CCL2 and neoplasm: Researchers have indicated that, in the TME, tumor cells and immune cells can release various chemokines and their receptors, which can guide the homing of MSCs to tumors [58,59], such as SDF-1/ CXCR4, hepatocyte growth factor (HGF)/tyrosine-protein kinase Met (c-Met), vascular endothelial growth factor (VEGF)/vascular endothelial growth factor receptor (VEGFR), and monocyte chemoattractant protein 1 (MCP1)/C-C chemokine receptor type 2 (CCR2) [59].