CXCL12 and B-cell chronic lymphocytic leukemia: Next, we analyzed the contribution of CXCL12-CXCR4 signals to CLL homing by pretreating the mice with the CXCR4 antagonist AMD3100, which competes with CXCL12 for receptor binding [23], or the anti-CXCL12 Spiegelmer® ola-PEG (also known as NOX-A12) [24], before injecting human CLL PBMCs intravenously.