CD274 and type 1 diabetes mellitus: Restoring the PD-1/PD-L1 function could represent a valid strategy to treat T1D at different stages, including regulating β cell autoimmunity and preventing T1D in individuals that are genetically at-risk or are autoantibody positive; promoting immune tolerance and preserving residual β cell mass in patients with new onset T1D; and reducing alloreactive responses and favoring the survival of transplanted islets in patients with established T1D disease (66).