CCL20 and breast cancer: To determine whether CCL20-modulated PMN-MDSCs played a critical role in promoting the stemness of breast cancer cells, pSIN- or CCL20-modulated PMN-MDSCs sorted from pSIN-/CCL20-overexpressing cell allograft tumors were co-cultured or mix-cultured with breast cancer cells for three days and the percentage of ALDH+ BCSCs was analyzed by flow cytometry.