Assessment of CD4+T Cell Responses to Glutamic Acid Decarboxylase 65 Using DQ8 Tetramers Reveals a Pathogenic Role of GAD65 121-140 and GAD65 250-266 in T1D Development

Susceptibility to type 1 diabetes (T1D) is strongly associated with MHC class II molecules, particularly HLA-DQ8 (DQ8: DQA1* 03: 01/DQB1* 03: 02). Monitoring T1D-specific T cell responses to DQ8-restricted epitopes may be key to understanding the immunopathology of the disease. In this study, we examined DQ8-restricted T cell responses to glutamic acid decarboxylase 65 (GAD65) using DQ8 tetramers. We demonstrated that GAD65(121-140) and GAD65(250-266) elicited responses from DQ8+ subjects. Circulating CD4+ T cells specific for these epitopes were detected significantly more often in T1D patients than in healthy individuals after in vitro expansion. T cell clones specific for GAD65(121-140) and GAD65(250)-(266) carried a Th1-dominant phenotype, with some of the GAD65(121)-(140)-specific T cell clones producing IL-17. GAD65(250)-(266)-specific CD4+ T cells could also be detected by direct ex vivo staining. Analysis of unmanipulated peripheral blood mononuclear cells (PBMCs) revealed that GAD65250-266-specific T cells could be found in both healthy and diabetic individuals but the frequencies of specific T cells were higher in subjects with type 1 diabetes. Taken together, our results suggest a proinflammatory role for T cells specific for DQ8-restricted GAD65121-140 and GAD65250-266 epitopes and implicate their possible contribution to the progression of T1D.