Abstract 1000: PD-L1 binding peptide identified by phage peptide display inhibits PD-1/PD-L1 interaction and activates T cells

Abstract

Abstract Immune suppressive mechanism within the tumor microenvironment inhibits antitumor T cell function, leading to evasion of tumor from immune attack. One of the mechanisms is the up-regulation of programmed death-ligand 1 (PD-L1) expression on tumor cells which binds to programmed cell death protein 1 (PD-1) on activated T cells and inhibits T cell functions. Inhibiting the PD-L1/PD-1 interaction could reverse the tumor microenvironment and enhance the endogenous antitumor immune response. To identify a novel peptide that selectively binds to PD-L1, we screened a phage-displayed peptide library against cells transiently expressing PD-L1 at high levels. After multiple rounds of screening, selected phage clones were sequenced. Of these, two phage clones showed more selective binding to cells expressing PD-L1 compared to a control clone. The peptides displayed on the clones were synthesized for further study and named as PD-L1Pep-1 (9mer) and PD-L1Pep-2 (7mer). Fluorescein-conjugated PD-L1Pep-1 and PD-L1Pep-2 selectively bound to cells highly expressing PD-L1, whereas only negligible binding to cells expressing PD-L1 at low levels. The cell binding of the PD-L1-binding peptides was enhanced after treatment of cells with interferon-γ which is a potent inducer of PD-L1 in many types of cancer cells. FACS analysis showed that the pre-treatment of cells with an anti-PD-L1 antibody competed and reduced the cell binding of the PD-L1-binding peptides, suggesting the antibody and peptides bind to the same epitope on PD-L1. Co-culture experiments of CT26 mouse colon tumor cells with primary T cells isolated from a mouse spleen showed that, similar to the anti-PD-L1 antibody, the PD-L1-binding peptides increased the secretion of Interleukin-2 and interferon-γ by the T cells, indicating that the PD-L1-binding peptides can reactivate the T cells that were suppressed by the co-cultured tumor cells. In-vivo fluorescence imaging of BALB/c mice bearing subcutaneously transplanted CT26 mouse colon tumor cells showed tumor targeting ability of the PD-L1-binding peptides to PD-L1-expressing tumor. These findings suggest that PD-L1Pep-1 and PD-L1Pep-2 can inhibit PD-L1/PD-1 interaction and activate T cells in vivo and hold a potential as a cancer immunotherapeutic. Keywords: Colon tumor, immunotherapy, PD-L1, peptide, phage display Citation Format: Smriti Gurung, Fatima Khan, Soo-Woong Lee, Jaewon Yoon, Byungheon Lee. PD-L1 binding peptide identified by phage peptide display inhibits PD-1/PD-L1 interaction and activates T cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1000.