CCL22 and neoplasm: M2 macrophages can recruit Tregs to the tumor microenvironment through release of chemokines (CCL20 and CCL22) to this milieu, and they can also induce the differentiation of myeloid cells into MDSCs probably through release of COX‐2 to the tumor microenvironment.[46] Therefore, the decrease of MDSCs and Treg cells was possibly due to the reduce of M2 cells caused by the engineered M1Exos.