Plays a critical role in induction and maintenance of immune tolerance to self (PubMed:11015443, PubMed:28813417, PubMed:28813410). 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:28813417, PubMed:28813410). Through a yet unknown activating receptor, may costimulate T-cell subsets that predominantly produce interleukin-10 (IL10) (PubMed:10581077). 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:28813417, PubMed:28813410). 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). Interacts with PDCD1 (PubMed:11015443, PubMed:18287011, PubMed:26602187). Interacts (via transmembrane domain) with CMTM4 and CMTM6 (PubMed:28813417, PubMed:28813410). Associates with CMTM6 at recycling endosomes, where it is protected from being targeted for lysosomal degradation. Highly expressed in the heart, skeletal muscle, placenta and lung. Weakly expressed in the thymus, spleen, kidney and liver. Expressed on activated T- and B-cells, dendritic cells, keratinocytes and monocytes. Up-regulated on T- and B-cells, dendritic cells, keratinocytes and monocytes after LPS and IFNG activation. Up-regulated in B-cells activated by surface Ig cross-linking. Ubiquitinated; STUB1 likely mediates polyubiquitination of PD-L1/CD274 triggering its degradation. Truncation of the 3'-untranslated (3'-UTR) region of CD274 transcripts leads to elevated expression of CD274 in multiple cancers including T-cell leukemia, diffuse large B-cell lymphoma and stomach adenocarcinoma (PubMed:27281199). Disruption of 3'-UTR region is caused by structural variants that stabilize CD274 transcripts, leading to overexpression (PubMed:27281199). Increased expression in tumors promotes immune evasion and tumor cell growth by allowing malignant cells to escape destruction by the immune system (PubMed:27281199). May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. Belongs to the immunoglobulin superfamily. BTN/MOG family. Truncated N-terminus.