Antigen-specific release of beta-chemokines by anti-HIV-1 cytotoxic T lymphocytes

Chimeric Human Papillomavirus-16 Virus-like Particles Presenting P18I10 and T20 Peptides from HIV-1 Envelope Induce HPV16 and HIV-1-Specific Humoral and T Cell-Mediated Immunity in BALB/c Mice

In this study, the HIV-1 P18I10 CTL peptide derived from the V3 loop of HIV-1 gp120 and the T20 anti-fusion peptide of HIV-1 gp41 were inserted into the HPV16 L1 capsid protein to construct chimeric HPV:HIV (L1:P18I10 and L1:T20) VLPs by using the mammalian cell expression system. The HPV:HIV VLPs were purified by chromatography. We demonstrated that the insertion of P18I10 or T20 peptides into the DE loop of HPV16 L1 capsid proteins did not affect in vitro stability, self-assembly and morphology of chimeric HPV:HIV VLPs. Importantly, it did not interfere either with the HIV-1 antibody reactivity targeting sequential and conformational P18I10 and T20 peptides presented on chimeric HPV:HIV VLPs or with the induction of HPV16 L1-specific antibodies in vivo. We observed that chimeric L1:P18I10/L1:T20 VLPs vaccines could induce HPV16- but weak HIV-1-specific antibody responses and elicited HPV16- and HIV-1-specific T-cell responses in BALB/c mice. Moreover, could be a potential booster to increase HIV-specific cellular responses in the heterologous immunization after priming with rBCG.HIVA vaccine. This research work would contribute a step towards the development of the novel chimeric HPV:HIV VLP-based vaccine platform for controlling HPV16 and HIV-1 infection, which is urgently needed in developing and industrialized countries.

Predicting Cross-Reactivity and Antigen Specificity of T Cell Receptors

Adaptive immune recognition is mediated by specific interactions between heterodimeric T cell receptors (TCRs) and their cognate peptide-MHC (pMHC) ligands, and the methods to accurately predict TCR:pMHC interaction would have profound clinical, therapeutic and pharmaceutical applications. Herein, we review recent developments in predicting cross-reactivity and antigen specificity of TCR recognition. We discuss current experimental and computational approaches to investigate cross-reactivity and antigen-specificity of TCRs and highlight how integrating kinetic, biophysical and structural features may offer valuable insights in modeling immunogenicity. We further underscore the close inter-relationship of these two interconnected notions and the need to investigate each in the light of the other for a better understanding of T cell responsiveness for the effective clinical applications.

Human CD8+ T Cells Exhibit a Shared Antigen Threshold for Different Effector Responses

CD8⁺ T cells produce TNF-α, IL-2, and IFN-γ with similar Ag thresholds.

Costimulation decreases Ag thresholds similarly for different cytokines.

A common rate-limiting switch downstream of the TCR can explain these findings.

T cells recognizing cognate pMHC Ags become activated to elicit a myriad of cellular responses, such as target cell killing and the secretion of different cytokines, that collectively contribute to adaptive immunity. These effector responses have been hypothesized to exhibit different Ag dose and affinity thresholds, suggesting that pathogen-specific information may be encoded within the nature of the Ag. In this study, using systematic experiments in a reductionist system, in which primary human CD8⁺ T cell blasts are stimulated by recombinant peptides presented on MHC Ag alone, we show that different inflammatory cytokines have comparable Ag dose thresholds across a 25,000-fold variation in affinity. Although costimulation by CD28, CD2, and CD27 increased cytokine production in this system, the Ag threshold remained comparable across different cytokines. When using primary human memory CD8⁺ T cells responding to autologous APCs, equivalent thresholds were also observed for different cytokines and killing. These findings imply a simple phenotypic model of TCR signaling in which multiple T cell responses share a common rate-limiting threshold and a conceptually simple model of CD8⁺ T cell Ag recognition, in which Ag dose and affinity do not provide any additional response-specific information.

GPU-Accelerated Discovery of Pathogen-Derived Molecular Mimics of a T-Cell Insulin Epitope

The strong links between (Human Leukocyte Antigen) HLA, infection and autoimmunity combine to implicate T-cells as primary triggers of autoimmune disease (AD). T-cell crossreactivity between microbially-derived peptides and self-peptides has been shown to break tolerance and trigger AD in experimental animal models. Detailed examination of the potential for T-cell crossreactivity to trigger human AD will require means of predicting which peptides might be recognised by autoimmune T-cell receptors (TCRs). Recent developments in high throughput sequencing and bioinformatics mean that it is now possible to link individual TCRs to specific pathologies for the first time. Deconvolution of TCR function requires knowledge of TCR specificity. Positional Scanning Combinatorial Peptide Libraries (PS-CPLs) can be used to predict HLA-restriction and define antigenic peptides derived from self and pathogen proteins. In silico search of the known terrestrial proteome with a prediction algorithm that ranks potential antigens in order of recognition likelihood requires complex, large-scale computations over several days that are infeasible on a personal computer. We decreased the time required for peptide searching to under 30 min using multiple blocks on graphics processing units (GPUs). This time-efficient, cost-effective hardware accelerator was used to screen bacterial and fungal human pathogens for peptide sequences predicted to activate a T-cell clone, InsB4, that was isolated from a patient with type 1 diabetes and recognised the insulin B-derived epitope HLVEALYLV in the context of disease-risk allele HLA A*0201. InsB4 was shown to kill HLA A*0201⁺ human insulin producing β-cells demonstrating that T-cells with this specificity might contribute to disease. The GPU-accelerated algorithm and multispecies pathogen proteomic databases were validated to discover pathogen-derived peptide sequences that acted as super-agonists for the InsB4 T-cell clone. Peptide-MHC tetramer binding and surface plasmon resonance were used to confirm that the InsB4 TCR bound to the highest-ranked peptide agonists derived from infectious bacteria and fungi. Adoption of GPU-accelerated prediction of T-cell agonists has the capacity to revolutionise our understanding of AD by identifying potential targets for autoimmune T-cells. This approach has further potential for dissecting T-cell responses to infectious disease and cancer.

Induction of influenza-specific local CD8 T-cells in the respiratory tract after aerosol delivery of vaccine antigen or virus in the Babraham inbred pig

There is increasing evidence that induction of local immune responses is a key component of effective vaccines. For respiratory pathogens, for example tuberculosis and influenza, aerosol delivery is being actively explored as a method to administer vaccine antigens. Current animal models used to study respiratory pathogens suffer from anatomical disparity with humans. The pig is a natural and important host of influenza viruses and is physiologically more comparable to humans than other animal models in terms of size, respiratory tract biology and volume. It may also be an important vector in the birds to human infection cycle. A major drawback of the current pig model is the inability to analyze antigen-specific CD8+ T-cell responses, which are critical to respiratory immunity. Here we address this knowledge gap using an established in-bred pig model with a high degree of genetic identity between individuals, including the MHC (Swine Leukocyte Antigen (SLA)) locus. We developed a toolset that included long-term in vitro pig T-cell culture and cloning and identification of novel immunodominant influenza-derived T-cell epitopes. We also generated structures of the two SLA class I molecules found in these animals presenting the immunodominant epitopes. These structures allowed definition of the primary anchor points for epitopes in the SLA binding groove and established SLA binding motifs that were used to successfully predict other influenza-derived peptide sequences capable of stimulating T-cells. Peptide-SLA tetramers were constructed and used to track influenza-specific T-cells ex vivo in blood, the lungs and draining lymph nodes. Aerosol immunization with attenuated single cycle influenza viruses (S-FLU) induced large numbers of CD8+ T-cells specific for conserved NP peptides in the respiratory tract. Collectively, these data substantially increase the utility of pigs as an effective model for studying protective local cellular immunity against respiratory pathogens.

Influenza virus infection in pigs represents a significant problem to industry and also carries substantial risks to human health. Pigs can be infected with both bird and human forms of influenza where these viruses can mix with swine influenza viruses to generate new pandemic strains that can spread quickly and kill many millions of people across the globe. To date, the study of immunology and vaccination against flu in pigs has been hampered by a lack of suitable tools and reagents. Here, we have built a complete molecular toolset that allows such study. These tools could also be applied to other important infections in pigs such as foot-and-mouth disease and the normally fatal African Swine Fever virus. Finally, pigs are set to become an important model organism for study of influenza A virus infection. Here, we make use of a new research toolset to study a Broadly Protective Influenza Vaccine (BPIV) candidate, S-FLU, which could offer protection against all influenza A viruses. These new tools have been used to demonstrate the induction of large numbers of antigen specific CD8+ T cells to conserved NP epitopes in the respiratory tract after aerosol immunization.

CRISPR-mediated TCR replacement generates superior anticancer transgenic T cells

Adoptive transfer of T cells genetically modified to express a cancer-specific T-cell receptor (TCR) has shown significant therapeutic potential for both hematological and solid tumors. However, a major issue of transducing T cells with a transgenic TCR is the preexisting expression of TCRs in the recipient cells. These endogenous TCRs compete with the transgenic TCR for surface expression and allow mixed dimer formation. Mixed dimers, formed by mispairing between the endogenous and transgenic TCRs, may harbor autoreactive specificities. To circumvent these problems, we designed a system where the endogenous TCR-β is knocked out from the recipient cells using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein-9 (Cas9) technology, simultaneously with transduction with a cancer-reactive receptor of choice. This TCR replacement strategy resulted in markedly increased surface expression of transgenic αβ and γδ TCRs, which in turn translated to a stronger, and more polyfunctional, response of engineered T cells to their target cancer cell lines. Additionally, the TCR-plus-CRISPR-modified T cells were up to a thousandfold more sensitive to antigen than standard TCR-transduced T cells or conventional model proxy systems used for studying TCR activity. Finally, transduction with a pan-cancer-reactive γδ TCR used in conjunction with CRISPR/Cas9 knockout of the endogenous αβ TCR resulted in more efficient redirection of CD4+ and CD8+ T cells against a panel of established blood cancers and primary, patient-derived B-cell acute lymphoblastic leukemia blasts compared with standard TCR transfer. Our results suggest that TCR transfer combined with genome editing could lead to new, improved generations of cancer immunotherapies.

Human leucocyte antigen class I-redirected anti-tumour CD4+ T cells require a higher T cell receptor binding affinity for optimal activity than CD8+ T cells

CD4⁺ T helper cells are a valuable component of the immune response towards cancer. Unfortunately, natural tumour‐specific CD4⁺ T cells occur in low frequency, express relatively low‐affinity T cell receptors (TCRs) and show poor reactivity towards cognate antigen. In addition, the lack of human leucocyte antigen (HLA) class II expression on most cancers dictates that these cells are often unable to respond to tumour cells directly. These deficiencies can be overcome by transducing primary CD4⁺ T cells with tumour‐specific HLA class I‐restricted TCRs prior to adoptive transfer. The lack of help from the co‐receptor CD8 glycoprotein in CD4⁺ cells might result in these cells requiring a different optimal TCR binding affinity. Here we compared primary CD4⁺ and CD8⁺ T cells expressing wild‐type and a range of affinity‐enhanced TCRs specific for the HLA A*0201‐restricted NY‐ESO‐1‐ and gp100 tumour antigens. Our major findings are: (i) redirected primary CD4⁺ T cells expressing TCRs of sufficiently high affinity exhibit a wide range of effector functions, including cytotoxicity, in response to cognate peptide; and (ii) optimal TCR binding affinity is higher in CD4⁺ T cells than CD8⁺ T cells. These results indicate that the CD4⁺ T cell component of current adoptive therapies using TCRs optimized for CD8⁺ T cells is below par and that there is room for substantial improvement.

Identification of human viral protein-derived ligands recognized by individual MHCI-restricted T-cell receptors

Evidence indicates that autoimmunity can be triggered by virus-specific CD8⁺ T cells that crossreact with self-derived peptide epitopes presented on the cell surface by major histocompatibility complex class I (MHCI) molecules. Identification of the associated viral pathogens is challenging because individual T-cell receptors can potentially recognize up to a million different peptides. Here, we generate peptide length-matched combinatorial peptide library (CPL) scan data for a panel of virus-specific CD8⁺ T-cell clones spanning different restriction elements and a range of epitope lengths. CPL scan data drove a protein database search limited to viruses that infect humans. Peptide sequences were ranked in order of likelihood of recognition. For all anti-viral CD8⁺ T-cell clones examined in this study, the index peptide was either the top-ranked sequence or ranked as one of the most likely sequences to be recognized. Thus, we demonstrate that anti-viral CD8⁺ T-cell clones are highly focused on their index peptide sequence and that ‘CPL-driven database searching' can be used to identify the inciting virus-derived epitope for a given CD8⁺ T-cell clone. Moreover, to augment access to CPL-driven database searching, we have created a publicly accessible webtool. Application of these methodologies in the clinical setting may clarify the role of viral pathogens in the etiology of autoimmune diseases.

T cell receptor binding affinity governs the functional profile of cancer-specific CD8+ T cells

Antigen-specific T cell receptor (TCR) gene transfer via patient-derived T cells is an attractive approach to cancer therapy, with the potential to circumvent immune regulatory networks. However, high-affinity tumour-specific TCR clonotypes are typically deleted from the available repertoire during thymic selection because the vast majority of targeted epitopes are derived from autologous proteins. This process places intrinsic constraints on the efficacy of T cell-based cancer vaccines and therapeutic strategies that employ naturally generated tumour-specific TCRs. In this study, we used altered peptide ligands and lentivirus-mediated transduction of affinity-enhanced TCRs selected by phage display to study the functional properties of CD8(+) T cells specific for three different tumour-associated peptide antigens across a range of binding parameters. The key findings were: (i) TCR affinity controls T cell antigen sensitivity and polyfunctionality; (ii) supraphysiological affinity thresholds exist, above which T cell function cannot be improved; and (iii) T cells transduced with very high-affinity TCRs exhibit cross-reactivity with self-derived peptides presented by the restricting human leucocyte antigen. Optimal system-defined affinity windows above the range established for natural tumour-specific TCRs therefore allow the enhancement of T cell effector function without off-target effects. These findings have major implications for the rational design of novel TCR-based biologics underpinned by rigorous preclinical evaluation.

A comparison of elasticities of viral levels to specific immune response mechanisms in human immunodeficiency virus infection

BACKGROUND

The presence of an asymptomatic phase in an HIV infection indicates that the immune system can partially control the infection. Determining the immune mechanisms that contribute significantly to the partial control of the infection enhance the HIV infection intervention strategies and is important in vaccine development. Towards this goal, a discrete time HIV model, which incorporates the life cycle aspects of the virus, the antibody (humoral) response and the cell-mediated immune response is formulated to determine immune system components that are most efficient in controlling viral levels. Ecological relationships are used to model the interplay between the immune system components and the HIV pathogen. Model simulations and transient elasticity analysis of the viral levels to immune response parameters are used to compare the different immune mechanisms.

RESULTS

It is shown that cell-mediated immune response is more effective in controlling the viral levels than the antibody response. Killing of infected cells is shown to be crucial in controlling the viral levels. Our results show a negative correlation between the antibody response and the viral levels in the early stages of the infection, but we predicted this immune mechanism to be positively correlated with the viral levels in the late stage of the infection. A result that suggests lack of relevance of antibody response with infection progression. On the contrary, we predicted the cell-mediated immune response to be always negatively correlated with viral levels.

CONCLUSION

Neutralizing antibodies can only control the viral levels in the early days of the HIV infection whereas cell-mediated immune response is beneficial during all the stages of the infection. This study predicts that vaccine design efforts should also focus on stimulating killer T cells that target infected cells.

Novel approaches in polyepitope T-cell vaccine development against HIV-1

RV144 clinical trial was modestly effective in preventing HIV infection. New alternative approaches are needed to design improved HIV-1 vaccines and their delivery strategies. One of these approaches is construction of synthetic polyepitope HIV-1 immunogen using protective T- and B-cell epitopes that can induce broadly neutralizing antibodies and responses of cytotoxic (CD8(+) CTL) and helpers (CD4(+) Th) T-lymphocytes. This approach seems to be promising for designing of new generation of vaccines against HIV-1, enables in theory to cope with HIV-1 antigenic variability, focuses immune responses on protective determinants and enables to exclude from the vaccine compound that can induce autoantibodies or antibodies enhancing HIV-1 infectivity. Herein, the authors will focus on construction and rational design of polyepitope T-cell HIV-1 immunogens and their delivery, including: advantages and disadvantages of existing T-cell epitope prediction methods; features of organization of polyepitope immunogens, which can generate high-level CD8(+) and CD4(+) T-lymphocyte responses; the strategies to optimize efficient processing, presentation and immunogenicity of polyepitope constructs; original software to design polyepitope immunogens; and delivery vectors as well as mucosal strategies of vaccination. This new knowledge may bring us a one step closer to developing an effective T-cell vaccine against HIV-1, other chronic viral infections and cancer.

Cellular-level versus receptor-level response threshold hierarchies in T-cell activation

Peptide-MHC (pMHC) ligand engagement by T-cell receptors (TCRs) elicits a variety of cellular responses, some of which require substantially more TCR-mediated stimulation than others. This threshold hierarchy could reside at the receptor level, where different response pathways branch off at different stages of the TCR/CD3 triggering cascade, or at the cellular level, where the cumulative TCR signal registered by the T-cell is compared to different threshold values. Alternatively, dual-level thresholds could exist. In this study, we show that the cellular hypothesis provides the most parsimonious explanation consistent with data obtained from an in-depth analysis of distinct functional responses elicited in a clonal T-cell system by a spectrum of biophysically defined altered peptide ligands across a range of concentrations. Further, we derive a mathematical model that describes how ligand density, affinity, and off-rate all affect signaling in distinct ways. However, under the kinetic regime prevailing in the experiments reported here, the TCR/pMHC class I (pMHCI) dissociation rate was found to be the main governing factor. The CD8 coreceptor modulated the TCR/pMHCI interaction and altered peptide ligand potency. Collectively, these findings elucidate the relationship between TCR/pMHCI kinetics and cellular function, thereby providing an integrated mechanistic understanding of T-cell response profiles.

High-avidity, high-IFNγ-producing CD8 T-cell responses following immune selection during HIV-1 infection

HIV-1 mutations, which reduce or abolish CTL responses against virus-infected cells, are frequently selected in acute and chronic HIV infection. Among population HIV-1 sequences, immune selection is evident as human leukocyte antigen (HLA) allele-associated substitutions of amino acids within or near CD8 T-cell epitopes. In these cases, the non-adapted epitope is susceptible to immune recognition until an escape mutation renders the epitope less immunogenic. However, several population-based studies have independently identified HLA-associated viral changes, which lead to the formation of a new T-cell epitope, suggesting that the immune responses that these variants or 'neo-epitopes' elicit provide an evolutionary advantage to the virus rather than the host. Here, we examined the functional characteristics of eight CD8 T-cell responses that result from viral adaptation in 125 HLA-genotyped individuals with chronic HIV-1 infection. Neo-epitopes included well-characterized immunodominant epitopes restricted by common HLA alleles, and in most cases the T-cell responses against the neo-epitope showed significantly greater functional avidity and higher IFNγ production than T cells for non-adapted epitopes, but were not more cytotoxic. Neo-epitope formation and emergence of cognate T-cell response coincident with a rise in viral load was then observed in vivo in an acutely infected individual. These findings show that HIV-1 adaptation not only abrogates the immune recognition of early targeted epitopes, but may also increase immune recognition to other epitopes, which elicit immunodominant but non-protective T-cell responses. These data have implications for immunodominance associated with polyvalent vaccines based on the diversity of chronic HIV-1 sequences.

Fitness costs and diversity of the cytotoxic T lymphocyte (CTL) response determine the rate of CTL escape during acute and chronic phases of HIV infection

HIV-1 often evades cytotoxic T cell (CTL) responses by generating variants that are not recognized by CTLs. We used single-genome amplification and sequencing of complete HIV genomes to identify longitudinal changes in the transmitted/founder virus from the establishment of infection to the viral set point at 1 year after the infection. We found that the rate of viral escape from CTL responses in a given patient decreases dramatically from acute infection to the viral set point. Using a novel mathematical model that tracks the dynamics of viral escape at multiple epitopes, we show that a number of factors could potentially contribute to a slower escape in the chronic phase of infection, such as a decreased magnitude of epitope-specific CTL responses, an increased fitness cost of escape mutations, or an increased diversity of the CTL response. In the model, an increase in the number of epitope-specific CTL responses can reduce the rate of viral escape from a given epitope-specific CTL response, particularly if CD8+ T cells compete for killing of infected cells or control virus replication nonlytically. Our mathematical framework of viral escape from multiple CTL responses can be used to predict the breadth and magnitude of HIV-specific CTL responses that need to be induced by vaccination to reduce (or even prevent) viral escape following HIV infection.

Anti-CD8 antibodies can trigger CD8+ T cell effector function in the absence of TCR engagement and improve peptide-MHCI tetramer staining

CD8(+) T cells recognize immunogenic peptides presented at the cell surface bound to MHCI molecules. Ag recognition involves the binding of both TCR and CD8 coreceptor to the same peptide-MHCI (pMHCI) ligand. Specificity is determined by the TCR, whereas CD8 mediates effects on Ag sensitivity. Anti-CD8 Abs have been used extensively to examine the role of CD8 in CD8(+) T cell activation. However, as previous studies have yielded conflicting results, it is unclear from the literature whether anti-CD8 Abs per se are capable of inducing effector function. In this article, we report on the ability of seven monoclonal anti-human CD8 Abs to activate six human CD8(+) T cell clones with a total of five different specificities. Six of seven anti-human CD8 Abs tested did not activate CD8(+) T cells. In contrast, one anti-human CD8 Ab, OKT8, induced effector function in all CD8(+) T cells examined. Moreover, OKT8 was found to enhance TCR/pMHCI on-rates and, as a consequence, could be used to improve pMHCI tetramer staining and the visualization of Ag-specific CD8(+) T cells. The anti-mouse CD8 Abs, CT-CD8a and CT-CD8b, also activated CD8(+) T cells despite opposing effects on pMHCI tetramer staining. The observed heterogeneity in the ability of anti-CD8 Abs to trigger T cell effector function provides an explanation for the apparent incongruity observed in previous studies and should be taken into consideration when interpreting results generated with these reagents. Furthermore, the ability of Ab-mediated CD8 engagement to deliver an activation signal underscores the importance of CD8 in CD8(+) T cell signaling.

The antiviral factor APOBEC3G improves CTL recognition of cultured HIV-infected T cells

The cytidine deaminase APOBEC3G (A3G) enzyme exerts an intrinsic anti–human immunodeficiency virus (HIV) defense by introducing lethal G-to-A hypermutations in the viral genome. The HIV-1 viral infectivity factor (Vif) protein triggers degradation of A3G and counteracts this antiviral effect. The impact of A3G on the adaptive cellular immune response has not been characterized. We examined whether A3G-edited defective viruses, which are known to express truncated or misfolded viral proteins, activate HIV-1–specific (HS) CD8⁺ cytotoxic T lymphocytes (CTLs). To this end, we compared the immunogenicity of cells infected with wild-type or Vif-deleted viruses in the presence or absence of the cytidine deaminase. The inhibitory effect of A3G on HIV replication was associated with a strong activation of cocultivated HS-CTLs. CTL activation was particularly marked with Vif-deleted HIV and with viruses harboring A3G. Enzymatically inactive A3G mutants failed to enhance CTL activation. We also engineered proviruses bearing premature stop codons in their genome as scars of A3G editing. These viruses were not infectious but potently activated HS-CTLs. Therefore, the pool of defective viruses generated by A3G represents an underestimated source of viral antigens. Our results reveal a novel function for A3G, acting not only as an intrinsic antiviral factor but also as an inducer of the adaptive immune system.

Peptide-major histocompatibility complex dimensions control proximal kinase-phosphatase balance during T cell activation

T cell antigen recognition requires binding of the T cell receptor (TCR) to a complex between peptide antigen and major histocompatibility complex molecules (pMHC), and this recognition occurs at the interface between the T cell and the antigen-presenting cell. The TCR and pMHC molecules are small compared with other abundant cell surface molecules, and it has been suggested that small size is functionally important. We show here that elongation of both mouse and human MHC class I molecules abrogates T cell antigen recognition as measured by cytokine production and target cell killing. This elongation disrupted tyrosine phosphorylation and Zap70 recruitment at the contact region without affecting TCR or coreceptor binding. Contact areas with elongated forms of pMHC showed an increase in intermembrane distance and less efficient segregation of CD3 from the large tyrosine phosphatase CD45. These findings demonstrate that T cell antigen recognition is strongly dependent on pMHC size and are consistent with models of TCR triggering requiring segregation or mechanical pulling of the TCR.

Antigen sensitivity is a major determinant of CD8+ T-cell polyfunctionality and HIV-suppressive activity

CD8(+) T cells are major players in the immune response against HIV. However, recent failures in the development of T cell-based vaccines against HIV-1 have emphasized the need to reassess our basic knowledge of T cell-mediated efficacy. CD8(+) T cells from HIV-1-infected patients with slow disease progression exhibit potent polyfunctionality and HIV-suppressive activity, yet the factors that unify these properties are incompletely understood. We performed a detailed study of the interplay between T-cell functional attributes using a bank of HIV-specific CD8(+) T-cell clones isolated in vitro; this approach enabled us to overcome inherent difficulties related to the in vivo heterogeneity of T-cell populations and address the underlying determinants that synthesize the qualities required for antiviral efficacy. Conclusions were supported by ex vivo analysis of HIV-specific CD8(+) T cells from infected donors. We report that attributes of CD8(+) T-cell efficacy against HIV are linked at the level of antigen sensitivity. Highly sensitive CD8(+) T cells display polyfunctional profiles and potent HIV-suppressive activity. These data provide new insights into the mechanisms underlying CD8(+) T-cell efficacy against HIV, and indicate that vaccine strategies should focus on the induction of HIV-specific T cells with high levels of antigen sensitivity to elicit potent antiviral efficacy.

Techniques to improve the direct ex vivo detection of low frequency antigen-specific CD8+ T cells with peptide-major histocompatibility complex class I tetramers

The ability to quantify and characterize antigen-specific CD8+ T cells irrespective of functional readouts using fluorochrome-conjugated peptide-major histocompatibility complex class I (pMHCI) tetramers in conjunction with flow cytometry has transformed our understanding of cellular immune responses over the past decade. In the case of prevalent CD8+ T cell populations that engage cognate pMHCI tetramers with high avidities, direct ex vivo identification and subsequent data interpretation is relatively straightforward. However, the accurate identification of low frequency antigen-specific CD8+ T cell populations can be complicated, especially in situations where T cell receptor-mediated tetramer binding occurs at low avidities. Here, we highlight a few simple techniques that can be employed to improve the visual resolution, and hence the accurate quantification, of tetramer binding CD8+ T cell populations by flow cytometry. These methodological modifications enhance signal intensity, especially in the case of specific CD8+ T cell populations that bind cognate antigen with low avidities, minimize background noise, and enable improved discrimination of true pMHCI tetramer binding events from nonspecific uptake.

CD8+ T cell efficacy in vaccination and disease

Much effort has been devoted to the design of vaccines that induce adaptive cellular immunity, in particular CD8+ T cells, which have a central role in the host response to viral infections and cancers. To date, however, the development of effective T cell vaccines remains elusive. This is due, in part, to the lack of clearly defined correlates of protection and the inherent difficulties that hinder full characterization of the determinants of successful T cell immunity in humans. Recent data from the disparate fields of infectious disease and tumor immunology have converged, with an emphasis on the functional attributes of individual antigen-specific T cell clonotypes, to provide a better understanding of CD8+ T cell efficacy. This new knowledge paves the way to the design of more effective T cell vaccines and highlights the importance of comprehensive immunomonitoring.

High frequencies of polyfunctional HIV-specific T cells are associated with preservation of mucosal CD4 T cells in bronchoalveolar lavage

The mechanisms underlying the massive gastrointestinal tract CD4 T-cell depletion in human immunodeficiency virus (HIV) infection are not well understood nor is it clear whether similar depletion is manifest at other mucosal surfaces. Studies of T-cell and virus dynamics in different anatomical sites have begun to illuminate the pathogenesis of HIV-associated disease. Here, we studied depletion and HIV infection frequencies of CD4 T cells from the gastrointestinal tract, bronchoalveolar lavage (BAL), and blood with the frequencies and functional profiles of HIV-specific T cells in these anatomically distinct sites in HIV-infected individuals. The major findings to emerge were as follows: (i) depletion of gastrointestinal CD4 T cells is associated with high frequencies of infected CD4 T cells; (ii) HIV-specific T cells are present at low frequencies in the gastrointestinal tract compared to blood; (iii) BAL CD4 T cells are not massively depleted during the chronic phase; (iv) infection frequencies of BAL CD4 T cells are similar to those in blood; (v) significantly higher frequencies and increased functionality of HIV-specific T cells were observed in BAL compared to blood. Taken together, these data suggest mechanisms for mucosal CD4 T-cell depletion and interventions that might circumvent global depletion of mucosal CD4 T cells.

High pro-inflammatory cytokine secretion and loss of high avidity cross-reactive cytotoxic T-cells during the course of secondary dengue virus infection

BACKGROUND

Dengue is one of the most important human diseases transmitted by an arthropod vector and the incidence of dengue virus infection has been increasing - over half the world's population now live in areas at risk of infection. Most infections are asymptomatic, but a subset of patients experience a potentially fatal shock syndrome characterised by plasma leakage. Severe forms of dengue are epidemiologically associated with repeated infection by more than one of the four dengue virus serotypes. Generally attributed to the phenomenon of antibody-dependent enhancement, recent observations indicate that T-cells may also influence disease phenotype.

METHODS AND FINDINGS

Virus-specific cytotoxic T lymphocytes (CTL) showing high level cross reactivity between dengue serotypes could be expanded from blood samples taken during the acute phase of secondary dengue infection. These could not be detected in convalescence when only CTL populations demonstrating significant serotype specificity were identified. Dengue cross-reactive CTL clones derived from these patients were of higher avidity than serotype-specific clones and produced much higher levels of both type 1 and certain type 2 cytokines, many previously implicated in dengue pathogenesis.

CONCLUSION

Dengue serotype cross-reactive CTL clones showing high avidity for antigen produce higher levels of inflammatory cytokines than serotype-specific clones. That such cells cannot be expanded from convalescent samples suggests that they may be depleted, perhaps as a consequence of activation-induced cell death. Such high avidity cross-reactive memory CTL may produce inflammatory cytokines during the course of secondary infection, contributing to the pathogenesis of vascular leak. These cells appear to be subsequently deleted leaving a more serotype-specific memory CTL pool. Further studies are needed to relate these cellular observations to disease phenotype in a large group of patients. If confirmed they have significant implications for understanding the role of virus-specific CTL in pathogenesis of dengue disease.

Availability of a diversely avid CD8+ T cell repertoire specific for the subdominant HLA-A2-restricted HIV-1 Gag p2419-27 epitope

HLA-A2-restricted CTL responses to immunodominant HIV-1 epitopes do not appear to be very effective in the control of viral replication in vivo. In this study, we studied human CD8+ T cell responses to the subdominant HLA-A2-restricted epitope TV9 (Gag p24(19-27), TLNAWVKVV) to explore the possibility of increasing its immune recognition. We confirmed in a cohort of 313 patients, infected by clade B or clade C viruses, that TV9 is rarely recognized. Of interest, the functional sensitivity of the TV9 response can be relatively high. The potential T cell repertoires for TV9 and the characteristics of constituent clonotypes were assessed by ex vivo priming of circulating CD8+ T cells from healthy seronegative donors. TV9-specific CTLs capable of suppressing viral replication in vitro were readily generated, suggesting that the cognate T cell repertoire is not limiting. However, these cultures contained multiple discrete populations with a range of binding avidities for the TV9 tetramer and correspondingly distinct functional dependencies on the CD8 coreceptor. The lack of dominant clonotypes was not affected by the stage of maturation of the priming dendritic cells. Cultures primed by dendritic cells transduced to present endogenous TV9 were also incapable of clonal maturation. Thus, a diffuse TCR repertoire appeared to be an intrinsic characteristic of TV9-specific responses. These data indicate that subdominance is not a function of poor immunogenicity, cognate TCR repertoire availability, or the potential avidity properties thereof, but rather suggest that useful responses to this epitope are suppressed by competing CD8+ T cell populations during HIV-1 infection.

Enhanced immunogenicity of CTL antigens through mutation of the CD8 binding MHC class I invariant region

CD8(+) cytotoxic T lymphocytes (CTL) are key determinants of immunity to intracellular pathogens and neoplastic cells. Recognition of specific antigens in the form of peptide-MHC class I complexes (pMHCI) presented on the target cell surface is mediated by T cell receptor (TCR) engagement. The CD8 coreceptor binds to invariant domains of pMHCI and facilitates antigen recognition. Here, we investigate the biological effects of a Q115E substitution in the alpha2 domain of human leukocyte antigen (HLA)-A*0201 that enhances CD8 binding by approximately 50% without altering TCR/pMHCI interactions. Soluble and cell surface-expressed forms of Q115E HLA-A*0201 exhibit enhanced recognition by CTL without loss of specificity. These CD8-enhanced antigens induce greater CD3 zeta chain phosphorylation in cognate CTL leading to substantial increases in cytokine production, proliferation and priming of naive T cells. This effect provides a fundamental new mechanism with which to enhance cellular immunity to specific T cell antigens.

CD8 exerts differential effects on the deployment of cytotoxic T lymphocyte effector functions

Cytotoxic T lymphocytes (CTL) are equipped with a range of effector functions that contribute both to the control of intracellular pathogens and dysregulated cellular proliferation and to the development of certain immunopathologies such as autoimmune disease. Qualitative analyses of various CTL responses have revealed substantial heterogeneity in the diversity of functions that are mobilized in response to antigen. Here, we studied the influence of the CD8 co-receptor, which is known to enhance antigen recognition by CTL, on the secretion of eight different cytokines and chemokines by human CTL clones using flow cytometric bead array. Our results show that abrogation of MHC class I/CD8 interactions exerts a differential influence on the distinct individual effector functions that are elicited in response to agonist ligands. The magnitude of this co-receptor blockade inhibitory effect was clearly related to the hierarchy of cytokine secretion in terms of activation threshold because those functions requiring the highest amounts of antigen were most affected. Thus, modulation of CD8 activity can effectively tune not only the sensitivity but also the qualitative profile of CTL responses.

Noninfectious papilloma virus-like particles inhibit HIV-1 replication: implications for immune control of HIV-1 infection by IL-27

Human papilloma virus (HPV)-like particles (VLPs) have been used as a vaccine to prevent HPV infection. Recent studies demonstrate that VLPs bind to dendritic cells and induce the expression of antiviral cytokines such as interferon-alpha (IFN-alpha), interleukin-10 (IL-10) and IFN-gamma. In the present study, we evaluated the effect of VLPs on HIV-1 replication in peripheral blood mononuclear cells (PBMCs), CD4+ T cells, and macrophages. Here, we show that VLPs suppress the replication of both X4 and R5 HIV-1 without affecting the expression of CD4, CXCR4, and CCR5. Soluble factor(s) released by PBMCs and macrophages on VLPs treatment inhibited HIV-1 replication. To determine the inhibitory factors, DNA microarray analysis was performed using VLP-treated PBMCs and macrophages. VLPs induced the genes associated with IFN induction, immune responses, and antiviral responses, among with the recently described cytokine IL-27. Subsequently, IL-27 was found to be a potent inhibitor of HIV-1 replication in PBMCs, CD4+ T cells, and macrophages. Taken together, our studies identify a novel role of IL-27 in restricting HIV-1 replication and suggest that further examination of the inhibitory property of IL-27 may pave the way for a novel therapy for HIV-1 infection.

Functional and biophysical characterization of an HLA-A*6801-restricted HIV-specific T cell receptor

HLA-A*6801 exhibits several unusual features. First, it is known to bind weakly to CD8 due to the presence of an A245V substitution in the alpha3 domain. Second, it is able to accommodate unusually long peptides as a result of peptide 'kinking' in the binding groove. Third, CD8+ cytotoxic T lymphocytes that recognise HLA-A*6801-restricted antigens can tolerate substantial changes in the peptide sequence without apparent loss of recognition. In addition, it has been suggested that HLA-A68-restricted TCR might bind with higher affinity than other TCR due to their selection in the presence of a decreased contribution from CD8. Here we (1) examine monoclonal T cell recognition of an HLA-A*6801-restricted HIV-1 Tat-derived 11-amino acid peptide (ITKGLGISYGR) and natural variant sequences thereof; (2) measure the affinity and kinetics of a TCR/pHLA-A68 interaction biophysically for the first time, showing that equilibrium binding occurs within the range previously determined for non-HLA-A68-restricted TCR (KD approx. 7 microM); and (3) show that "normalization" of the non-canonical HLA-A*6801 CD8-binding domain enhances recognition of agonist peptides without inducing non-specific activation. This latter effect may provide a fundamental new mechanism with which to enhance T cell immunity to specific antigens.

DNA vaccines against human immunodeficiency virus type 1

Development of a vaccine against human immunodeficiency virus type 1 (HIV-1) is the main hope for controlling the acquired immunodeficiency syndrome pandemic. An ideal HIV vaccine should induce neutralizing antibodies, CD4+ helper T cells, and CD8+ cytotoxic T cells. While the induction of broadly neutralizing antibodies remains a highly challenging goal, there are a number of technologies capable of inducing potent cell-mediated responses in animal models, which are now starting to be tested in humans. Naked DNA immunization is one of them. This review focuses on the stimulation of HIV-specific T cells and discusses in the context of the current 'state-of-art' of DNA vaccines, the areas where this technology might assist either alone or as a part of more complex vaccine formulations in the HIV vaccine development.

Engineering RENTA, a DNA prime-MVA boost HIV vaccine tailored for Eastern and Central Africa

For the development of human immunodeficiency virus type 1 (HIV-1) vaccines, traditional approaches inducing virus-neutralizing antibodies have so far failed. Thus the effort is now focused on elicitation of cellular immunity. We are currently testing in clinical trials in the United Kingdom and East Africa a T-cell vaccine consisting of HIV-1 clade A Gag-derived immunogen HIVA delivered in a prime-boost regimen by a DNA plasmid and modified vaccinia virus Ankara (MVA). Here, we describe engineering and preclinical development of a second immunogen RENTA, which will be used in combination with the present vaccine in a four-component DNA/HIVA-RENTA prime-MVA/HIVA-RENTA boost formulation. RENTA is a fusion protein derived from consensus HIV clade A sequences of Tat, reverse transcriptase, Nef and gp41. We inactivated the natural biological activities of the HIV components and confirmed immunogenicities of the pTHr.RENTA and MVA.RENTA vaccines in mice. Furthermore, we demonstrated in mice and rhesus monkeys broadening of HIVA-elicited T-cell responses by a parallel induction of HIVA- and RENTA-specific responses recognizing multiple HIV epitopes.

Recognition of nonpeptide antigens by human V gamma 9V delta 2 T cells requires contact with cells of human origin

SUMMARY It is becoming apparent that gamma delta T cells form an important part of the adaptive immune response. However, the ligands recognized by gamma delta T cell receptors (TCRs) and the exact biological function of the cells that express this receptor remain unclear. Numerous studies have shown that the dominant human peripheral blood subset of gamma delta T cells, which express a V gamma 9V delta 2 TCR, can activate in response to low molecular weight nonpeptidic molecules. Some of these components have been purified from bacteria or parasites. We examined the activation of polyclonal gamma delta T cell lines, clones with V gamma 9V delta 2 and V gamma 9V delta 1 TCRs, and gamma delta T cells directly ex vivo in response to multiple phosphate, alkylamine and aminobisphosphonate (nBP) antigens and purified protein derivative from Mycobacterium tuberculosis (PPD). V gamma 9V delta 2 T cells were able to respond to multiple small organic molecules of highly variable structure whereas cells expressing a similar V gamma 9 chain paired with a V delta 1 chain failed to recognize these antigens. Thus, the TCR delta chain appears to make an important contribution to the recognition of these antigens. The kinetics of responses to alkylphosphate and alkylamine antigens differ from those of responses to the nBP pamidronate. These different classes of antigen are believed to have differed mechanisms of action. Such differences explain why nBPs can be pulsed onto antigen presenting cells (APCs) and still retain their ability to activate gamma delta T cells while alkylphosphate and alkylamine antigens cannot. We also demonstrate that a substantial proportion of the cells that produce IFN gamma directly ex vivo in response to PPD are gamma delta T cells and that gamma delta T cell activation requires contact with cells of human origin.

A human immunodeficiency virus 1 (HIV-1) clade A vaccine in clinical trials: stimulation of HIV-specific T-cell responses by DNA and recombinant modified vaccinia virus Ankara (MVA) vaccines in humans

The immunogenicities of candidate DNA- and modified vaccinia virus Ankara (MVA)-vectored human immunodeficiency virus (HIV) vaccines were evaluated on their own and in a prime-boost regimen in phase I clinical trials in healthy uninfected individuals in the United Kingdom. Given the current lack of approaches capable of inducing broad HIV-neutralizing antibodies, the pTHr.HIVA DNA and MVA.HIVA vaccines focus solely on the induction of cell-mediated immunity. The vaccines expressed a common immunogen, HIVA, which consists of consensus HIV-1 clade A Gag p24/p17 proteins fused to a string of clade A-derived epitopes recognized by cytotoxic T lymphocytes (CTLs). Volunteers' fresh peripheral blood mononuclear cells were tested for HIV-specific responses in a validated gamma interferon enzyme-linked immunospot (ELISPOT) assay using four overlapping peptide pools across the Gag domain and three pools of known CTL epitopes present in all of the HIVA protein. Both the DNA and the MVA vaccines alone and in a DNA prime-MVA boost combination were safe and induced HIV-specific responses in 14 out of 18, seven out of eight and eight out of nine volunteers, respectively. These results are very encouraging and justify further vaccine development.

Designing and engineering of DNA-vaccine construction encoding multiple CTL-epitopes of major HIV-1 antigens

A synthetic T cell immunogen (TCI) has been designed as a candidate DNA-based vaccine against Human immunodeficiency virus (HIV)-1 using cytotoxic T lymphocytes (CD8(+) CTL) and T-helper lymphocytes (CD4(+) Th) epitopes retrieved from the Los Alamos HIV Molecular Immunology Database. The protein 392 amino acids in length contains about eighty CTL-epitopes, many of which are overlapping and are totally restricted by ten different HLA class I molecules. To be able to detect CTL responses induced by a DNA vaccine in experimental animals, additional epitopes, restricted by mouse and Macaque rhesus major histocompatibility complex (MHC) class I molecules, were included in the target immunogen. The gene encoding the TCI protein was assembled, cloned into vector plasmids and expressed in a prokaryotic and a eukaryotic system. The presence of HIV-1 protein fragments in the immunogen structure was ascertained by ELISA and immunoblotting using panels of HIV-1-positive sera and monoclonal antibodies to p24. It has been demonstrated that DNA vaccine can induce both specific T cell responses (CTL and blast transformation) and specific antibodies in mice immunized with pcDNA-TCI.

T-cell subsets that harbor human immunodeficiency virus (HIV) in vivo: implications for HIV pathogenesis

Identification of T-cell subsets that are infected in vivo is essential to understanding the pathogenesis of human immunodeficiency virus (HIV) disease; however, this goal has been beset with technical challenges. Here, we used polychromatic flow cytometry to sort multiple T-cell subsets to 99.8% purity, followed by quantitative PCR to quantify HIV gag DNA directly ex vivo. We show that resting memory CD4(+) T cells are the predominantly infected cells but that terminally differentiated memory CD4(+) T cells contain 10-fold fewer copies of HIV DNA. Memory CD8(+) T cells can also be infected upon upregulation of CD4; however, this is infrequent and HIV-specific CD8(+) T cells are not infected preferentially. Naïve CD4(+) T-cell infection is rare and principally confined to those peripheral T cells that have proliferated. Furthermore, the virus is essentially absent from naïve CD8(+) T cells, suggesting that the thymus is not a major source of HIV-infected T cells in the periphery. These data illuminate the underlying mechanisms that distort T-cell homeostasis in HIV infection.

The race between initial T-helper expansion and virus growth upon HIV infection influences polyclonality of the response and viral set-point

Infection with HIV is characterized by very diverse disease-progression patterns across patients, associated with a wide variation in viral set-points. Progression is a multifactorial process, but an important role has been attributed to the HIV-specific T-cell response. To explore the conditions under which different set-points may be explained by differences in initial CD4 and CD8 T-cell responses and virus inoculum, we have formulated a model assuming that HIV-specific CD4 cells are both targets for infection and mediators of a monoclonal or polyclonal immune response. Clones differ in functional avidity for HIV epitopes. Importantly, in contrast to previous models, in this model we obtained coexistence of multiple clones at steady-state viral set-point, as seen in HIV infection. We found that, for certain parameter conditions, multiple steady states are possible: with few initial CD4 helper cells and high virus inoculum, no immune response is established and target-cell-limited infection follows, with associated high viral load; when CD4 clones are initially large and virus inoculum is low, infection can be controlled by several clones. The conditions for the dependence of viral set-point on initial inoculum and CD4 T-helper clone availability are investigated in terms of the effector mechanism of the clones involved.

The CD8 T cell coreceptor exhibits disproportionate biological activity at extremely low binding affinities

T lymphocytes recognize peptides presented in the context of major histocompatibility complex (MHC) molecules on the surface of antigen presenting cells. Recognition specificity is determined by the alphabeta T cell receptor (TCR). The T lymphocyte surface glycoproteins CD8 and CD4 enhance T cell antigen recognition by binding to MHC class I and class II molecules, respectively. Biophysical measurements have determined that equilibrium binding of the TCR with natural agonist peptide-MHC (pMHC) complexes occurs with KD values of 1-50 microm. The pMHCI/CD8 and pMHCII/CD4 interactions are significantly weaker than this (KD >100 microm), and the relative roles of TCR/pMHC and pMHC/coreceptor affinity in T cell activation remain controversial. Here, we engineer mutations in the MHCI heavy chain and beta2-microglobulin that further reduce or abolish the pMHCI/CD8 interaction to probe the significance of pMHC/coreceptor affinity in T cell activation. We demonstrate that the pMHCI/CD8 coreceptor interaction retains the vast majority of its biological activity at affinities that are reduced by over 15-fold (KD > 2 mm). In contrast to previous reports, we observe that the weak interaction between HLA A68 and CD8, which falls within this spectrum of reduced affinities, retains substantial functional activity. These findings are discussed in the context of current concepts of coreceptor dependence and the mechanism by which TCR coreceptors facilitate T cell activation.

The induction of HIV Gag-specific CD8+ T cells in the spleen and gut-associated lymphoid tissue by parenteral or mucosal immunization with recombinant Listeria monocytogenes HIV Gag

The induction of mucosal immunity is crucial in controlling viral replication during HIV infection. In this study we compare the ability of a recombinant Listeria monocytogenes that expresses and secretes the HIV Ag Gag to induce CD8(+) T cells against this Ag in the spleen, mesenteric lymph nodes, and Peyer's patches and the ability to provide effector Gag-specific CD8(+) T cells to the lamina propria after i.v., oral, or rectal administration of the vaccine. The levels of Ag-specific CD8(+)-activated T cells were measured ex vivo using intracellular cytokine staining for IFN-gamma and H-2K(d) Gag peptide tetramer staining. We found that all routes of immunization induced Gag-specific CD8(+) T cells in the spleen. After secondary infection, we observed substantial increases in splenic levels of CD8(+) T cells, and levels of Gag-specific cells were similar to those against listeriolysin O, the immunodominant Ag of L. monocytogenes. Both primary and secondary oral immunization resulted in abundant Gag-specific CD8(+)-activated T cells in the lamina propria that constituted approximately 35% of the CD8 compartment. However, significant levels of Gag and listeriolysin O-specific CD8(+) T cells were observed in mucosal lymphoid tissue only after two immunizations, perhaps because they had already entered the lamina propria compartment after a single immunization. In the context of HIV, a mucosally administered vaccine seems best calculated to prompt an immune response that is capable of preventing infection. The data presented in this report demonstrate that mucosally administered Listeria can prompt such a response and that booster doses can maintain this response.

Construction and immunogenicity in a prime-boost regimen of a Semliki Forest virus-vectored experimental HIV clade A vaccine

A novel, experimental subunit human immunodeficiency virus (HIV) vaccine, SFV.HIVA, was constructed. This consists of Semliki Forest virus (SFV), which is a suitable vaccine vector for use in humans, and a passenger gene encoding HIVA, which is an immunogen derived from HIV-1 clade A that is being currently tested in clinical trials of combined DNA- and modified vaccinia virus Ankara (MVA)-vectored vaccines in Oxford (UK) and Nairobi (Kenya). In the mouse, the SFV.HIVA vaccine was highly immunogenic for T cell-mediated immune responses and induced T cell memory that lasted for at least 6 months. SFV.HIVA was also compared to the vaccines currently used in the clinical trials and was shown to be as effective in T cell induction as pTHr.HIVA DNA but less immunogenic than MVA.HIVA. When tested in a prime-boost regimen, SFV.HIVA-induced responses could be boosted by MVA.HIVA. This work is a part of a long-term effort to build a panel of subunit vaccines expressing a common immunogen, which will allow both a direct comparison of various vaccine vectors and combined vaccination regimens in humans and provide more flexibility and/or a potential optimization of vaccinations for individuals based on their pre-existing anti-vector immunity.

Novel CD8+ T cell antagonists based on beta 2-microglobulin

The CD8 coreceptor of cytotoxic T lymphocytes binds to a conserved region of major histocompatibility complex class I molecules during recognition of peptide-major histocompatibility complex (MHC) class I antigens on the surface of target cells. This event is central to the activation of cytotoxic T lymphocyte (CTL) effector functions. The contribution of the MHC complex class I light chain, beta(2)-microglobulin, to CD8alphaalpha binding is relatively small and is mediated mainly through the lysine residue at position 58. Despite this, using molecular modeling, we predict that its mutation should have a dramatic effect on CD8alphaalpha binding. The predictions are confirmed using surface plasmon resonance binding studies and human CTL activation assays. Surprisingly, the charge-reversing mutation, Lys(58) --> Glu, enhances beta(2)m-MHC class I heavy chain interactions. This mutation also significantly reduces CD8alphaalpha binding and is a potent antagonist of CTL activation. These results suggest a novel approach to CTL-specific therapeutic immunosuppression.

Development of a DNA-MVA/HIVA vaccine for Kenya

Without going into the details of the devastation that human immunodeficiency virus (HIV) infection causes especially in the developing world, the best hope for changing the course of this epidemic is development of a safe, effective, accessible prophylactic HIV vaccine. While the inaccessibility of potentially neutralising epitopes on primary HIV isolates has hampered the development of envelope-based vaccines, there is a number of new potent technologies capable of inducing high levels of circulating virus-specific CD8(+) cytotoxic T lymphocytes (CTL). Our original finding that a successive immunisation with DNA and modified vaccinia virus Ankara (MVA) vaccines expressing a common immunogen is a potent way of inducing CD8(+) CTL, which has been since reinforced by us and others, prompted us to test this approach in humans. With the view of proceeding into a high-risk cohort in Kenya for the efficacy trial, we designed the immunogen, termed HIVA, to match the HIV strain responsible locally for over 70% infections. It consists of a consensus clade A gag p24/p17 and a string of clade A-derived CTL epitopes. Pre-clinical studies demonstrated high immunogenicities of both the pTHr.HIVA and MVA.HIVA vaccines. In mice, these induced strong T cells-mediated immune responses which lasted at least 155 days. In rhesus macaques, the prime-boost immunisation elicited T cell responses specific for multiple HIV-derived epitopes. Phase I trials in healthy low-risk volunteers have commenced in Oxford and Nairobi, and the preliminary immunogenicity analysis from the Oxford site indicated that both vaccine components alone induced T cell responses in a majority of volunteers. These results have boosted expectations for the prime-boost vaccinations.

A DNA/MVA-based candidate human immunodeficiency virus vaccine for Kenya induces multi-specific T cell responses in rhesus macaques

The minimum requirement for candidate human immunodeficiency virus (HIV) vaccines to enter clinical evaluation in humans should be their demonstrable immunogenicity in non-human primates: induction of antibodies neutralizing primary HIV isolates or elicitation of broad T cell-mediated immune responses. Here, we showed in rhesus macaques that the very same vaccines that had entered clinical trials in Oxford and Nairobi, plasmid pTHr.HIVA DNA and recombinant modified vaccinia virus Ankara MVA.HIVA in a prime-boost protocol (Hanke & McMichael, Nature Medicine 6, 951-955, 2000), induced cellular immune responses specific for multiple HIV-derived epitopes. This was demonstrated by using the intracellular cytokine staining and ELISPOT assays detecting interferon-gamma and pools of peptides employed in the clinical studies. These results have both boosted our expectations for the performance of these vaccines in humans and increased our confidence about the choice of these assays as the primary readouts in the on-going human trials.

The human CD8 coreceptor effects cytotoxic T cell activation and antigen sensitivity primarily by mediating complete phosphorylation of the T cell receptor zeta chain

Recognition of antigen by cytotoxic T lymphocytes (CTL) is determined by interaction of both the T cell receptor and its CD8 coreceptor with peptide-major histocompatibility complex (pMHC) class I molecules. We examine the relative roles of these receptors in the activation of human CTL using mutations in MHC class I designed to diminish or abrogate the CD8/pMHC interaction. We use surface plasmon resonance to determine that point mutation of the alpha3 loop of HLA A2 abrogates the CD8/pMHC interaction without affecting the affinity of the T cell receptor/pMHC interaction. Antigen-presenting cells expressing HLA A2 which does not bind to CD8 fail to activate CTL at any peptide concentration. Comparison of CTL activation by targets expressing HLA A2 with normal, abrogated, or diminished CD8/pMHC interaction show that the CD8/pMHC interaction enhances sensitivity to antigen. We determine that the biochemical basis for coreceptor dependence is the activation of the 23-kDa phosphoform of the CD3zeta chain. In addition, we produce mutant MHC class I multimers that specifically stain but do not activate CTL. These reagents may prove useful in circumventing undesirable activation-related perturbation of intracellular processes when pMHC multimers are used to phenotype antigen-specific CD8+ lymphocytes.

Antibody-independent antiviral function of memory CD4+ T cells in vivo requires regulatory signals from CD8+ effector T cells

Previous studies have shown that vaccine-primed CD4(+) T cells can mediate accelerated clearance of respiratory virus infection. However, the relative contributions of Ab and CD8(+) T cells, and the mechanism of viral clearance, are poorly understood. Here we show that control of a Sendai virus infection by primed CD4(+) T cells is mediated through the production of IFN-gamma and does not depend on Ab. This effect is critically dependent on CD8(+) cells for the expansion of CD4(+) T cells in the lymph nodes and the recruitment of memory CD4(+) T cells to the lungs. Passive transfer of a CD8(+) T cell supernatant into CD8(+) T cell-depleted, hemagglutinin-neuraminidase (HN)(421-436)-immune muMT mice substantially restored the virus-specific memory CD4(+) response and enhanced viral control in the lung. Together, the data demonstrate for the first time that in vivo primed CD4(+) T cells have the capacity to control a respiratory virus infection in the lung by an Ab-independent mechanism, provided that CD8(+) T cell "help" in the form of soluble factor(s) is available during the virus infection. These studies highlight the importance of synergistic interactions between CD4(+) and CD8(+) T cell subsets in the generation of optimal antiviral immunity.

Perforin-low memory CD8+ cells are the predominant T cells in normal humans that synthesize the beta -chemokine macrophage inflammatory protein-1beta

The synthesis of antiviral beta-chemokines has joined cytolysis as a potential mechanism for the control of HIV-1 infection by CD8(+) T cells. Recent evidence suggests that these two effector functions can diverge in some individuals infected with HIV-1; however, little is known about the CD8(+) T cell subsets in normal individuals that synthesize antiviral beta-chemokines. In this report, we have used mutliparameter flow cytometry to characterize the T cell subsets that secrete the antiviral beta-chemokine macrophage inflammatory protein (MIP)-1beta. These studies have shown: (i) CD8(+) cells are the predominant T cell subset that synthesizes MIP-1beta; (ii) MIP-1beta and IFN-gamma are synthesized congruently in most CD8(+) T cells; however, significant numbers of these cells synthesize only one of these effector molecules; (iii) approximately 60% of the CD8(+) T cells that synthesize MIP-1beta lack perforin; (iv) MIP-1beta is synthesized with approximately equal frequency by CD28(+) and CD28(-) subpopulations of CD8(+) T cells; (v) MIP-1beta is synthesized by three distinct CD8(+) T cell subsets defined by the expression of CD45R0 and CD62L; and (vi) MIP-1beta is not synthesized in short-term cultures of naive CD8(+) T cells. These results demonstrate substantial subset heterogeneity of MIP-1beta synthesis among CD8(+) T cells and suggest that these subsets should be evaluated as correlates of protective immunity against HIV-1.

Cellular immune responses to HIV

The cellular immune response to the human immunodeficiency virus, mediated by T lymphocytes, seems strong but fails to control the infection completely. In most virus infections, T cells either eliminate the virus or suppress it indefinitely as a harmless, persisting infection. But the human immunodeficiency virus undermines this control by infecting key immune cells, thereby impairing the response of both the infected CD4+ T cells and the uninfected CD8+ T cells. The failure of the latter to function efficiently facilitates the escape of virus from immune control and the collapse of the whole immune system.

Aminooxypentane addition to the chemokine macrophage inflammatory protein-1alpha P increases receptor affinities and HIV inhibition

To enter its target cells, human immunodeficiency virus (HIV) must interact with CD4 and one of a family of chemokine receptors. CCR5 is widely used by the virus in this context, and its ligands can prevent HIV entry. Amino-terminal modified chemokine variants, in particular AOP-RANTES (aminooxypentane-linked regulated on activation normal T cell expressed and secreted), exhibit enhanced HIV entry inhibition. We have previously demonstrated that a non-allelic isoform of macrophage inflammatory protein (MIP)-1alpha, termed MIP-1alphaP, is the most active naturally occurring inhibitor of HIV entry known. Here we report the properties of a variant of MIP-1alphaP with an AOP group on the amino terminus. We show that, like RANTES, the addition of AOP to MIP-1alphaP enhances its interactions with CCR1 and CCR5, allows more effective internalization of CCR5, and increases the ligand's potency as an inhibitor of HIV entry through CCR5. Importantly, AOP-MIP-1alphaP is about 10-fold more active than AOP-RANTES at inhibiting HIV entry, making it the most effective chemokine-based inhibitor of HIV entry through CCR5 described to date. Surprisingly, the enhanced receptor interactions of AOP-MIP-1alphaP do not translate into increased chemotaxis or coupling to calcium ion fluxes, suggesting that this protein should be viewed as a partial, rather than a full, agonist for CCR1 and CCR5.

Highly active antiretroviral therapy normalizes the potential for MIP-1alpha production in HIV infection

DESIGN

The CC chemokines RANTES, MIP-1alpha and MIP-1beta are ligands for CCR5, which has been identified as the principal co-receptor for macrophage tropic strains of HIV-1. This study investigated whether the inducible levels of RANTES, MIP-1alpha and MIP-1beta produced by cultured whole blood samples related to different rates of progression of HIV infection and to the introduction of Nelfinavir-based highly active anti-retroviral therapy (HAART).

METHODS

Study subjects were HIV-positive and categorized as "slow progressors" (n= 8) or as "fast progressors" (n= 7); the latter group were treated with HAART. MIP-1alpha, MIP-1beta and RANTES production was determined using commercial ELISA kits.

RESULTS

The inducible production of MIP-1alpha by whole blood cells in culture was significantly depressed in patients starting therapy compared with "slow progressors" and "normal donors". The levels of MIP-1alpha significantly increased with therapy at 12 weeks compared with pre-HAART levels (P= O.05) and became comparable to that of "normals" and "slow progressors". Differences in the inducible levels of MIP-1beta and RANTES for the separate subject groups were not significant.

CONCLUSIONS

The increase in inducible MIP-1alpha production following HAART might suggest a role for the chemokines in HIV disease, either for monitoring the outcome of therapy of HIV disease, or as a direct therapeutic intervention.

T-lymphocyte production of macrophage inflammatory protein-1α is critical to the recruitment of CD8+ T cells to the liver, lung, and spleen during graft-versus-host disease

To investigate the mechanism by which macrophage inflammatory protein-1α (MIP-1α) affects graft-versus-host disease (GVHD), the expression and function of MIP-1α in 2 murine models of GVHD were evaluated. In irradiated class I and class II disparate recipients, the expression of messenger RNA (mRNA) and protein for MIP-1α was significantly increased in GVHD target organs after transfer of allogeneic lymphocytes compared to syngeneic lymphocytes. When lymphocytes unable to make MIP-1α were transferred, there was a decrease in the production of MIP-1α in the liver, lung, and spleen of bm1 (B6.C-H2bm1/By) and bm12 (B6.C-H2bm12/KhEg) recipients compared to the transfer of wild-type splenocytes. At day 6 there was a 4-fold decrease in the number of transferred CD8+ T cells in the lung and approximately a 2-fold decrease in the number of CD8+ T cells in the liver and spleen in bm1 recipients after transfer of MIP-1α–deficient (MIP-1α−/−) splenocytes compared to wild-type (MIP-1α+/+) splenocytes. These differences persisted for 13 days after splenocyte transfer. In contrast, the number of donor CD4+ T cells found in the liver and lung was significantly increased after the transfer of MIP-1α−/− compared to wild-type splenocytes in bm12 recipients from day 6 through day 10. Thus, the transfer of allogeneic T cells was associated with the enhanced expression of MIP-1α in both a class I and class II mismatch setting. However, the increased expression only led to enhanced recruitment of CD8+, but not CD4+, donor T cells. Production of MIP-1α by donor T cells is important in the occurrence of GVHD and functions in a tissue-dependent fashion.

T-lymphocyte production of macrophage inflammatory protein-1α is critical to the recruitment of CD8+ T cells to the liver, lung, and spleen during graft-versus-host disease

To investigate the mechanism by which macrophage inflammatory protein-1α (MIP-1α) affects graft-versus-host disease (GVHD), the expression and function of MIP-1α in 2 murine models of GVHD were evaluated. In irradiated class I and class II disparate recipients, the expression of messenger RNA (mRNA) and protein for MIP-1α was significantly increased in GVHD target organs after transfer of allogeneic lymphocytes compared to syngeneic lymphocytes. When lymphocytes unable to make MIP-1α were transferred, there was a decrease in the production of MIP-1α in the liver, lung, and spleen of bm1 (B6.C-H2bm1/By) and bm12 (B6.C-H2bm12/KhEg) recipients compared to the transfer of wild-type splenocytes. At day 6 there was a 4-fold decrease in the number of transferred CD8+ T cells in the lung and approximately a 2-fold decrease in the number of CD8+ T cells in the liver and spleen in bm1 recipients after transfer of MIP-1α–deficient (MIP-1α−/−) splenocytes compared to wild-type (MIP-1α+/+) splenocytes. These differences persisted for 13 days after splenocyte transfer. In contrast, the number of donor CD4+ T cells found in the liver and lung was significantly increased after the transfer of MIP-1α−/− compared to wild-type splenocytes in bm12 recipients from day 6 through day 10. Thus, the transfer of allogeneic T cells was associated with the enhanced expression of MIP-1α in both a class I and class II mismatch setting. However, the increased expression only led to enhanced recruitment of CD8+, but not CD4+, donor T cells. Production of MIP-1α by donor T cells is important in the occurrence of GVHD and functions in a tissue-dependent fashion.