Programed cell death 1 (PD-1) receptor and its ligand PD-L1 are crucial immune checkpoints to downregulate T cell activation, tolerance and immunopathology. Several types of cancer cells were identified to overexpress PD-L1 so as to escape from the PD-1/PD-L1 immunosurveillance mechanism. This peptide, hPDL-1 inhibitor I binds to human PD-1 and inhibits PD-1/PD-L1 binding. It has anchor residues, WDY that show a great impact on the binding of hPD-L1 to hPD-1. Developing inhibitors specifically blocking the PD-1/PD-L1 pathway has become a popular approach to cancer treatment.