MHC Recognition Research Articles

2023 MHC Awards and Recognition.

2023 MHC Awards and Recognition.

CD4+ T cell immunity against cutaneous melanoma encompasses multifaceted MHC II-dependent responses.

Whereas CD4+ T cells conventionally mediate antitumor immunity by providing help to CD8+ T cells, recent clinical studies have implied an important role for cytotoxic CD4+ T cells in cancer immunity. Using an orthotopic melanoma model, we provide a detailed account of antitumoral CD4+ T cell responses and their regulation by major histocompatibility complex class II (MHC II) in the skin. Intravital imaging revealed prominent interactions of CD4+ T cells with tumor debris-laden MHC II+ host antigen-presenting cells that accumulated around tumor cell nests, although direct recognition of MHC II+ melanoma cells alone could also promote CD4+ T cell control. CD4+ T cells stably suppressed or eradicated tumors even in the absence of other lymphocytes by using tumor necrosis factor-α and Fas ligand (FasL) but not perforin-mediated cytotoxicity. Interferon-γ was critical for protection, acting both directly on melanoma cells and via induction of nitric oxide synthase in myeloid cells. Our results illustrate multifaceted and context-specific aspects of MHC II-dependent CD4+ T cell immunity against cutaneous melanoma, emphasizing modulation of this axis as a potential avenue for immunotherapies.

Genetically modified and unmodified cellular approaches to enhance graft versus leukemia effect, without increasing graft versus host disease: the use of allogeneic cytokine-induced killer cells.

Although allogeneic hematopoietic cell transplantation (HCT) represents a curative approach for many patients with hematological diseases, post-transplantation relapse occurs in 20-50% of cases, representing the primary cause of treatment failure and mortality. Alloreactive donor T cells are responsible for the graft versus leukemia (GvL) effect, which represents the key mechanism for the long-term curative effect of HCT. However, the downside is represented by graft versus host disease (GvHD), largely contributing to transplant-related mortality (TRM). Multiple factors play a role in regulating the delicate balance between GvL and GvHD, such as the optimization of the donor HLA and KIR match, the type of graft source, and the adaptive use of post-transplant cellular therapy. In addition to the standard donor lymphocyte infusion (DLI), several attempts were made to favor the GvL effect without increasing the GvHD risk. Selected DLI, NK DLI, activated DLI and more sophisticated genetically engineered cells can be employed. In this scenario, cytokine-induced killer (CIK) cells represent a suitable tool to boost GvL while minimizing GvHD. CIK cells are T lymphocytes activated in culture in the presence of monoclonal antibodies against CD3 (OKT3), interferon-gamma (IFN-g), and interleukin-2 (IL-2), characterized by the expression of markers typical of NK cells and T cells (CD3+, CD56+, with a prevalent CD8+ phenotype). CIK cells can mediate cytotoxicity through both MHC and non-MHC restricted recognition, which is the so-called "dual-functional capability" and display minimum alloreactivity. Allogeneic CIK cells showed a favorable rate of response, especially in the setting of minimal residual disease, with a rate of GvHD not exceeding 25%. Finally, the CIK cell platform can be adapted for chimeric antigen receptor (CAR) cell strategy, showing promising results in both preclinical and clinical settings. In this review, we describe the main immunological basis for the development of the GvL and the possible cellular therapy approaches used to boost it, with a particular focus on the use of CIK cells.

Immunoinformatics and MD-simulation data suggest that Omicron spike epitopes are more interacting to IgG via better MHC recognition than Delta variant

BackgroundRecently, in Nov 2021, in South Africa, the SARS CoV-2 variant Omicron was found to be highly infectious and transmissible but with the least fatality. It occupies the nasopharynx-oropharynx and easily spreads. The epidemiological data/reports suggest that several vaccines failed to neutralize Omicron. It has a large number of spike mutations and the RNA/protein vaccines were developed from its predecessors that may justify its escape in most neutralization reactions. Its lower immuno-suppression/cytokine-storming/inflammatory-response effects need exploration. ObjectivesIn the current study, we attempted to delineate the comparative interaction of different variants’ spikes with multiple recognition sites on IgG and HLA-typing of MHC class and I and II. MethodsAll SARS-CoV-2 spike-proteins/human-IgG/MHC-I & II were obtained from the NCBI/ PDB/GISAID database. Initial 3D-structures of the unavailable proteins were constructed by Homology-Modeling (Swissmodel-Expasy) and optimized (PROCHECK). Molecular-docking of spike-IgG/spike- I & MHC-II was performed (HADDOCK2.4/HawkDock) with active-residue screening (CPORT). Antigenicity of epitopes was determined (Vaxigen v2.0-server) and the epitope-model prepared (PEP-FOLD3-server). The binding-affinity/biological-interfaces/visualize were performed (PRODIGY-PyMOL2). We also examined the genesis of feasible transition pathways of functional docked complexes (iMODs) of MHC with different epitopes and antibodies of IgG with different variants. Further, Molecular-Dynamic-Simulation was performed by GROMACS 2023.1 software package. The MD-simulation was run with 100 ns (300 k-heating/1-atm pressure). ResultsSurface-area with interactomes, H-bonding and polar/non-polar bonding were the highest in Omicron spike-IgG interaction. Unlike other variants, both the L and H chains of at least three different recognition sites of IgG interact with the N-terminal and C-terminal RBD of the S1-portion and partially bind to S2. In other cases, binding was observed in either NTD or CTD with a lesser number of bonding-interactomes, especially in Delta spike-Ab interaction. In the case of MHC class-I & II, the highest binding affinity/surface was noticed by Omicron and least by the Delta variant. The MD simulation data of lower RMSD values of the Delta and Omicron variants indicate improved structural stability and less departure from the initial conformation. Better binding to the IgG and MHC molecules explains Omicron’s little ability in immune invasion.

Robust Expansion Of Human Blood-derived γδ T Cells Using A Chemically-defined Medium

Abstract Gamma delta (γδ) T cells have recently emerged as an attractive candidate for cancer immunotherapy treatments due to their inherent cytotoxicity against cancer cells. Moreover, γδ T cells provide a platform for allogeneic cell therapies as they can recognize antigens independent of MHC recognition and do not cause graft-versus-host disease (GVHD). However, the lack of robust and GMP-compatible serum-free ex vivo expansion system for γδ T cells hinders the development of scalable expansion processes for advancing γδ T cell immunotherapies. In the current study, we characterize the expansion of human peripheral blood-derived γδ T cells from various donors using TheraPEAK ®T-VIVO™ Medium, a novel chemically-defined cell expansion medium which is free of undefined and animal-origin components. Peripheral blood mononuclear cells (PBMCs) stimulated with zoledronic acid resulted in more than 1,000 fold expansion of γδ T cells in only 14 days with TheraPEAK ®T-VIVO™ Medium containing 100 IU/mL human recombinant IL-2, without the need for human serum supplementation. Similarly, PBMCs stimulated with agonist antibodies targeting Vδ1 or Vδ2 T cell receptors (TCR) induced robust expansion of Vδ1 or Vδ2 T cells, respectively, in TheraPEAK ®T-VIVO™ Medium. Collectively, these data support the use of TheraPEAK ®T-VIVO™ Medium to advance the development of γδ T cell manufacturing processes.

Computationally profiling peptide:MHC recognition by T-cell receptors and T-cell receptor-mimetic antibodies.

T-cell receptor-mimetic antibodies (TCRms) targeting disease-associated peptides presented by Major Histocompatibility Complexes (pMHCs) are set to become a major new drug modality. However, we lack a general understanding of how TCRms engage pMHC targets, which is crucial for predicting their specificity and safety. Several new structures of TCRm:pMHC complexes have become available in the past year, providing sufficient initial data for a holistic analysis of TCRms as a class of pMHC binding agents. Here, we profile the complete set of TCRm:pMHC complexes against representative TCR:pMHC complexes to quantify the TCR-likeness of their pMHC engagement. We find that intrinsic molecular differences between antibodies and TCRs lead to fundamentally different roles for their heavy/light chains and Complementarity-Determining Region loops during antigen recognition. The idiotypic properties of antibodies may increase the likelihood of TCRms engaging pMHCs with less peptide selectivity than TCRs. However, the pMHC recognition features of some TCRms, including the two TCRms currently in clinical trials, can be remarkably TCR-like. The insights gained from this study will aid in the rational design and optimisation of next-generation TCRms.

Contribution of natural killer cells in innate immunity against colorectal cancer.

Natural killer cells are members of the innate immune system and promote cytotoxic activity against tumor or infected cells independently from MHC recognition. NK cells are modulated by the expression of activator/inhibitory receptors. The ratio of this activator/inhibitory receptors is responsible for the cytotoxic activity of NK cells toward the target cells. Owing to the potent anti-tumor properties of NK cells, they are considered as interesting approach in tumor treatment. Colorectal cancer (CRC) is the second most common cause of death in the world and the incidence is about 2 million new cases per year. Metastatic CRC is accompanied by a poor prognosis with less than three years of overall survival. Chemotherapy and surgery are the most adopted treatments. Besides, targeted therapy and immune checkpoint blockade are novel approach to CRC treatment. In these patients, circulating NK cells are a prognostic marker. The main target of CRC immune cell therapy is to improve the tumor cell's recognition and elimination by immune cells. Adaptive NK cell therapy is the milestone to achieve the purpose. Allogeneic NK cell therapy has been widely investigated within clinical trials. In this review, we focus on the NK related approaches including CAR NK cells, cell-based vaccines, monoclonal antibodies and immunomodulatory drugs against CRC tumoral cells.

Dissecting the cellular components of ex vivo γδ T cell expansions to optimize selection of potent cell therapy donors for neuroblastoma immunotherapy trials

ABSTRACT γδ T lymphocytes represent an emerging class of cellular immunotherapy with preclinical promise to treat cancer, notably neuroblastoma. The innate-like immune cell subset demonstrates inherent cytoxicity toward tumor cells independent of MHC recognition, enabling allogeneic administration of healthy donor-derived γδ T cell therapies. A current limitation is the substantial interindividual γδ T cell expansion variation among leukocyte collections. Overcoming this limitation will enable realization of the full potential of allogeneic γδ T-based cellular therapy. Here, we characterize γδ T cell expansions from healthy adult donors and observe that highly potent natural killer (NK) lymphocytes expand with γδ T cells under zoledronate and IL-2 stimulation. The presence of NK cells correlates with both the expansion potential of γδ T cells and the overall potency of the γδ T cell therapy. However, the potency of the cell therapy in combination with an antibody-based immunotherapeutic, dinutuximab, appears to be independent of γδ T/NK cell content both in vitro and in vivo, which minimizes the implication of interindividual expansion differences toward efficacy. Collectively, these studies highlight the utility of maintaining the NK cell population within expanded γδ T cell therapies and suggest a synergistic action of combined innate cell immunotherapy toward neuroblastoma.

Generation of FVIII-Specific Tregs Expressing a Chimeric Antigen Receptor (CAR) to Suppress Inhibitor Development in Hemophilia a Mice

Introduction: The development of inhibitory antibodies (inhibitors) against coagulation factor VIII (FVIII) is a critical complication in the treatment of hemophilia A, as hemostasis can no longer be re-established by FVIII replacement therapy. Cellular Treg therapy is an attractive candidate for targeted treatment of B and T cells involved in inhibitor formation, as it can suppress both cell types through direct and indirect mechanisms. Here, we generated antigen specific Tregs by engineering and retrovirally transducing a chimeric antigen receptor (CAR) molecule with specificity to human FVIII. Antigen recognition via the single chain antibody variable regions triggers signaling via the CD28 and CD3z co-stimulatory domains, which induces CAR-Treg activation and proliferation independent of MHC recognition. We show that human FVIII specific CAR-Tregs with second generation mouse signaling domains are activated and proliferate in response to antigen recognition, which can cause contact dependent or cytokine dependent suppression of inhibitor producing cells. Methods:A single chain variable fragment specific for human FVIII was cloned (Creative Biolabs, NY) out of an EBV transformed B cell from a hemophilia A patient (BO2C11), which produces IgG4 directed against residues 2125-2332 of huFVIII, corresponding to the carboxy-terminal end of C1 and the complete highly immunogenic C2 domain. This was fused to a 2nd generation CAR construct expressing CD28 and CD3ζ signaling molecules and packaged in a retroviral system (pMys-IRES-eGFP). CD3/CD28 activated polyclonal Tregs were retrovirally transduced to generate FVIII CAR-Tregs. Binding to Fc-FVIII was tested using an A647 conjugated Fc antibody. Upregulation of activation and exhaustion markers, specifically CD69, CD44, LAP, GARP and PD1 was tested 24 h after stimulation with either Fc-FVIII or B domain deleted (BDD) FVIII. Proliferation of CellTrace Violet labeled and FVIII stimulated CAR-Tregs was tested both in vitro and in vivo upon stimulation with BDD FVIII. 1x106 GFP+ FVIII CAR-Tregsorted cells were adoptively transferred into F8 e16−/− hemophilia A mice, and recipients were challenged, starting 1 day later, with weekly IV injections of 1 IU BDD-FVIII for 4 weeks. Plasma was tested for inhibitor formation at 4 and 8 weeks using the Bethesda assay and IgG1 ELISA. Results:FVIII CAR-Tregs bound Fc-FVIII (Eloctate) in a specific manner, with no binding observed to control Fc-FIX (Alprolix). Stimulation for 24 hours with either Fc-FVIII or BDD-FVIII resulted in upregulation of activation and exhaustion markers such as CD69, CD44, GARP and PD-1. No non-specific activation with the unrelated Fc-FIX antigen was observed. CellTrace Violet labeled CAR-Treg and CAR transduced conventional T cells underwent antigen-specific proliferation upon 72 hours of in vitro stimulation with FVIII. In vivo, persistence of adoptively transferred CAR-Tregs was observed only when antigen was concurrently administered. We are currently testing for the suppression of inhibitor development in BALB/c F8 e16−/− hemophilia A mice following adoptive immunotherapy with FVIII CAR-Tregs and continued weekly administrations of BDD-FVIII. Conclusions: Here, we demonstrate that CAR-Tregs directed to human FVIII show antigen-specific binding, activation and proliferation. We found persistence of adoptively transferred FVIII CAR-Tregs in response to antigen stimulation in mice. The suppressive activity of FVIII CAR-Treg on inhibitory antibody formation is now being evaluated in hemophilia A mice that are given factor replacement therapy with FVIII. CAR-Tregs represent an effective way to generate a large pool of antigen-specific cells, with no requirement for MHC restriction. DisclosuresBiswas:Bayer Hemophilia Awards Program: Research Funding. Herzog:Novo Nordisk: Research Funding; Applied Genetic Technologies Corporation: Consultancy; Spark Therapeutics: Patents & Royalties.

2020 MHC Awards and Recognition.

2020 MHC Awards and Recognition.

Abstract PO083: Treatment of CEA-positive solid tumors with anti-CEA chimeric antigen receptor T-cells in CEA transgenic mice

Abstract Chimeric antigen receptors (CARs) combine specificity of antibody to target antigen on cancer cells with the potent cytotoxic activity of T-cells without the need for MHC recognition. Chimeric antigen receptor (CAR) T-cells that were designed to express the single chain variable fragment binding domain of human anti-CEA antibody BW431/26 on mouse splenocytes were able to reduce CEA-expressing pancreatic adenocarcinoma tumor in CEA-transgenic (CEAtg) mice without significant off-target effects (Chmielewski et al., 2012). In this study, an anti-CEA CAR construct derived from murine anti-CEA antibody (T84.66) expressed on human T-cells targeted CEA+ colon carcinoma cells (LS174T/CEA and MC38CEA) with high specificity in vitro. When co-incubated with CEA-positive or CEA-negative mouse cancer cells, anti-CEA CAR expressed on mouse T-cells also specifically targeted CEA-positive cancer cells in vitro. Compared to mock T-cells control, anti-CEA CAR T-cells injected intravenously delayed subcutaneous MC38CEA tumor growth in CEA-transgenic mice (CEAtg). Lymphodepletion via cyclophosphamide injected before anti-CEA T-cells injection further delayed subcutaneous MC38CEA tumor growth and delayed orthotopic CEA+ breast carcinoma (E0771CEA) tumor growth in CEAtg mice. To improve the therapeutic potential of anti-CEA CAR T-cells, IL2 conjugated to humanized anti-CEA antibody (M5A-IL2, ICK) was interperitoneally injected after anti-CEA CAR T-cells into lymphodepleted CEAtg mice. A single injection of ICK after anti-CEA CAR T-cells delayed subcutaneous MC38CEA tumor growth even further. Two injections of ICK after anti-CEA T-cells delayed orthotopic E0771CEA tumor growth. Four injections of ICK after anti-CEA CAR T-cells eradicated subcutaneous MC38CEA tumors. These data show the therapeutic potential of anti-CEA CAR T-cells to target CEA-positive tumors. Citation Format: Seung Cha, Paul Yazaki, Christine Brown, John Shively. Treatment of CEA-positive solid tumors with anti-CEA chimeric antigen receptor T-cells in CEA transgenic mice [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr PO083.

Characterization of Donor Variability for γδ T Cell ex vivo Expansion and Development of an Allogeneic γδ T Cell Immunotherapy.

Gamma delta (γδ) T cells recently emerged as an attractive candidate for cancer immunotherapy treatments due to their inherent cytotoxicity against both hematological and solid tumors. Moreover, γδ T cells provide a platform for the development of allogeneic cell therapies, as they can recognize antigens independent of MHC recognition and without the requirement for a chimeric antigen receptor. However, γδ T cell adoptive cell therapy depends on ex vivo expansion to manufacture sufficient cell product numbers, which remains challenging and limited by inter-donor variability. In the current study, we characterize the differences in expansion of γδ T cells from various donors that expand (EX) and donors that fail to expand, i.e., non-expanders (NE). Further, we demonstrate that IL-21 can be used to increase the expansion potential of NE. In order to reduce the risk of graft vs. host disease (GVHD) induced by an allogeneic T cell product, αβ T cell depletions must be considered due to the potential for HLA mismatch. Typically, αβ T cell depletions are performed at the end of expansion, prior to infusion. We show that γδ T cell cultures can be successfully αβ depleted on day 6 of expansion, providing a better environment for the γδ T cells to expand, and that the αβ T cell population remains below clinically acceptable standards for T cell-depleted allogeneic stem cell products. Finally, we assess the potential for a mixed donor γδ T cell therapy and characterize the effects of cryopreservation on γδ T cells. Collectively, these studies support the development of an improved allogeneic γδ T cell product and suggest the possibility of using mixed donor γδ T cell immunotherapies.

Impact of Cysteine Residues on MHC Binding Predictions and Recognition by Tumor-Reactive T Cells.

The availability of MHC-binding prediction tools has been useful in guiding studies aimed at identifying candidate target Ags to generate reactive T cells and to characterize viral and tumor-reactive T cells. Nevertheless, prediction algorithms appear to function poorly for epitopes containing cysteine (Cys) residues, which can oxidize and form disulfide bonds with other Cys residues under oxidizing conditions, thus potentially interfering with their ability to bind to MHC molecules. Analysis of the results of HLA-A*02:01 class I binding assays carried out in the presence and absence of the reducing agent 2-ME indicated that the predicted affinity for 25% of Cys-containing epitopes was underestimated by a factor of 3 or more. Additional analyses were undertaken to evaluate the responses of human CD8+ tumor-reactive T cells against 10 Cys-containing HLA class I-restricted minimal determinants containing substitutions of α-aminobutyric acid (AABA), a cysteine analogue containing a methyl group in place of the sulfhydryl group present in Cys, for the native Cys residues. Substitutions of AABA for Cys at putative MHC anchor positions often significantly enhanced T cell recognition, whereas substitutions at non-MHC anchor positions were neutral, except for one epitope where this modification abolished T cell recognition. These findings demonstrate the need to evaluate MHC binding and T cell recognition of Cys-containing peptides under conditions that prevent Cys oxidation, and to adjust current prediction binding algorithms for HLA-A*02:01 and potentially additional class I alleles to more accurately rank peptides containing Cys anchor residues.

Treatment of CEA-positive solid tumors with anti-CEA chimeric antigen receptor T-cells in CEA transgenic mice

Abstract Chimeric antigen receptors (CARs) combine specificity of antibody to target antigen on cancer cells with the potent cytotoxic activity of T-cells without the need for MHC recognition. Chimeric antigen receptor (CAR) T-cells that were designed to express the single chain variable fragment binding domain of human anti-CEA antibody BW431/26 on mouse splenocytes were able to reduce CEA-expressing pancreatic adenocarcinoma tumor in CEA-transgenic (CEAtg) mice without significant off-target effects (Chmielewski et al., 2012). In this study, an anti-CEA CAR construct derived from murine anti-CEA antibody (T84.66) expressed on human T-cells targeted CEA+ colon carcinoma cells (LS174T/CEA and MC38CEA) with high specificity in vitro. When co-incubated with CEA-positive or CEA-negative mouse cancer cells, anti-CEA CAR expressed on mouse T-cells specifically targeted CEA-positive cancer cells in vitro. Compared to mock T-cells control, anti-CEA CAR T-cells injected intravenously delayed subcutaneous MC38CEA tumor growth in CEAtg mice. Lymphodepletion via cyclophosphamide injected before anti-CEA T-cells therapy further delayed subcutaneous MC38CEA tumor growth in CEAtg mice. To improve the therapeutic potential of anti-CEA CAR T-cells, IL2 was conjugated to a humanized anti-CEA antibody to form an immunocytokine (ICK). The ICK was injected interperitoneally after anti-CEA CAR T-cells into lymphodepleted CEAtg mice. A single injection of the ICK delayed subcutaneous MC38CEA tumor growth even further. Four injections of ICK after anti-CEA CAR T-cells eradicated subcutaneous MC38CEA tumors. These data show the therapeutic potential of anti-CEA CAR T-cells to target CEA-positive tumors.

Regulatory T cells and co-evolution of allele-specific MHC recognition by the TCR.

What is the evolutionary mechanism for the TCR‐MHC‐conserved interaction? We extend Dembic's model (Dembic Z. In, Scand J Immunol e12806, 2019) of thymus positive selection for high‐avidity anti–self‐MHC Tregs among double (CD4 + CD8+)‐positive (DP) developing thymocytes. This model is based on competition for self‐MHC (+ Pep) complexes presented on cortical epithelium. Such T cells exit as CD4 + CD25+FoxP3 + thymic‐derived Tregs (tTregs). The other positively selected DP T cells are then negatively selected on medulla epithelium removing high‐avidity anti–self‐MHC + Pep as T cells commit to CD4 + or CD8 + lineages. The process is likened to the competitive selection and affinity maturation in Germinal Centre for the somatic hypermutation (SHM) of rearranged immunoglobulin (Ig) variable region (V[D]Js) of centrocytes bearing antigen‐specific B cell receptors (BCR). We now argue that the same direct SHM processes for TCRs occur in post‐antigenic Germinal Centres, but now occurring in peripheral pTregs. This model provides a potential solution to a long‐standing problem previously recognized by Cohn and others (Cohn M, Anderson CC, Dembic Z. In, Scand J Immunol e12790, 2019) of how co‐evolution occurs of species‐specific MHC alleles with the repertoire of their germline TCR V counterparts. We suggest this is not by ‘blind’, slow, and random Darwinian natural selection events, but a rapid structured somatic selection vertical transmission process. The pTregs bearing somatic TCR V mutant genes then, on arrival in reproductive tissues, can donate their TCR V sequences via soma‐to‐germline feedback as discussed in this journal earlier. (Steele EJ, Lindley RA. In, Scand J Immunol e12670, 2018) The high‐avidity tTregs also participate in the same process to maintain a biased, high‐avidity anti–self‐MHC germline V repertoire.

Single T Cell Sequencing Demonstrates the Functional Role of αβ TCR Pairing in Cell Lineage and Antigen Specificity.

Although structural studies of individual T cell receptors (TCRs) have revealed important roles for both the α and β chain in directing MHC and antigen recognition, repertoire-level immunogenomic analyses have historically examined the β chain alone. To determine the amount of useful information about TCR repertoire function encoded within αβ pairings, we analyzed paired TCR sequences from nearly 100,000 unique CD4+ and CD8+ T cells captured using two different high-throughput, single-cell sequencing approaches. Our results demonstrate little overlap in the healthy CD4+ and CD8+ repertoires, with shared TCR sequences possessing significantly shorter CDR3 sequences corresponding to higher generation probabilities. We further utilized tools from information theory and machine learning to show that while α and β chains are only weakly associated with lineage, αβ pairings appear to synergistically drive TCR-MHC interactions. Vαβ gene pairings were found to be the TCR feature most informative of T cell lineage, supporting the existence of germline-encoded paired αβ TCR-MHC interaction motifs. Finally, annotating our TCR pairs using a database of sequences with known antigen specificities, we demonstrate that approximately a third of the T cells possess α and β chains that each recognize different known antigens, suggesting that αβ pairing is critical for the accurate inference of repertoire functionality. Together, these findings provide biological insight into the functional implications of αβ pairing and highlight the utility of single-cell sequencing in immunogenomics.

Salt bridge-forming residues positioned over viral peptides presented by MHC class I impacts T-cell recognition in a binding-dependent manner

The viral peptides presentation by major histocompatibility complex class I (MHC I) molecules play a pivotal role in T-cell recognition and the subsequent virus clearance. This process is delicately adjusted by the variant residues of MHC I, especially the residues in the peptide binding groove (PBG). In a series of MHC I molecules, a salt bridge is formed above the N-terminus of the peptides. However, the potential impact of the salt bridge on peptide binding and T-cell receptor (TCR) recognition of MHC I, as well as the corresponding molecular basis, are still largely unknown. Herein, we determined the structures of HLA-B*4001 and H-2Kd in which two different types of salt bridges (Arg62-Glu163 or Arg66-Glu163) across the PBG were observed. Although the two salt bridges led to different conformation shifts of both the MHC I α helix and the peptides, binding of the peptides with the salt bridge residues was relatively conserved. Furthermore, through a series of in vitro and in vivo investigations, we found that MHC I mutations that disrupt the salt bridge alleviate peptide binding and can weaken the TCR recognition of MHC I-peptide complexes. Our study may provide key references for understanding MHC I-restricted peptide recognition by T-cells.

Specialized Antitumor Functions for Skin γδ T Cells.

A central role for T cells in an immune response was well known, and their functional characterization proceeded for many years in the absence of molecular identification of the TCR. It was known that T cells could only see Ags presented on the surface of another cell and that recognition of MHC

Understanding the drivers of MHC restriction of T cell receptors.

T cell discrimination of self and non-self is predicated on αβ T cell receptor (TCR) co-recognition of peptides presented by MHC molecules. Over the past 20 years, structurally focused investigations into this MHC-restricted response have provided profound insights into T cell function. Simultaneously, two models of TCR recognition have emerged, centred on whether the TCR has, through evolution, acquired an intrinsic germline-encoded capacity for MHC recognition or whether MHC reactivity is conferred by developmental selection of TCRs. Here, we review the structural and functional data that pertain to these theories of TCR recognition, which indicate that it will be necessary to assimilate features of both models to fully account for the molecular drivers of this evolutionarily ancient interaction between the TCR and MHC molecules.

Simultaneous Recognition of Allogeneic MHC and Cognate Autoantigen by Autoreactive T Cells in Transplant Rejection.

The autoimmune condition is a primary obstacle to inducing tolerance in type 1 diabetes patients receiving allogeneic pancreas transplants. It is unknown how autoreactive T cells that recognize self-MHC molecules contribute to MHC-disparate allograft rejection. In this report, we show the presence and accumulation of dual-reactive, that is autoreactive and alloreactive, T cells in C3H islet allografts that were transplanted into autoimmune diabetic NOD mice. Using high-throughput sequencing, we discovered that T cells prevalent in allografts share identical TCRs with autoreactive T cells present in pancreatic islets. T cells expressing TCRs that are enriched in allograft lesions recognized C3H MHC molecules, and five of six cell lines expressing these TCRs were also reactive to NOD islet cells. These results reveal the presence of autoreactive T cells that mediate cross-reactive alloreactivity, and indicate a requirement for regulating such dual-reactive T cells in tissue replacement therapies given to autoimmune individuals.