Impact of viral dose and major histocompatibility complex class IB haplotype on viral outcome in mauritian cynomolgus monkeys vaccinated with Tat upon challenge with simian/human immunodeficiency virus SHIV89.6P

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.

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.

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.

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.

Limited available evidence supports theoretical predictions of reduced vaccine efficacy at higher exposure dose

Understanding the causes of vaccine failure is important for predicting disease dynamics in vaccinated populations and planning disease interventions. Pathogen exposure dose and heterogeneity in host susceptibility have both been implicated as important factors that may reduce overall vaccine efficacy and cause vaccine failure. Here, we explore the effect of pathogen dose and heterogeneity in host susceptibility in reducing efficacy of vaccines. Using simulation-based methods, we find that increases in pathogen exposure dose decrease vaccine efficacy, but this effect is modified by heterogeneity in host susceptibility. In populations where the mode of vaccine action is highly polarized, vaccine efficacy decreases more slowly with exposure dose than in populations with less variable protection. We compared these theoretical results to empirical estimates from a systematic literature review of vaccines tested over multiple exposure doses. We found that few studies (nine of 5,389) tested vaccine protection against infection over multiple pathogen challenge doses, with seven studies demonstrating a decrease in vaccine efficacy with increasing exposure dose. Our research demonstrates that pathogen dose has potential to be an important determinant of vaccine failure, although the limited empirical data highlight a need for additional studies to test theoretical predictions on the plausibility of reduced host susceptibility and high pathogen dose as mechanisms responsible for reduced vaccine efficacy in high transmission settings.

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.

"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.

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.

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.

Immunogenetic characterization of a captive colony of sooty mangabeys (Cercocebus atys) used for SIV research

BACKGROUND

African non-human primates are SIV natural hosts and do not develop disease following infection. Understanding disease avoidance mechanisms in these species is important for HIV vaccine development. The largest captive population of sooty mangabeys, a SIV natural host species, resides at the Yerkes National Primate Research Center.

METHODS

Thirteen primer sets that amplify polymorphic microsatellite loci within the MHC region were used to genotype 144 animals. Immunogenetic Management Software (IMS) was used to identify MHC haplotypes and organize data.

RESULTS

Seventy-three haplotypes were identified. Limited haplotype diversity was observed in this population with 88.2% of included animals carrying one of 18 haplotypes. Differences in haplotype frequency were observed between SIV (+) and SIV (-) populations.

CONCLUSIONS

We have developed a novel tool for others to use in the analysis of the role of the MHC in a natural host non-human primate model species used for SIV research.

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.

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.

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.

Immunogenicity of a recombinant measles HIV-1 subtype C vaccine

The HIV epidemic is greatest in Sub-Saharan Africa and India where HIV-1 subtype C is predominant. To control the spread of HIV in these parts of the world a preventive HIV-1 subtype C vaccine is urgently required. Here we report the immunogenicity of a candidate HIV-1 subtype C vaccine delivered by a recombinant measles vector carrying an insert encoding HIV-1 subtype C Gag, RT and Nef (MV1-F4), in MHC-typed non-human primates. HIV-1 specific cytokine secreting CD4+ and CD8+ T cell responses were detected in 15 out of 16 vaccinees. These HIV-specific T cell responses persisted in lymphoid tissues. Anti-HIV-1 antibody responses were detected in 15 out of 16 vaccinees and titres were boosted by a second immunisation carried out 84 days later. These findings support further exploration of the MV1-F4 vector as a candidate HIV-1 subtype C vaccine or as part of a wider vaccine strategy.

HIV-1 tat promotes integrin-mediated HIV transmission to dendritic cells by binding Env spikes and competes neutralization by anti-HIV antibodies

Use of Env in HIV vaccine development has been disappointing. Here we show that, in the presence of a biologically active Tat subunit vaccine, a trimeric Env protein prevents in monkeys virus spread from the portal of entry to regional lymph nodes. This appears to be due to specific interactions between Tat and Env spikes that form a novel virus entry complex favoring R5 or X4 virus entry and productive infection of dendritic cells (DCs) via an integrin-mediated pathway. These Tat effects do not require Tat-transactivation activity and are blocked by anti-integrin antibodies (Abs). Productive DC infection promoted by Tat is associated with a highly efficient virus transmission to T cells. In the Tat/Env complex the cysteine-rich region of Tat engages the Env V3 loop, whereas the Tat RGD sequence remains free and directs the virus to integrins present on DCs. V2 loop deletion, which unshields the CCR5 binding region of Env, increases Tat/Env complex stability. Of note, binding of Tat to Env abolishes neutralization of Env entry or infection of DCs by anti-HIV sera lacking anti-Tat Abs, which are seldom present in natural infection. This is reversed, and neutralization further enhanced, by HIV sera containing anti-Tat Abs such as those from asymptomatic or Tat-vaccinated patients, or by sera from the Tat/Env vaccinated monkeys. Thus, both anti-Tat and anti-Env Abs are required for efficient HIV neutralization. These data suggest that the Tat/Env interaction increases HIV acquisition and spreading, as a mechanism evolved by the virus to escape anti-Env neutralizing Abs. This may explain the low effectiveness of Env-based vaccines, which are also unlikely to elicit Abs against new Env epitopes exposed by the Tat/Env interaction. As Tat also binds Envs from different clades, new vaccine strategies should exploit the Tat/Env interaction for both preventative and therapeutic interventions.

Multilocus definition of MHC haplotypes in pedigreed cynomolgus macaques (Macaca fascicularis)

Cynomolgus macaques (Macaca fascicularis) are used widely in biomedical research, and the genetics of their MHC (Mhc-Mafa) has become the focus of considerable attention in recent years. The cohort of Indonesian pedigreed macaques that we present here was typed for Mafa-A, -B, and -DR, by sequencing, as described in earlier studies. Additionally, the DRB region of these animals was characterised by microsatellite analyses. In this study, full-length sequencing of Mafa-DPA/B and -DQA/B in these animals was performed. A total of 75 different alleles were observed; 22 of which have not previously been reported, plus 18 extended exon 2 alleles that were already known. Furthermore, two microsatellites, D6S2854 and D6S2859, were used to characterise the complex Mafa-A region. Sequencing and segregation analyses revealed that the length patterns of these microsatellites are unique for each Mafa-A haplotype. In this work, we present a pedigreed colony of approximately 120 cynomolgus macaques; all of which are typed for the most significant polymorphic MHC class I and class II markers. Offspring of these pedigreed animals are easily characterised for their MHC by microsatellite analyses on the Mafa-A and -DRB regions, which makes the cumbersome sequencing analyses redundant.

Variable prevalence and functional diversity of the antiretroviral restriction factor TRIMCyp in Macaca fascicularis

The retroviral restriction factor TRIMCyp, derived from the TRIM5 gene, blocks replication at a postentry step. TRIMCyp has so far been found in four species of Asian macaques, Macaca fascicularis, M. mulatta, M. nemestrina, and M. leonina. M. fascicularis is commonly used as a model for AIDS research, but TRIMCyp has not been analyzed in detail in this species. We analyzed the prevalence of TRIMCyp in samples from Indonesia, Indochina, the Philippines, and Mauritius. We found that TRIMCyp is present at a higher frequency in Indonesian than in Indochinese M. fascicularis macaques and is also present in samples from the Philippines. TRIMCyp is absent in Mauritian M. fascicularis macaques. We then analyzed the restriction specificity of TRIMCyp derived from three animals of Indonesian origin. One allele, like the prototypic TRIMCyp alleles described for M. mulatta and M. nemestrina, restricts human immunodeficiency virus type 2 (HIV-2) and feline immunodeficiency virus (FIV) but not HIV-1. The others restrict HIV-1 and FIV but not HIV-2. Mutagenesis studies confirmed that polymorphisms at amino acid residues 369 and 446 in TRIMCyp (or residues 66 and 143 in the cyclophilin A [CypA] domain) confer restriction specificity. Additionally, we identified a polymorphism in the coiled-coil domain that appears to affect TRIMCyp expression or stability. Taken together, these data show that M. fascicularis has the most diverse array of TRIM5 restriction factors described for any primate species to date. These findings are relevant to our understanding of the evolution of retroviral restriction factors and the use of M. fascicularis models in AIDS research.

Gold drug auranofin restricts the viral reservoir in the monkey AIDS model and induces containment of viral load following ART suspension

OBJECTIVES

A small pool of long-lived memory CD4 T cells harboring the retroviral genome is one main obstacle to HIV eradication. We tested the impact of the gold compound, auranofin, on phenotype and viability of CD4 T cells in vitro, and on persistence of lentiviral reservoir cells in vivo.

DESIGN

In-vitro and in-vivo study. The pro-differentiating effect of auranofin was investigated in human primary CD4 T cells, and its capacity to deplete the viral DNA (vDNA) reservoir was tested in a pilot study involving six SIVmac251-infected macaques with viral loads stably suppressed by antiretroviral therapy (ART) (tenofovir/emtricitabine/raltegravir). The study was then amplified by intensifying ART using darunavir/r and including controls under intensified ART alone. All therapies were eventually suspended and viro-immunological parameters were monitored over time.

METHODS

Cell subpopulations were quantitated by flow cytometry following proper hematological analyses. Viral load and cell-associated vDNA were quantitated by Taqman real-time PCR.

RESULTS

In naïve, central memory and transitional memory CD4 T cells, auranofin induced both phenotype changes and cell death which were more pronounced in the memory compartment. In the pilot study in vivo, auranofin transiently decreased the cell-associated vDNA reservoir in peripheral blood. When ART was intensified, a sustained decrease in vDNA was observed only in auranofin-treated monkeys but not in controls treated with intensified ART alone. After therapy suspension, only monkeys that had received auranofin showed a deferred and subsequently blunted viral load rebound.

CONCLUSION

These findings represent a first step towards a remission of primate lentiviral infections.

A combination HIV vaccine based on Tat and Env proteins was immunogenic and protected macaques from mucosal SHIV challenge in a pilot study

HIV native Tat and V2 loop-deleted Env (EnvΔV2) proteins already proved safe and immunogenic in phase I clinical testing as single vaccine components. Further, a phase II vaccine trial with Tat showed intensification of the therapeutic effects of HAART in successfully treated HIV-infected individuals. Here a pilot study assessed the immunogenicity and protective efficacy of an HIV/AIDS vaccine based on the combination of Tat and EnvΔV2 proteins in cynomolgus macaques against homologous intrarectal challenge with 35 MID(50) (monkey infectious dose 50) of an R5 simian-human immunodeficiency virus (SHIV(SF162P4cy)). Upon challenge, three of four macaques immunized with Tat and EnvΔV2, and two of three monkeys immunized with EnvΔV2 alone were protected from infection. In contrast, all three control animals, which had been either administered with the adjuvants only or left untreated, and an additional monkey immunized with Tat alone became systemically infected. Protection of the macaques vaccinated with EnvΔV2 or Tat/EnvΔV2 correlated with higher peak titers of pre-challenge neutralizing antibodies obtained during the immunization period (between 70 and 3 weeks before challenge) and with anti-Env V3 loop binding antibodies assessed 3 weeks before challenge. Compared to EnvΔV2 alone, the Tat and EnvΔV2 combined vaccine elicited faster antibody responses (IgM) with a trend, early in the vaccination schedule, after the second immunization including EnvΔV2, towards broader anti-Env IgG epitope specificity and a higher ratio of neutralizing to Env-binding antibody titers. As the number of immunizations increased, vaccination with EnvΔV2 approached the immune response assessed after two inocula with the Tat/EnvΔV2 combined vaccine, even though some differences remained between groups, as indicated by anti-Env IgG epitope mapping. In fact, three weeks before challenge, plasma IgG of animals in the EnvΔV2 group showed a trend towards stronger specificity for the V1 loop and V5 loop-C5 regions of Env, whereas the Tat/EnvΔV2 group displayed an overall higher reactivity for epitopes within the Env V3 loop throughout the immunization period. Although differences in terms of protection rate were not found between the EnvΔV2 or Tat/EnvΔV2 vaccination groups in this pilot study, vaccination with Tat/EnvΔV2 appeared to accelerate the induction of potentially protective antibody responses to Env. In particular, antibodies to the Env V3 loop, whose levels at pre-challenge correlated with protection, were already higher early in the vaccination schedule in monkeys immunized with Tat/EnvΔV2 as compared to EnvΔV2 alone. Further studies including larger vaccination groups and fewer immunizations with these two vaccine candidates are needed to confirm these findings and to assess whether the Tat/EnvΔV2 vaccine may afford superior protection against infection.

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

Although HAART suppresses HIV replication, it is often unable to restore immune homeostasis. Consequently, non-AIDS-defining diseases are increasingly seen in treated individuals. This is attributed to persistent virus expression in reservoirs and to cell activation. Of note, in CD4⁺ T cells and monocyte-macrophages of virologically-suppressed individuals, there is continued expression of multi-spliced transcripts encoding HIV regulatory proteins. Among them, Tat is essential for virus gene expression and replication, either in primary infection or for virus reactivation during HAART, when Tat is expressed, released extracellularly and exerts, on both the virus and the immune system, effects that contribute to disease maintenance. Here we report results of an ad hoc exploratory interim analysis (up to 48 weeks) on 87 virologically-suppressed HAART-treated individuals enrolled in a phase II randomized open-label multicentric clinical trial of therapeutic immunization with Tat (ISS T-002). Eighty-eight virologically-suppressed HAART-treated individuals, enrolled in a parallel prospective observational study at the same sites (ISS OBS T-002), served for intergroup comparison. Immunization with Tat was safe, induced durable immune responses, and modified the pattern of CD4⁺ and CD8⁺ cellular activation (CD38 and HLA-DR) together with reduction of biochemical activation markers and persistent increases of regulatory T cells. This was accompanied by a progressive increment of CD4⁺ T cells and B cells with reduction of CD8⁺ T cells and NK cells, which were independent from the type of antiretroviral regimen. Increase in central and effector memory and reduction in terminally-differentiated effector memory CD4⁺ and CD8⁺ T cells were accompanied by increases of CD4⁺ and CD8⁺ T cell responses against Env and recall antigens. Of note, more immune-compromised individuals experienced greater therapeutic effects. In contrast, these changes were opposite, absent or partial in the OBS population. These findings support the use of Tat immunization to intensify HAART efficacy and to restore immune homeostasis.