Human embryonic stem cells: Long term stability, absence of senescence and a potential cell source for neural replacement

Adult Stem Cells Freezing Processes and Cryopreservation Protocols

The development of simple but effective storage protocols for adult stem cells will greatly enhance their use and utility in tissue-engineering applications. Cryopreservation has shown the most promise but is a fairly complex process, necessitating the use of chemicals called cryoprotective agents (CPAs), freezing equipment, and obviously, storage in liquid nitrogen. The purpose of this chapter is to present a general overview of cryopreservation storage techniques and the optimal protocols/results obtained in our laboratory for long-term storage of adult stem cells using freezing storage.

A global perspective on a new paradigm shift in bio-based meat alternatives for healthy diet

A meat analogue is a casserole in which the primary ingredient is something other than meat. It goes by various other names, such as meat substitute, fake meat, alternative meat, and imitation meat. Consumers growing interest in improving their diets and the future of the planet have contributed to the move towards meat substitutes. This change is due to the growing popularity of low-fat and low-calorie diets, the rise of flexitarians, the spread of animal diseases, the loss of natural resources, and the need to cut down on carbon emissions, which lead to greenhouse effects. Plant-based meat, cultured meat, algal protein-based meat, and insect-based meat substitutes are available on the market with qualities like appearance and flavor similar to those of traditional meat. Novel ingredients like mycoprotein and soybean leg haemoglobin are mixed in with the more traditional soy proteins, cereals, green peas, etc. Plant-based meat is currently more popular in the West, but the growing interest in this product in Asian markets indicates the industry in this region will expand rapidly in the near future. Future growth in the food sector can be anticipated from technologies like lab-grown meat and its equivalents that do not require livestock breeding. Insect-based products also hold great potential as a new source of protein for human consumption. However, product safety and quality should be considered along with other factors such as marketability and affordability.

Introduction to stem cells

Stem cells have self-renewal capability and can proliferate and differentiate into a variety of functionally active cells that can serve in various tissues and organs. This review discusses the history, definition, and classification of stem cells. Human pluripotent stem cells (hPSCs) mainly include embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs). Embryonic stem cells are derived from the inner cell mass of the embryo. Induced pluripotent stem cells are derived from reprogramming somatic cells. Pluripotent stem cells have the ability to differentiate into cells derived from all three germ layers (endoderm, mesoderm, and ectoderm). Adult stem cells can be multipotent or unipotent and can produce tissue-specific terminally differentiated cells. Stem cells can be used in cell therapy to replace and regenerate damaged tissues or organs.

Stem Cells and Natural Agents in the Management of Neurodegenerative Diseases: A New Approach

Neurodegenerative diseases refer to a group of neurological disorders as a consequence of various destructive illnesses, that predominantly impact neurons in the central nervous system, resulting in impairments in certain brain functions. Alzheimer's disease, Parkinson's disease, Huntington's disease, multiple sclerosis, and other neurodegenerative disorders represent a major risk to human health. In order to optimize structural and functional recovery, reconstructive methods integrate many approaches now, to address the complex and multivariate pathophysiology of neurodegenerative disorders. Stem cells, with their unique property of regeneration, offer new possibilities in regenerative and reconstructive medicine. Concurrently, there is an important role for natural products in controlling many health sufferings and they can delay or even prevent the onset of various diseases. In addition, due to their therapeutic properties, they have been used as neuroprotective agents to treat neurodegenerative disorders. After decades of intensive research, scientists made advances in treating these disorders so far, but current therapies are still not capable of preventing the illnesses from progressing. Therefore, in this review, we focused on a new perspective combining stem cells and natural products as an innovative therapy option in the management of neurodegenerative diseases.

Clean meat: techniques for meat production and its upcoming challenges

Meat is traditionally obtained by sacrificing the animals. It is considered as one of the richest sources of proteins. There is an increasing demand for meat worldwide. It may not be possible to fulfill this demand for meat in future. Therefore, there is an urgent need to find out the alternative resources for proteins requirement shortly. Clean meat production is one of the best methods to be adopted as an alternative to traditional meat. The word 'clean' signifies that we can procure meat from animals without its monstrous slaughtering. Hence, it is prepared by isolating a single cell and culturing them in controlled growth conditions and medium that mimic the in vivo condition. It is not a brand new technology, but the tools for developing clean meat that mimics real meat have been technologically advanced recently. Many companies have marketed clean meat products worldwide from last five years. And it has been observed that there are mixed responses for its acceptance by consumers. The main driving forces for clean meat production derives from the concerns over environment, animal welfare, public and consumer health aspects of animal production, use of antibiotics in the animal industries, and food security. Since it's an upcoming meat production technology, there are many hurdles and challenges like nutritional attributes, flavor, shape, and structure compared to real meat. It requires many skills and understanding of muscle stem cells' regeneration and their growth under optimized scale-up production conditions. In this paper the complete details about clean meat, types of cells, and techniques used for its production has been discussed on a lab scale.

Bioinspired mineralized collagen scaffolds for bone tissue engineering

Successful regeneration of large segmental bone defects remains a major challenge in clinical orthopedics, thus it is of important significance to fabricate a suitable alternative material to stimulate bone regeneration. Due to their excellent biocompatibility, sufficient mechanical strength, and similar structure and composition of natural bone, the mineralized collagen scaffolds (MCSs) have been increasingly used as bone substitutes via tissue engineering approaches. Herein, we thoroughly summarize the state of the art of MCSs as tissue-engineered scaffolds for acceleration of bone repair, including their fabrication methods, critical factors for osteogenesis regulation, current opportunities and challenges in the future. First, the current fabrication methods for MCSs, mainly including direct mineral composite, in-situ mineralization and 3D printing techniques, have been proposed to improve their biomimetic physical structures in this review. Meanwhile, three aspects of physical (mechanics and morphology), biological (cells and growth factors) and chemical (composition and cross-linking) cues are described as the critical factors for regulating the osteogenic feature of MCSs. Finally, the opportunities and challenges associated with MCSs as bone tissue-engineered scaffolds are also discussed to point out the future directions for building the next generation of MCSs that should be endowed with satisfactorily mimetic structures and appropriately biological characters for bone regeneration.

Automated real-time monitoring of human pluripotent stem cell aggregation in stirred tank reactors

The culture of human induced pluripotent stem cells (hiPSCs) at large scale becomes feasible with the aid of scalable suspension setups in continuously stirred tank reactors (CSTRs). Innovative monitoring options and emerging automated process control strategies allow for the necessary highly defined culture conditions. Next to standard process characteristics such as oxygen consumption, pH, and metabolite turnover, a reproducible and steady formation of hiPSC aggregates is vital for process scalability. In this regard, we developed a hiPSC-specific suspension culture unit consisting of a fully monitored CSTR system integrated into a custom-designed and fully automated incubator. As a step towards cost-effective hiPSC suspension culture and to pave the way for flexibility at a large scale, we constructed and utilized tailored miniature CSTRs that are largely made from three-dimensional (3D) printed polylactic acid (PLA) filament, which is a low-cost material used in fused deposition modelling. Further, the monitoring tool for hiPSC suspension cultures utilizes in situ microscopic imaging to visualize hiPSC aggregation in real-time to a statistically significant degree while omitting the need for time-intensive sampling. Suitability of our culture unit, especially concerning the developed hiPSC-specific CSTR system, was proven by demonstrating pluripotency of CSTR-cultured hiPSCs at RNA (including PluriTest) and protein level.

Cryopreservation Protocols for Human Adipose Tissue Derived Adult Stem Cells

The development of simple but effective storage protocols for adult stem cells will greatly enhance their use and utility in tissue-engineering applications. Cryopreservation has shown to be most promising but is a fairly complex process, necessitating the use of chemicals called cryoprotective agents (CPAs), freezing equipment, and obviously, storage in liquid nitrogen. The purpose of this chapter is to present a general overview of cryopreservation storage techniques and the optimal protocols/results obtained in our laboratory for long-term storage of adult stem cells using freezing storage.

Porcine Neural Progenitor Cells Derived from Tissue at Different Gestational Ages Can Be Distinguished by Global Transcriptome

The impact of gestational age on mammalian neural progenitor cells is potentially important for both an understanding of neural development and the selection of donor cells for novel cell-based treatment strategies. In terms of the latter, it can be problematic to rely entirely on rodent models in which the gestational period is significantly shorter and the brain much smaller than is the case in humans. Here, we analyzed pig brain progenitor cells (pBPCs) harvested at 2 different gestational ages (E45 and E60) using gene expression profiles, obtained by microarray analysis and quantitative polymerase chain reaction (qPCR), across time in culture. Comparison of the global transcriptome of pBPCs from age-matched transgenic green flourescent protein (GFP)-expressing fetuses versus non-GFP-expressing fetuses did not reveal significant differences between the 2 cell types, whereas comparison between E45 and E60 pBPCs did show separation between the data sets by principle component analysis. Further examination by qPCR showed evidence of relative downregulation of proliferation markers and upregulation of glial markers in the gestationally older (E60) cells. Additional comparisons were made. This study provides evidence of age-related changes in the gene expression of cultured fetal porcine neural progenitors that are potentially relevant to the role of these cells during development and as donor cells for transplantation studies.

Transgenic human embryonic stem cells overexpressing FGF2 stimulate neuroprotection following spinal cord ventral root avulsion

Ventral root avulsion (VRA) triggers a strong glial reaction which contributes to neuronal loss, as well as to synaptic detachment. To overcome the degenerative effects of VRA, treatments with neurotrophic factors and stem cells have been proposed. Thus, we investigated neuroprotection elicited by human embryonic stem cells (hESC), modified to overexpress a human fibroblast growth factor 2 (FGF-2), on motoneurons subjected to VRA. Lewis rats were submitted to VRA (L4-L6) and hESC/FGF-2 were applied to the injury site using a fibrin scaffold. The spinal cords were processed to evaluate neuronal survival, synaptic stability, and glial reactivity two weeks post lesion. Then, qRT-PCR was used to assess gene expression of β2-microglobulin (β2m), TNFα, IL1β, IL6 and IL10 in the spinal cord in vivo and FGF2 mRNA levels in hESC in vitro. The results indicate that hESC overexpressing FGF2 significantly rescued avulsed motoneurons, preserving synaptic covering and reducing astroglial reactivity. The cells were also shown to express BDNF and GDNF at the site of injury. Additionally, engraftment of hESC led to a significant reduction in mRNA levels of TNFα at the spinal cord ventral horn, indicating their immunomodulatory properties. Overall, the present data suggest that hESC overexpressing FGF2 are neuroprotective and can shift gene expression towards an anti-inflammatory environment.

An Evaluation of the Stemness, Paracrine, and Tumorigenic Characteristics of Highly Expanded, Minimally Passaged Adipose-Derived Stem Cells

The use of adipose-derived stem cells (ADSC) in regenerative medicine is rising due to their plasticity, capacity of differentiation and paracrine and trophic effects. Despite the large number of cells obtained from adipose tissue, it is usually not enough for therapeutic purposes for many diseases or cosmetic procedures. Thus, there is the need for culturing and expanding cells in-vitro for several weeks remain. Our aim is to investigate if long- term proliferation with minimal passaging will affect the stemness, paracrine secretions and carcinogenesis markers of ADSC. The immunophenotypic properties and aldehyde dehydrogenase (ALDH) activity of the initial stromal vascular fraction (SVF) and serially passaged ADSC were observed by flow cytometry. In parallel, the telomerase activity and the relative expression of oncogenes and tumor suppressor genes were assessed by q-PCR. We also assessed the cytokine secretion profile of passaged ADSC by an ELISA. The expanded ADSC retain their morphological and phenotypical characteristics. These cells maintained in culture for up to 12 weeks until P4, possessed stable telomerase and ALDH activity, without having a TP53 mutation. Furthermore, the relative expression levels of TP53, RB, and MDM2 were not affected while the relative expression of c-Myc decreased significantly. Finally, the levels of the secretions of PGE₂, STC1, and TIMP2 were not affected but the levels of IL-6, VEGF, and TIMP 1 significantly decreased at P2. Our results suggest that the expansion of passaged ADSC does not affect the differentiation capacity of stem cells and does not confer a cancerous state or capacity in vitro to the cells.

Aging induced loss of stemness with concomitant gain of myogenic properties of a pure population of CD34(+)/CD45(-) muscle derived stem cells

Aging is accompanied by the functional decline of cells, tissues, and organs, as well as, a striking increase in susceptibility to a wide range of diseases. Within a tissue, both differentiated cells and adult stem cells are susceptible to intrinsic and extrinsic changes while aging. Muscle derived stem cells (MDSCs) are tissue specific stem cells which have been studied well for their multipotential nature. Although there are reports relating to diminished function and regenerative capacity of aged MDSCs as compared to their young counterparts, not much has been reported relating to the concomitant gain in unipotent nature of aged MDSCs. In this study, we report an inverse correlation between aging and expression of adult/mesenchymal stem cell markers and a direct correlation between aging and myogenecity in MDSCs. Aged MDSCs were able to generate a greater number of dystrophin positive myofibres, as compared to, the young MDSCs when transplanted in muscle of dystrophic mice. Our data, therefore, suggests that aging stress adds to the decline in stem cell characteristics with a concomitant increase in unipotency, in terms of, myogenecity of MDSCs. This study, hence, also opens the possibilities of using unipotent aged MDSCs as potential candidates for transplantation in patients with muscular dystrophies.

The role of stem cell therapies in degenerative lumbar spine disease: a review

Degenerative conditions of the lumbar spine are extremely common. Ninety percent of people over the age of 60 years have degenerative change on imaging; however, only a small minority of people will require spine surgery (Hicks et al. Spine (Phila Pa 1976) 34(12):1301-1306, 2009). This minority, however, constitutes a core element of spinal surgery practice. Whilst the patient outcomes from spinal surgeries have improved in recent years, some patients will remain with pain and disability despite technically successful surgery. Advances in regenerative medicine and stem cell therapies, particularly the use of mesenchymal stem cells and allogeneic mesenchymal precursor cells, have led to numerous clinical trials utilising these cell-based therapies to treat degenerative spinal conditions. Through cartilage formation and disc regeneration, fusion enhancement or via modification of pain pathways, stem cells are well suited to enhance spinal surgery practice. This review will focus on the outcomes of lumbar spinal procedures and the role of stem cells in the treatment of degenerative lumbar conditions to enhance clinical practice. The current status of clinical trials utilising stem cell therapies will be discussed, providing clinicians with an overview of the various cell-based treatments likely to be available to patients in the near future.

Regenerative medicine for the treatment of spinal cord injury: more than just promises?

Spinal cord injury triggers a complex set of events that lead to tissue healing without the restoration of normal function due to the poor regenerative capacity of the spinal cord. Nevertheless, current knowledge about the intrinsic regenerative ability of central nervous system axons, when in a supportive environment, has made the prospect of treating spinal cord injury a reality. Among the range of strategies under investigation, cell-based therapies offer the most promising results, due to the multifactorial roles that these cells can fulfil. However, the best cell source is still a matter of debate, as are clinical issues that include the optimal cell dose as well as the timing and route of administration. In this context, the role of biomaterials is gaining importance. These can not only act as vehicles for the administered cells but also, in the case of chronic lesions, can be used to fill the permanent cyst, thus creating a more favourable and conducive environment for axonal regeneration in addition to serving as local delivery systems of therapeutic agents to improve the regenerative milieu. Some of the candidate molecules for the future are discussed in view of the knowledge derived from studying the mechanisms that facilitate the intrinsic regenerative capacity of central nervous system neurons. The future challenge for the multidisciplinary teams working in the field is to translate the knowledge acquired in basic research into effective combinatorial therapies to be applied in the clinic.

Ameliorating replicative senescence of human bone marrow stromal cells by PSMB5 overexpression

Multipotent human bone marrow stromal cells (hBMSCs) potentially serve as a source for cell-based therapy in regenerative medicine. However, in vitro expansion was inescapably accompanied with cell senescence, characterized by inhibited proliferation and compromised pluripotency. We have previously demonstrated that this aging process is closely associated with reduced 20S proteasomal activity, with down-regulation of rate-limiting catalytic β-subunits particularly evident. In the present study, we confirmed that proteasomal activity directly contributes to senescence of hBMSCs, which could be reversed by overexpression of the β5-subunit (PSMB5). Knocking down PSMB5 led to decreased proteasomal activity concurrent with reduced cell proliferation in early-stage hBMSCs, which is similar to the senescent phenotype observed in late-stage cells. In contrast, overexpressing PSMB5 in late-stage cells efficiently restored the normal activity of 20S proteasomes and promoted cell growth, possibly via upregulating the Cyclin D1/CDK4 complex. Additionally, PSMB5 could enhance cell resistance to oxidative stress, as evidenced by the increased cell survival upon exposing senescent hBMSCs to hydrogen peroxide. Furthermore, PSMB5 overexpression retained the pluripotency of late-stage hBMSCs by facilitating their neural differentiation both in vitro and in vivo. Collectively, our work reveals a critical role of PSMB5 in 20S proteasome-mediated protection against replicative senescence, pointing to a possible strategy for maintaining the integrity of culture-expanded hBMSCs by manipulating the expression of PSMB5.

Improvement of Contused Spinal Cord in Rats by Cholinergic-like Neuron Therapy

Background

Disability in spinal cord injury is an important medical problem, and cell transplantation is considered as an option for the treatment.

Objectives

The purpose of this study is to use bone marrow stromal cells (BMSCs) derived cholinergic neuron-like cells (CNL) in order to ameliorate the contusion model of spinal cord injury in rats.

Materials and Methods

The CNLs were produced by pre inducing BMSCs with β-mercaptoethanol (BME) followed by inducing with nerve growth factor (NGF). The cells were immunoreactive to neurofilament 200, NeuN, synaptophysin, synapsin, microtubule associated protein-2 and choline acetyl transferase (ChAT). The CNL were transplanted in contused rats (CR), which were sacrificed after 12 weeks.

Results

The results showed that BBB test showed an improvement in the CR, while the quantitative analysis showed that the improvement rate was higher in the rats treated with CNL than those treated with BMSCs only or the untreated animals, similar results were noticed in the improvement index. Immunohistochemical analysis of the tissue section prepared from the CR showed that the transplanted cells were engrafted and integrated in the traumatized spinal cord. The morphometric analysis showed that the volume density of the cavity in the CNL treated rats was significantly lower than that of the untreated ones, while the spinal tissue regeneration index was significantly higher.

Conclusions

The conclusion of the study is that CNL can improve the injured spinal cord.

An analysis and validation pipeline for large-scale RNAi-based screens

Large-scale RNAi-based screens are a major technology, but require adequate prioritization and validation of candidate genes from the primary screen. In this work, we performed a large-scale pooled shRNA screen in mouse embryonic stem cells (ESCs) to discover genes associated with oxidative stress resistance and found several candidates. We then developed a bioinformatics pipeline to prioritize these candidates incorporating effect sizes, functional enrichment analysis, interaction networks and gene expression information. To validate candidates, we mixed normal cells with cells expressing the shRNA coupled to a fluorescent protein, which allows control cells to be used as an internal standard, and thus we could detect shRNAs with subtle effects. Although we did not identify genes associated with oxidative stress resistance, as a proof-of-concept of our pipeline we demonstrate a detrimental role of Edd1 silencing in ESC growth. Our methods may be useful for candidate gene prioritization of large-scale RNAi-based screens.

Aging, cellular senescence, and cancer

For most species, aging promotes a host of degenerative pathologies that are characterized by debilitating losses of tissue or cellular function. However, especially among vertebrates, aging also promotes hyperplastic pathologies, the most deadly of which is cancer. In contrast to the loss of function that characterizes degenerating cells and tissues, malignant (cancerous) cells must acquire new (albeit aberrant) functions that allow them to develop into a lethal tumor. This review discusses the idea that, despite seemingly opposite characteristics, the degenerative and hyperplastic pathologies of aging are at least partly linked by a common biological phenomenon: a cellular stress response known as cellular senescence. The senescence response is widely recognized as a potent tumor suppressive mechanism. However, recent evidence strengthens the idea that it also drives both degenerative and hyperplastic pathologies, most likely by promoting chronic inflammation. Thus, the senescence response may be the result of antagonistically pleiotropic gene action.

Responses of human embryonic stem cells and their differentiated progeny to ionizing radiation

Human embryonic stem cells (hESCs) hold promise for the treatment of many human pathologies. For example, hESCs and the neuronal stem cells (NSCs) and neurons derived from them have significant potential as transplantation therapies for a variety of neurodegenerative diseases. Two concerns about the use of hESCs and their differentiated derivatives are their ability to function and their ability to resist neoplastic transformation in response to stresses that inevitably arise during their preparation for transplantation. To begin to understand how these cells handle genotoxic stress, we examined the responses of hESCs and derived NSCs and neurons to ionizing radiation (IR). Undifferentiated hESCs were extremely sensitive to IR, with nearly all the cells undergoing cell death within 5-7 h. NSCs and neurons were substantially more resistant to IR, with neurons showing the most resistant. Of interest, NSCs that survived IR underwent cellular senescence and acquired astrocytic characteristics. Unlike IR-treated astrocytes, however, the NSC-derived astrocytic cells that survived IR did not display the typical pro-inflammatory, pro-carcinogenic senescence-associated secretory phenotype. These findings suggest distinct genotoxic stress-responses of hESCs and derived NSC and neuronal populations, and suggest that damaged NSCs, while failing to function, may not cause local inflammation.

Upregulation of p16INK4A promotes cellular senescence of bone marrow-derived mesenchymal stem cells from systemic lupus erythematosus patients

Previous studies have indicated that bone marrow-derived mesenchymal stem cells (MSCs) from patients with systemic lupus erythematosus (SLE) exhibited impaired proliferation, differentiation, and immune modulation capacities. Thus, MSCs may be associated with the pathogenesis of SLE. The aim of this study was to determine whether MSCs from SLE patients were senescent and to determine the mechanism underlying this phenomenon. MSCs from both untreated and treated SLE patients showed characteristics of senescence. The expression of p16(INK4A) was significantly increased, whereas levels of CDK4, CDK6 and p-Rb expression were decreased in the MSCs from both untreated and treated SLE patients. Knockdown of p16(INK4A) expression reversed the senescent features of MSCs and upregulated TGF-β expression. In vitro, when purified CD4+ T cells were incubated with p16(INK4A)-silenced SLE MSCs, the percentage of regulatory T cells was significantly increased. Further, we have found that p16(INK4A) promotes MSC senescence via the suppression of the extracellular signal regulated kinase (ERK) pathway. p16(INK4A) knockdown up-regulated ERK1/2 activation. Our results demonstrated that MSCs from SLE patients were senescent and that p16 (INK4A) plays an essential role in the process by inhibiting ERK1/2 activation.

Adult neural stem cells: isolation and propagation

Individualized therapy using adult stem cells constitutes a revolutionary vision for molecular medicine of the future. The field of stem cell biology has accelerated dramatically such that it now appears feasible to treat an individual patient's disease with native or modified stem cells collected from the same patient. Neurodegenerative disease is a high-priority goal for stem cell therapy due to the tremendous clinical urgency to reduce the worldwide suffering associated with this class of diseases. This chapter focuses on adult neural stem cells as a prototype for the general field of adult stem cell therapy. Studies of the origin and function of neural stem cells reveals that the adult brain can generate new neurons. This finding provides the rationale for the therapeutic application of adult neural stem cells to treat neuronal damage or loss. Experimental progress in treating Parkinson's disease is discussed in some detail as an example of one of the most promising areas for adult neural stem cell therapy. Methods for neural stem cell isolation and propagation are included.

Comparative Analysis of Telomere Length, Telomerase and Reverse Transcriptase Activity in Human Dental Stem Cells

Stem cells from dental tissues have been isolated and established for tooth regenerative applications. However, basic characterization on their biological properties still needs to be investigated before employing them for effective clinical trials. In this study, we compared the telomere length, relative telomerase activity (RTA), and relative reverse transcriptase activity (RRA) as well as the surface antigen profile and mesenchymal differentiation ability in human dental papilla stem cells (DPaSCs), dental pulp stem cells (DPuSCs), and dental follicle stem cells (DFSCs) with mesenchymal stem cells (MSCs) derived from bone marrow. Dental stem cells (DSCs) were strongly positive for cell surface markers, such as CD44 and CD90. However, slightly lower expression of CD105 was observed in DPaSCs and DPuSCs compared to DFSCs and MSCs. Following specific induction, DPaSCs, DFSCs, and MSCs were successfully differentiated into adipocytes and osteocytes. However, DPuSCS, in particular, were able to differentiate into adipocytes but failed to induce into osteogenic differentiation. Further, all DSCs, MSCs, and MRC-5 fibroblasts as control were investigated for telomere length by nonradioactive chemiluminescent assay, RTA by relative-quantitative telomerase repeat amplification protocol (RQ-TRAP), and RRA by PCR-based assay. Mean telomere lengths in DPaSCs, DPuSCs, DFSCs, and MSCs was ~11 kb, and the values did not differ significantly ( p < 0.05) among the cells analyzed. RTA levels in DPaSCs were significantly ( p < 0.05) higher than in MSCs, DPuSCs, DFSCs, and MRC-5 fibroblasts and among DSCs, DFSCs showed a significantly ( p < 0.05) lower RTA. Moreover, RRA levels were significantly ( p < 0.05) higher in DPaSCs, DPuSCs, and MSCs than in DFSCs. Based on these observations, we conclude that among DSCs, DPaSCs possessed ideal characteristics on telomere length, telomerase activity and reverse transcriptase (RTase) activity, and may serve as suitable alternative candidates for regenerative medicine.

Biomimetic nanofibrous scaffolds for bone tissue engineering

Bone tissue engineering is a highly interdisciplinary field that seeks to tackle the most challenging bone-related clinical issues. The major components of bone tissue engineering are the scaffold, cells, and growth factors. This review will focus on the scaffold and recent advancements in developing scaffolds that can mimic the natural extracellular matrix of bone. Specifically, these novel scaffolds mirror the nanofibrous collagen network that comprises the majority of the non-mineral portion of bone matrix. Using two main fabrication techniques, electrospinning and thermally-induced phase separation, and incorporating bone-like minerals, such as hydroxyapatite, composite nanofibrous scaffolds can improve cell adhesion, stem cell differentiation, and tissue formation. This review will cover the two main processing techniques and how they are being applied to fabricate scaffolds for bone tissue engineering. It will then cover how these scaffolds can enhance the osteogenic capabilities of a variety of cell types and survey the ability of the constructs to support the growth of clinically relevant bone tissue.

Cell-based therapy for neural disorders--anticipating challenges

Neurological syndromes, such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, Huntington's disease, amyotrophic lateral sclerosis, and lysosomal storage disorders, such as Battens disease, are devastating because they result in increasing loss of cognitive and physical function. Sadly, no drugs are currently available to halt their progression. The relative paucity of curative approaches for these and other conditions of the nervous system have led to a widespread evaluation of alternative treatment modalities including cell-based interventions. Several cell types have been tested successfully in animal models where safety and efficacy have been demonstrated. Early clinical trials have also been initiated in humans, and some have shown a degree of success albeit on a more limited scale than in animal experiments. Recent demonstrations that pluripotent stem cells, such as embryonic stem cells and induced pluripotent stem cells, can differentiate into a variety of specific neural phenotypes has stimulated worldwide enthusiasm for developing cell-based intervention of neurological disease. Indeed, several groups are preparing investigational new drug applications to treat disorders as diverse as macular degeneration, lysosomal storage diseases, and Parkinson's disease. It is noteworthy that cell replacement therapies for neurological conditions face key challenges, some of which are unique, because of the development and organization of the nervous system, its metabolism, and connectivity. Choice of the cell (or cells), the process of manufacturing them, defining the delivery pathway, developing and testing in an appropriate preclinical model, selecting a patient population, and visualizing and following or monitoring patients all pose specific issues as related to the central and peripheral nervous systems. In this review, we address a myriad of challenges that are solvable, but require careful planning and attention to the special demands of the human nervous system.

Stem cell sources for regenerative medicine: the immunological point of view

Stem cell transplantation consists in the introduction of stem cells or derived products in a diseased organism. Because of the differentiation properties of stem cells, the goal is to replace damaged cells or tissues. Numbers of stem cell were identified and isolated from embryos, fetuses, or adult organs, harboring different properties, and thus providing multiple strategies of regenerative medicine for different diseases. More recently, the artificial induction of stemness properties in adult somatic cells has proposed a new way to generate stem cells. One important concern of stem cell therapy is the possible risk that transplanted stem cells could be rejected by the recipient's immune system. Depending on their source, stem cell transplantation is associated with diverse immunological situations. If some sources allow autologous transplantation, others cannot bypass an allogeneic context between the donor and the recipient. This review summarizes all of the stem cell sources for regenerative medicine and the immunological questions associated to their use. Regarding the emerging strategies compatible with autologous transplantation, this article points notably the complexity of the choice between the immunological safety and the specific advantages of allogeneic stem cells.

Deep wells integrated with microfluidic valves for stable docking and storage of cells

In this paper, we describe a microfluidic mechanism that combines microfluidic valves and deep wells for cell localization and storage. Cells are first introduced into the device via externally controlled flow. Activating on-chip valves was used to interrupt the flow and to sediment the cells floating above the wells. Thus, valves could be used to localize the cells in the desired locations. We quantified the effect of valves in the cell storage process by comparing the total number of cells stored with and without valve activation. We hypothesized that in deep wells external flows generate low shear stress regions that enable stable, long-term docking of cells. To assess this hypothesis we conducted numerical calculations to understand the influence of well depth on the forces acting on cells. We verified those predictions experimentally by comparing the fraction of stored cells as a function of the well depth and input flow rate upon activation of the valves. As expected, upon reintroduction of the flow the cells in the deep wells were not moved whereas those in shallow wells were washed away. Taken together, our paper demonstrates that deep wells and valves can be combined to enable a broad range of cell studies.

In vitro regulation of neural differentiation and axon growth by growth factors and bioactive nanofibers

Human embryonic stem cell (ESC)-derived neural cells are a potential cell source for neural tissue regeneration. Understanding the biochemical and biophysical regulation of neural differentiation and axon growth will help us develop cell therapies and bioactive scaffolds. We demonstrated that basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF) had different effects on human ESC differentiation into neural cells. EGF was more effective in inducing expression of neuron and glial markers and cell extensions. In addition to biochemical cues, poly(l-lactic acid) scaffolds with aligned nanofibers increased axon growth from ESC-derived neural cells, demonstrating the significant effects of biophysical guidance at nanoscale. To combine the biochemical and biophysical cues, bFGF and EGF were either adsorbed or bound to heparin on nanofibrous scaffolds. EGF, but not bFGF, was effectively adsorbed onto nanofibers. However, adsorbed EGF and bFGF did not effectively enhance axon growth. In contrast, immobilization of bFGF or EGF onto nanofibers using heparin as the adapter molecule significantly promoted axon growth. This study elucidated the effect of bFGF and EGF in neural differentiation and axon growth, and demonstrated a method to immobilize active bFGF and EGF onto aligned nanofibers to promote neural tissue regeneration.

Preservation protocols for human adipose tissue-derived adult stem cells

The development of simple but effective storage protocols for adult stem cells will greatly enhance their use and utility in tissue-engineering applications. There are three primary storage techniques, freezing (cryopreservation), drying (anhydrobiosis), and freeze drying (lyophilization), each with its own advantages and disadvantages. Cryopreservation has shown the most promise but is a fairly complex process, necessitating the use of chemicals called cryoprotective agents (CPAs), freezing equipment, and obviously, storage in liquid nitrogen. Preservation by desiccation is an alternative that attempts to reproduce a naturally occurring preservative technique, namely, the phenomenon of anhydrobiosis and requires the use of high (and possibly, toxic) concentration of CPAs as well as disaccharides (sugars). Lyophilization works by first cryopreserving (freezing) the material and then desiccating (drying) it by the process of sublimation or the conversion of ice (solid) to water vapor (gas phase). The purpose of this chapter is to present a general overview of these storage techniques and the optimal protocols/results obtained in our laboratory for long-term storage of adult stem cells using freezing storage and drying storage.

In vitro differentiation potential of human embryonic versus adult stem cells

BACKGROUND

There is widespread controversy regarding the potential of human neural stem cells and human mesenchymal stem cells (hMSCs) to form cell types outside of their normal developmental lineage. A greater understanding of the differentiation potential and bias of these stem cell types would allow researchers to select the cell type that best suits the research or clinical need at hand.

MATERIALS & METHODS

We used identical in vitro protocols to quantitatively compare the potential of human embryonic stem cells, human neural stem cells and hMSCs to differentiate into specific ectodermal or mesodermal lineages.

RESULTS

Our findings demonstrate that human embryonic stem cells and human neural stem cells have the ability to differentiate into high purity neuronal progenitor or oligodendrocyte progenitor cultures. By contrast, hMSCs generated exceedingly limited numbers of neural lineages. Both human embryonic stem cells and hMSCs generated adipocytes and osteocytes when exposed to mesodermal differentiation conditions.

CONCLUSION

These studies underscore the importance of distinguishing differentiation potential from differentiation bias, an important consideration in the development of cell replacement strategies.

Predifferentiated embryonic stem cells promote functional recovery after spinal cord compressive injury

We tested the effects of mouse embryonic stem cells (mES) grafts in mice spinal cord injury (SCI). Young adult female C57/Bl6 mice were subjected to laminectomy at T9 and 1-minute compression of the spinal cord with a vascular clip. Four groups were analyzed: laminectomy (Sham), injured (SCI), vehicle (DMEM), and mES-treated (EST). mES pre-differentiated with retinoic acid were injected (8 x 10(5) cells/2 microl) into the lesion epicenter, 10 min after SCI. Basso mouse scale (BMS) and Global mobility test (GMT) were assessed weekly up to 8 weeks, when morphological analyses were performed. GMT analysis showed that EST animals moved faster (10.73+/-0.9076, +/-SEM) than SCI (5.581+/-0.2905) and DMEM (5.705+/-0.2848), but slower than Sham animals (15.80+/-0.3887, p<0.001). By BMS, EST animals reached the final phase of locomotor recovery (3.872+/-0.7112, p<0.01), while animals of the SCI and DMEM groups improved to an intermediate phase (2.037+/-0.3994 and 2.111+/-0.3889, respectively). White matter area and number of myelinated nerve fibers were greater in EST (46.80+/-1.24 and 279.4+/-16.33, respectively) than the SCI group (39.97+/-0.925 and 81.39+/-8.078, p<0.05, respectively). EST group also presented better G-ratio values when compared with SCI group (p<0.001). Immunohistochemical revealed the differentiation of transplanted cells into astrocytes, oligodendrocytes, and Schwann cells, indicating an integration of transplanted cells with host tissue. Ultrastructural analysis showed, in the EST group, better tissue preservation and more remyelination by oligodendrocytes and Schwann cells than the other groups. Our results indicate that acute transplantation of predifferentiated mES into the injured spinal cord increased the spared white matter and number of nerve fibers, improving locomotor function.

Enriched population of PNS neurons derived from human embryonic stem cells as a platform for studying peripheral neuropathies

Background

The absence of a suitable cellular model is a major obstacle for the study of peripheral neuropathies. Human embryonic stem cells hold the potential to be differentiated into peripheral neurons which makes them a suitable candidate for this purpose. However, so far the potential of hESC to differentiate into derivatives of the peripheral nervous system (PNS) was not investigated enough and in particular, the few trials conducted resulted in low yields of PNS neurons. Here we describe a novel hESC differentiation method to produce enriched populations of PNS mature neurons. By plating 8 weeks hESC derived neural progenitors (hESC-NPs) on laminin for two weeks in a defined medium, we demonstrate that over 70% of the resulting neurons express PNS markers and 30% of these cells are sensory neurons.

Methods/Findings

Our method shows that the hNPs express neuronal crest lineage markers in a temporal manner, and by plating 8 weeks hESC-NPs into laminin coated dishes these hNPs were promoted to differentiate and give rise to homogeneous PNS neuronal populations, expressing several PNS lineage-specific markers. Importantly, these cultures produced functional neurons with electrophysiological activities typical of mature neurons. Moreover, supporting this physiological capacity implantation of 8 weeks old hESC-NPs into the neural tube of chick embryos also produced human neurons expressing specific PNS markers in vivo in just a few days. Having the enriched PNS differentiation system in hand, we show for the first time in human PNS neurons the expression of IKAP/hELP1 protein, where a splicing mutation on the gene encoding this protein causes the peripheral neuropathy Familial Dysautonomia.

Conclusions/Significance

We conclude that this differentiation system to produce high numbers of human PNS neurons will be useful for studying PNS related neuropathies and for developing future drug screening applications for these diseases.

Detection of calcium transients in embryonic stem cells and their differentiated progeny

A central issue in stem cell biology is the determination of function and activity of differentiated stem cells, features that define the true phenotype of mature cell types. Commonly, physiological mechanisms are used to determine the functionality of mature cell types, including those of the nervous system. Calcium imaging provides an indirect method of determining the physiological activities of a mature cell. Camgaroos are variants of yellow fluorescent protein that act as intracellular calcium sensors in transfected cells. We expressed one version of the camgaroos, Camgaroo-2, in mouse embryonic stem (ES) cells under the control of the CAG promoter system. Under the control of this promoter, Camgaroo-2 fluorescence was ubiquitously expressed in all cell types derived from the ES cells that were tested. In response to pharmacological stimulation, the fluorescence levels in transfected cells correlated with cellular depolarization and hyperpolarization. These changes were observed in both undifferentiated ES cells as well as ES cells that had been neurally induced, including putative neurons that were differentiated from transfected ES cells. The results presented here indicate that Camgaroo-2 may be used like traditional fluorescent proteins to track cells as well as to study the functionality of stem cells and their progeny.

Growth factor erv1-like modulates Drp1 to preserve mitochondrial dynamics and function in mouse embryonic stem cells

The relationship of mitochondrial dynamics and function to pluripotency are rather poorly understood aspects of stem cell biology. Here we show that growth factor erv1-like (Gfer) is involved in preserving mouse embryonic stem cell (ESC) mitochondrial morphology and function. Knockdown (KD) of Gfer in ESCs leads to decreased pluripotency marker expression, embryoid body (EB) formation, cell survival, and loss of mitochondrial function. Mitochondria in Gfer-KD ESCs undergo excessive fragmentation and mitophagy, whereas those in ESCs overexpressing Gfer appear elongated. Levels of the mitochondrial fission GTPase dynamin-related protein 1 (Drp1) are highly elevated in Gfer-KD ESCs and decreased in Gfer-overexpressing cells. Treatment with a specific inhibitor of Drp1 rescues mitochondrial function and apoptosis, whereas expression of Drp1-dominant negative resulted in the restoration of pluripotency marker expression in Gfer-KD ESCs. Altogether, our data reveal a novel prosurvival role for Gfer in maintaining mitochondrial fission-fusion dynamics in pluripotent ESCs.

Embryonic stem cells promote motor recovery and affect inflammatory cell infiltration in spinal cord injured mice

The purpose of this study was to determine the fate and the effects of undifferentiated embryonic stem cells (ESCs) in mice after contusive lesion of the spinal cord (SCI). Reproducible traumatic lesion to the cord was performed at T8 level by means of the Infinite Horizon Device, and was followed by intravenous injection of one million of undifferentiated ESCs through the tail vein within 2 h from the lesion. The ESCs-treated animals showed a significant improvement of the recovery of motor function 28 days after lesion, with an average score of 4.61+/-0.13 points of the Basso Mouse Scale (n=14), when compared to the average score of vehicle treated mice, 3.58+/-0.23 (n=10). The number of identified ESCs found at the lesion site was 0.6% of the injected cells at 1 week after transplantation, and further reduced to 0.04% at 1 month. It is, thus, apparent that the promoted hind-limb recovery cannot be correlated to a substitution of the lost tissue performed by the exogenous ESC. The extensive evaluation of production of several neuroprotective and inflammatory cytokines did not reveal any effect by ESC-treatment, but unexpectedly the number of invading macrophages and neutrophils was greatly reduced. This may explain the improved preservation of lesion site ventral myelin, at both 1 week (29+/-11%) and 1 month (106+/-14%) after injury. No teratoma formation was observed, although an inappropriate colonization of the sacral cord by differentiated nestin- and beta-tubulin III-positive ESCs was detected.

microRNAs regulate human embryonic stem cell division

microRNAs (miRNAs) regulate numerous physiological processes such as cell division and differentiation in many tissue types including stem cells. To probe the role that miRNAs play in regulating processes relevant to embryonic stem cell biology, we used RNA interference to silence DICER and DROSHA, the two main miRNA processing enzymes. Consistent with a role for miRNAs in maintaining normal stem cell division and renewal, we found that perturbation of miRNA pathway function in human embryonic stem cells (hESCs) attenuates cell proliferation. Normal cell growth can be partially restored by introduction of the mature miRNAs miR-195 and miR-372. These miRNAs regulate two tumor suppressor genes, respectively: WEE1, which encodes a negative G2/M kinase modulator of the CycB/CDK complex and CDKN1A, which encodes p21, a CycE/CDK cyclin dependent kinase inhibitor that regulates the G1/S transition. We show that in wild-type hESCs, WEE 1 levels control the rate of hESC division, whereas p21 levels must be maintained at a low level for hESC division to proceed. These data support a model for hESC cell cycle control in which miRNAs regulate negative cell cycle modulators at two phases of the cell cycle to ensure proper replenishment of the stem cell population.

Induced pluripotent stem cells in regenerative medicine: an argument for continued research on human embryonic stem cells

Human embryonic stem cells (ESCs) can be induced to differentiate into a wide range of tissues that soon could be used for therapeutic applications in regenerative medicine. Despite their developmental potential, sources used to generate human ESC lines raise serious ethical concerns, which recently prompted efforts to reprogram somatic cells back to a pluripotent state. These efforts resulted in the generation of induced pluripotent stem (iPS) cells that are functionally similar to ESCs. However, the genetic manipulations required to generate iPS cells may complicate their growth and developmental characteristics, which poses serious problems in predicting how they will behave when used for tissue-regenerative purposes. In this article we summarize the recently developed methodologies used to generate iPS cells, including those that minimize their genetic manipulation, and discuss several important complicating features of iPS cells that may compromise their future use for therapies in regenerative medicine.

Nicotinamide rescues human embryonic stem cell-derived neuroectoderm from parthanatic cell death

Abundant cell death is observed when human embryonic stem cells (hESCs) undergo neuralization, a critical first step for future cell-based therapies addressing neurodegeneration. Using hESC neuralization as an in vitro model of human development, we demonstrated that the developing neuroepithelium acquires increased susceptibility to spontaneous cell death. We found that poly(ADP-ribose) polymerase-1 (PARP1)/apoptosis-inducing factor (AIF)-mediated cell death (parthanatos) is a dominant mechanism responsible for cell loss during hESC neuralization. The demise of neural progenitor cells, at least in part, is due to decreased endogenous antioxidant defenses and enhanced reactive oxygen species leakage from mitochondria fuelled by nonphysiological culture conditions. Under such conditions, PARP1 overactivation triggered cell death through the mitochondrial-nuclear translocation of AIF. Blocking PARP1 activity with small hairpin RNA interference or nicotinamide dramatically enhanced hESC neuralization, providing optimal survival of the developing neuroepithelium. Because nicotinamide is a physiological metabolite, our results raise the possibility that neural stem/progenitor cell survival in vivo requires a metabolic niche. We argue that small natural metabolites provide a powerful physiological tool to optimize hESC differentiation compatible with the requirements of regenerative medicine.

Stem cell-based therapies for spinal cord injury

Spinal cord injury (SCI) results in loss of nervous tissue and consequently loss of motor and sensory function. There is no treatment available that restores the injury-induced loss of function to a degree that an independent life can be guaranteed. Transplantation of stem cells or progenitors may support spinal cord repair. Stem cells are characterized by self-renewal and their ability to become any cell in an organism. Promising results have been obtained in experimental models of SCI. Stem cells can be directed to differentiate into neurons or glia in vitro, which can be used for replacement of neural cells lost after SCI. Neuroprotective and axon regeneration-promoting effects have also been credited to transplanted stem cells. There are still issues related to stem cell transplantation that need to be resolved, including ethical concerns. This paper reviews the current status of stem cell application for spinal cord repair.

Stem cell-based therapies for spinal cord injury

Spinal cord injury (SCI) results in loss of nervous tissue and consequently loss of motor and sensory function. There is no treatment available that restores the injury-induced loss of function to a degree that an independent life can be guaranteed. Transplantation of stem cells or progenitors may support spinal cord repair. Stem cells are characterized by self-renewal and their ability to become any cell in an organism. Promising results have been obtained in experimental models of SCI. Stem cells can be directed to differentiate into neurons or glia in vitro, which can be used for replacement of neural cells lost after SCI. Neuroprotective and axon regeneration-promoting effects have also been credited to transplanted stem cells. There are still issues related to stem cell transplantation that need to be resolved, including ethical concerns. This paper reviews the current status of stem cell application for spinal cord repair.

Strategies for future histocompatible stem cell therapy

Stem cell therapy based on the safe and unlimited self-renewal of human pluripotent stem cells is envisioned for future use in tissue or organ replacement after injury or disease. A gradual decline of regenerative capacity has been documented among the adult stem cell population in some body organs during the aging process. Recent progress in human somatic cell nuclear transfer and inducible pluripotent stem cell technologies has shown that patient-derived nuclei or somatic cells can be reprogrammed in vitro to become pluripotent stem cells, from which the three germ layer lineages can be generated, genetically identical to the recipient. Once differentiation protocols and culture conditions can be defined and optimized, patient-histocompatible pluripotent stem cells could be directed towards virtually every cell type in the human body. Harnessing this capability to enrich for given cells within a developmental lineage, would facilitate the transplantation of organ/tissue-specific adult stem cells or terminally differentiated somatic cells to improve the function of diseased organs or tissues in an individual. Here, we present an overview of various experimental cell therapy technologies based on the use of patient-histocompatible stem cells, the pending issues needed to be dealt with before clinical trials can be initiated, evidence for the loss and/or aging of the stem cell pool and some of the possible uses of human pluripotent stem cell-derivatives aimed at curing disease and improving health.

Neural stem cells and Alzheimer's disease: challenges and hope

Alzheimer's disease is characterized by degeneration and dysfunction of synapses and neurons in brain regions critical for learning and memory functions. The endogenous generation of new neurons in certain regions of the mature brain, derived from primitive cells termed neural stem cells, has raised hope that neural stem cells may be recruited for structural brain repair. Stem cell therapy has been suggested as a possible strategy for replacing damaged circuitry and restoring learning and memory abilities in patients with Alzheimer's disease. In this review, we outline the promising investigations that are raising hope, and understanding the challenges behind translating underlying stem cell biology into novel clinical therapeutic potential in Alzheimer's disease.

Expression of the p16INK4A Gene Is Associated Closely with Senescence of Human Mesenchymal Stem Cells and Is Potentially Silenced by DNA Methylation During In Vitro Expansion

The precise biological characteristics of human mesenchymal stem cells (hMSCs), including growth regulatory mechanisms, have not yet been defined. Using 29 strains of hMSCs isolated from bone marrow, we have performed extensive analyses of the growth profiles of hMSCs in vitro. All 29 strains stopped proliferating with a mean population doubling (PD) of 28, although there was a considerable difference among strains. The mean telomere restriction fragment length of the cells passaged twice correlated well with the final number of PDs in each strain, suggesting the value of this measurement to be predictive of the growth potential of hMSCs. The expression level of the p16INK4A gene was associated closely with the PD number of each strain (p = .00000001). Most of the p16INK4A-positive cells were Ki67-negative and senescence associated beta-galactosidase-positive, and the suppression of p16INK4A gene expression by small interfering RNA in senescent hMSCs reduced the number of senescent cells and endowed them with the ability to proliferate. Twenty-five of the 29 strains showed a steady gradual increase in the expression of p16INK4A. The remaining four strains (13.8%) showed different profiles, in which DNA methylation in the promoter region occurred in vitro. One of the four strains continued to proliferate for much longer than the others and showed chromosomal aberrations in the later stages. These results indicated p16INK4A to be a key factor in the regulation of hMSC growth, and, most importantly, careful monitoring of DNA methylation should be considered during the culture of hMSCs, particularly when a prolonged and extended propagation is required.

Neural transplantation and stem cells

Recent results have raised important questions on our ability to amplify stem cell populations in sufficient numbers as to be useful for therapy. Several reports have indicated that human stem cell populations harvested from the adult have low or undetectable telomerase levels, age in culture, and may not be propagated indefinitely. Other groups have shown that stem cells age and as such, their properties will have changed depending on the age of the individual from which they are harvested, and the time for which they are propagated in culture. Other groups have shown that cells maintained in culture may undergo alterations as they are propagated, and that these alterations may alter the predicted behavior of stem cells. Yet others have shown that human cells differ from their counterparts in other species in significant ways and have identified important difficulties in assessing cells in a xeno environment. Clinical colleagues have identified issues of variability and difficulties in the long-term follow-up that is being requested. Researchers in the stem cell field focused on translational work need to develop a practical plan that takes into account such difficulties while developing manufacturing protocols, designing animal studies, or developing trial protocols. Such proactive planning will be critical in ensuring a successful transition from the bench to the clinic.

Human embryonic stem cells: origins, characteristics and potential for regenerative therapy

Stem cells and their use in regenerative therapies are currently hot topics in both biology and medicine. For transfusion scientists the concept of cell therapy is not a new idea but rather a fundamental practice in this field. Bone marrow transplantation was pioneered in the 1960s and relies on the capacity of haemopoietic stem cells in the donated bone marrow to completely reconstitute the blood system of the recipient. Although this capacity of adult (or somatic) stem cells to regenerate the tissue from which they arise is extremely important, the isolation and cultivation of human embryonic stem cells (hESCs) have opened up the possibility to generate any cell or tissue of the body. This characteristic of hESC offers the hope of cell replacement and regenerative therapy for a whole array of diseases, many of which are currently untreatable. However, in order to understand the potential advantages and disadvantages of using stem cells in regenerative medicine, it is necessary to fully understand their origin, characteristics and potential. This review will concentrate particularly on hESCs and their derivation, characterization and capacity to differentiate into clinically useful tissue including haemopoietic lineages.