During the progression of colorectal cancer, CCR1 and CCR5 ligands (CCL2, CCL7, CCL8, CCL15, and so on) recruit monocytes and Th1 cells to the TME, where monocytes are precursors of macrophages and DCs and play a role in antigen presentation; Th1 produces IFN-γ and IL-2, and IFN-γ induces M1 polarization of macrophages. The gene discussed is CCL15; the disease is colorectal cancer.