The pathogenesis of T1D is complex and involves many distinct immune populations. Autoreactive CD8 T cells play a major role as the ultimate mediators of beta cell destruction in the pancreas, leading to the loss of glucose homeostasis. However, many aspects of the programming and regulation of CD8 T cells mediating autoimmunity remain enigmatic. Utilizing the clinically relevant non-obese diabetic (NOD) mouse model of T1D, we identified two phenotypically and transcriptionally distinct beta cell-specific CD8 T cell populations in the pancreatic lymph node and pancreas with distinct functional roles in driving T1D in the NOD mouse. We propose to use T1D patient samples to investigate whether similar beta cell-specific CD8 T cell populations play a role in human disease using a multidimensional approach including multi-parameter flow cytometric phenotypic analyses, bulk and single-cell RNA-SEQ (and if enough material available also ATAC-SEQ). These studies will provide crucial insights into the little-understood programming and transcriptional regulation of CD8 T cells driving beta cell destruction and could identify novel targets for the treatment or prevention of T1D.