Enhancement of the antitumor effect of HER2-directed CAR-T cells through blocking epithelial-mesenchymal transition in tumor cells.

The efficacy of chimeric antigen receptor T (CAR-T) cell therapy in solid tumors is far from satisfactory. In this study, we investigated the influence of epithelial-mesenchymal transition (EMT) on the antitumor effect of CAR-T cells and explored the potential efficacy of combining CAR-T cells with inhibitors targeting EMT. We successfully induced EMT in tumor cells with TGF-β1, and the antitumor effect of HER2-directed CAR-T cells was significantly suppressed by EMT. Upregulation of PD-L1 was observed in tumor cells undergoing EMT, and change in PD-L1 expression during the EMT process was dependent on the MEK/ERK and PI3K/Akt pathways. Inhibition of the TGF-β1 pathway could block the EMT process in tumor cells and restore their susceptibility to HER2-directed CAR-T cells in vitro. In addition, targeting the TGF-β1 pathway significantly enhanced the antitumor effect of HER2-directed CAR-T cells in vivo. Our findings suggest that blocking EMT could potently enhance the antitumor effect of CAR-T cells, which provides a promising approach to improving the therapeutic efficacy of CAR-T cell therapy in solid tumors.