Characterisation of islet antigen‐specific CD4+ and CD8+ T cells during the prodrome and after onset of T1D is crucial, in order to understand their role in disease pathogenesis, to relate T‐cell responses to treatment outcomes, to identify subjects potentially suited to immunotherapy and to characterise T‐cell responses to antigen‐specific immunotherapies. This evidence concerns the gene CD8A and type 1 diabetes mellitus.