We next studied in the same CLL cases the effects of BCR stimulation on VLA-4 activation by measuring VLA-4 affinity by flow cytometry using a peptide ligand derived from the LDV sequence of the VLA-4–binding region of fibronectin (hereafter LDV) as VLA-4 specific ligand, along with the conformation sensitive anti–CD29 HUTS-21 mAb, to measure the VLA-4 receptor occupancy (RO) in values ranging from 0.0 (no RO) to 1.0 (100% RO) as previously described (Chigaev et al., 2009). This evidence concerns the gene FN1 and B-cell chronic lymphocytic leukemia.