Altered PD-1/PD-L1 interactions are involved in type 1 diabetes pathogenesis: while PD-L1 expression on β-cells can be increased due to upregulation, lower PD-1 expression on CD4+ T lymphocytes increases islet infiltration with autoreactive CD4+ and CD8+ lymphocytes [20,21]. This evidence concerns the gene CD8A and type 1 diabetes mellitus.