Purity >98%. PD-1/PD-L1 inhibitor 1 is a compound that blocks the interaction of programmed cell death protein 1 (PD-1, CD279) with its ligand protein (PD-L1, CD274). In preliminary studies, PD-1/PD-L1 inhibitor 1 blocks this interaction with an IC50 value between 6 and 100 nM, as assessed by a homogenous time-resolved fluorescence binding assay. Antibodies that block PD-1/PD-L1 interaction reduce signaling between these co-inhibitory molecules and have shown promise as checkpoint immunomodulators in cancer clinical trials.