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

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.

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.

Impaired Priming of SARS-CoV-2-Specific Naive CD8+ T Cells in Older Subjects

Advanced age is associated with severe symptoms and death upon SARS-CoV-2 infection. Virus-specific CD8⁺ T-cell responses have shown to be protective toward critical COVID-19 manifestations, suggesting that suboptimal cellular immunity may contribute to the age-pattern of the disease. The induction of a CD8⁺ T-cell response against an emerging pathogen like SARS-CoV-2 relies on the activation of naive T cells. To investigate whether the primary CD8⁺ T-cell response against this virus is defective in advanced age, we used an in vitro approach to prime SARS-CoV-2-specific naive CD8⁺ T cells from healthy, unexposed donors of different age groups. Compared to younger adults, older individuals display a poor SARS-CoV-2-specific T-cell priming capacity in terms of both magnitude and quality of the response. In addition, older subjects recognize a lower number of epitopes. Our results implicate that immune aging is associated with altered primary SARS-CoV-2-specific CD8⁺ T-cell responses.

HIV Protein Tat Induces Macrophage Dysfunction and Atherosclerosis Development in Low-Density Lipoprotein Receptor-Deficient Mice

PURPOSE

HIV infection is consistently associated with an increased risk of atherosclerotic cardiovascular disease, but the underlying mechanisms remain elusive. HIV protein Tat, a transcriptional activator of HIV, has been shown to activate NF-κB signaling and promote inflammation in vitro. However, the atherogenic effects of HIV Tat have not been investigated in vivo. Macrophages are one of the major cell types involved in the initiation and progression of atherosclerosis. We and others have previously revealed the important role of IκB kinase β (IKKβ), a central inflammatory coordinator through activating NF-κB, in the regulation of macrophage functions and atherogenesis. This study investigated the impact of HIV Tat exposure on macrophage functions and atherogenesis.

METHODS

To investigate the effects of Tat on macrophage IKKβ activation and atherosclerosis development in vivo, myeloid-specific IKKβ-deficient LDLR-deficient (IKKβ^ΔMyeLDLR^-/-) mice and their control littermates (IKKβ^F/FLDLR^-/-) were exposed to recombinant HIV protein Tat.

RESULTS

Exposure to Tat significantly increased atherosclerotic lesion size and plaque vulnerability in IKKβ^F/FLDLR^-/- but not IKKβ^ΔMyeLDLR^-/- mice. Deficiency of myeloid IKKβ attenuated Tat-elicited macrophage inflammatory responses and atherosclerotic lesional inflammation in IKKβ^ΔMyeLDLR^-/- mice. Further, RNAseq analysis demonstrated that HIV protein Tat affects the expression of many atherosclerosis-related genes in vitro in an IKKβ-dependent manner.

CONCLUSIONS

Our findings reveal atherogenic effects of HIV protein Tat in vivo and demonstrate a pivotal role of myeloid IKKβ in Tat-driven atherogenesis.

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.

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.

The Role of the BCL-2 Family of Proteins in HIV-1 Pathogenesis and Persistence

Advances in HIV-1 therapy have transformed the once fatal infection into a manageable, chronic condition, yet the search for a widely applicable approach to cure remains elusive. The ineffectiveness of antiretroviral therapy (ART) in reducing the size of the HIV-1 latent reservoir has prompted investigation into the mechanisms of HIV-1 latency and immune escape. One of the major regulators of apoptosis, the BCL-2 protein, alongside its homologous family members, is a major target of HIV-1-induced change. Recent studies have now demonstrated the association of this protein with cells that support proviral forms in the setting of latency and have helped identify BCL-2 as a novel and promising therapeutic target for HIV-1 therapy directed at possible cure. This review aims to systematically review the interactions of HIV-1 with BCL-2 and its homologs and to examine the possibility of using BCL-2 inhibitors in the study and elimination of the latent reservoir.

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.

In Chronic Hepatitis C Infection, Myeloid-Derived Suppressor Cell Accumulation and T Cell Dysfunctions Revert Partially and Late After Successful Direct-Acting Antiviral Treatment

Chronic HCV infection is characterized by several immunological alterations, such as the accumulation of suppressor cells and of hyperactivated T lymphocytes. However, it is unclear whether direct-acting antiviral (DAA)-mediated HCV clearance restores immune dysfunctions. We performed a phenotypic characterization by flow cytometry of different immune cell subsets, including monocytic myeloid-derived suppressor cells (M-MDSCs) and T lymphocytes in 168 patients with persistent HCV infection not treated, under DAA therapies and sustained virological responders. Chronic HCV infection prompted the accumulation of M-MDSCs independently of patient and clinical characteristics, and altered their metabolic properties. HCV RNA was undetectable in the majority of patients just after few weeks of DAA therapy, whereas M-MDSC levels normalized only 6 months after therapy. In addition, HCV infection deeply perturbed the T cell compartment since a re-distribution of memory CD4⁺ and CD8⁺ T cells was observed at the expenses of naïve cells, and memory T lymphocytes displayed increased activation. Notably, these features were only partially restored by DAA therapies in the CD4, but not in the CD8, compartment as high immune activation levels persisted in the terminally differentiated memory CD8⁺ T cells even more than 1 year after sustained virological response. Together, these results suggest that successful DAA therapies do not lead to full immunological reconstitution as fast as viral clearance.

Naïve CD8+ T-Cells Engage a Versatile Metabolic Program Upon Activation in Humans and Differ Energetically From Memory CD8+ T-Cells

Background: Characterization of the intracellular biochemical processes that regulate the generation and maintenance of effector and memory CD8⁺ T-cells from naïve precursors is essential for our understanding of adaptive immune responses and the development of immunotherapies. However, the metabolic determinants of antigen-driven activation and differentiation remain poorly defined, especially in humans.

Methods: We used a variety of different approaches, including gene expression profiling and measurements of nutrient flux, to characterize the basal and activation-induced energetic requirements of naïve and phenotypically-defined subsets of human memory CD8⁺ T-cells.

Findings: Profound metabolic differences were apparent as a function of differentiation status, both at rest and in response to stimulation via the T cell receptor (TCR). Of particular note, resting naïve CD8⁺ T cells were largely quiescent, but rapidly upregulated diverse energetic pathways after ligation of surface-expressed TCRs. Moreover, autophagy and the mechanistic target of rapamycin (mTOR)-dependent glycolytic pathway were identified as critical mediators of antigen-driven priming in the naïve CD8⁺ T cell pool, the efficiency of which was dampened by the presence of neutral lipids and fatty acids.

Interpretation: These observations provide a metabolic roadmap of the CD8⁺ T-cell compartment in humans and reveal potentially selective targets for novel immunotherapies.

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.

Positive selection of the TRIM family regulatory region in primate genomes

Viral selection pressure has acted on restriction factors that play an important role in the innate immune system by inhibiting the replication of viruses during primate evolution. Tripartite motif-containing (TRIM) family members are some of these restriction factors. It is becoming increasingly clear that gene expression differences, rather than protein-coding regions changes, could play a vital role in the anti-retroviral immune mechanism. Increasingly, recent studies have created genome-scale catalogues of DNase I hypersensitive sites (DHSs), which demark potentially functional regulatory DNA. To improve our understanding of the molecular evolution mechanism of antiviral differences between species, we leveraged 14 130 DHSs derived from 145 cell types to characterize the regulatory landscape of the TRIM region. Subsequently, we compared the alignments of the DHSs across six primates and found 375 DHSs that are conserved in non-human primates but exhibit significantly accelerated rates of evolution in the human lineage (haDHSs). Furthermore, we discovered 31 human-specific potential transcription factor motifs within haDHSs, including the KROX and SP1, that both interact with HIV-1 Importantly, the corresponding haDHS was correlated with antiviral factor TRIM23 Thus, our results suggested that some viruses may contribute, through regulatory DNA differences, to organismal evolution by mediating TRIM gene expression to escape immune surveillance.

Host Methyltransferases and Demethylases: Potential New Epigenetic Targets for HIV Cure Strategies and Beyond

A successful HIV cure strategy may require reversing HIV latency to purge hidden viral reservoirs or enhancing HIV latency to permanently silence HIV transcription. Epigenetic modifying agents show promise as antilatency therapeutics in vitro and ex vivo, but also affect other steps in the viral life cycle. In this review, we summarize what we know about cellular DNA and protein methyltransferases (PMTs) as well as demethylases involved in HIV infection. We describe the biology and function of DNA methyltransferases, and their controversial role in HIV infection. We further explain the biology of PMTs and their effects on lysine and arginine methylation of histone and nonhistone proteins. We end with a focus on protein demethylases, their unique modes of action and their emerging influence on HIV infection. An outlook on the use of methylation-modifying agents in investigational HIV cure strategies is provided.

Strategies for Bispecific Single Chain Antibody in Cancer Immunotherapy

Genetic engineering has resulted in more than 50 recombinant bispecific antibody formats over the past two decades. Bispecific scFv antibodies represent a successful and promising immunotherapy platform that retargets cytotoxic T cells to tumor cells, with one scFv directed to tumor-associated antigens and the other to T cells. Based on this antibody construct, strategies for both specific tumor targeting and T cell activation are reviewed here. Three distinct types of tumor antigens are considered to optimize specificity and safety in bispecific scFv based treatment: cancer-testis antigens, neo-antigens and virus-associated antigens. In terms of T cell activation, although CD3 has been widely applied in bispecific scFvs being developed, CD28 and CD137 among co-stimulatory signals are also ideal candidates to be evaluated. Besides, LIGHT and HIV-Tat101 have drawn much attention as their potential roles in modulating antitumor responses.

New insights into Blimp-1 in T lymphocytes: a divergent regulator of cell destiny and effector function

B lymphocyte-induced maturation protein-1 (Blimp-1) serves as a master regulator of the development and function of antibody-producing B cells. Given that its function in T lymphocytes has been identified within the past decade, we review recent findings with emphasis on its role in coordinated control of gene expression during the development, differentiation, and function of T cells. Expression of Blimp-1 is mainly confined to activated T cells and is essential for the production of interleukin (IL)-10 by a subset of forkhead box (Fox)p3⁺ regulatory T cells with an effector phenotype. Blimp-1 is also required to induce cell elimination in the thymus and critically modulates peripheral T cell activation and proliferation. In addition, Blimp-1 promotes T helper (Th) 2 lineage commitment and limits Th1, Th17 and follicular helper T cell differentiation. Furthermore, Blimp-1 coordinates with other transcription factors to regulate expression of IL-2, IL-21 and IL-10 in effector T lymphocytes. In CD8⁺ T cells, Blimp-1 expression is distinct in heterogeneous populations at the stages of clonal expansion, differentiation, contraction and memory formation when they encounter antigens. Moreover, Blimp-1 plays a fundamental role in coordinating cytokine receptor signaling networks and transcriptional programs to regulate diverse aspects of the formation and function of effector and memory CD8⁺ T cells and their exhaustion. Blimp-1 also functions as a gatekeeper of T cell activation and suppression to prevent or dampen autoimmune disease, antiviral responses and antitumor immunity. In this review, we discuss the emerging roles of Blimp-1 in the complex regulation of gene networks that regulate the destiny and effector function of T cells and provide a Blimp-1-dominated transcriptional framework for T lymphocyte homeostasis.

PKM2-mediated inhibition of autophagy facilitates Tat's inducing HIV-1 transactivation

Considerable evidence has shown that autophagy has an important role in HIV-1 infection. However, it is still unknown whether metabolism-regulated autophagy pathway is involved in Tat-mediated HIV-1 transactivation. This study demonstrated that treatment of Tat in TZM-bl cells significantly down-regulated protein levels of Beclin-1, Atg-5, Atg-7, and LC3B-II and up-regulated of p62 levels. Blockage of autophagy enhanced Tat-induced HIV-1 transactivation in TZM-bl cells. Moreover, we found that Tat activated the Akt/mTOR and inhibited AMPK signaling pathway that was related to its up-regulation of PKM2 expression. In addition, we showed that PI3K/AKT activation and AMPK inhibtion was required for the PKM2-mediated inhibition of autophagy in Tat-treated TZM-bl cells. In conclusion, our data reveals that PKM2-mediated autophagy inhibition is required for Tat-mediated HIV-1 transactivation. Metabolism-related autophagic pathway may act as a promising diagnostic and therapeutic tool for HIV-1 infection in the future.

PKC-δ isoform plays a crucial role in Tat-TLR4 signalling pathway to activate NF-κB and CXCL8 production

HIV-1 Tat protein induces the production of CXCL8 chemokine in a TLR4/MD2 and PKC dependent manner. The objective of this study was to understand whether these two pathways were distinct or constituted a single common pathway, and to determine the nature of the PKC isoforms involved and their interrelation with the activation of NF-κB and CXCL8 gene product expression. Here, we show that Tat-induced CXCL8 production is essentially dependent on the activation of PKC delta isoform, as shown a) by the capacity of PKC delta dominant negative (DN), and Rottlerin, a selective PKC delta pharmacological inhibitor, to inhibit Tat-induced CXCL8 production and b) by the ability of the constitutively active (CAT) isoform of PKC delta to induce CXCL8 production in a HEK cell line in the absence of Tat stimulation. The finding that comparable amounts of CXCL8 were produced following stimulation with either Tat protein, PKC-delta CAT transfection, or both, argue for the implication of one common pathway where PKC delta is activated downstream of TLR4 recruitment and leads to the activation of NF-κB. Altogether, our results underline the crucial role of PKC delta isoform in activating gene expression of CXCL8, a cytokine largely implicated in the physiopathology of HIV-1 infection.

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.

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.

Systemic immunodominant CD8 responses with an effector-like phenotype are induced by intravaginal immunization with attenuated HSV vectors expressing HIV Tat and mediate protection against HSV infection

Mucosal HSV infection remains a public health issue in developing and developed world. However, an effective vaccine is still missing, partly because of the incomplete knowledge of correlates of protection. In this study we have investigated the kinetics and quality of immunity elicited by an attenuated HSV1 vector expressing the immunomodulatory Tat protein of HIV-1 (HSV1-Tat). Animals were immunized by intravaginal (IVag) or intradermal (ID) route with HSV1-Tat or with a control HSV1 vector expressing the LacZ gene (HSV1-LacZ) and immune responses were characterized in different anatomical districts. IVag immunization with HSV1-Tat enhanced both expansion and memory phases of HSV-specific immunodominant CD8 responses at systemic, but not local, level and induced short- and long-term protection against mucosal challenge. Conversely, ID immunization with HSV1-Tat favored HSV-subdominant CD8 responses, which protected mice only at early time points after immunization. IVag immunization, in particular with HSV1-Tat, compared to ID immunization, induced the differentiation of CD8(+) T lymphocytes into short-lived effector (SLEC) and effector memory (Tem) cells, generating more robust recall responses associated with increased control of virus replication. Notably, systemic SLEC and Tem contributed to generate protective local secondary responses, demonstrating their importance for mucosal control of HSV. Finally, IgG responses were observed mostly in IVag HSV1-Tat immunized animals, although seemed dispensable for protection, which occurred even in few IgG negative mice. Thus, HSV1 vectors expressing Tat induce protective anti-HSV1 immune responses.

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.

SjTat-TPI facilitates adaptive T-cell responses and reduces hepatic pathology during Schistosoma japonicum infection in BALB/c mice

Background

Schistosomiasis is a kind of parasitic zoonoses which causes serious damage to public health and social development. China is one of the countries most affected by Schistosoma japonicum and an effective vaccine is still needed. In this study, we adopted Tat-mediated protein transduction technology to investigate the impact of different antigen presented approaches on host’s immune response and the potential protection against Schistosoma japonicum infection.

Results

We successfully constructed the recombinant S. japonicum triosephosphate isomerase, Tat-TPI, as a vaccine candidate. Whether injected with Tat-TPI in foot pad or vaccinated with Tat-TPI in the back subcutaneously for three times, the draining popliteal lymph nodes and spleen both developed a stronger CD8⁺T response (Tc1) in mice. Not only that, but it also helped CD4⁺T cells to produce more IFN-γ than TPI immunisation. In addition, it could boost IgG production, especially IgG1 subclass. Most importantly, Tat-TPI immunisation led to the significant smaller area of a single egg granuloma in the livers as compared with TPI-vaccinated or control groups. However, the anti-infection efficiency induced by Tat-TPI was still restricted.

Conclusion

This study indicated that immunisation with Tat-fused TPI could contribute to enhance CD4⁺T-cell response and decrease hepatic egg granulomatous area after S. japonicum infection though it did not achieve our expected protection against Schistosoma japonicum infection. The optimal vaccine strategy warrants further research.

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.