Project description:The purpose of this study was to identify mRNA transcripts encoding tissue restricted cell surface proteins on human islet tissue that, in turn, might serve as markers for determination of healthy, transplanted and/or diseased islet cell mass. Using oligonucleotide microarrays and clinical grade human islets, we obtained the gene expression profiles of cultured normal islet tissue and compared them to profiles of islets treated with interferon alpha 2 beta, islet-depleted exocrine pancreas, pooled whole pancreas, pooled liver and pooled kidney tissue. Data set filtering and comparisons of gene expression patterns revealed a small set of genes corresponding to transmembrane or membrane associated proteins with limited tissue distributions (present in Islets of Langerhans and, often, central or peripheral nervous system tissues, but absent from exocrine pancreas, liver, kidney and other tissues) with possible utility as novel islet markers. Under the influence of IFN alpha, some of these transcripts show differential expression as confirmed by real time PCR. In addition, we found significant differential expression of two sets of transcripts expressed in islets but with broad tissue distributions, non classical MHC class I b (HLA-G and F) and MHC Class II locus (e.g. HLA-DR alpha and HLA-DQ alpha and beta).
Project description:Alternative splicing (AS) within the β cell has been proposed as one potential pathway that may exacerbate autoimmunity and unveil novel immunogenic epitopes in type 1 diabetes (T1D). We employed a computational strategy to prioritize pathogenic splicing events in human islets treated with IL-1β + IFN-γ as an ex vivo model of T1D and coupled this analysis with a k-mer based approach to predict RNA binding proteins involved in AS events. In total, 969 AS events were identified in cytokine-treated islets, with the majority (44.8%) involving a skipped exon. AS events occurred with high frequency in MHC Class II-related mRNAs, and targeted qPCR validated reduced inclusion of Exon5 in the MHC Class II gene HLA-DMB, while RNA FISH confirmed HLA-DMB splicing in pancreatic sections from human T1D donors. Together, these data suggest that dynamic control of AS plays a role in the β cell response to inflammatory signals during T1D evolution.
Project description:Classical antigen processing/presentation mechanisms lead to the presentation of antigenic peptides derived from endogenous and exogenous sources for MHC class I and class II molecules, respectively. We show here that, unlike other class II, prevalent HLA-DP molecules whose chains encode Gly84 (DP84Gly) constitutively present endogenous peptides.
Project description:Interferon (IFN)-α is the earliest cytokine signature observed in individuals at risk for type 1 diabetes (T1D), but its effect on the repertoire of HLA Class I (HLA-I)-bound peptides presented by pancreatic β-cells is unknown. Using immunopeptidomics, we characterized the peptide/HLA-I presentation in in-vitro resting and IFN-α-exposed β-cells. IFN-α increased HLA-I expression and peptide presentation, including neo-sequences derived from alternative mRNA splicing, post-translational modifications - notably glutathionylation - and protein cis-splicing. This antigenic landscape relied on processing by both the constitutive and immune proteasome. The resting β-cell immunopeptidome was dominated by HLA-A-restricted ligands. However, IFN-α only marginally upregulated HLA-A and largely favored HLA-B, translating into a major increase in HLA-B-restricted peptides and into an increased activation of HLA-B-restricted vs. HLA-A-restricted CD8+ T-cells. A preferential HLA-B hyper-expression was also observed in the islets of T1D vs. non-diabetic donors, and islet-infiltrating CD8+ T-cells from T1D donors were reactive to some HLA-B-restricted granule peptides. Thus, the inflammatory milieu of insulitis may skew the autoimmune response toward epitopes presented by HLA-B, hence recruiting a distinct T-cell repertoire that may be relevant to T1D pathogenesis.
Project description:In the context of HLA-DP-mismatched allogeneic stem cell transplantation, mismatched HLA-DP alleles can provoke profound allo-HLA-DP-specific immune responses from the donor T-cell repertoire leading to graft-versus-leukemia effect and/or graft-versus-host disease in the patient. The magnitude of allo-HLA-DP-specific immune responses has been shown to depend on the specific HLA-DP disparity between donor and patient and the immunogenicity of the mismatched HLA-DP allele(s). HLA-DP peptidome clustering (DPC) was developed to classify the HLA-DP molecules based on similarities and differences in their peptide-binding motifs. To investigate a possible categorization of HLA-DP molecules based on overlap of presented peptides, we identified and compared the peptidomes of the thirteen most frequently expressed HLA-DP molecules. Our categorization based on shared peptides was in line with the DPC classification. We found that the HLA-DP molecules within the previously defined groups DPC-1 or DPC-3 shared the largest numbers of presented peptides. However, the HLA-DP molecules in DPC-2 segregated into two subgroups based on the overlap in presented peptides. Besides overlap in presented peptides within the DPC groups, a substantial number of peptides was also found to be shared between HLA-DP molecules from different DPC groups, especially for groups DPC-1 and -2. The functional relevance of these findings was illustrated by demonstration of cross-reactivity of allo-HLA-DP-reactive T-cell clones not only against HLA-DP molecules within one DPC group, but also across different DPC groups. The promiscuity of peptides presented in various HLA-DP molecules and the cross-reactivity against different HLA-DP molecules demonstrate that these molecules cannot be strictly categorized in immunogenicity groups.
Project description:Assessing the self-peptides presented by susceptible major histocompatibility complex (MHC) molecules is crucial for evaluating the pathogenesis and therapeutics of tissue-specific autoimmune diseases. However, direct examination of such MHC-bound peptides displayed in the target organ remains largely impractical. Here, we demonstrate that the blood leukocytes from non-obese diabetic (NOD) mice presented peptide epitopes to autoreactive CD4 T cells. These peptides were bound to the autoimmune class II MHC molecule, I-Ag7, and originated from insulin B-chain and C-peptide. The presentation required a glucose challenge, which stimulated the release of insulin peptides from pancreatic islets. The circulating leukocytes, especially the B cells, promptly captured and presented these peptides. Although canonical intracellular processing of insulin was involved in the presentation, extracellular binding of catabolized insulin products to I-Ag7 gave rise to a unique pathogenic epitope. Administration of monoclonal antibodies recognizing insulin B-chain abolished the presentation and diminished diabetes incidence. Mass spectrometry analysis of the leukocyte MHC-II peptidomes revealed a series of beta cell derived peptides, with identical sequences to those previously in the islet MHC-II peptidome. Thus, the WBC peptidome echoes that found in islets and serves to identify immunogenic peptides in an otherwise inaccessible tissue.
Project description:A progressive increase in the breadth and specificity of autoantibodies over time, termed epitope spreading, drives pathogenic targeting of an ever-widening repertoire of self-components in many autoimmune diseases. Ostensibly, this progressive inclusion of additional B cell clones into an ongoing autoreactive response can occur through linked recognition, whereby proto-autoreactive B cells recognize distinct antigenic epitopes, which carry shared T cell epitopes. In a murine model displaying epitope spreading resembling that observed in systemic lupus erythematosus, we find that the epitope spreading process is compartmentalized by MHC. Antigen presentation by B cells carrying two MHC haplotypes can bridge the MHC barrier between two compartments of B cells that do not share MHC haplotypes, by communicating with two separate pools of MHC-restricted T cells. This leads to inclusion of distinct and diverse B cell reactivities in germinal centers. Our findings demonstrate a formidable capacity of B cells to drive the autoreactive response.
Project description:Current cancer immunotherapies are assumed to improve infiltration and cytotoxicity of immune cells in the tumor. However, tumor cells have developed a variety of resistance mechanisms to suppress the MHC class I antigen presentation, and thereby impair the cytotoxicity of CD8+ T cells. Here, we identified Mal2 as a key player that mediates the turnover of the antigen-MHC-I complex and reduce the antigen presentation on tumor cells. Mal2 promotes the endocytosis of tumor antigen via direct interaction with the MHC-I complex and endosome-associated Rab5/7. In mouse and human breast tumor models, inhibition of Mal2 profoundly enhanced the cytotoxicity of tumor-infiltrating CD8+ T cells and suppressed breast tumor growth, suggesting that Mal2 is a potential target for breast cancer immunotherapy.
Project description:MHC class I (MHC-I)-mediated tumor antigen processing and presentation (APP) pathway is essential for recruitment and activation of cytotoxic CD8+ T lymphocytes (CD8+ CTLs). However, this pathway is frequently dysregulated in many cancers, thus leading to a failure of immunotherapy. Here, we reported that activation of the tumoral intrinsic Hippo pathway positively correlated with the expression of MHC-I APP genes and the abundance of CD8+ CTLs in mouse tumors and patients. Blocking the Hippo pathway effector YAP/TEAD potently improved antitumor immunity. Mechanistically, the YAP/TEAD complex cooperated with the NuRD complex to repress the NLRC5 transcription. The upregulation of NLRC5 by YAP/TEAD depletion or pharmacological inhibition increased the expression of MHC-I APP genes and enhanced CD8+ CTLmediated killing of cancer cells. Collectively, our results suggest a novel tumorpromoting function of YAP depending on NLRC5 to impair MHC-I APP pathway and provide a rationale for inhibiting YAP activity in immunotherapy for cancer.