Plays a critical role in induction and maintenance of immune tolerance to self (PubMed:11015443, PubMed:28813410, PubMed:28813417, PubMed:31399419). As a ligand for the inhibitory receptor PDCD1/PD-1, modulates the activation threshold of T-cells and limits T-cell effector response (PubMed:11015443, PubMed:28813410, PubMed:28813417, PubMed:36727298). Through a yet unknown activating receptor, may costimulate T-cell subsets that predominantly produce interleukin-10 (IL10) (PubMed:10581077). Can also act as a transcription coactivator: in response to hypoxia, translocates into the nucleus via its interaction with phosphorylated STAT3 and promotes transcription of GSDMC, leading to pyroptosis (PubMed:32929201). {ECO:0000269|PubMed:10581077, ECO:0000269|PubMed:11015443, ECO:0000269|PubMed:28813410, ECO:0000269|PubMed:28813417, ECO:0000269|PubMed:31399419, ECO:0000269|PubMed:32929201, ECO:0000269|PubMed:36727298}. The PDCD1-mediated inhibitory pathway is exploited by tumors to attenuate anti-tumor immunity and escape destruction by the immune system, thereby facilitating tumor survival (PubMed:28813410, PubMed:28813417). The interaction with PDCD1/PD-1 inhibits cytotoxic T lymphocytes (CTLs) effector function (By similarity). The blockage of the PDCD1-mediated pathway results in the reversal of the exhausted T- cell phenotype and the normalization of the anti-tumor response, providing a rationale for cancer immunotherapy (By similarity). {ECO:0000250|UniProtKB:Q9EP73, ECO:0000269|PubMed:28813410, ECO:0000269|PubMed:28813417}. This is the function of ENSG00000120217 (CD274, CD274 molecule).