CD8 T Cell Reactivity to IGRP as an Autoimmunity Marker in Type 1 Diabetes

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DESCRIPTION (provided by applicant): Type 1 diabetes (T1D) is an autoimmune disease characterized by T cell-mediated destruction of the pancreatic islet beta cells. Studies of the nonobese diabetic (NOD) mouse model of the disease have shown that beta cell-cytotoxic CD8+ T cells are essential participants in the beta cell destruction that leads to T1D. CD8+ T cells are also suspected contributors to beta cell elimination in patients. We identified a peptide derived from islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) as the target of a prevalent population of pathogenic CD8+ T cells in NOD mice. In light of the similarities between T1D in NOD mice and humans, we hypothesize that IGRP-reactive CD8+ T cells will be important contributors to beta cell eradication in T1D patients as they are in NOD mice. To begin to translate our findings to patients, we used NOD mice transgenic for the human class I MHC molecule HLA-A*0201 to identify HLA-A*0201-binding IGRP peptides targeted by T cells during the spontaneous development of T1D. Reactivities identified using islet-infiltrating T cells from unimmunized HLA-transgenic mice are both spontaneously occurring and disease-relevant. Thus, these peptides represent excellent candidates for exploration as targets of T cells in human T1D patients. While HLA-A*0201 is a common class I MHC molecule, elucidation of the IGRP peptides recognized in the context of other human class I molecules would allow wider coverage of the population in terms of those that could benefit from the development of peptide- based predictive, diagnostic, and therapeutic strategies. To this end, we have generated three new NOD strains expressing HLA-A*1101, HLA-B*0702, or HLA-Cw*0304. These HLA molecules are representative of three different HLA supertypes, while HLA-A*0201 is representative of yet a fourth. Coverage of the population can be approximately 90% when all four supertypes are targeted. We will isolate islet-infiltrating T cells from the HLA-transgenic mice and determine the IGRP peptides recognized in the context of the different HLA molecules. We will then test the hypothesis that the same peptides will be recognized by T cells from T1D patients. Given the importance of IGRP as a target of the autoimmune response in both standard and HLA-A*0201-transgenic NOD mice, we hypothesize that CD8+ T cell responses to IGRP will also serve as markers for beta cell-specific autoimmune activity in humans. Monitoring of these T cell responses may permit assessment of the immunological impact of intervention therapies and allow earlier detection of autoimmune activity than is currently possible. Relevance in lay language: The proposed work may lead to new tests to identify individuals at risk of developing T1D. Tests may also be developed to monitor destructive T cell activity in patients undergoing treatment, so that doctors will be able to know if the treatments are working.