A Bispecific Chimeric-Antigen Receptor T-Cell Factory For Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a highly aggressive subtype of breast cancer with poor clinical prognosis. While treated with chemotherapies, the high incidence of relapse signifies the need for novel, targeted therapies. Immune therapies offer an exciting therapeutic option for TNBC. Our goal is to engineer a chimeric-antigen receptor (CAR) T-cell factory, a CAR T-cell that secretes immune-modulating antibodies, for TNBC. Chimeric-antigen receptor (CAR) T-cell therapies redirect a patient9s T-cells to kill tumor cells by the exogenous expression of a CAR. A CAR is a membrane spanning fusion protein that links the antigen recognition domain of an antibody to the intracellular signaling domains of the T-cell receptor and co-receptor. Solid tumors offer unique challenges for CAR-T therapies. Unlike blood cancers, tumor-associated target proteins are overexpressed between the tumor and healthy tissue resulting in on-target/off-tumor T-cell killing of healthy tissues. Furthermore, immune repression in the tumor microenvironment (TME) limits the activation of CAR-T cells towards killing the tumor. We hypothesize that a bispecific CAR targeting two antigens on TNBC will mitigate on-target/off-tumor T-cell killing and that the secretion of a checkpoint blockade antibody will remove repression in the tumor microenvironment. Following local immune restoration, the CAR-T cells and other cells in the TME will work synergistically to shrink and clear tumors. Our current work evaluates human single-chain variable fragments (scFvs) to serve as CAR-targeting moieties. We are evaluating the efficacy of scFvs to specifically kill target cells in vitro. This work will define lead scFvs used for engineering of our bispecific CAR. Future work will evaluate this therapy in humanized mouse models of TNBC. Citation Format: Emily G. Kuiper, Leo L. Chan, Matthew R. Chang, Quan K. Zhu, Wayne A. Marasco. A bispecific chimeric-antigen receptor T-cell factory for triple-negative breast cancer [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 1531.