Multilineage differentiation from human embryonic stem cell lines

Plasticity of rodent and human hair follicle dermal cells: implications for cell therapy and tissue engineering

The dermal components of the hair follicle exhibit a number of stem cell properties, including regenerative potential, roles in wound healing and the ability to produce a functional dermis. Here we examine the stem cell phenomenon of plasticity, focusing on recent observations of in vitro plasticity of dermal papilla and sheath cells, including previously unpublished data of neuronal-like differentiation. We then briefly address the implications of the stem cell potential of hair follicle dermal cells for the field of tissue engineering.

Temporal and parental-specific expression of imprinted genes in a newly derived Chinese human embryonic stem cell line and embryoid bodies

Although the study of imprinted genes in human development is very important, little is known about their expression and regulation in the early differentiation of human tissues due to lack of an appropriate model. In this study, a Chinese human embryonic stem (hES) cell line, SHhES1, was derived and fully characterized. Expression profiles of human imprinted genes were determined by Affymetrix Oligo micro-array in undifferentiated SHhES1 cells and SHhES1-derived embryoid bodies (EBs) at day 3, 8, 13 and 18. Thirty-two known human imprinted genes were detected in undifferentiated ES cells. Significantly, differential expression was found in nine genes at different stages of EB formation. Expression profile changes were confirmed by quantitative real-time reverse transcriptase-polymerase chain reaction in SHhES1 cells as well as in another independently derived hES cell line, HUES-7. In addition, the monoallelic expressions of four imprinted genes were examined in three different passages of undifferentiated ES cells and EBs of both hES cell lines. The monoallelic expressions of imprinted genes, H19, PEG10, NDNL1 and KCNQ1 were maintained in both undifferentiated hES cells and derived EBs. More importantly, with the availability of maternal peripheral blood lymphocyte sample, we demonstrated that the maternal expression of KCNQ1 and the paternal expression of NDNL1 and PEG10 were maintained in SHhES1 cells. These data provide the first demonstration that the parental-specific expression of imprinted genes is stable in EBs after extensive differentiation, also indicating that in vitro fertilization protocol does not disrupt the parental monoallelic expression of the imprinted genes examined.

Assessing self-renewal and differentiation in human embryonic stem cell lines

Like other cell populations, undifferentiated human embryonic stem cells (hESCs) express a characteristic set of proteins and mRNA that is unique to the cells regardless of culture conditions, number of passages, and methods of propagation. We sought to identify a small set of markers that would serve as a reliable indicator of the balance of undifferentiated and differentiated cells in hESC populations. Markers of undifferentiated cells should be rapidly downregulated as the cells differentiate to form embryoid bodies (EBs), whereas markers that are absent or low during the undifferentiated state but that are induced as hESCs differentiate could be used to assess the presence of differentiated cells in the cultures. In this paper, we describe a list of markers that reliably distinguish undifferentiated and differentiated cells. An initial list of approximately 150 genes was generated by scanning published massively parallel signature sequencing, expressed sequence tag scan, and microarray datasets. From this list, a subset of 109 genes was selected that included 55 candidate markers of undifferentiated cells, 46 markers of hESC derivatives, four germ cell markers, and four trophoblast markers. Expression of these candidate marker genes was analyzed in undifferentiated hESCs and differentiating EB populations in four different lines by immunocytochemistry, reverse transcription-polymer-ase chain reaction (RT-PCR), microarray analysis, and quantitative RT-PCR (qPCR). We show that qPCR, with as few as 12 selected genes, can reliably distinguish differentiated cells from undifferentiated hESC populations.

A simple method for forming embryoid body from mouse embryonic stem cells

We proposed a simple method for forming an embryoid body (EB) from mouse embryonic stem (ES) cells using a polypropylene 1.5-ml conical tube with a screw cap. An ES cell suspension containing 2 x 10(4) cells was incubated in a conical tube. After 5 d of incubation, a single EB of 440 microm average diameter was formed in the conical tube. The formation efficiency of EB, which is the ratio of the number of tubes showing EB formation to the number of tubes seeded with ES cells, was greater than 99% in the conical tube, while it was approximately 60% in a hanging drop culture. The 5-day-old EB formed by the conical tube method had a sufficient differentiation ability. The beating of the cardiac muscle was microscopically observed in the populations derived from the 5-day-old EB.

Characterization of multipotent mesenchymal stem cells from the bone marrow of rhesus macaques

The isolation and characterization of embryonic and adult stem cells from higher-order mammalian species will enhance the understanding of the biology and therapeutic application of stem cells. The aim of this study was to purify rhesus mesenchymal stem cells (MSCs) from adult bone marrow and to characterize functionally their abilities to differentiate along diverse lineages. Adherent cells from adult rhesus macaque bone marrow were characterized for their growth characteristics, lineage differentiation, cell-surface antigen expression, telomere length, chromosome content, and transcription factor gene expression. Rhesus bone marrow MSCs (BMSCs) are very heterogeneous, composed of primarily long, thin cells and some smaller, round cells. The cells are capable of differentiating along osteogenic, chondrogenic, and adipogenic lineages in vitro. The cell morphology and multipotential differentiation capabilities are maintained throughout extended culture. They express CD59, CD90 (Thy-1), CD105, and HLA-1 and were negative for hematopoietic markers such as CD3, CD4, CD8, CD11b, CD13, CD34, and platelet endothelial cell adhesion molecule-1 (CD31). BMSCs were also demonstrated to express the mRNA for important stem cell-related transcription factors such as Oct-4, Sox-2, Rex-1, and Nanog. Rhesus BMSCs have a normal chromosome content, and the shortening of telomeres is minimal during early passages. These data demonstrate that BMSCs isolated from rhesus macaques have a high degree of commonality with MSCs isolated from other species. Therefore, isolation of these cells provides an effective and convenient method for rapid expansion of pluripotent rhesus MSCs.

Nonhuman primate embryonic stem cells as a preclinical model for hematopoietic and vascular repair

Stem cell-based regenerative medicine therapies have been touted recently as a novel therapeutic approach to treat and cure a wide range of diseases. Both adult and embryonic stem (ES) cells can serve as important sources of precursor cells to derive more mature cells potentially utilized for clinical applications. Nonhuman primates have proven useful as a preclinical model, as demonstrated in studies of hematopoietic cell transplantation, gene therapy, and other areas. The derivation of nonhuman primate ES cells now provides an optimal resource to characterize and test ES cell-based therapies prior to trials with human ES cells. This review describes work to define strategies and mechanisms to derive blood and endothelial cells from nonhuman primate ES cells isolated from various species. Preclinical testing that solely relies on studies of putative therapeutic cells derived from mouse ES cells transplanted into other mice, or analyses of human ES cell-derived cells transplanted into immunodeficient or immunosuppressed rodents may not be predictive of efficacy in subsequent human trials. However, future testing using nonhuman primate ES cell-derived therapeutic cells done as an allogeneic transplant may best predict success for subsequent studies using human ES cells. Therefore, additional research on nonhuman primate ES cells, in addition to work on mouse and human ES cells, is greatly needed to facilitate clinical translation of new stem cell treatments.

Differentiation of embryonic stem cells after transplantation into peritoneal cavity of irradiated mice and expression of specific germ cell genes in pluripotent cells

Permanent embryonic stem cell lines (ES cells) are considered as one of the most promising cellular sources for regenerative medicine. ES cells have a high proliferative potency and ability to differentiate into all kinds of somatic and germ cells. However, transplantation of undifferentiated ES cells into adult recipient tissue results in the formation of teratomas. To understand the mechanisms underlying self-renewal and determination of pluripotent cells, we investigated differentiation potencies of undifferentiated ES cells and differentiating embryoid bodies (EB). ES cells and EBs growing on acetate-cellulose membranes were transplanted into the peritoneal cavity of irradiated mice. Behavior and differentiation of transplanted cells were studied within 1, 2, 3, and 6 weeks after transplantation. No differences in the cell composition were found in the teratomas formed by ES cells and differentiating EBs. The pattern of expression of the genes specific for pluripotent and germ cells was studied in all types of experimental teratomas. The expression of oct4, stella, fragilis was detected in the teratomas, but nanog was not expressed. We conclude that pluripotent cells are retained in the experimental teratomas formed after transplantation of ES cells and EBs but the pattern of expression of the studied genes underwent changes.

Designer blood: creating hematopoietic lineages from embryonic stem cells

Embryonic stem (ES) cells exhibit the remarkable capacity to become virtually any differentiated tissue upon appropriate manipulation in culture, a property that has been beneficial for studies of hematopoiesis. Until recently, the majority of this work used murine ES cells for basic research to elucidate fundamental properties of blood-cell development and establish methods to derive specific mature lineages. Now, the advent of human ES cells sets the stage for more applied pursuits to generate transplantable cells for treating blood disorders. Current efforts are directed toward adapting in vitro hematopoietic differentiation methods developed for murine ES cells to human lines, identifying the key interspecies differences in biologic properties of ES cells, and generating ES cell-derived hematopoietic stem cells that are competent to repopulate adult hosts. The ultimate medical goal is to create patient-specific and generic ES cell lines that can be expanded in vitro, genetically altered, and differentiated into cell types that can be used to treat hematopoietic diseases.

Cardiac stem cells and mechanisms of myocardial regeneration

This review discusses current understanding of the role that endogenous and exogenous progenitor cells may have in the treatment of the diseased heart. In the last several years, a major effort has been made in an attempt to identify immature cells capable of differentiating into cell lineages different from the organ of origin to be employed for the regeneration of the damaged heart. Embryonic stem cells (ESCs) and bone marrow-derived cells (BMCs) have been extensively studied and characterized, and dramatic advances have been made in the clinical application of BMCs in heart failure of ischemic and nonischemic origin. However, a controversy exists concerning the ability of BMCs to acquire cardiac cell lineages and reconstitute the myocardium lost after infarction. The recognition that the adult heart possesses a stem cell compartment that can regenerate myocytes and coronary vessels has raised the unique possibility to rebuild dead myocardium after infarction, to repopulate the hypertrophic decompensated heart with new better functioning myocytes and vascular structures, and, perhaps, to reverse ventricular dilation and wall thinning. Cardiac stem cells may become the most important cell for cardiac repair.

Regenerating the heart

Cell-based cardiac repair offers the promise of rebuilding the injured heart from its component parts. Work began with committed cells such as skeletal myoblasts, but recently the field has expanded to explore an array of cell types, including bone marrow cells, endothelial progenitors, mesenchymal stem cells, resident cardiac stem cells, and both mouse and human embryonic stem cells. A related strategy for cardiac repair involves cell mobilization with factors such as cytokines. Translation of cell-based approaches to the clinic has progressed rapidly, and clinical trials using autologous skeletal myoblasts and bone marrow cells are under way. Many challenges remain before the vision of healing an infarct by muscle regeneration can be realized. Future research is likely to focus on improving our ability to guide the differentiation of stem cells, control their survival and proliferation, identify factors that mediate their homing and modulate the heart's innate inflammatory and fibrotic responses.

Epithelial-mesenchymal transition in colonies of rhesus monkey embryonic stem cells: a model for processes involved in gastrulation

Rhesus monkey embryonic stem (rhES) cells were grown on mouse embryonic fibroblast (MEF) feeder layers for up to 10 days to form multilayered colonies. Within this period, stem cell colonies differentiated transiently into complex structures with a disc-like morphology. These complex colonies were characterized by morphology, immunohistochemistry, and marker mRNA expression to identify processes of epithelialization as well as epithelial-mesenchymal transition (EMT) and pattern formation. Typically, differentiated colonies were comprised of an upper and a lower ES cell layer, the former growing on top of the layer of MEF cells whereas the lower ES cell layer spread out underneath the MEF cells. Interestingly, in the central part of the colonies, a roundish pit developed. Here the feeder layer disappeared, and upper layer cells seemed to ingress and migrate through the pit downward to form the lower layer while undergoing a transition from the epithelial to the mesenchymal phenotype, which was indicated by the loss of the marker proteins E-cadherin and ZO-1 in the lower layer. In support of this, we found a concomitant 10-fold upregulation of the gene Snail2, which is a key regulator of the EMT process. Conversion of epiblast to mesoderm was also indicated by the regulated expression of the mesoderm marker Brachyury. An EMT is a characteristic process of vertebrate gastrulation. Thus, these rhES cell colonies may be an interesting model for studies on some basic processes involved in early primate embryogenesis and may open new ways to study the regulation of EMT in vitro.

Regenerative medicine: a radical reappraisal of the spleen

The spleen has long been considered a dispensable organ. Recent research, however, has found that the spleen of adult mice holds a reservoir of stem cells that can rapidly and robustly differentiate into functional cells of diverse lineages. Splenic stem cells express Hox11, a key embryonic transcription factor that regulates organogenesis. The presence of multi-lineage stem cells in the spleen might represent lifelong persistence of cells from a primitive embryonic region called the aorta-gonad-mesonephros. By bringing together findings from diverse disciplines, we propose that the adult spleen is an important source of multi-lineage stem cells for future cellular therapies for diabetes and other diseases.

Genetic regulation of stem cell origins in the mouse embryo

'Stem cell' has practically become a household term, but what is a stem cell and where does it come from? Insight into these questions has come from the early mouse embryo, or blastocyst, from which three kinds of stem cells have been derived: embryonic stem (ES) cells, trophoblast stem (TS) cells, and extraembryonic endoderm (XEN) cells. These stem cells appear to derive from three distinct tissue lineages within the blastocyst: the epiblast, the trophectoderm, and the extraembryonic endoderm. Understanding how these lineages arise during development will illuminate efforts to understand the establishment and maintenance of the stem cell state and the mechanisms that restrict stem cell potency. Genetic analysis has enabled the identification of several genes important for lineage decisions in the mouse blastocyst. Among these, Oct4, Nanog, Cdx2, and Gata6 encode transcription factors required for the three lineages of the blastocyst and for the maintenance their respective stem cell types. Interestingly, genetic manipulation of several of these factors can cause lineage switching among these stem cells, suggesting that knowledge of key lineage-determining genes could help control differentiation of stem cells more generally. Pluripotent stem cells have also been isolated from the human blastocyst, but the relationship between these cells and stem cells of the mouse blastocyst remains to be explored. This review describes the genetic regulation of lineage allocation during blastocyst formation and discusses similarities and differences between mouse and human ES cells.

Generation of skeletal muscle from transplanted embryonic stem cells in dystrophic mice

Embryonic stem (ES) cells have great therapeutic potential because of their capacity to proliferate extensively and to form any fully differentiated cell of the body, including skeletal muscle cells. Successful generation of skeletal muscle in vivo, however, requires selective induction of the skeletal muscle lineage in cultures of ES cells and following transplantation, integration of appropriately differentiated skeletal muscle cells with recipient muscle. Duchenne muscular dystrophy (DMD), a severe progressive muscle wasting disease due to a mutation in the dystrophin gene and the mdx mouse, an animal model for DMD, are characterized by the absence of the muscle membrane associated protein, dystrophin. Here, we show that co-culturing mouse ES cells with a preparation from mouse muscle enriched for myogenic stem and precursor cells, followed by injection into mdx mice, results occasionally in the formation of normal, vascularized skeletal muscle derived from the transplanted ES cells. Study of this phenomenon should provide valuable insights into skeletal muscle development in vivo from transplanted ES cells.

[Human embryonic stem cells: practical problems and scientific potentialities]

Human embryonic stem cells (hESCs) are derived from pre-implantation embryos given to research with the informed consent of the parents. These cells cannot give rise to a human being: they are not totipotent. They have an unlimited self-renewal capacity and they can generate the three embryonic germ layers, their respective derivatives and the extra-embryonic tissues: they are pluripotent. These cells represent an outstanding material for understanding functional genomics of not yet characterized human genes. They will be an important tool for pharmaceutical and clinical research.

Homologous Feeder Cells Support Undifferentiated Growth and Pluripotency in Monkey Embryonic Stem Cells

In the present study, five homologous feeder cell lines were developed for the culture and maintenance of rhesus monkey embryonic stem cells (rESCs). Monkey ear skin fibroblasts (MESFs), monkey oviductal fibroblasts (MOFs), monkey follicular granulosa fibroblast-like (MFG) cells, monkey follicular granulosa epithelium-like (MFGE) cells, and clonally derived fibroblasts from MESF (CMESFs) were established and compared with the ability of mouse embryonic fibroblasts (MEFs) to support rESC growth. MESF, MOF, MFG, and CMESF cells, but not MFGE cells, were as good as or better than MEFs in supporting undifferentiated growth while maintaining the differentiation potential of the rESCs. In an effort to understand the unique properties of supportive feeder cells, expression levels for a number of candidate genes were examined. MOF, MESF, and MEF cells highly expressed leukemia inhibitory factor, ciliary neurotrophic factor, basic fibroblast growth factor, stem cell factor, transforming growth factor beta1, bone morphogenetic protein 4, and WNT3A, whereas WNT2, WNT4, and WNT5A were downregulated, compared with MFGE cells. Additionally, all monkey feeder cell lines expressed Dkk1 and LRP6, antagonists of the WNT signaling pathway, but not WNT1, WNT8B, or Dkk2. rESCs grown on homologous feeders maintained normal karyotypes, displayed the characteristics of ESCs, including morphology, alkaline phosphatase, Oct4, the cell surface markers stage-specific embryonic antigen (SSEA)-3, SSEA-4, tumor-related antigen (TRA)-1-60, and TRA-1-81, and formed cystic embryoid bodies in vitro that included differentiated cells representing the three major germ layers. These results indicate that the four homologous feeder cell lines can be used to support the undifferentiated growth and maintenance of pluripotency in rESCs.

An autogeneic feeder cell system that efficiently supports growth of undifferentiated human embryonic stem cells

Human embryonic stem cells (hESCs) have great potential as a source of cells for therapeutic uses, but their culture requires the support of mouse or human cells, either directly as a feeder cell layer or indirectly as a source of conditioned medium in feeder-free culture systems. Unfortunately, the risks of cross-transfer of pathogens from xenogeneic or allogeneic feeders or cell by-products limit their medical applications. In addition, not all human feeders support the growth of hESCs equally well, and ethical concerns have been raised regarding the derivation of feeder cells from aborted human fetuses. We report here the culture of hESCs on a novel feeder cell system, comprising fibroblast-like cells derived from the spontaneous differentiation of hESCs. Isogenicity of the hESCs and hESC-derived fibroblasts was confirmed by micro satellite analysis. The nature of the hESC-derived fibroblasts was identified by the expression of specific markers. This feeder system permits continuous growth of undifferentiated and pluripotent hESCs, as demonstrated by the expression of specific hESC markers, by the formation of teratomas after injection of hESCs into severely combined immunodeficient mice, and by in vitro differentiation of hESCs into differentiated cells of ectodermal, endodermal, and mesodermal origin. Feeder cells derived from hESCs offers a potentially more secure autogeneic and genotypically homogenous system for the growth of undifferentiated hESCs.

Stem cells

Stem cells derived from adult and embryonic sources have great therapeutic potential, but much research is still needed before their clinical use becomes commonplace. There is debate about whether adult stem cells can be used instead of those derived from embryos. Rationalisation is needed but can be exercised only once the various cells have been carefully compared and contrasted under appropriate experimental conditions. Some characteristics that might help resolve the issue of cell source can already be applied to the debate. Accessibility is important; some adult cells, such as neural stem cells, are difficult to obtain, at least from living donors. Other factors include the frequency and abundance of adult stem cells and their numbers and potency, which might decline with age or be affected by disease. For embryonic stem cells, ethical concerns have been raised, and the proposed practice of therapeutic cloning tends to be misrepresented in the lay media. For both adult and embryonic stem cells, stability, potential to transmit harmful pathogens or genetic mutations, and risk of forming unwanted tissues or even teratocarcinomas have yet to be fully assessed.

Genetic basis of human testicular germ cell cancer: insights from the fruitfly and mouse

The prevalence of tumours of the germ line is increasing in the male population. This complex disease has a complex aetiology. We examine the contribution of genetic mutations to the development of germ line tumours in this review. In particular, we concentrate on fly and mouse experimental systems in order to demonstrate that mutations in some conserved genes cause pathologies typical of certain human germ cell tumours, whereas other mutations elicit phenotypes that are unique to the experimental model. Despite these experimental systems being imperfect, we show that they are useful models of human testicular germ cell tumourigenesis.

Embryonic stem cells: differentiation into cardiomyocytes and potential for heart repair and regeneration

Many forms of heart disease are associated with the loss of cardiomyocytes both via apoptosis or necrosis, and despite the recent identification of resident cardiac stem cells, the native capacity for renewal and repair is inadequate. Cell transplantation strategies have emerged as a potential therapeutic approach for repairing injured myocardium. Many different cell types including embryonic stem cells have been transplanted in myocardial infarction (MI) models with resulting improvement in myocardial function. Here, we review the current state of knowledge with regard to the potential of embryonic stem (ES) cells to differentiate into cardiomyocytes in the embryonic stem cell derived-embryoid body (EB) in vitro system as well as for myocardial regeneration following myocardial infarction.

Whether modern cell technologies can break down biological limitations of tissue-specific regeneration of the myocardium

The paper reviews modern concepts of physiological and reparative regeneration of the myocardium as a highly specific and highly differentiated tissue system. Special attention was given to evaluation of the proliferative potential of cardiomyocytes, in particular, to the existence of a population of resident cardiac stem cells in the myocardium. Modern approaches to replenishment of massive cardiomyocyte loss via transplantation and transdifferentiation of adult and embryonic stem cells are discussed and the possibilities of using cell technologies for induction of tissue-specific regeneration of the myocardium are analyzed.

Embryonic stem cell differentiation: emergence of a new era in biology and medicine

The discovery of mouse embryonic stem (ES) cells >20 years ago represented a major advance in biology and experimental medicine, as it enabled the routine manipulation of the mouse genome. Along with the capacity to induce genetic modifications, ES cells provided the basis for establishing an in vitro model of early mammalian development and represented a putative new source of differentiated cell types for cell replacement therapy. While ES cells have been used extensively for creating mouse mutants for more than a decade, their application as a model for developmental biology has been limited and their use in cell replacement therapy remains a goal for many in the field. Recent advances in our understanding of ES cell differentiation, detailed in this review, have provided new insights essential for establishing ES cell-based developmental models and for the generation of clinically relevant populations for cell therapy.

The derivation of two additional human embryonic stem cell lines from day 3 embryos with low morphological scores

BACKGROUND

Immune rejection can lead to the failure of human embryonic stem cell (hES cell) transplantation. One approach to address the problem is to establish hES cell line banks. Due to the limited source of human embryos and to ethical reasons, the hES cell lines are not readily available. This study was undertaken to determine whether discarded day 3 embryos with low morphological scores could develop into blastocysts and produce hES cell lines.

METHODS

A total of 130 day 3 embryos with low morphological scores were cultured to blastocyst stage, and inner cell masses (ICM) were isolated by immunosurgery. Colonies derived from the ICM were passaged every 4-7 days and evaluated for cell surface markers, differentiation potentials and karyotypes.

RESULTS

A total of 19 blastocysts were obtained from 130 embryos (quality score <16), which resulted in the formation of 10 ICM, and two cell lines. Both cell lines satisfied the criteria that characterize pluripotent hES cells.

CONCLUSION

Our results suggest that a subset with poor quality day 3 embryos judged on the basis of morphological assessment can form blastocysts and give rise to hES cell lines.

Differentiation of in vitro-modified human peripheral blood monocytes into hepatocyte-like and pancreatic islet-like cells

BACKGROUND & AIMS

Adult stem cells provide a promising alternative for the treatment of diabetes mellitus and end-stage liver diseases. We evaluated the differentiation potential of human peripheral blood monocytes into hepatocyte-like and pancreatic islet-like cells.

METHODS

Monocytes were treated with macrophage colony-stimulating factor and interleukin 3 for 6 days, followed by incubation with hepatocyte and pancreatic islet-specific differentiation media. Cells were characterized by flow cytometry, gene-expression analysis, metabolic assays, and transplantation for their state of differentiation and tissue-specific functions.

RESULTS

In response to macrophage colony-stimulating factor and interleukin 3, monocytes resumed cell division in a CD115-dependent fashion, which was associated with a down-regulation of the PRDM1 and ICSBP genes. These programmable cells of monocytic origin were capable of differentiating into neohepatocytes, which closely resemble primary human hepatocytes with respect to morphology, expression of hepatocyte markers, and specific metabolic functions. After transplantation into the liver of severe combined immunodeficiency disease/nonobese diabetic mice, neohepatocytes integrated well into the liver tissue and showed a morphology and albumin expression similar to that of primary human hepatocytes transplanted under identical conditions. Programmable cells of monocytic origin-derived pancreatic neoislets expressed beta cell-specific transcription factors, secreted insulin and C peptide in a glucose-dependent manner, and normalized blood glucose levels when xenotransplanted into immunocompetent, streptozotocin-treated diabetic mice. Programmable cells of monocytic origin retained monocytic characteristics, notably CD14 expression, a monocyte-specific methylation pattern of the CD115 gene, and expression of the transcription factor PU.1.

CONCLUSIONS

The ability to reprogram, expand, and differentiate peripheral blood monocytes in large quantities opens the real possibility of the clinical application of programmable cells of monocytic origin in tissue repair and organ regeneration.

Cell Extract-Derived Differentiation of Embryonic Stem Cells

Various means have been used to encourage the differentiation of embryonic stem cells (ESCs) toward specific lineages, including growth factor administration, genetic modification, and coculture with relevant cells/tissues. Cell extract-based reprogramming has recently been used to derive mature cells from nonrelated phenotypes. In this communication, we tested whether this in vitro reprogramming approach can be used to direct ESC differentiation. Permeabilized murine ESCs exposed to extracts of murine type II pneumocytes showed increased expression of surfactant protein C and its corresponding mRNA, reflecting enhanced differentiation of pneumocytes. Subsequent differentiation to a type I phenotype was demonstrated by expression of aquaporin 5. Pneumocyte formation occurred quicker than with growth factor-induced differentiation. Our findings establish that ESCs can be differentiated in vitro using cellular extracts. This model provides a tool for analysis of the key factors involved in the differentiation of ESCs to type II pneumocytes.

Perfusion cultures of human embryonic stem cells

Human embryonic stem cells (hESC) are self-renewing pluripotent cells capable of differentiating into cells representative of all three embryonic germ layers. Hence, they hold great potential for regenerative medicine. However, significant cell numbers are required to fulfill their potential therapeutic applications. In this study, perfusion with supplemented conditioned media (SCM), produced by mouse embryonic fibroblasts (MEF), was adopted to improve cell densities of hESC cultures. Perfusion enhanced hESC numbers by 70% compared to static conditions, on both organ culture dish (OCD) and petri dish cultures. All cultures maintained healthy expression of the pluripotent marker, Oct-4 transcription factor. In vivo, perfused hESC formed teratomas in severe combined immunodeficiency (SCID) mice models that represent the three embryonic germ layers. When SCM was produced with lower concentrations of MEF, hESC densities and Oct-4 levels were reduced. Hence, perfusion with SCM is a potential feeding method for scale-up production of hESC.

Ectodermal commitment of insulin‐producing cells derived from mouse embryonic stem cells

Embryonic stem cells possess the ability to differentiate in vitro into a variety of cell lineages, including insulin-producing cells. Pancreatic beta-cells derive from foregut endoderm during embryonic development. However, previous reports using transgenic mice strongly indicate that insulin-positive cells may be generated also through the neuroectoderm pathway. To analyze this point, a culture system was performed in which only ectoderm committed cells were present. Based on published work, we achieved this by maintaining transfected clonal R1 mouse embryonic stem cells in monolayer in the absence of LIF. Contrary to differentiation protocols via embryoid body formation, monolayer cultured cells displayed ectodermal fates according to the marker gene expression pattern. Under these particular conditions, neomycin was added in order to select insulin-expressing cells. The cell lineage obtained expressed Pdx1, Pax6, Isl1, AChE, MBP, TH, and GS genes, confirming ectodermal commitment, even though some of these factors are also expressed in endoderm. In addition these cells displayed excitatory properties similar to astrocytes. Co-expression of insulin II and nestin was observed in monolayer culture and in the presence of specific conditioned media. No expression of early endodermal markers was detected along monolayer cultures. Altogether, these observations suggest that cells with ectoderm fates could participate in vitro in the derivation of insulin-producing cells. These results have implications for insulin gene regulation and hormone secretion in order to generate insulin-producing cells for replacement protocols in the treatment of diabetes.

Routes to regenerating islet cells: stem cells and other biological therapies for type 1 diabetes

New biological therapies for type 1 diabetes are emerging from the forefront of stem cell and islet cell biology. Basic research in animal models has uncovered a variety of mechanisms by which natural regeneration of pancreatic islet cells occurs, despite the underlying autoimmune defect. Two mechanisms - in particular, beta-islet cell proliferation and stem cell differentiation - can be harnessed in innovative ways in order to regenerate islets lost to disease. This review provides a background on stem cells and describes a range of potential biological therapies for type 1 diabetes, including the use of adult stem cells from the spleen, an organ not previously considered a source of pancreatic stem cells. Stem cells of the spleen have been demonstrated to home to the pancreas, where they mature into fully functional islet cells responsible for restoring normoglycemia. If the underlying autoimmune defect can be eradicated, stem cells of the spleen, as well as related strategies, can be used in order to regrow islets destroyed by type 1 diabetes.

Ovarian follicular development stimulated by leuprorelin acetate plus human menopausal gonadotropin in chimpanzees

We attempted ovarian stimulation using gonadotropins in 14 chimpanzees. Subjects were given a single administration of leuprorelin acetate, followed by repeated administration of human menopausal gonadotropin (hMG) for 16-21 days. During the dosing period, the ovarian follicle diameter and count were measured by transvaginal ultrasonography. The hormone administration induced the development of multiple follicles, and multiple oocytes were subsequently retrieved. However, the follicle count was decreased, suggesting atresia, in some subjects. Statistically, the final follicle diameter was dependent on the dosing duration and the hMG dose in the late stage, while the maximum follicle count during hMG administration was dependent on age and the hMG dose in the early stage. Five subjects showed mild ovarian hyperstimulation syndrome (OHSS)-like symptoms with a high serum estradiol (E2) concentration. These results suggest that leuprorelin acetate plus hMG administration successfully stimulates the development of multiple ovarian follicles for oocyte retrieval and that the serum E2 concentration is predictive of OHSS-like symptoms in chimpanzees.

Embryonic stem cells: prospects for developmental biology and cell therapy

Stem cells represent natural units of embryonic development and tissue regeneration. Embryonic stem (ES) cells, in particular, possess a nearly unlimited self-renewal capacity and developmental potential to differentiate into virtually any cell type of an organism. Mouse ES cells, which are established as permanent cell lines from early embryos, can be regarded as a versatile biological system that has led to major advances in cell and developmental biology. Human ES cell lines, which have recently been derived, may additionally serve as an unlimited source of cells for regenerative medicine. Before therapeutic applications can be realized, important problems must be resolved. Ethical issues surround the derivation of human ES cells from in vitro fertilized blastocysts. Current techniques for directed differentiation into somatic cell populations remain inefficient and yield heterogeneous cell populations. Transplanted ES cell progeny may not function normally in organs, might retain tumorigenic potential, and could be rejected immunologically. The number of human ES cell lines available for research may also be insufficient to adequately determine their therapeutic potential. Recent molecular and cellular advances with mouse ES cells, however, portend the successful use of these cells in therapeutics. This review therefore focuses both on mouse and human ES cells with respect to in vitro propagation and differentiation as well as their use in basic cell and developmental biology and toxicology and presents prospects for human ES cells in tissue regeneration and transplantation.

Senescent cells, tumor suppression, and organismal aging: good citizens, bad neighbors

Cells from organisms with renewable tissues can permanently withdraw from the cell cycle in response to diverse stress, including dysfunctional telomeres, DNA damage, strong mitogenic signals, and disrupted chromatin. This response, termed cellular senescence, is controlled by the p53 and RB tumor suppressor proteins and constitutes a potent anticancer mechanism. Nonetheless, senescent cells acquire phenotypic changes that may contribute to aging and certain age-related diseases, including late-life cancer. Thus, the senescence response may be antagonistically pleiotropic, promoting early-life survival by curtailing the development of cancer but eventually limiting longevity as dysfunctional senescent cells accumulate.

Immortalized fibroblast-like cells derived from human embryonic stem cells support undifferentiated cell growth

Human embryonic stem cells (hESCs) have the potential to generate multiple cell types and hold promise for future therapeutic applications. Although undifferentiated hESCs can proliferate indefinitely, hESC derivatives significantly downregulate telomerase and have limited replication potential. In this study we examine whether the replicative lifespan of hESC derivatives can be extended by ectopic expression of human telomerase reverse transcriptase (hTERT), the catalytic component of the telomerase complex. To this end, we have derived HEF1 cells, a fibroblast-like cell type, differentiated from hESCs. Infection of HEF1 cells with a retrovirus expressing hTERT extends their replicative capacity, resulting in immortal human HEF1-hTERT cells. HEF1-hTERT cells can be used to produce conditioned medium (CM) capable of supporting hESC growth under feeder-free conditions. Cultures maintained in HEF1-CM show characteristics similar to mouse embryonic fibroblast CM control cultures, including morphology, surface marker and transcription factor expression, telomerase activity, differentiation, and karyotypic stability. In addition, HEF1-hTERT cells have the capacity to differentiate into cells of the osteogenic lineage. These results suggest that immortalized cell lines can be generated from hESCs and that cells derived from hESCs can be used to support their own growth, creating a genotypically homogeneous system for the culture of hESCs.

Therapeutic applications of embryonic stem cells

Embryonic stem (ES) cells have the potential to proliferate indefinitely in culture and can differentiate into any cell type. The emergence of ES cell lines from human embryos in the past 5 years has attracted profound public and scientific interest, given the far-reaching potential applications of these cells in regenerative medicine. In the future, it is possible that human ES (hES) cells might serve as an unlimited source of cells for transplantation therapy under conditions that result from cell degeneration or malfunction, and that genetically manipulated hES cells might serve as vectors to carry and express genes in target organs following transplantation in the course of gene therapy. This chapter reviews the properties of hES cells and their potential advantages and limitations for cell-based therapies. We also describe various approaches that might be utilized with hES cells to avoid potential immune rejection after allogeneic transplantation and hence circumvent the need for systemic immune suppression. Up-to-date research in establishing committed tissue-specific progenitors from ES cells and evidence of their function after transplantation in various animal disease models is also reviewed. The chapter concludes that hES cells show great promise for regenerative medicine although significant developments are still required to exploit their potential for cell and gene therapy.

Generation of tyrosine hydroxylase positive neurons from human embryonic stem cells after coculture with cellular substrates and exposure to GDNF

Tyrosine hydroxylase (TH)-positive neurons were generated from human embryonic stem (hES) cells by coculturing on astrocytes or PA6 stromal cells. After 3 to 4 weeks in culture, TH-positive cells with neuronal morphology developed. Coculture with astrocytes from the embryonic striatum produced a larger number of TH-positive cells than did coculture with astrocytes from embryonic mesencephalon (329 +/- 149 versus 33 +/- 16 TH-positive cells per well, p < .05). In other experiments using PA6 cells as a substrate, glial-derived neurotrophic factor (GDNF) was added to the media of differentiating hES cells, and this led to a doubling of the number of TH-positive cells (PA6: 443 +/- 105 TH-positive cells per well versus PA6 + GDNF: 934 +/- 136, p < .05). We conclude that substrates of striatal astrocytes and PA6 cells can promote differentiation of human embryonic stem cells to a TH-positive phenotype and that GDNF can increase the number of cells expressing that phenotype.

Derivation of human embryonic stem cells from day-8 blastocysts recovered after three-step in vitro culture

Human embryonic stem cells (hESCs) have been derived from the inner cell mass (ICM) of day 5-7 blastocysts and hold great promise for research into human developmental biology and the development of cell therapies for the treatment of human diseases. We report here that our novel three-step culture conditions successfully support the development of day-8 human blastocysts, which possess significantly (p <.01) more ICM cells than day-6 blastocysts. Plating of ICMs isolated from day-8 blastocysts resulted in the formation of a colony with hESC morphology from which a new hESC line (hES-NCL1) was derived. Our stem cell line is characterized by the expression of specific cell surface and gene markers: GTCM-2, TG343, TRA1-60, SSEA-4, alkaline phosphatase, OCT-4, NANOG, and REX-1. Cytogenetic analysis of the hESCs revealed that hES-NCL1 line has a normal female (46, XX) karyotype. The pluripotency of the cell line was confirmed by the formation of teratomas after injection into severely combined immunodeficient mice and spontaneous differentiation under in vitro conditions.

Low O2 tensions and the prevention of differentiation of hES cells

Early-stage mammalian embryos develop in a low O(2) environment (hypoxia). hES cells, however, are generally cultured under an atmosphere of 21% O(2) (normoxia), under which conditions they tend to differentiate spontaneously. Such conditions may not be the most suitable, therefore, for hES cell propagation. Here we have tested two hypotheses. The first hypothesis was that hES cells would grow as well under hypoxic as under normoxic conditions. The second hypothesis was that hypoxic culture would reduce the amount of spontaneous cell differentiation that occurs in hES colonies. Both hypotheses proved to be correct. Cells proliferated as well under 3% and 5% O(2) as they did under 21% O(2), and growth was only slightly reduced at 1% O(2). The appearance of differentiated regions as assessed morphologically, biochemically (by the production of human chorionic gonadotropin and progesterone), and immunohistochemically (by the loss of stage-specific embryonic antigen-4 and Oct-4 and gain of stage-specific embryonic antigen-1 marker expression) was markedly reduced under hypoxic conditions. In addition, hES cell growth under hypoxia provided enhanced formation of embryoid bodies. Hypoxic culture would appear to be necessary to maintain full pluripotency of hES cells.

Stem cells today: B1. Bone marrow stem cells

This review is the second in a series of four devoted to the analysis of recent studies on stem cells. The first considered embryo stem cells (ES). This review covers bone marrow stem cells. They are analysed initially in a historical perspective, and then in relation to foundation studies in the later 20th century before a detailed analysis is presented on very recent studies. Methods of identifying, culturing, expanding and grafting stem cells are described, including the separation of haemopoietic and mesenchyme cell lines (HSC and MSC) and recent more detailed analyses using numerous CD and other markers to identify very small subsets of stem cells such as multipotent adult progenitor cells (MAPC) and bone marrow stromal stem cells (BMSSC) from MSC. Queries arising on the immense potential of these stem cell lines due to the discovery of epigentic factors and cell fusions influencing their development and potency are described. A section on cord blood stem cells is followed by a detailed discussion on the modern situation regarding the clinical use of stem cells, its recent setbacks due to epigenetic factors, different approaches to the discovery of a highly multipotent bone marrow stem cell, and a brief description of embryological approaches to identifying the basic bone marrow stem cell in very early mammalian embryos.

Basic Fibroblast Growth Factor Supports Undifferentiated Human Embryonic Stem Cell Growth Without Conditioned Medium

Previous studies have shown that prolonged propagation of undifferentiated human embryonic stem cells (hESCs) requires conditioned medium from mouse embryonic feeders (MEF-CM) as well as matrix components. Because hESCs express growth factor receptors, including those for basic fibroblast growth factor (bFGF), stem cell factor (SCF), and fetal liver tyrosine kinase-3 ligand (Flt3L), we evaluated these and other growth factors for their ability to maintain undifferentiated hESCs in the absence of conditioned medium. We found cultures maintained in bFGF alone or in combination with other factors showed characteristics similar to MEF-CM control cultures, including morphology, surface marker and transcription factor expression, telomerase activity, differentiation, and karyotypic stability. In contrast, cells in media containing Flt-3L, thrombopoietin, and SCF, individually or in combination, showed almost complete differentiation after 6 weeks in culture. These data demonstrate that hESCs can be maintained in nonconditioned medium using growth factors.

Donor bone marrow transplantation: chimerism and tolerance

Infusion of donor bone marrow (DBM)-derived cells continue to be tested in clinical protocols intended to induce specific immunologic tolerance. Central clonal deletion of donor-specific alloreactive cells associated with mixed chimerism reliably produced long-term graft tolerance. In this setting, depletion of recipient T cells by antilymphocyte antibodies and subsequent repopulation by donor hematopoietic cells after donor bone marrow infusion (DBMI) are prerequisites for tolerance induction. Major advances have been made in animal models and in pilot clinical trials and the key questions with the future perspectives are presented in this article.

Embryonic Stem Cells Generate Airway Epithelial Tissue

Embryonic stem (ES) cells are self-renewable and pluripotent cells derived from the inner cell mass of a blastocyst-stage embryo. ES cell pluripotency is being investigated increasingly to obtain specific cell lineages for therapeutic treatments and tissue engineering. Type II alveolar epithelial cells have been derived from murine ES cells, but the capacity of the latter to generate differentiated airway epithelial tissue has never been reported. Herein, we show by RT-PCR and immunocytochemistry that murine ES cells are able to differentiate into nonciliated secretory Clara cells, and that type I collagen induces this commitment. Moreover, when cultured at the air-liquid interface, ES cells give rise to a fully differentiated airway epithelium. By quantitative histologic examination, immunohistochemistry, and scanning electron microscopy, we show that the bioengineered epithelium is composed of basal, ciliated, intermediate, and Clara cells, similar to those of native tracheobronchial airway epithelium. Transmission electron microscopy and Western blotting reveal that the generated epithelium also exhibits the ultrastructural features and secretory functions characteristic of airway epithelial tissue. These results open new perspectives for cell therapy of injured epithelium in airway diseases, such as bronchopulmonary dysplasia, cystic fibrosis, or bronchiolitis obliterans.

Embryonic stem cells: a promising tool for cell replacement therapy

Embryonic stem (ES) cells are revolutionizing the field of developmental biology as a potential tool to understand the molecular mechanisms occurring during the process of differentiation from the embryonic stage to the adult phenotype. ES cells harvested from the inner cell mass (ICM) of the early embryo can proliferate indefinitely in vitro while retaining the ability to differentiate into all somatic cells. Emerging results from mice models with ES cells are promising and raising tremendous hope among the scientific community for the ES-cell based cell replacement therapy (CRT) of various severe diseases. ES cells could potentially revolutionize medicine by providing an unlimited renewable source of cells capable of replacing or repairing tissues that have been damaged in almost all degenerative diseases such as diabetes, myocardial infarction and Parkinson's disease. This review updates the progress of ES cell research in CRT, discusses about the problems encountered in the practical utility of ES cells in CRT and evaluates how far this approach is successful experimentally.

Diabetes and Stem Cell Researchers Turn to the Lowly Spleen

The spleen gets no respect. Long seen as superfluous, the adult spleen of the mouse has recently been shown to hold stem cells that, in diabetic mice or genetically altered mice that lack a pancreas, effectively regenerate insulin-producing islet cells of the pancreas. Stem cells of the spleen express Hox11, a highly conserved transcription factor that plays a major role in the development of organs in vertebrate and invertebrate embryos. Hox11 and other members of the Hox family of genes may give stem cells of the spleen the capacity to mature into cell types other than islet cells, including neurons and bone cells. Multilineage splenic stem cells may trace to the embryogenesis and possible persistence into adulthood of a fetal stem cell region called the aorta-gonad-mesonephros (AGM). This Perspective calls for reappraisal of the lowly spleen for treating diabetes and other diseases of aging.

Isolation, culture, and characterization of embryonic cell lines from vitrified sheep blastocysts

This study was conducted to isolate, to culture, and to characterize embryonic cell lines from in vitro produced vitrified sheep blastocysts. Embryos were produced and vitrified at the expanded blastocyst stage. Ten inner cell masses arising from day 6-7 blastocysts were isolated by immunosurgery, disaggregated, and cultured onto mitomocin-C-inactivated mouse STO fibroblasts (MIF). After 5 or 6 days of culture the primary cell colonies were disaggregated, seeded in a new MIF, and cultured for 3 or 4 days to form new colonies called Passage 1. These cells were then disaggregated and cultured for other two passages. The primary cell colonies and Passage 2 colonies expressed stage specific embryonic markers SSEA-1, SSEA-3, and SSEA-4, and were alkaline phosphatase positive. In the absence of feeder layer and human leukemia inhibitory factor (LIF), these cells differentiated into variety of cell types and formed embryoid bodies. When cultured for an extended period of time, embryoid bodies differentiated into derivatives of three embryonic germ (EG) layers. These were characterized by detection of specific markers for differentiation such early mesoderm (FE-C6), embryonic myosin (F1-652), neural precursor (FORSE-1), and endoderm (anti-cytokeratin 18). To our knowledge, this is the first time that embryonic cell lines from in vitro produced and vitrified ovine blastocysts have been isolated and examined for detection of SSEA markers, and embryoid bodies have been cultured and examined for specific cell surface markers for differentiation.

Sintered hydroxyfluorapatites--IV: The effect of fluoride substitutions upon colonisation of hydroxyapatites by mouse embryonic stem cells

Biodegradable scaffolds serve a central role for tissue engineering scaffolds and guiding tissue regeneration. Some of these scaffolds, including apatites, display a significant effect upon cell adhesion and cell proliferation. The incorporation of scaffold technology with the developing embryonic stem (ES) cell field and the capacity of ES cells for self-renewal and differentiation are believed to hold enormous potential for applications in biomedical research and regenerative medicine. The purpose of this work was to determine the effect of hydroxyapatite (HAP) and fluoride substitutions of HAP upon ES cell growth and colonisation. Sintered hydroxyfluorapatite discs were found to support cellular proliferation and colonisation, and the ES cells displayed a tendency for differentiation on the apatite surface as determined by reductions in colony Oct4 immunoreactivity. Fluoride-containing HAPs were found to provide equivalent support to gelatin in terms of cell numbers, yet superior support for cellular colonisation when compared to HAP. This study indicates that fluoride substitutions of HAP may represent a viable strategy for the development of certain engineered tissue replacements and tissue regeneration systems using ES cells.

Derivation, growth and applications of human embryonic stem cells

Human embryonic stem (hES) cells are pluripotent cells derived from the inner cell mass cells of blastocysts with the potential to maintain an undifferentiated state indefinitely. Fully characterised hES cell lines express typical stem cell markers, possess high levels of telomerase activity, show normal karyotype and have the potential to differentiate into numerous cell types under in vitro and in vivo conditions. Therefore, hES cells are potentially valuable for the development of cell transplantation therapies for the treatment of various human diseases. However, there are a number of factors which may limit the medical application of hES cells: (a) continuous culture of hES cells in an undifferentiated state requires the presence of feeder layers and animal-based ingredients which incurs a risk of cross-transfer of pathogens; (b) hES cells demonstrate high genomic instability and non-predictable differentiation after long-term growth; and (c) differentiated hES cells express molecules which could cause immune rejection. In this review we summarise recent progress in the derivation and growth of undifferentiated hES cells and their differentiated progeny, and the problems associated with these techniques. We also examine the potential use of the therapeutic cloning technique to derive isogenic hES cells.

Embryonic stem cells for basic research and potential clinical applications in cardiology

Embryonic stem (ES) cells are pluripotent, possessing the unique property to differentiate into any somatic cell type while retaining the ability to proliferate indefinitely. Due to their ability to recapitulate embryonic differentiation, ES cells are an ideal tool to study the process of early embryogenesis in vitro. Signalling cascades and genes involved in differentiation can be easily studied, and functional genomics approaches aim to identify the regulatory networks underlying lineage commitment. Their unique ability to differentiate into any cell type make ES cells a prime candidate for cell replacement therapy (CRT) of various degenerative disorders. Results from various disease models are promising and have demonstrated their principal suitability as a therapeutic agent in diseases such as myocardial infarctions, diabetes mellitus and Parkinson's disease. Prior to clinical trials in humans, two issues remain to be solved: due to their high proliferative potential, ES cells can form teratocarcinomas in the recipient, and depending on the source of the cells, ES cell grafts may be rejected by the host organism. This review discusses the current state of basic ES cell research with a focus on cardiac differentiation and gives an overview of their use in CRT approaches.

Screening of bioactive metabolites for pancreatic regeneration chemotherapy

Plants and microorganisms are the treasury of bioactive metabolites including useful chemical ligands. Chemical ligands that induce beta-cell differentiation may be useful as new therapeutic agents for both type-1 and type-2 diabetes mellitus. We isolated conophylline from the leaves of Ervatamia microphylla as an agent that induce insulin production in rat pancreatic acinar carcinoma cells.