CD80 and cancer: Among these immune cells, T cells, especially CTLs, are exhausted, and the anticancer functions of the immune system are weakened by these negative costimulatory molecules binding with ligands of cancers, including PD-L1 and B7 (CD80/CD86), of which ICIs act as negative regulators, resulting in the reactivation of anticancer functions and the infiltration of immune cells into tumors.