Circulating β-cell-specific CD8+ T cells restricted by high risk HLA class I molecules show antigen experience in children with and at risk of type 1 diabetes

In type 1 diabetes (T1D), autoreactive cytotoxic CD8 ⁺ T cells are implicated in the destruction of insulin-producing β cells. The HLA-B*3906 and HLA-A*2402 class I genes confer increased risk and promote early disease onset, suggesting that CD8 ⁺ T cells that recognize peptides presented by these class I molecules on pancreatic β cells play a pivotal role in the autoimmune response. We examined the frequency and phenotype of circulating preproinsulin (PPI)-specific and insulin B (InsB)-specific CD8 ⁺ T cells in HLA-B*3906 ⁺ children newly diagnosed with T1D and in high-risk HLA-A*2402 ⁺ children before the appearance of disease-specific autoantibodies and before diagnosis of T1D. Antigen-specific CD8 ⁺ T cells were detected using human leucocyte antigen (HLA) class I tetramers and flow cytometry was used to assess memory status. In HLA-B*3906 ⁺ children with T1D, we observed an increase in PPI _5–12-specific transitional memory CD8 ⁺ T cells compared to non-diabetic, age- and HLA-matched subjects. Furthermore, PPI _5–12-specific CD8 ⁺ T cells in HLA-B*3906 ⁺ children with T1D showed a significantly more antigen-experienced phenotype compared to polyclonal CD8 ⁺ T cells. In longitudinal samples from high-risk HLA-A*2402 ⁺ children, the percentage of terminal effector cells within the InsB _15–24-specific CD8 ⁺ T cells was increased before diagnosis relative to samples taken before the appearance of autoantibodies. This is the first study, to our knowledge, to report HLA-B*3906-restricted autoreactive CD8 ⁺ T cells in T1D. Collectively, our results provide evidence that β cell-reactive CD8 ⁺ T cells restricted by disease-associated HLA class I molecules display an antigen-experienced phenotype and acquire enhanced effector function during the period leading to clinical diagnosis, implicating these cells in driving disease.