Multipotent mesenchymal stromal/stem cells (MSC) have shown potential clinical utility. However, previous assessments of MSC behavior in recipients have relied on visual detection in host tissue following sacrifice, failing to monitor in vivo MSC dispersion in a single animal and limiting the number of variables that can be observed concurrently. In this study, we utilized noninvasive, in vivo bioluminescent imaging to determine conditions under which MSC selectively engraft in sites of inflammation. MSC modified to express firefly luciferase (MSC-ffLuc) were injected into healthy mice or mice bearing inflammatory insults, and MSC localization was followed with bioluminescent imaging. Inflammatory insults investigated included cutaneous needle-stick and surgical incision wounds, as well as xenogeneic and syngeneic tumors. We also compared tumor models in which MSC were intraveneously or intraperitoneally delivered. Our results demonstrate hMSC-ffLuc systemically delivered to non-tumor bearing animals initially reside in the lungs, then egress to the liver and spleen and decrease in signal over time. However, hMSC in wounded mice engraft and remain detectable only in injured sites. Similarly, in syngeneic and xenogeneic breast carcinoma-bearing mice, bioluminescent detection of systemically delivered MSC revealed persistent, specific co-localization with sites of tumor development. This pattern of tropism was also observed in an ovarian tumor model in which MSC were IP injected. In this study we have identified conditions under which MSC tropism and selective engraftment in sites of inflammation can be monitored by bioluminescent imaging over time. Importantly, these consistent findings were independent of tumor type, immunocompetence and route of MSC delivery.

The isolation of mesenchymal stem cells (MSC) from primary tissue is hampered by the limited selectivity of available markers. So far, CD271 is one of the most specific markers for bone marrow (BM)-derived MSC. In search of additional markers, monoclonal antibodies (mAbs) with specificity for immature cells were screened by flow cytometry for their specific reactivity with the rare CD271(+) population. The recognized CD271(+) populations were fractionated by fluorescence-activated cell sorting and the clonogenic capacity of the sorted cells was analyzed for their ability to give rise to CFU-F. The results showed that only the CD271(bright) but not the CD271(dim) population contained CFU-F. Two-color flow cytometry analysis revealed that only the CD271(bright) population was positive for the established MSC markers CD10, CD13, CD73, and CD105. In addition, a variety of mAbs specific for novel and partially unknown antigens selectively recognized the CD271(bright) population but no other BM cells. The new MSC-specific molecules included the platelet-derived growth factor receptor-beta (CD140b), HER-2/erbB2 (CD340), frizzled-9 (CD349), the recently described W8B2 antigen, as well as cell-surface antigens defined by the antibodies W1C3, W3D5, W4A5, W5C4, W5C5, W7C6, 9A3, 58B1, F9-3C2F1, and HEK-3D6. In conclusion, the described markers are suitable for the prospective isolation of highly purified BM-MSC. These MSC may be used as an improved starting population for transplantation in diseases like osteogenesis imperfecta, cartilage repair, and myocardial infarction.

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Resistance to chemotherapy and metastases are the major causes of breast cancer-related mortality. Moreover, cancer stem cells (CSCs) play critical roles in cancer progression and treatment resistance. Previously, it was found that CSC-like cells can be generated by aberrant activation of EMT, thereby making anti-EMT strategies a novel therapeutic option for treatment of aggressive breast cancers. Here, we report that the transcription factor FOXC2 induced in response to multiple EMT signaling pathways as well as elevated in stem cell-enriched factions is a critical determinant of mesenchymal and stem cell properties, in cells induced to undergo EMT and CSC-enriched breast cancer cell lines. More specifically, attenuation of FOXC2 expression using lentiviral short hairpin RNA led to inhibition of the mesenchymal phenotype and associated invasive and stem cell properties, which included reduced mammosphere forming ability and tumor initiation. Whereas, overexpression of FOXC2 was sufficient to induce CSC properties and spontaneous metastasis in transformed human mammary epithelial cells. Furthermore, a FOXC2-induced gene expression signature was enriched in the claudin-low/basal B breast tumor subtype that contains EMT and CSC features. Having identified PDGFR-β to be regulated by FOXC2, we demonstrate that the FDA-approved PDGFR inhibitor, sunitinib, targets FOXC2-expressing tumor cells leading to reduced CSC and metastatic properties. Thus, FOXC2 or its associated gene expression program may provide an effective target for anti-EMT based therapies for the treatment of claudin-low/basal B breast tumors or other EMT/CSC-enriched tumors.

Key Points VCAM-1/VLA-4 triggers reciprocal NF-κB activation in leukemia and stromal cells and mediates cross-talk between leukemia and stromal cells. VCAM-1/VLA-4 and NF-κB signaling plays a pivotal role in the development of leukemia chemoresistance.

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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.