Therapeutic immunization with HIV-1 Tat reduces immune activation and loss of regulatory T-cells and improves immune function in subjects on HAART

Emerging roles of senolytics/senomorphics in HIV-related co-morbidities

Human immunodeficiency virus (HIV) is known to cause cellular senescence and inflammation among infected individuals. While the traditional antiretroviral therapies (ART) have allowed the once fatal infection to be managed effectively, the quality of life of HIV patients on prolonged ART use is still inferior. Most of these individuals suffer from life-threatening comorbidities like chronic obstructive pulmonary disease (COPD), pulmonary arterial hypertension (PAH), and diabetes, to name a few. Interestingly, cellular senescence is known to play a critical role in the pathophysiology of these comorbidities as well. It is therefore important to understand the role of cellular senescence in the disease progression and co-morbidity development in HIV-infected individuals. In this respect, use of senolytic/senomorphic drugs as combination therapy with ART would be beneficial for HIV patients. This review provides a critical analysis of the current literature to determine the potential and efficacy of using senolytics/senotherapeutics in managing HIV infection, latency, and associated co-morbidities in humans. The various classes of senolytics have been studied in detail to focus on their potential to combat against HIV infections and associated pathologies with advancing age.

Role of HIV-1 Tat Protein Interactions with Host Receptors in HIV Infection and Pathogenesis

Each time the virus starts a new round of expression/replication, even under effective antiretroviral therapy (ART), the transactivator of viral transcription Tat is one of the first HIV-1 protein to be produced, as it is strictly required for HIV replication and spreading. At this stage, most of the Tat protein exits infected cells, accumulates in the extracellular matrix and exerts profound effects on both the virus and neighbor cells, mostly of the innate and adaptive immune systems. Through these effects, extracellular Tat contributes to the acquisition of infection, spreading and progression to AIDS in untreated patients, or to non-AIDS co-morbidities in ART-treated individuals, who experience inflammation and immune activation despite virus suppression. Here, we review the role of extracellular Tat in both the virus life cycle and on cells of the innate and adaptive immune system, and we provide epidemiological and experimental evidence of the importance of targeting Tat to block residual HIV expression and replication. Finally, we briefly review vaccine studies showing that a therapeutic Tat vaccine intensifies ART, while its inclusion in a preventative vaccine may blunt escape from neutralizing antibodies and block early events in HIV acquisition.

HIV-1 therapeutic vaccines in clinical development to intensify or replace antiretroviral therapy: the promising results of the Tat vaccine

INTRODUCTION

Upon the introduction of the combination antiretroviral therapy (cART), HIV infection has become a chronic disease. However, cART is unable to eradicate the virus and fails to restore the CD4 counts in about 30% of the treated individuals. Furthermore, treatment is life-long, and it does not protect from morbidities typically observed in the elderly. Therapeutic vaccines represent the most cost-effective intervention to intensify or replace cART.

AREAS COVERED

Here, we briefly discuss the obstacles to the development and evaluation of the efficacy of therapeutic vaccines and review recent approaches evaluated in clinical trials.

EXPERT OPINION

Although vaccines were generally safe and immunogenic, evidence of efficacy was negligible or marginal in most trials. A notable exception is the therapeutic Tat vaccine approach showing promising results of cART intensification, with CD4 T-cell increase and proviral load reduction beyond those afforded by cART alone. Rationale and evidence in support of choosing Tat as the vaccine target are thoroughly discussed.

Gene-specific MicroRNA antagonism protects against HIV Tat and TGF-β-mediated suppression of CFTR mRNA and function

BACKGROUND

MicroRNAs play an important role in health and disease. TGF-β signaling, upregulated by HIV Tat, and in chronic airway diseases and smokers upregulates miR-145-5p to suppress cystic fibrosis transmembrane conductance regulator (CFTR). CFTR suppression in chronic airway diseases like Cystic Fibrosis, COPD and smokers has been associated with suppressed MCC and recurrent lung infections and inflammation. This can explain the emergence of recurrent lung infections and inflammation in people living with HIV.

METHODS

Tat-induced aberrant microRNAome was identified by miRNA expression analysis. microRNA mimics and antagomirs were used to validate the identified miRNAs involved in Tat mediated CFTR mRNA suppression. CRISPR-based editing of the miRNA target sites in CFTR 3'UTR was used to determine rescue of CFTR mRNA and function in airway epithelial cell lines and in primary human bronchial epithelial cells exposed to TGF-β and Tat.

FINDINGS

HIV Tat upregulates miR-145-5p and miR-509-3p. The two miRNAs demonstrate co-operative effects in suppressing CFTR. CRISPR-based editing of the miRNA target site preserves CFTR mRNA and function in airway epithelial cells INTERPRETATION: Given the important roles of TGF-β signaling and the multitude of genes regulated by miRNAs, we demonstrate that CRISPR-based gene-specific microRNA antagonism approach can preserve CFTR mRNA and function in the context of HIV Tat and TGF-β signaling without suppressing expression of other genes regulated by miR-145-5p.

New insights into pathogenesis point to HIV-1 Tat as a key vaccine target

Despite over 30 years of enormous effort and progress in the field, no preventative and/or therapeutic vaccines against human immunodeficiency virus (HIV) are available. Here, we briefly summarize the vaccine strategies and vaccine candidates that in recent years advanced to efficacy trials with mostly unsatisfactory results. Next, we discuss a novel and somewhat contrarian approach based on biological and epidemiological evidence, which led us to choose the HIV protein Tat for the development of preventive and therapeutic HIV vaccines. Toward this goal, we review here the role of Tat in the virus life cycle as well as experimental and epidemiological evidence supporting its key role in the natural history of HIV infection and comorbidities. We then discuss the preclinical and clinical development of a Tat therapeutic vaccine, which, by improving the functionality and homeostasis of the immune system and by reducing the viral reservoir in virologically suppressed vaccinees, helps to establish key determinants for intensification of combination antiretroviral therapy (cART) and a functional cure. Future developments and potential applications of the Tat therapeutic vaccine are also discussed, as well as the rationale for its use in preventative strategies. We hope this contribution will lead to a reconsideration of the current paradigms for the development of HIV/AIDS vaccines, with a focus on targeting of viral proteins with key roles in HIV pathogenesis.

Use of a Novel Peptide Welding Technology Platform for the Development of B- and T-Cell Epitope-Based Vaccines

Peptide vaccines incorporating B- and T-cell epitopes have shown promise in the context of various cancers and infections. These vaccines are relatively simple to manufacture, but more immunogenic formulations are considered a priority. We developed tetrabranched derivatives for this purpose based on a novel peptide welding technology (PWT). PWTs provide molecular scaffolds for the efficient synthesis of ultrapure peptide dendrimers, which allow the delivery of multiple ligands within a single macromolecular structure. Peptide vaccines incorporating T-cell epitopes derived from melanoma and B-cell epitopes derived from human immunodeficiency virus, synthesized using this approach, elicited primary immune responses in vitro and in vivo. Subcutaneous administration of the B-cell epitope-based vaccines also elicited more potent humoral responses than subcutaneous administration of the corresponding peptides alone. Highly immunogenic peptide epitope-based vaccines can therefore be generated quickly and easily using a novel PWT.

Anti-Tat immunity defines CD4+ T-cell dynamics in people living with HIV on long-term cART

BACKGROUND

Low-level HIV viremia originating from virus reactivation in HIV reservoirs is often present in cART treated individuals and represents a persisting source of immune stimulation associated with sub-optimal recovery of CD4⁺ T cells. The HIV-1 Tat protein is released in the extracellular milieu and activates immune cells and latent HIV, leading to virus production and release. However, the relation of anti-Tat immunity with residual viremia, persistent immune activation and CD4⁺ T-cell dynamics has not yet been defined.

METHODS

Volunteers enrolled in a 3-year longitudinal observational study were stratified by residual viremia, Tat serostatus and frequency of anti-Tat cellular immune responses. The impact of anti-Tat immunity on low-level viremia, persistent immune activation and CD4⁺ T-cell recovery was investigated by test for partitions, longitudinal regression analysis for repeated measures and generalized estimating equations.

FINDINGS

Anti-Tat immunity is significantly associated with higher nadir CD4⁺ T-cell numbers, control of low-level viremia and long-lasting CD4⁺ T-cell recovery, but not with decreased immune activation. In adjusted analysis, the extent of CD4⁺ T-cell restoration reflects the interplay among Tat immunity, residual viremia and immunological determinants including CD8⁺ T cells and B cells. Anti-Env immunity was not related to CD4⁺ T-cell recovery.

INTERPRETATION

Therapeutic approaches aiming at reinforcing anti-Tat immunity should be investigated to improve immune reconstitution in people living with HIV on long-term cART.

TRIAL REGISTRATION

ISS OBS T-002 ClinicalTrials.gov identifier: NCT01024556 FUNDING: Italian Ministry of Health, special project on the Development of a vaccine against HIV based on the Tat protein and Ricerca Corrente 2019/2020.

Comparison of the efficacy of HIV-1 Nef-Tat-Gp160-p24 polyepitope vaccine candidate with Nef protein in different immunization strategies

OBJECTIVES

One of the promising strategies for effective HIV-1 vaccine design involves finding the polyepitope immunogens using T cell epitopes.

METHODS

Herein, an HIV-1 polyepitope construct (i.e., Nef-Tat-Gp160-P24) comprising of several epitopes from Nef, Tat, Gp160, and P24 proteins was designed. To improve its immunogenicity in BALB/c mice, cell-penetrating peptides (HR9 & MPG for DNA delivery, and LDP-NLS & CyLoP-1 for protein transfer), Montanide adjuvant, and heterologous DNA prime/polypeptide boost strategy were used. To compare the immunogenicity, Nef was utilized as a vaccine candidate. The levels of total IgG and its subclasses, cytokines, and Granzyme B were assessed using ELISA.

RESULTS

Immunological studies showed that heterologous prime-boost regimens for both antigens could considerably augment the levels of IgG2a, IgG2b, IFN-γ, and Granzyme B directed toward Th1 and CTL immune responses in comparison with homologous prime-boost strategies. The levels of IFN-γ, IL-10, total IgG, IgG1, and IgG2b were drastically higher in groups immunized with Nef-Tat-Gp160-P24 in heterologous prime-boost regimens than those in groups immunized with Nef.

CONCLUSIONS

The use of the Nef-Tat-Gp160-P24 polyepitope immunogen in heterologous prime-boost strategy could generate the mixture of Th1 and Th2 responses directed further toward Th1 response as a hopeful method for improvement of HIV-1 vaccine.

HIV-1 Tat Protein Enters Dysfunctional Endothelial Cells via Integrins and Renders Them Permissive to Virus Replication

Previous work has shown that the Tat protein of Human Immunodeficiency Virus (HIV)-1 is released by acutely infected cells in a biologically active form and enters dendritic cells upon the binding of its arginine-glycine-aspartic acid (RGD) domain to the α5β1, αvβ3, and αvβ5 integrins. The up-regulation/activation of these integrins occurs in endothelial cells exposed to inflammatory cytokines that are increased in HIV-infected individuals, leading to endothelial cell dysfunction. Here, we show that inflammatory cytokine-activated endothelial cells selectively bind and rapidly take up nano-micromolar concentrations of Tat, as determined by flow cytometry. Protein oxidation and low temperatures reduce Tat entry, suggesting a conformation- and energy-dependent process. Consistently, Tat entry is competed out by RGD-Tat peptides or integrin natural ligands, and it is blocked by anti-α5β1, -αvβ3, and -αvβ5 antibodies. Moreover, modelling–docking calculations identify a low-energy Tat-αvβ3 integrin complex in which Tat makes contacts with both the αv and β3 chains. It is noteworthy that internalized Tat induces HIV replication in inflammatory cytokine-treated, but not untreated, endothelial cells. Thus, endothelial cell dysfunction driven by inflammatory cytokines renders the vascular system a target of Tat, which makes endothelial cells permissive to HIV replication, adding a further layer of complexity to functionally cure and/or eradicate HIV infection.

The Tat Protein of HIV-1 Prevents the Loss of HSV-Specific Memory Adaptive Responses and Favors the Control of Viral Reactivation

The development of therapeutic strategies to control the reactivation of the Herpes Simplex Virus (HSV) is an unaddressed priority. In this study, we evaluated whether Tat, a HIV-1 protein displaying adjuvant functions, could improve previously established HSV-specific memory responses and prevent viral reactivation. To this aim, mice were infected with non-lethal doses of HSV-1 and, 44 days later, injected or not with Tat. Mice were then monitored to check their health status and measure memory HSV-specific cellular and humoral responses. The appearance of symptoms associated with HSV-reactivation was observed at significantly higher frequencies in the control group than in the Tat-treated mice. In addition, the control animals experienced a time-dependent decrease in HSV-specific Immunoglobulin G (IgG), while the Tat-treated mice maintained antibody titers over time. IgG levels were directly correlated with the number of HSV-specific CD8⁺ T cells, suggesting an effect of Tat on both arms of the adaptive immunity. Consistent with the maintenance of HSV-specific immune memory, Tat-treated mice showed a better control of HSV-1 re-infection. Although further studies are necessary to assess whether similar effects are observed in other models, these results indicate that Tat exerts a therapeutic effect against latent HSV-1 infection and re-infection by favoring the maintenance of adaptive immunity.

Cellular stress responses and dysfunctional Mitochondrial-cellular senescence, and therapeutics in chronic respiratory diseases

The abnormal inflammatory responses due to the lung tissue damage and ineffective repair/resolution in response to the inhaled toxicants result in the pathological changes associated with chronic respiratory diseases. Investigation of such pathophysiological mechanisms provides the opportunity to develop the molecular phenotype-specific diagnostic assays and could help in designing the personalized medicine-based therapeutic approaches against these prevalent diseases. As the central hubs of cell metabolism and energetics, mitochondria integrate cellular responses and interorganellar signaling pathways to maintain cellular and extracellular redox status and the cellular senescence that dictate the lung tissue responses. Specifically, as observed in chronic obstructive pulmonary disease (COPD) and pulmonary fibrosis, the mitochondria-endoplasmic reticulum (ER) crosstalk is disrupted by the inhaled toxicants such as the combustible and emerging electronic nicotine-delivery system (ENDS) tobacco products. Thus, the recent research efforts have focused on understanding how the mitochondria-ER dysfunctions and oxidative stress responses can be targeted to improve inflammatory and cellular dysfunctions associated with these pathologic illnesses that are exacerbated by viral infections. The present review assesses the importance of these redox signaling and cellular senescence pathways that describe the role of mitochondria and ER on the development and function of lung epithelial responses, highlighting the cause and effect associations that reflect the disease pathogenesis and possible intervention strategies.

Parallel studies of mucosal immunity in the reproductive and gastrointestinal mucosa of HIV-infected women

PROBLEM

The effects of HIV on the gastrointestinal tract (GIT), including CD4 depletion, epithelial disruption, and collagen deposition, are well documented and only partially reversed by combination antiretroviral therapy (cART). However, the effects of HIV on the female reproductive tract (FRT) are poorly understood, and most studies have focused on ectocervix and vagina without assessing the upper tract. Here, we investigated CD4⁺ T-cell frequency, phenotype, and HIV-specific T-cell responses in the endocervix and endometrium of HIV-infected women, comparing these tissues to the GIT.

METHOD OF STUDY

Mucosal samples and blood were obtained from 18 women: four who were HIV-positive and not on cART for at least 3 years prior to sampling, including two natural controllers (viral load [VL] undetectable and CD4 >350); nine women on cART with low to undetectable VL; and five HIV-uninfected women. Mucosal samples included terminal ileum, sigmoid colon, endocervical cytobrush, endocervical curettage, and endometrial biopsy. T-cell frequency, phenotypes, and HIV-specific T-cell responses were analyzed by multiparameter flow cytometry.

RESULTS

T-cell activation, measured by CD38/HLA-DR co-expression, remained significantly elevated in endometrium following cART, but was lower in gastrointestinal tissues. HIV-specific CD8⁺ T-cell responses were detected in ileum, colon, and endometrial tissues of women both on and off cART, and were of higher magnitude on those not on cART.

CONCLUSION

Our findings reveal differences in CD4⁺ T-cell frequencies, immune activation, and HIV-specific T-cell responses between the gastrointestinal and reproductive tracts, and highlight differences between HIV controllers and women on cART.

A therapeutic HIV-1 vaccine reduces markers of systemic immune activation and latent infection in patients under highly active antiretroviral therapy

HIV infection is characterized by chronic immune activation and the establishment of a pool of latently infected cells. Antiretroviral therapy (ART) can suppress viral load to undetectable levels in peripheral blood by standard measure, however immune activation/chronic inflammation and latent infection persist and affect quality of life. We have now shown that a novel therapeutic HIV vaccine consisting of replication-defective HIV (HIVAX), given in the context of viral suppression under ART, can reduce both immune activation/chronic inflammation and latent infection. Immune activation, as measured by percent of CD8 + HLA-DR + CD38 + T cells, approached levels of healthy controls at week 16 following vaccination. Reduced immune activation was accompanied by a reduction in pro-inflammatory cytokines and peripheral α4β7 + plasmacytoid DC (a marker of mucosal immune activation). Levels of both HIV-1 DNA and 2-LTR circles were reduced at week 16 following vaccination, suggesting HIVAX can impact HIV-1 latency and reduce viral replication. Surprisingly, reduced immune activation/chronic inflammation was accompanied by an increase in the percent of memory CD4 + T cells expressing markers PD-1 and TIM-3. In addition, evaluation of HIV-1 Gag-specific CD4 + T cells for expression of 96 T cell related genes pre- and post-therapy revealed increased expression of a number of genes involved in the regulation of immune activation, T cell activation, and antiviral responses. Overall this study provides evidence that vaccination with HIVAX in subjects under long term antiviral suppression can reduce immune activation/chronic inflammation and latent infection (Clinicaltrials.gov, identifier NCT01428596).

Tat-Based Therapies as an Adjuvant for an HIV-1 Functional Cure

The human immunodeficiency virus type 1 (HIV) establishes a chronic infection that can be well controlled, but not cured, by combined antiretroviral therapy (cART). Interventions have been explored to accomplish a functional cure, meaning that a patient remains infected but HIV is undetectable in the blood, with the aim of allowing patients to live without cART. Tat, the viral transactivator of transcription protein, plays a critical role in controlling HIV transcription, latency, and viral rebound following the interruption of cART treatment. Therefore, a logical approach for controlling HIV would be to block Tat. Tackling Tat with inhibitors has been a difficult task, but some recent discoveries hold promise. Two anti-HIV proteins, Nullbasic (a mutant of Tat) and HT1 (a fusion of HEXIM1 and Tat functional domains) inhibit viral transcription by interfering with the interaction of Tat and cellular factors. Two small molecules, didehydro-cortistatin A (dCA) and triptolide, inhibit Tat by different mechanisms: dCA through direct binding and triptolide through enhanced proteasomal degradation. Finally, two Tat-based vaccines under development elicit Tat-neutralizing antibodies. These vaccines have increased the levels of CD4⁺ cells and reduced viral loads in HIV-infected people, suggesting that the new vaccines are therapeutic. This review summarizes recent developments of anti-Tat agents and how they could contribute to a functional cure for HIV.

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.

TGF-β1 increases viral burden and promotes HIV-1 latency in primary differentiated human bronchial epithelial cells

Combination antiretroviral therapy (cART) has increased the life expectancy of HIV patients. However, the incidence of non-AIDS associated lung comorbidities, such as COPD and asthma, and that of opportunistic lung infections have become more common among this population. HIV proteins secreted by the anatomical HIV reservoirs can have both autocrine and paracrine effects contributing to the HIV-associated comorbidities. HIV has been recovered from cell-free bronchoalveolar lavage fluid, alveolar macrophages, and intrapulmonary lymphocytes. We have recently shown that ex-vivo cultured primary bronchial epithelial cells and the bronchial brushings from human subjects express canonical HIV receptors CD4, CCR5 and CXCR4 and can be infected with HIV. Together these studies suggest that the lung tissue can serve as an important reservoir for HIV. In this report, we show that TGF-β1 promotes HIV latency by upregulating a transcriptional repressor BLIMP-1. Furthermore, we identify miR-9-5p as an important intermediate in TGF-β-mediated BLIMP-1 upregulation and consequent HIV latency. The transcriptionally suppressed HIV can be reactivated by common latency reactivating agents. Together our data suggest that in patients with chronic airway diseases, TGF-β can elevate the HIV viral reservoir load that could further exacerbate the HIV associated lung comorbidities.

Anti-Tat Immunity in HIV-1 Infection: Effects of Naturally Occurring and Vaccine-Induced Antibodies Against Tat on the Course of the Disease

HIV-1 Tat is an essential protein in the virus life cycle, which is required for virus gene expression and replication. Most Tat that is produced during infection is released extracellularly and it plays a key role in HIV pathogenesis, including residual disease upon combination antiretroviral therapy (cART). Here, we review epidemiological and experimental evidence showing that antibodies against HIV-1 Tat, infrequently occurring in natural infection, play a protective role against disease progression, and that vaccine targeting Tat can intensify cART. In fact, Tat vaccination of subjects on suppressive cART in Italy and South Africa promoted immune restoration, including CD4+ T-cell increase in low immunological responders, and a reduction of proviral DNA even after six years of cART, when both CD4+ T-cell gain and DNA decay have reached a plateau. Of note, DNA decay was predicted by the neutralization of Tat-mediated entry of Env into dendritic cells by anti-Tat antibodies, which were cross-clade binding and neutralizing. Anti-Tat cellular immunity also contributed to the DNA decay. Based on these data, we propose the Tat therapeutic vaccine as a pathogenesis-driven intervention that effectively intensifies cART and it may lead to a functional cure, providing new perspectives and opportunities also for prevention and virus eradication strategies.

Continued Decay of HIV Proviral DNA Upon Vaccination With HIV-1 Tat of Subjects on Long-Term ART: An 8-Year Follow-Up Study

Introduction: Tat, a key HIV virulence protein, has been targeted for the development of a therapeutic vaccine aimed at cART intensification. Results from phase II clinical trials in Italy (ISS T-002) and South Africa (ISS T-003) indicated that Tat vaccination promotes increases of CD4⁺ T-cells and return to immune homeostasis while reducing the virus reservoir in chronically cART-treated patients. Here we present data of 92 vaccinees (59% of total vaccinees) enrolled in the ISS T-002 8-year extended follow-up study (ISS T-002 EF-UP, ClinicalTrials.gov NCT02118168). Results: Anti-Tat antibodies (Abs) induced upon vaccination persisted for the entire follow-up in 34/92 (37%) vaccinees, particularly when all 3 Ab classes (A/G/M) were present (66% of vaccinees), as most frequently observed with Tat 30 μg regimens. CD4⁺ T cells increased above study-entry levels reaching a stable plateau at year 5 post-vaccination, with the highest increase (165 cells/μL) in the Tat 30 μg, 3 × regimen. CD4⁺ T-cell increase occurred even in subjects with CD4⁺ nadir ≤ 250 cells/uL and in poor immunological responders and was associated with a concomitant increase of the CD4⁺/CD8⁺ T-cell ratio, a prognostic marker of morbidity/mortality inversely related to HIV reservoir size. Proviral DNA load decreased over time, with a half-life of 2 years and an estimated 90% reduction at year 8 in the Tat 30 μg, 3 × group. In multivariate analysis the kinetic and amplitude of both CD4⁺ T-cell increase and proviral DNA reduction were fastest and highest in subjects with all 3 anti-Tat Ab classes and in the 30 μg, 3 × group, irrespective of drug regimens (NNRTI/NRTI vs. PI). HIV proviral DNA changes from baseline were inversely related to CD4⁺/CD8⁺ T-cell ratio and CD4⁺ T-cell changes, and directly related to the changes of CD8⁺ T cells. Further, HIV DNA decay kinetics were inversely related to the frequency and levels of intermittent viremia. Finally, Tat vaccination was similarly effective irrespective of the individual immunological status or HIV reservoir size at study entry. Conclusions: Tat immunization induces progressive immune restoration and reduction of virus reservoirs above levels reached with long-term cART, and may represent an optimal vaccine candidate for cART intensification toward HIV reservoirs depletion, functional cure, and eradication strategies.

The role of HIV Tat protein in HIV-related cardiovascular diseases

The human immunodeficiency virus (HIV) is a major global public health issue. HIV-related cardiovascular disease remains a leading cause of morbidity and mortality in HIV positive patients. HIV Tat is a regulatory protein encoded by tat gene of HIV-1, which not only promotes the transcription of HIV, but it is also involved in the pathogenesis of HIV-related complications. This review is aimed at summarizing the current understanding of Tat in HIV-related cardiovascular diseases.

The HIV-1 Tat protein affects human CD4+ T-cell programing and activation, and favors the differentiation of naïve CD4+ T cells

OBJECTIVE

HIV infection is characterized by several immune dysfunctions, such as chronic activation of the immune system, premature aging and loss of CD4 T cells, in particular within the naïve compartment. The Tat protein of HIV is released extracellularly and enters neighboring cells affecting their functionality, for instance impacting on CD8 T-cell programs and activity. As the presence and/or induction of anti-Tat immune responses is associated with reduced T-cell dysfunction and CD4 T-cell loss, we investigated whether Tat impacts human resting or activated CD4 T cells.

METHODS

Purified CD4 T cells were activated by T cell receptor engagement in the presence or absence of Tat. Cytokine production, surface phenotype and expression of transcription factors important for T-cell programing were measured. Purified naïve CD4 T cells were cultured in nonpolarizing conditions in the presence or absence of Tat and their proliferation and differentiation was evaluated.

RESULTS

Tat favors the secretion of IL2, IFNγ and TNFα in CD4 T cells, as well as the upregulation of T-bet and Eomes expression. Naïve CD4 T cells cultured in the presence of Tat showed enhanced expansion and differentiation toward memory phenotype, showing in particular recruitment into the effector memory T-cell pool.

CONCLUSION

Tat affects the programing and functionality of CD4 T lymphocytes favoring the differentiation of naïve CD4 T cells.

Aptamers in HIV research diagnosis and therapy

Aptamers are high affinity single-stranded nucleic acid or protein ligands which exhibit specificity and avidity comparable to, or exceeding that of antibodies and can be generated against most targets. The functionality of aptamers is based on their unique tertiary structure, complexity and their ability to attain unique binding pockets by folding. Aptamers are selected in vitro by a process called Systematic Evolution of Ligands by Exponential enrichment (SELEX). The Kd values for the selected aptamer are often in the picomolar to low nanomolar range. Stable and nontoxic aptamers could be selected for a wide range of ligands including small molecules to large proteins. Aptamers have shown tremendous potential and have found multipurpose application in the field of therapeutic, diagnostic, biosensor and bio-imaging. While their mechanism of action can be similar to that of monoclonal antibodies, aptamers provide additional advantages in terms of production cost, simpler regulatory approval and lower immunogenicity as they are synthesized chemically. Human immunodeficiency virus (HIV) is the primary cause of acquired immune deficiency syndrome (AIDS), which causes significant morbidity and mortality with a significant consequent decrease in the quality of patient's lives. While cART has led to good viral control, people living with HIV now suffer from non-HIV comorbidities due to viral protein expression that cannot be controlled by cART. Hence pathophysiological mechanisms that govern these comorbidities with a focus on therapies that neutralize these HIV effects gained increased attention. Recent advances in HIV/AIDS research have identified several molecular targets and for the development of therapeutic and diagnostic using aptamers against HIV/AIDS. This review presents recent advances in aptamers technology for potential application in HIV diagnostics and therapeutics towards improving the quality of life of people living with HIV.

"cART intensification by the HIV-1 Tat B clade vaccine: progress to phase III efficacy studies"

INTRODUCTION

In spite of its success at suppressing HIV replication, combination antiretroviral therapy (cART) only partially reduces immune dysregulation and loss of immune functions. These cART-unmet needs appear to be due to persistent virus replication and cell-to-cell transmission in reservoirs, and are causes of increased patients' morbidity and mortality. Up to now, therapeutic interventions aimed at cART-intensification by attacking the virus reservoir have failed.

AREAS COVERED

We briefly review the rationale and clinical development of Tat therapeutic vaccine in cART-treated subjects in Italy and South Africa (SA). Vaccination with clade-B Tat induced cross-clade neutralizing antibodies, immune restoration, including CD4⁺ T cell increase particularly in low immunological responders, and reduction of proviral DNA. Phase III efficacy trials in SA are planned both in adult and pediatric populations.

EXPERT COMMENTARY

We propose the Tat therapeutic vaccine as a pathogenesis-driven intervention that effectively intensifies cART and may lead to a functional cure and provide new perspectives for prevention and virus eradication strategies.

Therapeutic vaccines and immunological intervention in HIV infection: a paradigm change

PURPOSE OF REVIEW

The purpose is to review current knowledge of immunological interventions in HIV infection and discuss strategies for the establishment of functional cure and/or HIV eradication.

RECENT FINDINGS

Therapeutic vaccines and cytokines have been historically the immunological interventions developed with the objective to enhance the HIV-specific cell-mediated immune responses and to suppress virus replication. Both these interventions have shown only partial antiviral effects. The recent identification and generation of human broad neutralizing antibodies provides potent immunological intervention associated with effective suppression of virus replication in the absence of antiretroviral therapy. Furthermore, the identification that the major HIV cell reservoir containing replication competent and infectious virus is composed by programed cell death protein 1 (PD-1) positive memory CD4 T cells offers the opportunity to target directly the HIV cell reservoir with anti-PD-1 antibodies. Anti-PD-1 antibody therapy may be also critical to prevent exhaustion of CD8 T cells.

SUMMARY

The availability of a diverse armamentarium of immunological intervention offers the opportunity to investigate the efficacy of the combined use of different immunological interventions in inducing prolonged virus suppression in the absence of antiretroviral therapy and functional cure HIV or HIV eradication.

New challenges in therapeutic vaccines against HIV infection

INTRODUCTION

There is a growing interest in developing curative strategies for HIV infection. Therapeutic vaccines are one of the most promising approaches. We will review the current knowledge and the new challenges in this research field. Areas covered: PubMed and ClinicalTrial.gov databases were searched to review the progress and prospects for clinical development of immunotherapies aimed to cure HIV infection. Dendritic cells (DC)-based vaccines have yielded the best results in the field. However, major immune-virologic barriers may hamper current vaccine strategies. We will focus on some new challenges as the antigen presentation by DCs, CTL escape mutations, B cell follicle sanctuary, host immune environment (inflammation, immune activation, tolerance), latent reservoir and the lack of surrogate markers of response. Finally, we will review the rationale for designing new therapeutic vaccine candidates to be used alone or in combination with other strategies to improve their effectiveness. Expert commentary: In the next future, the combination of DCs targeting candidates, inserts to redirect responses to unmutated parts of the virus, adjuvants to redirect responses to sanctuaries or improve the balance between activation/tolerance (IL-15, anti-PD1 antibodies) and latency reversing agents could be necessary to finally achieve the remission of HIV-1 infection.

Mucosal Vaccination with Heterologous Viral Vectored Vaccine Targeting Subdominant SIV Accessory Antigens Strongly Inhibits Early Viral Replication

Conventional HIV T cell vaccine strategies have not been successful in containing acute peak viremia, nor in providing long-term control. We immunized rhesus macaques intramuscularly and rectally using a heterologous adenovirus vectored SIV vaccine regimen encoding normally weakly immunogenic tat, vif, rev and vpr antigens fused to the MHC class II associated invariant chain. Immunizations induced broad T cell responses in all vaccinees. Following up to 10 repeated low-dose intrarectal challenges, vaccinees suppressed early viral replication (P = 0.01) and prevented the peak viremia in 5/6 animals. Despite consistently undetectable viremia in 2 out of 6 vaccinees, all animals showed evidence of infection induced immune responses indicating that infection had taken place. Vaccinees, with and without detectable viremia better preserved their rectal CD4 + T cell population and had reduced immune hyperactivation as measured by naïve T cell depletion, Ki-67 and PD-1 expression on T cells. These results indicate that vaccination towards SIV accessory antigens vaccine can provide a level of acute control of SIV replication with a suggestion of beneficial immunological consequences in infected animals of unknown long-term significance.

In conclusion, our studies demonstrate that a vaccine encoding subdominant antigens not normally associated with virus control can exert a significant impact on acute peak viremia.

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Mucosal heterologousvirus-vectored vaccine used with MHC class II associated invariant chain linked SIV accessory antigens

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Mucosal vaccination targeting subdominant antigens delay SIV mac251 replication in rhesus macaques.

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Longterm reduction of immune hyperactivation following SIV infection of vaccinated macaques.

Mucosal immunization is used with heterologous viral vectors and a genetic adjuvant to raise responses against poorly immunogenic SIV antigens. Following repeated low-dose challenge we observed delayed establishment of chronic phase viremia and reduced immune hyperactivation 6 months after established infection. Vaccination was found to strongly reduce viremia at early, but not late time points, after detected infection and in 2 out of 6 animals infection could only observed as virus induced T cell responses. Subdominant antigen vaccines may thus be used to delay SIV mac251 infection and can enable control of chronic viremia in a minority of cases.

HIV Infects Bronchial Epithelium and Suppresses Components of the Mucociliary Clearance Apparatus

Recurrent lung infections and pneumonia are emerging as significant comorbidities in the HIV-infected population in the era of combination antiretroviral therapy (cART). HIV infection has been reported to suppress nasal mucociliary clearance (MCC). Since the primary components driving nasal MCC and bronchial MCC are identical, it is possible that bronchial MCC is affected as well. Effective MCC requires optimal ciliary beating which depends on the maintenance of the airway surface liquid (ASL), a function of cystic fibrosis transmembrane conductance regulator (CFTR) activity and the integrity of the signaling mechanism that regulates ciliary beating and fluid secretion. Impairment of either component of the MCC apparatus can compromise its efficacy and promote microbial colonization. We demonstrate that primary bronchial epithelium expresses HIV receptor CD4 and co-receptors CCR5 and CXCR4 and can be infected by both R5 and X4 tropic strains of HIV. We show that HIV Tat suppresses CFTR biogenesis and function in primary bronchial epithelial cells by a pathway involving TGF-β signaling. HIV infection also interferes with bronchial epithelial cell differentiation and suppresses ciliogenesis. These findings suggest that HIV infection suppresses tracheobronchial mucociliary clearance and this may predispose HIV-infected patients to recurrent lung infections, pneumonia and chronic bronchitis.

HIV-1 Tat protein vaccination in mice infected with Mycobacterium tuberculosis is safe, immunogenic and reduces bacterial lung pathology

Background

The therapeutic HIV-1 Tat protein vaccine is in advanced clinical development. Tuberculosis, the main AIDS co-infection, is highly endemic in areas where AIDS prevention through vaccination is needed. However, safety and immunogenicity of Tat vaccination in the course of Mycobacterium tuberculosis (Mtb) infection is still unknown and it prevents the possibility to administer the vaccine to Mtb-infected individuals. We addressed the interplay and effects of Tat vaccination on Mtb infection in immunocompetent mice.

Methods

C57BL/6 mice were vaccinated or not with Bacillus Calmette-Guerin (BCG), the current tuberculosis vaccine, and after 5 weeks were infected with Mtb by intravenous route. The Tat protein was injected intradermally at 1, 2 and 4 weeks after Mtb challenge. Eight weeks after Mtb infection, all mice were sacrificed, and both the degree of pathology and immune responses to Mtb and Tat were evaluated. As additional control, some mice were either vaccinated or not with BCG, were not challenged with Mtb, but received the Tat protein. Statistical significances were evaluated by one-way or two-way ANOVA and Tukey’s multiple comparisons post-test.

Results

In the lungs of Mtb-infected mice, Tat-vaccine did not favour Mtb replication and indeed reduced both area of cellular infiltration and protein levels of Interferon-γ, Chemokine (C-C motif) ligand-4 and Interleukin-1β, pathological events triggered by Mtb-infection. Moreover, the protection against Mtb infection conferred by BCG remained good after Tat protein treatment. In spleen cells of Mtb-infected mice, Tat vaccination enhanced Mtb-specific Interferon-γ and Interleukin-17 responses, which may have a protective role. Of note, Mtb infection reduced, but did not suppress, the development of anti-Tat antibodies, required for Tat vaccine efficacy and the titer of anti-Tat IgG was potentiated by BCG vaccination in Mtb-free mice. In general, Tat treatment was well tolerated in both Mtb-infected and Mtb-free mice.

Conclusions

Tat protein vaccine, administered in Mtb-infected mice with a protocol resembling that used in the clinical trials, was safe, immunogenic, limited the lung Mtb-associated immunopathology and did not abrogate the protective efficacy of BCG. These data provide preliminary evidence for a safe use of Tat vaccine in people vaccinated with BCG and/or suffering from tuberculosis.

Association between different anti-Tat antibody isotypes and HIV disease progression: data from an African cohort

BACKGROUND

The presence of IgG and IgM against Tat, an HIV protein important for viral replication and immune dysfunction, is associated with slow disease progression in clade B HIV-infected individuals. However, although Tat activities strictly depend on the viral clade, our knowledge about the importance of anti-Tat antibodies in non-clade B HIV infection is poor. The objective of this study was to investigate the association of different anti-Tat antibody isotypes with disease progression in non-clade B HIV-infected subjects and to study the relationship between anti-Tat humoral responses and immunological abnormalities.

METHODS

Anti-clade B and -clade C Tat IgG, IgM and IgA titers were assessed in serum samples from 96 cART-naïve subjects with chronic HIV infection from Mbeya, Tanzania, and associated with CD4(+) T cell count, plasma viremia and CD4(+) and CD8(+) T cell phenotypes.

RESULTS

Anti-Tat IgM were preferentially detected in chronic HIV-infected subjects with low T cell activation (p-value = 0.03) and correlated with higher CD4(+) T cell counts and lower viral loads irrespective of the duration of infection (p-value = 0.019 and p-value = 0.037 respectively). Conversely, anti-Tat IgA were preferentially detected in individuals with low CD4(+) T cell counts and high viral load (p-value = 0.02 and p-value < 0.001 respectively). The simultaneous presence of anti-Tat IgG and IgM protected from fast CD4(+) T cell decline (p-value < 0.01) and accumulation of CD38(+)HLADR(+)CD8(+) T cells (p- value = 0.029).

CONCLUSIONS

Anti-Tat IgG alone are not protective in non-clade B infected subjects, unless concomitant with IgM, suggesting a protective role of persistent anti-Tat IgM irrespective of the infecting clade.

Molecular and Genetic Characterization of HIV-1 Tat Exon-1 Gene from Cameroon Shows Conserved Tat HLA-Binding Epitopes: Functional Implications

HIV-1 Tat plays a critical role in viral transactivation. Subtype-B Tat has potential use as a therapeutic vaccine. However, viral genetic diversity and population genetics would significantly impact the efficacy of such a vaccine. Over 70% of the 37-million HIV-infected individuals are in sub-Saharan Africa (SSA) and harbor non-subtype-B HIV-1. Using specimens from 100 HIV-infected Cameroonians, we analyzed the sequences of HIV-1 Tat exon-1, its functional domains, post-translational modifications (PTMs), and human leukocyte antigens (HLA)-binding epitopes. Molecular phylogeny revealed a high genetic diversity with nine subtypes, CRF22_01A1/CRF01_AE, and negative selection in all subtypes. Amino acid mutations in Tat functional domains included N24K (44%), N29K (58%), and N40K (30%) in CRF02_AG, and N24K in all G subtypes. Motifs and phosphorylation analyses showed conserved amidation, N-myristoylation, casein kinase-2 (CK2), serine and threonine phosphorylation sites. Analysis of HLA allelic frequencies showed that epitopes for HLAs A*0205, B*5301, Cw*0401, Cw*0602, and Cw*0702 were conserved in 58%-100% of samples, with B*5301 epitopes having binding affinity scores > 100 in all subtypes. This is the first report of N-myristoylation, amidation, and CK2 sites in Tat; these PTMs and mutations could affect Tat function. HLA epitopes identified could be useful for designing Tat-based vaccines for highly diverse HIV-1 populations, as in SSA.

A HIV-Tat/C4-binding protein chimera encoded by a DNA vaccine is highly immunogenic and contains acute EcoHIV infection in mice

DNA vaccines are cost-effective to manufacture on a global scale and Tat-based DNA vaccines have yielded protective outcomes in preclinical and clinical models of human immunodeficiency virus (HIV), highlighting the potential of such vaccines. However, Tat-based DNA vaccines have been poorly immunogenic, and despite the administration of multiple doses and/or the addition of adjuvants, these vaccines are not in general use. In this study, we improved Tat immunogenicity by fusing it with the oligomerisation domain of a chimeric C4-binding protein (C4b-p), termed IMX313, resulting in Tat heptamerisation and linked Tat to the leader sequence of tissue plasminogen activator (TPA) to ensure that the bulk of heptamerised Tat is secreted. Mice vaccinated with secreted Tat fused to IMX313 (pVAX-sTat-IMX313) developed higher titres of Tat-specific serum IgG, mucosal sIgA and cell-mediated immune (CMI) responses, and showed superior control of EcoHIV infection, a surrogate murine HIV challenge model, compared with animals vaccinated with other test vaccines. Given the crucial contribution of Tat to HIV-1 pathogenesis and the precedent of Tat-based DNA vaccines in conferring some level of protection in animal models, we believe that the virologic control demonstrated with this novel multimerised Tat vaccine highlights the promise of this vaccine candidate for humans.

HIV-Tat immunization induces cross-clade neutralizing antibodies and CD4(+) T cell increases in antiretroviral-treated South African volunteers: a randomized phase II clinical trial

BACKGROUND

Although combined antiretroviral therapy (cART) has saved millions of lives, it is incapable of full immune reconstitution and virus eradication. The transactivator of transcription (Tat) protein is a key human immunodeficiency virus (HIV) virulence factor required for virus replication and transmission. Tat is expressed and released extracellularly by infected cells also under cART and in this form induces immune dysregulation, and promotes virus reactivation, entry and spreading. Of note, anti-Tat antibodies are rare in natural infection and, when present, correlate with asymptomatic state and reduced disease progression. This suggested that induction of anti-Tat antibodies represents a pathogenesis-driven intervention to block progression and to intensify cART. Indeed Tat-based vaccination was safe, immunogenic and capable of immune restoration in an open-label, randomized phase II clinical trial conducted in 168 cART-treated volunteers in Italy. To assess whether B-clade Tat immunization would be effective also in patients with different genetic background and infecting virus, a phase II trial was conducted in South Africa.

METHODS

The ISS T-003 was a 48-week randomised, double-blinded, placebo-controlled trial to evaluate immunogenicity (primary endpoint) and safety (secondary endpoint) of B-clade Tat (30 μg) given intradermally, three times at 4-week intervals, in 200 HIV-infected adults on effective cART (randomised 1:1) with CD4(+) T-cell counts ≥200 cells/µL. Study outcomes also included cross-clade anti-Tat antibodies, neutralization, CD4(+) T-cell counts and therapy compliance.

RESULTS

Immunization was safe and well-tolerated and induced durable, high titers anti-Tat B-clade antibodies in 97 % vaccinees. Anti-Tat antibodies were cross-clade (all vaccinees tested) and neutralized Tat-mediated entry of oligomeric B-clade and C-clade envelope in dendritic cells (24 participants tested). Anti-Tat antibody titers correlated positively with neutralization. Tat vaccination increased CD4(+) T-cell numbers (all participants tested), particularly when baseline levels were still low after years of therapy, and this had a positive correlation with HIV neutralization. Finally, in cART non-compliant patients (24 participants), vaccination contained viral load rebound and maintained CD4(+) T-cell numbers over study entry levels as compared to placebo.

CONCLUSIONS

The data indicate that Tat vaccination can restore the immune system and induces cross-clade neutralizing anti-Tat antibodies in patients with different genetic backgrounds and infecting viruses, supporting the conduct of phase III studies in South Africa. Trial registration ClinicalTrials.gov NCT01513135, 01/23/2012.

Approaches to preventative and therapeutic HIV vaccines

Novel strategies are being researched to discover vaccines to prevent and treat HIV-1. Non-efficacious preventative vaccine approaches include bivalent recombinant gp120 alone, HIV gene insertion into an Adenovirus 5 (Ad5) virus vector and the DNA prime/Ad5 boost vaccine regimen. However, the ALVAC-HIV prime/AIDSVAX® B/E gp120 boost regimen showed 31.2% efficacy at 3.5 years, and is being investigated as clade C constructs with an additional boost. Likewise, although multiple therapeutic vaccines have failed in the past, in a non-placebo controlled trial, a Tat vaccine demonstrated immune cell restoration, reduction of immune activation, and reduced HIV-1 DNA viral load. Monoclonal antibodies for passive immunization or treatment show promise, with VRC01 entering advanced clinical trials.

Effects of different routes of administration on the immunogenicity of the Tat protein and a Tat-derived peptide

The use of the Tat protein of HIV in vaccines against AIDS showed promising results in primate and human studies. To characterize the impact of the administration route on the induction of humoral responses at systemic and mucosal levels, we compared intradermal, intramuscular and mucosal immunizations with Tat and a Tat-derived peptide. Mice were immunized with the Tat protein by different routes and the titer and isotype of anti-Tat antibodies were assessed in serum and mucosal lavages. Intramuscular and intradermal administrations showed comparable immunogenicity, while the mucosal administration was unable to induce IgM in serum and IgG at mucosal sites but showed superior immunogenicity in terms of IgA induction. Anti-Tat antibodies were also obtained upon vaccination with the immunodominant Tat 1-20 peptide which was, however, less immunogenic than the whole Tat protein.

Mucociliary dysfunction in HIV and smoked substance abuse

Impaired mucociliary clearance (MCC) is a hallmark of acquired chronic airway diseases like chronic bronchitis associated with chronic obstructive pulmonary disease (COPD) and asthma. This manifests as microbial colonization of the lung consequently leading to recurrent respiratory infections. People living with HIV demonstrate increased incidence of these chronic airway diseases. Bacterial pneumonia continues to be an important comorbidity in people living with HIV even though anti-retroviral therapy has succeeded in restoring CD4+ cell counts. People living with HIV demonstrate increased microbial colonization of the lower airways. The microbial flora is similar to that observed in diseases like cystic fibrosis and COPD suggesting that mucociliary dysfunction could be a contributing factor to the increased incidence of chronic airway diseases in people living with HIV. The three principal components of the MCC apparatus are, a mucus layer, ciliary beating, and a periciliary airway surface liquid (ASL) layer that facilitates ciliary beating. Cystic fibrosis transmembrane conductance regulator (CFTR) plays a pivotal role in regulating the periciliary ASL. HIV proteins can suppress all the components of the MCC apparatus by increasing mucus secretion and suppressing CFTR function. This can decrease ASL height leading to suppressed ciliary beating. The effects of HIV on MCC are exacerbated when combined with other aggravating factors like smoking or inhaled substance abuse, which by themselves can suppress one or more components of the MCC system. This review discusses the pathophysiological mechanisms that lead to MCC suppression in people living with HIV who also smoke tobacco or abuse illicit drugs.

Development of a novel AIDS vaccine: the HIV-1 transactivator of transcription protein vaccine

INTRODUCTION

Classical approaches aimed at targeting the HIV-1 envelope as well as other structural viral proteins have largely failed. The HIV-1 transactivator of transcription (Tat) is a key HIV virulence factor, which plays pivotal roles in virus gene expression, replication, transmission and disease progression. Notably, anti-Tat Abs are uncommon in natural infection and, when present, correlate with the asymptomatic state and lead to lower or no disease progression. Hence, targeting Tat represents a pathogenesis-driven intervention.

AREAS COVERED

Here, we review the rationale and the translational development of a therapeutic vaccine targeting the Tat protein. Preclinical and Phase I studies, Phase II trials with Tat in anti-Tat Ab-negative, virologically suppressed highly active antiretroviral therapy-treated subjects in Italy and South Africa were conducted. The results indicate that Tat-induced immune responses are necessary to restore immune homeostasis, to block the replenishment and to reduce the size of the viral reservoir. Additionally, they may help in establishing key parameters for highly active antiretroviral therapy intensification and a functional cure.

EXPERT OPINION

We propose the therapeutic setting as the most feasible to speed up the testing and comparison of preventative vaccine candidates, as the distinction lies in the use of the vaccine in uninfected versus infected subjects and not in the vaccine formulation.

HIV-1 Tat immunization restores immune homeostasis and attacks the HAART-resistant blood HIV DNA: results of a randomized phase II exploratory clinical trial

BACKGROUND

The phase II multicenter, randomized, open label, therapeutic trial (ISS T-002, Clinicaltrials.gov NCT00751595) was aimed at evaluating the immunogenicity and the safety of the biologically active HIV-1 Tat protein administered at 7.5 or 30 μg, given 3 or 5 times monthly, and at exploring immunological and virological disease biomarkers. The study duration was 48 weeks, however, vaccinees were followed until the last enrolled subject reached the 48 weeks. Reported are final data up to 144 weeks of follow-up. The ISS T-002 trial was conducted in 11 clinical centers in Italy on 168 HIV positive subjects under Highly Active Antiretroviral Therapy (HAART), anti-Tat Antibody (Ab) negative at baseline, with plasma viremia <50 copies/mL in the last 6 months prior to enrollment, and CD4(+) T-cell number ≥200 cells/μL. Subjects from a parallel observational study (ISS OBS T-002, Clinicaltrials.gov NCT0102455) enrolled at the same clinical sites with the same criteria constituted an external reference group to explore biomarkers of disease.

RESULTS

The vaccine was safe and well tolerated and induced anti-Tat Abs in most patients (79%), with the highest frequency and durability in the Tat 30 μg groups (89%) particularly when given 3 times (92%). Vaccination promoted a durable and significant restoration of T, B, natural killer (NK) cells, and CD4(+) and CD8(+) central memory subsets. Moreover, a significant reduction of blood proviral DNA was seen after week 72, particularly under PI-based regimens and with Tat 30 μg given 3 times (30 μg, 3x), reaching a predicted 70% decay after 3 years from vaccination with a half-life of 88 weeks. This decay was significantly associated with anti-Tat IgM and IgG Abs and neutralization of Tat-mediated entry of oligomeric Env in dendritic cells, which predicted HIV-1 DNA decay. Finally, the 30 μg, 3x group was the only one showing significant increases of NK cells and CD38(+)HLA-DR(+)/CD8(+) T cells, a phenotype associated with increased killing activity in elite controllers.

CONCLUSIONS

Anti-Tat immune responses are needed to restore immune homeostasis and effective anti-viral responses capable of attacking the virus reservoir. Thus, Tat immunization represents a promising pathogenesis-driven intervention to intensify HAART efficacy.

The grafting of universal T-helper epitopes enhances immunogenicity of HIV-1 Tat concurrently improving its safety profile

Extracellular Tat (eTat) plays an important role in HIV-1 pathogenesis. The presence of anti-Tat antibodies is negatively correlated with disease progression, hence making Tat a potential vaccine candidate. The cytotoxicity and moderate immunogenicity of Tat however remain impediments for developing Tat-based vaccines. Here, we report a novel strategy to concurrently enhance the immunogenicity and safety profile of Tat. The grafting of universal helper T-lymphocyte (HTL) epitopes, Pan DR Epitope (PADRE) and Pol₇₁₁ into the cysteine rich domain (CRD) and the basic domain (BD) abolished the transactivation potential of the Tat protein. The HTL-Tat proteins elicited a significantly higher titer of antibodies as compared to the wild-type Tat in BALB/c mice. While the N-terminal epitope remained immunodominant in HTL-Tat immunizations, an additional epitope in exon-2 was recognized with comparable magnitude suggesting a broader immune recognition. Additionally, the HTL-Tat proteins induced cross-reactive antibodies of high avidity that efficiently neutralized exogenous Tat, thus blocking the activation of a Tat-defective provirus. With advantages such as presentation of multiple B-cell epitopes, enhanced antibody response and importantly, transactivation-deficient Tat protein, this approach has potential application for the generation of Tat-based HIV/AIDS vaccines.

Biocompatible anionic polymeric microspheres as priming delivery system for effetive HIV/AIDS Tat-based vaccines

Here we describe a prime-boost regimen of vaccination in Macaca fascicularis that combines priming with novel anionic microspheres designed to deliver the biologically active HIV-1 Tat protein and boosting with Tat in Alum. This regimen of immunization modulated the IgG subclass profile and elicited a balanced Th1-Th2 type of humoral and cellular responses. Remarkably, following intravenous challenge with SHIV89.6P_cy243, vaccinees significantly blunted acute viremia, as compared to control monkeys, and this control was associated with significantly lower CD4⁺ T cell depletion rate during the acute phase of infection and higher ability to resume the CD4⁺ T cell counts in the post-acute and chronic phases of infection. The long lasting control of viremia was associated with the persistence of high titers anti-Tat antibodies whose profile clearly distinguished vaccinees in controllers and viremics. Controllers, as opposed to vaccinated and viremic cynos, exhibited significantly higher pre-challenge antibody responses to peptides spanning the glutamine-rich and the RGD-integrin-binding regions of Tat. Finally, among vaccinees, titers of anti-Tat IgG1, IgG3 and IgG4 subclasses had a significant association with control of viremia in the acute and post-acute phases of infection. Altogether these findings indicate that the Tat/H1D/Alum regimen of immunization holds promise for next generation vaccines with Tat protein or other proteins for which maintenance of the native conformation and activity are critical for optimal immunogenicity. Our results also provide novel information on the role of anti-Tat responses in the prevention of HIV pathogenesis and for the design of new vaccine candidates.

Expression of the IL-7 receptor alpha-chain is down regulated on the surface of CD4 T-cells by the HIV-1 Tat protein

HIV infection elicits defects in CD4 T-cell homeostasis in both a quantitative and qualitative manner. Interleukin-7 (IL-7) is essential to T-cell homeostasis and several groups have shown reduced levels of the IL-7 receptor alpha-chain (CD127) on both CD4 and CD8 T-cells in viremic HIV+ patients. We have shown previously that soluble HIV Tat protein specifically down regulates cell surface expression of CD127 on human CD8 T-cells in a paracrine fashion. The effects of Tat on CD127 expression in CD4 T-cells has yet to be described. To explore this effect, CD4 T-cells were isolated from healthy individuals and expression levels of CD127 were examined on cells incubated in media alone or treated with Tat protein. We show here that, similar to CD8 T-cells, the HIV-1 Tat protein specifically down regulates CD127 on primary human CD4 T-cells and directs the receptor to the proteasome for degradation. Down regulation of CD127 in response to Tat was seen on both memory and naive CD4 T-cell subsets and was blocked using either heparin or anti-Tat antibodies. Tat did not induce apoptosis in cultured primary CD4 T-cells over 72 hours as determined by Annexin V and PI staining. Pre-incubation of CD4 T-cells with HIV-1 Tat protein did however reduce the ability of IL-7 to up regulate Bcl-2 expression. Similar to exogenous Tat, endogenously expressed HIV Tat protein also suppressed CD127 expression on primary CD4 T-cells. In view of the important role IL-7 plays in lymphocyte proliferation, homeostasis and survival, down regulation of CD127 by Tat likely plays a central role in immune dysregulation and CD4 T-cell decline. Understanding this effect could lead to new approaches to mitigate the CD4 T-cell loss evident in HIV infection.

Surface-bound Tat inhibits antigen-specific CD8+ T-cell activation in an integrin-dependent manner

OBJECTIVE

The identification of still unrevealed mechanisms affecting the anti-HIV CD8 T-cell response in HIV-1 infection.

DESIGN

Starting from the observation that anti-Tat immunization is associated with improved CD8 T-cell immunity, we developed both in-vitro and ex-vivo assays to characterize the effects of extra-cellular Tat on the adaptive CD8 T-cell response.

METHODS

The effects of Tat on CD8 T-cell activation were assayed using CD8 T-cell clones specific for either cellular (MART-1) or viral (HIV-1 Nef) antigens, and HIV-1 Gag-specific CD8 T cells from HIV-1 patients.

RESULTS

The interaction between CD8 T lymphocytes and immobilized Tat, but not its soluble form, inhibits peptide-specific CD8 T-lymphocyte activation. The inhibition does not depend on Tat trans-activation activity, but on the interaction of the Tat RGD domain with α5β1 and αvβ3 integrins. Impaired CD8 T-cell activation was also observed in cocultures of CD8 T cells with HIV-1-infected cells. Anti-Tat Abs abrogate the inhibitory effect, consistently with the evidence that extracellular Tat accumulates on the cell membrane of virus-producing cells. The Tat-induced inhibition of cell activation associates with increased apoptosis of CD8 T cells. Finally, the inhibition of cell activation also takes place in Gag-specific CD8 T lymphocytes from HIV-1-infected patients.

CONCLUSION

Our results support the idea that CD8 T-cell apoptosis induced by surface-bound extracellular Tat can contribute to the dysregulation of the CD8 T-cell adaptive response against HIV as well as other pathogens present in AIDS patients.

Challenges in HIV Vaccine Research for Treatment and Prevention

Many attempts have been made or are ongoing for HIV prevention and HIV cure. Many successes are in the list, particularly for HIV drugs, recently proposed also for prevention. However, no eradication of infection has been achieved so far with any drug. Further, a residual immune dysregulation associated to chronic immune activation and incomplete restoration of B and T cell subsets, together with HIV DNA persistence in reservoirs, are still unmet needs of the highly active antiretroviral therapy, causing novel “non-AIDS related” diseases that account for a higher risk of death even in virologically suppressed patients. These “ART unmet needs” represent a problem, which is expected to increase by ART roll out. Further, in countries such as South Africa, where six millions of individuals are infected, ART appears unable to contain the epidemics. Regretfully, all the attempts at developing a preventative vaccine have been largely disappointing. However, recent therapeutic immunization strategies have opened new avenues for HIV treatment, which might be exploitable also for preventative vaccine approaches. For example, immunization strategies aimed at targeting key viral products responsible of virus transmission, activation, and maintenance of virus reservoirs may intensify drug efficacy and lead to a functional cure providing new perspectives also for prevention and future virus eradication strategies. However, this approach imposes new challenges to the scientific community, vaccine developers, and regulatory bodies, such as the identification of novel immunological and virological biomarkers to assess efficacy end-points, taking advantage from the natural history of infection and exploiting lessons from former trials. This review will focus first on recent advancement of therapeutic strategies, then on the progresses made in preventative approaches, discussing concepts, and problems for the way ahead for the development of vaccines for HIV treatment and prevention.

HIV-1 Tat affects the programming and functionality of human CD8⁺ T cells by modulating the expression of T-box transcription factors

OBJECTIVE

HIV infection is characterized by several immune dysfunctions of both CD8⁺ and CD4⁺ T cells as hyperactivation, impairment of functionality and expansion of memory T cells. CD8⁺ T-cell dysfunctions have been associated with increased expression of T-bet, Eomesdermin and pro-inflammatory cytokines, and with down-regulation of CD127. The HIV-1 trans-activator of transcription (Tat) protein, which is released by infected cells and detected in tissues of HIV-positive individuals, is known to contribute to the dysregulation of CD4⁺ T cells; however, its effects on CD8⁺ T cells have not been investigated. Thus, in this study, we sought to address whether Tat may affect CD8⁺ T-cell functionality and programming.

METHODS

CD8⁺ T cells were activated by T-cell receptor engagement in the presence or absence of Tat. Cytokine production, killing capacity, surface phenotype and expression of transcription factors important for T-cell programming were evaluated.

RESULTS

Tat favors the secretion of interleukin-2, interferon-γ and granzyme B in CD8⁺ T cells. Behind this functional modulation we observed that Tat increases the expression of T-bet, Eomesdermin, Blimp-1, Bcl-6 and Bcl-2 in activated but not in unstimulated CD8⁺ T lymphocytes. This effect is associated with the down-regulation of CD127 and the up-regulation of CD27.

CONCLUSION

Tat deeply alters the programming and functionality of CD8⁺ T lymphocytes.

IL-7 receptor recovery on CD8 T-cells isolated from HIV+ patients is inhibited by the HIV Tat protein

Expression of the IL-7 receptor α-chain (CD127) is decreased on CD8 T-cells in HIV infected patients and partially recovers in those receiving antiretroviral therapy with sustained viral suppression. We have shown that soluble HIV Tat protein down regulates CD127 expression on CD8 T-cells isolated from healthy HIV-negative individuals. Tat is taken up by CD8 T-cells via endocytosis, exits the endosome and then translocates to the inner leaflet of the cell membrane where it binds to the cytoplasmic tail of CD127 inducing receptor internalization and degradation by the proteasome. This down regulation of CD127 by Tat results in impaired CD8 T-cell function. Interestingly, suppression of CD127 by Tat is reversible and requires the continual presence of Tat in the culture media. We thus questioned whether the low IL-7 receptor expression evident on CD8 T-cells in HIV+ patients was similarly reversible and if suppression of the receptor could be maintained ex vivo by Tat protein alone. We show here that when CD8 T-cells isolated from HIV+ patients are incubated alone in fresh medium, low CD127 expression on the cell surface recovers to normal levels. This recovery of CD127, however, is completely inhibited by the addition of HIV Tat protein to the culture media. This study then provides evidence that soluble factor(s) are responsible for low CD127 expression on circulating CD8 T-cells in HIV+ individuals and further implicates Tat in suppressing this receptor essential to CD8 T-cell proliferation and function.

An attenuated herpes simplex virus type 1 (HSV1) encoding the HIV-1 Tat protein protects mice from a deadly mucosal HSV1 challenge

Herpes simplex virus types 1 and 2 (HSV1 and HSV2) are common infectious agents in both industrialized and developing countries. They cause recurrent asymptomatic and/or symptomatic infections, and life-threatening diseases and death in newborns and immunocompromised patients. Current treatment for HSV relies on antiviral medications, which can halt the symptomatic diseases but cannot prevent the shedding that occurs in asymptomatic patients or, consequently, the spread of the viruses. Therefore, prevention rather than treatment of HSV infections has long been an area of intense research, but thus far effective anti-HSV vaccines still remain elusive. One of the key hurdles to overcome in anti-HSV vaccine development is the identification and effective use of strategies that promote the emergence of Th1-type immune responses against a wide range of epitopes involved in the control of viral replication. Since the HIV1 Tat protein has several immunomodulatory activities and increases CTL recognition of dominant and subdominant epitopes of heterologous antigens, we generated and assayed a recombinant attenuated replication-competent HSV1 vector containing the tat gene (HSV1-Tat). In this proof-of-concept study we show that immunization with this vector conferred protection in 100% of mice challenged intravaginally with a lethal dose of wild-type HSV1. We demonstrate that the presence of Tat within the recombinant virus increased and broadened Th1-like and CTL responses against HSV-derived T-cell epitopes and elicited in most immunized mice detectable IgG responses. In sharp contrast, a similarly attenuated HSV1 recombinant vector without Tat (HSV1-LacZ), induced low and different T cell responses, no measurable antibody responses and did not protect mice against the wild-type HSV1 challenge. These findings strongly suggest that recombinant HSV1 vectors expressing Tat merit further investigation for their potential to prevent and/or contain HSV1 infection and dissemination.

The presence of anti-Tat antibodies in HIV-infected individuals is associated with containment of CD4+ T-cell decay and viral load, and with delay of disease progression: results of a 3-year cohort study

Background

Tat is a key HIV-1 virulence factor, which plays pivotal roles in virus gene expression, replication, transmission and disease progression. After release, extracellular Tat accumulates in tissues and exerts effects on both the virus and the immune system, promoting immune activation and virus spreading while disabling the host immune defense. In particular, Tat binds Env spikes on virus particles forming a virus entry complex, which favors infection of dendritic cells and efficient transmission to T cells via RGD-binding integrins. Tat also shields the CCR5-binding sites of Env rendering ineffective virus neutralization by anti-Env antibodies (Abs). This is reversed by the anti-Tat Abs present in natural infection or induced by vaccination.

Findings

Here we present the results of a cohort study, showing that the presence of anti-Tat Abs in asymptomatic and treatment-naïve HIV-infected subjects is associated with containment of CD4⁺ T-cell loss and viral load and with a delay of disease progression. In fact, no subjects with high anti-Tat Ab titers initiated antiretroviral therapy during the three years of follow-up. In contrast, no significant effects were seen for anti-Env and anti-Gag Abs. The increase of anti-Env Ab titers was associated with a reduced risk of starting therapy only in the presence of anti-Tat Abs, suggesting an effect of combined anti-Tat and anti-Env Abs on the Tat/Env virus entry complex and on virus neutralization.

Conclusions

Anti-Tat immunity may help delay HIV disease progression, thus, targeting Tat may offer a novel therapeutic intervention to postpone antiretroviral treatment or to increase its efficacy.

Induction of antibodies and T cell responses by a recombinant influenza virus carrying an HIV-1 TatΔ51-59 protein in mice

Recombinant influenza viruses hold promise as vectors for vaccines to prevent transmission of mucosal pathogens. In this study, we generated a recombinant WSN/TatΔ(51-59) virus in which Tat protein lacking residues 51 to 59 of the basic domain was inserted into the N-terminus of the hemagglutinin (HA) of A/WSN/33 virus. The TatΔ(51-59) insertion into the viral HA caused a 2-log reduction in viral titers in cell culture, compared with the parental A/WSN/33 virus, and severely affected virus replication in vivo. Nevertheless, Tat-specific antibodies and T cell responses were elicited upon a single intranasal immunization of BALB/c mice with WSN/TatΔ(51-59) virus. Moreover, Tat-specific immune responses were also detected following vaccine administration via the vaginal route. These data provide further evidence that moderately large HIV antigens can be delivered by chimeric HA constructs and elicit specific immune responses, thus increasing the options for the potential use of recombinant influenza viruses, and their derivatives, for prophylactic and therapeutic vaccines.

Developments in HIV-1 immunotherapy and therapeutic vaccination

Since the human immunodeficiency virus (HIV-1) pandemic began, few prophylactic vaccines have reached phase III trials. Only one has shown partial efficacy in preventing HIV-1 infection. The introduction of antiretroviral therapy (ART) has had considerable success in controlling infection and reducing transmission but in so doing has changed the nature of HIV-1 infection for those with access to ART. Access, compliance, and toxicity alongside the emergence of serious non-AIDS morbidity and the sometimes poor immune reconstitution in ART-treated patients have emphasized the need for additional therapies. Such therapy is intended to contribute to control of HIV-1 infection, permit structured treatment interruptions, or even establish a functional cure of permanently suppressed and controlled infection. Both immunotherapy and therapeutic vaccination have the potential to reach these goals. In this review, the latest developments in immunotherapy and therapeutic vaccination are discussed.

Clustered epitopes within a new poly-epitopic HIV-1 DNA vaccine shows immunogenicity in BALB/c mice

Despite a huge number of studies towards vaccine development against human immunodeficiency virus-1, no effective vaccine has been approved yet. Thus, new vaccines should be provided with new formulations. Herein, a new DNA vaccine candidate encoding conserved and immunogenic epitopes from HIV-1 antigens of tat, pol, gag and env is designed and constructed. After bioinformatics analyses to find the best epitopes and their tandem, nucleotide sequence corresponding to the designed multiepitope was synthesized and cloned into pcDNA3.1+ vector. Expression of pcDNA3.1-tat/pol/gag/env plasmid was evaluated in HEK293T cells by RT-PCR and western-blotting. Seven groups of BALB/c mice were intramuscularly immunized three times either with 50, 100, 200 µg of plasmid in 2-week intervals or with similar doses of insert-free plasmid. Two weeks after the last injection, proliferation of T cells and secretion of IL4 and IFN-γ cytokines were evaluated using Brdu and ELISA methods, respectively. Results showed the proper expression of the plasmid in protein and mRNA levels. Moreover, the designed multiepitope plasmid was capable of induction of both proliferation responses as well as IFN-γ and IL-4 cytokine production in a considerable level compared to the control groups. Overall, our primary data warranted further detailed studies on the potency of this vaccine.