Ibrutinib inhibits BCR- and chemokine-induced adhesion of primary MCL cells. (A) CD19⁺ cells isolated from PBMCs of healthy volunteers or MCL patients were treated with ibrutinib at 100 nM for 10 minutes prior to cell harvest, lysate generation, and western blotting. Primary MCL cells have increased BTK activity compared with B lymphocytes from healthy volunteers, which is further inhibited by ibrutinib in a dose-dependent manner. Tyrosine phosphorylation sites of PLC-γ are also inhibited dose-dependently by drug. (B) Ibrutinib inhibited adhesion of primary MCL cells to fibronectin- or VCAM-1–coated plates co-coated with anti-IgM, CXCL12, or CXCL13 (*P < .05; **P < .01). The n values represent the number of independent experiments performed in triplicate; the averages of these experiments are displayed. (C) Schematic of mechanism of action of ibrutinib. Since BTK is downstream to both BCR and CXCR4 signaling, ibrutinib inhibits chemokine and BCR-mediated cell adhesion/migration of malignant cells thereby disrupting the microenvironment in the tissues, LNs, and BM, which results in the malignant cells egressing and eventually entering the peripheral circulation where they are presumably cleared.