Evidence for in vivo primed and expanded autoreactive T cells as a specific feature of patients with type 1 diabetes

Identifying β cell autoantigen-reactive T cells that are involved in the pathogenesis of type 1 diabetes has been troublesome for many laboratories. Disease-relevant autoreactive T cells should be in vivo Ag experienced. The aim of this study was to test this hypothesis and then use this principle as a strategy for identifying diabetes-relevant autoreactive T cells. In this study, a CSFE dilution assay was used to detect glutamic acid decarboxylase 65 (GAD65)- and insulin-responsive T cells and HLA-0201*-GAD65_114-122 pentamers were used to detect CD8⁺ GAD-responsive T cells in memory CD45RO⁺ and naive CD45RO^- cell populations from patients with type 1 diabetes and healthy control subjects. T cell proliferative history was evaluated by flow cytometry telomere length measurement. CD4⁺ and CD8⁺ T cells specific for GAD65 and insulin were present in patients with type 1 diabetes and control subjects. Within the naive CD45RO^- cells, CD4⁺ and CD8⁺ T cell responses were similar between patients and controls. Within the memory CD45RO⁺ cells, CD4 ⁺ T cell responses against whole GAD65 and insulin and HLA-0201*-GAD65_114-122 pentamer-positive CD8⁺ T cells were found in patients with type 1 diabetes, but not in control subjects (p < 0.05 for all). Responding cells from the CD45RO⁺ T cell population had substantially shorter telomere lengths than responding cells from the CD45RO^- cell population. Diabetes-specific autoreactive T cells in the circulation have uniquely undergone sustained in vivo proliferation and differentiation into memory T cells. Prior selection of these cells is possible and is a way to identify diabetes-relevant target Ags and epitopes.