TPP-1 is a potent inhibitor of the?PD-1/PD-L1 interaction. TPP-1 binds specifically to PD-L1 with a high affinity (KD=95 nM). TPP-1 inhibits human tumor growth in vivo via reactivating T-cell function.In Vitro: TPP-1 binds to PD-L1 with high affinity and blocks PD-1/PD-L1 interaction.?The?KD?value of PD-L1 with TPP-1 peptide is about 95 nmol/L (around five times less than that with PD-1), The binding site of TPP-1 to PD-L1 is close to the interactive site of PD-1 and PD-L1.TPP-1 (4 μM) reactivates T-cell functions, it induces IFNγ release significantly higher than control and SPP-1, and the TPP-1 group shows similar outcomes for cell proliferation.In Vivo: TPP-1 (subcutaneous injection; 4 mg/kg; every other day eight times; 32 days) inhibits tumor growth (compared with SPP-1 and control). The growth rate in TPP-1-treated mice is 56%. And when administered in the absence of T cells (control group), TPP-1 has no effect on the growth of the H460-luc tumors.