In the case of primary CLL cells that were co-cultured in conditions mimicking the microenvironment, there was an upregulation of miR-21 expression that could be explained in part by the concomitant increase of ZAP-70, while other signals from the microenvironment are probably involved in the upregulation of miR-21. Here, ZAP70 is linked to B-cell chronic lymphocytic leukemia.