The use of tMUC1 highly specific chimeric antigen receptor-redirected T cells for the eradication of triple negative breast cancer

Antibody-derived Chimeric Antigen Receptor (CAR) T cells have great success in reduction of liquid form of tumor, but not solid tumor. Our novel antibody TAB 004 can specifically recognize the tumor form of MUC1 (tMUC1) while sparing the normal MUC1 in several subtypes of breast cancers including u003e95% of triple negative breast cancer (TNBC). In vivo delivery of TAB 004 specifically accumulates in the xenograft TNBC tumor only. Therefore, we hypothesize that TNBC can be specifically targeted with TAB 004-derived tMUC1-specific CAR T cells. A panel of 45 human breast cancer cell lines were tested for tMUC1 level, and 11 out of 13 TNBC cell lines showed higher frequency of tMUC1 expression compared to that on normal cells. We engineered a 2 nd generation human CAR using TAB 004 that was coupled to the CD28-CD3zeta. CAR was well expressed on activated human primary CD8 and CD4 T cells. Compared to their mock control, CAR-T cells expressed higher CD25 and CD11c, particularly on CD8 T cells. Those CAR-T cells specifically recognized the tMUC1 antigen and formed tight synapse with tMUC1 high tumor cells in vitro. The susceptibility of TNBC cells to CAR-T cell cytolysis was dramatic while still corresponding to their tMUC1 level. Only the tMUC1-specific CAR-T cells expressed and released large amount of IFN-gamma after antigen recognition on TNBC cells. However, IFN-gamma was not directly involved in the tumor killing by CAR-T cells. The in vivo treatment of TNBC tumor by CAR-T cells is ongoing. Taken together, our TAB 004-originated CAR-T cells are very potent at killing TNBC tumor cells in a tMUC1-highly specific manner, which is very promising to provide a safe, effective and tumor antigen-specific immunotherapeutic intervention.