PDCD1 and neoplasm: However, an Asian study on gastric adenocarcinoma also found no association between immunosuppressive proteins, such as PD-L1, cytotoxic T-lymphocyte-associated protein 4, and indoleamine 2,3-dioxygenase, and infiltration density of immune cells, including CD3(+), CD4(+), CD8(+), and PD-1(+) cells, in the tumor microenvironment [20].