CXCL13 and B-cell chronic lymphocytic leukemia: The supportive stromal cells produce not only chemoattractants CXCL12 and CXCL13 but also BAFF, APRIL, CD31, and plexin B1 which protect CLL cells from spontaneous and induced apoptosis by activating BCR and NFκB signaling (43, 49, 51, 52).