Activation of Insulin-Reactive CD8 T-Cells for Development of Autoimmune Diabetes

OBJECTIVE: We have previously reported a highly diabetogenic CD8 T-cell clone, G9C8, in the nonobese diabetic (NOD) mouse, specific to low-avidity insulin peptide B15-23, and cells responsive to this antigen are among the earliest islet infiltrates. We aimed to study the selection, activation, and development of the diabetogenic capacity of these insulin-reactive T-cells. RESEARCH DESIGN AND METHODS: We generated a T-cell receptor (TCR) transgenic mouse expressing the cloned TCR Vα18/Vβ6 receptor of the G9C8 insulin-reactive CD8 T-cell clone. The mice were crossed to TCRCα(−/−) mice so that the majority of the T-cells expressed the clonotypic TCR, and the phenotype and function of the cells was investigated. RESULTS: There was good selection of CD8 T-cells with a predominance of CD8 single-positive thymocytes, in spite of thymic insulin expression. Peripheral lymph node T-cells had a naïve phenotype (CD44(lo), CD62L(hi)) and proliferated to insulin B15-23 peptide and to insulin. These cells produced interferon-γ and tumor necrosis factor-α in response to insulin peptide and were cytotoxic to insulin peptide–coated targets. In vivo, the TCR transgenic mice developed insulitis but not spontaneous diabetes. However, the mice developed diabetes on immunization, and the activated transgenic T-cells were able to transfer diabetes to immunodeficient NOD.scid mice. CONCLUSIONS: Autoimmune CD8 T-cells responding to a low-affinity insulin B-chain peptide escape from thymic negative selection and require activation in vivo to cause diabetes.