The function of CMTM6 (CKLF like MARVEL transmembrane domain containing 6, Ensembl gene identifier ENSG00000091317) is as follows. Master regulator of recycling and plasma membrane expression of PD-L1/CD274, an immune inhibitory ligand critical for immune tolerance to self and antitumor immunity. Associates with both constitutive and IFNG-induced PD-L1/CD274 at recycling endosomes, where it protects PD-L1/CD274 from being targeted for lysosomal degradation, likely by preventing its STUB1-mediated ubiquitination. May stabilize PD-L1/CD274 expression on antigen presenting cells and potentiates inhibitory signaling by PDCD1/CD279, its receptor on T-cells, ultimately triggering T-cell anergy. {ECO:0000269|PubMed:28813410, ECO:0000269|PubMed:28813417}.