HLA homology within the C5 domain promotes peptide binding by HIV type 1 gp120

Passively Acquired Constant Region 5-Specific Antibodies Associated With Improved Survival in Infants Who Acquire Human Immunodeficiency Virus

Studying vertical human immunodeficiency virus (HIV) transmission enables the impact of passively transferred antibodies on HIV transmission and pathogenesis to be examined. Using phage display of HIV envelope peptides and peptide enzyme-linked immunosorbent assay (ELISA), we found that, in infants who acquired HIV, passive antibody responses to constant region 5 (C5) were associated with improved survival in 2 cohorts. In a combined analysis, C5 peptide ELISA activity was correlated directly with survival and estimated infection time and inversely with set point viral load. These results suggest that preexisting C5-specific antibodies may be correlated with the survival of infants living with HIV, motivating additional research into their protective potential.

The therapeutic HIV Env C5/gp41 vaccine candidate Vacc-C5 induces specific T cell regulation in a phase I/II clinical study

Background

Levels of non-neutralising antibodies (AB) to the C5 domain of HIV Env gp120 are inversely related to progression of HIV infection. In this phase I/II clinical study we investigated safety of Vacc-C5, a peptide-based therapeutic vaccine candidate corresponding to C5/gp41^732–744 as well as the effects on pre-existing AB levels to C5/gp41^732–744, immune activation and T cell responses including exploratory assessments of Vacc-C5-induced T cell regulation. Our hypothesis was that exposure of the C5 peptide motif may have detrimental effects due to several of its HLA-like features and that enhancement of non-neutralising anti-C5 AB by vaccination could reduce C5 exposure and thereby chronic immune activation.

Methods

Thirty-six HIV patients on effective antiretroviral therapy were randomised to one of three dose levels of Vacc-C5 administered intramuscularly with Alhydrogel or intradermally with GM-CSF as adjuvant through initial immunisation and two booster periods over 26 weeks. Vacc-C5-specific AB were measured by ELISA and T cell responses by both IFN-γ ELISPOT and proliferative assays analysed by flow cytometry. Immune regulation was assessed by functional blockade of the two inhibitory cytokines IL-10 and TGF-β in parallel cultures. Non-parametric statistical tests were applied.

Results

Vacc-C5 was found safe and well tolerated in all patients. Only marginal changes in humoral and cellular responses were induced, without any effect on immune activation. Overall, anti-Vacc-C5 AB levels seemed to decrease compared to pre-existing levels. Whereas Vacc-C5-specific CD8⁺ T cell proliferative responses increased after the first booster period (p = 0.020; CD4⁺, p = 0.057), they were reduced after the second. In contrast, Vacc-C5-induced T cell regulation increased after completed vaccination (p ≤ 0.027) and was lower at baseline in the few AB responders identified (p = 0.027).

Conclusions

The therapeutic HIV vaccine candidate Vacc-C5 safely induced only marginal immune responses, whereas Vacc-C5-induced T cell regulation markedly increased. Our data support further attention on immune regulation during therapeutic HIV vaccination studies.

Trial registration

NCT01627678.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-017-2316-x) contains supplementary material, which is available to authorized users.

Changes in Structure and Antigenicity of HIV-1 Env Trimers Resulting from Removal of a Conserved CD4 Binding Site-Proximal Glycan

The envelope glycoprotein (Env) is the major target for HIV-1 broadly neutralizing antibodies (bNAbs). One of the mechanisms that HIV has evolved to escape the host's immune response is to mask conserved epitopes on Env with dense glycosylation. Previous studies have shown that the removal of a particular conserved glycan at N197 increases the neutralization sensitivity of the virus to antibodies targeting the CD4 binding site (CD4bs), making it a site of significant interest from the perspective of vaccine design. At present, the structural consequences that result from the removal of the N197 glycan have not been characterized. Using native-like SOSIP trimers, we examine the effects on antigenicity and local structural dynamics resulting from the removal of this glycan. A large increase in the binding of CD4bs and V3-targeting antibodies is observed for the N197Q mutant in trimeric Env, while no changes are observed with monomeric gp120. While the overall structure and thermostability are not altered, a subtle increase in the flexibility of the variable loops at the trimeric interface of adjacent protomers is evident in the N197Q mutant by hydrogen-deuterium exchange mass spectrometry. Structural modeling of the glycan chains suggests that the spatial occupancy of the N197 glycan leads to steric clashes with CD4bs antibodies in the Env trimer but not monomeric gp120. Our results indicate that the removal of the N197 glycan enhances the exposure of relevant bNAb epitopes on Env with a minimal impact on the overall trimeric structure. These findings present a simple modification for enhancing trimeric Env immunogens in vaccines.

IMPORTANCE

The HIV-1 Env glycoprotein presents a dense patchwork of host cell-derived N-linked glycans. This so-called glycan shield is considered to be a major protective mechanism against immune recognition. While the positions of many N-linked glycans are isolate specific, some are highly conserved and are believed to play key functional roles. In this study, we examine the conserved, CD4 binding site-proximal N197 glycan and demonstrate that its removal both facilitates neutralizing antibody access to the CD4 binding site and modestly impacts the structural dynamics at the trimer crown without drastically altering global Env trimer stability. This indicates that surgical glycosylation site modification may be an effective way of sculpting epitope presentation in Env-based vaccines.

The potential of immunomodulatory drugs in the treatment of solid tumors

Lenalidomide (REVLIMID®) CC-5013 (Celgene, NJ, USA) is approved, in both the USA and Europe, in combination with dexamethasone for the treatment of multiple myeloma patients who have received at least one prior therapy, and is rapidly being accepted worldwide for this condition. Lenalidomide is also approved in the USA and Canada for use in transfusion-dependent anemia in patients with low- and intermediate-1-risk myelodysplastic syndromes associated with del (5q) abnormality with or without additional abnormalities. Lenalidomide is an IMiD® immunomodulatory compound, incorporating structural modification of the drug thalidomide, which is active against a wide variety of autoimmune Th-2-dependent disorders, including erythema nodosum of leprosy, leishmaniasis, as well as severe ulcerative disorders such as Behcet's syndrome. Unfortunately, long-term use of thalidomide is limited, particularly by neurotoxicity. To date, results suggest that lenalidomide is more active than thalidomide and does not cause the neurotoxicity seen with thalidomide. Lenalidomide has multiple properties, including anti-inflammatory, antiangiogenic and costimulatory effects, as well as being able to inhibit T-regulatory cells, all of which are properties deemed desirable for anticancer activity. This article covers the evidence that lenalidomide may have a major role in the treatment and control of many cancer types other than del (5q) myelodysplastic syndrome and multiple myeloma.

Genetic determinants of HIV-1 infection and progression to AIDS: immune response genes

Genomic studies involving well-defined multicenter cohorts of HIV-1/AIDS covering multiple populations have led to a greater understanding of the role of host determinants in viral acquisition, disease progression, transmission, and response to anti-retroviral therapy. Similarly, recent knowledge on the virus genetic diversity has helped in elucidating mechanisms leading to the evolution of viral escape mutants and the role played by host immune determinants, in particular the major histocompatibility complex (MHC) associated genes. At least two alleles, HLA-B*27 and B*57, have been identified as 'protective' against HIV-1 while B*35 and B*53 act as susceptibility favoring factors. How human leukocyte antigen (HLA)-mediated selection drives the evolution of HIV-1 and which circulating variants are more likely to evade immune surveillance of the population are now beginning to become clear. Importantly, the rare HLA alleles in a population bear a selective advantage to the host because these can induce immune responses against pre-adapted viruses. It is conceivable that previously established protective HLA associations are shifting with the evolving cytotoxic T lymphocyte (CTL) epitopes and may not remain protective in future. At the same time, this process is unraveling novel sub-dominant epitopes of the virus which could now be incorporated as the dominant target CTL epitopes. An insight into the population-specific correlates of protection is hence necessary for designing future anti-HIV therapeutic and/or prophylactic vaccine formulation(s).

HIV immunopathogenesis and strategies for intervention

Therapeutic options aimed at tackling the HIV pandemic face many obstacles. The lack of readily accessible and affordable therapies means that most of those affected go untreated. The array of escape mechanisms used by HIV has undermined the efficiency of many antiviral products and continually represents a barrier to the development of an effective vaccine. Recent developments have seen a shift away from a cytopathic viral model of HIV pathogenesis towards the crucial role of immunopathogenic features--notably generalised immune activation--in the development of AIDS. As conventional vaccine strategies have sought to promote viral neutralisation and suppressive cellular responses, novel strategies that aim to address HIV immunopathogenesis should be sought. We review current opinion on HIV-induced pathogenic immune activation and strategies aimed at eliminating HIV, including a potential role for non-neutralising antibodies as part of a therapeutic vaccine option.

Special anniversary review: twenty-five years of human immunodeficiency virus research: successes and challenges

During 25 years of research since HIV-1 was first identified in Paris, there have been great advances in our understanding of the virus and of the immune system. Practical advances include the early development of diagnostic tests of infection that made blood donation safe, and since 1996, combination anti-retroviral therapy that has great reduced incidence of AIDS in HIV-infected people who have access to the drugs. HIV prevention through behavioural change has been successful, and we do not yet have any safe and efficacious microbicides or vaccines.