CXCR4 and neuroblastoma: Thus, these data showed that the CXCR7/CXCL12 pair could not stimulate NB chemotaxis, and further suggested CXCR7 as a negative regulator of CXCR4 signaling, as it altered CXCR4/CXCL12-mediated chemotaxis of NB cells in vitro.