CXCR4 and B-cell chronic lymphocytic leukemia: Moreover, despite the similar CXCR4 levels, the analysis of migration toward CXCL12 of primary CLL cells revealed that those CLL cells subclones expressing ZAP-70 where enriched among cells with migrative capacity, highlighting the role of ZAP-70 in CXCR4-mediated migration also in primary CLL cells.