The increased MHC-I expression in the islet microenvironment due to ongoing inflammatory processes [55] makes β-cells more visible to the effector T-cells and possibly explains β-cell vulnerability in T1D patients despite the similar frequency of circulating β-cell reactive CD8+ T-cells in both T1D patients and healthy individuals [2,56]. The gene discussed is CD8A; the disease is type 1 diabetes mellitus.