CXCR4 and acute myeloid leukemia: Although CXCR4 has been shown to regulate leukemia-initiating cells in T cell acute lymphoblastic leukemia (Passaro et al., 2015), the functional role of CXCR4 in AML development has remained elusive (Monaco et al., 2004; Tavor et al., 2004) and has so far not been investigated using genetic deletion of Cxcr4 in AML cells.