The programmed death-1/programmed death-ligand 1 (PD-1/PD-L1) interaction plays a dominant role in the suppression of T cell responses, especially in a tumor microenvironment, protecting tumor cells from lysis. PD-1/PD-L1 inhibitor 2 is reported to prevent the interaction of PD-L1 with PD-1 with an IC50 value of 18 nM.