PDCD1 and neoplasm: This process includes immune checkpoints (primarily programmed cell death 1 [PD-1 and programmed cell death 1 ligand 1 [PD-L1), as well as regulatory T cells, original source of suppressor cells and tumor-associated macrophages (TAM; macrophages in primary or secondary tumor tissues) and type 2 innate and adaptive lymphocytes (4).