IntroductionNormal and leukemic hematopoietic cells and stem cells reside in the bone marrow in specialized areas ("niches") that provide the structural and physiologic conditions for their growth and survival. 1 Subpopulations of leukemic cells can be sequestered in niches and thereby evade chemotherapy-induced death. 2 We and others have reported that stromal cells protect acute myeloid leukemia (AML) and chronic lymphocytic leukemia cells from the apoptosis induced by chemotherapy. [3][4][5][6] While the mechanisms of stroma-mediated protection are pleiotropic and involve a complex interplay of stroma-produced cytokines, chemokines, and adhesion molecules, the stroma-secreted chemokine stromal-derived factor 1␣ (SDF-1␣) and its cognate receptor CXCR4 have recently emerged as critical mediators of stromal/leukemic cell interactions. 7,8 SDF-1␣ and CXCR4 primarily regulate the migration, homing, and mobilization of hematopoietic cells. 9,10 Binding of SDF-1␣ to CXCR4 causes CXCR4 to be incorporated into lipid rafts 11 and increases its phosphorylation. 12 The latter leads to prolonged activation of the extracellular signaling-regulated kinase (ERK) and phosphoinositol 3-kinase (PI3K) pathways, 13 which are key signaling pathways that promote leukemia cells survival. 14,15 Both surface and intracellular 16 CXCR4 levels were found to be elevated in a subset of AML cases. Further, CXCR4 has been shown to mediate the homing and engraftment of AML cells to the bone marrow of nonobese diabetes (NOD)/severe combined immunodeficiency (SCID) mice. 17,18 Finally, CXCR4 was recently reported to be expressed at higher levels in cases of AML associated with an internal tandem duplication (ITD) type of mutation of the gene that encodes fetal liver tyrosine . 19 This is one of the most frequent mutations in AML, which confers poor response to chemotherapy and only transient response to FLT3 inhibitors. 20,21 Our recent studies, in addition, indicated that CXCR4 expression is associated with poor prognosis in patients with diploid AML regardless of FLT3 mutation status. 22,23 Altogether, these findings suggest that disruption of these interactions by SDF-1␣/CXCR4 antagonists represents a novel strategy for targeting leukemia/bone marrow microenvironment interactions. We have reported that inhibition of CXCR4 by specific synthetic peptides (ie, RCP168) interferes with stromal/ leukemic cell interactions and increases the sensitivity of leukemic cells to chemotherapy. 24 In this study, we used AMD3465 (Anormed and Genzyme, Cambridge, MA), a second-generation smallmolecule reversible inhibitor of SDF-1␣/CXCR4 with a half maximal inhibitory concentration (IC 50 An Inside Blood analysis of this article appears at the front of this issue.The online version of this article contains a data supplement.The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked ''advertisement'' in accordance with 18 USC section 1734. For personal use on...

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Summary The epithelial-to-mesenchymal transition (EMT) is an embryonic process that becomes latent in most normal adult tissues. Recently, we have shown that induction of EMT endows breast epithelial cells with stem cell traits. In this report, we have further characterized the EMT-derived cells and shown that these cells are similar to mesenchymal stem cells (MSCs) with the capacity to differentiate into multiple tissue lineages. For this purpose, we induced EMT by ectopic expression of Twist, Snail or TGF-β in immortalized human mammary epithelial cells (HMECs). We found that the EMT-derived cells and MSCs share many properties including the antigenic profile typical of MSCs, i.e. CD44+, CD24− and CD45−. Conversely, MSCs express EMT-associated genes, such as Twist, Snail and FOXC2. Interestingly, CD140b (PDGFR-β), a marker for naive MSCs, is exclusively expressed in EMT-derived cells and not in their epithelial counterparts. Moreover, functional analyses revealed that EMT-derived cells but not the control cells can differentiate into Alizarin Red S-positive mature osteoblasts, Oil Red O-positive adipocytes and Alcian Blue-positive chondrocytes similar to MSCs. We also observed that EMT-derived cells but not the control cells invade and migrate towards MDA-MB-231 breast cancer cells similar to MSCs. In vivo wound homing assays in nude mice revealed that the EMT-derived cells home to wound sites similar to MSCs. In conclusion, we have demonstrated that the EMT-derived cells are similar to MSCs in gene expression, multi-lineage differentiation, and ability to migrate towards tumor cells and wound sites.