CCL2 and B-cell chronic lymphocytic leukemia: Chronic lymphocytic leukemia- (CLL-) derived exosomes containing the noncoding Y RNA hY4 can turn monocytes into procarcinogenic cells through Toll-like receptor 7 (TLR7) signaling, and these cells may release tumor-related cytokines such as C-C motif chemokine ligand 2 (CCL2), CCL4, and IL-6 to generate an inflammatory environment and increase the expression of PD-L1 on the surface of tumor cells to induce immune escape [76].