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Background: Major histocompatibility complex class-1-related protein (MR1), unlike human leukocyte antigen (HLA) class-1, was until recently considered to be monomorphic. MR1 presents metabolites in the context of host responses to bacterial infection. MR1-restricted TCRs specific to tumor cells have been described, raising interest in their potential therapeutic application for cancer treatment. The diversity of MR1-ligand biology has broadened with the observation that single nucleotide variants (SNVs) exist within MR1 and that allelic variants can impact host immunity. Methods: The TCR from a MR1-restricted T-cell clone, MC.7.G5, with reported cancer specificity and pan-cancer activity, was cloned and expressed in Jurkat E6.1 TCRab-b2M-CD8+ NF-kB:CFP NFAT:eGFP AP-1:mCherry cells or in human donor T cells. Functional activity of 7G5. TCR-T was demonstrated using cytotoxicity assays and by measuring cytokine release after co-culture with cancer cell lines with or without loading of previously described MR1 ligands. MR1 allele sequencing was undertaken after the amplification of the MR1 gene region by PCR. In vivo studies were undertaken at Labcorp Drug Development (Ann Arbor, MI, USA) or Epistem Ltd (Manchester, UK). Results: The TCR cloned from MC.7.G5 retained MR1-restricted functional cytotoxicity as 7G5. TCR-T. However, activity was not pan-cancer, as initially reported with the clone MC.7.G5. Recognition was restricted to cells expressing a SNV of MR1 (MR1*04) and was not cancer-specific. 7G5. TCR-T and 7G5-like TCR-T cells reacted to both cancer and healthy cells endogenously expressing MR1*04 SNVs, which encode R9H and H17R substitutions. This allelic specificity could be overcome by expressing supraphysiological levels of the wild-type MR1 (MR1*01) in cell lines. Conclusions: Healthy individuals harbor T cells reactive to MR1 variants displaying self-ligands expressed in cancer and benign tissues. Described "cancer-specific" MR1-restricted TCRs need further validation, covering conserved allomorphs of MR1. Ligands require identification to ensure targeting MR1 is restricted to those specific to cancer and not normal tissues. For the wider field of immunology and transplant biology, the observation that MR1*04 may behave as an alloantigen warrants further study. [ABSTRACT FROM AUTHOR]

Influenza B viruses (IBVs) cause substantive morbidity and mortality, and yet immunity towards IBVs remains understudied. CD8+ T-cells provide broadly cross-reactive immunity and alleviate disease severity by recognizing conserved epitopes. Despite the IBV burden, only 18 IBV-specific T-cell epitopes restricted by 5 HLAs have been identified currently. A broader array of conserved IBV T-cell epitopes is needed to develop effective cross-reactive T-cell based IBV vaccines. Here we identify 9 highly conserved IBV CD8+ T-cell epitopes restricted to HLA-B*07:02, HLA-B*08:01 and HLA-B*35:01. Memory IBVspecific tetramer+ CD8+ T-cells are present within blood and tissues. Frequencies of IBV-specific CD8+ T-cells decline with age, but maintain a central memory phenotype. HLA-B*07:02 and HLA-B*08:01-restricted NP30-38 epitopespecific T-cells have distinct T-cell receptor repertoires. We provide structural basis for the IBV HLA-B*07:02-restricted NS1196-206 (11-mer) and HLA-B*07:02- restricted NP30-38 epitope presentation. Our study increases the number of IBV CD8+ T-cell epitopes, and defines IBV-specific CD8+ T-cells at cellular and molecular levels, across tissues and age. [ABSTRACT FROM AUTHOR]

HLA-A*11:01 is one of the most prevalent human leukocyte antigens (HLAs), especially in East Asian and Oceanian populations. It is also highly expressed in Indigenous people who are at high risk of severe influenza disease. As CD8+ T cells can provide broadly cross-reactive immunity to distinct influenza strains and subtypes, including influenza A, B and C viruses, understanding CD8+ T cell immunity to influenza viruses across prominent HLA types is needed to rationally design a universal influenza vaccine and generate protective immunity especially for high-risk populations. As only a handful of HLA-A*11:01-restricted CD8+ T cell epitopes have been described for influenza A viruses (IAVs) and epitopes for influenza B viruses (IBVs) were still unknown, we embarked on an epitope discovery study to define a CD8+ T cell landscape for HLA-A*11:01-expressing Indigenous and non-Indigenous Australian people. Using mass-spectrometry, we identified IAV- and IBV-derived peptides presented by HLA-A*11:01 during infection. 79 IAV and 57 IBV peptides were subsequently screened for immunogenicity in vitro with peripheral blood mononuclear cells from HLA-A*11:01-expressing Indigenous and non-Indigenous Australian donors. CD8+ T cell immunogenicity screening revealed two immunogenic IAV epitopes (A11/PB2320-331 and A11/PB2323-331) and the first HLA-A*11:01-restricted IBV epitopes (A11/M41-49, A11/NS1186-195 and A11/NP511-520). The immunogenic IAV- and IBV-derived peptides were >90% conserved among their respective influenza viruses. Identification of novel immunogenic HLA-A*11:01-restricted CD8+ T cell epitopes has implications for understanding how CD8+ T cell immunity is generated towards IAVs and IBVs. These findings can inform the development of rationally designed, broadly cross-reactive influenza vaccines to ensure protection from severe influenza disease in HLA-A*11:01-expressing individuals. Author summary: Influenza A and influenza B viral infections cause significant morbidity and mortality. Established CD8+ T cell immunity directed at conserved viral regions provides protection against influenza viruses, drives rapid recovery, and leads to less severe clinical outcomes. Killer CD8+ T cells recognising viral peptides presented by HLA class I glycoproteins can provide broad immunity across distinct influenza strains and subtypes. Using immunopeptidomics, we identified novel CD8+ T cell targets for influenza A and influenza B viruses in the context of HLA-A*11:01, an HLA-I allomorph highly prevalent in East Asia and Oceania, including Indigenous populations. Our study provides key insights for T cell-directed vaccines and immunotherapies. [ABSTRACT FROM AUTHOR]

Penicillin refers to a group of beta‐lactam antibiotics that are the first‐line treatment for a range of infections. However, they also possess the ability to form novel antigens, or neoantigens, through haptenation of proteins and can stimulate a range of immune‐mediated adverse reactions—collectively known as drug hypersensitivity reactions (DHRs). IgE‐mediated reactions towards these neoantigens are well studied; however, IgE‐independent reactions are less well understood. These reactions usually manifest in a delayed manner as different forms of cutaneous eruptions or liver injury consistent with priming of an immune response. Ex vivo studies have confirmed the infiltration of T cells into the site of inflammation, and the subsets of T cells involved appear dependent on the nature of the reaction. Here, we review the evidence that has led to our current understanding of these immune‐mediated reactions, discussing the nature of the lesional T cells, the characterization of drug‐responsive T cells isolated from patient blood, and the potential mechanisms by which penicillins enter the antigen processing and presentation pathway to stimulate these deleterious responses. Thus, we highlight the need for a more comprehensive understanding of the underlying genetic and molecular basis of penicillin‐induced DHRs. [ABSTRACT FROM AUTHOR]

Background: Abacavir is associated with hypersensitivity reactions in individuals positive for the HLA‐B*57:01 allele. The drug binds within the peptide binding groove of HLA‐B*57:01 altering peptides displayed on the cell surface. Presentation of these HLA‐abacavir‐peptide complexes to T‐cells is hypothesized to trigger a CD8+ T‐cell response underpinning the hypersensitivity. Thus, the aim of this study was to explore the relationship between the structure of abacavir with HLA‐B*57:01 binding and the CD8+ T‐cell activation. Methods: Seventeen abacavir analogues were synthesized and cytokine secretion from abacavir/abacavir analogue‐responsive CD8+ T‐cell clones was measured using IFN‐γ ELIspot. In silico docking studies were undertaken to assess the predicted binding poses of the abacavir analogues within the HLA‐B*57:01 peptide binding groove. In parallel, the effect of selected abacavir analogues on the repertoire of self‐peptides presented by cellular HLA‐B*57:01 was characterized using mass spectrometry. Results: Abacavir and ten analogues stimulated CD8+ T‐cell IFN‐γ release. Molecular docking of analogues that retained antiviral activity demonstrated a relationship between predicted HLA‐B*57:01 binding orientations and the ability to induce a T‐cell response. Analogues that stimulated T‐cells displayed a perturbation of the natural peptides displayed by HLA‐B*57:01. The antigen‐specific CD8+ T‐cell response was dependent on the enantiomeric form of abacavir at both cyclopropyl and cyclopentyl regions. Conclusion: Alteration of the chemical constitution of abacavir generates analogues that retain a degree of pharmacological activity, but have variable ability to activate T‐cells. Modelling and immunopeptidome analysis delineate how drug HLA‐B*57:01 binding and peptide display by antigen presenting cells relate to the activation of CD8+ T‐cells. [ABSTRACT FROM AUTHOR]