We aimed to analyze the expression of PD-1 in resting and stimulated PBMCs in 5 study groups: children with new onset T1D (T1D), their unaffected siblings (SIBS), unaffected, unrelated controls (CTRL) and children with chronic inflammation without autoimmunity (newly diagnosed, untreated Crohn disease—CD), and the same T1D 4–6 months post diagnosis (T1D follow up). Here, PDCD1 is linked to type 1 diabetes mellitus.