ZAP70 and B-cell chronic lymphocytic leukemia: In this sense, ZAP-70-positive cells have been also found to be enriched within the fraction of primary CLL cells that migrate towards mesenquimal stromal cells conditioned media [17]; however, CLL cells from patients with high ZAP-70 expression only showed significantly higher migration toward CXCL12 after BCR stimulation [12], [14], [17].