenesis. We have identified a gp41 peptide inducing antibodies with such dual properties, therefore representing a future vaccine candidate to test functional capacities to fight HIV infection.

Report of the 2014 Cent Gardes HIV Vaccine Conference-Part 2: Cell-mediated immunity, mucosal protection, and clinical trials: Fondation Mérieux Conference Center, Veyrier du Lac, France, 5-7 October, 2014

The 2014 Cent Gardes Conference took place on October 5-7, 2014, at the Fondation Mérieux Conference Center, on the shores of the Annecy Lake and aimed to review the progress and promise of HIV vaccines. The elicitation of broadly neutralizing antibodies (bNAbs), their use in passive immunization, as well as their genetic delivery (vector immunoprophylaxis) by a recombinant Adenovirus-associated virus (AAV) vector were reviewed in a preceding article [1]. Approaches to the elicitation of long-lasting T cell or mucosal immunity were also discussed and are now reviewed here. The possibility of eliciting mucosal IgAs was discussed, since it was demonstrated that transcytosis-blocking IgAs can protect monkeys against repeated vaginal challenge with a pathogenic chimeric simian and human immunodeficiency virus (SHIV). The possibility of purging the HIV reservoirs from HIV-infected persons and developing a cure of the disease was also discussed.

The transmembrane proteins contribute to immunodeficiencies induced by HIV-1 and other retroviruses

Many microorganisms including retroviruses suppress the immune system of the infected host in order to maintain infection. Unfortunately, it is still unclear how retroviruses induce immunosuppression. There is increasing evidence of a common mechanism based on their transmembrane envelope proteins. This review therefore summarizes evidence of the involvement of the transmembrane envelope proteins in the immunopathogenesis of different retroviruses including HIV-1. Mutations in the immunosuppressive (isu) domain of the transmembrane envelope protein of several retroviruses abrogate the immunosuppressive activities in vitro and in vivo. Most importantly, virus sequences with such abrogating mutations were never found in HIV-1-infected individuals despite the fact that the mutated viruses are replication-competent. However, there is also evidence for additional, perhaps even divergent, strategies for each retrovirus. For example, in contrast to many other retroviruses, the HIV directly interacts with immune cells and infects them. In addition, HIV uses several accessory proteins to evade the immune response. Furthermore, the possible contribution of the transmembrane envelope proteins of endogenous retroviruses to immunosuppression when expressed on tumor cells or in the placenta is analyzed.

Baseline and Dynamic Expression of Activating NK Cell Receptors in the Control of Chronic Viral Infections: The Paradigm of HIV-1 and HCV

Natural killer (NK) cell function is regulated by a balance between the triggering of activating and inhibitory receptors expressed on their surface. A relevant effort has been focused so far on the study of KIR carriage/expression setting the basis for NK cell education and self-tolerance. Focus on the evolution and regulation of activating NK receptors has lagged behind so far. Our understanding of activating receptor expression and regulation has recently improved by evidences derived from in vitro and in vivo studies. Virus infection - either acute or chronic - determines preferential expansion of NK cells with specific phenotype, activating receptors, and with recall-like functional activity. Studies on patients with viral infection (HIV and HCV) and specific diverging clinical courses confirm that inter-individual differences may exist in baseline expression of natural cytotoxicity receptors (NKp46 and NKp30). The findings that patients with divergent clinical courses have different kinetics of activating receptor density expression upon NK cell activation in vitro provide an additional, time-dependent, functional parameter. Kinetic changes in receptor expression thus represent an additional parameter to basal receptor density expression. Different expression and inducibilities of activating receptors on NK cells contribute to the high diversity of NK cell populations and may help our understanding of the inter-individual differences in innate responses that underlie divergent disease courses.

Natural killer cells in HIV controller patients express an activated effector phenotype and do not up-regulate NKp44 on IL-2 stimulation

Control of HIV replication in elite controller (EC) and long-term nonprogressor (LTNP) patients has been associated with efficient CD8(+)cytotoxic T-lymphocyte function. However, innate immunity may play a role in HIV control. We studied the expression of natural cytotoxicity receptors (NKp46, NKp30, and NKp44) and their induction over a short time frame (2-4 d) on activation of natural killer (NK) cells in 31 HIV controller patients (15 ECs, 16 LTNPs). In EC/LTNP, induction of NKp46 expression was normal but short (2 d), and NKp30 was induced to lower levels vs. healthy donors. Notably, in antiretroviral-treated aviremic progressor patients (TAPPs), no induction of NKp46 or NKp30 expression occurred. More importantly, EC/LTNP failed to induce expression of NKp44, a receptor efficiently induced in activated NK cells in TAPPs. The specific lack of NKp44 expression resulted in sharply decreased capability of killing target cells by NKp44, whereas TAPPs had conserved NKp44-mediated lysis. Importantly, conserved NK cell responses, accompanied by a selective defect in the NKp44-activating pathway, may result in lack of killing of uninfected CD4(+)NKp44Ligand(+) cells when induced by HIVgp41 peptide-S3, representing a relevant mechanism of CD4(+) depletion. In addition, peripheral NK cells from EC/LTNP had increased NKG2D expression, significant HLA-DR up-regulation, and a mature (NKG2A-CD57(+)killer cell Ig-like receptor(+)CD85j(+)) phenotype, with cytolytic function also against immature dendritic cells. Thus, NK cells in EC/LTNP can maintain substantially unchanged functional capabilities, whereas the lack of NKp44 induction may be related to CD4 maintenance, representing a hallmark of these patients.

Regulation of self-ligands for activating natural killer cell receptors

Natural killer (NK) cells are able to lyse infected and tumor cells while sparing healthy cells. Recognition of diseased cells by NK cells is governed by several activating and inhibitory receptors. We review numerous pathways that have been implicated in the regulation of self-ligands for activating receptors, including NKG2D, DNAM-1, LFA-1, NKp30, NKp44, NKp46, NKp65, and NKp80 found on NK cells and some T cells. Understanding how the regulation of self-encoded ligand expression is regulated may provide novel avenues for future therapeutic approaches to infections and cancer.