Derivation of clinically compliant MSCs from CD105+, CD24- differentiated human ESCs

Human Gingival Integration-Free iPSCs; a Source for MSC-Like Cells

Mesenchymal stem cells (MSCs) are considered a potential autologous therapy for tissue engineering. The available procedures for MSC retrieval from patients are invasive, and their limited in vitro proliferation restricts their use in the treatment of damaged tissues. Therefore, it is important to establish an alternative and safe source of MSCs. The objective of this study was to demonstrate induced pluripotent stem cell (iPSC) generation from a combination of an accessible source tissue and an integration-free method; we also attempted the differentiation of iPSCs into MSC-like cells (MSLCs) for future autologous tissue engineering. iPSCs were derived from human gingival tissues, which are easily accessible in the field of dentistry, via the use of non-integrating episomal plasmids. Established iPSCs expressed embryonic stem (ES) cell-specific markers, as assessed by gene analysis and immunocytochemistry. Embryoid bodies and teratoma formation were formed from iPSCs, showing their capacity to differentiate into three germ layers. Furthermore, we were successful in differentiating iPSCs into MSLCs. They tested positively for their capacity of trilineage differentiation. Our results demonstrate that human gingival integration-free iPSCs, readily accessible stem cells generated using episomal plasmid vectors, are a promising source of MSLCs, which can be used in tissue regeneration.

Mesenchymal Stromal Cell-Like Cells Set the Balance of Stimulatory and Inhibitory Signals in Monocyte-Derived Dendritic Cells

The major reservoir of human multipotent mesenchymal stem/stromal cells (MSCs) is the bone marrow (BM) with the capability to control hematopoietic stem cell development. The regenerative potential of MSCs is associated with enhanced endogenous repair and healing mechanisms that modulate inflammatory responses. Our previous results revealed that MSC-like (MSCl) cells derived from pluripotent human embryonic stem cells resemble BM-derived MSCs in morphology, phenotype, and differentiating potential. In this study, we investigated the effects of MSCl cells on the phenotype and functions of dendritic cells (DCs). To assess how antiviral immune responses could be regulated by intracellular pattern recognition receptors of DCs in the presence of MSCl cells, we activated DCs with the specific ligands of retinoic acid-inducible gene-I (RIG-I) helicases and found that activated DCs cocultured with MSCl cells exhibited reduced expression of CD1a and CD83 cell surface molecules serving as phenotypic indicators of DC differentiation and activation, respectively. However, RIG-I-mediated stimulation of DCs through specific ligands in the presence of MSCl cells resulted in significantly higher expression of the costimulatory molecules, CD80 and CD86, than in the presence of BM-MSCs. In line with these results, the concentration of IL-6, IL-10, and CXCL8 was increased in the supernatant of the DC-MSCl cocultures, while the secretion of TNF-α, CXCL10, IL-12, and IFNγ was reduced. Furthermore, the concerted action of mechanisms involved in the regulation of DC migration resulted in the blockade of cell migration, indicating altered DC functionality mediated by MSCl cell-derived signals and mechanisms resulting in a suppressive microenvironment.

Augmenting peripheral nerve regeneration using stem cells: A review of current opinion

Outcomes following peripheral nerve injury remain frustratingly poor. The reasons for this are multifactorial, although maintaining a growth permissive environment in the distal nerve stump following repair is arguably the most important. The optimal environment for axonal regeneration relies on the synthesis and release of many biochemical mediators that are temporally and spatially regulated with a high level of incompletely understood complexity. The Schwann cell (SC) has emerged as a key player in this process. Prolonged periods of distal nerve stump denervation, characteristic of large gaps and proximal injuries, have been associated with a reduction in SC number and ability to support regenerating axons. Cell based therapy offers a potential therapy for the improvement of outcomes following peripheral nerve reconstruction. Stem cells have the potential to increase the number of SCs and prolong their ability to support regeneration. They may also have the ability to rescue and replenish populations of chromatolytic and apoptotic neurons following axotomy. Finally, they can be used in non-physiologic ways to preserve injured tissues such as denervated muscle while neuronal ingrowth has not yet occurred. Aside from stem cell type, careful consideration must be given to differentiation status, how stem cells are supported following transplantation and how they will be delivered to the site of injury. It is the aim of this article to review current opinions on the strategies of stem cell based therapy for the augmentation of peripheral nerve regeneration.

Umbilical cord mesenchymal stromal cells affected by gestational diabetes mellitus display premature aging and mitochondrial dysfunction

Human umbilical cord mesenchymal stromal cells (hUC-MSCs) of Wharton's jelly origin undergo adipogenic, osteogenic, and chondrogenic differentiation in vitro. Recent studies have consistently shown their therapeutic potential in various human disease models. However, the biological effects of major pregnancy complications on the cellular properties of hUC-MSCs remain to be studied. In this study, we compared the basic properties of hUC-MSCs obtained from gestational diabetes mellitus (GDM) patients (GDM-UC-MSCs) and normal pregnant women (N-UC-MSCs). Assessments of cumulative cell growth, MSC marker expression, cellular senescence, and mitochondrial function-related gene expression were performed using a cell count assay, senescence-associated β-galactosidase staining, quantitative real-time reverse transcription-polymerase chain reaction, immunoblotting, and cell-based mitochondrial functional assay system. When compared with N-UC-MSCs, GDM-UC-MSCs showed decreased cell growth and earlier cellular senescence with accumulation of p16 and p53, even though they expressed similar levels of CD105, CD90, and CD73 MSC marker proteins. GDM-UC-MSCs also displayed significantly lower osteogenic and adipogenic differentiation potentials than N-UC-MSCs. Furthermore, GDM-UC-MSCs exhibited a low mitochondrial activity and significantly reduced expression of the mitochondrial function regulatory genes ND2, ND9, COX1, PGC-1α, and TFAM. Here, we report intriguing and novel evidence that maternal metabolic derangement during gestation affects the biological properties of fetal cells, which may be a component of fetal programming. Our findings also underscore the importance of the critical assessment of the biological impact of maternal-fetal conditions in biological studies and clinical applications of hUC-MSCs.

Ethical considerations in stem cell research on neurologic and orthopedic conditions

The range and gravity of ethical considerations in stem cell research are remarkable and, quite possibly, unprecedented. From the point of securing stem cells for implantation, through the translational and first-in-humans process, and then proceeding through clinical trials culminating in product or service line launch, the entire research trajectory is replete with risk, uncertainty, and problems overweighing foreseeable harms against hoped-for benefits. This article offers an overview of some of the most salient ethical challenges of stem cell research, including ones involving moral status, the intersection of research risks and informed consent processes, methodologic considerations in early phase 1 trials, the temptation to exaggerate the benefits of research discoveries, managing conflicts of interest, and the ethical obligation to conduct various monitoring practices throughout a trial, which could last years. The article will conclude with a glimpse into the future of these technologies wherein the need for ethical scrutiny will likely not diminish.

A therapy-grade protocol for differentiation of pluripotent stem cells into mesenchymal stem cells using platelet lysate as supplement

Introduction

Mesenchymal stem cells (MSCs) are a promising source of cells for regenerative therapies. Although they can be isolated easily from several tissues, cell expansion is limited since their properties are lost with successive passages. Hence, pluripotent derived MSCs (PD-MSCs) arise as a suitable alternative for MSC production. Nevertheless, at present, PD-MSC derivation protocols are either expensive or not suitable for clinical purposes.

Methods

In this work we present a therapy-grade, inexpensive and simple protocol to derive MSCs from pluripotent stem cells (PSCs) based on the use of platelet lysate (PL) as medium supplement.

Results

We showed that the PD-MSC_PL expressed multiple MSC markers, including CD90, CD73, CD105, CD166, and CD271, among others. These cells also show multilineage differentiation ability and immunomodulatory effects on pre-stimulated lymphocytes. Thorough characterization of these cells showed that a PD-MSC_PL resembles an umbilical cord (UC) MSC and differs from a PSC in surface marker and extracellular matrix proteins and integrin expression. Moreover, the OCT-4 promoter is re-methylated with mesenchymal differentiation comparable with the methylation levels of UC-MSCs and fibroblasts. Lastly, the use of PL-supplemented medium generates significantly more MSCs than the use of fetal bovine serum.

Conclusions

This protocol can be used to generate a large amount of PD-MSCs with low cost and is compatible with clinical therapies.

Electronic supplementary material

The online version of this article (doi:10.1186/scrt540) contains supplementary material, which is available to authorized users.

MSCs derived from iPSCs with a modified protocol are tumor-tropic but have much less potential to promote tumors than bone marrow MSCs

Mesenchymal stem or stromal cells (MSCs) have many potential therapeutic applications including therapies for cancers and tissue damages caused by cancers or radical cancer treatments. However, tissue-derived MSCs such as bone marrow MSCs (BM-MSCs) may promote cancer progression and have considerable donor variations and limited expandability. These issues hinder the potential applications of MSCs, especially those in cancer patients. To circumvent these issues, we derived MSCs from transgene-free human induced pluripotent stem cells (iPSCs) efficiently with a modified protocol that eliminated the need of flow cytometric sorting. Our iPSC-derived MSCs were readily expandable, but still underwent senescence after prolonged culture and did not form teratomas. These iPSC-derived MSCs homed to cancers with efficiencies similar to BM-MSCs but were much less prone than BM-MSCs to promote the epithelial-mesenchymal transition, invasion, stemness, and growth of cancer cells. The observations were probably explained by the much lower expression of receptors for interleukin-1 and TGFβ, downstream protumor factors, and hyaluronan and its cofactor TSG6, which all contribute to the protumor effects of BM-MSCs. The data suggest that iPSC-derived MSCs prepared with the modified protocol are a safer and better alternative to BM-MSCs for therapeutic applications in cancer patients. The protocol is scalable and can be used to prepare the large number of cells required for "off-the-shelf" therapies and bioengineering applications.

Biomimetic Material-Assisted Delivery of Human Embryonic Stem Cell Derivatives for Enhanced In Vivo Survival and Engraftment

The ability of human embryonic stem cells (hESCs) and their derivatives to differentiate and contribute to tissue repair has enormous potential to treat various debilitating diseases. However, improving the in vivo viability and function of the transplanted cells, a key determinant of translating cell-based therapies to the clinic, remains a daunting task. Here, we develop a hybrid biomaterial consisting of hyaluronic acid (HA) grafted with 6-aminocaproic acid moieties (HA-6ACA) to improve cell delivery and their subsequent in vivo function using skeletal muscle as a model system. Our findings show that the biomimetic material-assisted delivery of hESC-derived myogenic progenitor cells into cardiotoxin-injured skeletal muscles of NOD/SCID mice significantly promotes survival and engraftment of transplanted cells in a dose-dependent manner. The donor cells were found to contribute to the regeneration of damaged muscle fibers and to the satellite cell (muscle specific stem cells) compartment. Such biomimetic cell delivery vehicles that are cost-effective and easy-to-synthesize could play a key role in improving the outcomes of other stem cell-based therapies.

A porous membrane-mediated isolation of mesenchymal stem cells from human embryonic stem cells

Pluripotent human embryonic stem cells (hESCs) acquire mesenchymal characteristics during the epithelial-mesenchymal transition (EMT) process. Here, we report a simple and an efficient isolation method for mesenchymal stem cells (MSCs) from hESCs undergoing EMT using a commercialized porous membrane transwell culture insert. Suspension culture of hESC colonies results in the formation of embryoid bodies, which adhered on the upper compartment of 8 μm porous membrane in the presence of EMG2-MV media. The population migrating through the permeable membrane to the lower compartment not only exhibited EMT markers but also expressed high levels of a panel of typical MSC surface antigen markers, and demonstrated multipotent differentiation capability. In addition, they have a prolonged proliferation capacity without characteristics and chromosomal changes. Furthermore, the isolated MSCs significantly enhanced cardiac functions in a rat model of myocardial infarction (MI) as measured by the left ventricle wall thickness (MI control, 32.9%±3.2% vs. hESCs-MSCs, 38.7%±2.4%), scar length (MI control, 46.1%±2.5% vs. hESCs-MSCs, 41.8%±1.3%), fibrosis area (MI control, 34.3%±1.6% vs. hESCs-MSCs, 28.9%±3.5%), and capillary density. Our findings demonstrate an ease with which hESCs-MSCs can be effectively isolated using the porous membrane, which overcomes the lack of availability of MSCs for therapeutic applications in various diseased animal models.

Human embryonic stem cells and macroporous calcium phosphate construct for bone regeneration in cranial defects in rats

Human embryonic stem cells (hESCs) are an exciting cell source as they offer an unlimited supply of cells that can differentiate into all cell types for regenerative medicine applications. To date, there has been no report on hESCs with calcium phosphate cement (CPC) scaffolds for bone regeneration in vivo. The objectives of this study were to: (i) investigate hESCs for bone regeneration in vivo in critical-sized cranial defects in rats; and (ii) determine the effects of cell seeding and platelets in macroporous CPC on new bone and blood vessel formation. hESCs were cultured to yield mesenchymal stem cells (MSCs), which underwent osteogenic differentiation. Four groups were tested in rats: (i) CPC control without cells; (ii) CPC with hESC-derived MSCs (CPC+hESC-MSC); (iii) CPC with hESC-MSCs and 30% human platelet concentrate (hPC) (CPC+hESC-MSC+30% hPC); and (iv) CPC+hESC-MSC+50% hPC. In vitro, MSCs were derived from embryoid bodies of hESCs. Cells on CPC were differentiated into the osteogenic lineage, with highly elevated alkaline phosphatase and osteocalcin expressions, as well as mineralization. At 12weeks in vivo, the groups with hESC-MSCs and hPC had three times as much new bone as, and twice the blood vessel density of, the CPC control. The new bone in the defects contained osteocytes and blood vessels, and the new bone front was lined with osteoblasts. The group with 30% hPC and hESC-MSCs had a blood vessel density that was 49% greater than the hESC-MSC group without hPC, likely due to the various growth factors in the platelets enhancing both new bone and blood vessel formation. In conclusion, hESCs are promising for bone tissue engineering, and hPC can enhance new bone and blood vessel formation. Macroporous CPC with hESC-MSCs and hPC may be useful for bone regeneration in craniofacial and orthopedic applications.

Concise review: combining human leukocyte antigen G and mesenchymal stem cells for immunosuppressant biotherapy

Both human leukocyte antigen G (HLA-G) and multipotential mesenchymal stem/stromal cells (MSCs) exhibit immunomodulatory functions. In allogeneic tranplantation, the risks of acute and chronic rejection are still high despite improvement in immunosuppressive treatments, and the induction of a state of tolerance to alloantigens is not achieved. Immunomodulatory properties of MSCs and HLA-G in human allogeneic tranplantation to induce tolerance appears attractive and promising. Interestingly, we and others have demonstrated that MSCs can express HLA-G. In this review, we focus on the expression of HLA-G by MSCs and discuss how to ensure and improve the immunomodulatory properties of MSCs by selectively targeting MSCs expressing HLA-G (MSCs(HLA-G+)). We also discuss the possible uses of MSCs(HLA-G+) for therapeutic purposes, notably, to overcome acute and chronic immune rejection in solid-organ allogeneic transplantation in humans. Since MSCs are phenotypically and functionally heterogeneous, it is of primary interest to have specific markers ensuring that they have strong immunosuppressive potential and HLA-G may be a valuable candidate.

Modulating the biochemical and biophysical culture environment to enhance osteogenic differentiation and maturation of human pluripotent stem cell-derived mesenchymal progenitors

Advances in the fields of stem cell biology, biomaterials, and tissue engineering over the last decades have brought the possibility of constructing tissue substitutes with a broad range of applications in regenerative medicine, disease modeling, and drug discovery. Different types of human stem cells have been used, each presenting a unique set of advantages and limitations with regard to the desired research goals. Whereas adult stem cells are at the frontier of research for tissue and organ regeneration, pluripotent stem cells represent a more challenging cell source for clinical translation. However, with their unlimited growth and wide differentiation potential, pluripotent stem cells represent an unprecedented resource for the construction of advanced human tissue models for biological studies and drug discovery. At the heart of these applications lies the challenge to reproducibly expand, differentiate, and organize stem cells into mature, stable tissue structures. In this review, we focus on the derivation of mesenchymal tissue progenitors from human pluripotent stem cells and the control of their osteogenic differentiation and maturation by modulation of the biophysical culture environment. Similarly to enhancing bone development, the described principles can be applied to the construction of other mesenchymal tissues for basic and applicative studies.

Mesenchymal stem cell population derived from human pluripotent stem cells displays potent immunomodulatory and therapeutic properties

Mesenchymal stem cells (MSCs) are being tested in a wide range of human diseases; however, loss of potency and inconsistent quality severely limit their use. To overcome these issues, we have utilized a developmental precursor called the hemangioblast as an intermediate cell type in the derivation of a highly potent and replenishable population of MSCs from human embryonic stem cells (hESCs). This method circumvents the need for labor-intensive hand-picking, scraping, and sorting that other hESC-MSC derivation methods require. Moreover, unlike previous reports on hESC-MSCs, we have systematically evaluated their immunomodulatory properties and in vivo potency. As expected, they dynamically secrete a range of bioactive factors, display enzymatic activity, and suppress T-cell proliferation that is induced by either allogeneic cells or mitogenic stimuli. However, they also display unique immunophenotypic properties, as well as a smaller size and >30,000-fold proliferative capacity than bone marrow-derived MSCs. In addition, this is the first report which demonstrates that hESC-MSCs can inhibit CD83 up-regulation and IL-12p70 secretion from dendritic cells and enhance regulatory T-cell populations induced by interleukin 2 (IL-2). This is also the first report which shows that hESC-MSCs have therapeutic efficacy in two different autoimmune disorder models, including a marked increase in survival of lupus-prone mice and a reduction of symptoms in an autoimmune model of uveitis. Our data suggest that this novel and therapeutically active population of MSCs could overcome many of the obstacles that plague the use of MSCs in regenerative medicine and serve as a scalable alternative to current MSC sources.

Differentiation of hESCs into Mesodermal Subtypes: Vascular-, Hematopoietic- and Mesenchymal-lineage Cells

To date, studies on the application of mesodermally derived mesenchymal-, hematopoietic- and vascular-lineage cells for cell therapy have provided either poor or insufficient data. The results are equivocal with regard to therapeutic efficiency and yield. Since the establishment of human embryonic stem cells (hESCs) in 1998, the capacity of hESCs to differentiate into various mesodermal lineages has sparked considerable interest in the regenerative medicine community, a group interested in generating specialized cells to treat patients suffering from degenerative diseases. Even though hESCs are sensitive, effective methods for guiding the differentiation of hESCs into specific mesodermal cell types are still being developed. In addition, to understand the functional properties of hESC derivatives, numerous animal model studies have been performed by many research groups over the last decade. In this review, we describe and summarize the protocols currently used for differentiation of hESCs into multiple mesodermal lineages and their therapeutic efficiency in different animal models. Furthermore, we discuss the technical hurdles associated with each protocol and the safety of hESC derivatives for therapeutic applications. Technical improvement of the methods used to produce hESC derivatives for therapeutic use in patients with degenerative diseases should remain an objective of future studies, as should the development of effective and stable induction systems.

Functional comparison of human-induced pluripotent stem cell-derived mesenchymal cells and bone marrow-derived mesenchymal stromal cells from the same donor

Mesenchymal stem cells (MSCs) have a high potential for therapeutic efficacy in treating diverse musculoskeletal injuries and cardiovascular diseases, and for ameliorating the severity of graft-versus-host and autoimmune diseases. While most of these clinical applications require substantial cell quantities, the number of MSCs that can be obtained initially from a single donor is limited. Reports on the derivation of MSC-like cells from pluripotent stem cells (PSCs) are, thus, of interest, as the infinite proliferative capacity of PSCs opens the possibility to generate large amounts of uniform batches of MSCs. However, characterization of such MSC-like cells is currently inadequate, especially with regard to the question of whether these cells are equivalent or identical to MSCs. In this study, we have derived MSC-like cells [induced PSC-derived MSC-like progenitor cells (iMPCs)] using four different methodologies from a newly established induced PSC line reprogrammed from human bone marrow stromal cells (BMSCs), and compared the iMPCs directly with the originating parental BMSCs. The iMPCs exhibited typical MSC/fibroblastic morphology and MSC-typical surface marker profile, and they were capable of differentiation in vitro along the osteogenic, chondrogenic, and adipogenic lineages. However, compared with the parental BMSCs, iMPCs displayed a unique expression pattern of mesenchymal and pluripotency genes and were less responsive to traditional BMSC differentiation protocols. We, therefore, conclude that iMPCs generated from PSCs via spontaneous differentiation represent a distinct population of cells which exhibit MSC-like characteristics.

An update of human mesenchymal stem cell biology and their clinical uses

In the past decade, an increasing urge to develop new and novel methods for the treatment of degenerative diseases where there is currently no effective therapy has lead to the emerging of the cell therapy or cellular therapeutics approach for the management of those conditions where organ functions are restored through transplantation of healthy and functional cells. Stem cells, because of their nature, are currently considered among the most suitable cell types for cell therapy. There are an increasing number of studies that have tested the stromal stem cell functionality both in vitro and in vivo. Consequently, stromal (mesenchymal) stem cells (MSCs) are being introduced into many clinical trials due to their ease of isolation and efficacy in treating a number of disease conditions in animal preclinical disease models. The aim of this review is to revise MSC biology, their potential translation in therapy, and the challenges facing their adaptation in clinical practice.

Age-related decreases of serum-response factor levels in human mesenchymal stem cells are involved in skeletal muscle differentiation and engraftment capacity

Skeletal muscle (SkM) comprise ∼40% of human body weight. Injury or damage to this important tissue can result in physical disability, and in severe cases is difficult for its endogenous stem cell-the satellite cell-to reverse effectively. Mesenchymal stem cells (MSC) are postnatal progenitor/stem cells that possess multilineage mesodermal differentiation capacity, including toward SkM. Adult bone marrow (BM) is the best-studied source of MSCs; however, aging also decreases BMMSC numbers and can adversely affect differentiation capacity. Therefore, we asked whether human sources of developmentally early stage mesenchymal stem cells (hDE-MSCs) isolated from embryonic stem cells, fetal bone, and term placenta could be cellular sources for SkM repair. Under standard muscle-inducing conditions, hDE-MPCs differentiate toward a SkM lineage rather than cardiomyocytic or smooth muscle lineages, as evidenced by increased expression of SkM-associated markers and in vitro myotube formation. In vivo transplantation revealed that SkM-differentiated hDE-MSCs can efficiently incorporate into host SkM tissue in a mouse model of SkM injury. In contrast, adult BMMSCs do not express SkM-associated genes after in vitro SkM differentiation nor engraft in vivo. Further investigation of possible factors responsible for this difference in SkM differentiation potential revealed that, compared with adult BMMSCs, hDE-MSCs expressed higher levels of serum response factor (SRF), a transcription factor critical for SkM lineage commitment. Moreover, knockdown of SRF in hDE-MSCs resulted in decreased expression of SkM-related genes after in vitro differentiation and decreased in vivo engraftment. Our results implicate SRF as a key factor in age-related SkM differentiation capacity of MSCs, and demonstrate that hDE-MSCs are possible candidates for SkM repair.

Unravelling the pluripotency paradox in fetal and placental mesenchymal stem cells: Oct-4 expression and the case of The Emperor's New Clothes

Mesenchymal stem cells (MSC) from fetal-placental tissues have translational advantages over their adult counterparts, and have variably been reported to express pluripotency markers. OCT-4 expression in fetal-placental MSC has been documented in some studies, paradoxically without tumourogenicity in vivo. It is possible that OCT-4 expression is insufficient to induce true "stemness", but this issue is important for the translational safety of fetal-derived MSC. To clarify this, we undertook a systematic literature review on OCT-4 in fetal or adnexal MSC to show that most studies report OCT-4 message or protein expression, but no study provides definitive evidence of true OCT-4A expression. Discrepant findings were attributable not to different culture conditions, tissue sources, or gestational ages but instead to techniques used. In assessing OCT-4 as a pluripotency marker, we highlight the challenges in detecting the correct OCT-4 isoform (OCT-4A) associated with pluripotency. Although specific detection of OCT-4A mRNA is achievable, it appears unlikely that any antibody can reliably distinguish between OCT-4A and the pseudogene OCT-4B. Finally, using five robust techniques we demonstrate that fetal derived-MSC do not express OCT-4A (or by default OCT-4B). Reports suggesting OCT-4 expression in fetal-derived MSC warrant reassessment, paying attention to gene and protein isoforms, pseudogenes, and antibody choice as well as primer design. Critical examination of the OCT-4 literature leads us to suggest that OCT-4 expression in fetal MSC may be a case of "The Emperor's New Clothes" with early reports of (false) positive expression amplified in subsequent studies without critical attention to emerging refinements in knowledge and methodology.

Functional assessment of hematopoietic niche cells derived from human embryonic stem cells

To evaluate hematopoietic niche cell populations isolated from human embryonic stem cells (hESCs), we tested the ability of hESC-derived stromal lines to support CD34(+) umbilical cord blood (UCB)- and hESC-derived CD34(+)45(+) cells in long-term culture initiating cell (LTC-IC) assays. Specifically, these hematopoietic populations were cocultured with hESC-derived mesenchymal stromal cells (hESC-MSCs) and hESC-derived endothelial cells (hESC-ECs), and then assessed for their LTC-IC potential in comparison to coculture with bone marrow (BM)-derived MSCs and the mouse stromal line M2-10B4. We found that the hESC-derived stromal lines supported LTC-ICs from UCB similar to M2-10B4 cells and better than BM-MSCs. However, none of the stromal populations supported LTC-IC from hESC-derived CD34(+)45(+) cells. Engraftment data using the output from LTC-IC assays showed long-term repopulation (12 weeks) of NSG mice to correlate with LTC-IC support on a given stromal layer. Therefore, hESC-derived stromal lines can be used to efficiently evaluate putative hematopoietic stem/progenitor cells derived from hESCs or other cell sources.

Mesenchymal stem cells secrete immunologically active exosomes

Mesenchymal stem cells (MSCs) have been shown to secrete exosomes that are cardioprotective. Here, we demonstrated that MSC exosome, a secreted membrane vesicle, is immunologically active. MSC exosomes induced polymyxin-resistant, MYD88-dependent secreted embryonic alkaline phosphatase (SEAP) expression in a THP1-Xblue, a THP-1 reporter cell line with an NFκB-SEAP reporter gene. In contrast to lipopolysaccharide, they induced high levels of anti-inflammatory IL10 and TGFβ1 transcript at 3 and 72 h, and much attenuated levels of pro-inflammatory IL1B, IL6, TNFA and IL12P40 transcript at 3-h. The 3-h but not 72-h induction of cytokine transcript was abrogated by MyD88 deficiency. Primary human and mouse monocytes exhibited a similar exosome-induced cytokine transcript profile. Exosome-treated THP-1 but not MyD88-deficient THP-1 cells polarized activated CD4(+) T cells to CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs) at a ratio of one exosome-treated THP-1 cell to 1,000 CD4(+) T cells. Infusion of MSC exosomes enhanced the survival of allogenic skin graft in mice and increased Tregs.

Therapeutic MSC exosomes are derived from lipid raft microdomains in the plasma membrane

Background

Mesenchymal stem cell (MSC) was previously shown to secrete lipid vesicles that when purified by high performance liquid chromatography as a population of homogenously sized particles with a hydrodynamic radius of 55–65 nm reduce infarct size in a mouse model of myocardial ischemia/reperfusion injury. As these vesicles exhibit many biophysical and biochemical properties of exosomes, they were identified as exosomes. Here we investigated if these lipid vesicles were indeed exosomes that have an endosomal biogenesis.

Method

In most cells, endocytosis is thought to occur at specialized microdomains known as lipid rafts. To demonstrate an endosomal origin for MSC exosomes, MSCs were pulsed with ligands e.g. transferrin (Tfs) and Cholera Toxin B (CTB) that bind receptors in lipid rafts. The endocytosed ligands were then chased to determine if they were incorporated into the exosomes.

Results

A fraction of exogenous Tfs was found to recycle into MSC exosomes. When MSCs were pulsed with labelled Tfs in the presence of chlorpromazine, an inhibitor of clathrin-mediated endocytosis, Tf incorporation in CD81-immunoprecipitate was reduced during the chase. CTB which binds GM1 gangliosides that are enriched in lipid rafts extracted exosome-associated proteins, CD81, CD9, Alix and Tsg101 from MSC-conditioned medium. Exogenous CTBs were pulse-chased into secreted vesicles. Extraction of Tf- or CTB-binding vesicles in an exosome preparation mutually depleted each other. Inhibition of sphingomyelinases reduced CTB-binding vesicles.

Conclusion

Together, our data demonstrated that MSC exosomes are derived from endocytosed lipid rafts and that their protein cargo includes exosome-associated proteins CD81, CD9, Alix and Tsg101.

Embryonic stem cells and induced pluripotent stem cells for skeletal regeneration

Tissue engineering for skeletal tissues including bone and cartilage have been focused on the use of adult stem cells. Although there are several pioneering researches on skeletal tissue regeneration from embryonic stem cells (ESCs), ethical issues and the possibility of immune rejection clouded further attention to the application of ESCs for nonlethal orthopedic conditions. However, the recent discovery of induced pluripotent stem cells (iPSCs) led to reconsider the use of these pluripotential cells for skeletal regeneration. The purpose of this review was to summarize the current knowledge of osteogenic and chondrogenic induction from ESCs and iPSCs and to provide a perspective on the application of iPSCs for skeletal regeneration.

Measurement of precursor miRNA in exosomes from human ESC-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) derived from human embryonic stem cells (ESCs) have been shown to secrete exosomes that are cardioprotective against myocardial ischemia reperfusion injury in a mouse model. To elucidate this cardioprotective mechanism, we have characterized the protein, nucleic acid, and lipid composition of MSC exosomes. Here we describe the isolation and analysis of RNA in MSC exosome. We have previously reported that RNAs in MSC exosome are primarily small RNA molecules of <300 nt and they include many miRNAs. Many of these miRNAs are in the precursor form suggesting that pre-miRNAs, and not mature miRNAs are preferentially loaded into exosomes. The protocols described here include assays to ascertain the presence of pre-miRNAs, profiling of miRNA and pre-miRNA, and quantitative estimation of mature and pre-miRNA.

Cartilage repair: 2013 Asian update

Despite financial and regulatory hurdles, Asian scientists and clinicians have made important contributions in the area of cartilage repair. Because it is impossible to include observations on all the published articles in one review, our attempt is to highlight Asian progress in this area during recent years (2005 to the present), reviewing research development and clinical studies. In the former, our discussion of in vitro studies focuses on (1) potential sources of stem cells--such as mesenchymal stem cells (MSCs) from marrow, cord blood, synovium, and mobilized peripheral blood--which are capable of enhancing cartilage repair and (2) the use of growth factors and scaffolds with and without cells. Our discussion of animal studies attempts to summarize activities in evaluating surgical procedures and determining the route of cell administration, as well as studies on matrices and scaffolds. It ranges from the use of small animals such as rats and rabbits to larger animals like pigs and dogs. The local adherent technique, enhancement of microfracture with poly(l-lactic-co-glycolic acid) scaffold, adenovirus-mediated bone morphogenic protein (BMP) genes, and MSCs--whether they are magnetically labeled, suspended in hyaluronic acid, or immobilized with transforming growth factor-β (TGF-β)--have all been able to engineer a repair of the osteochondral defect. Although published Asian reports of clinical studies on cartilage repair are few, the findings of relevant trials are summarized in our discussion of these investigations. There has been a long history of use of laboratory-derived MSCs for cartilage repair. Recent progress has suggested the potential utility of cord blood and mobilized peripheral blood in this area, as well as more injectable bone marrow (BM)-derived stem cells. Finally, we make a few suggestions on the direction of research and development activities and the need for collaborative approaches by regulatory agencies.

Repair of cartilage defects in arthritic tissue with differentiated human embryonic stem cells

Chondrocytes have been generated in vitro from a range of progenitor cell types and by a number of strategies. However, achieving reconstitution of actual physiologically relevant, appropriately-laminated cartilage in situ that would be applicable to conditions, such as arthritis and cartilage degeneration remains elusive. This lack of success is multifactorial and includes limited cell source, decreased proliferation rate of mature chondrocytes, lack of maintenance of phenotype, reduced matrix synthesis, and poor integration with host tissue. We report an efficient approach for deriving mesenchymal chondroprogenitor cells from human embryonic stem cells. These cells generated tissue containing cartilage-specific matrix proteins that integrated in situ in a partial-thickness defect in ex vivo articular cartilage harvested from human arthritic joints. Given that stem cells provide a virtually inexhaustible supply of starting material and that our technique is easily scalable, cartilaginous tissue primed and grafted in this manner could be suitable for clinical translation.

Perspective and challenges of mesenchymal stem cells for cardiovascular regeneration

Mesenchymal stem cells (MSCs) exhibit multipotent differentiation potential and can be derived from embryonic, neonatal and adult differentiation stage III tissue sources. While increasing preclinical studies and clinical trials have indicated that MSC-based therapy is a promising strategy for cardiovascular regeneration, there are major challenges to overcome before this stem-cell technology can be widely applied in clinical settings. In this review, the following important issues will be addressed. First, optimal sources of MSC derivation suitable for myocardial repair are not determined. Second, assessments for preclinical and clinical studies of MSCs require more scientific data analysis. Third, mechanisms of MSC-based therapy for cardiovascular regeneration have not been fully understood yet. Finally, the potential benefit-risk ratio of MSC therapy needs to be evaluated systematically. Additionally, future development of MSC therapy will be discussed.

Generating cartilage repair from pluripotent stem cells

The treatment of degeneration and injury of articular cartilage has been very challenging for scientists and surgeons. As an avascular and hypocellular tissue, cartilage has a very limited capacity for self-repair. Chondrocytes are the only cell type in cartilage, in which they are surrounded by the extracellular matrix that they secrete and assemble. Autologous chondrocyte implantation for cartilage defects has achieved good results, but the limited resources and complexity of the procedure have hindered wider application. Stem cells form an alternative to chondrocytes as a source of chondrogenic cells due to their ability to proliferate extensively while retaining the potential for differentiation. Adult stem cells such as mesenchymal stem cells have been differentiated into chondrocytes, but the limitations in their proliferative ability and the heterogeneous cell population hinder their adoption as a prime alternative source for generating chondrocytes. Human embryonic stem cells (hESCs) are attractive as candidates for cell replacement therapy because of their unlimited self-renewal and ability for differentiation into mesodermal derivatives as well as other lineages. In this review, we focus on current protocols for chondrogenic differentiation of ESCs, in particular the chemically defined culture system developed in our lab that could potentially be adapted for clinical application.

Human pluripotent stem cell-derived mesenchymal stem cells prevent allergic airway inflammation in mice

We previously found that mesenchymal stem cells (MSCs) derived from human-induced pluripotent stem cells (iPSCs) exerted immunomodulatory effects on Th2-mediated allergic rhinitis in vitro. However, their contribution to the asthma and allergic rhinitis in animal models remains unclear. In this study, we developed a mouse model of ovalbumin (OVA)-induced allergic inflammation in both the upper and lower airways and evaluated the effects of the systemic administration of human iPSC-MSCs and bone marrow-derived MSCs (BM-MSCs) on allergic inflammation. Our results showed that treatments with both the iPSC-MSCs and BM-MSCs before the challenge phase protected the animals from the majority of allergy-specific pathological changes. This protection included an inhibition of inflammatory cell infiltration and mucus production in the lung, a reduction in eosinophil infiltration in the nose, and a decrease in inflammatory cell infiltration in both the bronchoalveolar and nasal lavage fluids. In addition, treatment with iPSC-MSCs or BM-MSCs before the challenge phase resulted in reduced serum levels of Th2 immunoglobulins (e.g., IgE) and decreased levels of Th2 cytokines including interleukin (IL)-4, IL-5, or IL-13 in the bronchoalveolar and/or nasal lavage fluids. Similar therapeutic effects were observed when the animals were pretreated with human iPSC-MSCs before the sensitization phase. These data suggest that iPSC-MSCs may be used as an alternative strategy to adult MSCs in the treatment of asthma and allergic rhinitis. Stem Cells 2012;30:2692–2699

In vitro characterization and engraftment of adipocytes derived from human induced pluripotent stem cells and embryonic stem cells

Human induced pluripotent stem (iPS) and embryonic stem (ES) cells can differentiate into a variety of cell types. We reported on adipogenic potential of human iPS and ES cells in vitro. In the present study, we investigate the survival and maintenance of adipocytes differentiated in vitro from human iPS and ES cells after transplantation. Following adipogenic induction in vitro, the differentiated cells exhibited functional properties of adipocytes such as lipid storage, lipolysis, and insulin responsiveness. Subsequently, Matrigel containing the differentiated human iPS and ES cells was transplanted into the subcutaneous tissue of nude mice. After 1-4 weeks, the cells with adipocyte-like features were observed in transplanted Matrigel by histological analysis. The human origin of the cells, their lipid accumulation, and gene expression of adipocyte markers in transplanted cells were then confirmed, suggesting the presence of adipocytes in transplanted Matrigel. When the relative areas of these cells were calculated by dividing the adipocyte areas by the total Matrigel areas, we found that they peaked at 2 weeks after transplantation, and that the adipocytes persisted at 4 weeks. The present study demonstrates that human iPS and ES cells can differentiate into adipocytes with functional properties and that adipocytes derived from human iPS and ES cells can survive and maintain the differentiated properties of adipocytes for at least 4 weeks after transplantation. Adipocytes derived from human iPS and ES cells thus have the potential to open new avenues for stem cell-based research into metabolic diseases and future therapeutic applications.

Short periods of cyclic mechanical strain enhance triple-supplement directed osteogenesis and bone nodule formation by human embryonic stem cells in vitro

Human embryonic stem cells (hESCs) are uniquely endowed with a capacity for both self-renewal and multilineage differentiation. The aim of this investigation was to determine if short periods of cyclic mechanical strain enhanced dexamethasone, ascorbic acid, and β-glycerophosphate (triple-supplement)-induced osteogenesis and bone nodule formation by hESCs. Colonies were cultured for 21 days and divided into control (no stretch) and three treatment groups; these were subjected to in-plane deformation of 2% for 5 s (0.2 Hertz) every 60 s for 1 h on alternate days in BioFlex plates linked to a Flexercell strain unit over the following periods (day 7-13), (day 15-21), and (day 7-21). Numerous bone nodules were formed, which stained positively for osteocalcin and type I collagen; in addition, MTS assays for cell number as well as total collagen assays showed a significant increase in the day 7-13 group compared to controls and other treatment groups. Alizarin Red staining further showed that cyclic mechanical stretching significantly increased the nodule size and mineral density between days 7-13 compared to control cultures and the other two experimental groups. We then performed a real-time polymerase chain reaction (PCR) microarray on the day 7-13 treatment group to identify mechanoresponsive osteogenic genes. Upregulated genes included the transcription factors RUNX2 and SOX9, bone morphogenetic proteins BMP1, BMP4, BMP5, and BMP6, transforming growth factor-β family members TGFB1, TGFB2, and TGFB3, and three genes involved in mineralization-ALPL, BGLAP, and VDR. In conclusion, this investigation has demonstrated that four 1-h episodes of cyclic mechanical strain acted synergistically with triple supplement to enhance osteogenesis and bone nodule formation by cultured hESCs. This suggests the development of methods to engineer three-dimensional constructs of mineralized bone in vitro, could offer an alternative approach to osseous regeneration by producing a biomaterial capable of providing stable surfaces for osteoblasts to synthesize new bone, while at the same time able to be resorbed by an osteoclastic activity-in other words, one that can recapitulate the remodeling dynamics of a naturally occurring bone matrix.

Effect of ex vivo culture conditions on immunosuppression by human mesenchymal stem cells

A microarray analysis was performed to investigate whether ex vivo culture conditions affect the characteristics of MSCs. Gene expression profiles were mainly influenced by the level of cell confluence rather than initial seeding density. The analysis showed that 276 genes were upregulated and 230 genes downregulated in MSCs harvested at ~90% versus ~50% confluence (P < 0.05, FC > 2). The genes that were highly expressed in MSCs largely corresponded to chemotaxis, inflammation, and immune responses, indicating direct or indirect involvement in immunomodulatory functions. Specifically, PTGES and ULBP1 were up-regulated in MSCs harvested at high density. Treatment of MSCs with PTGES or ULBP1 siRNA reversed their inhibition of T-cell proliferation in vitro. The culture conditions such as cell confluence at harvest seem to be important for gene expression profile of MSCs; therefore, the results of this study may provide useful guidelines for the harvest of MSCs that can appropriately suppress the immune response.

Biomaterials directed in vivo osteogenic differentiation of mesenchymal cells derived from human embryonic stem cells

Spontaneous differentiation of human embryonic stem cells (hESCs) is generally inefficient and leads to a heterogeneous population of differentiated and undifferentiated cells, limiting the potential use of hESCs for cell-based therapy and studies of specific differentiation programs. Here, we demonstrate biomaterial-dependent commitment of a mesenchymal cell population derived from hESCs toward the osteogenic lineage in vivo. In skeletal development, bone formation from condensing mesenchymal cells involves two distinct pathways: endochondral and intramembraneous bone formation. In this study, we demonstrate that the hESC-derived mesenchymal cells differentiate and regenerate in vivo bone tissues through two different pathways depending upon the local cues present in a scaffold microenvironment. Hydroxyapatite (HA) was incorporated into biodegradable poly(lactic-co-glycolic acid)/poly(l-lactic acid) (PLGA/PLLA) scaffolds to enhance bone formation. The HA microenvironment stabilized the β-catenin and upregulated Runx2, resulting in faster bone formation through intramembraneous ossification. hESC-derived mesenchymal cells seeded on the PLGA/PLLA scaffold without HA, however, showed minimal levels Runx2, and differentiated via endochondral ossification, as evidenced by formation of cartilaginous tissue, followed by calcification and increased blood vessel invasion. These results indicate that the ossification mechanisms of the hESC-derived mesenchymal stem cells can be regulated by the scaffold-mediated microenvironments, and bone tissue can be formed.

Does mesenchymal stem cell population in umbilical cord blood vary at different gestational periods?

OBJECTIVE

To identify and quantitatively determine Mesenchymal stem cells (MSCs) in the umbilical cord blood (UCB) of neonates born at different gestational periods.

METHODS

UCB was collected at birth in neonates of three different gestational groups. The mononuclear cells (MNCs) were phenotypically analyzed by flow cytometer.

RESULTS

The yield of total MNCs did not differ much with gestation; the average values were 22.6 ± 6.48 × 106 cells/ml. The MSCs were significantly higher in the lower gestation group. These were 0.0219 ± 0.012 %, 0.0044 ± 0.003 % and 0.0022 ± 0.003 % in 28 to 31 wk, 32 to 35 wk and >36 wk, respectively (P = 0.00). There was a significant inverse correlation between the gestational age and the presence of MSCs with a correlation co-efficient of -0.54 (P = 0.0001).

CONCLUSIONS

The MSCs population was significantly higher in infants born at lesser gestation than those born at term gestation.

Mesenchymal stem cell: an efficient mass producer of exosomes for drug delivery

Advances in biomedical research have generated an unprecedented number of potential targets for therapeutic intervention to treat disease or delay disease progression. Unfortunately, many of these targets are not druggable as they are intracellular, present in many cell types, poorly soluble or rapidly inactivated. Although synthetic drug vehicles have successfully circumvented many of these problems, natural particulates such as exosomes that intrinsically possess many attributes of a drug delivery vehicle are highly attractive as potentially better alternatives. Of the cell types known to produce exosomes, the readily available proliferative, immunosuppressive and clinically tested human mesenchymal stem cell (MSC) is the most prolific producer. Its exosomes are therapeutic in animal model of disease and exhibit immunosuppressive activity. The quality and quantity of exosome production is not compromised by immortalization to create a permanent MSC cell line. Therefore, MSC is well suited for mass production of exosomes that are ideal for drug delivery.

Therapeutic potential of human induced pluripotent stem cell-derived mesenchymal stem cells in mice with lethal fulminant hepatic failure

Large-scale production and noninvasive methods for harvesting mesenchymal stem cells (MSCs), particularly in elderly individuals, has prompted researchers to find new patient-specific sources for MSCs in regenerative medicine. This study aims to produce MSCs from human induced pluripotent stem cells (hiPSCs) and to evaluate their therapeutic effects in a CCl4-induced mouse model of fulminant hepatic failure (FHF). hiPSC-MSCs have shown MSC morphology, antigen profile and differentiation capabilities, and improved hepatic function in our model. hiPSC-MSC-transplanted animals provide significant benefit in terms of survival, serum LDH, total bilirubin, and lipid peroxidation. hiPSC-MSC therapy resulted in a one-third reduction of histologic activity index and a threefold increase in the number of proliferating hepatocytes. This was accompanied by a significant decrease in the expression levels of collagen type I, Mmp13, Mmp2, and Mmp9 genes and increase in Timp1 and Timp2 genes in transplanted groups. hiPSC-MSCs secreted hepatocyte growth factor (HGF) in vitro and also expressed HGF in evaluated liver sections. Similar results were observed with human bone marrow (hBM)-derived MSCs. In conclusion, our results have demonstrated that hiPSC-MSCs might be valuable appropriate alternatives for hBM-MSCs in FHF liver repair and support liver function by cell therapy with a large-scale production capacity, patient-specific nature, and no invasive MSC harvesting.

Generation of human induced pluripotent stem cells from osteoarthritis patient-derived synovial cells

OBJECTIVE

This study was undertaken to generate and characterize human induced pluripotent stem cells (PSCs) from patients with osteoarthritis (OA) and to examine whether these cells can be developed into disease-relevant cell types for use in disease modeling and drug discovery.

METHODS

Human synovial cells isolated from two 71-year-old women with advanced OA were characterized and reprogrammed into induced PSCs by ectopic expression of 4 transcription factors (Oct-4, SOX2, Klf4, and c-Myc). The pluripotency status of each induced PSC line was validated by comparison with human embryonic stem cells (ESCs).

RESULTS

We found that OA patient-derived human synovial cells had human mesenchymal stem cell (MSC)-like characteristics, as indicated by the expression of specific markers, including CD14-, CD19-, CD34-, CD45-, CD44+, CD51+, CD90+, CD105+, and CD147+. Microarray analysis of human MSCs and human synovial cells further determined their unique and overlapping gene expression patterns. The pluripotency of established human induced PSCs was confirmed by their human ESC-like morphology, expression of pluripotency markers, gene expression profiles, epigenetic status, normal karyotype, and in vitro and in vivo differentiation potential. The potential of human induced PSCs to differentiate into distinct mesenchymal cell lineages, such as osteoblasts, adipocytes, and chondrocytes, was further confirmed by positive expression of markers for respective cell types and positive staining with alizarin red S (osteoblasts), oil red O (adipocytes), or Alcian blue (chondrocytes). Functional chondrocyte differentiation of induced PSCs in pellet culture and 3-dimensional polycaprolactone scaffold culture was assessed by chondrocyte self-assembly and histology.

CONCLUSION

Our findings indicate that patient-derived synovial cells are an attractive source of MSCs as well as induced PSCs and have the potential to advance cartilage tissue engineering and cell-based models of cartilage defects.

Human embryonic stem cell derived mesenchymal progenitors express cardiac markers but do not form contractile cardiomyocytes

Mesenchymal progenitors or stromal cells have shown promise as a therapeutic strategy for a range of diseases including heart failure. In this context, we explored the growth and differentiation potential of mesenchymal progenitors (MPs) derived in vitro from human embryonic stem cells (hESCs). Similar to MPs isolated from bone marrow, hESC derived MPs (hESC-MPs) efficiently differentiated into archetypical mesenchymal derivatives such as chondrocytes and adipocytes. Upon treatment with 5-Azacytidine or TGF-β1, hESC-MPs modified their morphology and up-regulated expression of key cardiac transcription factors such as NKX2-5, MEF2C, HAND2 and MYOCD. Nevertheless, NKX2-5⁺ hESC-MP derivatives did not form contractile cardiomyocytes, raising questions concerning the suitability of these cells as a platform for cardiomyocyte replacement therapy. Gene profiling experiments revealed that, although hESC-MP derived cells expressed a suite of cardiac related genes, they lacked the complete repertoire of genes associated with bona fide cardiomyocytes. Our results suggest that whilst agents such as TGF-β1 and 5-Azacytidine can induce expression of cardiac related genes, but treated cells retain a mesenchymal like phenotype.

Time-dependent processes in stem cell-based tissue engineering of articular cartilage

Articular cartilage (AC), situated in diarthrodial joints at the end of the long bones, is composed of a single cell type (chondrocytes) embedded in dense extracellular matrix comprised of collagens and proteoglycans. AC is avascular and alymphatic and is not innervated. At first glance, such a seemingly simple tissue appears to be an easy target for the rapidly developing field of tissue engineering. However, cartilage engineering has proven to be very challenging. We focus on time-dependent processes associated with the development of native cartilage starting from stem cells, and the modalities for utilizing these processes for tissue engineering of articular cartilage.

Clinical utility of stem cells for periodontal regeneration

The aim of this review is to discuss the clinical utility of stem cells in periodontal regeneration by reviewing relevant literature that assesses the periodontal-regenerative potential of stem cells. We considered and described the main stem cell populations that have been utilized with regard to periodontal regeneration, including bone marrow-derived mesenchymal stem cells and the main dental-derived mesenchymal stem cell populations: periodontal ligament stem cells, dental pulp stem cells, stem cells from human exfoliated deciduous teeth, stem cells from apical papilla and dental follicle precursor cells. Research into the use of stem cells for tissue regeneration has the potential to significantly influence periodontal treatment strategies in the future.

Cell sources for the regeneration of articular cartilage: the past, the horizon and the future

Avascular, aneural articular cartilage has a low capacity for self-repair and as a consequence is highly susceptible to degradative diseases such as osteoarthritis. Thus the development of cell-based therapies that repair focal defects in otherwise healthy articular cartilage is an important research target, aiming both to delay the onset of degradative diseases and to decrease the need for joint replacement surgery. This review will discuss the cell sources which are currently being investigated for the generation of chondrogenic cells. Autologous chondrocyte implantation using chondrocytes expanded ex vivo was the first chondrogenic cellular therapy to be used clinically. However, limitations in expansion potential have led to the investigation of adult mesenchymal stem cells as an alternative cell source and these therapies are beginning to enter clinical trials. The chondrogenic potential of human embryonic stem cells will also be discussed as a developmentally relevant cell source, which has the potential to generate chondrocytes with phenotype closer to that of articular cartilage. The clinical application of these chondrogenic cells is much further away as protocols and tissue engineering strategies require additional optimization. The efficacy of these cell types in the regeneration of articular cartilage tissue that is capable of withstanding biomechanical loading will be evaluated according to the developing regulatory framework to determine the most appropriate cellular therapy for adoption across an expanding patient population.