In vitro, human NK-cell PD-1 expression can be increased by cytokine and glucocorticoid stimulation (84, 85), and an increase in NK-cell PD-1 expression has been reported in human and mouse models of cancer, infection, and autoimmune diseases, including T1D (20, 25–37, 85–88). This evidence concerns the gene PDCD1 and type 1 diabetes mellitus.