pd-1/pd-l1 inhibitor 1 has been identified to be a potent and selective small molecule inhibitor blocking the interaction of programmed cell death protein 1 (pd-1) with its ligand protein (pd-l1). pd-1/pd-l1 inhibitor 1 was also found to act as an immunomodulator. in preclinical studies, pd-1/pd-l1 inhibitor 1 was able to block pd-1/pd-ll interactions with an ic50 value between 6 and 100 nm, which was measured by a homogenous time-resolved fluorescence (htrf) binding assay. thus, pd-1/pd-l1 inhibitor 1 might potentially be used for the treatment of cancer as well as infectious diseases, such as hepatitis c [1].