MBTPS1 and B-cell chronic lymphocytic leukemia: Taken together with the experiments examining the effects of the three BCR signaling inhibitors on S1P migration, it can be deduced that the CLL cell–mobilizing effects of these drugs are mediated by different mechanisms; fostamatinib and ibrutinib inhibit signals required for entry and retention of CLL cells into lymph nodes, whereas idelalisib promotes egress by facilitating the upregulation of functional S1PR1.