Type 1A Diabetes mellitus (T1D) is a predominantly T cell mediated autoimmune endocrine disease. Both CD4+ and CD8+ T cells reactive to diabetic autoantigens can be identified at low frequency in the peripheral blood of diabetic subjects and their at-risk relatives, but the extent to which these peripheral responses reflect those in the pancreatic draining lymph nodes (PLN) and insulitic lesions is currently unclear, mainly due to the relative inaccessibility of these tissues in living subjects. Answering this question is of central importance to the development of mechanistically relevant biomarker assays for staging disease and monitoring therapeutic efficacy, as well as for identifying appropriate targets for antigen specific immunotherapy. The goal of our project is to isolate and characterize T cells reactive to the major T1D autoantigens (with special focus on insulin, GAD65, IA-2, IGRP, and ZnT8) from the PLN and spleen of nPOD donors. The frequency, phenotype, epitope specificity and clonal diversity of islet-reactive T cells from these tissues will be compared with those present in islets and peripheral blood from the same donors (when available), and in PBMCs from HLA-matched living subjects at various stages of disease.