Morphological and molecular characterization of novel population of CXCR4+ SSEA-4+ Oct-4+ very small embryonic-like cells purified from human cord blood: preliminary report

Stem cell-based therapeutic applications in retinal degenerative diseases

Retinal degenerative diseases that target photoreceptors or the adjacent retinal pigment epithelium (RPE) affect millions of people worldwide. Retinal degeneration (RD) is found in many different forms of retinal diseases including retinitis pigmentosa (RP), age-related macular degeneration (AMD), diabetic retinopathy, cataracts, and glaucoma. Effective treatment for retinal degeneration has been widely investigated. Gene-replacement therapy has been shown to improve visual function in inherited retinal disease. However, this treatment was less effective with advanced disease. Stem cell-based therapy is being pursued as a potential alternative approach in the treatment of retinal degenerative diseases. In this review, we will focus on stem cell-based therapies in the pipeline and summarize progress in treatment of retinal degenerative disease.

Neurogenic properties and a clinical relevance of multipotent stem cells derived from cord blood samples stored in the biobanks

Several innovative therapies with human umbilical cord blood stem cells (SCs) are currently developing to treat central nervous system (CNS) diseases. It has been shown that cord blood contains multipotent lineage-negative (LinNEG) SCs capable of neuronal differentiation. Clinically useful cord blood samples are stored in different biobanks worldwide, but the content and neurogenic properties of LinNEG cells are unknown. Here we have compared 5 major methods of blood processing: Sepax, Hetastarch, plasma depletion, Prepacyte-SC, and density gradient. We showed that Sepax-processed blood units contained 10-fold higher number of LinNEG cells after cryopreservation in comparison to all other methods. We showed in this study that multipotent SCs derived from fresh and frozen cord blood samples could be efficiently induced in defined serum-free medium toward neuronal progenitors (NF200+, Ki67+). During neuronal differentiation, the multipotent SCs underwent precise sequential changes at the molecular and cellular levels: Oct4 and Sox2 downregulation and Ngn1, NeuN, and PSD95 upregulation, similar to neurogenesis process in vivo. We expect that data presented here will be valuable for clinicians, researchers, biobanks, and patients and will contribute for better efficacy of future clinical trials in regeneration of CNS.

Neural stem/progenitor cells circulating in peripheral blood of patients with neovascular form of AMD: a novel view on pathophysiology

Background

The neovascular form of age-related macular degeneration (AMD) manifested with choroidal neovascularization (CNV) is one of the leading causes of rapid and irreversible visual loss. Recent reports suggest that bone marrow-derived stem/progenitor cells (SPCs) play a crucial role in the development and progression of the disease. The purpose of this study was to investigate whether or not undifferentiated non-haematopoietic stem cells, including those capable of differentiating into neural phenotypes, play a role in the pathological state of CNV formation.

Methods

Peripheral blood samples were collected from 46 patients diagnosed with CNV and from 46 controls. The CXCR4⁺Lin^-CD45^- stem cells were counted and analysed by flow cytometry. Using qRT-PCR and immunocytofluorescence, the expression of early neural and glial cell markers (β-III-tubulin, nestin, and glial fibrillary acidic protein) in the sorted cells was analysed, and correlated with plasma concentrations of stromal cell-derived factor 1 (SDF-1) (enzyme-linked immunosorbent assay), which is a pivotal chemokine that regulates the trafficking of SPCs.

Results

We found that the number of circulating CXCR4⁺Lin^-CD45^- cells did not differ in patients with active CNV as compared to the controls. However, we noticed significant intracellular overexpression of β-III-tubulin in the cells derived from AMD patients. Moreover, we observed significantly lower SDF-1 plasma levels in neovascular AMD patients compared to healthy individuals.

Conclusions

Our findings suggest that neural progenitor cells, together with low SDF-1 concentrations, may play a considerable role in the process of AMD progression. Further investigations aimed at the precise elucidation of these issues may help with the future development of effective prevention against, and the treatment of, this disease.

Bone marrow stem cell mobilization in stroke: a 'bonehead' may be good after all!

Mobilizing bone cells to the head, astutely referred to as 'bonehead' therapeutic approach, represents a major discipline of regenerative medicine. The last decade has witnessed mounting evidence supporting the capacity of bone marrow (BM)-derived cells to mobilize from BM to peripheral blood (PB), eventually finding their way to the injured brain. This homing action is exemplified in BM stem cell mobilization following ischemic brain injury. Here, I review accumulating laboratory studies implicating the role of therapeutic mobilization of transplanted BM stem cells for brain plasticity and remodeling in stroke.

The umbilical cord: a rich and ethical stem cell source to advance regenerative medicine

Science and medicine place a lot of hope in the development of stem cell research and regenerative medicine. This review will define the concept of regenerative medicine and focus on an abundant stem cell source - neonatal tissues such as the umbilical cord. Umbilical cord blood has been used clinically for over 20 years as a cell source for haematopoietic stem cell transplantation. Beyond this, cord blood and umbilical cord-derived stem cells have demonstrated potential for pluripotent lineage differentiation (liver, pancreatic, neural tissues and more) in vitro and in vivo. This promising research has opened up a new era for utilization of neonatal stem cells, now used beyond haematology in clinical trials for autoimmune disorders, cerebral palsy or type I diabetes.

Hematopoietic differentiation of umbilical cord blood-derived very small embryonic/epiblast-like stem cells

A population of CD133⁺lin⁻CD45⁻ very small embryonic-like stem cells (VSELs) has been purified by multiparameter sorting from umbilical cord blood (UCB). In order to speed up isolation of these cells, we employed anti-CD133-conjugated paramagnetic beads followed by staining with Aldefluor to detect aldehyde dehydrogenase (ALDH) activity; we subsequently sorted CD45⁻/GlyA⁻/CD133⁺/ALDH^high and CD45⁻/GlyA⁻/CD133⁺/ALDH^low cells, which are enriched for VSELs, and CD45⁺/GlyA⁻/CD133⁺/ALDH^high and CD45⁺/GlyA⁻/CD133⁺/ALDH^low cells, which are enriched for hematopoietic stem/progenitor cells (HSPCs). While freshly isolated CD45⁻ VSELs did not grow hematopoietic colonies, the same cells, when activated/expanded over OP9 stromal support, acquired hematopoietic potential and grew colonies composed of CD45⁺ hematopoietic cells in methylcellulose cultures. We also observed that CD45⁻/GlyA⁻/CD133⁺/ALDH^high VSELs grew colonies earlier than CD45⁻/GlyA⁻/CD133⁺/ALDH^low VSELs, which suggests that the latter cells need more time to acquire hematopoietic commitment. In support of this possibility, real-time PCR analysis confirmed that, while freshly isolated CD45⁻/GlyA⁻/CD133⁺/ALDH^high VSELs express more hematopoietic transcripts (e.g., c-myb), CD45⁻/GlyA⁻/CD133⁺/ALDH^low VSELs exhibit higher levels of pluripotent stem cell markers (e.g., Oct-4). More importantly, hematopoietic cells derived from VSELs that were co-cultured over OP9 support were able to establish human lympho-hematopoietic chimerism in lethally irradiated NOD/SCID mice 4–6 weeks after transplantation. Overall, our data suggest that UCB-VSELs correspond to the most primitive population of HSPCs in UCB.

Umbilical cord blood cell transplantation after brain ischemia--from recovery of function to cellular mechanisms

Cell transplantation has been proposed as a potential approach to the treatment of neurological disorders. One cell population of interest consists of human umbilical cord blood (hUCB) cells, which have previously been shown to be useful for reparative medicine in haematological diseases. However, hUCB cells are also capable of differentiating into various non-haematopoietic cells, including those of the neural lineage. Moreover, hUCB cells can secrete numerous neurotrophic factors and modulate immune function and inflammatory reaction. Several studies on animal models of ischemic brain injury have demonstrated the potential of hUCB cells to minimize damage and promote recovery after ischemic brain injury.This review focuses on the treatment of both stroke and perinatal hypoxic-ischemic brain injury using hUCB cells. We discuss the therapeutic effects demonstrated after hUCB cell transplantation and emphasize possible mechanisms counteracting pathophysiological events of ischemia, thus leading to the generation of a regenerative environment that allows neural plasticity and functional recovery. The therapeutic functional effects of hUCB cells observed in animal models make the transplantation of hUCB cells a promising experimental approach in the treatment of ischemic brain injury. Together with its availability, low risk of transplantation, immaturity of cells, and simple route of application, hUCB transplantation may stand a good chance of being translated into a clinical setting for the therapy of ischemic brain injury.

A novel insight into aging: are there pluripotent very small embryonic-like stem cells (VSELs) in adult tissues overtime depleted in an Igf-1-dependent manner?

Tissue and organ rejuvenation and senescence/aging are closely related to the function of stem cells. Recently, we demonstrated that a population of pluripotent Oct-4+ SSEA-1+Sca-1+Lin-CD45- very small embryonic-like stem cells (VSELs) resides in the adult murine bone marrow (BM) and other murine tissues. We hypothesize that these pluripotent stem cells play an important role in tissue/organ rejuvenation, and have demonstrated that their proliferation and potentially premature depletion is negatively controlled by epigenetic changes of some imprinted genes that regulate insulin factor signaling (Igf2-H19 locus, Igf2R and RasGRF1). Since the attenuation of insulin/insulin growth factor (Ins/Igf) signaling positively correlates with longevity, we propose, based on our experimental data, that gradual decrease in the number of VSELs deposited in adult tissues, which occurs throughout life in an Ins/Igf signaling-dependent manner is an important mechanism of aging. In contrast, a decrease in Ins/Igf stimulation of VSELs that extends the half life of these cells in adult organs would have a beneficial effect on life span. Our preliminary data in long-living Igf-1-signaling-deficient mice show that these animals possess a 3-4 times higher number of VSELs deposited in adult BM, lending support to this novel hypothesis.

The role of pluripotent embryonic-like stem cells residing in adult tissues in regeneration and longevity

From the point of view of regenerative potential, the most important cells are pluripotent stem cells (PSCs). Such cells must fulfill certain in vitro as well as in vivo criteria that have been established by work with PSCs isolated from embryos, which are known as embryonic stem cells (ESCs). According to these criteria, pluripotent stem cells should: (i) give rise to cells from all three germ layers, (ii) complete blastocyst development, and (iii) form teratomas after inoculation into experimental animals. Unfortunately, in contrast to immortalized embryonic ESC lines or induced PSCs (iPSCs), these last two criteria have thus far not been obtained in a reproducible manner for any potential PSC candidates isolated from adult tissues. There are two possible explanations for this failure. The first is that PSCs isolated from adult tissues are not fully pluripotent; the second is that there are some physiological mechanisms involved in keeping these cells quiescent in adult tissues that preclude their "unleashed proliferation", thereby avoiding the risk of teratoma formation. In this review we present an evidence that adult tissues contain remnants from development; a population of PSCs that is deposited in various organs as a backup for primitive stem cells, plays a role in rejuvenation of the pool of more differentiated tissue-committed stem cells (TCSCs), and is involved in organ regeneration. These cells share several markers with epiblast/germ line cells and have been named very small embryonic-like stem cells (VSELs). We suggest that, on one hand, VSELs maintain mammalian life span but, on the other hand, they may give rise to several malignancies if they mutate. We provide an evidence that the quiescent state of these cells in adult tissues, which prevents teratoma formation, is the result of epigenetic changes in some of the imprinted genes.

Prospective identification and skeletal localization of cells capable of multilineage differentiation in vivo

A prospective in vivo assay was used to identify cells with potential for multiple lineage differentiation. With this assay, it was first determined that the 5-fluorouracil resistant cells capable of osseous tissue formation in vivo also migrated toward stromal derived factor-1 (SDF-1) in vitro. In parallel, an isolation method based on fluorescence-activated cell sorting was employed to identify a very small cell embryonic-like Lin-/Sca-1+CD45- cell that with as few as 500 cells was capable of forming bone-like structures in vivo. Differential marrow fractionation studies determined that the majority of the Lin-Sca-1+CD45- cells reside in the subendosteal regions of marrow. To determine whether these cells were capable of differentiating into multiple lineages, stromal cells harvested from Col2.3 Delta TK mice were implanted with a gelatin sponge into SCID mice to generate thymidine kinase sensitive ossicles. At 1.5 months, 2,000 green fluorescent protein (GFP)+ Lin-Sca-1+CD45- cells were injected into the ossicles. At harvest, colocalization of GFP-expressing cells with antibodies to the osteoblast-specific marker Runx-2 and the adipocyte marker PPAP gamma were observed. Based on the ability of the noncultured cells to differentiate into multiple mesenchymal lineages in vivo and the ability to generate osseous tissues at low density, we propose that this population fulfills many of the characteristics of mesenchymal stem cells.

Identification and isolation from either adult human bone marrow or G-CSF-mobilized peripheral blood of CD34(+)/CD133(+)/CXCR4(+)/ Lin(-)CD45(-) cells, featuring morphological, molecular, and phenotypic characteristics of very small embryonic-like (VSEL) stem cells

OBJECTIVE

Recently, we demonstrated that normal human bone marrow (hBM)-derived CD34(+) cells, released into the peripheral blood after granulocyte colony-stimulating factor mobilization, contain cell subpopulations committed along endothelial and cardiac differentiation pathways. These subpopulations could play a key role in the regeneration of post-ischemic myocardial lesion after their direct intracardiac delivery. We hypothesized that these relevant cells might be issued from very small embryonic-like stem cells deposited in the BM during ontogenesis and reside lifelong in the adult BM, and that they could be mobilized into peripheral blood by granulocyte colony-stimulating factor.

MATERIALS AND METHODS

Samples of normal hBM and leukapheresis products harvested from cancer patients after granulocyte colony-stimulating factor mobilization were analyzed and sorted by multiparameter flow cytometry strategy. Immunofluorescence and reverse transcription quantitative polymerase chain reaction assays were performed to analyze the expression of typical pluripotent stem cells markers.

RESULTS

A population of CD34(+)/CD133(+)/CXCR4(+)/Lin(-) CD45(-) immature cells was first isolated from the hBM or from leukapheresis products. Among this population, very small (2-5 μm) cells expressing Oct-4, Nanog, and stage-specific embryonic antigen-4 at protein and messenger RNA levels were identified.

CONCLUSIONS

Our study supports the hypothesis that very small embryonic-like stem cells constitute a "mobile" pool of primitive/pluripotent stem cells that could be released from the BM into the peripheral blood under the influence of various physiological or pathological stimuli. In order to fully support that hBM- and leukapheresis product-derived very small embryonic-like stem cells are actually pluripotent, we are currently testing their ability to differentiate in vitro into cells from all three germ layers.

Cord blood transplantation and stem cell regenerative potential

The past 20 years of experience with umbilical cord blood transplantation have demonstrated that cord blood is effective in the treatment of a spectrum of diseases, including hematological malignancies, bone marrow failure, hemoglobinopathies, and inborn errors of metabolism. Cord blood can be obtained with ease and then safely cryopreserved for either public or private use without loss of viability. As compared to other unrelated donor cell sources, cord blood transplantation allows for greater human leukocyte antigen disparity without a corresponding increase in graft-vs.-host disease. Moreover, cord blood has a lower risk of transmitting infections by latent viruses and is less likely to carry somatic mutations than other adult cells. Recently, multiple populations of stem cells with primitive stem cell properties have been identified from cord blood. Meanwhile, there is an increasing interest in applying cord blood mononuclear cells or enriched stem cell populations to regenerative therapies. Accumulating evidence has suggested functional improvements after cord blood transplantation in various animal models for treatments of cardiac infarction, diabetes, neurological diseases, etc. In this review, we will summarize the most recent updates on clinical applications of cord blood transplantation and the promises and limitations of cell-based therapies for tissue repair and regeneration.

Could autologous cord blood stem cell transplantation treat cerebral palsy?

The young human brain is highly plastic and thus early brain lesions can lead to aberrant development of connectivity and mapping of functions. This is why initially in cerebral palsy only subtle changes in spontaneous movements are seen after the time of lesion, followed by a progressive evolution of a movement disorder over many months and years. Thus we propose that interventions to treat cerebral palsy should be initiated as soon as possible in order to restore the nervous system to the correct developmental trajectory. One such treatment might be autologous stem cell transplantation either intracerebrally or intravenously. All babies come with an accessible supply of stem cells, the umbilical cord, which can supply cells that could theoretically replace missing neural cell types, or act indirectly by supplying trophic support or modulating inflammatory responses to hypoxia/ischaemia. However, for such radical treatment to be proposed, it is necessary to be able to detect and accurately predict the outcomes of brain injury from a very early age. This article reviews our current understanding of perinatal injuries that lead to cerebral palsy, how well modern imaging might predict outcomes, what stem cells are yielded from umbilical cord blood and experimental models of brain repair using stem cells.

Analytical capabilities of the ImageStream cytometer

Imaging cytometry has recently become an important achievement in development of flow cytometric technologies. The ImageStream cytometer combines the vast features of classical flow cytometry including an impartial analysis of great number of cells in short period of time which results in strong statistical data output, with essential features of fluorescence microscopy such us collecting of real multiparameter images of analyzed objects. In this chapter, we would like to introduce an overview of imaging cytometry platform and emphasize the potential advantages of using this system for several experimental purposes. Moreover, both well established as well as potential applications of imaging cytometry will be described. Eventually, we would like to illustrate the unique use of ImageStream cytometer for identification and characterization of subpopulations of stem/ progenitor cells present in different biological specimens.

Very small embryonic-like stem cells (VSELs)-a new promising candidate for use in cardiac regeneration

In recent years, stem cell-based therapy has been given increased attention in terms of its potential contribution to cardiac regeneration and repair, after acute myocardial infarction (AMI). The published studies have identified many kinds of stem cells with the ability to regenerate and repair damaged myocardium after AMI. These include embryonic stem cells (ESCs), mesenchymal stem cells (MSCs), multipotent adult progenitor cells, unrestricted somatic stem cells, etc. More recently, very small embryonic-like stem cells (VSELs) were identified from murine, as a population of very small CXCR4(+) Lin(-) CD45(-) cells and from human, as a population of very small CD34(+) CD133(+) CXCR4(+) Lin(-) CD45(-) cells. These cells exhibit beneficial effects on improving cardiac function and attenuating cardiac remodeling after AMI. However, the mechanisms underlying the benefits associated with VSELs therapy, in cardiac regeneration and repair, remain poorly understood. This review summarizes the current studies on cardiac repair with VSELs after AMI, and discusses the potential mechanisms and implications of these cells in cardiac repair.

Circulating very small embryonic-like stem cells in cardiovascular disease

Very small embryonic-like cells (VSELs) are a population of stem cells residing in the bone marrow (BM) and several organs, which undergo mobilization into peripheral blood (PB) following acute myocardial infarction and stroke. These cells express markers of pluripotent stem cells (PSCs), such as Oct-4, Nanog, and SSEA-1, as well as early cardiac, endothelial, and neural tissue developmental markers. VSELs can be effectively isolated from the BM, umbilical cord blood, and PB. Peripheral blood and BM-derived VSELs can be expanded in co-culture with C2C12 myoblast feeder layer and undergo differentiation into cells from all three germ layers, including cardiomyocytes and vascular endothelial cells. Isolation of VSLEs using fluorescence-activated cell sorting multiparameter live cell sorting system is dependent on gating strategy based on their small size and expression of PSC and absence of hematopoietic lineage markers. VSELs express early cardiac and endothelial lineages markers (GATA-4, Nkx2.5/Csx, VE-cadherin, and von Willebrand factor), SDF-1 chemokine receptor CXCR4, and undergo rapid mobilization in acute MI and ischemic stroke. Experiments in mice showed differentiation of BM-derived VSELs into cardiac myocytes and effectiveness of expanded and pre-differentiated VSLEs in improvement of left ventricular ejection fraction after myocardial infarction.

Cell therapy for heart failure: the need for a new therapeutic strategy

Improvements in the treatment of ischemic heart disease have led to a significant growth in the numbers of patients with systolic heart failure secondary to myocardial injury. Current therapies fail to address the loss of contractile tissue due to myocardial injury. Cell therapy is singular in its promise of primarily treating this underlying issue through salvage of viable myocardium or generation of new contractile tissue. Multiple cell types have been used to target acute myocardial infarction, chronic ischemic heart disease and heart failure due to infarction. Bone marrow mononuclear cells have been used to increase myocardial salvage after acute infarction. Randomized trials of over 800 patients have demonstrated no safety issues, and meta-analyses have suggested an improvement in left ventricular function in treated patients with trends toward improvements in hard cardiac end points. Cell therapy for chronic ischemic heart disease with bone marrow angiogenic progenitors has shown similar safety and trends toward improvement in function. While these therapies have targeted patients with viable myocardium, myoblasts have been used to treat patients with left ventricular dysfunction secondary to transmural infarction. Cell types with cardiomyogenic potential, including induced pluripotent stem cells and cardiac progenitor cells, offer the promise of true myocardial regeneration. Future studies with these cells may open the door for true myocardial regeneration.

Very small embryonic-like stem cells in cardiovascular repair

Adult bone marrow (BM) harbors several small populations of cells which may contribute to cardiac and endothelial repair, such as endothelial progenitor cells (EPCs), mesenchymal stromal cells (MSCs) and very small embryonic-like cells (VSELs) expressing several markers of pluripotent stem cells (PSCs), such as Oct-4, Nanog and SSEA-1. Such cells were identified in mice bone marrow, peripheral blood and solid organs as well as in umbilical cord blood (UCB) and peripheral blood (PB) in humans. The adult BM-derived VSELs may undergo differentiation into cells derived for all three germ layers, including cardiomyocytes and vascular endothelial cells. VSELs can be isolated using a multiparameter live cell sorting technique with special gating strategy based on their small size, expression of stem cell markers (Sca-1 in mice, CXCR4 and CD133 in humans) and absence of hematopoietic lineage markers (CD45(-) Lin(-)). Experiments in murine models of myocardial infarction (MI) demonstrated population of VSELs expressed also early markers of cardiac and endothelial lineages (GATA-4, Nkx2.5/Csx, VE-cadherin, von Willebrand factor) which migrated to stromal-derived factor-1 (SDF-1) and other chemoattractant gradient and underwent rapid mobilization into peripheral blood in experimental MI mice models. Recently, we demonstrated the mobilization of VSELs expressing PSC, early cardiac and endothelial markers in patients with acute MI. In addition to BM, VSELs were also identified in several murine solid organs including the heart and brain, as well as in umbilical cord blood and peripheral blood in adult humans. We hypothesized that VSELs are quiescent progeny of epiblast-derived PSCs that are deposited during organogenesis in developing organs. In experimental MI intramyocardial injection of VSELs was more efficient than that of HSCs at improving left ventricular ejection fraction and attenuation of myocardial hypertrophy. VSELs can be useful in translational studies of cardiovascular repair.

Horizontal DNA transfer from donor to host cells as an alternative mechanism of epithelial chimerism after allogeneic hematopoietic cell transplantation

Animal and human studies have shown that after allogeneic hematopoietic cell transplantation, epithelial cells containing donor-derived genome emerge. The mechanisms underlying this phenomenon are still unclear. We hypothesized that horizontal transfer of the hematopoietic donor-DNA to the host epithelium confers a possible operating mechanism. In an in vitro model mimicking the lymphocyte-epithelial interaction, we cocultivated keratinocyte HaCaT cells (Y-chromosome negative) with nonapoptotic or apoptotic, CMFDA, or BrdU-labeled hematopoietic Jurkat cells (Y+) and looked for the emergence of HaCaT cells bearing Jurkat genome. We found that DNA can be horizontally transferred from hematopoietic to epithelial cell lines through phagocytosis of apoptotic bodies. The ingested genomic material was also found within the nuclear compartment and in isolated chromosomes obtained from HaCaT metaphases. Both lysosomal inhibition in HaCaT cells and repetitive load of HaCaT cells with apoptotic bodies increased the intercellular and intranuclear DNA delivery. Although recipient cells remained viable and showed to express the foreign DNA, this expression was transient. Taking into consideration these findings of horizontal DNA transfer between hematopoietic and epithelial cells, we evaluated by quantitative microsatellite analysis the amount of donor DNA in 176 buccal swabs obtained from 71 patients after allogeneic transplantation. We found a high amount of donor-DNA (mean 26.6%) in the majority (89.7%) of them, although no donor hematopoietic cells were evident in the samples by immunofluorescence. We propose that the incessant charge of the transplant recipient with donor-DNA and its "inappropriate" intranuclear delivery in host epithelium may explain the emergence of epithelial cells with donor-derived genome.

Mesenchymal stromal cells from human perinatal tissues: From biology to cell therapy

Cell-based regenerative medicine is of growing interest in biomedical research. The role of stem cells in this context is under intense scrutiny and may help to define principles of organ regeneration and develop innovative therapeutics for organ failure. Utilizing stem and progenitor cells for organ replacement has been conducted for many years when performing hematopoietic stem cell transplantation. Since the first successful transplantation of umbilical cord blood to treat hematological malignancies, non-hematopoietic stem and progenitor cell populations have recently been identified within umbilical cord blood and other perinatal and fetal tissues. A cell population entitled mesenchymal stromal cells (MSCs) emerged as one of the most intensely studied as it subsumes a variety of capacities: MSCs can differentiate into various subtypes of the mesodermal lineage, they secrete a large array of trophic factors suitable of recruiting endogenous repair processes and they are immunomodulatory.Focusing on perinatal tissues to isolate MSCs, we will discuss some of the challenges associated with these cell types concentrating on concepts of isolation and expansion, the comparison with cells derived from other tissue sources, regarding phenotype and differentiation capacity and finally their therapeutic potential.

Evidence of mobilization of pluripotent stem cells into peripheral blood of patients with myocardial ischemia

OBJECTIVE

The ischemic myocardium releases multiple chemotactic factors responsible for the mobilization and recruitment of bone marrow-derived cells to injured myocardium. However, the mobilization of primitive pluripotent stem cells (PSCs) enriched in very small embryonic-like stem cells (VSELs) in various cardiac ischemic scenarios is not well understood.

MATERIALS AND METHODS

Fifty-four ischemic heart disease patients, including subjects with stable angina, non-ST elevation myocardial infarction, and ST elevation myocardial infarction (STEMI) and 12 matched controls were enrolled. The absolute numbers of circulating stem/primitive cells in samples of peripheral blood (PB) were quantitated by ImageStream analysis and conventional flow cytometry. Gene expression of PSC (Oct-4 and Nanog), early cardiomyocyte (Nkx-2.5 and GATA-4), and endothelial (von Willebrand factor) markers was analyzed by real-time polymerase chain reaction.

RESULTS

The absolute numbers of PSCs, stem cell populations enriched in VSELs, and hematopoietic stem cells present in PB were significantly higher in STEMI patients at presentation and declined over time. There was a corresponding increase in pluripotent, cardiac, and endothelial gene expression in unfractionated PB cells and sorted PB-derived primitive CD34(+) cells. The absolute numbers of circulating VSELs and hematopoietic stem cells in STEMI correlated negatively with patient age.

CONCLUSIONS

Myocardial ischemia mobilizes primitive PSCs including pluripotent VSELs into the circulation. The peak of mobilization occurs within 12 hours in patients presenting with STEMI, which may represent a therapeutic window for future clinical applications. Reduced stem cell mobilization with advancing age could explain, in part, the observation that age is associated with poor prognosis in patients with myocardial infarction.

Biological characteristics of stem cells from foetal, cord blood and extraembryonic tissues

Foetal stem cells (FSCs) can be isolated during gestation from many different tissues such as blood, liver and bone marrow as well as from a variety of extraembryonic tissues such as amniotic fluid and placenta. Strong evidence suggests that these cells differ on many biological aspects such as growth kinetics, morphology, immunophenotype, differentiation potential and engraftment capacity in vivo. Despite these differences, FSCs appear to be more primitive and have greater multi-potentiality than their adult counterparts. For example, foetal blood haemopoietic stem cells proliferate more rapidly than those found in cord blood or adult bone marrow. These features have led to FSCs being investigated for pre- and post-natal cell therapy and regenerative medicine applications. The cells have been used in pre-clinical studies to treat a wide range of diseases such as skeletal dysplasia, diaphragmatic hernia and respiratory failure, white matter damage, renal pathologies as well as cancers. Their intermediate state between adult and embryonic stem cells also makes them an ideal candidate for reprogramming to the pluripotent status.

Immune regulatory cells in umbilical cord blood and their potential roles in transplantation tolerance

Umbilical cord blood (UCB) is a source of primitive hematopoietic stem (HSC) and progenitor cells, that served as an alternative to bone marrow (BM) for effective transplantation therapy. Success of HSC transplantation (HSCT) is limited in part by graft-versus-host disease (GVHD), graft rejection and delayed immune reconstitution, which all relate to immunological complications. GVHD after UCB transplantation is lower compared to that of BM HSCT. This may relate to the tolerogenic nature of T cells, mononuclear cells (MNCs) and especially immune regulatory cells existing in UCB. UCB contains limiting numbers of HSC or CD34(+) cell dose for adult patients resulting in delayed engraftment after UCB transplantation (UCBT). This needs to be improved for optimal transplantation outcomes. Approaches have been undertaken to promote HSC engraftment, including co-infusion of multiple units of UCB cells. These new methods however added additional immunological complications. Herein, we describe current knowledge on features of UCB immune cells, including regulatory T cells (Tregs) and mesenchymal stem/stromal cells (MSCs) and their potential future usage to reduce GVHD.

Both interleukin-3 and interleukin-6 are necessary for better ex vivo expansion of CD133+ cells from umbilical cord blood

Umbilical cord blood (UCB), an ideal source for transplantable hematopoietic stem cells (HSC), is readily available and is rich in progenitor cells. Identification of conditions favoring UCB-HSC ex vivo expansion and of repopulating potential remains a major challenge in hematology. CD133+ cells constitute an earlier, less-differentiated HSC group with a potentially higher engraftment capacity. The presence of SCF, Flt3-L, and TPO are essential for CD133+ and/or CD34+ cells ex vivo expansion; however, IL-3 and IL-6 influence has not yet been clearly established. We investigated this influence on CD133+ cells from UCB ex vivo expansion and the effect of these cytokines upon cell phenotype. Immediately after isolation an 85% of CD133+ cell purity was obtained, diminishing after 4 and 8 days of ex vivo expansion. CD133+ fold-increase was higher using IMDM with SCF, Flt3-L, and TPO (BM)+IL-3 or BM+IL-3+IL-6 on day 8 (13.83- and 17.47-fold increase, respectively). BM+IL-6 presented no significant difference from BM alone. We demonstrated that 5.1% of the CD133+ cells expressed IL-6 receptor (IL-6R) after isolation. After 4 and 8 days in culture, the percentage of CD133+ cells that expressed IL-6R was as follows: BM alone (9.8% and 22.02%, respectively); BM+IL-3 (8.33% and 16.74%); BM+IL-6 (9.2% and 17.67%); and BM+IL-3+IL-6 (12.5% and 61.20%). Cell cycle analysis revealed quiescent cells after isolation, 95.5% CD133+ cells in the G0/G1 phase. Regardless of culture period or cytokine incubation, CD133+ cell cycle altered to 70% of CD133+ in the G0/G1 phase. Colony-forming unit (CFU) doubled in BM+IL-3+IL-6 after 8 days of incubation compared with BM group. SOX-2 and NANOG-relative gene expression was detected on day 0 after isolation. BM+IL-6 prevented the decrease in NANOG and SOX-2 gene expression level compared to BM+IL-3 or BM+IL-3+IL-6 incubated cells. Our results indicated that UCB-isolated CD133+ cells were better ex vivo expanded in the presence of SCF, Flt3-L, TPO, IL-3+IL-6. IL-3 probably promotes higher CD133+ cell expansion and IL-6 maintains immature phenotype.

Germ plasm-like Dot cells maintain their wound regenerative function after in vitro expansion

1. Wounds in fetal skin heal without scarring; however, the mechanism for this is unknown. We have identified a novel group of protein and nucleotides-positive particles in fetal and adult mouse blood and in human blood, and termed them 'Dot cells'. Freshly isolated Dot cells regenerate wounds with less scarring and can be cultured without feeder layers. 2. Because the morphology of Dot cells has never been described, in the present study we describe the specific characterizations of Dot cells, including their growth pattern in vitro, and their expressions of stem cell markers using fluorescent cell sorting analyses and immunofluorescent histology. Our data indicates that cultured Dot cells express stem cell surface markers and embryonic stem cell transcription markers, such as Oct4, Nanog and Sox-2. In addition, Dot cells express VASA, the germ plasm specific marker. 3. To confirm whether Dot cells maintain their wound regenerative activity after in vitro expansion, in vitro cultured Dot cells were transplanted to wounded mice. Dot cells from albino mice maintain their wound regenerative activities after intravenous transplantation to black-background diabetic mice. In addition, Dot cells regenerate both the epithelial and dermal cells in the wounds of wild-type mice. The regenerated hair follicles, smooth muscle and dermal tissues express transiently to VASA. 4. Our data demonstrate that Dot cells are newly identified organisms located in the blood and bone marrow of mammals. They express germ cell, embryonic stem cell and adult stem cell markers. Dot cells maintain their regenerative function after in vitro expansion.

Immune regulatory cells in umbilical cord blood: T regulatory cells and mesenchymal stromal cells

A major goal in haematopoietic cell transplantation (HCT) is to retain the lymphohaematopoietic potential of the cell transfer without its side effects. In addition to the physical injury caused by the conditioning regimen, donor T cells can react to alloantigens of the recipient and cause graft-versus-host disease (GVHD), which accounts for the largest share of morbidity and mortality after HCT. Immune modulator cells, such as regulatory T cells (Tregs) and mesenchymal stromal cells (MSCs) have shown promise in their ability to control GVHD and yet, in preclinical models, preserve the graft-versus-malignancy effect. Initially, MSCs and Tregs have been isolated from adult sources, such as bone marrow or peripheral blood, respectively. More recent studies have indicated that umbilical cord blood (UCB) is a rich source of both cell types. We will review the current data on UCB-derived Tregs and MSCs and their therapeutic implications.

Non-haematological uses of cord blood stem cells

Embryonic stem (ES) cell therapies are often promoted as the optimal stem cell source for regenerative medicine applications because of their ability to develop into any tissue in the body. Unfortunately, ES cell applications are currently limited by ethical, political, biological and regulatory hurdles. However, multipotent non-ES cells are available in large numbers in umbilical cord blood (CB). CB stem cells are capable of giving rise to hematopoietic, epithelial, endothelial and neural tissues both in vitro and in vivo. Thus, CB stem cells are amenable to treat a wide variety of diseases including cardiovascular, ophthalmic, orthopaedic, neurological and endocrine diseases. In addition, the recent use of CB in several regenerative medicine clinical studies has demonstrated its pluripotent nature. Here we review the latest developments in the use of CB in regenerative medicine. Examples of these usages include cerebral palsy and type I diabetes. The numbers of individuals affected with each of these diseases are estimated at 10 000 infants diagnosed with cerebral palsy annually and 15 000 youths diagnosed with type 1 diabetes annually. A summary of the initial results from such clinical studies using autologous cord blood stem cells will be presented.

Nuclear and chromatin reorganization during cell senescence and aging - a mini-review

Genetic material in the nucleus governs mechanisms related to cell proliferation, differentiation, and function. Thus, senescence and aging are directly tied to the change of nuclear function and structure. The most important mechanisms that affect cell senescence are: (i) telomere shortening; (ii) environmental stress-mediated accumulation of DNA mutations, and (iii) the intrinsically encoded biological clock that dictates lifespan events of any particular cell type. Overall, these changes lead to modification of the expression of genes that are responsible for: (i) organization of the nuclear structure; (ii) integrity of transcriptionally inactive heterochromatin, and (iii) epigenetic modification of chromosomes due to DNA methylation and/or histone modifications. These aging-related nuclear alterations do not only affect somatic cells. More importantly, they affect stem cells, which are responsible for proper tissue rejuvenation. In this review, we focus on epigenetic changes in the chromatin structure and their impact on the biology and function of adult cells as they age. We will also address aging-related changes in a compartment of the most primitive pluripotent stem cells that were recently identified by our team and named 'very small embryonic/epiblast-like stem cells'.

Long-term benefit of intracardiac delivery of autologous granulocyte-colony-stimulating factor-mobilized blood CD34+ cells containing cardiac progenitors on regional heart structure and function after myocardial infarct

BACKGROUND AIMS

Starting from experimental data proposing hematopoietic stem cells as candidates for cardiac repair, we postulated that human peripheral blood (PB) CD34+ cells mobilized by hematopoietic growth-factor (G-CSF) would contain cell subpopulations capable of regenerating post-ischemic myocardial damages.

METHODS

In a phase I clinical assay enrolling seven patients with acute myocardial infarct, we directly delivered to the injured myocardium autologous PB CD34+ cells previously mobilized by G-CSF, collected by leukapheresis and purified by immunoselection. In parallel, we looked for the eventual presence of cardiomyocytic and endothelial progenitor cells in leukapheresis products of these patients and controls, using flow cytometry, reverse transcription-quantitative (RTQ)-polymerase chain reaction (PCR), cell cultures and immunofluorescence analyzes.

RESULTS

The whole clinical process was feasible and safe. All patients were alive at an average follow-up of 49 months (range 24-76 months). Improvement of heart function parameters became obvious from the third month following cell reinjection. Left ventricular ejection fraction values progressively and dramatically increased with time, associated with PetScan demonstration of myocardial structure regeneration and revascularization and New York Heart Association (NYHA) grade improvement. Furthermore, we identified PB CD34+ cell subpopulations expressing characteristics of both immature and mature endothelial and cardiomyocyte progenitor cells. In vitro CD34+ cell cultures on a specific medium induced development of adherent cells featuring morphologies, gene expression and immunocytochemistry characteristics of endothelial and cardiac muscle cells.

CONCLUSIONS

Mobilized CD34+ cells contain stem cells committed along endothelial and cardiac differentiation pathways, which could play a key role in a proposed two-phase mechanism of myocardial regeneration after direct intracardiac delivery, probably being responsible for the long-term clinical benefit observed.

Isolation procedure and characterization of multipotent adult progenitor cells from rat bone marrow

Multipotent adult progenitor cells (MAPCs) are adult stem cells derived from the bone marrow of mouse and rat and were described for the first time in 2002 (Jiang et al., Nature 418:41-49, 2002), and subsequently (Breyer et al., Exp Hematol 34:1596-1601, 2006; Jiang et al., Exp Hematol 30:896-904, 2002; Ulloa-Montoya et al., Genome Biol 8:R163, 2007). The capacity of rodent MAPC to differentiate at the single-cell level into some of the cell types of endoderm, mesoderm, and neuroectoderm germ layer lineages makes them promising candidates for the study of developmental processes. MAPC are isolated using adherent cell cultures and are selected based on morphology after a period of about 8-18 weeks. Here, we describe a step-by-step reproducible method to isolate rat MAPC from fetal and adult bone marrow. We elaborate on several aspects of the isolation protocol including, cell density and medium components, and methods for selecting and obtaining potential MAPC clones and their characterization.

Potential application of adult stem cells in retinal repair--challenge for regenerative medicine

Stem cells (SCs) maintain the balance among somatic cell populations in various tissues and are responsible for organ regeneration. The remarkable progress of regenerative medicine in the last few years indicates promise for the use of SCs in ophthalmic disorder treatment. This review describes the current view on hierarchy in the SC compartment and presents the latest attempts to use adult SCs in the regeneration of the retina. Research performed primarily in animal models gives hope for using similar strategies in humans. However, the search for the optimal source of SCs for cell therapy continues. We briefly discuss various potential sources of adult SCs that could be employed in regenerative medicine, particularly focusing on recently identified, very small embryonic-like SCs (VSEL-SCs). These cells are even present in the bone marrow and adult tissues of older patients and could be harvested from cord blood. We believe that VSEL-SCs, after the establishment of ex vivo expansion and differentiation protocols, could be harnessed for retina regeneration.

Novel epigenetic mechanisms that control pluripotency and quiescence of adult bone marrow-derived Oct4(+) very small embryonic-like stem cells

Recently, we identified in adult tissues a population of Oct4(+)SSEA-1(+)Sca-1(+)lin(-)CD45(-) very small embryonic-like stem cells (VSELs). First, to address recent controversies on Oct4 expression in cells isolated from adult organs, we show here evidence that Oct4 promoter in bone marrow (BM)-derived VSELs has an open chromatin structure and is actively transcribed. Next, to explain VSELs quiescence and lack of teratoma formation, we demonstrate a unique DNA methylation pattern at some developmentally crucial imprinted genes, showing hypomethylation/erasure of imprints in paternally methylated and hypermethylation of imprints in maternally methylated ones. These epigenetic characteristics leading to upregulation in VSELs of H19 and p57(KIP2) (also known as Cdkn1c) and repression of Igf2 and Rasgrf1 explain VSEL's quiescent status. Interestingly, this unique pattern in imprinted gene methylation is reverted in cocultures with a C2C12 supportive cell-line when VSELs are induced to form VSEL-derived spheres (VSEL-DSs) enriched for stem cells able to differentiate into all three germ layers. Therefore, we suggest that the proliferative/developmental potential of Oct4(+) VSELs is epigenetically regulated by expression of Oct4 and some imprinted genes, and postulate that restoring the proper methylation pattern of imprinted genes will be a crucial step for using these cells in regenerative medicine.

Fetal liver very small embryonic/epiblast like stem cells follow developmental migratory pathway of hematopoietic stem cells

Fetal liver (FL) has been described as a source of both hematopoietic and nonhematopoietic stem cells. Recently we have purified from murine adult bone marrow (BM) a population of CXCR4(+)Oct-4(+)SSEA-1(+)Sca-1(+)Lin(-)CD45(-) very small embryonic/epiblast-like stem cells (VSELs). By employing several complementary imaging and molecular strategies, we report in this study that VSELs, like hematopoietic stem cells (HSCs), are highly enriched in murine FL during the second trimester of gestation. Subsequently, at the beginning of the third trimester of gestation their number decreases, which corresponds to the time when HSCs egress FL and follow the stromal derived factor-1 (SDF-1) gradient in order to colonize developing BM. Thus, our data support the hypothesis that VSELs are a mobile pool of primitive stem cells that respond to similar chemotactic gradients as HSCs and follow their developmental migratory route.

Optimization of isolation and further characterization of umbilical-cord-blood-derived very small embryonic/ epiblast-like stem cells (VSELs)

Because of their small size and density, umbilical cord blood (UCB)-derived very small embryonic/epiblast-like stem cells (VSELs) are usually lost at various steps of UCB preparation. Accordingly, we noticed that a significant number of these cells, which are smaller than erythrocytes, are lost during gradient centrifugation over Ficoll-Paque as well as during routine volume depletion of UCB units before freezing. To preserve these cells in final UCB preparations, we propose a relatively short and economical three-step isolation protocol that allows recovery of approximately 60% of the initial number of Lin(-)/CD45(-)/CD133(+) UCB-VSELs present in freshly harvested UCB units. In this novel approach (i) UCB is lysed in a hypotonic ammonium chloride solution to deplete erythrocytes; (ii) CD133(+) including VSELs cells are enriched by employing immunomagnetic beads; and subsequently (iii) Lin(-)/CD45(-)/CD133(+) cells are sorted by fluorescence-activated cell sorting. The whole isolation procedure takes approximately 2-3 h per UCB unit and isolated cells are highly enriched for an Oct-4(+) and SSEA-4(+) population of small Lin(-)/CD45(-)/CD133(+) cells.

Membrane glycolipids in stem cells

Stem cells, such as embryonic stem cells, hematopoietic stem cells, neural stem cells, mesenchymal stem cells, and very small embryonic-like stem cells, are undifferentiated cells that are endowed with a high potential for proliferation and the capacity for self-renewal with retention of pluri/multipotency to differentiate into their progenies. Recently, studies regarding the biological functions of glycolipids and cell surface microdomains (caveolae, lipid rafts, or glycolipid-enriched microdomains) in stem cells are emerging. In this review, we introduce the expression patterns of glycolipids and the functional roles of cell surface microdomains in stem cells.