Human embryonic stem cells: origin, properties and applications

The Use of Stem Cell-Derived Organoids in Disease Modeling: An Update

Organoids represent one of the most important advancements in the field of stem cells during the past decade. They are three-dimensional in vitro culturing models that originate from self-organizing stem cells and can mimic the in vivo structural and functional specificities of body organs. Organoids have been established from multiple adult tissues as well as pluripotent stem cells and have recently become a powerful tool for studying development and diseases in vitro, drug screening, and host-microbe interaction. The use of stem cells-that have self-renewal capacity to proliferate and differentiate into specialized cell types-for organoids culturing represents a major advancement in biomedical research. Indeed, this new technology has a great potential to be used in a multitude of fields, including cancer research, hereditary and infectious diseases. Nevertheless, organoid culturing is still rife with many challenges, not limited to being costly and time consuming, having variable rates of efficiency in generation and maintenance, genetic stability, and clinical applications. In this review, we aim to provide a synopsis of pluripotent stem cell-derived organoids and their use for disease modeling and other clinical applications.

Co-administration of TiO2-nanowired dl-3-n-butylphthalide (dl-NBP) and mesenchymal stem cells enhanced neuroprotection in Parkinson's disease exacerbated by concussive head injury

dl-3-n-butylphthalide (dl-NBP) is a powerful antioxidant compound with profound neuroprotective effects in stroke and brain injury. However, its role in Parkinson's disease (PD) is not well known. Traumatic brain injury (TBI) is one of the key factors in precipitating PD like symptoms in civilians and particularly in military personnel. Thus, it would be interesting to explore the possible neuroprotective effects of NBP in PD following concussive head injury (CHI). In this chapter effect of nanowired delivery of NBP together with mesenchymal stem cells (MSCs) in PD with CHI is discussed based on our own investigations. It appears that CHI exacerbates PD pathophysiology in terms of p-tau, α-synuclein (ASNC) levels in the cerebrospinal fluid (CSF) and the loss of TH immunoreactivity in substantia niagra pars compacta (SNpc) and striatum (STr) along with dopamine (DA), dopamine decarboxylase (DOPAC). And homovanillic acid (HVA). Our observations are the first to show that a combination of NBP with MSCs when delivered using nanowired technology induces superior neuroprotective effects in PD brain pathology exacerbated by CHI, not reported earlier.

Embryonic Stem Cells in Clinical Trials: Current Overview of Developments and Challenges

The first isolation of human embryonic stem cells (hESC) reported in the late 90s opened a new window to promising possibilities in the fields of human developmental biology and regenerative medicine. Subsequently, the differentiation of hESC lines into different precursor cells showed their potential in treating different incurable diseases. However, this promising field has consistently had remarkable ethical and experimental limitations. This paper is a review of clinical trial studies dealing with hESC and their advantages, limitations, and other specific concerns. Some of the hESC limitations have been solved, and several clinical trial studies are ongoing so that recent clinical trials have strived to improve the clinical applications of hESC, especially in macular degeneration and neurodegenerative diseases. However, regarding hESC-based therapy, several important issues need more research and discussion. Despite considerable studies to Date, hESC-based therapy is not available for conventional clinical applications, and more studies and data are needed to overcome current clinical and ethical limitations. When all the limitations of Embryonic stem cells (ESC) are wholly resolved, perhaps hESC can become superior to the existing stem cell sources. This overview will be beneficial for understanding the standard and promising applications of cell and tissue-based therapeutic approaches and for developing novel therapeutic applications of hESC.

The STAT3/Slug Axis Enhances Radiation-Induced Tumor Invasion and Cancer Stem-like Properties in Radioresistant Glioblastoma

Glioblastoma multiforme (GBM) requires radiotherapy (RT) as a part of definitive management strategy. RT is highly effective, destroying cancer cells that may exist around the surgical tumor bed. However, GBM still has a poor prognosis and a high local recurrence rate after RT. Accumulating research indicates that GBM contains cancer stem-like cells (CSCs), which are radioresistant and result in therapeutic failure. Additionally, GBM cells can aggressively invade normal brain tissue, inducing therapeutic failure. Using clinical observations, we evaluated the effect of radiation on tumor control. We also explored the biomolecular pathways that connect radioresistance and CSC- and epithelial-mesenchymal transition (EMT)-associated phenotypes in patient-derived GBM cells. Transwell and microarray assay demonstrated that radioresistant GBM cells (GBM-R2I2) exhibit increased invasion and self-renewal abilities compared with parental GBM cells. Finally, to identify potential mechanisms underlying these observations, we used a PCR array to search for molecular markers of cell motility. Signal transducer and activator of transcription 3 (STAT3) directly bound to the Slug promoter in a chromatin immunoprecipitation assay. Reduced STAT3 decreased Slug expression and suppressed cell invasion in GBM-R2I2 cells while increasing Slug reversed these effects. In addition, STAT3 knockdown significantly inhibited CSC properties, synergistically increased the radiotherapeutic effect, and effectively increased the survival rate in vivo. We deciphered a new pathway of GBM radioresistance, invasion, and recurrence via the STAT3/Slug axis that could be a new target of GBM therapy.

I, Pandey S, Panda BSK, Thakur N, Sarkar M, Chandra V, Saikumar G, Sharma GT. A Comparative Study of Growth Kinetics, In Vitro Differentiation Potential and Molecular Characterization of Fetal Adnexa Derived Caprine Mesenchymal Stem Cells

The present study was conducted with an objective of isolation, in vitro expansion, growth kinetics, molecular characterization and in vitro differentiation of fetal adnexa derived caprine mesenchymal stem cells. Mid-gestation gravid caprine uteri (2–3 months) were collected from abattoir to derive mesenchymal stem cells (MSCs) from fetal adnexa {amniotic fluid (cAF), amniotic sac (cAS), Wharton’s jelly (cWJ) and cord blood (cCB)} and expanded in vitro. These cultured MSCs were used at the 3^rd passage (P3) to study growth kinetics, localization as well as molecular expression of specific surface antigens, pluripotency markers and mesenchymal tri-lineage differentiation. In comparison to cAF and cAS MSCs, cWJ and cCB MSCs showed significantly (P<0.05) higher clonogenic potency, faster growth rate and low population doubling (PDT) time. All the four types of MSCs were positive for alkaline phosphatase (AP) and differentiated into chondrogenic, osteogenic, and adipogenic lineages. These stem cells expressed MSC surface antigens (CD73, CD90 and CD105) and pluripotency markers (Oct4, Sox2, Nanog, KLF, cMyc, FoxD3) but did not express CD34, a hematopoietic stem cell marker (HSC) as confirmed by RT-PCR, immunocytochemistry and flow cytometric analysis. The relative mRNA expression of MSC surface antigens (CD73, CD90 and CD105) was significantly (P<0.05) higher in cWJ MSCs compared to the other cell lines. The mRNA expression of Oct4 was significantly (P<0.05) higher in cWJ, whereas mRNA expression of KLF and cMyc was significantly (P<0.05) higher in cWJ and cAF than that of cAS and cCB. The comparative assessment revealed that cWJ MSCs outperformed MSCs from other sources of fetal adnexa in terms of growth kinetics, relative mRNA expression of surface antigens, pluripotency markers and tri-lineage differentiation potential, hence, these MSCs could be used as a preferred source for regenerative medicine.

In vitro culture of stem-like cells derived from somatic cell nuclear transfer bovine embryos of the Korean beef cattle species, HanWoo

We established and maintained somatic cell nuclear transfer embryo-derived stem-like cells (SCNT-eSLCs) from the traditional Korean beef cattle species, HanWoo (Bos taurus coreanae). Each SCNT blastocyst was placed individually on a feeder layer with culture medium containing three inhibitors of differentiation (3i). Primary colonies formed after 2-3 days of culture and the intact colonies were passaged every 5-6 days. The cells in each colony showed embryonic stem cell-like morphologies with a distinct boundary and were positive to alkaline phosphatase staining. Immunofluorescence and reverse transcription-polymerase chain reaction analyses also confirmed that these colonies expressed pluripotent markers. The colonies were maintained over 50 passages for more than 270 days. The cells showed normal karyotypes consisting of 60 chromosomes at Passage 50. Embryoid bodies were formed by suspension culture to analyse in vitro differentiation capability. Marker genes representing the differentiation into three germ layers were expressed. Typical embryonal carcinoma was generated after injecting cells under the testis capsule of nude mice, suggesting that the cultured cells may also have the potential of in vivo differentiation. In conclusion, we generated eSLCs from SCNT bovine embryos, using a 3i system that sustained stemness, normal karyotype and pluripotency, which was confirmed by in vitro and in vivo differentiation.

Tissue engineering of the temporomandibular joint disc: current status and future trends

INTRODUCTION

Temporomandibular joint disorders are extremely prevalent and there is no ideal treatment clinically for the moment. For severe cases, a discectomy often need to be performed, which will further result in the development of osteoarthritis. In the past thirty years, tissue engineering has provided a promising approach for the effective remedy of severe TMJ disease through the creation of viable, effective, and biological functional implants.

METHODS

Although TMJ disc tissue engineering is still in early stage, unremitting efforts and some achievements have been made over the past decades. In this review, a comprehensive summary of the available literature on the progress and status in tissue engineering of the TMJ disc regarding cell sources, scaffolds, biochemical and biomechanical stimuli, and other prospects relative to this field is provided.

RESULTS AND CONCLUSIONS

Even though research studies in this field are too few compared to other fibrocartilage (e.g., knee meniscus) and numerous, difficult tasks still exist, we believe that our ultimate goal of regenerating a biological implant whose histological, biochemical, and biomechanical properties parallel native TMJ discs for clinical therapy will be achieved in the near future.

Reproductive stem cell differentiation: extracellular matrix, tissue microenvironment, and growth factors direct the mesenchymal stem cell lineage commitment

The mesenchymal stem cells (MSCs) have awakened interest in regenerative medicine due to its high capability to proliferate and differentiate in multiple specialized lineages under defined conditions. The reproductive system is considered a valuable source of MSCs, which needs further investigations. Many factors have been reported as critical for these cell lineage specification and determination. In this review, we discuss the main effects of extracellular matrix or tissue environment and growth factors in the cell lineage commitment, including the reproductive stem cells. The MSCs responses to culture medium stimuli or to soluble factors probably occur through several intracellular activation pathways. However, the molecular mechanisms in which the cells respond to these mechanical or chemical perturbations remain elusive. Recent findings suggest a synergic effect of microenvironment and soluble cell culture factors affecting cell differentiation. For future applications in cell therapy, protocols of reproductive MSCs differentiation must be established.

[Oro-maxillofacial bone tissue engineering combining biomaterials, stem cells, and gene therapy]

Improvements have been made in regenerative medicine, due to the development of tissue engineering and cellular therapy. Bone regeneration is an ambitious project, leading to many applications involving skull, maxillofacial, and orthopaedic surgery. Scaffolds, stem cells, and signals support bone tissue engineering. The scaffold physical and chemical properties promote cell invasion, guide their differentiation, and enable signal transmission. Scaffold may be inorganic or organic. Their conception was improved by the use of new techniques: self-assembled nanofibres, electrospinning, solution-phase separation, micropatterned hydrogels, bioprinting, and rapid prototyping. Cellular biology processes allow us to choose between embryonic stem cells or adult stem cells for regenerative medicine. Finally, communication between cells and their environment is essential; they use various signals to do so. The study of signals and their transmission led to the discovery and the use of Bone Morphogenetic Protein (BMP). The development of cellular therapy led to the emergence of a specific field: gene therapy. It relies on viral vectors, which include: retroviruses, adenoviruses and adeno-associated vectors (AAV). Non-viral vectors include plasmids and lipoplex. Some BMP genes have successfully been transfected. The ability to control transfected cells and the capacity to combine and transfect many genes involved in osseous healing will improve gene therapy.

Effect of leukotriene D4 on mouse embryonic stem cell migration and proliferation: involvement of PI3K/Akt as well as GSK-3β/β-catenin signaling pathways

The actual leukotriene D(4) (LTD(4)) signaling pathways that regulate cell proliferation have not been elucidated thoroughly although fatty acid and its metabolites play a key role in regulations of embryonic functions. Thus, this study investigated the response of mouse embryonic stem (ES) cells exposed to LTD(4) and elucidated the signaling pathways as well. LTD(4) increased DNA synthesis in concentration-dependent (≥10(-7) M) and time-dependent (≥12 h) manners, as determined by [(3)H] thymidine incorporation and increased cell number. LTD(4) induced the phosphorylation of signal transducer and activator of transcription-3 (STAT3) and the increase of intracellular Ca(2+) levels via cysteinyl leukotriene (CysLT) 1 and 2 receptors. LTD(4) increased Akt activation and calcineurin expression, which were blocked by STAT3 inhibitor and calcium chelators. LTD(4)-induced glycogen synthase kinase (GSK)-3β phosphorylation was decreased by LY294002, Akt inhibitor, and cyclosporine A. LTD(4) inhibited the phosphorylation of β-catenin. In addition, LTD(4)-stimulated migration through increased activation of focal adhesion kinase (FAK) and paxillin which were blocked by Akt inhibitor and cyclosporine A. LTD(4)-induced increases in protooncogene and cell cycle regulatory proteins were blocked by cyclosporine A, FAK siRNA, and β-catenin siRNA. In conclusion, LTD(4)-stimulated mouse ES cell proliferation and migration via STAT3, phosphoinositide 3-kinases (PI3K)/Akt, Ca(2+)-calcineurin, and GSK-3β/β-catenin pathway.

Establishment and characterization of human embryonic stem cell lines, Turkey perspectives

Human embryonic stem cells (hESC), which are derived from the inner cell mass (ICM) of blastocyst stage embryos, are of great importance because of their unpredictable two unique features: their differentiation ability into all types of cells derived from three germ layers and their potentially unlimited capacity of self renewing with stable karyotype. These distinguished properties make hESC very promising cell source for regenerative medicine, tissue replacement therapies, and drug screening studies as well as genomics. However, due to the several technical problems, such as risk of teratoma formation, immune response, and unknown genetic pathways for lineage specific differentiation, and ethical drawbacks of their using in clinical treatments, hESC researches are still waiting to advance beyond to animal trials and drug studies. During the last decade, more than 300 new hESC lines have been derived and published by researchers worldwide. However, despite their similar well-known unique properties, recent studies reported that hESC lines have very individual properties and are differed from each other with regards to their differentiation ability and gene expression profiles. Therefore, all hESC lines should be characterized in detail and then registered in a stem cell bank for generating global database. In this report, the characteristic of hESC lines, which were established in Istanbul Memorial Hospital between 2003 and 2005, and derivation methods were described in detail to inform researchers and to facilitate new prospective cooperative studies.

Adipose stem cells for intervertebral disc regeneration: current status and concepts for the future

New regenerative treatment strategies are being developed for intervertebral disc degeneration of which the implantation of various cell types is promising. All cell types used so far require in vitro expansion prior to clinical use, as these cells are only limited available. Adipose-tissue is an abundant, expendable and easily accessible source of mesenchymal stem cells. The use of these cells therefore eliminates the need for in vitro expansion and subsequently one-step regenerative treatment strategies can be developed. Our group envisioned, described and evaluated such a one-step procedure for spinal fusion in the goat model. In this review, we summarize the current status of cell-based treatments for intervertebral disc degeneration and identify the additional research needed before adipose-derived mesenchymal stem cells can be evaluated in a one-step procedure for regenerative treatment of the intervertebral disc. We address the selection of stem cells from the stromal vascular fraction, the specific triggers needed for cell differentiation and potential suitable scaffolds. Although many factors need to be studied in more detail, potential application of a one-step procedure for intervertebral disc regeneration seems realistic.

Effect of passage and topography on gene expression of temporomandibular joint disc cells

The temporomandibular joint (TMJ) disc is maintained by a population of fibrochondrocytes. Although articular chondrocytes exhibit zonal differences and de-differentiate in monolayer culture, such variations are unknown for fibrochondrocytic populations. This study's objective was to define topographical cellular variations in the porcine TMJ disc and investigate changes in the disc's gene expression levels over multiple passages using quantitative reverse transcriptase polymerase chain reaction. For topographical characterization, samples were acquired from posterior, anterior, lateral, medial, and intermediate zone sections and subdivided into inferior and superior halves. For passage characterization, cells were plated and passaged for 35 days, with samples acquired at every passage. The medial region had the lowest expression of genes indicative of fibroblastic activity, but in general, topographical variations were limited. Passage effects were evident; gene expression levels of aggrecan, collagen type I, and collagen type II dropped 20%, 23%, and 73% per passage, respectively. In contrast, decorin and glyseraldehyde-3-phosphate dehydrogenase gene expression increased 33% and 27% per passage, respectively. These data indicate that TMJ disc cells undergo significant changes due to monolayer expansion, experiencing losses in major chondrocytic markers (aggrecan and collagen type II) and fibroblastic markers (collagen type I) and posing a serious impediment to studies in which cell passaging is required.

Combination of automated high throughput platforms, flow cytometry, and hierarchical clustering to detect cell state

BACKGROUND

This study examined whether hierarchical clustering could be used to detect cell states induced by treatment combinations that were generated through automation and high-throughput (HT) technology. Data-mining techniques were used to analyze the large experimental data sets to determine whether nonlinear, non-obvious responses could be extracted from the data.

METHODS

Unary, binary, and ternary combinations of pharmacological factors (examples of stimuli) were used to induce differentiation of HL-60 cells using a HT automated approach. Cell profiles were analyzed by incorporating hierarchical clustering methods on data collected by flow cytometry. Data-mining techniques were used to explore the combinatorial space for nonlinear, unexpected events. Additional small-scale, follow-up experiments were performed on cellular profiles of interest.

RESULTS

Multiple, distinct cellular profiles were detected using hierarchical clustering of expressed cell-surface antigens. Data-mining of this large, complex data set retrieved cases of both factor dominance and cooperativity, as well as atypical cellular profiles. Follow-up experiments found that treatment combinations producing "atypical cell types" made those cells more susceptible to apoptosis. CONCLUSIONS Hierarchical clustering and other data-mining techniques were applied to analyze large data sets from HT flow cytometry. From each sample, the data set was filtered and used to define discrete, usable states that were then related back to their original formulations. Analysis of resultant cell populations induced by a multitude of treatments identified unexpected phenotypes and nonlinear response profiles.

Checkpoint-apoptosis uncoupling in human and mouse embryonic stem cells: a source of karyotpic instability

Karyotypic abnormalities in cultured embryonic stem cells (ESCs), especially near-diploid aneuploidy, are potential obstacles to ESC use in regenerative medicine. Events causing chromosomal abnormalities in ESCs may be related to events in tumor cells causing chromosomal instability (CIN) in human disease. However, the underlying mechanisms are unknown. Using multiparametric permeabilized-cell flow cytometric analysis, we found that the mitotic-spindle checkpoint, which helps maintain chromosomal integrity during all cell divisions, functions in human and mouse ESCs, but does not initiate apoptosis as it does in somatic cells. This allows an unusual tolerance to polyploidy resulting from failed mitosis, which is common in rapidly proliferating cell populations and which is reduced to near-diploid aneuploidy, which is also common in human neoplastic disease. Checkpoint activation in ESC-derived early-differentiated cells results in robust apoptosis without polyploidy/aneuploidy similar to that in somatic cells. Thus, the spindle checkpoint is "uncoupled" from apoptosis in ESCs and is a likely source of karyotypic abnormalities. This natural behavior of ESCs to tolerate/survive varying degrees of ploidy change could complicate genome-reprogramming studies and stem-cell plasticity studies, but could also reveal clues about the mechanisms of CIN in human tumors.

Stem cells for regeneration of urological structures

OBJECTIVES

This review focuses on advances in regenerative therapies using stem cells in urology.

METHODS

A detailed literature search was performed using the PubMed database of the National Center of Biotechnology Information. Publications of experimental investigations and clinical trials using stem cells in reconstructive urology have been summarized and critically reviewed.

RESULTS

Tissue engineering and autologous cell therapy techniques have been developed to generate prostheses for different urological tissues and organ systems. During the last decade, increasing numbers of studies have described stem cells in the context of therapeutic tools. The ability of adult and embryonic stem cells as well as progenitors to improve bladder wall architecture, improve renal tubule formation, or promote restoration of spermatogenesis or recovery of continence has been investigated in several animal models. Although results have been encouraging, only a myoblast-based therapy of incontinence has reached clinical trials.

CONCLUSIONS

Several populations of adult stem cells and progenitor cells have been studied as useful cellular sources in the treatment and reconstruction of urological organs. However, considerable basic research still needs to be performed to ensure the controlled differentiation and long-term fate of stem cells following transplantation.

Microchimerism and Stem Cell Transplantation in Multiple Sclerosis

Scientific advances have demonstrated that autoreactive cells are a component of the healthy immune repertoire. If we define autoimmunity as an active induction of autoreaction, the solution should be an active induction of self-tolerance, and may indicate the direction to explore the future therapies. Microchimerism (MC) refers to the presence of a limited number of nonhost cells in the body of an individual. These cells can enter via blood transfusion and organ transplantation or naturally through pregnancy. Chimeric cells engraft in the host body, develop, proliferate, and are accepted by the immune system as self. These include stem cells that enter the maternal body during fetal stages. These stem cells are also postulated to be helpful reservoirs in protecting the host body. MC has been considered a risk factor in autoimmune disease induction. However, today we know it is a natural phenomenon. MC can be considered a natural model of successful transplantation, the earliest engrafting cells being fetal mesenchymal stem cells (MSCs). MSCs have two notable features. They have an immunosuppressive quality when encountering the adoptive immune system and they display repair-inducing potential within damaged tissues. For the fetus, MC appears to be an effective factor in maternal tolerance induction toward the fetal graft and for the mother; these novel fetal cells might be useful in disease conditions occurring after pregnancy. Hematopoietic stem cell transplantation has become an accepted treatment option for both malignant and nonmalignant diseases and this unique procedure is now being investigated as a potential therapy for multiple sclerosis (MS). Due to the dichotomous properties of MSC, suppressing aggressive immune dysfunction while promoting damaged tissue repair, they may be appropriate therapy for MS.

Growth factor effects on passaged TMJ disk cells in monolayer and pellet cultures

OBJECTIVES

Previously, we demonstrated rapid changes in temporomandibular joint (TMJ) disk gene expression during monolayer expansion. This study's objective was to investigate the ability of pellet culture and growth factors to rescue TMJ disk gene expression changes.

DESIGN

Temporomandibular joint disk cells were isolated from mature porcine tissue and passaged up to five times. At each passage, 300 000 cells were placed in a monolayer or pellet culture environment before being exposed to transforming growth factor-beta 3 (TGF-beta3) (5 ng/ml), TGF-beta1 (5 ng/ml), and insulin-like growth factor I (IGF-I) (10 ng/ml).

OUTCOME MEASURE

After 24 h, gene expression was analyzed via reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

Pelleting was detrimental to TMJ disk gene expression, marked by gene expression decreases in collagen type I (5.5-fold), aggrecan (1.4-fold), decorin (0.73-fold), and biglycan (0.73-fold) relative to monolayer cultures. IGF-I, TGF-beta1, and TGF-beta3 demonstrated limited ability to rescue TMJ disk gene expression in the pellet culture. In monolayer, TGF-beta3 and TGF-beta1 increased decorin and biglycan gene expression relative to passaged controls. Collagen type I expression, the TMJ disk's primary matrix constituent, was highest in TGF-beta3 cultures; however, differences were not statistically significant.

CONCLUSION

These results indicate that pellet cultures are a poor choice for TMJ disk tissue engineering, and the effects of TGF-beta1, TGF-beta3, and IGF-I on TMJ disk gene expression are minimal relative to passaging and pelleting effects.

Human embryo and early fetus research

Studies of human embryos and fetuses have highlighted developmental differences between humans and model organisms. In addition to describing the normal biology of our own species, a justification in itself, studies of early human development have aided identification of candidate disease genes mapped by positional cloning strategies, understanding pathophysiology, where human disorders are not faithfully reproduced by models in other species, and, more recently, potential therapies based on human embryonic stem and embryonic germ cells. In this article, we review these applications. We also discuss when and how to study human embryo and early fetuses and some of the regulations of this research.

Differences between human embryonic stem cell lines

The promise of human embryonic stem cell (hESC) lines for treating injuries and degenerative diseases, for understanding early human development, for disease modelling and for drug discovery, has brought much excitement to scientific communities as well as to the public. Although all of the lines derived worldwide share the expression of characteristic pluripotency markers, many differences are emerging between lines that may be more associated with the wide range of culture conditions in current use than the inherent genetic variation of the embryos from which embryonic stem cells were derived. Thus, the validity of many comparisons between lines published thus far is difficult to interpret. This article reviews the evidence for differences between lines, focusing on studies of pluripotency marker molecules, transcriptional profiling, genetic stability and epigenetic stability, for which there is most evidence. Recognition and assessment of environmentally induced differences will be important to facilitate the development of culture systems that maximize stability in culture and provide lines with maximal potential for safety and success in the range of possible applications.

Regeneration of intervertebral disc by mesenchymal stem cells: potentials, limitations, and future direction

Over the past few years, substantial progress has been made in the field of stem cell regeneration of the intervertebral disc. Autogenic mesenchymal stem cells in animal models can arrest intervertebral disc degeneration or even partially regenerate it and the effect is suggested to be dependent on the severity of degeneration. Mesenchymal stem cells (MSCs) are able to escape alloantigen recognition which is an advantage for allogenic transplantation. A number of injectable scaffolds have been described and various methods to pre-modulate MSCs' activity have been tested. In future, work will need to address the use of mesenchymal stem cells in large animal models and the fate of the implanted mesenchymal stem cells, particularly in the long term, in animals. This review examines the state-of-the-art in the field of stem cell regeneration of the intervertebral disc, and critically discusses, with scientific support, the issues involved, before stem cells could be used in human subjects.