Abstract 1779: Fourth-generation chimeric antigen receptor T cells targeting mucin 1 against breast cancer

Abstract Breast cancer (BC) is the most common cause of deaths worldwide, which is required effective treatment strategies. The second-generation chimeric antigen receptor (CAR) T cell therapy was approved by U.S. Food and Drug Administration for hematological malignancies, exhibiting impressive efficacy. However, CAR T cell therapy has not been approved in solid tumors and it has intensively been the subjects of research and development. To develop CAR T cell therapy, it is crucial to identify target antigen specifically expressed on tumor cells. Mucin 1 (MUC1) was previously reported to be overexpressed in several tumors. In this study, we examined MUC1 expression in BC tissues and cultured cell lines, and to improve CAR T cell efficiency, we generated fourth-generation anti-MUC1 CAR T cells (αM.CAR4 T cells), containing anti-MUC1 single-chain variable fragment (scFv), three costimulatory molecules (CD28, CD137, CD27) and CD3ζ. High levels of MUC1 expression were observed in the tissues and cell lines. Comparing to second- and third-generations (αM.CAR2 T and αM.CAR3 T cells), the αM.CAR4 T cells showed greater proliferation in the CAR T cell production process. The anti-tumor functions of all CAR T cells were specific to MUC1 expression since their killing activities were illustrated against MUC1-positive but not MUC1-negative BC cells. Interestingly, at low effector to target ratios, the αM.CAR4 T cells exhibited higher tumor cell lysis than those of αM.CAR2 T and αM.CAR3 T cells. Furthermore, after exposure to MUC1-positive BC cells, the αM.CAR4 T cells expressed lower programmed cell death protein 1 (PD-1) level. Taken together, the αM.CAR4 T cells are potential to be further developed for treatments of MUC1-positive BC and other cancers. Citation Format: Kamonlapat Supimon, Thanich Sangsuwannukul, Mutita Junking, Pa-thai Yenchitsomanus. Fourth-generation chimeric antigen receptor T cells targeting mucin 1 against breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1779.