CXCR4 interacts with CXCL12 (CXC motif chemokine 12)/Stromal cell-derived factor-1 (SDF-1), that is a chemokine with a critical role for cells escaping from thymus to bone marrow, leukemia initiating cells and trans-endothelial migration [187, 188]. The gene discussed is CXCL12; the disease is leukemia.