PDCD1 and neoplasm: LAG3 (Lymphocyte-activation gene 3), PDCD1LG2 (Programmed cell death 1 ligand 2), CD274 (cluster of differentiation 274), IDO1 (indoleamine 2,3-dioxygenase 1), PDCD1 (Programmed Cell Death 1), CTLA4 (Cytotoxic T-lymphocyte-associated protein 4), and TIGIT (T cell immunoreceptor with Ig and ITIM domains) were considered important immune checkpoint genes because these genes are activated when T lymphocytes recognize and connect to related proteins on other cells, such as certain tumor cells.