CXCL12 and B-cell chronic lymphocytic leukemia: To investigate the contribution of CXCL12-CXCR4 signals to VLA-4 dependent BM homing of tri12 versus no tri12 CLL cells, we first compared CXCR4 expression in a cohort of 226 CLL samples expressing or not expressing the VLA-4 rate limiting subunit CD49d, according to the well established prognostic cutoff of 30% positive cells [16, 22], and bearing or not bearing tri12 (Supplemental Table 1).