Bruton tyrosine kinase (BTK), a key element of B-cell antigen receptor (BCR) signalosome, plays vital roles for CLL homing and retention in lymph nodes by controlling integrin α4β1-mediated adhesion to fibronectin and VCAM-1, as well as chemotaxis signals mediated by CXCL12-, CXCL13-, and CCL19-induced signaling532. Here, BTK is linked to B-cell chronic lymphocytic leukemia.