Characterization of disulfide modified diabetogenic neoepitopes

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SUMMARY Polymorphisms within major histocompatibility complex class II (MHC II) genes confer significant risk for developing type 1 diabetes (T1D) in both murine models and humans. MHC class II molecules function to present processed antigens to CD4 T cells, and recent studies have identified a number of different post-translational modifications (PTM) of self-antigens in T1D including peptide fusion, deamidation, citrullination, and disulfide bond formation (S-S). Autoimmune T cell responses to neoantigens formed in peripheral tissues may explain how and why T cell responses are not subject to usual thymic education and tolerance mechanisms. Disulfide bond formation is an important PTM, with implications for structure, function, and stability of numerous proteins. We have shown that an epitope from islet amyloid polypeptide (IAPP), which is co-secreted with insulin by pancreatic beta cells, forms a disulfide bond that activates diabetogenic CD4 T cells when presented by the non- obese diabetic mouse (NOD) MHC class II molecule, IAg7. Our overarching goal is to study the pathogenicity of CD4 T cells responding to disulfide modified self-peptides in mouse and human T1D. The first 20 amino acids of IAPP, termed, is the target antigen for a highly diabetogenic CD4 T cell clone, BDC-5.2.9. KS20-reactive CD4 T cells can be detected in the pancreatic islets of prediabetic and diabetic NOD mice. We showed that the KS20 N-terminal disulfide loop contributes to a large portion of TCR contact, necessary for T cell activation. Increasing evidence indicates that pancreatic beta-cells undergo oxidative and endoplasmic reticulum stress during T1D development that can lead to the generation of reactive oxygen species (ROS), which are capable of inducing post-translational modifications including disulfide bond formation. Thus a potential mechanism exists to form disulfide modified antigens within pancreatic beta-cells that are capable of activating diabetogenic CD4 T cells. Taken together, this leads us to hypothesize that disulfide bonds are a common post-translational modification formed during T1D development that activate islet-antigen specific CD4 T cells. Understanding T cell responses to disulfide modified antigens will enhance our understanding of T1D disease development and identify therapeutic targets to prevent tissue-specific disulfide bond formation and potentially prevent T1D. We propose to determine epitopes for disulfide-reactive CD4 T cells and their necessity for NOD diabetes development and identify T cells responding to disulfide modified self-antigens in patients at-risk and with newly diagnosed type 1 diabetes.