PL120131 is a PD-1/PD-L1 inhibitory peptide that disrupts the interaction between PD-1 and PD-L1 by binding to PD-1. This compound can inhibit the apoptosis signaling pathway mediated by PD-1, thereby preventing apoptosis (apoptosis) in Jurkat cells and primary lymphocytes. Additionally, PL120131 supports cytotoxic T lymphocytes (CTL) in exhibiting antitumor activity.