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 Non Obese 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 diabetogenic capacity of these insulin-reactive T cells. Research Design and Methods: We generated a 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 (CD44lo, CD62Lhi) and proliferated to insulin B15-23 peptide and to insulin. These cells produced interferon-γ and TNF-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. Conclusion: 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