The chemokine CXC-motif ligand 12 (CXCL12), formerly named stromal cell-derived factor 1 (SDF1), represents one of the most prominent and first recognized examples of cytokine-mediated interactions of CLL and bystander cells in co-cultures [13,14]. The gene discussed is CXCL12; the disease is B-cell chronic lymphocytic leukemia.