PDCD1 and type 1 diabetes mellitus: CD8 T cells, most likely islet-specific, are found within islets and the insulitic lesions as well as in the exocrine pancreas of T1D patients (5, 16, 65–69), hence the PD-1/PD-L1-mediated control of CD8 T cell infiltration may play an important role in prevention of T1D.