CCL5 and neoplasm: Tumor cells and other components in the tumor microenvironment (TME) can secrete various soluble factors, such as CC chemokine ligand 2 (CCL2), CCL5, CXC chemokine ligand 12 (CXCL12), transforming growth factor β (TGF-β) and interleukin 6 (IL-6) [27,28,29,30], which can regulate MSC chemotaxis and favor the homing of MSCs to the tumor.