SDF-1 mediates its effects on chemotaxis through its receptor, CXCR4, which is highly expressed on putative stem and progenitor cells.(7) Another chemokine, CXCL5, is significantly elevated in response to deleted or diminished transforming growth factor β (TGF-β) signaling in tumor epithelial cells. This evidence concerns the gene TGFB1 and neoplasm.