ITGA4 and B-cell chronic lymphocytic leukemia: It is tempting to speculate that the relative reduction of CD49d expression observed in PB CLL cells from ibrutinib-treated CD49d+ CLL cases, also documented in the context of the early released CLL cell subpopulations expressing the CXCR4dim/CD5bright phenotype (Calissano et al., 2011), could be caused by the release from tissue sites of the cells with fewer surface CD49d molecules within the CLL clone, whereas CLL cells with the highest CD49d expression within the clone can be more likely retained in tissue sites.