Accordingly, treatment of CLL cells with ibrutinib inhibited CXCL12/CXCL13-induced in vitro cell adhesion and migration [27, 28] and in CLL patients ibrutinib treatment resulted in a transient lymphocytosis, further underscoring the role of Btk in CLL-cell trafficking and homing [12]. This evidence concerns the gene BTK and B-cell chronic lymphocytic leukemia.