CD80 and cancer: The cell-intrinsic PD-L1 signaling can be modulated by: (1) its post-translational modifications such as acetylation or glycosylation, or by forming cis-heterodimers (i.e., the ligand binding to receptors expressed on the same cell), such as PD-L1/PD-1 or PD-L1/CD80 heterodimers (CD80 being a shared receptor for CTLA4 and CD28); (2) PD-L1 signaling in cancer cells triggered by engagement of PD-1; and (3) PD-L1 binding to co-receptor integrins.