CXCL12 and B-cell chronic lymphocytic leukemia: The role macrophages play in CLL was first discovered in 2000 when Burger et al. found that differentiated peripheral mononuclear cells from B-cell CLL patients could protect CLL cells from undergoing spontaneous apoptosis through the action of stromal cell-derived factor-1 (SDF-1; also known as CXCL12) in vitro and the authors coined the term “nurse-like cells” (NLCs) [30].