TEM8/ANTXR1-Specific CAR T cells as a targeted therapy for triple-negative breast cancer

Triple-negative breast cancer (TNBC) is an aggressive disease lacking targeted therapy. In this study, we developed a CAR T cell–based immunotherapeutic strategy to target TEM8, a marker initially defined on endothelial cells in colon tumors that was discovered recently to be upregulated in TNBC. CAR T cells were developed that upon specific recognition of TEM8 secreted immunostimulatory cytokines and killed tumor endothelial cells as well as TEM8-positive TNBC cells. Notably, the TEM8 CAR T cells targeted breast cancer stem–like cells, offsetting the formation of mammospheres relative to nontransduced T cells. Adoptive transfer of TEM8 CAR T cells induced regression of established, localized patient-derived xenograft tumors, as well as lung metastatic TNBC cell line–derived xenograft tumors, by both killing TEM8^þ TNBC tumor cells and targeting the tumor endothelium to block tumor neovascular-ization. Our findings offer a preclinical proof of concept for immunotherapeutic targeting of TEM8 as a strategy to treat TNBC. Significance: These findings offer a preclinical proof of concept for immunotherapeutic targeting of an endothelial antigen that is overexpressed in triple-negative breast cancer and the associated tumor vasculature.