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AIM Human embryonic stem cells (hESCs) represent a novel cell source to treat diseases such as heart failure and for use in drug screening. In this study,we aim to promote efficient generation of cardiomyocytes from hESCs by combining the current optimal techniques of controlled growth of undifferentiated cells and specific induction for cardiac differentiation. We also aim to examine whether these methods are scalable and whether the differentiated cells can be cryopreserved. METHODS & RESULTS hESCs were maintained without conditioned medium or feeders and were sequentially treated with activin A and bone morphogenetic protein-4 in a serum-free medium. This led to differentiation into cell populations containing high percentages of cardiomyocytes. The differentiated cells expressed appropriate cardiomyocyte markers and maintained contractility in culture,and the majority of the cells displayed working chamber (atrial and ventricular) type electrophysiological properties. In addition,the cell growth and differentiation process was adaptable to large culture formats. Moreover,the cardiomyocytes survived following cryopreservation,and viable cardiac grafts were detected after transplantation of cryopreserved cells into rat hearts following myocardial infarctions. CONCLUSION These results demonstrate that cardiomyocytes of high quality can be efficiently generated and cryopreserved using hESCs maintained in serum-free medium,a step forward towards the application of these cells to human clinical use or drug discovery. View Publication

Because lymphoid progenitors can give rise to natural killer (NK) cells,NK ontogeny has been considered to be exclusively lymphoid. Here,we show that rare human CD34(+) hematopoietic progenitors develop into NK cells in vitro in the presence of cytokines (interleukin-7,interleukin-15,stem cell factor,and fms-like tyrosine kinase-3 ligand). Adding hydrocortisone and stromal cells greatly increases the frequency of progenitor cells that give rise to NK cells through the recruitment of myeloid precursors,including common myeloid progenitors and granulocytic-monocytic precursors to the NK-cell lineage. WNT signaling was involved in this effect. Cells at more advanced stages of myeloid differentiation (with increasing expression of CD13 and macrophage colony-stimulating factor receptor [M-CSFR]) could also differentiate into NK cells in the presence of cytokines,stroma,and hydrocortisone. NK cells derived from myeloid precursors (CD56(-)CD117(+)M-CSFR(+)) showed more expression of killer immunoglobulin-like receptors,a fraction of killer immunoglobulin-like receptor-positive-expressing cells that lacked NKG2A,a higher cytotoxicity compared with CD56(-)CD117(+)M-CSFR(-) precursor-derived NK cells and thus resemble the CD56(dim) subset of NK cells. Collectively,these studies show that NK cells can be derived from the myeloid lineage. View Publication

The reprogramming of human somatic cells to induced pluripotent stem (hiPS) cells enables the possibility of generating patient-specific autologous cells for regenerative medicine. A number of human somatic cell types have been reported to generate hiPS cells,including fibroblasts,keratinocytes and peripheral blood cells,with variable reprogramming efficiencies and kinetics. Here,we show that human astrocytes can also be reprogrammed into hiPS (ASThiPS) cells,with similar efficiencies to keratinocytes,which are currently reported to have one of the highest somatic reprogramming efficiencies. ASThiPS lines were indistinguishable from human embryonic stem (ES) cells based on the expression of pluripotent markers and the ability to differentiate into the three embryonic germ layers in vitro by embryoid body generation and in vivo by teratoma formation after injection into immunodeficient mice. Our data demonstrates that a human differentiated neural cell type can be reprogrammed to pluripotency and is consistent with the universality of the somatic reprogramming procedure. View Publication

Cancer-initiating cells (CIC) comprise a rare subpopulation of cells in tumors that are proposed to be responsible for tumor growth. Starting from CICs identified in head and neck squamous cell carcinomas (HNSCC),termed head and neck cancer-initiating cells (HN-CIC),we determined as a candidate stemness-maintaining molecule for HN-CICs the proinflammatory mediator S100A4,which is also known to be an inducer of epithelial-mesenchymal transition. S100A4 knockdown in HN-CICs reduced their self-renewal capability and their stemness and tumorigenic properties,both in vitro and in vivo. Conversely,S100A4 overexpression in HNSCC cells enhanced their stem cell properties. Mechanistic investigations indicated that attenuation of endogenous S100A4 levels in HNSCC cells caused downregulation of Notch2 and PI3K (phosphoinositide 3-kinase)/pAKT along with upregulation of PTEN,consistent with biological findings. Immunohistochemical analysis of HNSCC clinical specimens showed that S100A4 expression was positively correlated with clinical grading,stemness markers,and poorer patient survival. Together,our findings reveal a crucial role for S100A4 signaling pathways in maintaining the stemness properties and tumorigenicity of HN-CICs. Furthermore,our findings suggest that targeting S100A4 signaling may offer a new targeted strategy for HNSCC treatment by eliminating HN-CICs. View Publication

Human embryonic stem (hES) cells show an atypical cell-cycle regulation characterized by a high proliferation rate and a short G1 phase. In fact,a shortened G1 phase might protect ES cells from external signals inducing differentiation,as shown for certain stem cells. It has been suggested that self-renewal and pluripotency are intimately linked to cell-cycle regulation in ES cells,although little is known about the overall importance of the cell-cycle machinery in maintaining ES cell identity. An appealing model to address whether the acquisition of stem cell properties is linked to cell-cycle regulation emerged with the ability to generate induced pluripotent stem (iPS) cells by expression of defined transcription factors. Here,we show that the characteristic cell-cycle signature of hES cells is acquired as an early event in cell reprogramming. We demonstrate that induction of cell proliferation increases reprogramming efficiency,whereas cell-cycle arrest inhibits successful reprogramming. Furthermore,we show that cell-cycle arrest is sufficient to drive hES cells toward irreversible differentiation. Our results establish a link that intertwines the mechanisms of cell-cycle control with the mechanisms underlying the acquisition and maintenance of ES cell identity. View Publication

Various combinations of antibodies directed to cell surface markers have been used to isolate human and rhesus macaque hematopoietic stem cells (HSCs). These protocols result in poor enrichment or require multiple complex steps. Recently,a simple phenotype for HSCs based on cell surface markers from the signaling lymphocyte activation molecule (SLAM) family of receptors has been reported in the mouse. We examined the possibility of using the SLAM markers to facilitate the isolation of highly enriched populations of HSCs in humans and rhesus macaques. We isolated SLAM (CD150(+)CD48(-)) and non-SLAM (not CD150(+)CD48(-)) cells from human umbilical cord blood CD34(+) cells as well as from human and rhesus macaque mobilized peripheral blood CD34(+) cells and compared their ability to form colonies in vitro and reconstitute immune-deficient (nonobese diabetic/severe combined immunodeficiency/interleukin-2 γc receptor(null),NSG) mice. We found that the CD34(+) SLAM population contributed equally or less to colony formation in vitro and to long-term reconstitution in NSG mice compared with the CD34(+) non-SLAM population. Thus,SLAM family markers do not permit the same degree of HSC enrichment in humans and rhesus macaques as in mice. View Publication

The balance of bone morphogenic protein (BMP),transforming growth factor-β (TGFβ)/activin/nodal,and Wnt signals regulates the early lineage segregation of human embryonic stem cells (ESCs). Here we demonstrate that a combination of small-molecule inhibitors of BMP (Dorsomorphin) and TGFβ/activin/nodal (SB431542) signals promotes highly efficient neural induction from both human ESCs and induced pluripotent stem cells (iPSCs). The combination of small molecules had effects on both cell survival and purity of neural differentiation,under conditions of stromal (PA6) cell coculture and feeder-free floating aggregation culture,for all seven pluripotent stem cell lines that we studied,including three ESC and four iPSC lines. Small molecule compounds are stable and cost effective,so our findings provide a promising strategy for controlled production of neurons in regenerative medicine. View Publication

Cell-fate transitions involve the integration of genomic information encoded by regulatory elements,such as enhancers,with the cellular environment. However,identification of genomic sequences that control human embryonic development represents a formidable challenge. Here we show that in human embryonic stem cells (hESCs),unique chromatin signatures identify two distinct classes of genomic elements,both of which are marked by the presence of chromatin regulators p300 and BRG1,monomethylation of histone H3 at lysine 4 (H3K4me1),and low nucleosomal density. In addition,elements of the first class are distinguished by the acetylation of histone H3 at lysine 27 (H3K27ac),overlap with previously characterized hESC enhancers,and are located proximally to genes expressed in hESCs and the epiblast. In contrast,elements of the second class,which we term 'poised enhancers',are distinguished by the absence of H3K27ac,enrichment of histone H3 lysine 27 trimethylation (H3K27me3),and are linked to genes inactive in hESCs and instead are involved in orchestrating early steps in embryogenesis,such as gastrulation,mesoderm formation and neurulation. Consistent with the poised identity,during differentiation of hESCs to neuroepithelium,a neuroectoderm-specific subset of poised enhancers acquires a chromatin signature associated with active enhancers. When assayed in zebrafish embryos,poised enhancers are able to direct cell-type and stage-specific expression characteristic of their proximal developmental gene,even in the absence of sequence conservation in the fish genome. Our data demonstrate that early developmental enhancers are epigenetically pre-marked in hESCs and indicate an unappreciated role of H3K27me3 at distal regulatory elements. Moreover,the wealth of new regulatory sequences identified here provides an invaluable resource for studies and isolation of transient,rare cell populations representing early stages of human embryogenesis. View Publication

Although oral dendritic cells (DCs) were shown to induce cell-mediated immunity,the identity and function of the various oral DC subsets involved in this process is unclear. In this study,we examined the mechanisms used by DCs of the buccal mucosa and of the lining mucosa to elicit immunity. After plasmid DNA immunization,buccally immunized mice generated robust local and systemic CD8(+) T cell responses,whereas lower responses were seen by lining immunization. A delayed Ag presentation was monitored in vivo in both groups; yet,a more efficient presentation was mediated by buccal-derived DCs. Restricting transgene expression to CD11c(+) cells resulted in diminished CD8(+) T cell responses in both oral tissues,suggesting that immune induction is mediated mainly by cross-presentation. We then identified,in addition to the previously characterized Langerhans cells (LCs) and interstitial dendritic cells (iDCs),a third DC subset expressing the CD103(+) molecule,which represents an uncharacterized subset of oral iDCs expressing the langerin receptor (Ln(+)iDCs). Using Langerin-DTR mice,we demonstrated that whereas LCs and Ln(+)iDCs were dispensable for T cell induction in lining-immunized mice,LCs were essential for optimal CD8(+) T cell priming in the buccal mucosa. Buccal LCs,however,failed to directly present Ag to CD8(+) T cells,an activity that was mediated by buccal iDCs and Ln(+)iDCs. Taken together,our findings suggest that the mechanisms engaged by oral DCs to prime T cells vary between oral mucosal tissues,thus emphasizing the complexity of the oral immune network. Furthermore,we found a novel regulatory role for buccal LCs in potentiating CD8(+) T cell responses. View Publication

Maintenance of genomic integrity is essential for adult tissue homeostasis and defects in the DNA-damage response (DDR) machinery are linked to numerous pathologies including cancer. Here,we present evidence that the DDR exerts tumor suppressor activity in gliomas. We show that genes encoding components of the DDR pathway are frequently altered in human gliomas and that loss of elements of the ATM/Chk2/p53 cascade accelerates tumor formation in a glioma mouse model. We demonstrate that Chk2 is required for glioma response to ionizing radiation in vivo and is necessary for DNA-damage checkpoints in the neuronal stem cell compartment. Finally,we observed that the DDR is constitutively activated in a subset of human GBMs,and such activation correlates with regions of hypoxia. View Publication

BACKGROUND: The radiation-induced bystander effect" (RIBE) was shown to occur in a number of experimental systems both in vitro and in vivo as a result of exposure to ionizing radiation (IR). RIBE manifests itself by intercellular communication from irradiated cells to non-irradiated cells which may cause DNA damage and eventual death in these bystander cells. It is known that human stem cells (hSC) are ultimately involved in numerous crucial biological processes such as embryologic development; maintenance of normal homeostasis; aging; and aging-related pathologies such as cancerogenesis and other diseases. However� View Publication

Although microbial infections can alter steady-state hematopoiesis,the mechanisms that drive such changes are not well understood. We addressed a role for IFN-γ signaling in infection-induced bone marrow suppression and anemia in a murine model of human monocytic ehrlichiosis,an emerging tick-borne disease. Within the bone marrow of Ehrlichia muris-infected C57BL/6 mice,we observed a reduction in myeloid progenitor cells,as defined both phenotypically and functionally. Infected mice exhibited a concomitant increase in developing myeloid cells within the bone marrow,an increase in the frequency of circulating monocytes,and an increase in splenic myeloid cells. The infection-induced changes in progenitor cell phenotype were critically dependent on IFN-γ,but not IFN-α,signaling. In mice deficient in the IFN-γ signaling pathway,we observed an increase in myeloid progenitor cells and CDllb(lo)Gr1(lo) promyelocytic cells within the bone marrow,as well as reduced frequencies of mature granulocytes and monocytes. Furthermore,E. muris-infected IFN-γR-deficient mice did not exhibit anemia or an increase in circulating monocytes,and they succumbed to infection. Gene transcription studies revealed that IFN-γR-deficient CDllb(lo)Gr1(lo) promyelocytes from E. muris-infected mice exhibited significantly reduced expression of irf-1 and irf-8,both key transcription factors that regulate the differentiation of granulocytes and monocytes. Finally,using mixed bone marrow chimeric mice,we show that IFN-γ-dependent infection-induced myelopoiesis occurs via the direct effect of the cytokine on developing myeloid cells. We propose that,in addition to its many other known roles,IFN-γ acts to control infection by directly promoting the differentiation of myeloid cells that contribute to host defense. View Publication