PDCD1 and type 1 diabetes mellitus: In the pancreas, PD-L1 (Programmed death-ligand 1) – Programmed cell death protein-1 (PD-1) binding between macrophages and CD8+ memory T cells regulate immune homeostasis [215] as well as these cells represent 43% of CD8+ T cells in the insulitis lesions in the T1D [216].