CCL2 and neoplasm: A large number of studies have confirmed that malignant tumor cells can recruit a variety of inhibitory immune cells into the tumor microenvironment (TME) by secreting cytokines and chemokines (such as CCL2 and CCL3), including tumor-associated macrophages (TAMs), regulatory T cells (Regulatory T cells, Tregs), and bone marrow-derived inhibitory cells (Myeloid-derived suppressor cells, MDSCs)4-7.