Abstract 576: Shark VNAR single domain-based CAR T cells targeting PD-L1 for cancer therapy

Abstract

Abstract Background: Chimeric antigen receptor (CAR)-T therapy shows great potency against hematological malignancies, whereas it is difficult to transfer CAR T into solid tumors due to lack of appropriate antigenic targets and immunosuppressive tumor microenvironment. Checkpoint molecule PD-L1 is widely overexpressed on multiple tumor types, and PD-1/PD-L1 interaction is a primary mediator of immunosuppression in the TME. Here, we generated anti-PD-L1-specific shark single domain VNAR-based CAR T cell strategy and explored its anti-tumor efficacy in xenograft mouse models. Methods: We isolated anti-PD-L1 single domain antibodies from semi-synthetic shark VNAR phage display libraries. The binding of isolated VNARs was validated by ELISA, flow cytometry, and Octet. A peptide library based on human PD-L1 was synthesized to predict the epitope of select VNARs. Anti-tumor efficacy of CAR T cells was determined via cell luciferase-based cell assay as well as xenograft mouse models. Two tumor models, MDA-MB-231 (triple-negative breast cancer) and Hep3B (hepatocellular carcinoma or HCC) were used in the present study. Glypican-3 (GPC3) is a tumor-specific target in the Hep3B model. Results: We identified three anti-PD-L1 phage binders, B2, A11, and F5 from our shark phage libraries. All three binders showed cross-activity to human, mouse, and canine antigens, whereas only B2 functionally blocked the interaction of human PD-1 to PD-L1. Moreover, CAR (B2) T cells specifically lysed both MDA-MB-231 and Hep3B tumor cells by targeting constitutive and inducible expression of PD-L1. Importantly, the combination of anti-GPC3 CAR (hYP7) T cells with CAR (B2) T cells regress Hep3B tumors synergistically in mice. Conclusions: PD-L1-targeted shark VNAR single domain-based CAR T cell therapy is a novel strategy to treat breast cancer and liver cancer. This work provides a rationale for a potential use of anti-PD-L1 CAR T cells as a monotherapy or combination with a tumor-specific therapy in clinical studies for solid tumors. Citation Format: Dan Li, Hejiao English, Jessica Hong, Tianyuzhou Liang, Glenn Merlino, Chi-Ping Day, Mitchell Ho. Shark VNAR single domain-based CAR T cells targeting PD-L1 for cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 576.