CXCR4 and acute myeloid leukemia: Previously, Petit I et al. demonstrated that up-regulation of CXCR4 could serve to increase the sensitivity of cells to lower CXCL12 signals (Petit et al., 2002), and Mandawat et al. found that exposure to CXCL12 caused the lowering of the surface expression of CXCR4 on AML cells (Mandawat et al., 2010), which might provide an explanation for this phenomenon.