Insulin B-chain fusion peptides as novel targets for pancreatic islet-infiltrating CD4+ T cells 4157

Abstract Description Type 1 diabetes (T1D) is an autoimmune disease wherein insulin-producing beta cells are destroyed by self- reactive T cells, but how loss of tolerance to beta cells occurs is poorly understood. Increasing evidence in mice and humans has shown that post-translational fusion of insulin with beta cell secretory granule proteins produces a class of neo-self-antigens termed Hybrid Insulin Peptides (HIPs). We hypothesize that islet- infiltrating CD4+ T cells react to a new class of HIPs containing sequences from the B-chain of insulin (B-chain HIPs). We carried out antigen discovery using signaling and antigen-presenting bifunctional receptors (SABRs) developed by the Joglekar lab on islet-infiltrating CD4+ T cell isolated from non-obese diabetic (NOD) mice. Here, we show that multiple highly expanded CD4+ T clones specific for unmodified insulin B-chain are also cross-reactive with B-chain HIPs and more specifically, we found that several intra-islet, clonally-expanded CD4+ T cells were reactive to a novel B-chain/Calreticulin HIP. Using an I-Ag7 tetramer loaded with the B- chain/Calreticulin HIP, we detected tetramer-positive CD4+ T cells in islets and pancreatic lymph nodes of NOD mice displaying an antigen-experienced, effector phenotype. Currently, we are using tetramers paired with scRNAseq to determine the TCR repertoire of B-chain HIP-reactive T cells, explore their transcriptional phenotypes within the islets, and investigate their diabetogenic potential. Funding Sources JDRF (Breakthrough T1D) 3-SRA-2023-1354-S-B; Training Grant (Autoimmunity and Immunopathology) 5T32AI089443-15 Topic Categories Basic Autoimmunity (BA)