We cultured CLL cells together with the murine BM-derived cell line M2-10B4, a commonly used model system for tumor cell-marrow interactions [17], Expression of the VLA-4 ligand, VCAM-1, on the surface of M2-10B4 cells was confirmed by flow cytometry (Fig. 8A). This evidence concerns the gene VCAM1 and B-cell chronic lymphocytic leukemia.