Marrow stromal cells migrate throughout forebrain and cerebellum, and they differentiate into astrocytes after injection into neonatal mouse brains

Magnetic resonance tracking of transplanted bone marrow and embryonic stem cells labeled by iron oxide nanoparticles in rat brain and spinal cord

Nuclear magnetic resonance (MR) imaging provides a noninvasive method for studying the fate of transplanted cells in vivo. We studied, in animals with a cortical photochemical lesion or with a balloon-induced spinal cord compression lesion, the fate of implanted rat bone marrow stromal cells (MSCs) and mouse embryonic stem cells (ESCs) labeled with superparamagnetic iron oxide nanoparticles (Endorem). MSCs were colabeled with bromodeoxyuridine (BrdU), and ESCs were transfected with pEGFP-C1 (eGFP ESCs). Cells were either grafted intracerebrally into the contralateral hemisphere of the adult rat brain or injected intravenously. In vivo MR imaging was used to track their fate; Prussian blue staining and electron microscopy confirmed the presence of iron oxide nanoparticles inside the cells. During the first week postimplantation, grafted cells migrated to the lesion site and populated the border zone of the lesion. Less than 3% of MSCs differentiated into neurons and none into astrocytes; 5% of eGFP ESCs differentiated into neurons, whereas 70% of eGFP ESCs became astrocytes. The implanted cells were visible on MR images as a hypointense area at the injection site, in the corpus callosum and in the lesion. The hypointense signal persisted for more than 50 days. The presence of GFP-positive or BrdU-positive and nanoparticle-labeled cells was confirmed by histological staining. Our study demonstrates that both grafted MSCs and eGFP ESCs labeled with a contrast agent based on iron oxide nanoparticles migrate into the injured CNS. Iron oxide nanoparticles can therefore be used as a marker for the long-term noninvasive MR tracking of implanted stem cells.

Use of bone marrow stromal cells for tendon graft-to-bone healing: histological and immunohistochemical studies in a rabbit model

BACKGROUND

Despite increasing attention on the issue of tendon-to-bone integration, there has been no animal study on the use of cell therapy for promoting the insertion healing of tendon to bone.

PURPOSE

To determine the efficacy of using a large number of bone marrow stromal cells (bMSCs) to enhance tendon-to-bone healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

The hallucis longus tendons were translated into 2.5-mm diameter calcaneal bone tunnels in a New Zealand white rabbit model. The bone tunnels were treated with or without bMSCs. Three specimens from each group were harvested at 2, 4, and 6 weeks postoperatively and evaluated by conventional histological and immunohistochemical methods.

RESULTS

At 4 weeks, the specimens with bMSCs exhibited more perpendicular collagen fiber formation and increased proliferation of cartilage-like cells, which was indicated by positive collagen type-II immuno-staining of the tendon-bone interface. In contrast, the specimens without bMSCs demonstrated progressive maturation and reorganization of fibrous tissue aligned along the load axis.

CONCLUSION

Introduction of a large number of bone marrow stromal cells to the bone tunnel have shown to improve the insertion healing of tendon to bone in a rabbit model through formation of fibrocartilagenous attachment at early time points.

Comparison of multi-lineage cells from human adipose tissue and bone marrow

Our laboratory has recently characterized a population of cells from adipose tissue, termed processed lipoaspirate (PLA) cells, which have multi-lineage potential similar to bone-marrow-derived mesenchymal stem cells (MSCs). This study is the first comparison of PLA cells and MSCs isolated from the same patient. No significant differences were observed for yield of adherent stromal cells, growth kinetics, cell senescence, multi-lineage differentiation capacity, and gene transduction efficiency. Adipose tissue is an abundant and easily procured source of PLA cells, which have a potential like MSCs for use in tissue-engineering applications and as gene delivery vehicles.

Epidermal cells accelerate the restoration of the blood flow in diabetic ischemic limbs

Epidermal progenitor cells (EpPCs) were long thought to be unipotent, giving rise only to other keratinocytes but recent studies question this assumption. Here, we investigated whether mouse EpPCs can adopt other antigenic and functional phenotypes. To test this, we injected freshly isolated and cultured EpPCs and transient amplifying cells into diabetic and non-diabetic mouse ischemic hindlimb and followed the cells' fate and the recovery of the ischemic limb blood flow over time. Both freshly isolated and cultured EpPCs and transient amplifying cells were incorporated into the vasculature of the ischemic limb 2 and 5 weeks post-injection, and some expressed endothelial cell but not keratinocyte antigens. Additionally, in the non-diabetic animals, first transient amplifying cells and then EpPCs accelerated the restoration of the blood flow. By contrast, in diabetic animals, only injected EpPCs or unsorted epidermal cells accelerated the restoration of the blood flow. These data indicate that epidermal cells can adopt non-skin phenotypes and functions, and that this apparent pluripotency is not lost by differentiation of EpPCs into transient amplifying cells. They also suggest that epidermal cell therapy might be of therapeutic value in the treatment of diabetic ischemia. Finally, because epidermal cells are readily accessible and expandable, they appear to be ideally suited for use as a non-viral gene delivery therapy.

Neurosphere and neurosphere-forming cells: morphological and ultrastructural characterization

Despite recent advances in our understanding of neural stem cell (NSC) biology, the free-floating structures generated by these cells in vitro, the "neurospheres", have not been fully characterized. To fill this gap, we examined neurospheres and neurosphere-derived NSCs by confocal microscopy, electron microscopy (EM) and cytofluorimetry. Here, we show that neurospheres and neurosphere-forming cells are morphologically and functionally heterogeneous. Confocal microscopy reveals differences in cell size, viability, cytoplasmic content and in the presence and distribution of active mitochondria. By electron microscopy, neurospheres appear as complex structures in which biological events such as mitosis, apoptosis and even phagocytosis are influenced by NSCs localization within the architecture of the neurosphere. NSCs derived from neurospheres are not synchronized and are represented in all phases of the cell cycle. Cytofluorimetric studies demonstrate NSCs' heterogeneity in cell size by forward scatter (FSC) analysis, and in cytoplasmic granularity by side scatter (SSC) profiling. These findings may contribute to our understanding of the morphogenesis of the neurospheres, particularly as this process relates to the high environmental adaptability of the NSCs and the reported existence of different subpopulations of neural stem cells.

Adult stem cell plasticity: fact or artifact?

There has been unprecedented recent interest in stem cells, mainly because of the hope they offer for cell therapy. Adult stem cells are an attractive source of cells for therapy, especially in view of the recent claims that they are remarkably plastic in their developmental potential when exposed to new environments. Some of these claims have been either difficult to reproduce or shown to be misinterpretations, leaving the phenomenon of adult stem cell plasticity under a cloud. There are, however, other examples of plasticity where differentiated cells or their precursors can be reprogrammed by extracellular cues to alter their character in ways that could have important implications for cell therapy and other forms of regenerative treatment.

In vivo and in vitro differentiation of myocytes from human bone marrow-derived multipotent progenitor cells

OBJECTIVE

Recent studies have shown that bone marrow (BM) contains cells capable of differentiating into myocytes in vivo. However, addition of demethylation drugs has been necessary to induce myocyte differentiation from BM cells in vitro, and precise mechanisms of BM cells' conversion to myocytes and the origin of those cells have not been established. We investigated the expression of myogenic markers during differentiation and maturation of myocytes from BM-derived multipotent adult progenitor cells (MAPC) under physiological culture condition.

MATERIALS AND METHODS

Frozen BM samples from 21 healthy donors were used as a source of MAPC. To induce myocyte differentiation MAPC was cultured in the presence of 5% FCS, VEGF, bFGF, and IGF-1, and the expressions of myocyte markers were examined at various time points. We also investigated engraftment and differentiation of MAPC-derived myocytes in vivo.

RESULTS

Frozen BM-derived MAPC, cultured under the physiological myogenic condition, demonstrated spatial expression patterns of several myocyte markers similar to that of authentic myocyte differentiation. When injected into murine muscles, MAPC treated with the myogenic condition engrafted and differentiated into myocyte marker-positive cells and myotubes in vivo.

CONCLUSION

For the first time, we were able to induce myocyte formation from BM cells under the physiological condition in vitro and demonstrated that treating cells with this condition prior to intramuscular injection increased efficiency of engraftment and differentiation in vivo.

Imaging the fate of implanted bone marrow stromal cells labeled with superparamagnetic nanoparticles

Bone marrow stromal cells (MSCs) are pluripotent progenitor cells that have the capacity to migrate toward lesions and induce or facilitate site-dependent differentiation in response to environmental signals. In animals with a cortical photochemical lesion, the fate of rat MSCs colabeled with magnetic iron-oxide nanoparticles (Endorem) and bromodeoxyuridine (BrdU) was studied. MSCs were either grafted intracerebrally into the contralateral hemisphere of adult rat brain or injected intravenously. In vivo MRI was used to track their fate; Prussian blue staining and transmission electron microscopy (TEM) confirmed the presence of iron-oxide nanoparticles inside the cells. During the first week posttransplantation, the transplanted cells migrated to the lesion site and populated the border zone of the damaged cortical tissue. The implanted cells were visible on MR images as a hypointense area at the injection site and in the lesion. The hypointense signal persisted for more than 50 days. The presence of BrdU-positive and iron-containing cells was confirmed by subsequent histological staining. Three to 4 weeks after injection, <3% of MSCs around the lesion expressed the neuronal marker NeuN. Our study demonstrates that a commercially available contrast agent can be used as a marker for the long-term noninvasive MR tracking of implanted cells.

Local Environmental Factors Determine Hematopoietic Differentiation of Neural Stem Cells

Stem cells exhibit unique properties and hold high therapeutic promise, but factors influencing their differentiation after transplantation need to be recognized and defined for this promise to be fully met. Here, we demonstrate that endogenous colony-forming unit spleen (CFU-S) colonies are not generated in lethally irradiated mice transplanted with neural stem cells obtained from brain tissue of syngeneic donors. We investigated the proportion of transplanted neural stem cells that contributed to hematopoietic reconstitution and compared the distribution of transplanted cells in nonsplenectomized to that of splenectomized mice following sublethal whole-body irradiation. We also used clonogenic assays, colony assays, and histochemical analyses to explore conditions under which transplanted, beta-galactosidase-tagged neural stem cells underwent hematopoietic differentiation. Our results suggest that neural stem cells do undergo extramedullary hematopoiesis, even while no endogenous hematopoietic colonies develop in the spleen. Furthermore, we found that neural stem cells effectively colonized the bone marrow of splectomized recipients. We conclude that the hematopoietic differentiation of neural stem cells is highly dependent on the extramedullary environment. We also conclude that the bone marrow does not provide an environment supportive of hematopoietic differentiation by neural stem cells.

Hematopoietic progenitor cells as possible origins of epithelial thymoma in a human T lymphocyte virus type I pX gene transgenic rat model

We earlier reported that Fischer 344/jcl strain (F344) rats carrying a unique pX gene of human T lymphocyte virus type I (HTLV-I) under control of a rat lymphocyte-specific protein tyrosine kinase (p56lck) type I promoter (lck-pX rats) spontaneously developed epithelial thymomas from the thymic medulla. To investigate the role of bone marrow cells carrying the HTLV-I pX gene in development of thymomas, the bone marrow of normal F344 rats after lethal irradiation was reconstituted by bone marrow mononuclear cells (BMMC) of lck-pX rats. Epithelial thymomas similar to the original thymoma of lck-pX rats frequently developed in the nontransgenic recipients within 5 months after the BMMC transplantation. The thymomas expressed the pX gene, thereby indicating the thymoma cells to be of donor BMMC origin. Since the thymoma also developed in nontransgenic recipients reconstituted by BMMC depleted of adherent cells, it is suggested that nonadherent BMMC of donor lck-pX rats may migrate to and lodge in the thymus of recipient nontransgenic rats then transform into thymoma cells with epithelial characteristics. The thymoma cells were shown to bind to Ulex europaeus Agglutinin-1 (UEA-1) lectin, which binds epithelial cells in the thymic medulla. It was also shown that the nonadherent BMMC fraction used for bone marrow reconstitution contained a number of UEA-1-positive cells. Taken together, UEA-1 positive BMMC may be progenitor cells of the epithelial thymoma. The epithelial thymoma in lck-pX rats sheds light on epithelial cell development in thymic medulla and for oncogenesis of epithelial thymoma in humans.

Cell death and long-term maintenance of neuron-like state after differentiation of rat bone marrow stromal cells: a comparison of protocols

Recent literature suggests that bone marrow stromal cells (BMSCs) may be differentiated into neuron-like and/or glia-like cells, implying that differentiated BMSCs may have potential use in cell replacement therapy for central nervous system disorders. However, many questions remain concerning the nature of BMSCs differentiated to express CNS antigens. For example, how long after differentiation do cells express CNS markers, and do differentiation procedures alter cell viability? This study compared neuronal differentiation methods in sister cell preparations, evaluating cell death and maintenance of the CNS antigen positivity after the Deng or Woodbury methods. Rat BMSCs were harvested, passaged, differentiated, placed in growth or maintenance media, and processed for cell viability or immunocytochemistry for NeuN and GFAP post-differentiation. We report that the Woodbury differentiation protocol produced maximally 51% neuron-like cells, yet also produced significant cell death. The Deng differentiation method produced 13% neuron-like cells and without marked cell death. No significant increases in GFAP immunoreactivity (IR) were seen after differentiation by either protocol. Following both protocols, removal of cells from the maintenance media significantly decreased expression of NeuN. Thus, differentiation procedures may be substantially affected BMSC potential, and maintenance of immunoreactivity to neuronal antigens was dependent on specific, nonphysiological environmental conditions.

Induction of neuronal markers in bone marrow cells: differential effects of growth factors and patterns of intracellular expression

Bone marrow cells (BMC) can be induced to express neuronal phenotypic features in vitro, but the extent to which they can transdifferentiate to mature, functional neurons is uncertain. We examined the effects of different growth factors and combinations thereof on the expression of neuronal marker proteins in cultures of BMC enriched in marrow stromal cells. Patterns of neuronal marker expression varied depending on the growth factor or factors to which BMC cultures were exposed. Cultures treated for up to 5 weeks with epidermal growth factor, fibroblast growth factor-2, retinoic acid, and nerve growth factor displayed neuron-like cellular processes and expressed neuronal markers, including the neuronal nuclear antigen NeuN, microtubule-associated protein 2, tau, synaptophysin, alpha(1A) and alpha(1B) calcium channel subunits, NR2A glutamate receptor subunits, and gamma-aminobutyric acid. However, the intracellular distribution of these markers was distinct from their usual distribution in mature neurons. We conclude that a variety of growth factors can drive BMC toward a neuronal phenotype or phenotypes, but that morphological neuronal features and the ectopic expression of neuronal proteins and neurotransmitters may not equate with the ability to execute normal neuronal functions.

Plasticity of Human Stem Cells in the Fetal Sheep Model of Human Stem Cell Transplantation

Experimental models that allow the evaluation of the full potential of stem cells under normal physiological conditions and in the absence of genetic or injury-induced dysfunction would serve as valuable tools for the study of the mechanisms underlying stem cell differentiation. Ideally, such a model would also permit the robust formation of donor-derived tissue-specific cells. Because studies have shown that the differentiation of stem cells into cells of a different germinal layer is highly inefficient in the absence of selective pressure, it is very unlikely that a healthy adult animal can fulfill these requirements. In this review, we describe the advantages of the permissive aspects of the developing preimmune fetus in the early gestational age that led us to develop the sheep as a large-animal model of human stem cell plasticity.

Choroidal neovascularization is provided by bone marrow cells

Choroidal neovascularization (CNV) is a known cause of age-related macular degeneration (ARMD). Moreover, the most common cause of blindness in the elderly in advanced countries is ARMD with CNV. It has recently been shown that bone marrow cells (BMCs) can differentiate into various cell lineages in vitro and in vivo. Adults maintain a reservoir of hematopoietic stem cells included in BMCs that can enter the circulation to reach various organs in need of regeneration. It has recently been reported that endothelial progenitor cells (EPCs) included in BMCs are associated with neovascularization. We examine the role of BMCs in CNV using a model of CNV in adult mice. Using methods consisting of fractionated irradiation (6.0 Gy x 2) followed by bone marrow transplantation (BMT), adult mice were engrafted with whole BMCs isolated from transgenic mice expressing enhanced green fluorescent protein (EGFP). Three months after BMT, we confirmed that the hematopoietic cells in the recipients had been completely replaced with donor cells. We then carried out laser photocoagulation to induce CNV in chimeric mice (donor cells >95%). Two weeks after the laser photocoagulation, by which time CNV had occurred, immunohistochemical examination was carried out. The vascular wall cells of the CNV expressed both EGFP and CD31. These findings indicate that newly developed blood vessels in the CNV are derived from the BMCs and suggest that the inhibition of EPC mobilization from the bone marrow to the eyes could be a new approach to the fundamental treatment of CNV in ARMD.

Retinoic acid-mediated induction of neurons and glial cells from human umbilical cord-derived hematopoietic stem cells

Recent studies reporting trans-differentiation of mononucleated cells derived from human umbilical cord blood into neuronal cells aroused interest among investigators for their clinical implication and significance in regenerative medicine. In the present study, purified populations of hematopoietic stem cells were isolated via magnetic bead sorting and fluorescence-activated cell sorter (FACS) using a specific CD133 antibody, a cell type-specific marker for hematopoietic stem cells, and grown in culture in the presence of retinoic acid (RA). CD133+ hematopoietic stem cells expressed neuronal and glial phenotypes after RA treatment. RT-PCR analysis indicated that the RA treated CD133+ cells expressed mRNA transcripts for ATP-binding cassettes transporter ABCG2 (a universal stem cell marker), nestin (a specific cell type marker for neural stem cells), Musashi1 (a specific marker for neural stem cells) and RA receptors (RAR) including RAR-alpha, RAR-beta, and retinoid X receptor (RXR)-gamma. RA-treated CD133+ cells expressed mRNA transcripts for neuron-specific markers neurofilament proteins (NF-L, -M, -H) and synaptophysin as determined by RT-PCR, structural proteins characteristic of neurons including tubulin beta III and neuron specific enolase (NSE) by Western blot, and neuron-specific markers NeuN and microtubule-associated protein-2 (MAP2) by immunocytochemistry. RA-treated CD133+ cells also expressed the astrocyte-specific marker glial fibrillary acidic protein (GFAP), as demonstrated by RT-PCR, Western blot, and immunocytochemistry. In addition, RA-treated CD133+ cells expressed cell type-specific markers for oligodendrocytes including myelin basic protein (MBP) as shown by RT-PCR, proteolipid protein (PLP) by Western blot analysis, and cyclic nucleotide phosphodiesterase (CNPase) by immunostaining. Upregulated expression of several basic helix-loop-helix (bHLH) transcription factors important for early neurogenesis, including Otx2, Pax6, Wnt1, Olig2, Hash1 and NeuroD1, was also demonstrated in CD133+ cells after RA treatment. These results indicate that human cord blood-derived CD133+ hematopoietic stem cells could trans-differentiate into neural cell types of neuron-like cells, astrocytes, and oligodendrocytes by RA treatment.

Cellular transplants: steps toward restoration of function in spinal injured animals

Severe spinal cord injury results in severe, persisting deficits with little hope for substantial recovery. Recent developments in transplantation protocols, gene therapy, and methods of evaluation now offer hope of developing treatments that will lead to better prognoses. This review discusses the consequences of spinal injury, animal models used to study injury and recovery, types of cellular transplants, selection of behavioral and physiological tests of recovery, and ways to test the efficacy of the interventions and to improve transplant-mediated recovery.

Comparative analysis of remyelinating potential of focal and intravenous administration of autologous bone marrow cells into the rat demyelinated spinal cord

The remyelinating potential of autologous bone marrow cells was studied after direct injection and following intravenous injection into rats with a demyelinated lesion in the spinal cord. Both focal and intravenous injections of acutely isolated mononuclear bone marrow cell fractions resulted in varying degrees of remyelination. Suspensions of bone marrow cells collected from the same rat were delivered at varied concentrations (10(2) to 10(5) for direct injection and 10(4) to 10(7) for i.v. injections). The lesions were examined histologically 3 weeks after transplantation. Light microscopic examination revealed remyelination in the dorsal funiculus with both injection protocols, but the extent of remyelination was proportional to the number of injected cells. To attain the same relative density of remyelination achieved by direct injection, intravenous administration of cells required delivery of substantially more cells (two orders of magnitude). However, the availability of autologous bone marrow cells in large number and the potential for systemically delivering cells to target lesion areas without neurosurgical intervention suggest the potential utility of intravenous cell delivery as a prospective therapeutic approach in demyelinating disease.

Ex vivo gene therapy using bone marrow-derived cells: combined effects of intracerebral and intravenous transplantation in a mouse model of niemann–pick disease

Normal murine bone marrow cells were transduced with a retroviral vector to overexpress and release human acid sphingomyelinase (ASM). The transduced cells were then transplanted intravenously into 3-day-old, irradiated ASM-deficient mice, a model of human Niemann-Pick disease (NPD). At 4 weeks, engrafted mice received intracerebral injections of mesenchymal stem cells obtained from the original, transduced bone marrow. By 16 weeks, most of the treated NPD mice had near-normal levels of ASM activity in their tissues, including the brain; dramatically improved histology; and marked reductions in sphingomyelin. Cerebellar function also was normal, and the number of Purkinje cells was > 80% of normal. Remarkably, in certain regions of the cerebellum many of the surviving Purkinje cells expressed human ASM RNA, suggesting that either they were donor-derived or that the transplanted bone marrow cells had fused with existing Purkinje cells. However, despite these positive results, by 24 weeks the ASM activities were dramatically reduced and cerebellar function began to decline, coincident with the detection of anti-human ASM antibodies in the plasma. We conclude that this gene therapy procedure might be useful in Type A NPD and other neurological lysosomal storage disorders, particularly since it is an approach that could be beneficial for both the neurological and the visceral organ features of these diseases.

Exploitation of stem cell plasticity

For many years, adult haemopoietic stem cells (HSCs) have been considered 'plastic' in their proliferative and differentiation capacities. Recently, evidence that supports newer concepts of adult stem cell plasticity has been reported. In particular, stem cells from haemopoietic tissues seem to have 'extraordinary' abilities to generate or switch between haemopoietic and nonhaemopoietic lineages, exhibiting an unexpected degree of developmental or differentiation potential. The mechanisms by which cell fate reprogramming occurs are still poorly understood. Nevertheless, an increasing number of studies is challenging one of the main dogmas in biology, namely that mammalian cell differentiation follows established programmes in a hierarchical fashion, and once committed to a particular somatic cell lineage, cells do not change into another somatic lineage. The 'nonhierarchical', 'reversible' phenotype of stem cells in haemopoietic tissues, if it exists, would be an advantage that could be exploited in regenerative medicine. Here, we review the recent advances in HSC biology and discuss the general concepts of adult stem cell plasticity with respect to these cells and how these might be exploited clinically.

Postnatal Astrocytes Promote Neural Induction from Adult Human Bone Marrow–Derived Stem Cells

Neural stem cells (NSCs) have generated considerable interest because of their potential as a source of defined cells for drug screening or cell-based therapies for neurodegenerative diseases. Ethical and practical considerations limit the availability of human fetal-derived neural tissue and highlight the need to consider alternative sources of human NSCs. Because of their ready availability, their ability to be easily expanded, and reports of neural potential, bone marrow-derived populations have become the focus of intense study with regard to their potential clinical utility. However, recent identification of spontaneous cell fusion and limited neuronal differentiation has tempered initial optimism. In this study, we demonstrate the monoclonal neural and mesodermal potential of adult human bone marrow mesenchymal cells. Critically, we show that sequential treatment with the mitogens epidermal growth factor (EGF) and fibroblast growth factor-2 (FGF-2) followed by postnatal hippocampal astrocyte conditioned medium significantly promotes the generation of neurofilament(+)/beta-tubulin(+) cells from bone marrow precursors. The ability to generate almost limitless numbers of neural precursors from a readily accessible autologous adult human source provides a platform for further studies and potentially has important therapeutic implications.

Migration and differentiation of nuclear fluorescence-labeled bone marrow stromal cells after transplantation into cerebral infarct and spinal cord injury in mice

There is increasing evidence that bone marrow stromal cells (BMSC) have the potential to migrate into the injured neural tissue and to differentiate into the CNS cells, indicating the possibility of autograft transplantation therapy. The present study was aimed to clarify whether the mouse BMSC can migrate into the lesion and differentiate into the CNS cells when transplanted into the mice subjected to focal cerebral infarct or spinal cord injury. The BMSC were harvested from mice and characterized by flow cytometry. Then, the BMSC were labeled by bis-benzimide, a nuclear fluorescence dye, over 24 h, and were stereotactically transplanted into the brain or spinal cord of the mice. The cultured BMSC expressed low levels of CD45 and high levels of CD90 and Sca-1 on flow cytometry. A large number of grafted cells survived in the normal brain 4 weeks after transplantation, many of which were located close to the transplanted sites. They expressed the neuronal marker including NeuN, MAP2, and doublecortin on fluorescent immunohistochemistry. However, when the BMSC were transplanted into the ipsilateral striatum of the mice subjected to middle cerebral artery occlusion, many of the grafted cells migrated into the corpus callosum and injured cortex, and also expressed the neuronal markers 4 weeks after transplantation. In particular, NeuN was very useful to validate the differentiation of the grafted cells, because the marker was expressed in the nuclei and was overlapped with bis-benzimide. Similar results were obtained in the mice subjected to spinal cord injury. However, many of the transplanted BMSC expressed GFAP, an astrocytic protein, in injured spinal cord. The present results indicate that the mouse BMSC can migrate into the CNS lesion and differentiate into the neurons or astrocytes, and that bis-benzimide is a simple and useful marker to label the donor cells and to evaluate their migration and differentiation in the host neural tissues over a long period.

Hematopoietic progenitors express neural genes

Bone marrow, or cells selected from bone marrow, were reported recently to give rise to cells with a neural phenotype after in vitro treatment with neural-inducing factors or after delivery into the brain. However, we showed previously that untreated bone marrow cells express products of the neural myelin basic protein gene, and we demonstrate here that a subset of ex vivo bone marrow cells expresses the neurogenic transcription factor Pax-6 as well as neuronal genes encoding neurofilament H, NeuN (neuronal nuclear protein), HuC/HuD (Hu-antigen C/Hu-antigen D), and GAD65 (glutamic acid decarboxylase 65), as well as the oligodendroglial gene encoding CNPase (2',3' cyclic nucleotide 3'-phosphohydrolase). In contrast, astroglial glial fibrillary acidic protein (GFAP) was not detected. These cells also were CD34+, a marker of hematopoietic stem cells. Cultures of these highly proliferative CD34+ cells, derived from adult mouse bone marrow, uniformly displayed a phenotype comparable with that of hematopoietic progenitor cells (CD45+, CD34+, Sca-1+, AA4.1+, cKit+, GATA-2+, and LMO-2+). The neuronal and oligodendroglial genes expressed in ex vivo bone marrow also were expressed in all cultured CD34+ cells, and GFAP was not observed. After CD34+ cell transplantation into adult brain, neuronal or oligodendroglial markers segregated into distinct nonoverlapping cell populations, whereas astroglial GFAP appeared, in the absence of other neural markers, in a separate set of implanted cells. Thus, neuronal and oligodendroglial gene products are present in a subset of bone marrow cells, and the expression of these genes can be regulated in brain. The fact that these CD34+ cells also express transcription factors (Rex-1 and Oct-4) that are found in early development elicits the hypothesis that they may be pluripotent embryonic-like stem cells.

Plasticity of marrow-derived stem cells

Bone marrow (BM) contains hematopoietic stem cells (HSCs), which differentiate into every type of mature blood cell; endothelial cell progenitors; and marrow stromal cells, also called mesenchymal stem cells (MSCs), which can differentiate into mature cells of multiple mesenchymal tissues including fat, bone, and cartilage. Recent findings indicate that adult BM also contains cells that can differentiate into additional mature, nonhematopoietic cells of multiple tissues including epithelial cells of the liver, kidney, lung, skin, gastrointestinal (GI) tract, and myocytes of heart and skeletal muscle. Experimental results obtained in vitro and in vivo are the subject of this review. The emphasis is on how these experiments were performed and under what conditions differentiation from bone marrow to epithelial and neural cells occurs. Questions arise regarding whether tissue injury is necessary for this differentiation and the mechanisms by which it occurs. We also consider which bone marrow subpopulations are capable of this differentiation. Only after we have a better understanding of the mechanisms involved and of the cells required for this differentiation will we be able to fully harness adult stem cell plasticity for clinical purposes.

Isolation of multipotent mesenchymal stem cells from umbilical cord blood

It is well accepted that umbilical cord blood has been a source for hematopoietic stem cells. However, controversy exists as to whether cord blood can serve as a source of mesenchymal stem cells, which can differentiate into cells of different connective tissue lineages such as bone, cartilage, and fat, and little success has been reported in the literature about the isolation of such cells from cord blood. Here we report a novel method to obtain single cell-derived, clonally expanded mesenchymal stem cells that are of multilineage differentiation potential by negative immunoselection and limiting dilution. The immunophenotype of these clonally expanded cells is consistent with that reported for bone marrow mesenchymal stem cells. Under appropriate induction conditions, these cells can differentiate into bone, cartilage, and fat. Surprisingly, these cells were also able to differentiate into neuroglial- and hepatocyte-like cells under appropriate induction conditions and, thus, these cells may be more than mesenchymal stem cells as evidenced by their ability to differentiate into cell types of all 3 germ layers. In conclusion, umbilical cord blood does contain mesenchymal stem cells and should not be regarded as medical waste. It can serve as an alternative source of mesenchymal stem cells to bone marrow.

Protective effects of transplanted and mobilized bone marrow stem cells on mice with severe acute pancreatitis

AIM: To evaluate the protective effects of transplanted and mobilized bone marrow stem cells (BMSCs) on mice with severe acute pancreatitis (SAP) and to probe into their possible mechanisms.

METHODS: A mouse model of SAP induced by intraperitoneal injections of L-arginine was employed in the present study. Two hundred female Balb/c mice weighing 18-22 g were randomly assigned into 4 groups. Group A was the stem cell mobilized group treated by injection of granulocyte-colony stimulating factor (G-CSF) into mice for 4 d at a dose of 40 μg·kg^-1·d^-1 before induction of SAP. Group B was the group of BMSCs transplantation, in which the mice were given the isolated BMSCs via the tail vein 4 d prior to induction of SAP. Group C served as the model control and only SAP was induced. The mice without induction of SAP in group D acted as the normal control. At the time of animal sacrifice at 24, 48 and 72 h after induction of SAP, blood samples were obtained and prepared to detect serum amylase, while the abdominal viscera were examined both grossly and microscopically for the observation of pathological changes.

RESULTS: The mortality of mice in the model control, groups A and B was 34%, 8% and 10% respectively within 72 h after induction of SAP. The serum level of amylase in the model control was significantly increased at all time points after induction of SAP as compared with that of the normal control (P < 0.05-0.01). When the mice were pretreated with BMSCs’ transplantation or G-CSF injection, their serum level of amylase was significantly reduced at 48 h and 72 h after induction of SAP in comparison with that of the model control (P < 0.05-0.01). In accordance with these observations, both gross and microscopic examinations revealed that the pathological changes of SAP in mice pretreated with BMSCs transplantation or G-CSF injection were considerably attenuated as compared with those in the model control at all observed time points.

CONCLUSION: Both transplanted allogenic and mobilized autologous BMSCs can protect mouse pancreas from severe damage in the process of SAP.

Interactions between human adipose stromal cells and mouse neural stem cells in vitro

Transplantation of adult mesenchymal stem cells (MSCs) into adult rat brain has been known to reduce functional deficits associated with stroke and traumatic brain injury. However, in injured brains, there is no evidence that transplanted MSCs replace lost host brain tissue. In this study, we determined in vitro interaction between human adipose tissue stromal cells (hATSCs), a kind of MSC, and neural stem cells (NSCs). hATSCs were isolated and proliferated from human adipose tissues, and NSCs from the subventricular zone of postnatal mice. When NSCs were cultured on mitomycin-treated hATSC monolayers, their proliferation was decreased, but neuronal differentiation was significantly induced. The percentage of neurons significantly increased in 7 days in cultures of NSCs on hATSCs feeder as compared to NSCs cultured on laminin-coated dishes. When the duration of the cultures was extended to 14 days, hATSCs supported the survival of neurons derived from NSCs. To determine the role of soluble factors from hATSCs, NSCs were cultured with hATSCs conditioned medium or co-cultured with permeable filter on which hATSCs were grown. Although proliferation of NSCs significantly decreased and glial differentiation increased under these experimental conditions, their neuronal differentiation was not affected, indicating that direct physical contact between hATSCs and NSCs is required for induction of neuronal differentiation. These data indicate that hATSCs may provide supportive roles on endogenous neural stem cells, when they are transplanted into damaged brain.

Functional and immunophenotypic characteristics of isolated CD105(+) and fibroblast(+) stromal cells from AML: implications for their plasticity along endothelial lineage

BACKGROUND

In vitro cultures of BM cells from newly diagnosed patients with AML displayed a defective BM stromal compartment, with a reduced number of fibroblast-colony-forming unit (CFU-F: 1 +/- 1.25 SD) and a decreased proliferative ability. The purposes of our study were: 1). to select BM mesenchymal stem cells (MSC) and BM-derived stromal cells (BMDSCs) from AML patients at diagnosis and from healthy subjects, using an immunomagnetic system and either anti-CD105 or anti-fibroblast MAbs; 2). to study the immunophenotypic and functional properties of freshly isolated and cultured mesenchymal cells; 3). to test the in vitro plasticity of the selected cells to differentiate towards an endothelial phenotype.

METHODS

Fresh mononuclear cells obtained from BM of 20 patients newly diagnosed with AML and from eight healthy subjects were selected by using anti-fibroblast and anti-CD105 MAbs. Freshly isolated cells were analyzed, characterized by flow cytometry using a wide panel of MAbs and seeded in long-term culture medium to assess CFU-F formation. The level of confluence after 30 days and functional capacity in a long-term colony-forming cell culture (LTC-CFC) were tested. Furthermore, the cultured selected cell populations were assayed for their ability to differentiate into an endothelial-like cell phenotype with the addition of vascular endothelial growth factor (VEFG) and endothelial cell growth supplement (ECGS).

RESULTS

In normal subjects the selection produced an increase of the CFU-F number of 2.6-fold with anti-fibroblast MAb and 2.7-fold with the anti-CD105 MAb. Anti-fibroblast and anti-CD105 MAb selection from AML BM cells resulted in a statistically significant greater count of CFU-F that was respectively 10.6-fold (P = 0.04) and 14.4-fold (P = 0.00001) higher in comparison with the unselected AML samples. Interestingly, in 80% of AML samples immunoselection was also able to restore the capacity of the CFU-F to proliferate and form confluent stromal layers. The isolation of those layers sustained the proliferation and differentiation of hematopoietic stem cells in the LTC-CFC. The phenotypic profile of cultured BMDSCs was different from that of the freshly isolated cells, and changed in relation to the culture conditions: CD105+ selected cells cultured with VEGF and ECGS expressed endothelial markers, a finding that suggests that this cell subpopulation may have the potential to differentiate toward an endothelial-like phenotype.

DISCUSSION

We report that immunomagnetic selection represents a valid tool for the selection of BM mesenchymal cells in samples obtained from both healthy subjects and patients with AML. This technique was able to rescue two functional and immunophenotypic compartments related to two different selected populations. In particular, the CD105+ cells isolated in AML displayed, after stimulation with VEGF and ECGS, the ability to change towards an endothelial-like cell phenotype, thus revealing an unexpected plasticity. Both CD105+ and fibroblast+ cells once successfully isolated might represent sources of mesenchymal cells populations useful for in vitro investigations and, above all, as therapeutic devices.

Quantifying levels of transplanted murine and human mesenchymal stem cells in vivo by real-time PCR

BACKGROUND

Previously, we demonstrated that murine mesenchymal stem cells (MSCs) injected intracranially into mice expand throughout the central nervous system (CNS). This paper describes real-time PCR (RT-PCR) assays that enables accurate quantification of transplanted cells in vivo.

METHODS

RT-PCR assays that amplify sequences in the mouse Y chromosome or human Alu repeats were developed and used to quantify the number of male, murine, or human MSCs in the CNS at various times after intracranial injection into neonatal mice, or in various organs of adult mice after i.p. injection of cells into 3 day-old embryos.

RESULTS

In the CNS, levels of male mouse DNA in female transplant recipients increased on average 30-fold between 3 and 60 days post-injection but then was unchanged at 140 days post-transplant (P = 0.107). Male DNA accounted for up to 0.309% of the total DNA content of the brain, representing maximally 600000 donor cells. Human DNA was detected in the CNS up to 300 days post-transplant, but levels never exceeded 7.63 x 10 (-4) % of the total brain content. After in utero transplantation, human DNA levels ranged from 0.36 x 10(-5) % to 2.14 x 10 (-5) % of the total DNA content of liver, kidney and spleen. significantly higher levels were found in heart (P = 0.06), femur and brain (P = 0.0025).

DISCUSSION

RT-PCR assays were developed to quantify levels of male, murine and human cells in vivo following sex-mismatched or xeno-transplants. Due to their accuracy, precision, and sensitivity, these assays provide a versatile alternative to measuring stem-cell engraftment in vivo.

Human adult marrow cells support prolonged expansion of human embryonic stem cells in culture

Prolonged propagation of human embryonic stem (hES) cells is currently achieved by coculture with primary mouse embryonic fibroblasts (MEFs) serving as feeder cells. Unlike mouse ES cells, adding growth factors such as leukemia inhibitory factor is insufficient to maintain undifferentiated hES cells without feeder cells. The presence of uncharacterized rodent cells or crude extracts imposes a risk to the clinical applications of hES cells. While others looked for a replacement of MEFs with human fetal cells, we attempted to use easily accessible postnatal human cells such as human marrow stromal cells (hMSCs). Culture-expanded hMSCs from multiple donors were used as feeder cells to support growth of the H1 hES cell line under a serum-free culture condition. Human ES cell colonies cultured on irradiated hMSCs amplified >100-fold during the 30-day continuous culture (in five passages). The longest continuous expansion of hES cells on hMSCs tested to date is 13 passages. The expanded hES cells displayed the unique morphology and molecular markers characteristic of undifferentiated hES cells as observed when they were cultured on MEFs. They expressed the transcription factor Oct-4, a membrane alkaline phosphatase, and the stage-specific embryonic antigen (SSEA)-4, but not the SSEA-1 marker. Expanded hES cells on hMSCs retained unique differentiation potentials in culture and a normal diploid karyotype. The well-studied hMSCs (and this animal cell- and serum-free system) may provide a clinically and ethically feasible method to expand hES cells for novel cell therapies. In addition, this system may help to identify cytokines and adhesion molecules that are required for the self-renewal of hES cells.

One strategy for cell and gene therapy: harnessing the power of adult stem cells to repair tissues

Most recent evidence suggests that the process of tissue repair is driven by stem-like cells that reside in multiple tissues but are replenished by precursor cells from bone marrow. Among the candidates for the reparative cells are the adult stem cells from bone marrow referred to as either mesenchymal stem cells or marrow stromal cells (MSCs). We recently found that after MSCs were replated at very low densities to generate single-cell-derived colonies, they did not exit a prolonged lag period until they synthesized and secreted considerable quantities of Dickkopf-1, an inhibitor of the canonical Wnt signaling pathway. We also found that when the cells were cocultured with heat-shocked pulmonary epithelial cells, they differentiated into epithelial cells. Most of the MSCs differentiated without evidence of cell fusion but up to one-quarter underwent cell fusion with the epithelial cells. A few also underwent nuclear fusion. The results are consistent with the interesting possibility that MSCs and similar cells repair tissue injury by three different mechanisms: creation of a milieu that enhances regeneration of endogenous cells, transdifferentiation, and perhaps cell fusion.

Derivation of lung epithelium from bone marrow cells

Recent studies demonstrate the capacity of BM-derived cells to engraft as differentiated cells of a variety of organs, including lung. In this paper, we review the current state-of-the-art in this area. We also summarize our work demonstrating that cultured adherent marrow cells can serve as progenitors of lung alveolar epithelium.

Veto-Like Activity of Mesenchymal Stem Cells: Functional Discrimination Between Cellular Responses to Alloantigens and Recall Antigens

Trans-differentiation of stem cells shows promise for use in tissue repair medicine. Although poorly defined, mesenchymal stem cells (MSC) appear useful for applications in repair medicine. Despite the low frequency of MSC, they are relatively easy to expand. The expression of MHC class II on MSC, however, could deter their use in repair medicine, since these molecules could stimulate an allogeneic host response. This study sought to compare the immune stimulatory and suppressive effects of MSC. Primary human MSC were cultured from bone marrow aspirates and then passaged at least three times before use in assays. Morphologically, MSC were symmetrical; were SH2(+), MHC class II(+), CD45(-), CD44(+), CD31(-), CD14(-), proly-4-hydroxylase(-); and showed normal karyotype patterns and elevated telomerase activities. MSC elicited significant stimulatory responses when cocultured with allogeneic PBMC. Despite the production of different types of growth factors, allogeneic effects of MSC could not be explained by the production of these growth factors. One-way MLR reactions were significantly blunted by third-party MSC. Similar suppression was not observed for responses to three different recall Ags. Based on these functional differences by MSC in responses to allo- and recall Ags, we examined whether MSC could exert veto-like functions. We showed that MSC could blunt the cytotoxic effects of allogeneic-induced effectors to mitogen-activated targets. The results showed that although MSC elicited allogeneic responses in a model that mimics a graft-vs-host reaction, they also exerted veto-like activity, but caused no effect on responses to recall Ags.

Differentiation of marrow stromal cells into photoreceptors in the rat eye

Retinal degenerations and dystrophies are the major causes of genetically inherited blindness that are characterized by the apoptotic death of the photoreceptor cell layer of the retina. To date, no treatment exists for these diseases and only recently have they been considered as candidates for gene and stem cell therapies. Here we report the ability of adult CD90+ marrow stromal cells (MSCs) to be induced by activin A, taurine, and EGF into cells (20-32%) expressing photoreceptor-specific markers rhodopsin, opsin, and recoverin in vitro. CD90+ cells were either transduced with recombinant adeno-associated virus expressing green fluorescent protein (GFP) or bromodeoxyuridine (BrdU) labeled and then injected into the subretinal space of adult Royal College of Surgeons rats. Fundus photography and angiography showed no adverse effects of CD90+ MSC transplantation. GFP-expressing cells or BrdU-positive cells covered approximately 30% of the entire retinal area. By 2 weeks after injection, CD90+ MSCs integrated into the host retina, forming structures similar to the photoreceptor layer and expressed a photoreceptor-specific marker. No teratoma formation was observed in the recipient retina. The subretinally delivered CD90+ MSCs did not stain for proliferating cell nuclear antigen, indicating that they primarily undergo differentiation rather than proliferation. In addition, we established that transplanted cells can attract synaptic vesicles and hence are potentially capable of signal transduction. This study demonstrates for the first time the partial differentiation of adult CD90+ MSCs into photoreceptors in vitro and in vivo. Our results establish a proof of concept for CD90+ MSC differentiation with autologous transplantation, which may provide a promising therapeutic strategy for the treatment of some forms of genetically inherited retinal degenerations.

Intravenous bone marrow stromal cell therapy reduces apoptosis and promotes endogenous cell proliferation after stroke in female rat

The present study investigates the induction of neurogenesis, reduction of apoptosis, and promotion of basic fibroblast growth factor (bFGF) expression as possible mechanisms by which treatment of stroke with bone marrow stromal cells (MSCs) improves neurological functional recovery. Additionally, for the first time, we treated cerebral ischemia in female rats with intraveneous administration of MSCs. Female rats were subjected to 2 hr of middle cerebral artery occlusion (MCAo), followed by an injection of 3 x 10(6) male (for Y chromosome labeling) rat MSCs or phosphate-buffered saline (PBS) into the tail vein 24 hr after MCAo. All animals received daily injection of bromodeoxyuridine (BrdU; 50 mg/kg, i.p.) for 13 days after treatment for identification of newly synthesized DNA. Animals were sacrificed at 14 days after MCAo. Behavioral tests (rotarod and adhesive-removal tests) were performed. In situ hybridization, immunohistochemistry, and terminal deoxynucleotidyltransferase (TdT)-mediated dUTP-biotin nick-end labeling (TUNEL) were performed to identify transplanted MSCs (Y chromosome), BrdU, bFGF, and apoptotic cells in the brain. Significant recovery of behavior was found in MSC-treated rats at 7 days in the somatosensory test and at 14 days in the motor test after MCAo compared with control, PBS-treated animals (P<.05). MSCs were found to survive and preferentially localize to the ipsilateral ischemic hemisphere. Significantly more BrdU-positive cells were located in the subventricular zone (P<.05), and significantly fewer apoptotic cells and more bFGF immunoreactive cell were found in the ischemic boundary area (P<.05) of MSC-treated rats than in PBS-treated animals. Here we demonstrate that intravenously administered male MSCs increase bFGF expression, reduce apoptosis, promote endogenous cellular proliferation, and improve functional recovery after stroke in female rats.

Clinical and experimental study on therapeutic effect of umbilical cord blood transplantation on severe viral hepatitis

AIM: To investigate the therapeutic effect of umbilical cord blood transplantation (UCBT) on patients with severe viral hepatitis and on liver lesions in rats.

METHODS: One hundred and fifty three patients with severe viral hepatitis were included in the study between April 1990 and July 2002. The patients were treated with adult plasma transfusion (control), UCBT, plasma exchange (PE) and UCBT combined with PE (UCBT+PE) respectively. The therapeutic effectiveness was evaluated by serial determinations of liver function, lipids and immune function in all patients before and after the treatment. The model of experimental hepatic failure was constructed in SD rats by injecting carbon tetrachloride. Then, the rats were given normal saline, adult plasma or neonate cord blood intraperitoneally. After detection of liver function, the rats were killed and morphological changes of the liver were microscopically observed.

RESULTS: UCBT group and UCBT+PE group had much better improvement in liver and immune functions than control group and PE group. The patients in UCBT+PE group had the best clinical efficacy. UCBT was safe and had no side effects. The animal experiment showed significant improvements in liver function and survival rate in neonate cord blood group as compared with adult plasma group. The histopathology of rat’s liver indicated that neonate cord blood application could decrease the liver injury and increase hepatocellular regeneration.

CONCLUSION: UCBT demonstrated a good therapeutic effect on severe viral hepatitis and no obvious side effects. Umbilical cord blood can attenuate the liver lesions and reproduce hepatocyte. The treatment of UCBT combined with PE was much better than that of single plasma exchange, thus UCBT can enhance the therapeutic effect of plasma exchange on severe viral hepatitis.

Matrix cells from Wharton's jelly form neurons and glia

We have identified an easily attainable source of primitive, potentially multipotent stem cells from Wharton's jelly, the matrix of umbilical cord. Wharton's jelly cells have been propagated in culture for more than 80 population doublings. Several markers for stem cells, including c-kit (CD117), and telomerase activity are expressed in these cells. Treatment with basic fibroblast growth factor overnight and low-serum media plus butylated hydroxyanisole and dimethylsulfoxide induced Wharton's jelly cells to express a neural phenotype. Within several hours of this treatment, Wharton's jelly cells developed rounded cell bodies with multiple neurite-like extensions, similar to the morphology of neural stem cells. Neuron-specific enolase (NSE), a neural stem cell marker, was expressed in these cells, as shown by immunocytochemistry. Immunoblot analysis showed similar levels of NSE expression in both untreated and induced Wharton's jelly cells. After 3 days, the induced Wharton's jelly cells resembled bipolar or multipolar neurons, with processes that formed networks reminiscent of primary cultures of neurons. The neuron-like cells in these cultures stained positively for several neuronal proteins, including neuron-specific class III beta-tubulin, neurofilament M, an axonal growth-cone-associated protein, and tyrosine hydroxylase. Immunoblot analysis showed increasing levels of protein markers for mature neurons over time post induction. Markers for oligodendrocytes and astrocytes were also detected in Wharton's jelly cells. These exciting findings show that cells from the matrix of umbilical cord have properties of stem cells and may, thus, be a rich source of primitive cells. This study shows their capacity to differentiate into a neural phenotype in vitro.

Multilineage gene expression in human bone marrow stromal cells as evidenced by single-cell microarray analysis

The nonhematopoietic stromal cells of the bone marrow are critical for the development of hematopoietic stem cells into functionally competent blood cells. This study addresses the question of whether bone marrow stromal cell cultures in the Dexter system propagate multiple different mesenchymal stromal cell types or one stromal cell type that expresses multiple phenotypes. Results show that isolated single stromal cells simultaneously express transcripts associated with osteoblast, fibroblast, muscle, and adipocyte differentiation. Furthermore, isolated single stromal cells simultaneously express transcripts characteristic of epithelial cells, endothelial cells, and neural/glial cells. Isolated single stromal cells also express transcripts for CD45, CD19, CD10, CD79a, and representative proto-oncogenes and transcription factors, which are typically associated with normal and neoplastic hematopoietic cells. These findings suggest that the nonhematopoietic mesenchymal cells and the hematopoietic B-lymphocytes have a common progenitor. This is consistent with the idea that progenitor cells express genes that are characteristic of the multiple lineage paths that such cells may be capable of adopting. This study demonstrates the technical feasibility of transcriptome analysis of individual primary cell-culture grown stromal cells and supports the concept that bone marrow stromal cells are relatively homogeneous and show a phenotypic signature of potential multilineage differentiation capacity.

Differentiation of marrow stromal cells into photoreceptors in the rat eye

Retinal degenerations and dystrophies are the major causes of genetically inherited blindness that are characterized by the apoptotic death of the photoreceptor cell layer of the retina. To date, no treatment exists for these diseases and only recently have they been considered as candidates for gene and stem cell therapies. Here we report the ability of adult CD90+ marrow stromal cells (MSCs) to be induced by activin A, taurine, and EGF into cells (20-32%) expressing photoreceptor-specific markers rhodopsin, opsin, and recoverin in vitro. CD90+ cells were either transduced with recombinant adeno-associated virus expressing green fluorescent protein (GFP) or bromodeoxyuridine (BrdU) labeled and then injected into the subretinal space of adult Royal College of Surgeons rats. Fundus photography and angiography showed no adverse effects of CD90+ MSC transplantation. GFP-expressing cells or BrdU-positive cells covered approximately 30% of the entire retinal area. By 2 weeks after injection, CD90+ MSCs integrated into the host retina, forming structures similar to the photoreceptor layer and expressed a photoreceptor-specific marker. No teratoma formation was observed in the recipient retina. The subretinally delivered CD90+ MSCs did not stain for proliferating cell nuclear antigen, indicating that they primarily undergo differentiation rather than proliferation. In addition, we established that transplanted cells can attract synaptic vesicles and hence are potentially capable of signal transduction. This study demonstrates for the first time the partial differentiation of adult CD90+ MSCs into photoreceptors in vitro and in vivo. Our results establish a proof of concept for CD90+ MSC differentiation with autologous transplantation, which may provide a promising therapeutic strategy for the treatment of some forms of genetically inherited retinal degenerations.

Practical Modeling Concepts for Connective Tissue Stem Cell and Progenitor Compartment Kinetics

Stem cell activation and development is central to skeletal development, maintenance, and repair, as it is for all tissues. However, an integrated model of stem cell proliferation, differentiation, and transit between functional compartments has yet to evolve. In this paper, the authors review current concepts in stem cell biology and progenitor cell growth and differentiation kinetics in the context of bone formation. A cell-based modeling strategy is developed and offered as a tool for conceptual and quantitative exploration of the key kinetic variables and possible organizational hierarchies in bone tissue development and remodeling, as well as in tissue engineering strategies for bone repair.

Characterization of mesenchymal stem cells isolated from murine bone marrow by negative selection

Mesenchymal stem cells (MSCs) are typically enriched from bone marrow via isolation of the plastic adherent, fibroblastoid cell fraction. However, plastic adherent cultures elaborated from murine bone marrow are an admixture of fibroblastoid and hematopoietic cell types. Here we report a reliable method based on immunodepletion to fractionate fibroblastoid cells from hematopoietic cells within plastic adherent murine marrow cultures. The immunodepleted cells expressed the antigens Sca-1, CD29, CD44, CD81, CD106, and the stem cell marker nucleostemin (NST) but not CD11b, CD31, CD34, CD45, CD48, CD90, CD117, CD135, or the transcription factor Oct-4. They were also capable of differentiating into adipocytes, chondrocytes, and osteoblasts in vitro as well as osteoblasts/osteocytes in vivo. Therefore, immunodepletion yields a cell population devoid of hematopoietic and endothelial cells that is phenotypically and functionally equivalent to MSCs. The immunodepleted cells exhibited a population doubling time of approximately 5-7 days in culture. Poor growth was due to the dramatic down regulation of many genes involved in cell proliferation and cell cycle progression as a result of immunodepletion. Exposure of immunodepleted cells to fibroblast growth factor 2 (FGF2) but not insulin-like growth factor (IGF), murine stem cell factor, or leukemia inhibitory factor (LIF) significantly increased their growth rate. Moreover, 82% of the transcripts down regulated by immunodepletion remain unaltered in the presence of FGF2. Exposure to the later also reversibly inhibited the ability of the immunodepleted cells to differentiate into adipocytes, chondrocytes, and osteoblasts in vitro. Therefore, FGF2 appears to function as a mitogen and self-maintenance factor for murine MSCs enriched from bone marrow by negative selection.

Neuronal Stem Cells Biology and Plasticity

Recent studies have suggested that stem cells are able to cross primordial tissue barriers. Their ability to respond to unrelated microenvironmental signals strongly suggest that they have greater potential than previously imagined especially for their future clinical use for the regeneration of tissues or even perhaps organ systems. In particular there is an intriguing reciprocal relationship between the hematopoietic and neuronal stem cell systems. Both stem cell pools appear to respond to microenvironmental signals that are not developmental related. These intriguing observations have led to a number of studies that have attempted to explore this apparent phenomenon of plasticity associated with both hematopoietic and neuronal stem cell populations.

Bone marrow-derived cells expressing green fluorescent protein under the control of the glial fibrillary acidic protein promoter do not differentiate into astrocytes in vitro and in vivo

Differentiation of bone marrow (BM) cells into astroglia expressing the glial fibrillary acidic protein (GFAP) has been reported in vitro and after intracerebral or systemic BM transplantation. In contrast, recent data suggest that astrocytic differentiation does not occur from BM-derived cells in vivo. Using transgenic mice that express the enhanced green fluorescent protein (GFP) under the control of the human glial fibrillary acidic protein (GFAP) promoter, we investigated the potential of adult murine BM-derived cells to differentiate into macroglia. In the brains of GFAP-GFP transgenic mice, astrocytes were brightly fluorescent from the expression of GFP. When BM from these animals was transplanted into lethally irradiated wild-type animals, the transgene was detected in the reconstituted hematopoietic system, but no GFP expression was found in the nervous system. In contrast, GFAP-GFP neuroectodermal anlage grafted into adult wild-type striatum gave rise to GFP-expressing astrocytes. Because cerebral ischemia has been suggested to promote the differentiation of BM-derived cells into astrocytes, BM chimeric mice were subjected to focal cerebral ischemia. No GFP-positive cells were found in the ischemic or contralateral hemispheres of these brains. Even after direct injection of GFAP-GFP transgenic BM cells into wild-type striatum, no GFP-expressing astroglia were detected. To test the hypothesis that the in vitro environment might be more permissible for astroglial differentiation, we cultured BM from mice that constitutively express GFP, BM cells expressing GFP from a retroviral vector, and BM from GFAP-GFP transgenic mice on astrocytes and on organotypic hippocampal slices. In all experimental paradigms, BM-derived cells were found to differentiate into ramified microglia but not into GFAP-expressing astrocytes.

Bone marrow-derived cells that populate the adult mouse brain preserve their hematopoietic identity

Cytogenesis in the adult brain can result from the recruitment of circulating precursors, but the proposal that some such cells transdifferentiate into neural elements is controversial. We have reinvestigated this issue by following the phenotypic fate of bone marrow cells expressing the green fluorescent protein transplanted into the systemic circulation of irradiated mice. Thousands of donor-derived cells were detected throughout brains of recipients killed 1-12 months after transplantation, but none displayed neuronal, macroglial, or endothelial characteristics, even after injury. Among those that crossed the endothelium of the cerebral cortex, >99.7% were identified as perivascular macrophages. Newly formed parenchymal microglia were found in significant numbers only in the cerebellum and at injury sites. Therefore, bone marrow does supply the mature brain with new specialized cells; however, mesenchymal precursors neither adopt neural phenotypes nor contribute to cerebral vascular remodeling. This continuous traffic of macrophages across the blood-brain barrier provides a vehicle to introduce therapeutic genes into the nervous system.

Human pulmonary chimerism after hematopoietic stem cell transplantation

Many of the body's tissues once thought to be only locally regenerative may, in fact, be actively replaced by circulating stem cells after hematopoietic stem cell transplantation. Localization of donor-derived cells ("chimerism") has recently been shown to occur in the lungs of mice after either hematopoietic stem cell transplantation or infusion of cultured marrow. To determine whether tissues of the human lung might be similarly derived from extrapulmonary sources, we examined lung specimens from a retrospective cohort of female allogeneic hematopoietic stem cell transplant recipients who received stem cells from male donors. Tissue samples from three such patients who had undergone diagnostic lung biopsy or autopsy were examined. Slides were stained by immunohistochemistry for cytokeratin (epithelium) and platelet endothelial cell adhesion molecule, CD31 (PECAM) (endothelium) and were imaged and then examined by fluorescent in situ hybridization analysis to identify male cells. The resulting overlapping in situ hybridization and immunohistochemistry images were examined for the presence and, if present, cell type of donor cells in the lung. We found significant rates of epithelial (2.5-8.0%) and endothelial (37.5-42.3%) chimerism. These results suggest that significant chimerism of the human lung may follow hematopoietic stem cell transplantation and that adult human stem cells could potentially play a therapeutic role in treatment of the damaged lung.

Endothelial cells but not epithelial cells or cardiomyocytes are partially replaced by donor cells after allogeneic bone marrow and stem cell transplantation

Recent studies have convincingly demonstrated that adult bone marrow contains cells capable of differentiating into a variety of cell types. To investigate whether such bone marrow-derived cells participate on self-renewal and proliferation of nonhematopoietic tissues, we studied tissue obtained by autopsy from female recipients after sex-mismatched allogeneic bone marrow and stem cell transplantation for the presence of donor-derived cells. Epithelial, endothelial, and smooth muscle cells and hematopoietic cells were characterized by double-staining immunohistochemistry with a panel of antibodies and nonisotopic in situ hybridization with a Y-chromosome-specific probe. The present study showed that the capillary endothelium was the only nonhematopoietic cell type that was replaced in a significant amount by donor cells after allogeneic stem cell and bone marrow transplantation. We could not demonstrate any participation of graft-derived cells on repopulation of cardiomyocytes or epithelial cells of the skin and gastrointestinal mucosa and of hepatocytes.

Neural trans-differentiation potential of hepatic oval cells in the neonatal mouse brain

Although the existence of the hepatic oval cell (HOC), the liver stem cell has been known for almost 70 years, little is known about the potential for this adult stem cell to trans-differentiate into cells of other tissues. While their origin remains enigmatic, HOCs share many similarities with hematopoietic stem cells. Recent studies have revealed that a small percentage of HOCs can arise from a bone marrow-derived stem cell source. Here we report that, like bone marrow stem cells, HOCs can survive transplantation to the neonatal mouse brain and show signs of trans-differentiation by adopting the morphology and antigenic phenotype of both macro- and microglia cells. Trans-differentiated microglia cells were functional, showing active phagocytosis when cotransplanted with latex microbeads in vivo. In addition to glial markers, a small number of transplanted HOCs were immunopositive for neuronal markers, but displayed ambiguous phenotype, making their characterization difficult.

Transplantation of porcine umbilical cord matrix cells into the rat brain

Immune rejection of transplanted material is a potential complication of organ donation. In response to tissue transplantation, immune rejection has two components: a host defense directed against the grafted tissue and an immune response from the grafted tissue against the host (graft vs host disease). To treat immune rejection, transplant recipients are typically put on immunosuppression therapy. Complications may arise from immune suppression or from secondary effects of immunosuppression drugs. Our preliminary work indicated that stem cells may be xenotransplanted without immunosuppression therapy. Here, we investigated the survival of pig stem cells derived from umbilical cord mucous connective tissue (UCM) after transplantation into rats. Our data demonstrate that UCM cells survive at least 6 weeks without immune suppression of the host animals after transplantation into either the brain or the periphery. In the first experiment, UCM cells were transplanted into the rat brain and recovered in that tissue 2-6 weeks posttransplantation. At 4 weeks posttransplantation, the UCM cells engrafted into the brain along the injection tract. The cells were small and roughly spherical. The transplanted cells were positively immunostained using a pig-specific antibody for neuronal filament 70 (NF70). In contrast, 6 weeks posttransplantation, about 10% of the UCM cells that were recovered had migrated away from the injection site into the region just ventral to the corpus callosum; these cells also stained positively for NF70. In our second experiment, UCM cells that were engineered to constitutively express enhanced green fluorescent protein (eGFP) were transplanted. These cells were recovered 2-4 weeks after brain transplantation. Engrafted cells expressing eGFP and positively staining for NF70 were recovered. This finding indicates a potential for gene therapy. In the third experiment, to determine whether depositing the graft into the brain protected UCM cells from immune detection/clearance, UCM cells were injected into the tail vein and/or the semitendinosis muscle in a group of animals. UCM cells were recovered from the muscle or within the kidney 3 weeks posttransplantation. In control experiments, rat brains were injected with PKH 26-labeled UCM cells that had been lysed by repeated sonic disruption. One and 2 weeks following injection, no PKH 26-labeled neurons or glia were observed. Taken together, these data indicate that UCM cells can survive xenotransplantation and that a subset of the UCM cells respond to local signals to differentiate along a neural lineage.

The Wnt signaling inhibitor dickkopf-1 is required for reentry into the cell cycle of human adult stem cells from bone marrow

Adult human mesenchymal stem cells from bone marrow stroma (hMSCs) differentiate into numerous mesenchymal tissue lineages and are attractive candidates for cell and gene therapy. When early passage hMSCs are plated or replated at low density, the cultures display a lag phase of 3-5 days, a phase of rapid exponential growth, and then enter a stationary phase without the cultures reaching confluence. We found that as the cultures leave the lag phase, they secrete high levels of dickkopf-1 (Dkk-1), an inhibitor of the canonical Wnt signaling pathway. The addition of recombinant Dkk-1 toward the end of the lag period increased proliferation and decreased the cellular concentration of beta-catenin. The addition of antibodies to Dkk-1 in the early log phase decreased proliferation. Also, expression of Dkk-1 in hMSCs decreased during cell cycle arrest induced by serum starvation. The results indicated that high levels of Dkk-1 allow the cells to reenter the cell cycle by inhibiting the canonical Wnt/beta-catenin signaling pathway. Since antibodies to Dkk-1 also increased the lag phase of an osteosarcoma line that expressed the gene, Dkk-1 may have a similar role in some other cell systems.

Mesenchymal stem cell engraftment in lung is enhanced in response to bleomycin exposure and ameliorates its fibrotic effects

Previously we described a reliable method based on immunodepletion for isolating mesenchymal stem cells (MSCs) from murine bone marrow and showed that, after intracranial transplantation, the cells migrated throughout forebrain and cerebellum and adopted neural cell fates. Here we systemically administered MSCs purified by immunodepletion from male bleomycin (BLM)-resistant BALB/c mice into female BLM-sensitive C57BL/6 recipients and quantified engraftment levels in lung by real-time PCR. Male DNA accounted for 2.21 x 10(-5)% of the total lung DNA in control-treated mice but was increased 23-fold (P = 0.05) in animals exposed to BLM before MSC transplantation. Fluorescence in situ hybridization revealed that engrafted male cells were localized to areas of BLM-induced injury and exhibited an epithelium-like morphology. Moreover, purification of type II epithelial cells from the lungs of transplant recipients resulted in a 3-fold enrichment of male, donor-derived cells as compared with whole lung tissue. MSC administration immediately after exposure to BLM also significantly reduced the degree of BLM-induced inflammation and collagen deposition within lung tissue. Collectively, these studies demonstrate that murine MSCs home to lung in response to injury, adopt an epithelium-like phenotype, and reduce inflammation and collagen deposition in lung tissue of mice challenged with BLM.