Engineering a High-Affinity PD-1 Peptide for Optimized Immune Cell–Mediated Tumor Therapy

PURPOSE: The purpose of this study was to optimize a peptide (nABP284) that binds to programmed cell death protein 1 (PD-1) by a computer-based protocol in order to increase its affinity. Then, this study aimed to determine the inhibitory effects of this peptide on cancer immune escape by coculturing improving cytokine-induced killer (ICIK) cells with cancer cells. MATERIALS AND METHODS: nABP284 that binds to PD-1 was identified by phage display technology in our previous study. AutoDock and PyMOL were used to optimize the sequence of nABP284 to design a new peptide (nABPD1). Immunofluorescence was used to demonstrate that the peptides bound to PD-1. Surface plasmon resonance was used to measure the binding affinity of the peptides. The blocking effect of the peptides on PD-1 was evaluated by a neutralization experiment with human recombinant programmed death-ligand 1 (PD-L1) protein. The inhibition of activated lymphocytes by cancer cells was simulated by coculturing of human acute T lymphocytic leukemia cells (Jurkat T cells) with human tongue squamous cell carcinoma cells (Cal27 cells). The anticancer activities were determined by coculturing ICIK cells with Cal27 cells in vitro. RESULTS: A high-affinity peptide (nABPD1, K(D)=11.9 nM) for PD-1 was obtained by optimizing the nABP284 peptide (K(D)=11.8 μM). nABPD1 showed better efficacy than nABP284 in terms of increasing the secretion of interkeulin-2 by Jurkat T cells and enhancing the in vitro antitumor activity of ICIK cells. CONCLUSION: nABPD1 possesses higher affinity for PD-1 than nABP284, which significantly enhances its ability to block the PD-1/PD-L1 interaction and to increase ICIK cell-mediated antitumor activity by armoring ICIK cells.