CXCL12 and B-cell chronic lymphocytic leukemia: As an example, the CXCR4 chemokine receptor is highly expressed on the surface of CLL cells in the peripheral blood and mediates CLL cells chemotaxis and migration in response to CXCR4 ligand stromal cell-derived factor 1 (SDF-1α, CXCL12) produced by NLC.