CD274 and diabetes mellitus: Furthermore, the co-inhibitory PD-1/PD-L1 pathway plays a crucial role in the regulation of autoimmune diabetes in non-obese diabetic NOD mice14, 15, 16, diabetes development in man17, 18, 19, 20 and, in particular may affect the induction and function of autoantigen-specific Foxp3+ CD25+ CD4+ Treg cells20, 21, 22.