Human embryonic stem cells for brain repair?

Human Induced Pluripotent Stem Cells : Clinical Significance and Applications in Neurologic Diseases

The generation of human induced pluripotent stem cells (iPSCs) from somatic cells using gene transfer opens new areas for precision medicine with personalized cell therapy and encourages the discovery of essential platforms for targeted drug development. iPSCs retain the genome of the donor, may regenerate indefinitely, and undergo differentiation into virtually any cell type of interest using a range of published protocols. There has been enormous interest among researchers regarding the application of iPSC technology to regenerative medicine and human disease modeling, in particular, modeling of neurologic diseases using patient-specific iPSCs. For instance, Parkinson’s disease, Alzheimer’s disease, and spinal cord injuries may be treated with iPSC therapy or replacement tissues obtained from iPSCs. In this review, we discuss the work so far on generation and characterization of iPSCs and focus on recent advances in the use of human iPSCs in clinical setting.

Transplantation of human meningioma stem cells loaded on a self-assembling peptide nanoscaffold containing IKVAV improves traumatic brain injury in rats

Traumatic brain injury (TBI) can result in permanent brain function impairment due to the poor regenerative ability of neural tissue. Tissue engineering has appeared as a promising approach to promote nerve regeneration and to ameliorate brain damage. The present study was designed to investigate the effect of transplantation of the human meningioma stem-like cells (hMgSCs) seeded in a promising three-dimensional scaffold (RADA4GGSIKVAV; R-GSIK) on the functional recovery of the brain and neuroinflammatory responses following TBI in rats. After induction of TBI, hMgSCs seeded in R-GSIK was transplanted within the injury site and its effect was compared to several control groups. Application of hMgSCs with R-GSIK improved functional recovery after TBI. A significant higher number of hMgSCs was observed in the brain when transplanted with R-GSIK scaffold compared to the control groups. Application of hMgSCs seeded in R-GSIK significantly decreased the lesion volume, reactive gliosis, and apoptosis at the injury site. Furthermore, treatment with hMgSCs seeded in R-GSIK significantly inhibited the expression of Toll-like receptor 4 and its downstream signaling molecules, including interleukin-1β and tumor necrosis factor. These data revealed the potential for hMgSCs seeded in R-GSIK to improve the functional recovery of the brain after TBI; possibly via amelioration of inflammatory responses. STATEMENT OF SIGNIFICANCE: Tissue engineered scaffolds that mimic the natural extracellular matrix of the brain may modulate stem cell fate and contribute to tissue repair following traumatic brain injury (TBI). Among several scaffolds, self-assembly peptide nanofiber scaffolds markedly promotes cellular behaviors, including cell survival and differentiation. We developed a novel three-dimensional scaffold (RADA16GGSIKVAV; R-GSIK). Transplantation of the human meningioma stem-like cells seeded in R-GSIK in an animal model of TBI significantly improved functional recovery of the brain, possibly via enhancement of stem cell survival as well as reduction of the lesion volume, inflammatory process, and reactive gliosis at the injury site. R-GSIK is a suitable microenvironment for human stem cells and could be a potential biomaterial for the reconstruction of the injured brain after TBI.

Transplanting GABAergic Neurons Differentiated from Neural Stem Cells into Hippocampus Inhibits Seizures and Epileptiform Discharges in Pilocarpine-Induced Temporal Lobe Epilepsy Model

OBJECTIVE

This study aimed to explore whether intrahippocampal transplantation of GABAergic neurons generated in vitro ameliorated seizures and epileptiform discharges via increasing γ-aminobutyric acid (GABA)-associated inhibition mediated by the addition of new GABAergic neurons.

METHODS

Neural stem cells (NSCs) isolated from newborn rats were induced and differentiated into GABAergic neurons. A total of 36 Pilocarpine-induced pharmacoresistant epileptic rats were divided into 3 groups: PBS (phosphate-buffered saline) group, NSCs group, and GABAergic neurons group (GABA group), with an additional 10 normal rats used (normal rat control group). The effects of grafting on spontaneous recurrent seizures (SRS) were examined and hippocampal GABA content was measured after grafting.

RESULTS

In the GABA group, the frequency of electroencephalography decreased significantly compared with the PBS group (P < 0.001), but there was no significant difference between the GABA group and NSCs group. Compared with the PBS group, the overall frequency and duration of SRS significantly decreased in the transplantation group, especially in the GABA group (P < 0.01). The number of GABAergic neurons was highest in the GABA group compared with the other groups (P < 0.001). Furthermore, hippocampal GABA concentrations significantly increased in the GABA group.

CONCLUSIONS

We show that GABAergic neurons generated in vitro from NSCs and grafted into the hippocampi of chronically epileptic rats can significantly reduce the frequency of electroencephalography and frequency and duration of SRS via increasing GABA-associated inhibition mediated by the addition of new GABAergic neurons.

Cellular and Molecular Aspects of Parkinson Treatment: Future Therapeutic Perspectives

Parkinson's disease is a neurodegenerative disorder accompanied by depletion of dopamine and loss of dopaminergic neurons in the brain that is believed to be responsible for the motor and non-motor symptoms in this disease. The main drug prescribed for Parkinsonian patients is L-dopa, which can be converted to dopamine by passing through the blood-brain barrier. Although L-dopa is able to improve motor function and improve the quality of life in the patients, there is inter-individual variability and some patients do not achieve the therapeutic effect. Variations in treatment response and side effects of current drugs have convinced scientists to think of treating Parkinson's disease at the cellular and molecular level. Molecular and cellular therapy for Parkinson's disease include (i) cell transplantation therapy with human embryonic stem (ES) cells, human induced pluripotent stem (iPS) cells and human fetal mesencephalic tissue, (ii) immunological and inflammatory therapy which is done using antibodies, and (iii) gene therapy with AADC-TH-GCH gene therapy, viral vector-mediated gene delivery, RNA interference-based therapy, CRISPR-Cas9 gene editing system, and alternative methods such as optogenetics and chemogenetics. Although these methods currently have a series of challenges, they seem to be promising techniques for Parkinson's treatment in future. In this study, these prospective therapeutic approaches are reviewed.

Current understanding of the molecular mechanisms in Parkinson's disease: Targets for potential treatments

Gradual degeneration and loss of dopaminergic neurons in the substantia nigra, pars compacta and subsequent reduction of dopamine levels in striatum are associated with motor deficits that characterize Parkinson’s disease (PD). In addition, half of the PD patients also exhibit frontostriatal-mediated executive dysfunction, including deficits in attention, short-term working memory, speed of mental processing, and impulsivity. The most commonly used treatments for PD are only partially or transiently effective and are available or applicable to a minority of patients. Because, these therapies neither restore the lost or degenerated dopaminergic neurons, nor prevent or delay the disease progression, the need for more effective therapeutics is critical. In this review, we provide a comprehensive overview of the current understanding of the molecular signaling pathways involved in PD, particularly within the context of how genetic and environmental factors contribute to the initiation and progression of this disease. The involvement of molecular chaperones, autophagy-lysosomal pathways, and proteasome systems in PD are also highlighted. In addition, emerging therapies, including pharmacological manipulations, surgical procedures, stem cell transplantation, gene therapy, as well as complementary, supportive and rehabilitation therapies to prevent or delay the progression of this complex disease are reviewed.

A robust vitronectin-derived peptide for the scalable long-term expansion and neuronal differentiation of human pluripotent stem cell (hPSC)-derived neural progenitor cells (hNPCs)

Despite therapeutic advances, neurodegenerative diseases and disorders remain some of the leading causes of mortality and morbidity in the United States. Therefore, cell-based therapies to replace lost or damaged neurons and supporting cells of the central nervous system (CNS) are of great therapeutic interest. To that end, human pluripotent stem cell (hPSC) derived neural progenitor cells (hNPCs) and their neuronal derivatives could provide the cellular 'raw material' needed for regenerative medicine therapies for a variety of CNS disorders. In addition, hNPCs derived from patient-specific hPSCs could be used to elucidate the underlying mechanisms of neurodegenerative diseases and identify potential drug candidates. However, the scientific and clinical application of hNPCs requires the development of robust, defined, and scalable substrates for their long-term expansion and neuronal differentiation. In this study, we rationally designed a vitronectin-derived peptide (VDP) that served as an adhesive growth substrate for the long-term expansion of several hNPC lines. Moreover, VDP-coated surfaces allowed for the directed neuronal differentiation of hNPC at levels similar to cells differentiated on traditional extracellular matrix protein-based substrates. Overall, the ability of VDP to support the long-term expansion and directed neuronal differentiation of hNPCs will significantly advance the future translational application of these cells in treating injuries, disorders, and diseases of the CNS.

Changes in Laminin Expression Pattern during Early Differentiation of Human Embryonic Stem Cells

Laminin isoforms laminin-511 and -521 are expressed by human embryonic stem cells (hESC) and can be used as a growth matrix to culture these cells under pluripotent conditions. However, the expression of these laminins during the induction of hESC differentiation has not been studied in detail. Furthermore, the data regarding the expression pattern of laminin chains in differentiating hESC is scarce. In the current study we aimed to fill this gap and investigated the potential changes in laminin expression during early hESC differentiation induced by retinoic acid (RA). We found that laminin-511 but not -521 accumulates in the committed cells during early steps of hESC differentiation. We also performed a comprehensive analysis of the laminin chain repertoire and found that pluripotent hESC express a more diverse range of laminin chains than shown previously. In particular, we provide the evidence that in addition to α1, α5, β1, β2 and γ1 chains, hESC express α2, α3, β3, γ2 and γ3 chain proteins and mRNA. Additionally, we found that a variant of laminin α3 chain—145 kDa—accumulated in RA-treated hESC showing that these cells produce prevalently specifically modified version of α3 chain in early phase of differentiation.

Regenerative potential of endometrial stem cells: a mini review

Recent findings in stem cell biology have opened a new window in regenerative medicine. The endometrium possesses mesenchymal stem cells (MSCs) called endometrial stem cells (EnSCs) having specific regenerative properties linked to adult stem cells. They contribute in tissue remodeling and engineering and were shown to have immuno-modulating effects. Many clinical trials were undertaken to ascertain the therapeutic potential of EnSCS. In this mini review, we showed that EnSCs are readily available sources of adult stem cells in the uterus that can be highlighted for their renewable multipotent and differentiation properties. This cell population may be a practical solution of choice in reproductive biology, regenerative medicine and autologous stem cell therapy.

Endogenous WNT signaling regulates hPSC-derived neural progenitor cell heterogeneity and specifies their regional identity

Neural progenitor cells (NPCs) derived from human pluripotent stem cells (hPSCs) are a multipotent cell population that is capable of nearly indefinite expansion and subsequent differentiation into the various neuronal and supporting cell types that comprise the CNS. However, current protocols for differentiating NPCs toward neuronal lineages result in a mixture of neurons from various regions of the CNS. In this study, we determined that endogenous WNT signaling is a primary contributor to the heterogeneity observed in NPC cultures and neuronal differentiation. Furthermore, exogenous manipulation of WNT signaling during neural differentiation, through either activation or inhibition, reduces this heterogeneity in NPC cultures, thereby promoting the formation of regionally homogeneous NPC and neuronal cultures. The ability to manipulate WNT signaling to generate regionally specific NPCs and neurons will be useful for studying human neural development and will greatly enhance the translational potential of hPSCs for neural-related therapies.

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Heterogeneous endogenous WNT signaling regulates hPSC-derived neuronal diversity

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Endogenous WNT signaling specifies the regional identity of hPSC-derived neurons

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Exogenous WNT signaling leads to uniform neuronal cultures from hPSCs

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Effects of WNT signaling on neurogenesis are recapitulated in an hPSC-based system

Noggin versus basic fibroblast growth factor on the differentiation of human embryonic stem cells

The difference between Noggin and basic fibroblast growth factor for the neural precursor differentiation from human embryonic stem cells has not been studied. In this study, 100 μg/L Noggin or 20 μg/L basic fibroblast growth factor in serum-free neural induction medium was used to differentiate human embryonic stem cells H14 into neural precursors using monolayer differentiation. Two weeks after induction, significantly higher numbers of neural rosettes formed in the Noggin-induced group than the basic fibroblast growth factor-induced group, as detected by phase contrast microscope. Immunofluorescence staining revealed expression levels of Nestin, β-III Tubulin and Sox-1 were higher in the induced cells and reverse-transcription PCR showed induced cells expressed Nestin, Sox-1 and Neurofilament mRNA. Protein and mRNA expression in the Noggin-induced group was increased compared with the basic fibroblast growth factor-induced group. Noggin has a greater effect than basic fibroblast growth factor on the induction of human embryonic stem cell differentiation into neural precursors by monolayer differentiation, as Noggin accelerates and increases the differentiation of neural precursors.

MicroRNA-based promotion of human neuronal differentiation and subtype specification

MicroRNAs are key regulators of neural cell proliferation, differentiation and fate choice. Due to the limited access to human primary neural tissue, the role of microRNAs in human neuronal differentiation remains largely unknown. Here, we use a population of long-term self-renewing neuroepithelial-like stem cells (lt-NES cells) derived from human embryonic stem cells to study the expression and function of microRNAs at early stages of human neural stem cell differentiation and neuronal lineage decision. Based on microRNA expression profiling followed by gain- and loss-of-function analyses in lt-NES cells and their neuronal progeny, we demonstrate that miR-153, miR-324-5p/3p and miR-181a/a contribute to the shift of lt-NES cells from self-renewal to neuronal differentiation. We further show that miR-125b and miR-181a specifically promote the generation of neurons of dopaminergic fate, whereas miR-181a inhibits the development of this neurotransmitter subtype. Our data demonstrate that time-controlled modulation of specific microRNA activities not only regulates human neural stem cell self-renewal and differentiation but also contributes to the development of defined neuronal subtypes.

Motoneuron replacement for reinnervation of skeletal muscle in adult rats

Reinnervation is needed to rescue muscle when motoneurons die in disease or injury. Embryonic ventral spinal cord cells transplanted into peripheral nerve reinnervate muscle and reduce atrophy, but low motoneuron survival may limit motor unit formation. We tested whether transplantation of a purified population of embryonic motoneurons into peripheral nerve (mean ± SE, 146,458 ± 4,011 motoneurons) resulted in more motor units and reinnervation than transplantation of a mixed population of ventral spinal cord cells (72,075 ± 12,329 motoneurons). Ten weeks after either kind of transplant, similar numbers of neurons expressed choline acetyl transferase and/or Islet-1. Motoneuron numbers always exceeded the reinnervated motor unit count. Most motor end plate were simple plaques. Reinnervation significantly reduced muscle fiber atrophy. These data show that the number of transplanted motoneurons and motoneuron survival do not limit muscle reinnervation. Incomplete differentiation of motoneurons in nerve and lack of muscle activity may result in immature neuromuscular junctions that limit reinnervation and function.

Progress in cell grafting therapy for temporal lobe epilepsy

Temporal lobe epilepsy (TLE), exemplified by complex partial seizures, is recognized in ~30% of epileptic patients. Seizures in TLE are associated with cognitive dysfunction and are resistant to antiepileptic drug therapy in ~35% of patients. Although surgical resection of the hippocampus bestows improved seizure regulation in most cases of intractable TLE, this choice can cause lasting cognitive deficiency and reliance on antiepileptic drugs. Thus, alternative therapies that are proficient in both containing the spontaneous recurrent seizures and reversing the cognitive dysfunction are needed. The cell transplantation approach is promising in serving as an adept alternate therapy for TLE, because this strategy has shown the capability to curtail epileptogenesis when used soon after an initial precipitating brain injury, and to restrain spontaneous recurrent seizures and improve cognitive function when utilized after the occurrence of TLE. Nonetheless, this treatment needs further advancement and rigorous evaluation in animal prototypes of chronic TLE before the conceivable clinical use. It is especially vital to gauge the efficacy of distinct donor cell types, such as the hippocampal precursor cells, γ-aminobutyric acid-ergic progenitors, and neural stem cells derived from diverse human sources (including the embryonic stem cells and induced pluripotent stem cells) for longstanding seizure suppression using continuous electroencephalographic recordings for prolonged periods. Additionally, the identification of the mechanisms underlying the graft-mediated seizure suppression and improved cognitive function, and the development of apt grafting strategies that enhance the anti-seizure and pro-cognitive effects of grafts will be necessary. The goal of this review is to evaluate the progress made hitherto in this area and to discuss the prospect for cell-based therapy for TLE.

In vivo stem cell tracking in neurodegenerative therapies

INTRODUCTION

Cell transplants to replace cells lost due to injury or degenerative diseases, for which there are currently no cures, are being pursued in a wide range of experimental models. Thus, the application of stem cell-based therapies to treat neurodegenerative and traumatic injuries is now a clinical reality. However, the monitoring of cellular grafts, non-invasively, is an important aspect of the ongoing efficacy and safety assessment of cell-based therapies. Hence, there is a need for non-invasive imaging techniques to ensure that transplants are not only administered to the relevant site, but also allow the monitoring of inappropriate cellular migration to improve our understanding of stem cell migration in the context of the whole organism.

AREAS COVERED

This review provides an up to date overview of molecular imaging approaches that have been used for visualizing and tracking transplanted stem cells, in vivo.

EXPERT OPINION

It's important to emphasize that the application of molecular imaging to interrogate transplanted cells may require one or even two imaging modalities to provide a reasonable assessment of transplanted cells in specific organs.

Inhibition of notch signaling in human embryonic stem cell-derived neural stem cells delays G1/S phase transition and accelerates neuronal differentiation in vitro and in vivo

The controlled in vitro differentiation of human embryonic stem cells (hESCs) and other pluripotent stem cells provides interesting prospects for generating large numbers of human neurons for a variety of biomedical applications. A major bottleneck associated with this approach is the long time required for hESC-derived neural cells to give rise to mature neuronal progeny. In the developing vertebrate nervous system, Notch signaling represents a key regulator of neural stem cell (NSC) maintenance. Here, we set out to explore whether this signaling pathway can be exploited to modulate the differentiation of hESC-derived NSCs (hESNSCs). We assessed the expression of Notch pathway components in hESNSCs and demonstrate that Notch signaling is active under self-renewing culture conditions. Inhibition of Notch activity by the gamma-secretase inhibitor N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT) in hESNSCs affects the expression of human homologues of known targets of Notch and of several cell cycle regulators. Furthermore, DAPT-mediated Notch inhibition delays G1/S-phase transition and commits hESNSCs to neurogenesis. Combined with growth factor withdrawal, inhibition of Notch signaling results in a marked acceleration of differentiation, thereby shortening the time required for the generation of electrophysiologically active hESNSC-derived neurons. This effect can be exploited for neural cell transplantation, where transient Notch inhibition before grafting suffices to promote the onset of neuronal differentiation of hESNSCs in the host tissue. Thus, interference with Notch signaling provides a tool for controlling human NSC differentiation both in vitro and in vivo.

Stem cell potential in Parkinson's disease and molecular factors for the generation of dopamine neurons

Parkinson's disease (PD) involves the loss of dopamine (DA) neurons, making it the most expected neurodegenerative disease to be treated by cell replacement therapy. Stem cells are a promising source for cell replacement therapy due to their ability to self-renew and their pluripotency/multipotency that allows them to generate various types of cells. However, it is challenging to derive midbrain DA neurons from stem cells. Thus, in this review, I will discuss the molecular factors that are known to play critical roles in the generation and survival of DA neurons. The developmental process of DA neurons and functions of extrinsic soluble factors and homeodomain proteins, forkhead box proteins, proneural genes, Nurr1 and genes involved in epigenetic control are discussed. In addition, different types of stem cells that have potential for future cell replacement therapy are reviewed.

Mechanisms of neural specification from embryonic stem cells

While embryonic stem (ES) cells have been used for several years to generate specific populations of neural cells in a translational perspective, they have also emerged as a promising approach in developmental neurobiology, by providing reductionist models of neural development. Here we review recent work that indicates that ES-based models are not only able to mimic normal brain development, but also provide novel tools to dissect the relative contribution of intrinsic and extrinsic mechanisms of neural specification. These have thus not only revealed insights on early steps such as neural induction and regional patterning, but also temporal specification of distinct neuronal subtypes, as well as the later acquisition of more complex features such as cytoarchitecture and hodological properties.

Highly efficient differentiation and enrichment of spinal motor neurons derived from human and monkey embryonic stem cells

Background

There are no cures or efficacious treatments for severe motor neuron diseases. It is extremely difficult to obtain naïve spinal motor neurons (sMNs) from human tissues for research due to both technical and ethical reasons. Human embryonic stem cells (hESCs) are alternative sources. Several methods for MN differentiation have been reported. However, efficient production of naïve sMNs and culture cost were not taken into consideration in most of the methods.

Methods/Principal Findings

We aimed to establish protocols for efficient production and enrichment of sMNs derived from pluripotent stem cells. Nestin+ neural stem cell (NSC) clusters were induced by Noggin or a small molecule inhibitor of BMP signaling. After dissociation of NSC clusters, neurospheres were formed in a floating culture containing FGF2. The number of NSCs in neurospheres could be expanded more than 30-fold via several passages. More than 33% of HB9+ sMN progenitor cells were observed after differentiation of dissociated neurospheres by all-trans retinoic acid (ATRA) and a Shh agonist for another week on monolayer culture. HB9+ sMN progenitor cells were enriched by gradient centrifugation up to 80% purity. These HB9+ cells differentiated into electrophysiologically functional cells and formed synapses with myotubes during a few weeks after ATRA/SAG treatment.

Conclusions and Significance

The series of procedures we established here, namely neural induction, NSC expansion, sMN differentiation and sMN purification, can provide large quantities of naïve sMNs derived from human and monkey pluripotent stem cells. Using small molecule reagents, reduction of culture cost could be achieved.

The Characterization Tool: A knowledge-based stem cell, differentiated cell, and tissue database with a web-based analysis front-end

In the rapidly growing field of stem cell research, there is a need for universal databases and web-based applications that provide a common knowledge base on the characteristics of stem cells, differentiated cells, and tissues by collecting, processing, and making available diverse types of characterization data. The Characterization Tool is such a novel knowledge database that allows the storage of various characteristics of cells, cell lines, and tissues across different species as well as the analysis of associated marker profiles. Its broad ontology-based framework facilitates the integration of characterization data on the morphological, molecular, and functional level acquired in vivo and in vitro including published marker expressions, cross-references to other databases, text descriptions, information on characterization experiments, and image storage. Data input and modification are recorded on the basis of a secure user management. By means of several easy-to-use data mining tools, marker profiles can be searched and analyzed. The Characterization Tool will aid in the establishment of standards for cell characterization, needed, for example, for stem cell isolation, propagation, and differentiation. The Characterization Tool is available at http://characterizationtool.cellnet.org. It currently holds more than 7000 marker expressions for different human embryonic stem cell lines, adult stem cells, and differentiated cells.

Engineered adenosine-releasing cells for epilepsy therapy: human mesenchymal stem cells and human embryonic stem cells

Adenosine is a modulator of neuronal activity with anticonvulsant and neuroprotective properties. Conversely, focal deficiency in adenosine contributes to ictogenesis. Thus, focal reconstitution of adenosine within an epileptogenic brain region constitutes a rational therapeutic approach, whereas systemic augmentation of adenosine is precluded by side effects. To meet the therapeutic goal of focal adenosine augmentation, genetic disruption of the adenosine metabolizing enzyme, adenosine kinase (ADK) in rodent cells was used as a molecular strategy to induce adenosine release from cellular brain implants, which demonstrated antiepileptic and neuroprotective properties. Currently, the second generation of adenosine-releasing cells is under development based on the rationale to use human stem cell-derived brain implants to avoid xenotransplantation. To effectively engineer human stem cells to release adenosine, a lentiviral vector was constructed to express inhibitory micro-RNA directed against ADK. Lentiviral knockdown of ADK induced therapeutic adenosine release in human mesenchymal stem cells, which reduced acute injury and seizures, as well as chronic seizures, when grafted into the mouse hippocampus. The therapeutic potential of this approach suggests the feasibility to engineer autologous adenosine-releasing stem cells derived from a patient. Human embryonic stem cells (hESCs) have a high proliferative capacity and can be subjected to specific cellular differentiation pathways. hESCs, differentiated in vitro into neuroepithelial cells and grafted into the mouse brain, displayed intrahippocampal location and neuronal morphology. Using the same lentiviral micro-RNA vector, we demonstrated knockdown of ADK in hESCs. New developments and therapeutic challenges in using human mesenchymal stem cells and hESCs for epilepsy therapy will be critically evaluated.

Human embryonic stem cells: a potential source of transplantable neural progenitor cells

The primary therapeutic goal of embryonic stem cell (ESC) research is cell replacement therapy. During the last decade, great strides have been made in developing in vitro protocols for differentiating human ESCs into neuroepithelial progenitors. More recent progress has been made in further directing them into becoming cells with specialized regional and neurotransmitter identities, such as midbrain dopaminergic and spinal motor neurons. Along with directed differentiation, other current efforts are aimed at efficient enrichment, avoidance of immune rejection, demonstration of functional integration, genetic modification to regulate neurotransmitter and factor release, directed axon growth, in vivo cell tracking, and measures to ensure safety. This review will focus on the potential of ESCs as a source of transplantable cells for use in cell replacement therapy.

Cellular therapy for childhood neurodegenerative disease. Part I: rationale and preclinical studies

✓ Successful cellular replacement in the diseased human central nervous system (CNS) faces numerous hurdles. In this first installment of a 2-part review, the authors report on the preclinical challenges involved in preparing for a major Phase I trial investigating the safety of human neural stem cell transplantation in a lysosomal storage disorder. Specifically, they discuss choice of the ideal disease for treatment, best donor cell type and source for implantation, the in vitro and in vivo methods used to estimate safety and efficacy, the challenges to noninvasive tracking of cells after transplantation, and the unique issues related to the immunology of CNS cellular transplantation.

Embryonic stem cell biology

ES cell research represents an exploding field of exploration. Initially predicted to provide rapid cures for numerous human diseases, the clinical usefulness of ES cell-derived cells remains untested in humans. However, ES cells have rapidly expanded our knowledge of human development and the molecular details of differentiation. Our ability to generate relatively pure populations of specifically differentiated cells for transplantation has markedly improved. It is hoped that soon researchers will overcome the biologic impediments to successful treatment of human disease with ES cell-derived cells.

Endometrial regenerative cells: a novel stem cell population

Angiogenesis is a critical component of the proliferative endometrial phase of the menstrual cycle. Thus, we hypothesized that a stem cell-like population exist and can be isolated from menstrual blood. Mononuclear cells collected from the menstrual blood contained a subpopulation of adherent cells which could be maintained in tissue culture for >68 doublings and retained expression of the markers CD9, CD29, CD41a, CD44, CD59, CD73, CD90 and CD105, without karyotypic abnormalities. Proliferative rate of the cells was significantly higher than control umbilical cord derived mesenchymal stem cells, with doubling occurring every 19.4 hours. These cells, which we termed "Endometrial Regenerative Cells" (ERC) were capable of differentiating into 9 lineages: cardiomyocytic, respiratory epithelial, neurocytic, myocytic, endothelial, pancreatic, hepatic, adipocytic, and osteogenic. Additionally, ERC produced MMP3, MMP10, GM-CSF, angiopoietin-2 and PDGF-BB at 10-100,000 fold higher levels than two control cord blood derived mesenchymal stem cell lines. Given the ease of extraction and pluripotency of this cell population, we propose ERC as a novel alternative to current stem cells sources.