Marrow-isolated adult multilineage inducible (MIAMI) cells, a unique population of postnatal young and old human cells with extensive expansion and differentiation potential

Cord blood Lin(-)CD45(-) embryonic-like stem cells are a heterogeneous population that lack self-renewal capacity

Human umbilical cord blood (hUCB) has been proposed to contain not only haematopoietic stem cells, but also a rare pluripotent embryonic-like stem cell (ELSc) population that is negative for hematopoietic markers (Lin⁻CD45⁻) and expresses markers typical of pluripotent cells. The aim of this work was to isolate, characterise and expand this ELSc fraction from hUCB, as it may provide a valuable cell source for regenerative medicine applications. We found that we could indeed isolate a Lin⁻CD45⁻ population of small cells (3–10 µm diameter) with a high nucleus to cytoplasm ratio that expressed the stem cell markers CD34 and CXCR4. However, in contrast to some previous reports, this fraction was not positive for CD133. Furthermore, although these cells expressed transcripts typical of pluripotent cells, such as SOX2, OCT3/4, and NANOG, they were not able to proliferate in any of the culture media known to support stem cell growth that we tested. Further analysis of the Lin⁻CD45⁻ population by flow cytometry showed the presence of a Lin⁻CD45⁻Nestin⁺ population that were also positive for CD34 (20%) but negative for CXCR4. These data suggest that the Lin⁻CD45⁻ stem cell fraction present in the cord blood represents a small heterogeneous population with phenotypic characteristics of stem cells, including a Lin⁻CD45⁻Nestin⁺ population not previously described. This study also suggests that heterogeneity within the Lin⁻CD45⁻ cell fraction is the likely explanation for differences in the hUCB cell populations described by different groups that were isolated using different methods. These populations have been widely called “embryonic-like stem cell” on the basis of their phenotypical similarity to embryonic stem cells. However, the fact they do not seem to be able to self-renew casts some doubt on their identity, and warns against defining them as “embryonic-like stem cell” at this stage.

Isolation, culture and evaluation of multilineage-differentiating stress-enduring (Muse) cells

Multilineage-differentiating stress-enduring (Muse) cells are distinct stem cells in mesenchymal cell populations with the capacity to self-renew, to differentiate into cells representative of all three germ layers from a single cell, and to repair damaged tissues by spontaneous differentiation into tissue-specific cells without forming teratomas. We describe step-by-step procedures for isolating and evaluating these cells. Muse cells are also a practical cell source for human induced pluripotent stem (iPS) cells with markedly high generation efficiency. They can be collected as cells that are double positive for stage-specific embryonic antigen-3 (SSEA-3) and CD105 from commercially available mesenchymal cells, such as adult human bone marrow stromal cells and dermal fibroblasts, or from fresh adult human bone marrow samples. Under both spontaneous and induced differentiation conditions, they show triploblastic differentiation. It takes 4-6 h to collect and 2 weeks to confirm the differentiation and self-renewal capacity of Muse cells.

Phenotype, donor age and gender affect function of human bone marrow-derived mesenchymal stromal cells

BACKGROUND

Mesenchymal stromal cells (MSCs) are attractive for cell-based therapies ranging from regenerative medicine and tissue engineering to immunomodulation. However, clinical efficacy is variable and it is unclear how the phenotypes defining bone marrow (BM)-derived MSCs as well as donor characteristics affect their functional properties.

METHODS

BM-MSCs were isolated from 53 (25 female, 28 male; age: 13 to 80 years) donors and analyzed by: (1) phenotype using flow cytometry and cell size measurement; (2) in vitro growth kinetics using population doubling time; (3) colony formation capacity and telomerase activity; and (4) function by in vitro differentiation capacity, suppression of T cell proliferation, cytokines and trophic factors secretion, and hormone and growth factor receptor expression. Additionally, expression of Oct4, Nanog, Prdm14 and SOX2 mRNA was compared to pluripotent stem cells.

RESULTS

BM-MSCs from younger donors showed increased expression of MCAM, VCAM-1, ALCAM, PDGFRβ, PDL-1, Thy1 and CD71, and led to lower IL-6 production when co-cultured with activated T cells. Female BM-MSCs showed increased expression of IFN-γR1 and IL-6β, and were more potent in T cell proliferation suppression. High-clonogenic BM-MSCs were smaller, divided more rapidly and were more frequent in BM-MSC preparations from younger female donors. CD10, β1integrin, HCAM, CD71, VCAM-1, IFN-γR1, MCAM, ALCAM, LNGFR and HLA ABC were correlated to BM-MSC preparations with high clonogenic potential and expression of IFN-γR1, MCAM and HLA ABC was associated with rapid growth of BM-MSCs. The mesodermal differentiation capacity of BM-MSCs was unaffected by donor age or gender but was affected by phenotype (CD10, IFN-γR1, GD2). BM-MSCs from female and male donors expressed androgen receptor and FGFR3, and secreted VEGF-A, HGF, LIF, Angiopoietin-1, basic fibroblast growth factor (bFGF) and NGFB. HGF secretion correlated negatively to the expression of CD71, CD140b and Galectin 1. The expression of Oct4, Nanog and Prdm14 mRNA in BM-MSCs was much lower compared to pluripotent stem cells and was not related to donor age or gender. Prdm14 mRNA expression correlated positively to the clonogenic potential of BM-MSCs.

CONCLUSIONS

By identifying donor-related effects and assigning phenotypes of BM-MSC preparations to functional properties, we provide useful tools for assay development and production for clinical applications of BM-MSC preparations.

Adult bone marrow neural crest stem cells and mesenchymal stem cells are not able to replace lost neurons in acute MPTP-lesioned mice

Adult bone marrow stroma contains multipotent stem cells (BMSC) that are a mixed population of mesenchymal and neural-crest derived stem cells. Both cells are endowed with in vitro multi-lineage differentiation abilities, then constituting an attractive and easy-available source of material for cell therapy in neurological disorders. Whereas the in vivo integration and differentiation of BMSC in neurons into the central nervous system is currently matter of debate, we report here that once injected into the striatum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice, pure populations of either bone marrow neural crest stem cells (NCSC) or mesenchymal stem cells (MSC) survived only transiently into the lesioned brain. Moreover, they do not migrate through the brain tissue, neither modify their initial phenotype, while no recovery of the dopaminergic system integrity was observed. Consequently, we tend to conclude that MSC/NCSC are not able to replace lost neurons in acute MPTP-lesioned dopaminergic system through a suitable integration and/or differentiation process. Altogether with recent data, it appears that neuroprotective, neurotrophic and anti-inflammatory features characterizing BMSC are of greater interest as regards CNS lesions management.

Genome-wide analysis of murine bone marrow‑derived very small embryonic-like stem cells reveals that mitogenic growth factor signaling pathways play a crucial role in the quiescence and ageing of these cells

It has been postulated that the most primitive population of stem cells, Oct4⁺Sca-1⁺Lin⁻CD45⁻ very small embryonic-like stem cells (VSELs), differentiate into tissue-committed stem cells in adult mice. However, Oct4⁺ VSELs remain quiescent in adult tissues and do not form teratomas. In thi study, we report the characteristics of the VSEL transcriptome by gene set enrichment analysis employing a microarray database established from 20 murine bone marrow-derived, FACS-sorted VSELs in comparison with hematopoietic stem cells and embryonic stem cells. In the Oct4⁺ VSELs, we observed the upregulation of tissue-specific gene sets and a gene set encoding the complement-coagulation cascade. By contrast, in the VSELs, we observed the downregulation of genes involved in the UV radiation response, mRNA processing and mitogenic growth factor signaling [e.g., insulin-like growth factor-1 (IGF-1) and neurotrophic tyrosine kinase receptor A (TRKA), as well as the ERK and PI3K pathways]. Employing leading-edge subset analysis and real-time PCR assays, we observed that several genes, such as growth factor receptor-bound protein 2 (GRB2), son of sevenless homolog 1 (SOS1), SHC (Src homology 2 domain containing) transforming protein 1 (SHC1), mitogen-activated protein kinase kinase 1 (MAP2K1), v-akt murine thymoma viral oncogene homolog 3 (AKT3), ELK1, ribosomal protein S6 kinase, 90kDa, polypeptide 3 (RPS6KA3), glycogen synthase kinase 3β (GSK3β) and casein kinase 2, alpha 1 polypeptide (CSNK2A1), which are involved in mitogenic growth factor signaling pathways, were commonly downregulated in the VSELs. Notably, this repression was reversed in the VSELs co-cultured over a C2C12 supportive cell-line, whereby they are induced to form VSEL-derived spheres (VSEL-DSs); thus, they are enriched, forming more differentiated stem cells. Therefore, we suggest that the repression of mitogenic growth factor signaling (e.g., through the IGF-1 receptor) may prevent uncontrolled Oct4⁺ VSEL proliferation and teratoma formation. Thus, restoring the responsiveness to mitogenic growth factors may be a crucial step in employing these cells in regenerative medicine.

Comparative analysis of reference gene stability in human mesenchymal stromal cells during osteogenic differentiation

Mesenchymal stromal cells (MSCs) are one of the most frequently used cell sources for tissue engineering strategies. Cultivation of osteogenic MSCs is a prerequisite for cell-based concepts that aim at bone regeneration. Quantitative real time reverse transcription polymerase chain reaction (qRT-PCR) analysis is a commonly used method for the examination of mRNA expression levels. However, data on suitable reference genes for osteogenically cultivated MSCs is scarce. Hence, the aim of the study was to compare the regulation of different potential reference genes in osteogenically stimulated MSCs. Human MSCs were isolated from bone marrow aspirates of N = 6 hematologically healthy individuals, expanded by polystyrene-adherence, and maintained with and without osteogenic supplements for 14 days. Cellular proliferation and osteogenic differentiation were assessed by total DNA quantification, cell-specific alkaline phosphatase (ALP) activity and by qualitative staining for ALP and alizarin red, respectively. mRNA expression levels of N = 32 potential reference genes were quantified using the human Endogenous Control TaqMan® assays. mRNA expression stability was calculated using geNorm. The combined use of the most stable reference genes and DNA-damage-inducible alpha, Pumilio homolog 1, and large ribosomal protein P0 significantly improved gene expression accuracy as compared to the use of the commonly used reference genes beta actin and glyceraldehyde-3-phosphate dehydrogenase during qRT-PCR-based target gene expression analysis of osteogenically stimulated MSCs.

Pre-stem cell formation by non-platelet RNA-containing particle fusion

We found a group of non-platelet RNA-containing particles (NPRCP) in human umbilical cord blood. To understand the origin, characterization and differentiation of NPRCP, we examined cord blood-isolated NPRCP in vitro. The NPRCP range in size from < 1 to 5 μm, have a thin bilayer membrane and various morphological features, contain short RNA and microRNA and express octamer-binding transcription factor 4 (OCT4), sex-determining region Y 2 (SOX2) and DEAD box polypeptide 4 (DDX4). On coculture with nucleated cells from umbilical cord blood, NPRCP fuse to small, active, non-nucleated cells called 'particle fusion-derived non-nucleated cells' (PFDNC). The PFDNC are approximately 8 μm in diameter and are characterized by their twisting movement in culture plates. They can easily move into and out of nucleated cells and finally differentiate into mesenchymal-like cells. In addition, the larger non-nucleated cellular structures that are derived from the aggregation and fusion of multiple NPRCP can further differentiate into large stem cells that also release OCT4- and SOX2-positive non-nucleated small cells. Our data provide strong evidence that NPRCP can fuse into PFDNC, which further differentiate into mesenchymal-like cells. Multiple NPRCP also fuse into other types of large stem cells. We believe that stem cells are derived from NPRCP fusion. There is considerable potential for the use of NPRCP in clinical therapy.

Very small embryonic-like cells: biology and function of these potential endogenous pluripotent stem cells in adult tissues

Very small embryonic-like cells (VSELs), found in murine bone marrow and other adult tissues, are small, non-hematopoietic cells expressing markers of pluripotent embryonic and primordial germ cells. A similar cell type in humans has begun to be characterized, though with a slightly different phenotype and surface markers. Consistent with expression of pluripotency genes, murine VSELs differentiate into cell types from three germ-layer lineages in vitro, though pluripotency has yet to be shown at the single-cell level or in vivo. VSELs appear to be quiescent under steady state conditions, apparently due to partially erased imprinting and overexpression of cell cycle inhibitory genes. In vivo, VSELs can enter the cell cycle under stress conditions, but which factors regulate quiescence versus proliferation and self-renewal versus differentiation are as yet unknown, and in vitro conditions that induce proliferation and self-renewal have yet to be defined. Future experiments are needed to address whether a VSEL niche actively regulates quiescence in vivo or quiescence is cell autonomous under steady state conditions. Insights into these mechanisms may help to address whether or not VSELs could play a role in regenerative medicine in the future.

Histologic, biomechanical, and biological evaluation of fan-folded iliotibial band allografts for anterior cruciate ligament reconstruction

PURPOSE

The purpose of this study was to thoroughly characterize the fan-folded iliotibial band (FITB) allograft and compare it with anterior tibialis tendons (ATs) and native anterior cruciate ligaments (ACLs) to determine whether it measures up to those tissues.

METHODS

We compared the histologic structure, tensile strength to failure, creep, and stress-relaxation properties of FITBs with those of ATs and ACLs. In vitro cytotoxicity and biocompatibility of FITBs were also compared with ATs.

RESULTS

No structural difference was observed between the tissues studied. FITB ultimate tensile strength (3,459 ± 939 N) was not significantly different (P > .9999) from ultimate tensile strength of ATs (3,357 ± 111 N) and was significantly greater (P = .0005) than that of ACLs (886 ± 254 N). No significant difference (P > .9999) was observed in the increase in length resulting from creep testing between FITBs (9.5 ± 3.0 mm) and ATs (9.7 ± 4.0 mm). During stress-relaxation testing, FITBs reached 181 ± 46 N, which was not significantly different (P > .9999) from ATs (166 ± 40 N). Finally, we showed that cytotoxicity of FITBs and ATs was negligible. In vitro biocompatibility of FITBs and ATs was very good, whereas FITBs had a higher propensity to favor the attachment and infiltration of cells that proliferated for at least 4 weeks on their contact.

CONCLUSIONS

We found that FITBs, ACLs, and ATs shared a similar structure made of aligned collagen fibers. No significant difference was observed between FITB and AT ultimate tensile strength, creep, and stress-relaxation viscoelastic properties. Ultimate tensile strength to failure of ACLs was lower than that of FITBs and ATs, whereas ACLs were superior to both FITBs and ATs during creep and stress-relaxation testing. FITBs and ATs showed low cytotoxicity and excellent biocompatibility in vitro, with a somewhat higher propensity of FITBs to favor cell attachment and infiltration over time.

CLINICAL RELEVANCE

This study suggests that FITBs have the potential to perform as well as ATs for ACL reconstruction.

Bone progenitors produced by direct osteogenic differentiation of the unprocessed bone marrow demonstrate high osteogenic potential in vitro and in vivo

Tissue-engineered bone grafts seeded with mesenchymal stem cells (MSCs) have been sought as a replacement for bone grafts currently used for bone repair. For production of osteogenic constructs, MSCs are isolated from bone marrow (BM) or other tissues, expanded in culture, then trypsinized, and seeded on a scaffold. Predifferentiation of seeded cells is often desired. We describe here bone progenitor cells (BPCs) obtained by direct osteogenic differentiation of unprocessed BM bypassing isolation of MSCs. Human BM aspirates were incubated for 2 weeks with a commonly used osteogenic medium (OM), except no fetal calf serum, serum substitutes, or growth factors were added, because responding stem and/or progenitor cells were present in the BM milieu. The adherent cells remaining after the culture medium and residual BM were washed out, expressed high levels of bone-specific alkaline phosphatase (ALP) on their surface, demonstrated high ALP activity, were capable of mineralization of the intercellular space, and expressed genes associated with osteogenesis. These parameters in BPCs were similar and even at higher levels compared to MSCs subjected to osteogenic differentiation for 2 weeks. The yield of BPCs per 1 mL BM was 0.71±0.39×10(6). In comparison, the yield of MSCs produced by adhesion of mononuclear cells derived from the same amount of BM and cultured in a commercial growth medium for 2 weeks was 0.3±0.17×10(6). When a scaffold was added to the BM-OM mixture, and the mixture was cultured in a simple rotational bioreactor; the resulting BPCs were obtained already seeded on the scaffold. BPCs seeded on scaffolds were capable of proliferation for at least 6 weeks, keeping high levels of ALP activity, expressing osteogenic genes, and mineralizing the scaffolds. Autologous rat BPCs seeded on various scaffolds were transplanted into critical-size calvarial defects. Six weeks after transplantation of polylactic acid/polyglycolic acid scaffolds, 76.1%±18.3% of the defects were filled with a new bone, compared to 37.9%±28.4% in the contralateral defects transplanted with the scaffolds without cells.

Concise review: adult mesenchymal stem cells, adult neural crest stem cells, and therapy of neurological pathologies: a state of play

Adult stem cells are endowed with in vitro multilineage differentiation abilities and constitute an attractive autologous source of material for cell therapy in neurological disorders. With regard to lately published results, the ability of adult mesenchymal stem cells (MSCs) and neural crest stem cells (NCSCs) to integrate and differentiate into neurons once inside the central nervous system (CNS) is currently questioned. For this review, we collected exhaustive data on MSC/NCSC neural differentiation in vitro. We then analyzed preclinical cell therapy experiments in different models for neurological diseases and concluded that neural differentiation is probably not the leading property of adult MSCs and NCSCs concerning neurological pathology management. A fine analysis of the molecules that are secreted by MSCs and NCSCs would definitely be of significant interest regarding their important contribution to the clinical and pathological recovery after CNS lesions.

Basal expression of pluripotency-associated genes can contribute to stemness property and differentiation potential

Pluripotency and stemness is believed to be associated with high Oct-3/4, Nanog, and Sox-2 (ONS) expression. Similar to embryonic stem cells (ESCs), high ONS expression eventually became the measure of pluripotency in any cell. The threshold expression of ONS genes that underscores pluripotency, stemness, and differentiation potential is still unclear. Therefore, we raised a question as to whether pluripotency and stemness is a function of basal ONS gene expression. To prove this, we carried out a comparative study between basal ONS expressing NIH3T3 cells with pluripotent mouse bone marrow mesenchymal stem cells (mBMSC) and mouse ESC. Our studies on cellular, molecular, and immunological biomarkers between NIH3T3 and mBMSC demonstrated stemness property of undifferentiated NIH3T3 cells that was similar to mBMSC and somewhat close to ESC as well. In vivo teratoma formation with all three germ layer derivatives strengthen the fact that these cells in spite of basal ONS gene expression can differentiate into cells of multiple lineages without any genetic modification. Conclusively, our novel findings suggested that the phenomenon of pluripotency which imparts ability for multilineage cell differentiation is not necessarily a function of high ONS gene expression.

[Conception and studies of micro and nanomedicines for brain applications]

As far as micromedicines are concerned, we are interested in the microencapsulation of recombinant proteins, to generate microcarriers upon which living cells can be adsorbed, a highly challenging technology. The whole system forms a Pharmacologically Active Microcarrier (PAM) to be used in cell therapy in the context of neurodegenerative diseases. More precisely, the PAMs are used for tissue engineering, they will increase cell survival time as well as the differentiation and integration of grafted cells following transplants in animals, these micromedicines can also activate the regenerative potential of adult stem cells such as the MIAMI cells. Within the domain of nanomedicines, we are pursuing the development of lipid nanocapsules that act as biomimetic nanovectors resembling lipoproteins. We are studying systematically the biodistribution profiles of these nanomedicines depending on their route of administration, local or systemic. In particular, we are trying to define the essential physicochemical parameters of these nanovectors that, after administration, control the targeting of tumours. In the same way, we are trying to understand how these nanomedicines cross biological barriers and how they interact with cells. In terms of preclinical applications, we are focusing on glioblastomas. The route of administration can be systemic or local. The most promising results in terms of survival of tumour-bearing animals were obtained by infusing radioactive nanocapsules intratumourally, in order to achieve an in-situ radiotherapy approach.

Multipotent adult progenitor cell-loaded demineralized bone matrix for bone tissue engineering

Multipotent adult progenitor cells (MAPCs) from bone marrow have been shown to be capable of forming bone, cartilage and other connective tissues. In addition, MAPCs differentiate into lineages that are different from their germ layers of origin. Previous studies showed the ability of MAPCs to improve cardiac function and control allogenic-reactive responses associated with acute graft versus host disease. In the current study, we evaluated the ability of MAPCs to produce bone matrix on demineralized bone allograft substrates. Specifically, MAPCs expressed alkaline phosphatase, produced extracellular matrix proteins and deposited calcium-containing mineral on demineralized bone matrices. Furthermore, the addition of MAPCs on demineralized bone matrix (DBM) scaffolds enhanced osteoinductivity of the carrier in a rat ectopic pouch model. These results demonstrated the potential of MAPCs as a new approach for bone repair in tissue-engineering applications.

Mesenchymal stem cells promote alveolar epithelial cell wound repair in vitro through distinct migratory and paracrine mechanisms

Background

Mesenchymal stem cells (MSC) are in clinical trials for widespread indications including musculoskeletal, neurological, cardiac and haematological disorders. Furthermore, MSC can ameliorate pulmonary fibrosis in animal models although mechanisms of action remain unclear. One emerging concept is that MSCs may have paracrine, rather than a functional, roles in lung injury repair and regeneration.

Methods

To investigate the paracrine role of human MSC (hMSC) on pulmonary epithelial repair, hMSC-conditioned media (CM) and a selected cohort of hMSC-secretory proteins (identified by LC-MS/MS mass spectrometry) were tested on human type II alveolar epithelial cell line A549 cells (AEC) and primary human small airway epithelial cells (SAEC) using an in vitro scratch wound repair model. A 3D direct-contact wound repair model was further developed to assess the migratory properties of hMSC.

Results

We demonstrate that MSC-CM facilitates AEC and SAEC wound repair in serum-dependent and –independent manners respectively via stimulation of cell migration. We also show that the hMSC secretome contains an array of proteins including Fibronectin, Lumican, Periostin, and IGFBP-7; each capable of influencing AEC and SAEC migration and wound repair stimulation. In addition, hMSC also show a strong migratory response to AEC injury as, supported by the observation of rapid and effective AEC wound gap closure by hMSC in the 3D model.

Conclusion

These findings support the notion for clinical application of hMSCs and/or their secretory factors as a pharmacoregenerative modality for the treatment of idiopathic pulmonary fibrosis (IPF) and other fibrotic lung disorders.

Enrichment and characterization of human dermal stem/progenitor cells by intracellular granularity

Adult stem cells from the dermis would be an attractive cell source for therapeutic purposes as well as studying the process of skin aging. Several studies have reported that human dermal stem/progenitor cells (hDSPCs) with multipotent properties exist within the dermis of adult human skin. However, these cells have not been well characterized, because methods for their isolation or enrichment have not yet been optimized. In the present study, we enriched high side scatter (SSC(high))-hDSPCs from normal human dermal fibroblasts using a structural characteristic, intracellular granularity, as a sorting parameter. The SSC(high)-hDSPCs had high in vitro proliferation properties and expressed high levels of SOX2 and S100B, similar to previously identified mouse SOX2+ hair follicle dermal stem cells. The SSC(high)-hDSPCs could differentiate into not only mesodermal cell types, for example, adipocytes, chondrocytes, and osteoblasts, but also neuroectodermal cell types, such as neural cells. In addition, the SSC(high)-hDSPCs exhibited no significant differences in the expression of nestin, vimentin, SNAI2, TWIST1, versican, and CORIN compared with non-hDSPCs. These cells are therefore different from the previously identified multipotent fibroblasts and skin-derived progenitors. In this study, we suggest that hDSPCs can be enriched by using characteristic of their high intracellular granularity, and these SSC(high)-hDSPCs exhibit high in vitro proliferation and differentiation potentials.

Isolation of viable human hepatic progenitors from adult livers is possible even after 48 hours of cold ischemia

Liver transplantation, utilized routinely for end-stage liver disease, has been constrained by the paucity of organ donors, and is being complemented by alternative strategies such as liver cell transplantation. One of the most promising forms of liver cell transplantation is hepatic stem cell therapies, as the number of human hepatic stem cells (hHpSCs) and other early hepatic progenitor cells (HPCs) are sufficient to provide treatment for multiple patients from a single liver source. In the present study, human adult livers were exposed to cold ischemia and then processed after <24 or 48 h. Cells positive for epithelial cell adhesion molecule (EpCAM), a marker on early lineage stage HPCs, were immunoselected and counted. Approximately 100,000 EpCAM(+) cells/gram of tissue was obtained from surgical resection of livers subjected to cold ischemia up to 24 h and comparable numbers, albeit somewhat lower, were obtained from those exposed to 48 h of cold ischemia. The yields are similar to those reported from livers with minimal exposure to ischemia. When cultured on plastic dishes and in Kubota's Medium, a serum-free medium designed for early lineage stage HPCs, colonies of rapidly expanding cells formed. They were confirmed to be probable hHpSCs by their ability to survive and expand on plastic and in Kubota's Medium for months, by co-expression of EpCAM and neural cell adhesion molecule, minimal if any albumin expression, with EpCAM found throughout the cells, and no expression of alpha-fetoprotein. The yields of viable EpCAM(+) cells were surprisingly large, and the numbers from a single donor liver are sufficient to treat approximately 50-100 patients given the numbers of EpCAM(+) cells currently used in hepatic stem cell therapies. Thus, cold ischemic livers for up to 48 h are a new source of cells that might be used for liver cell therapies.

Mesenchymal stromal/stem cells markers in the human bone marrow

BACKGROUND AIMS

Mesenchymal stromal/stem cells (MSCs) can be isolated from human bone marrow (BM), expanded ex vivo and identified via numerous surface antigens. Despite the importance of these cells in regenerative therapy programs, it is unclear whether the cell membrane signature defining MSC preparations ex vivo is determined during culture or may reflect an in vivo counterpart. BM-MSC phenotype in vivo requires further investigation.

METHODS

To characterize cells in their natural BM environment, we performed multi-parametric immunohistochemistry on trabecular bone biopsy specimens from multiple donors and described cells by different morphology and micro-anatomic localization in relationship to a precise pattern of MSC antigen expression.

RESULTS

Microscopically examined high-power field marrow sections revealed an overlapping in vivo expression of antigens characterizing ex vivo expanded BM-MSCs, including CD10, CD73, CD140b, CD146, GD2 and CD271. Expanding this panel to proteins associated with pluripotency, such as Oct4, Nanog and SSEA-4, we were able to identify different cellular populations in the human trabecular bone and BM expressing different progenitor cell markers.

CONCLUSIONS

Targeting several multipotency and pluripotency markers, we found that the BM contains identifiable and distinct progenitor cells further justifying their introduction for a wide range of applications in regenerative medicine.

Isolation of mesenchymal stem cells from human bone and long-term cultivation under physiologic oxygen conditions

Bone-derived stroma cells contain a rare subpopulation, which exhibits enhanced stemness characteristics. Therefore, this particular cell type is often attributed the mesenchymal stem cell (MSC). Due to their high proliferation potential, multipotential differentiation capacity, and immunosuppressive properties, MSCs are now widely appreciated for cell therapeutic applications in a multitude of clinical aspects. In line with this, maintenance of MSC stemness during isolation and culture expansion is considered pivot. Here, we provide step-by-step protocols which allow selection for, and in vitro propagation of high quality MSC from human bone.

CD133 Expression Strongly Correlates with the Phenotype of Very Small Embryonic-/Epiblast-Like Stem Cells

CD133 antigen (prominin-1) is a useful cell surface marker of very small embryonic-like stem cells (VSELs). Antibodies against it, conjugated to paramagnetic beads or fluorochromes, are thus powerful biological tools for their isolation from human umbilical cord blood, mobilized peripheral blood, and bone marrow. VSELs are described with the following characteristics: (1) are slightly smaller than red blood cells; (2) display a distinct morphology, typified by a high nuclear/cytoplasmic ratio and an unorganized euchromatin; (3) become mobilized during stress situations into peripheral blood; (4) are enriched in the CD133(+)Lin(-)CD45(-) cell fraction in humans; and (5) express markers of pluripotent stem cells (e.g., Oct-4, Nanog, and stage-specific embryonic antigen-4). The most recent in vivo data from our and other laboratories demonstrated that human VSELs exhibit some characteristics of long-term repopulating hematopoietic stem cells and are at the top of the hierarchy in the mesenchymal lineage. However, still more labor is needed to characterize better at a molecular level these rare cells.

Isolation, enumeration, and expansion of human mesenchymal stem cells in culture

Human bone marrow (BM) contains a population of non-hematopoietic stem cells also termed stromal cells, mesenchymal cells or multipotent mesenchymal stromal cells (MSCs). These cells have unique stem cell-like properties including their ability to self-renew, differentiate into multiple tissue types, and modulate immune cell responses through paracrine effects. These properties have positioned mesenchymal cells as biological agents in clinical trials for various diseases since the 1990s. Mesenchymal cells have been isolated from various tissues and cultured using various media and methods resulting in a lack of standardization in culture methods for these cells. Consequently, cells cultured in different laboratories exhibit different characteristics of MSC-like cells. This chapter outlines protocols for optimal isolation, enumeration, and expansion of human MSCs from BM in fetal bovine serum (FBS)-containing medium, as well as in xeno-free medium.

Density gradient centrifugation compromises bone marrow mononuclear cell yield

Bone marrow mononuclear cells (BMNCs) are widely used in regenerative medicine, but recent data suggests that the isolation of BMNCs by commonly used Ficoll-Paque density gradient centrifugation (DGC) causes significant cell loss and influences graft function. The objective of this study was to determine in an animal study whether and how Ficoll-Paque DGC affects the yield and composition of BMNCs compared to alternative isolation methods such as adjusted Percoll DGC or immunomagnetic separation of polymorphonuclear cells (PMNs). Each isolation procedure was confounded by a significant loss of BMNCs that was maximal after Ficoll-Paque DGC, moderate after adjusted Percoll DGC and least after immunomagnetic PMN depletion (25.6±5.8%, 51.5±2.3 and 72.3±6.7% recovery of total BMNCs in lysed bone marrow). Interestingly, proportions of BMNC subpopulations resembled those of lysed bone marrow indicating symmetric BMNC loss independent from the isolation protocol. Hematopoietic stem cell (HSC) content, determined by colony-forming units for granulocytes-macrophages (CFU-GM), was significantly reduced after Ficoll-Paque DGC compared to Percoll DGC and immunomagnetic PMN depletion. Finally, in a proof-of-concept study, we successfully applied the protocol for BMNC isolation by immunodepletion to fresh human bone marrow aspirates. Our findings indicate that the common method to isolate BMNCs in both preclinical and clinical research can be considerably improved by replacing Ficoll-Paque DGC with adapted Percoll DGC, or particularly by immunodepletion of PMNs.

Murine and human very small embryonic-like cells: a perspective

In 2006, very small embryonic-like (VSEL) stem cells were described as a pluripotent population of prospectively isolated stem cells in adult murine bone marrow (mBM) and human umbilical cord blood (hUCB). While rigorous proof of pluripotency is still lacking, murine VSEL cells have been shown to overlap with an independently identified population of neural crest derived mesenchymal stem cells (MSC). The presence of primitive mesenchymal precursors within the VSEL cell population may partially explain the findings that have led to the concept of an "embryonic-like" stem cell in mBM. However, our own studies on human VSEL cells revealed very little similarity between murine VSEL cells and their reportedly equivalent population in hUCB. On the contrary, our data strongly suggest that human VSEL cells are an aberrant and inactive population that cannot expand in vitro and has neither embryonic nor adult stem cell like properties. Here we critically re-examine the data supporting stemness and pluripotency of murine and human VSEL cells, respectively.

Continuous and uninterrupted oxygen tension influences the colony formation and oxidative metabolism of human mesenchymal stem cells

Mesenchymal stem cells (MSCs) are an attractive cell source for tissue engineering applications due to their multipotentiality and increased expansion potential compared to mature cells. However, the full potential of MSCs for cellular therapies is not realised, due, in part, to premature proliferative senescence and impaired differentiation capacity following expansion under 20% oxygen. Bone marrow MSCs reside under reduced oxygen levels (4%-7% oxygen), thus this study investigates the effects of uninterrupted physiological oxygen tensions (2%, 5%) on MSC expansion and subsequent differentiation. Expansion potential was evaluated from colony formation efficiency, population-doubling rates, and cellular senescence. Colony formation was significantly reduced under 5% oxygen compared to 2% and 20% oxygen. Population-doubling time was initially shorter with 20% oxygen, but subsequently no significant differences in doubling time were detected between the oxygen conditions. MSCs expanded with 20% oxygen contained a greater proportion of senescent cells than those under physiological oxygen levels, indicated by a three to fourfold increase in β-galactosidase staining. This may be related to the approximately twofold enhanced mitochondrial oxygen consumption under this culture condition. Chondrogenic differentiation was achieved following expansion at each oxygen condition. However, osteogenesis was only achieved for cells expanded and differentiated at 20% oxygen, indicated by alkaline phosphatase activity and alizarin red staining. These studies demonstrate that uninterrupted hypoxia may enhance long-term MSC expansion, but results in a population with impaired osteogenic differentiation potential. Thus, novel differentiation conditions are required to enable differentiation to nonchondrogenic lineages using hypoxia-cultured MSCs.

Stem cell educator therapy and induction of immune balance

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease that causes the deficit of pancreatic islet β cells. A true cure has proven elusive despite intensive research pressure by using conventional approaches over the past 25 years. The situation highlights the challenges we face in conquering this disease. Alternative approaches are needed. Increasing evidence demonstrates that stem cells possess the function of immune modulation. We established the Stem Cell Educator therapy by using cord blood-derived multipotent stem cells (CB-SCs). A closed-loop system that circulates a patient's blood through a blood cell separator, briefly co-cultures the patient's lymphocytes with adherent CB-SCs in vitro, and returns the educated lymphocytes (but not the CB-SCs) to the patient's circulation. Our clinical trial reveals that a single treatment with the Stem Cell Educator provides lasting reversal of autoimmunity that allows regeneration of islet β cells and improvement of metabolic control in subjects with long-standing T1D.

Recombinant IL-7/HGFβ efficiently induces transplantable murine hematopoietic stem cells

Difficulty obtaining sufficient hematopoietic stem cells (HSCs) directly from the donor has limited the clinical use of HSC transplantation. Numerous attempts to stimulate the ex vivo growth of purified HSCs with cytokines and growth factors generally have induced only modest increases in HSC numbers while decreasing their in vivo reconstituting ability. We previously developed a recombinant single-chain form of a naturally occurring murine hybrid cytokine of IL-7 and the β chain of hepatocyte growth factor (rIL-7/HGFβ) that stimulates the in vitro proliferation and/or differentiation of common lymphoid progenitors, pre-pro-B cells, and hematopoietic progenitor cells (day 12 spleen colony-forming units) in cultures of mouse BM. Here we used the rIL-7/HGFβ in culture to induce large numbers of HSCs from multiple cell sources, including unseparated BM cells, purified HSCs, CD45- BM cells, and embryonic stem cells. In each instance, most of the HSCs were in the G0 phase of the cell cycle and exhibited reduced oxidative stress, decreased apoptosis, and increased CXCR4 expression. Furthermore, when injected i.v., these HSCs migrated to BM, self-replicated, provided radioprotection, and established long-term hematopoietic reconstitution. These properties were amplified by injection of rIL-7/HGFβ directly into the BM cavity but not by treatment with rIL-7, rHGF, and/or rHGFβ.

Generation of neural stem cell-like cells from bone marrow-derived human mesenchymal stem cells

Under appropriate culture conditions, bone marrow (BM)-derived mesenchymal stem cells are capable of differentiating into diverse cell types unrelated to their phenotypical embryonic origin, including neural cells. Here, we report the successful generation of neural stem cell (NSC)-like cells from BM-derived human mesenchymal stem cells (hMSCs). Initially, hMSCs were cultivated in a conditioned medium of human neural stem cells. In this culture system, hMSCs were induced to become NSC-like cells, which proliferate in neurosphere-like structures and express early NSC markers. Like central nervous system-derived NSCs, these BM-derived NSC-like cells were able to differentiate into cells expressing neural markers for neurons, astrocytes, and oligodendrocytes. Whole-cell patch clamp recording revealed that neuron-like cells, differentiated from NSC-like cells, exhibited electrophysiological properties of neurons, including action potentials. Transplantation of NSC-like cells into mouse brain confirmed that these NSC-like cells retained their capability to differentiate into neuronal and glial cells in vivo. Our data show that multipotent NSC-like cells can be efficiently produced from BM-derived hMSCs in culture and that these cells may serve as a useful alternative to human neural stem cells for potential clinical applications such as autologous neuroreplacement therapies.

Dental pulp stem cells differentiation reveals new insights in Oct4A dynamics

Although the role played by the core transcription factor network, which includes c-Myc, Klf4, Nanog, and Oct4, in the maintenance of embryonic stem cell (ES) pluripotency and in the reprogramming of adult cells is well established, its persistence and function in adult stem cells are still debated. To verify its persistence and clarify the role played by these molecules in adult stem cell function, we investigated the expression pattern of embryonic and adult stem cell markers in undifferentiated and fully differentiated dental pulp stem cells (DPSC). A particular attention was devoted to the expression pattern and intracellular localization of the stemness-associated isoform A of Oct4 (Oct4A). Our data demonstrate that: Oct4, Nanog, Klf4 and c-Myc are expressed in adult stem cells and, with the exception of c-Myc, they are significantly down-regulated following differentiation. Cell differentiation was also associated with a significant reduction in the fraction of DPSC expressing the stem cell markers CD10, CD29 and CD117. Moreover, a nuclear to cytoplasm shuttling of Oct4A was identified in differentiated cells, which was associated with Oct4A phosphorylation. The present study would highlight the importance of the post-translational modifications in DPSC stemness maintenance, by which stem cells balance self-renewal versus differentiation. Understanding and controlling these mechanisms may be of great importance for stemness maintenance and stem cells clinical use, as well as for cancer research.

In vitro and in vivo interactions between glioma and marrow-isolated adult multilineage inducible (MIAMI) cells

The prognosis of patients with malignant glioma remains extremely poor despite surgery and improvements in radio- and chemo-therapies. We recently showed that marrow-isolated adult mutilineage inducible (MIAMI) cells, a subpopulation of human mesenchymal stromal cells (MSCs), can serve as cellular carriers of drug-loaded nanoparticles to brain tumors. However, the safety of MIAMI cells as cellular treatment vectors in glioma therapy must be evaluated, in particular their effect on glioma growth and their fate in a tumor environment. In this study, we showed that MIAMI cells were able to specifically migrate toward the orthotopic U87MG tumor model and did not influence its growth. In this model, MIAMI cells did not give rise to cells resembling endothelial cells, pericytes, cancer-associated fibroblasts (CAFs), or astrocytes. Despite these encouraging results, the effects of MIAMI cells may be glioma-dependent. MIAMI cells did not migrate toward the orthotopic Lab1 GB and they can induce the proliferation of other glioma cell lines in vitro. Furthermore, a fraction of MIAMI cells was found to be in a state of proliferation in the U87MG tumor environment. These findings indicate that the use of MIAMI cells as cellular treatment vectors for malignant tumors must be controlled. These cells may be used as "suicide vectors": vectors for killing not only tumor cells but themselves.

Mesoderm-derived stem cells: the link between the transcriptome and their differentiation potential

Human adult stem cells (hASCs) have become an attractive source for autologous cell transplantation, tissue engineering, developmental biology, and the generation of human-based alternative in vitro models. Among the 3 germ cell layers, the mesoderm is the origin of today's most widely used and characterized hASC populations. A variety of isolated nonhematopoietic mesoderm-derived stem cell populations exist, and all of them show important differences in terms of function, efficacy, and differentiation potential both in vivo and in vitro. To better understand whether the intrinsic properties of these cells contribute to the overall differentiation potential of hASCs, we compared the global gene expression profiles of 4 mesoderm-derived stem cell populations: human adipose tissue-derived stromal cells, human bone marrow-derived stromal cells (hBMSCs), human (fore)skin-derived precursor cells (hSKPs), and human Wharton's jelly-derived mesenchymal stem cells (hWJs). Significant differences in gene expression profiles were detected between distinct stem cell types. hSKPs predominantly expressed genes involved in neurogenesis, skin, and bone development, whereas hWJs and, to some extent, hBMSCs showed an increased expression of genes involved in cardiovascular and liver development. Interestingly, the observed differential gene expression of distinct hASCs could be linked to existing differentiation data in which hASCs were differentiated toward specific cell types. As such, our data suggest that the intrinsic gene expression of the undifferentiated stem cells has an important impact on their overall differentiation potential as well as their application in stem cell-based research. Yet, the factors that define these intrinsic properties remain to be determined.

Mesenchymal stem cells: a potential targeted-delivery vehicle for anti-cancer drug, loaded nanoparticles

The targeted delivery of anticancer agents is a promising field in anticancer therapy. Mesenchymal stem cells (MSCs) have inherent tumor-tropic and migratory properties, which allow them to serve as vehicles for targeted drug delivery systems for isolated tumors and metastatic diseases. MSCs have been successfully studied and discussed as a vehicle for cancer gene therapy. However, MSCs have not yet been discussed adequately as a potential vehicle for traditional anticancer drugs. In this review, we will examine the potential of MSCs as a targeted-delivery vehicle for anticancer drug-loaded nanoparticles (NPs), summarize various challenges, and discuss possible solutions for these challenges.

FROM THE CLINICAL EDITOR

In this review, the feasibility of mesenchymal stem cell-based targeted delivery of anticancer agents is discussed.

Gene expression of single human mesenchymal stem cell in response to fluid shear

Stem cell therapy may rely on delivery and homing through the vascular system to reach the target tissue. An optical tweezer model has been employed to exert different levels of shear stress on a single non-adherent human bone marrow–derived mesenchymal stem cell to simulate physiological flow conditions. A single-cell quantitative polymerase chain reaction analysis showed that collagen type 1, alpha 2 (COL1A2), heat shock 70-kDa protein 1A (HSPA1A) and osteopontin (OPN) are expressed to a detectable level in most of the cells. After exposure to varying levels of shear stress, there were significant variations in gene transcription levels across human mesenchymal stem cells derived from four individual donors. Significant trend towards upregulation of COL1A2 and OPN gene expression following shear was observed in some donors with corresponding variations in HSPA1A gene expression. The results indicate that shear stress associated with vascular flow may have the potential to significantly direct non-adherent stem cell expression towards osteogenic phenotypic expression. However, our results demonstrate that these results are influenced by the selection process and donor variability.

Department of Veterans Affairs Geriatric Research, Education and Clinical Centers: translating aging research into clinical geriatrics

Department of Veterans Affairs (VA) Geriatric Research, Education and Clinical Centers (GRECCs) originated in 1975 in response to the rapidly aging veteran population. Since its inception, the GRECC program has made major contributions to the advancement of aging research, geriatric training, and clinical care within and outside the VA. GRECCs were created to conduct translational research to enhance the clinical care of future aging generations. GRECC training programs also provide leadership in educating healthcare providers about the special needs of older persons. GRECC programs are also instrumental in establishing robust clinical geriatric and aging research programs at their affiliated university schools of medicine. This report identifies how the GRECC program has successfully adapted to changes that have occurred in VA since 1994, when the program's influence on U.S. geriatrics was last reported, focusing on its effect on advancing clinical geriatrics in the last 10 years. This evidence supports the conclusion that, after more than 30 years, the GRECC program remains a vibrant "jewel in the crown of the VA" and is poised to make contributions to aging research and clinical geriatrics well into the future.

Pluripotent and multipotent stem cells in adult tissues

One of the most intriguing questions in stem cell biology is whether pluripotent stem cells exist in adult tissues. Several groups of investigators employing i) various isolation protocols, ii) detection of surface markers, and iii) experimental in vitro and in vivo models, have reported the presence of cells that possess a pluripotent character in adult tissues. Such cells were assigned various operational abbreviations and names in the literature that added confusion to the field and raised the basic question of whether these are truly distinct or overlapping populations of the same primitive stem cells. Unfortunately, these cells were never characterized side-by-side to address this important issue. Nevertheless, taking into consideration their common features described in the literature, it is very likely that various investigators have described overlapping populations of developmentally early stem cells that are closely related. These different populations of stem cells will be reviewed in this paper.

Sarcomas as a mise en abyme of mesenchymal stem cells: exploiting interrelationships for cell mediated anticancer therapy

Mise en abyme meaning "placed into abyss or infinite recurrence" is an apt paradigm for the relentless growth of sarcoma cells. Its alternative meaning, "self-reflexive embedding" fits the central role attributed to cancer stem cells (CSCs). Diversely sourced and defined, mesenchymal stem cells (MSCs) may be the cells of sarcoma origin, evolve a CSC phenotype and/or contribute to tumor growth through inherent qualities for homing, neovascularization, paracrine cross-feeding, microvesicle secretion, cell fusion, entosis and immune modulation. Exploiting these qualities, MSC expressing modified forms of the TNF-related apoptosis-inducing ligand (Apo2L/TRAIL) are being developed to complement more conventional radiation and chemotherapy.

Fluorescent protein engineering by in vivo site-directed mutagenesis

In vivo site-directed mutagenesis by single-stranded deoxyribonucleic acid recombineering is a facile method to change the color of fluorescent proteins (FPs) without cloning. Two different starting alleles of GFP were targeted for mutagenesis: gfpmut3* residing in the Escherichia coli genome and egfp carried by a bacterial/mammalian dual expression lentiviral plasmid vector. Fluorescent protein spectra were shifted by subtle modification of the chromophore region and residues interacting with the chromophore of the FP. Eight different FPs (Violeta, Azure, Aqua, Mar, Celeste, Amarillo, Mostaza, and Bronze) were isolated and shown to be useful in multicolor imaging and flow cytometry of bacteria and transgenic human stem cells. To make in vivo site-directed mutagenesis more efficient, the recombineering method was optimized using the fluorescence change as a sensitive quantitative assay for recombination. A set of rules to simplify mutant isolation by recombineering is provided.

Very small embryonic-like stem cells purified from umbilical cord blood lack stem cell characteristics

Very small embryonic-like (VSEL) cells have been described as putatively pluripotent stem cells present in murine bone marrow and human umbilical cord blood (hUCB) and as such are of high potential interest for regenerative medicine. However, there remain some questions concerning the precise identity and properties of VSEL cells, particularly those derived from hUCB. For this reason, we have carried out an extensive characterisation of purified populations of VSEL cells from a large number of UCB samples. Consistent with a previous report, we find that VSEL cells are CXCR4⁺, have a high density, are indeed significantly smaller than HSC and have an extremely high nuclear/cytoplasmic ratio. Their nucleoplasm is unstructured and stains strongly with Hoechst 33342. A comprehensive FACS screen for surface markers characteristic of embryonic, mesenchymal, neuronal or hematopoietic stem cells revealed negligible expression on VSEL cells. These cells failed to expand in vitro under a wide range of culture conditions known to support embryonic or adult stem cell types and a microarray analysis revealed the transcriptional profile of VSEL cells to be clearly distinct both from well-defined populations of pluripotent and adult stem cells and from the mature hematopoietic lineages. Finally, we detected an aneuploid karyotype in the majority of purified VSEL cells by fluorescence in situ hybridisation. These data support neither an embryonic nor an adult stem cell like phenotype, suggesting rather that hUCB VSEL cells are an aberrant and inactive population that is not comparable to murine VSEL cells.

Characterization of adult stem/progenitor cell populations from bone marrow in a three-dimensional collagen gel culture system

Stem cell transplantation therapy using mesenchymal stem cells (MSCs) is considered a useful strategy. Although MSCs are commonly isolated by exploiting their plastic adherence, several studies have suggested that there are other populations of stem and/or osteoprogenitor cells that are removed from primary culture during media replacement. Therefore, we developed a three-dimensional (3D) culture system in which adherent and nonadherent stem cells are selected and expanded. Here, we described the characterization of 3D culture-derived cell populations in vitro and the capacity of these cells to differentiate into bone and/or cartilage tissue when placed inside of demineralized bone matrix (DBM) cylinders, implanted subcutaneously into the backs of rat for 2, 4, and 8 weeks. Our results demonstrates that 3D culture cells were a heterogeneous population of uncommitted cells that express pluripotent-, hematopoietic-, mesenchymal-, and endothelial-specific markers in vitro and can undergo osteogenic differentiation in vivo.

Very small embryonic/epiblast-like stem cells (VSELs) and their potential role in aging and organ rejuvenation--an update and comparison to other primitive small stem cells isolated from adult tissues

Very small embryonic-like stem cells (VSELs) are a population of developmentally early stem cells residing in adult tissues. These rare cells, which are slightly smaller than red blood cells, i) become mobilized during stress situations into peripheral blood, ii) are enriched in the Sca1+Lin-CD45- cell fraction in mice and the CD133+ Lin-CD45- cell fraction in humans, iii) express markers of pluripotent stem cells (e.g., Oct4, Nanog, and SSEA), and iv) display a distinct morphology characterized by a high nuclear/cytoplasmic ratio and undifferentiated chromatin. Recent evidence indicates that murine VSELs are kept quiescent in adult tissues and protected from teratoma formation by epigenetic modification of imprinted genes that regulate insulin/insulin like growth factor signaling (IIS). The successful reversal of these epigenetic changes in VSELs that render them quiescent will be crucial for efficient expansion of these cells. The most recent data in vivo from our and other laboratories demonstrated that both murine and human VSELs exhibit some characteristics of long-term repopulating hematopoietic stem cells (LT-HSCs), are at the top of the hierarchy in the mesenchymal lineage, and may differentiate into organ-specific cells (e.g., cardiomyocytes). Moreover, as recently demonstrated the number of these cells positively correlates in several murine models with longevity. Finally, while murine BM-derived VSELs have been extensively characterized more work is needed to better characterize these small cells at the molecular level in humans.

A comparison of stem cells for therapeutic use

A critical comparison of the attributes of several types of stem cells is presented, with particular emphasis on properties that are critical for the application of these cells for therapeutic purposes. The importance of an autologous source of pluripotent stem cells is stressed. It is apparent that two sources currently exist for non-embryonic pluripotent stem cells--very small embryonic-like stem cells (VSELs) and induced pluripotent stem cells (iPS). The impact of the emerging iPS research on therapy is considered.

From tendon to nerve: an MSC for all seasons

The potential of mesenchymal stem cells (MSCs) to regenerate damaged tissue is well documented, as this specialized progenitor cell type exhibits superior cellular properties, and would allow medical as well as ethical limitations to be overcome. By now, MSCs have been successfully introduced in manifold experimental approaches within the newly defined realm of Regenerative Medicine. Advanced methods for in vitro cell expansion, defined induction of distinct differentiation processes, 3-dimensional culture on specific scaffold material, and tissue engineering approaches have been designed, and many clinical trials not only have been launched, but recently could be completed. To date, most of the MSC-based therapeutic approaches have been executed to address bone, cartilage, or heart regeneration; further, prominent studies have shown the efficacy of ex vivo expanded and infused MSCs to countervail graft-versus-host disease. Yet more fields of application emerge in which MSCs unfold beneficial effects, and presently, therapies that effectively ameliorate nonhealing conditions after tendon or spinal cord injury are, courtesy of scientific research, forging ahead to the clinical trial stage.

Comparative analysis of protein expression of three stem cell populations: models of cytokine delivery system in vivo

Several mechanisms mediate the regenerative and reparative capacity of stem cells, including cytokine secretion; therefore these cells can act as delivery systems of therapeutic molecules. Here we begin to address the molecular and cellular basis of their regenerative potential by characterizing the proteomic profile of human embryonic stem cells (hESCs), mesenchymal stem cells (hMSCs) and marrow isolated adult multilineage inducible (MIAMI) cells, followed by analysis of the secretory profile of the latter stem cell population. Proteomic analysis establishes the closer relationship between hMSCs and MIAMI cells, while hESCs are more divergent. However, MIAMI cells appear to have more proteins in common with hESCs than hMSCs. Proteins characteristic of hMSCs include transgelin-2, phosphatidylethanolamine-binding protein 1 (PEBP1), Heat-Shock 20 kDa protein (HSP20/HSPβ6), and programmed cell death 6-interacting protein (PDC6I) among others. MIAMI cells are characterized by the high level expression of ubiquitin carboxyl-terminal hydrolase isoenzyme L1 (UCHL1), 14-3-3 zeta, HSP27 (HSPβ1), and tropomyosin 4 and 3. For hESC, elongation factor Tu (EFTu), isocitrate dehydrogenase (IDH1) and the peroxiredoxins 1, 2, and 6 (PRDX1, PRDX2, and PRDX6) were the most characteristic. Secretome analysis indicates that MIAMI cells secrete higher levels of vascular endothelial growth factor (VEGF), Fractalkine, Interleukin-6, interlukin-8, and growth related oncogene (GRO), compared to hMSCs. These soluble mediators are known to play key roles in angiogenesis, arteriogenesis, atheroprotection, immunomodulation, neuroprotection, axonal growth, progenitor cell migration, and prevention of apoptosis. All these roles are consistent with a reparative pro-survival secretory phenotype. We further discuss the potential of these cells as therapeutic vehicles.

Expression pattern of embryonic stem cell markers in DFAT cells and ADSCs

Mature adipocytes can revert to a more primitive phenotype and gain cell proliferative ability under the condition of ceiling method, named dedifferentiated fat cells (DFAT cells). These cells exhibit multilineage potential as adipose tissue-derived stromal cells (ADSCs). However, the stem molecular signature of DFAT cells and the difference distinct from ADSCs are still not sure. To study the molecular signature of DFAT cells better, highly purified mature adipocytes were obtained from rats and the purity was more than 98%, and about 98.6% were monocytes. These mature adipocytes dedifferentiated into fibroblast-like cells spontaneously by the ceiling culture method, these cells proliferated rapidly in vitro, grew in the same direction and formed vertex, and expressed extensively embryonic stem cell markers such as Oct4, Sox2, c-Myc, and Nanog, surface antigen SSEA-1, CD105, and CD31, moreover, these cells possessed ALP and telomerase activity. The expression level was Oct4 1.3%, Sox2 1.3%, c-Myc 1.2%, Nanog 1.2%, CD105 0.6%, CD31 0.6% and SSEA-1 0.4%, respectively, which was lower than that in ADSCs, but the purity of DFAT cells was much higher than that of ADSCs. In conclusion, DFAT cells is a highly purified stem cell population, and expressed some embryonic stem cell markers like ADSCs, which seems to be a good candidate source of adult stem cells for the future cell replacement therapy.

Mesenchymal cell populations: development of the induction systems for Schwann cells and neuronal cells and finding the unique stem cell population

Mesenchymal cell populations, referred to as mesenchymal stem cells or multipotent stromal cells (MSCs), which include bone marrow stromal cells (BMSCs), umbilical cord stromal cells and adipose stromal cells (ASCs), participate in tissue repair when transplanted into damaged or degenerating tissues. The trophic support and immunomodulation provided by MSCs can protect against tissue damage, and the differentiation potential of these cells may help to replace lost cells. MSCs are easily accessible and can be expanded on a large scale. In addition, BMSCs and ASCs can be harvested from the patient himself. Thus, MSCs are considered promising candidates for cell therapy. In this review, I will discuss recently discovered high-efficiency induction systems for deriving Schwann cells and neurons from MSCs. Other features of MSCs that are important for tissue repair include the self-renewing property of stem cells and their potential for differentiation. Thus, I will also discuss the stemness of MSCs and describe the discovery of a certain stem cell type among adult MSCs that can self-renew and differentiate into cells of all three germ layers. Furthermore, I will explore the prospects of using this cell population for cell therapy.