Identification of the cognate epitopes of autoreactive T cells in Type 1 Diabetes

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ABSTRACT Type 1 Diabetes (T1D), affects approximately 4 million individuals worldwide, including 1.6 million Americans. T1D is caused by progressive destruction of pancreatic  cells, resulting in a significantly diminished capacity to produce insulin. Diabetogenic CD8+ and CD4+ effector T cells that infiltrate pancreatic islets mediate  cell destruction in an antigen-specific manner by recognizing peptide epitopes presented on class I and class II MHC molecules respectively. In contrast, regulatory T cells can suppress diabetogenic T cells, thereby preventing T1D pathogenesis. Recognition of epitopes presented by  cells is critical for the function of these autoreactive T cells. Only a small number of self-epitopes recognized by autoreactive CD8+, CD4+ effector and regulatory T cells in T1D have been uncovered. However, the epitopes recognized by the majority of islet-infiltrating T cells are not known. The knowledge of these epitopes is critical for understanding disease pathogenesis and for developing targeted therapies. Currently, widely applicable and efficient methods for T cell antigen discovery for uncovering autoreactivity are lacking. The overarching goal of this project is to uncover the cognate epitopes of autoreactive T cells in T1D using a novel and generalizable antigen discovery technology developed by our group. In this proposal, we will employ T cell epitope discovery using Signaling and Antigen-presenting Bifunctional Receptors (SABRs) to identify the epitopes recognized by effector and regulatory T cells in a mouse model of T1D, NOD mice. We propose that constructing a library of epitopes derived from genes expressed specifically in pancreatic  cells will lead to identification of novel targets of islet-infiltrating T cells. We will construct epitope libraries from published mass spectrometry and gene expression datasets from NOD mice. We will obtain islet-reactive TCRs by performing single cell TCR sequencing on pancreatic islets of NOD mice. Using  cell derived SABR libraries, we will determine the cognate epitopes of islet-reactive TCRs and validate them in vitro. The epitopes identified by these studies will lead to future studies aiming to understand the breakage of immune tolerance by autoreactive T cells and to develop targeted immunotherapy approaches to combat T1D. This approach will also establish the foundation for antigen discovery for T cells from T1D patient samples in affiliation with Human Islet Research Network. 1