Epitope specific T‐cell responses against influenza A in a healthy population

Pre‐existing human CD4⁺ and CD8⁺ T‐cell‐mediated immunity may be a useful correlate of protection against severe influenza disease. Identification and evaluation of common epitopes recognized by T cells with broad cross‐reactivity is therefore important to guide universal influenza vaccine development, and to monitor immunological preparedness against pandemics. We have retrieved an optimal combination of MHC class I and class II restricted epitopes from the Immune Epitope Database ( www.iedb.org ), by defining a fitness score function depending on prevalence, sequence conservancy and HLA super‐type coverage. Optimized libraries of CD4⁺ and CD8⁺ T‐cell epitopes were selected from influenza antigens commonly present in seasonal and pandemic influenza strains from 1934 to 2009. These epitope pools were used to characterize human T‐cell responses in healthy donors using interferon‐γ ELISPOT assays. Upon stimulation, significant CD4⁺ and CD8⁺ T‐cell responses were induced, primarily recognizing epitopes from the conserved viral core proteins. Furthermore, the CD4⁺ and CD8⁺ T cells were phenotypically characterized regarding functionality, cytotoxic potential and memory phenotype using flow cytometry. Optimized sets of T‐cell peptide epitopes may be a useful tool to monitor the efficacy of clinical trials, the immune status of a population to predict immunological preparedness against pandemics, as well as being candidates for universal influenza vaccines.     

Selective antigen‐specific CD4+ T‐cell,but not CD8+ T‐ or B‐cell,tolerance corrupts cancer immunotherapy

Self‐tolerance, presumably through lineage‐unbiased elimination of self‐antigen‐specific lymphocytes (CD4⁺ T, CD8⁺ T, and B cells), creates a formidable barrier to cancer immunotherapy. In contrast to this prevailing paradigm, we demonstrate that for some antigens, self‐tolerance reflects selective elimination of antigen‐specific CD4⁺ T cells, but preservation of CD8⁺ T‐ and B‐cell populations. In mice, antigen‐specific CD4⁺ T‐cell tolerance restricted CD8⁺ T‐ and B‐cell responses targeting the endogenous self‐antigen guanylyl cyclase c (GUCY2C) in colorectal cancer. Although selective CD4⁺ T‐cell tolerance blocked GUCY2C‐specific antitumor immunity and memory responses, it offered a unique solution to the inefficacy of GUCY2C vaccines through recruitment of self‐antigen‐independent CD4⁺ T‐cell help. Incorporating CD4⁺ T‐cell epitopes from foreign antigens into vaccines against GUCY2C reconstituted CD4⁺ T‐cell help, revealing the latent functional capacity of GUCY2C‐specific CD8⁺ T‐ and B‐cell pools, producing durable antitumor immunity without autoimmunity. Incorporating CD4⁺ T‐cell epitopes from foreign antigens into vaccines targeting self‐antigens in melanoma (Trp2) and breast cancer (Her2) produced similar results, suggesting selective CD4⁺ T‐cell tolerance underlies ineffective vaccination against many cancer antigens. Thus, identification of self‐antigens characterized by selective CD4⁺ T‐cell tolerance and abrogation of such tolerance through self‐antigen‐independent T‐cell help is essential for future immunotherapeutics.     

Vaccine molecules targeting Xcr1 on cross‐presenting DCs induce protective CD8+ T‐cell responses against influenza virus

Targeting antigens to cross‐presenting dendritic cells (DCs) is a promising method for enhancing CD8⁺ T‐cell responses. However, expression patterns of surface receptors often vary between species, making it difficult to relate observations in mice to other animals. Recent studies have indicated that the chemokine receptor Xcr1 is selectively expressed on cross‐presenting murine CD8α⁺ DCs, and that the expression is conserved on homologous DC subsets in humans (CD141⁺ DCs), sheep (CD26⁺ DCs), and macaques (CADM1⁺ DCs). We therefore tested if targeting antigens to Xcr1 on cross‐presenting DCs using antigen fused to Xcl1, the only known ligand for Xcr1, could enhance immune responses. Bivalent Xcl1 fused to model antigens specifically bound CD8α⁺ DCs and increased proliferation of antigen‐specific T cells. DNA vaccines encoding dimeric Xcl1‐hemagglutinin (HA) fusion proteins induced cytotoxic CD8⁺ T‐cell responses, and mediated full protection against a lethal challenge with influenza A virus. In addition to enhanced CD8⁺ T‐cell responses, targeting of antigen to Xcr1 induced CD4⁺ Th1 responses and highly selective production of IgG2a antibodies. In conclusion, targeting of dimeric fusion vaccine molecules to CD8α⁺ DCs using Xcl1 represents a novel and promising method for induction of protective CD8⁺ T‐cell responses.     

Cross‐reactive responses to modified M158–66 peptides by CD8+ T cells that use noncanonical BV genes can describe unknown repertoires

Memory T‐cell repertoires are populated by clonotypes selected by an individual's history of antigen exposures. Our previous analysis of middle‐age CD8⁺ T‐cell memory repertoires to the influenza‐derived epitope M1_58–66, described a network of highly cross‐reactive BV19 clonotypes responding to M1_58–66 and at least one peptide with a conservative amino acid substitution at either of two TCR contact positions. Here, we report that some substitutions abrogate BV19 responses and favor responses with different BV. Cross‐reactive T cells using seven other BV families responded to 12 of 13 peptides tested. BV12 clonotypes define the most extensive cross‐reactive network that encompasses seven peptides. We generated 3D networks based on the peptides recognized and BV family used and observed a cluster of five peptides that includes M1_58–66 and another cluster of five peptides that does not include M1_58–66. The first cluster represents peptides structurally similar to M1_58–66, and the second represents peptides with more considerable changes in epitope recognition surface. We hypothesize that the second cluster represents the cross‐reactive network around another unknown epitope or epitopes. This data supports a model of stable CD8⁺ T‐cell memory networks that include a substantial contribution from cross‐reactive T cells.     

pDCs efficiently process synthetic long peptides to induce functional virus‐ and tumour‐specific T‐cell responses

Robust cell‐mediated immunity is required for immune control of tumours and protection from viral infections, with both CD4⁺ and CD8⁺ T cells playing a pivotal role. Synthetic long peptides (SLPs) represent an attractive way to induce such combined responses, as they contain both class I and class II epitopes. The ability of plasmacytoid dendritic cells (pDCs) to cross‐present SLPs has not yet been investigated; yet, pDCs play a critical role in shaping immune responses and have emerged as novel vectors for immunotherapy. Using overlapping 15‐mer peptide pools covering the entire sequence of CMVpp65 and MelA, representing a viral disease (cytomegalovirus, CMV) and a tumour (melanoma), respectively, we showed that human pDCs can effectively process SLPs. Our results demonstrated that pDCs potently cross‐present virus‐ and tumour‐derived SLPs and cross‐prime broad‐ranging, effective and long‐lived CD4⁺ and CD8⁺ T‐cell responses, triggering more efficient immune responses than short peptide loaded pDCs. This ability required intracellular processing by the proteasome and was enhanced by co‐exposure to TLR7/9‐L. Combining SLPs with pDCs represents a powerful immunotherapeutic strategy to elicit potent immune responses, which are required for clinical success in cancers and viral infections.     

Memory CD4+ T cells enhance B‐cell responses to drifting influenza immunization

Influenza A annually infects 5–10% of the world's human population resulting in one million deaths. Influenza causes annual epidemics and reinfects previously exposed individuals because of antigenic drift in the glycoprotein hemagglutinin. Due to antigenic drift, the immune system is simultaneously exposed to novel and conserved parts of the influenza virus via vaccination and/or infection throughout life. Preexisting immunity has long been known to augment subsequent hemagglutination inhibitory antibody (hAb) responses. However, the preexisting immunological contributors that influence hAb responses are not understood. Therefore, we adapted and developed sequential infection and immunization mouse models using drifted influenza strains to show that MHC Class II haplotype and T‐cell reactivity influences subsequent hAb responses. We found that CB6F1 mice infected with A/CA followed by immunization with A/PR8 have increased hAb responses to A/PR8 compared to C57BL/6 mice. Increased hAb responses in CB6F1 mice were CD4⁺ T‐cell and B‐cell dependent and corresponded to increased germinal center A/PR8‐specific B and T‐follicular helper cells. These results suggest conserved MHC Class II restricted epitopes within HA are essential for B cells to respond to drifting influenza and could be leveraged to boost hAb responses.     

Protein and modified vaccinia virus Ankara‐based influenza virus nucleoprotein vaccines are differentially immunogenic in BALB/c mice

Because of the high variability of seasonal influenza viruses and the eminent threat of influenza viruses with pandemic potential, there is great interest in the development of vaccines that induce broadly protective immunity. Most probably, broadly protective influenza vaccines are based on conserved proteins, such as nucleoprotein (NP). NP is a vaccine target of interest as it has been shown to induce cross‐reactive antibody and T cell responses. Here we tested and compared various NP‐based vaccine preparations for their capacity to induce humoral and cellular immune responses to influenza virus NP. The immunogenicity of protein‐based vaccine preparations with Matrix‐M? adjuvant as well as recombinant viral vaccine vector modified Vaccinia virus Ankara (MVA) expressing the influenza virus NP gene, with or without modifications that aim at optimization of CD8⁺ T cell responses, was addressed in BALB/c mice. Addition of Matrix‐M? adjuvant to NP wild‐type protein‐based vaccines significantly improved T cell responses. Furthermore, recombinant MVA expressing the influenza virus NP induced strong antibody and CD8⁺ T cell responses, which could not be improved further by modifications of NP to increase antigen processing and presentation.     

DNGR‐1 is dispensable for CD8+ T‐cell priming during respiratory syncytial virus infection

During respiratory syncytial virus (RSV) infection CD8⁺ T cells both assist in viral clearance and contribute to immunopathology. CD8⁺ T cells recognize viral peptides presented by dendritic cells (DCs), which can directly present viral antigens when infected or, alternatively, “cross‐present” antigens after endocytosis of dead or dying infected cells. Mouse CD8α⁺ and CD103⁺ DCs excel at cross‐presentation, in part because they express the receptor DNGR‐1 that detects dead cells by binding to exposed F‐actin and routes internalized cell debris into the cross‐presentation pathway. As RSV causes death in infected epithelial cells, we tested whether cross‐presentation via DNGR‐1 is necessary for CD8⁺ T‐cell responses to the virus. DNGR‐1‐deficient or wild‐type mice were intranasally inoculated with RSV and the magnitude of RSV‐specific CD8⁺ T‐cell induction was measured. We found that during live RSV infection, cross‐presentation via DNGR‐1 did not have a major role in the generation of RSV–specific CD8⁺ T‐cell responses. However, after intranasal immunization with dead cells infected with RSV, a dependence on DNGR‐1 for RSV‐specific CD8⁺ T‐cell responses was observed, confirming the ascribed role of the receptor. Thus, direct presentation by DCs may be the major pathway initiating CD8⁺ T‐cell responses to RSV, while DNGR‐1‐dependent cross‐presentation has no detectable role.     

Human leucocyte antigen‐Bw4 and Gag‐specific T cell responses are associated with slow disease progression in HIV‐1B‐infected anti‐retroviral therapy‐naive Chinese

In China, the majority of human immunodeficiency virus (HIV) infections are predominately subtype B. It is important to characterize the HIV‐1 subtype B‐specific and its T cell response within the Chinese population, with the aim of identifying protective correlates of immunity to control HIV‐1 infections. In this study, we performed a comprehensive analysis looking into the magnitude/strength of T cell responses directed at the Gag protein of the HIV‐1 subtype B, one of the most conserved HIV‐1 proteins. The study group consisted of anti‐retroviral native and chronic HIV‐1 subtype B‐infected individuals. We used enzyme‐linked immunospot (ELISPOT) assay to quantify the total T cell responses to HIV‐1 Gag at the single peptide level. Twenty‐eight (38%) peptides were recognized in 24 (82·8%) individuals. The p24 was identified as the most frequently recognized subunit protein with the greatest T cell response in the test, which correlated positively with CD4⁺ T cell count and inversely with viral load (VL). At the level of the human leucocyte antigen (HLA) supertypes, we detected the highest levels and a significant correlation with both the CD4⁺ T cell count and the VL with Gag T cell responses in Bw4/Bw4. These findings demonstrate that (i) the HIV‐1B Gag p24‐specific immune responses play an important role in controlling viral replication and slowing clinical progression; and (ii) HLA‐Bw4/Bw4 allele has stronger T cell responses, which is associated with slow clinical progression in Chinese HIV patients.     

Dengue virus‐infected human dendritic cells reveal hierarchies of naturally expressed novel NS3 CD8 T cell epitopes

Detailed knowledge of dengue virus (DENV) cell‐mediated immunity is limited. In this study we characterize CD8⁺ T lymphocytes recognizing three novel and two known non‐structural protein 3 peptide epitopes in DENV‐infected dendritic cells. Three epitopes displayed high conservation (75–100%), compared to the others (0–50%). A hierarchy ranking based on magnitude and polyfunctionality of the antigen‐specific response showed that dominant epitopes were both highly conserved and cross‐reactive against multiple DENV serotypes. These results are relevant to DENV pathogenesis and vaccine design.     

Dominant CD4‐dependent RNA‐dependent RNA polymerase‐specific T‐cell responses in children acutely infected with human enterovirus 71 and healthy adult controls

Human enterovirus 71 (EV71) is one of the major causes of hand, foot and mouth disease (HFMD), which leads to significant mortality in infected children. A prophylactic vaccine is urgently needed. However, little is known about the protective T‐cell immunity in individuals infected with the EV71 virus. In this study, we performed a comprehensive ex vivo interferon‐γ ELISPOT analysis in 31 children infected with EV71 as well as in 40 healthy adult controls of the CD4⁺ and CD8⁺ T‐cell responses to overlapping peptides spanning the VP1 structural protein and RNA‐dependent RNA polymerase (RdRp) non‐structural protein. EV71‐specific CD4 T‐cell responses were detected in most of the acute patients and were mostly CD4‐dependent RdRp‐specific responses. CD8‐dependent VP1 and RdRp‐specific responses were also detected in a small proportion of recently infected children. There was no significant association between the strength of the T‐cell responses and disease severity observed during the acute EV71 infection phase. Interestingly, an RdRp‐specific, but no VP1‐specific, CD4‐dependent T‐cell response was detected in 30% of the adult controls, and no T‐cell responses were detected in healthy children. In addition, 24 individual peptides containing potential T‐cell epitope regions were identified. The data suggest that CD4‐dependent RdRp‐specific T‐cell responses may play an important role in protective immunity, and the epitopes identified in this study should provide valuable information for future therapeutic and prophylactic vaccine design as well as basic research.     

Predominance of heterosubtypic IFN‐γ‐only‐secreting effector memory T cells in pandemic H1N1 naive adults

The 2009/10 pandemic (pH1N1) highlighted the need for vaccines conferring heterosubtypic immunity against antigenically shifted influenza strains. Although cross‐reactive T cells are strong candidates for mediating heterosubtypic immunity, little is known about the population‐level prevalence, frequency, and cytokine‐secretion profile of heterosubtypic T cells to pH1N1. To assess this, pH1N1 sero‐negative adults were recruited. Single‐cell IFN‐γ and IL‐2 cytokine‐secretion profiles to internal proteins of pH1N1 or live virus were enumerated and characterised. Heterosubtypic T cells recognising pH1N1 core proteins were widely prevalent, being detected in 90% (30 of 33) of pH1N1‐naïve individuals. Although the last exposure to influenza was greater than 6 months ago, the frequency and proportion of the IFN‐γ‐only‐secreting T‐cell subset was significantly higher than the IL‐2‐only‐secreting subset. CD8⁺ IFN‐γ‐only‐secreting heterosubtypic T cells were predominantly CCR7^?CD45RA^? effector‐memory phenotype, expressing the tissue‐homing receptor CXCR3 and degranulation marker CD107. Receipt of the 2008–09 influenza vaccine did not alter the frequency of these heterosubtypic T cells, highlighting the inability of current vaccines to maintain this heterosubtypic T‐cell pool. The surprisingly high prevalence of pre‐existing circulating pH1N1‐specific CD8⁺ IFN‐γ‐only‐secreting effector memory T cells with cytotoxic and lung‐homing potential in pH1N1‐seronegative adults may partly explain the low case fatality rate despite high rates of infection of the pandemic in young adults.     

Biphasic role of 4‐1BB in the regulation of mouse cytomegalovirus‐specific CD8+ T cells

The initial requirement for the emergence of CMV‐specific CD8⁺ T cells is poorly understood. Mice deficient in the cosignaling TNF superfamily member, 4‐1BB, surprisingly developed exaggerated early CD8⁺ T‐cell responses to mouse CMV (MCMV). CD8⁺ T cells directed against acute MCMV epitopes were enhanced, demonstrating that 4‐1BB naturally antagonizes these primary populations. Paradoxically, 4‐1BB‐deficient mice displayed reduced accumulation of memory CD8⁺ T cells that expand during chronic/latent infection. Importantly, the canonical TNF‐related ligand, 4‐1BBL, promoted the accumulation of these memory CD8⁺ T cells, whereas suppression of acute CD8⁺ T cells was independent of 4‐1BBL. These data highlight the dual nature of the 4‐1BB/4‐1BBL system in mediating both stimulatory and inhibitory cosignaling activities during the generation of anti‐MCMV immunity.     

Comprehensive analysis of HIV Gag‐specific IFN‐γ response in HIV‐1‐ and HIV‐2‐infected asymptomatic patients from a clinical cohort in The Gambia

Majority of HIV‐2‐infected individuals meet the criteria of long‐term non‐progressors. This has been linked to superior qualitative HIV‐2‐specific cellular immune responses that correlate with viral control. However, it is unknown whether this is due to frequent targeting of immunodominant Gag epitopes in HIV‐2 than HIV‐1 infection. We describe a comprehensive comparison of the magnitude, breadth and frequency of Gag responses and the degree of cross‐recognition of frequently targeted, immunodominant Gag peptides in a cross‐sectional study of asymptomatic HIV‐1‐ and HIV‐2‐infected individuals. Fresh PBMC from 20 HIV‐1‐ and 20 HIV‐2‐infected patients with similar CD4⁺ T‐cell counts (p=0.36) were stimulated with pools of HIV‐1 and/or HIV‐2 Gag peptides in an IFN‐γ ELISPOT assay. We found no difference in the cumulative magnitude of IFN‐γ responses (p=0.75) despite significantly lower plasma viral loads in HIV‐2‐infected people (p<0.0001). However, Gag211–290 was targeted with significantly higher magnitude in HIV‐2‐infected subjects (p=0.03) although this did not correlate with viral control. There was no difference in frequently targeted Gag peptides, the breadth, immunodominance or cross‐recognition of Gag peptide pools between the two infections. This suggests that other factors may control viral replication in HIV‐2 infection.     

Spontaneous CD4+ and CD8+ T‐cell responses directed against cancer testis antigens are present in the peripheral blood of testicular cancer patients

Cancer/testis antigen (CTAg) expression is restricted to spermatogenic cells in an immune‐privileged site within the testis. However, these proteins are expressed aberrantly by malignant cells and T‐cell responses against CTAgs develop in many cancer patients. We investigated the prevalence, magnitude and phenotype of CTAg‐specific T cells in the blood of patients with testicular germ cell tumors (TGCTs). CD8⁺ and CD4⁺ T‐cell responses against MAGE‐A family antigens were present in 44% (20/45) of patients’ samples assayed by ex vivo IFN‐γ ELISPOT. The presence of MAGE‐specific CD8⁺ T cells was further determined following short‐term in vitro expansion through the use of pMHC‐I multimers containing known immunogenic peptides. Longitudinal analysis revealed that the frequency of MAGE‐specific T cells decreased by 89% following orchidectomy suggesting that persistence of tumor antigen is required to sustain CTAg‐specific T‐cell immunity. Notably, this decrease correlated with a decline in the global effector/memory T‐cell pool following treatment. Spontaneous T‐cell immunity against CTAg proteins therefore develops in many patients with testicular cancer and may play an important role in the excellent clinical outcome of patients with this tumor subtype.     

CD4+ and CD8+ T‐cell immunity to Dengue – lessons for the study of Zika virus

Dengue virus (DENV) and Zika virus (ZIKV) are rapidly emerging mosquito‐borne flaviviruses that represent a public health concern. Understanding host protective immunity to these viruses is critical for the design of optimal vaccines. Over a decade of research has highlighted a significant contribution of the T‐cell response to both protection and/or disease enhancement during DENV infection, the latter being mainly associated with sub‐optimal cross‐reactive T‐cell responses during secondary infections. Phase IIb/III clinical trials of the first licensed tetravalent dengue vaccine highlight increased vaccine efficacy in dengue‐immune as opposed to dengue‐naive vaccinees, suggesting a possible immunoprotective role of pre‐existing DENV‐specific T cells that are boosted upon vaccination. No vaccine is available for ZIKV and little is known about the T‐cell response to this virus. ZIKV and DENV are closely related viruses with a sequence identity ranging from 44% and 56% for the structural proteins capsid and envelope to 68% for the more conserved non‐structural proteins NS3/NS5, which represent the main targets of the CD4⁺ and CD8⁺ T‐cell response to DENV, respectively. In this review we discuss our current knowledge of T‐cell immunity to DENV and what it can teach us for the study of ZIKV. The extent of T‐cell cross‐reactivity towards ZIKV of pre‐existing DENV‐specific memory T cells and its potential impact on protective immunity and/or immunopathology will also be discussed.     

Vaccinia‐based influenza vaccine overcomes previously induced immunodominance hierarchy for heterosubtypic protection

Growing concerns about unpredictable influenza pandemics require a broadly protective vaccine against diverse influenza strains. One of the promising approaches was a T cell‐based vaccine, but the narrow breadth of T‐cell immunity due to the immunodominance hierarchy established by previous influenza infection and efficacy against only mild challenge condition are important hurdles to overcome. To model T‐cell immunodominance hierarchy in humans in an experimental setting, influenza‐primed C57BL/6 mice were chosen and boosted with a mixture of vaccinia recombinants, individually expressing consensus sequences from avian, swine, and human isolates of influenza internal proteins. As determined by IFN‐γ ELISPOT and polyfunctional cytokine secretion, the vaccinia recombinants of influenza expanded the breadth of T‐cell responses to include subdominant and even minor epitopes. Vaccine groups were successfully protected against 100 LD₅₀ challenges with PR/8/34 and highly pathogenic avian influenza H5N1, which contained the identical dominant NP₃₆₆ epitope. Interestingly, in challenge with pandemic A/Cal/04/2009 containing mutations in the dominant epitope, only the group vaccinated with rVV‐NP + PA showed improved protection. Taken together, a vaccinia‐based influenza vaccine expressing conserved internal proteins improved the breadth of influenza‐specific T‐cell immunity and provided heterosubtypic protection against immunologically close as well as distant influenza strains.     

Altered effector functions of virus‐specific and virus cross‐reactive CD8+ T cells in mice immunized with related flaviviruses

Memory cross‐reactive CD8⁺ T‐cell responses may induce protection or immunopathology upon secondary viral challenge. To elucidate the potential role of T cells in sequential flavivirus infection, we characterized cross‐reactive CD4⁺ and CD8⁺ T‐cell responses between attenuated and pathogenic Japanese encephalitis virus (JEV) and pathogenic West Nile virus (WNV). A previously reported WNV NS4b CD8⁺ T‐cell epitope and its JEV variant elicited CD8⁺ T‐cell responses in both JEV‐ and WNV‐infected mice. The peptide variant homologous to the immunizing virus induced greater cytokine secretion and activated higher frequencies of epitope‐specific CD8⁺ T cells. However, there was a virus‐dependent, peptide variant‐independent pattern of cytokine secretion; the IFNγ⁺‐to‐IFNγ⁺TNFα⁺ CD8⁺ T‐cell ratio was greater in JEV‐ than in WNV‐infected mice. Despite similarities in viral burden for pathogenic WNV and JEV viruses, CD8⁺ T cells from pathogenic JEV‐immunized mice exhibited functional and phenotypic profiles similar to those seen for the attenuated JEV strain. Patterns of killer cell lectin‐like receptor G1 (KLRG1) and CD127 expression differed by virus type, with a rapid expansion and contraction of short‐lived effector cells in JEV infection and persistence of high levels of short‐lived effector cells in WNV infection. Such cross‐reactive T‐cell responses to primary infection may affect the outcomes of sequential flavivirus infections.     

Antigen‐specific Treg impair CD8+ T‐cell priming by blocking early T‐cell expansion

Foxp3⁺ Treg are crucial for the maintenance of self‐tolerance and have been shown to control CD8⁺ T‐cell effector functions. In addition, Treg are thought to control the priming of CD8⁺ T cells, which recognize the same antigens as Treg. Taking advantage of our model of peripheral tolerance induction to influenza hemagglutinin (HA) after HA gene transfer, we found that HA‐specific Treg suppress antigen‐linked CTL responses through early blockade of CD8⁺ T‐cell expansion. Confronted with their cognate antigen, Treg expand more rapidly than CD8⁺ T cells and are highly suppressive only during the initial stages of immune priming. They nullify HA‐specific CD8⁺ T‐cell responses, local inflammatory responses and rejection of HA transduced cells. When HA gene transfer is performed with extensive tissue inflammation, HA‐specific Treg are less effective but still reduce the frequency of newly primed HA‐specific CD8⁺ T cells and the ensuing frequency of memory CD8⁺ T cells. Our results demonstrate that Treg control CTL priming in an antigen‐specific manner at the level of T‐cell expansion, highlighting how self‐reactive Treg could prevent the induction of autoimmune responses through selective blockade of autoreactive T‐cell proliferation.     

CTL recognition of HIV‐1‐infected cells via cross‐recognition of multiple overlapping peptides from a single 11‐mer Pol sequence

It is known that overlapping HIV‐1 peptides of different lengths can be presented by a given HLA class I molecule. However, the role of those peptides in CD8⁺ T cells recognition of HIV‐1‐infected cells remains unclear. Here we investigated the recognition of overlapping 8‐mer to 11‐mer peptides of Pol 155–165 by HLA‐B*54:01‐restricted CD8⁺ T cells. The analysis of ex vivo T cells using ELISPOT and tetramer binding assays showed that there were different patterns of CD8⁺ T‐cell responses to these peptides among chronically HIV‐1‐infected HLA‐B*54:01⁺ individuals, though the response to the 9‐mer peptide was the strongest among them. CD8⁺ T‐cell clones with TCRs specific for the 9‐mer, 10‐mer, and/or 11‐mer peptides effectively killed HIV‐1‐infected cells. Together, these results suggest that the 9‐mer and 10‐mer peptides could be predominantly presented by HLA‐B*54:01, though it remains possible that the 11‐mer peptide was also presented by this HLA allele. The present study demonstrates effective CD8⁺ T‐cell recognition of HIV‐1‐infected cells via presentation of multiple overlapping HIV‐1 peptides and cross‐recognition by the CD8⁺ T cells.