Type 1 diabetes (T1D) is most likely caused by killing of β cells by autoreactive CD8 T cells. Methods to isolate and identify these cells are limited by their low frequency in the peripheral blood. We analyzed CD8 T cells， reactive with diabetes Ags， with T cell libraries and further characterized their phenotype by CyTOF using class I MHC tetramers. In the libraries， the frequency of islet Ag-specific CD45ROIFN-γCD8 T cells was higher in patients with T1D compared with healthy control subjects. Ag-specific cells from the libraries of patients with T1D were reactive with ZnT8， whereas those from healthy control recognized ZnT8 and other Ags. ZnT8-reactive CD8 cells expressed an activation phenotype in T1D patients. We found TCR sequences that were used in multiple library wells from patients with T1D， but these sequences were private and not shared between individuals. These sequences could identify the Ag-specific T cells on a repeated draw， ex vivo in the IFN-γ CD8 T cell subset. We conclude that CD8 T cell libraries can identify Ag-specific T cells in patients with T1D. The T cell clonotypes can be tracked in vivo with identification of the TCR gene sequences.