CXCR3 and myeloid sarcoma: Given that NTZ (anti–VLA-4 antibody) is an effective MS drug, which causes peripheral accumulation of possibly brain-homing CXCR3+ B cells (Figure 2C) (8), we next studied how BTK protein levels and phosphorylation coincided with CXCR3 expression in B cells from NTZ-treated patients with MS.