PTPN2’s importance in T cell tolerance is substantiated by studies demonstrating that the conditional deletion of Ptpn2 in T cells can result in overt autoimmunity in aged C57BL/6 mice21, or accelerate the onset of type 1 diabetes and co-morbidities in autoimmune-prone NOD mice34, whereas its global deletion35 or inducible deletion in hematopoietic cells25 can promote marked systemic inflammation and autoimmunity. Here, PTPN2 is linked to type 1 diabetes mellitus.