This finding could also explain the clinical observation that in M-CLL (a subset in which about 50% of cases express high levels of SLAMF1 or SLAMF7), treatment with the BTK inhibitor ibrutinib results in prolonged lymphocytosis and lower tissue cell death rate in comparison to cases of U-CLL while sensitivity to chemotherapy is generally satisfactory [39]. Here, BTK is linked to B-cell chronic lymphocytic leukemia.