For example, the chemokine CXC ligand 12 (CXCL12; also known as stromal cell-derived factor-1, SDF-1), which is produced by nurse-like cells [12], mediates anti-apoptotic effects in CLL cells via the CXC chemokine receptor type 4 (CXCR4). Here, CXCL12 is linked to B-cell chronic lymphocytic leukemia.