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

Transplanted adult bone marrow cells repair myocardial infarcts in mice

Occlusion of the anterior descending left coronary artery leads to ischemia, infarction, and loss of function in the left ventricle. We have studied the repair of infarcted myocardium in mice using highly enriched stem/progenitor cells from adult bone marrow. The left coronary artery was ligated and 5 hours later Lin- c-kit+ bone marrow cells obtained from transgenic male mice expressing enhanced green fluorescent protein (EGFP) were injected into the healthy myocardium adjacent to the site of the infarct. After 9 days the damaged hearts were examined for regenerating myocardium. A band of new myocardium was observed in 12 surviving mice. The developing myocytes were small and resembled fetal and neonatal myocytes. They were positive for EGFP, Y chromosome, and several myocyte-specific proteins including cardiac myosin, and the transcription factors GATA-4, MEF2, and Csx/Nkx2.5. The cells were also positive for connexin 43, a gap junction/intercalated disc component indicating the onset of intercellular communication. Myocyte proliferation was demonstrated by incorporation of BrdU into the DNA of dividing cells and by the presence of the cell cycle-associated protein K167 in their nuclei. Neo-vascularization was also observed in regenerating myocardium. Endothelial and smooth muscle cells in developing capillaries and small arterioles were EGFP-positive. These cells were positive for Factor VIII and alpha smooth muscle actin, respectively. No myocardial regeneration was observed in damaged hearts transplanted with Lin- c-kit- bone marrow cells, which lack bone marrow-regenerating activity. Functional competence of the repaired left ventricle was improved for several hemodynamic parameters. These in vivo findings demonstrate the capacity of highly enriched Lin- c-kit+ adult bone marrow cells to acutely regenerate functional myocardium within an infarcted region.

Human mesenchymal stem cells persist, demonstrate site-specific multipotential differentiation, and are present in sites of wound healing and tissue regeneration after transplantation into fetal sheep

Prenatal transplantation of stem cells is an exciting frontier for the treatment of many congenital diseases. The fetus may be an ideal recipient for stem cells, as it is immunologically immature and has rapidly proliferating cellular compartments that may support the engraftment of transplanted cells. Mesenchymal stem cells (MSC), given their ability to differentiate into multiple cell types, could potentially be used to treat diseases such as osteogenesis imperfecta, muscular dystrophy, and other mesenchymal disorders that can be diagnosed in utero. We have shown, using a human-sheep in utero xenotransplantation model, that human MSC have the ability to engraft, undergo site-specific differentiation into multiple cell types, and survive for more than 1 year in fetal lamb recipients. In addition, in this model MSC-derived cells appear to be present in increased numbers in wounded or regenerating tissues. This observation warrants further studies of the biology of MSCs following systemic or site-directed transplantation.

The neural stem cells and their transdifferentiation capacity

Stem cells play a critical role during embryo and tissue formation throughout development. Thanks to their multipotentiality - i.e., the ability to give rise to different lineages of mature cells - and to their extensive capacity for self-renewal and expansive growth, stem cells can also contribute to the maintenance of tissue integrity in adulthood. Historically, it has been held that fetal and adult (somatic) stem cells are tissue-specific 'entities' whose differentiation potential is limited to the generation of mature cell types of the tissue/organ in which they reside. Yet, recent years have seen the publication of an impressive sequence of reports dealing with what is now emerging as one of the most striking functional attributes of somatic stem cells, that is, their capacity to undergo transdifferentiation. Thanks to this peculiar characteristic adult stem cells display an unexpected ability to give rise to differentiated cells of tissues and organs different from those in which they reside. This commentary briefly illustrates the characteristics of the neural stem cell and its capacity as a neuroectodermal derivative to undergo transdifferentiation, thus giving rise to differentiated cells that normally originate from the mesoderm, like blood or skeletal muscle cells.

Therapeutic benefit of intravenous administration of bone marrow stromal cells after cerebral ischemia in rats

BACKGROUND AND PURPOSE

We tested the hypothesis that intravenous infusion of bone marrow derived-marrow stromal cells (MSCs) enter the brain and reduce neurological functional deficits after stroke in rats.

METHODS

Rats (n=32) were subjected to 2 hours of middle cerebral artery occlusion (MCAO). Test groups consisted of MCAO alone (group 1, n=6); intravenous infusion of 1x10(6) MSCs at 24 hours after MCAO (group 2, n=6); or infusion of 3x10(6) MSCs (group 3, n=7). Rats in groups 1 to 3 were euthanized at 14 days after MCAO. Group 4 consisted of MCAO alone (n=6) and group 5, intravenous infusion of 3x10(6) MSCs at 7 days after MCAO (n=7). Rats in groups 4 and 5 were euthanized at 35 days after MCAO. For cellular identification, MSCs were prelabeled with bromodeoxyuridine. Behavioral tests (rotarod, adhesive-removal, and modified Neurological Severity Score [NSS]) were performed before and at 1, 7, 14, 21, 28, and 35 days after MCAO. Immunohistochemistry was used to identify MSCs or cells derived from MSCs in brain and other organs. RESULTS Significant recovery of somatosensory behavior and Neurological Severity Score (P<0.05) were found in animals infused with 3x10(6) MSCs at 1 day or 7 days compared with control animals. MSCs survive and are localized to the ipsilateral ischemic hemisphere, and a few cells express protein marker phenotypic neural cells.

CONCLUSIONS

MSCs delivered to ischemic brain tissue through an intravenous route provide therapeutic benefit after stroke. MSCs may provide a powerful autoplastic therapy for stroke.

Intracranial bone marrow transplantation after traumatic brain injury improving functional outcome in adult rats

OBJECT

The authors tested the hypothesis that intracranial bone marrow (BM) transplantation after traumatic brain injury (TBI) in rats provides therapeutic benefit.

METHODS

Sixty-six adult Wistar rats, weighing 275 to 350 g each, were used for the experiment. Bone marrow prelabeled with bromodeoxyuridine (BrdU) was harvested from tibias and femurs of healthy adult rats. Other animals were subjected to controlled cortical impact, and BM was injected adjacent to the contusion 24 hours after the impact. The animals were killed at 4, 7, 14, or 28 days after transplantation. Motor function was evaluated both before and after the injury by using the rotarod test. After the animals had been killed, brain sections were examined using hemotoxylin and eosin and immunohistochemical staining methods. Histological examination revealed that, after transplantation, BM cells survived, proliferated, and migrated toward the injury site. Some of the BrdU-labeled BM cells were reactive, with astrocytic (glial fibrillary acid protein) and neuronal (NeuN and microtubule-associated protein) markers. Transplanted BM expressed proteins phenotypical of intrinsic brain cells, that is, neurons and astrocytes. A statistically significant improvement in motor function in rats that underwent BM transplantation, compared with control rats, was detected at 14 and 28 days posttransplantation.

CONCLUSIONS

On the basis of their findings, the authors assert that BM transplantation improves neurological outcome and that BM cells survive and express nerve cell proteins after TBI.

Chimeric stem cells

There is growing excitement over stem cell biology. It has stirred strong ethical and moral debates over the status and rights of small clusters of cells. It has promised a panacea for illnesses ranging from diabetes to stroke. It has challenged historical dogmas in developmental biology. There have been many commentaries on all of these issues in prominent journals and newspapers over recent months. In this article, we take a critical look at new data that underpin the last of these claims: the chimeric stem cell.

In vitro differentiation of human marrow stromal cells into early progenitors of neural cells by conditions that increase intracellular cyclic AMP

Human marrow stromal cells (hMSCs) are multipotential stem cells that can be differentiated into bone, cartilage, fat, and muscle. In the experiments here, we found that undifferentiated cultures of hMSCs express some markers characteristic of neural cells such as microtubule-associated protein 1B (MAP1B), neuron-specific tubulin (TuJ-1), neuron-specific enolase (NSE), and vimentin. By treating hMSCs with 0.5 mM isobutylmethylxanthine (IBMX)/1 mM dibutyryl cyclic AMP (dbcAMP) for 6 days, about 25% of the hMSCs differentiated into cells with a typical neural cell morphology and with increased levels of both NSE and vimentin. The data suggested that the hMSCs may have been differentiated into early progenitors of neural cells in vitro under conditions that increase the intracellular level of cAMP.

Tracking oligodendrocytes during development and regeneration

Over the past decade, advances in strategies to tag cells have opened new avenues for examining the development of myelin-forming glial cells and for monitoring transplanted cells in animal models of myelin insufficiency. The strategies for labelling glial cells have encompassed a range of genetic modifications as well as methods for directly attaching labels to cells. Genetically modified oligodendrocytes have been engineered to express enzymatic (e.g., beta-galactosidase, alkaline phosphatase), naturally fluorescent (e.g., green fluorescent protein), and antibiotic resistance (e.g., neomycin, zeomycin) reporters. Genes have been introduced in vivo and in vitro with viral or plasmid vectors to somatically label glial cells. To generate germ-line transmission of tagged oligodendrocytes, transgenic mice have been created both by direct injection into mouse fertilized eggs and by "knock-in" of reporters targetted to myelin gene loci in embryonic stem cells. Each experimental approach has advantages and limitations that need to be considered for individual applications. The availability of tagged glial cells has expanded our basic understanding of how oligodendrocytes are specified from stem cells and should continue to fill in the gaps in our understanding of how oligodendrocytes differentiate, myelinate, and maintain their myelin sheaths. Moreover, the ability to select oligodendrocytes by virtue of their acquired antibiotic resistance has provided an important new tool for isolating and purifying oligodendrocytes. Tagged glial cells have also been invaluable in evaluating cell transplant therapies in the nervous system. The tracking technologies that have driven these advances in glial cell biology are continuing to evolve and present new opportunities for examining oligodendrocytes in living systems. Microsc. Res. Tech. 52:766-777, 2001. Published 2001 Wiley-Liss, Inc.

Versatile stem cells, young and old. A review

Both embryonic and somatic stem cells have been studied in recent years with particular regard to their differentiation potential. In vitro studies allow a considerable amplification of such cells in culture as well as the induction of commitment in different directions under proper stimulating factors. Moreover, a surprising versatility has been discovered,which makes possible a ;reprogramming' of stem cells into a lineage pathway which may be completely different from the expected direction: for instance, a production of brain cells from blood progenitors has been obtained. It is thus possible to envisage methods of producing in culture sufficient amounts of stem cells, committed to a certain pathway, which can be transplanted in vivo to replace damaged tissues and organs.

Connexin 26 and basic fibroblast growth factor are expressed primarily in the subpial and subependymal layers in adult brain parenchyma: roles in stem cell proliferation and morphological plasticity?

The gap junction protein connexin 26 (Cx26) has been detected previously in the parenchyma of the developing brain and in the developing and adult meninges, but there is no clear evidence for the presence of this connexin in adult brain parenchyma. Confocal mapping of Cx26 through serial sections of the meningeal-intact rat brain with four antibodies revealed an intense Cx26 immunoreactivity in both parenchyma and extraparenchyma. In the extraparenchyma, a continuum of Cx26-immunoreactive puncta was observed throughout the three meningeal layers, the perineurium of cranial nerves, and meningeal projections into the brain, including sheaths of blood vessels and stroma of the choroid plexus. In the parenchyma, Cx26-immunoreactive puncta were located primarily in subependymal, subpial, and perivascular zones and were associated primarily with glial fibrillary acidic protein-positive (GFAP+) astrocytes, the nuclei of which are strongly immunoreactive for basic fibroblast growth factor (bFGF). Although it was found to a lesser extent than in astrocytes, bFGF immunoreactivity also was intense in the nuclei of meningeal fibroblasts. In addition, we have found a close correlation between the distribution of Cx26 and vimentin immunoreactivities in the meninges and their projections into the brain. We previously showed vimentin and S100beta immunoreactivities through a network of meningeal fibroblasts in the three layers of meninges, perivascular cells, and ependymocytes and in a population of astrocytes. The related topography of this network with GFAP+ astrocytes has also been demonstrated. Considering that connexin immunoreactivity may reflect the presence of functional gap junctions, the present results are consistent with our hypothesis that all of these various cell types may communicate in a cooperative network.

Immortalized multipotential mesenchymal cells and the hematopoietic microenvironment

In an attempt to analyze the cellular and molecular basis of the capacity of bone marrow stromal cells to support hematopoiesis in culture, we developed a series of murine stromal cell lines from a single long-term bone marrow culture (BMC). The cytokines produced by these cells were analyzed using immunohistochemical techniques, ribonuclease protection assays (RPA) and RT-PCR. We examined the capacity of these cloned cell lines to replace primary bone marrow-derived stromal cells in long-term bone marrow cultures (LT-BMC) and sought correlations between the capacity to support hematopoiesis in culture with the production of known cytokines. These immortalized lines replicate many of the functions of the hematopoietic microenvironment. They express cytokines known to play a role in hematopoiesis. All of the lines constitutively express mRNA for PBSF (SDF-1), macrophage colony-stimulating factor (M-CSF), stem cell factor (SCF), FLT-3, thrombopoietin (TPO), interleukin 7 (IL-7), leukemia inhibitory factor (LIF), tumor necrosis factor-beta (TNF-beta), and interferon-gamma (IFN-gamma). Most lines also express granulocyte-macrophage colony-stimulating factor (GM-CSF) and G-CSF. They vary in their expression of IL-6, tumor growth factor-beta1 (TGF-beta1), TGF-beta2, and TNF-alpha. Growing these lines in the presence of cytokines that influence hematopoiesis alters the levels of cytokine message. The most striking effects were produced by TNF-alpha. In addition to the cytokine mRNAs, the cell lines express factors associated with bone formation such as osteoblast-specific factor-2 (OSF-2) and bone morphogenetic protein-1 (BMP-1). They also express the neural cell-adhesion molecule neuropilin and neurotrophic factors including nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). Several of the lines can maintain hematopoiesis in culture, as measured by the continuous production of myeloid colony-forming cells (CFU-c), for months. This capacity to support hematopoiesis does not correlate with any pattern of cytokine expression. Several of these lines also support the growth of human hematopoietic cells, and human CFU-c can be detected in the cultures in which CD34(+) bone marrow cells (BMC) are cultured on murine stromal cells. No correlation between the production of any of the known cytokines and the ability to support murine hematopoiesis was detected. In addition, there was no correlation between the capacity to support murine hematopoiesis and the capacity to maintain human HSC. Despite repeated cloning, the lines remain heterogeneous and are capable of producing cells with the properties of fibroblasts, osteoblasts, adipocytes, and myoblasts. In addition to the cytokine mRNAs, the cell lines express factors associated with bone formation such as OSF-2 and BMP-1. They also express the neural cell-adhesion molecule neuropilin and neurotrophic factors including NGF and BDNF.

Stem cell transplantation into the central nervous system and the control of differentiation

Recent advances in stem cell biology, including methods of cell amplification and control of differentiation in vitro, provide us with new and powerful tools with which to explore the cellular, molecular, and genetic factors affecting cell survival, proliferation, differentiation, and differentiation potential. Mitigating this vein of enthusiasm are the results of stem cell transplantation studies, which highlight our inability to control the fate of stem cell populations following transplantation to the central nervous system (CNS). Differentiation of transplanted cells is strongly influenced by the environmental signals and cellular deficiencies operating at the site of implantation, over which we can exert little or no control. Where stem cell transplantation-mediated repair of the injured CNS has been demonstrated most successfully, the transplant environments have invariably been simplistic, and transplantation into the complex and reactive environment of a CNS injury site generally results in migration from the site of implantation followed by glial cell differentiation. Together, these findings suggest that the most significant advances for the stem cell transplantation field will come from research strategies that include predifferentiation of stem cells prior to transplant and studies that further our understanding of the factors affecting stem cell differentiation in the complex environment of the CNS in vivo.

From gene transfer to gene therapy in lysosomal storage diseases affecting the central nervous system

Gene transfer into the central nervous system (CNS) is one of the foremost scientific challenges today. To give a brief survey of possible approaches to gene therapy in diseases affecting the CNS, we have selected the lysosomal storage diseases (LDS), which are an excellent model of both early-onset infantile neurological forms and late-onset adult psychiatric forms. Lysosomal storage diseases represent a group of about 50 monogenic metabolic disorders resulting from a deficiency in intralysosomal enzymes involved in macromolecule catabolism. The clinical severity, including neuropsychiatric symptoms, and the absence of an efficient therapy for the majority of these disorders prompted the various trials of gene therapy now in progress. Most of the genes encoding the normal lysosomal enzymes have been cloned, and the size of the corresponding cDNAs is generally compatible with their transfer by recombinant vectors. New vectors with improved immunogenicity, transduction efficacy, insert capacity, and specificity of targeting are under development. Here we discuss several gene therapy strategies for the correction of LSD-induced anomalies in the CNS. Interesting results have been obtained by animal model brain, which raises hopes that large-scale clinical trials may soon be started.

Mesenchymal stem cells are capable of homing to the bone marrow of non-human primates following systemic infusion

OBJECTIVE

The human bone marrow contains mesenchymal stem cells capable of differentiating along multiple mesenchymal cell lineages. Using a non-human primate model, we sought to determine whether the systemic infusion of baboon-derived mesenchymal stem cells was associated with toxicity and whether these cells were capable of homing to and persisting within the bone marrow.

MATERIALS AND METHODS

Five baboons (Papio anubis) were administered lethal irradiation followed by intravenous autologous hematopoietic progenitor cells combined with either autologous (n = 3) or allogeneic (n = 2) mesenchymal stem cells that had been expanded in culture. In four of these baboons, the mesenchymal stem cells were genetically modified with a retroviral vector encoding either the enhanced green fluorescent protein gene (n = 3) or the human placental alkaline phosphatase gene (n = 1) for tracking purposes. A sixth animal received only intravenous gene marked autologous mesenchymal stem cells but no hematopoietic stem cells or conditioning irradiation.

RESULTS

Following culture, baboon mesenchymal stem cells appeared morphologically as a homogeneous population of spindle-shaped cells that were identified by the monoclonal antibodies SH-3 and SH-4. These cells did not express the hematopoietic markers CD34 or CD45. Baboon mesenchymal stem cells isolated from primary culture were capable of differentiating along both adipogenic and osteogenic lineages. There was no acute or chronic toxicity associated with the intravenous infusion of mesenchymal stem cells. In all five recipients of gene marked mesenchymal stem cells, transgene was detected in post-transplant bone marrow biopsies. In two animals receiving autologous mesenchymal stem cells, including the one non-conditioned recipient, transgene could be detected over 1 year following infusion. In one recipient of allogeneic gene marked mesenchymal stem cells, transgene was detected in the bone marrow at 76 days following infusion.

CONCLUSION

These data demonstrate that baboon mesenchymal stem cells: 1) are not associated with significant toxicity when administered intravenously, 2) are capable of homing to the bone marrow following intravenous infusion, and 3) have the capacity to establish residence within the bone marrow for an extended duration following systemic administration.

Differentiation of osteoblasts and in vitro bone formation from murine embryonic stem cells

Pluripotent embryonic stem (ES) cells have the potential to differentiate to all fetal and adult cell types and might represent a useful cell source for tissue engineering and repair. Here we show that differentiation of ES cells toward the osteoblast lineage can be enhanced by supplementing serum-containing media with ascorbic acid, beta-glycerophosphate, and/or dexamethasone/retinoic acid or by co-culture with fetal murine osteoblasts. ES cell differentiation into osteoblasts was characterized by the formation of discrete mineralized bone nodules that consisted of 50-100 cells within an extracellular matrix of collagen-1 and osteocalcin. Dexamethasone in combination with ascorbic acid and beta-glycerophosphate induced the greatest number of bone nodules and was dependent on time of stimulation with a sevenfold increase when added to ES cultures after, but not before, 14 days. Co-culture with fetal osteoblasts also provided a potent stimulus for osteogenic differentiation inducing a fivefold increase in nodule number relative to ES cells cultured alone. These data demonstrate the application of a quantitative assay for the derivation of osteoblast lineage progenitors from pluripotent ES cells. This could be applied to obtain purified osteoblasts to analyze mechanisms of osteogenesis and for use of ES cells in skeletal tissue repair.

Transplantation and gene therapy: combined approaches for repair of spinal cord injury

Motor and sensory functions are lost after spinal cord injury because neurons die or atrophy and axons fail to regenerate. Until fairly recently, it was believed that damaged neurons could not be replaced and injured axons could not regenerate, and, therefore, functions dependent on injured neurons could not be recovered. We now know that damaged neurons can be rescued by providing therapeutic factors or replaced by grafting. In addition, the adult CNS contains a population of precursor cells with a potential to generate new neural cells, whose numbers and composition can be modified by extrinsic factors. The pioneering studies of Aguayo demonstrated that CNS axons could regenerate in the right environment. Subsequent studies have revealed the identity of some of the inhibitory molecules in myelin and scar tissue, and we now have a better understanding of how the CNS environment can be modified to become more permissive to regeneration. Axons that regenerate must find an appropriate target, but it may not be essential to reestablish the precise topography for some functions to be restored. There are now new and promising strategies for delivery of therapeutic genes to protect neurons and to stimulate regeneration. The ability to engineer cells by gene therapy combines the therapeutic values of cell transplantation and gene delivery. These remarkable developments from many disciplines have generated a new level of optimism in the search for a cure for CNS injury and in particular spinal cord injury. In this review, the authors summarize recent progress in these strategies and some of the challenges that remain in elucidating the most efficacious protocols for rescuing injured neurons, encouraging regeneration of their axons, and promoting recovery of function.

Stem cell potential: can anything make anything?

Recent results suggest that stem cells from one tissue can give rise to cells from developmentally unrelated tissues. These results strongly support the idea that certain progenitors retain much broader developmental potentials than expected, and other progenitors may be able to acquire broader potentials in culture.

Human periosteum-derived cells maintain phenotypic stability and chondrogenic potential throughout expansion regardless of donor age

OBJECTIVE

To assess the in vitro chondrogenic potential of adult human periosteum-derived cells (PDCs) with regard to the number of cell passages and the age of the donor.

METHODS

Cells were enzymatically released from the periosteum of the proximal tibia obtained from adult human donors and expanded in monolayer. PDCs were harvested at multiple passages for total RNA extraction and semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) gene expression analysis. For the chondrogenesis assay, cells were plated in micromass and treated with transforming growth factor beta1 (TGFbeta1) in a chemically defined medium. At different time points, micromasses were either harvested for RT-PCR analysis for cartilage and bone markers or fixed, paraffin-embedded, and stained for cartilage matrix, and immunostained for type II collagen.

RESULTS

At the first 2 passages, human PDCs from young donors formed chondrogenic nodules. This spontaneous chondrogenic activity was lost upon passaging, and it was not observed in donors older than 30 years. Using a panel of marker genes, PDCs were shown to be phenotypically stable during cell expansion. Regardless of donor age or cell passage, chondrogenesis could be induced consistently by combining micromass culture and TGFbeta1 treatment. Histochemical and immunohistochemical analyses demonstrated the hyaline-like cartilage phenotype of the tissue generated in vitro. Other TGFbeta superfamily members, such as growth differentiation factor 5/cartilage-derived morphogenetic protein 1, and bone morphogenetic proteins 2, 4, and 7, were poorly chondrogenic under the same culture conditions.

CONCLUSION

Adult human PDCs have the potential to differentiate toward the chondrocytic lineage in vitro, retaining this property even after extensive subculture. Human PDCs are easily accessible, expandable, and maintain their chondrogenic potential, and are therefore promising progenitor cells for use in the repair of joint surface defects.

Plasticity of bone marrow-derived stem cells

Recently, concepts for the transplantation of hematopoietic stem cells have changed dramatically. High-dose myeloablative conditioning regimens are in the process of being replaced by immuno-suppressive regimens, ablating host myelopoiesis, and neoplastic cells by the co-transplanted donor lymphocytes. Furthermore, the presence of stem cells in the bone marrow, capable of differentiating into a variety of nonhematopoietic tissues as well as the presence of cells in other organs, capable of differentiating into hematopoietic cells, has led to the novel concept of the plasticity of stem cells derived from different tissues. It is anticipated that these remarkable studies will also lead to novel therapeutic strategies.

Turning blood into brain: cells bearing neuronal antigens generated in vivo from bone marrow

Bone marrow stem cells give rise to a variety of hematopoietic lineages and repopulate the blood throughout adult life. We show that, in a strain of mice incapable of developing cells of the myeloid and lymphoid lineages, transplanted adult bone marrow cells migrated into the brain and differentiated into cells that expressed neuron-specific antigens. These findings raise the possibility that bone marrow-derived cells may provide an alternative source of neurons in patients with neurodegenerative diseases or central nervous system injury.

Developmental potential of somatic stem cells in mammalian adults

Traditionally, somatic tissue-derived stem cells of mammalian adults have been viewed as pluripotent precursors capable of lifelong maintenance of cellular compartments typical of the tissue in which they reside. However in recent years, in vitro cultures and in vivo transplantation assays have indicated that adult somatic stem cell of various species are capable of adopting multiple fates. Bone marrow cells can give rise to a wide array of phenotypes, including blood, endothelial, bone, cartilage, fat, tendon, lung, liver, muscle, marrow stroma, and even brain cells. Conversely, neural stem cells as well as progenitors present in the muscle may contribute to blood cell production, indicating that adult stem cells present in numerous tissues may generate multiple cell types even of different dermal origin. Therefore, the developmental potential of adult somatic stem cells might be reassessed, although the mechanisms that ultimately lead to determination of cell fate are not completely defined. The successful long-term culturing and expansion of somatic adult stem cells together with their intrinsic versatility leads to future hope of stem cell therapeutic use in a wide spectrum of diseases and disorders of several, even not easily accessible, tissues.

Limited engraftment capacity of bone marrow–derived mesenchymal cells following T-cell–depleted hematopoietic stem cell transplantation

The engraftment capacity of bone marrow–derived mesenchymal cells was investigated in 41 patients who had received a sex-mismatched, T-cell–depleted allograft from human leukocyte antigen (HLA)–matched or –mismatched family donors. Polymerase chain reaction (PCR) analysis of the human androgen receptor (HUMARA) or the amelogenin genes was used to detect donor-derived mesenchymal cells. Only 14 marrow samples (34%) from 41 consenting patients generated a marrow stromal layer adequate for PCR analysis. Monocyte-macrophage contamination of marrow stromal layers was reduced below the levels of sensitivity of HUMARA and amelogenin assays (5% and 3%, respectively) by repeated trypsinizations and treatment with the leucyl-leucine (leu-leu) methyl ester. Patients who received allografts from 12 female donors were analyzed by means of the HUMARA assay, and in 5 of 12 cases a partial female origin of stromal cells was demonstrated. Two patients who received allografts from male donors were analyzed by amplifying the amelogenin gene, and in both cases a partial male origin of stromal cells was shown. Fluorescent in situ hybridization analysis using a Y probe confirmed the results of PCR analysis and demonstrated in 2 cases the existence of a mixed chimerism at the stromal cell level. There was no statistical difference detected between the dose of fibroblast progenitors (colony-forming unit–F [CFU-F]) infused to patients with donor- or host-derived stromal cells (1.18 ± 0.13 × 104/kg vs 1.19 ± 0.19 × 104/kg; P ≥ .97). In conclusion, marrow stromal progenitors reinfused in patients receiving a T-cell–depleted allograft have a limited capacity of reconstituting marrow mesenchymal cells.

Limited engraftment capacity of bone marrow–derived mesenchymal cells following T-cell–depleted hematopoietic stem cell transplantation

The engraftment capacity of bone marrow–derived mesenchymal cells was investigated in 41 patients who had received a sex-mismatched, T-cell–depleted allograft from human leukocyte antigen (HLA)–matched or –mismatched family donors. Polymerase chain reaction (PCR) analysis of the human androgen receptor (HUMARA) or the amelogenin genes was used to detect donor-derived mesenchymal cells. Only 14 marrow samples (34%) from 41 consenting patients generated a marrow stromal layer adequate for PCR analysis. Monocyte-macrophage contamination of marrow stromal layers was reduced below the levels of sensitivity of HUMARA and amelogenin assays (5% and 3%, respectively) by repeated trypsinizations and treatment with the leucyl-leucine (leu-leu) methyl ester. Patients who received allografts from 12 female donors were analyzed by means of the HUMARA assay, and in 5 of 12 cases a partial female origin of stromal cells was demonstrated. Two patients who received allografts from male donors were analyzed by amplifying the amelogenin gene, and in both cases a partial male origin of stromal cells was shown. Fluorescent in situ hybridization analysis using a Y probe confirmed the results of PCR analysis and demonstrated in 2 cases the existence of a mixed chimerism at the stromal cell level. There was no statistical difference detected between the dose of fibroblast progenitors (colony-forming unit–F [CFU-F]) infused to patients with donor- or host-derived stromal cells (1.18 ± 0.13 × 104/kg vs 1.19 ± 0.19 × 104/kg; P ≥ .97). In conclusion, marrow stromal progenitors reinfused in patients receiving a T-cell–depleted allograft have a limited capacity of reconstituting marrow mesenchymal cells.

Purified hematopoietic stem cells can differentiate into hepatocytes in vivo

The characterization of hepatic progenitor cells is of great scientific and clinical interest. Here we report that intravenous injection of adult bone marrow cells in the FAH(-/-) mouse, an animal model of tyrosinemia type I, rescued the mouse and restored the biochemical function of its liver. Moreover, within bone marrow, only rigorously purified hematopoietic stem cells gave rise to donor-derived hematopoietic and hepatic regeneration. This result seems to contradict the conventional assumptions of the germ layer origins of tissues such as the liver, and raises the question of whether the cells of the hematopoietic stem cell phenotype are pluripotent hematopoietic cells that retain the ability to transdifferentiate, or whether they are more primitive multipotent cells.

Stem cell generation and choice of fate: role of cytokines and cellular microenvironment

Hematopoietic stem cells (HSC) have provided a model for the isolation, enrichment and transplantation of stem cells. Gene targeting studies in mice have shown that expression of the thrombopoietin receptor (TpoR) is linked to the accumulation of HSCs capable to generate long-term blood repopulation when injected into irradiated mice. The powerful increase in vivo in HSC numbers by retrovirally transduced HOX4B, a homeotic gene, along with the role of the TpoR, suggested that stem cell fate, renewal, differentiation and number can be controlled. The discovery of the precise region of the mouse embryo where HSCs originate and the isolation of supporting stromal cell lines open the possibility of identifying the precise signals required for HSC choice of fate. The completion of human genome sequencing coupled with advances in gene expression profiling using DNA microarrays will enable the identification of key genes deciding the fate of stem cells. Downstream from HSCs, multipotent hematopoietic progenitor cells appear to co-express a multiplicity of genes characteristic of different blood lineages. Genomic approaches will permit the identification of the select group of genes consolidated by the commitment of these multipotent progenitors towards one or the other of the blood lineages. Studies with neural stem cells pointed to the unexpected plastic nature of these cells. Isolation of stem cells from multiple tissues may suggest that, providing the appropriate environment/ signal, tissues could be regenerated in the laboratory and used for transplantation. A spectacular example of influence of the environment on cell fate was revealed decades ago by using mouse embryonic stem cells (ES). Injected into blastocysts, ES cells contribute to the formation of all adult tissues. Injected into adult mice, ES cells become cancer cells. After multiple passages as ascites, when injected back into the blastocyst environment, ES- derived cancer cells behaved again as ES cells. More recently, the successful cloning of mammals and reprogramming of transferred nuclei by factors in the cytoplasm of oocytes turned back the clock by showing that differentiated nuclei can be "re-booted" to generate again the stem cells for different tissues.

Skeletal myogenic potential of human and mouse neural stem cells

Distinct cell lineages established early in development are usually maintained throughout adulthood. Thus, adult stem cells have been thought to generate differentiated cells specific to the tissue in which they reside. This view has been challenged; for example, neural stem cells can generate cells that normally originate from a different germ layer. Here we show that acutely isolated and clonally derived neural stem cells from mice and humans could produce skeletal myotubes in vitro and in vivo, the latter following transplantation into adult animals. Myogenic conversion in vitro required direct exposure to myoblasts, and was blocked if neural cells were clustered. Thus, a community effect between neural cells may override such myogenic induction. We conclude that neural stem cells, which generate neurons, glia and blood cells, can also produce skeletal muscle cells, and can undergo various patterns of differentiation depending on exposure to appropriate epigenetic signals in mature tissues.

Neurons from stem cells: Implications for understanding nervous system development and repair

Neurodegenerative diseases cost the economies of the developed world billions of dollars per annum. Given ageing population profiles and the increasing extent of this problem, there has been a surge of interest in neural stem cells and in neural differentiation protocols that yield neural cells for therapeutic transplantation. Due to the oncogenic potential of stem cells a better characterisation of neural differentiation, including the identification of new neurotrophic factors, is required. Stem cell cultures undergoing synchronous in vitro neural differentiation provide a valuable resource for gene discovery. Novel tools such as microarrays promise to yield information regarding gene expression in stem cells. With the completion of the yeast, C. elegans, Drosophila, human, and mouse genome projects, the functional characterisation of genes using genetic and bioinformatic tools will aid in the identification of important regulators of neural differentiation.Key words: neural differentiation, neural precursor cell, brain repair, central nervous system repair, CNS.

Gene therapy in lysosomal diseases

Lysosomal storage diseases are monogenic metabolic disorders resulting from a deficiency in intralysosomal enzymes involved in macromolecule catabolism. Various groups have been delineated according to the affected pathway and the accumulated substrate: mucopolysaccharidoses, lipidoses, glycoproteinoses and glycogenosis type II. Their clinical severity and the absence of efficient therapy for the majority of these disorders justify the development of gene transfer methods. Most of the genes encoding the normal lysosomal enzymes have been cloned and recently numerous animal models have been obtained for nearly all these diseases. Due to the clinical heterogeneity of lysosomal diseases, showing multivisceral involvement or affecting predominantly the reticuloendothelial system, muscle or central nervous system, various gene therapy strategies have to be developed. Vectors, ways of access, results and limits will be reviewed. Interesting results have already been obtained in the gene transfer for lysosomal diseases, but improvements are needed before a future application to humans.

Bone marrow: a possible alternative source of cells in the adult nervous system

There is increasing evidence that stem cell populations can undergo a transition between mesodermal and neural ectodermal cell fates. Bone marrow-derived cells have been shown to be extremely versatile: they can become brain and liver cells and muscle, while other mesodermal derived cells have been shown to migrate into the brain and differentiate into neurons. Moreover, under the appropriate conditions, neural stem cells can differentiate into hematopoietic and muscle cell fates. It is now well established that newly differentiated cell types are continuously generated from immature stem cells throughout development and in adult mammals, including humans. This review addresses the contribution that bone marrow-derived stem cells may play during neurogenesis. We transplanted male bone marrow into female recipients to track and characterize the Y chromosome containing cells in the CNS (central nervous system) of mice.

Spinal cord injury in rat: treatment with bone marrow stromal cell transplantation

We tested the hypothesis that transplantation of bone marrow stromal cells (MSCs) into the spinal cord after a contusion injury promotes functional outcome. Rats (n = 31) were subjected to a weight driven implant injury. MSCs or phosphate buffered saline was injected into the spinal cord 1 week after injury. Sections of tissue were analyzed by double-labeled immunohistochemistry for MSC identification. Functional outcome measurements using the Basso-Beattie-Bresnehan score were performed weekly to 5 weeks post-injury. The data indicate significant improvement in functional outcome in animals treated with MSC transplantation compared to control animals. Scattered cells derived from MSCs expressed neural protein markers. These data suggest that transplantation of MSCs may have a therapeutic role after spinal cord injury.

Intrastriatal transplantation of bone marrow nonhematopoietic cells improves functional recovery after stroke in adult mice

The authors transplanted adult bone marrow nonhematopoietic cells into the striatum after embolic middle cerebral artery occlusion (MCAO). Mice (n = 23; C57BL/6J) were divided into four groups: (1) mice (n = 5) were subjected to MCAO and transplanted with bone marrow nonhematopoietic cells (prelabeled by bromodeoxyuridine, BrdU) into the ischemic striatum, (2) MCAO alone (n = 8), (3) MCAO with injection of phosphate buffered saline (n = 5), and (4) bone marrow nonhematopoietic cells injected into the normal striatum (n = 5). Mice were killed at 28 days after stroke. BrdU reactive cells survived and migrated a distance of approximately 2.2 mm from the grafting areas toward the ischemic areas. BrdU reactive cells expressed the neuronal specific protein NeuN in 1% of BrdU stained cells and the astrocytic specific protein glial fibrillary acidic protein (GFAP) in 8% of the BrdU stained cells. Functional recovery from a rotarod test (P < 0.05) and modified neurologic severity score tests (including motor, sensory, and reflex; P < 0.05) were significantly improved in the mice receiving bone marrow nonhematopoietic cells compared with MCAO alone. The current findings suggest that the intrastriatal transplanted bone marrow nonhematopoietic cells survived in the ischemic brain and improved functional recovery of adult mice even though infarct volumes did not change significantly. Bone marrow nonhematopoietic cells may provide a new avenue to promote recovery of injured brain.

The thin red line: angiogenesis in normal and malignant hematopoiesis

This review describes the current knowledge about cell subsets involved in vasculogenesis (i.e., differentiation of endothelial cells from mesodermal precursors) and angiogenesis (i.e., blood vessel generation from pre-existing vessels), together with recent findings about angiogenesis and antiangiogenic therapies in hematopoietic malignancies such as leukemia, lymphoma, myeloma, and myelodysplastic syndromes.

Adult rat and human bone marrow stromal cells differentiate into neurons

Bone marrow stromal cells exhibit multiple traits of a stem cell population. They can be greatly expanded in vitro and induced to differentiate into multiple mesenchymal cell types. However, differentiation to non-mesenchymal fates has not been demonstrated. Here, adult rat stromal cells were expanded as undifferentiated cells in culture for more than 20 passages, indicating their proliferative capacity. A simple treatment protocol induced the stromal cells to exhibit a neuronal phenotype, expressing neuron-specific enolase, NeuN, neurofilament-M, and tau. With an optimal differentiation protocol, almost 80% of the cells expressed NSE and NF-M. The refractile cell bodies extended long processes terminating in typical growth cones and filopodia. The differentiating cells expressed nestin, characteristic of neuronal precursor stem cells, at 5 hr, but the trait was undetectable at 6 days. In contrast, expression of trkA, the nerve growth factor receptor, persisted from 5 hr through 6 days. Clonal cell lines, established from single cells, proliferated, yielding both undifferentiated and neuronal cells. Human marrow stromal cells subjected to this protocol also differentiated into neurons. Consequently, adult marrow stromal cells can be induced to overcome their mesenchymal commitment and may constitute an abundant and accessible cellular reservoir for the treatment of a variety of neurologic diseases.

Biology and clinical utilization of mesenchymal progenitor cells

Within the complex cellular arrangement found in the bone marrow stroma there exists a subset of nonhematopoietic cells referred to as mesenchymal progenitor cells (MPC). These cells can be expanded ex vivo and induced, either in vitro or in vivo, to terminally differentiate into at least seven types of cells: osteocytes, chondrocytes, adipocytes, tenocytes, myotubes, astrocytes and hematopoietic-supporting stroma. This broad multipotentiality, the feasibility to obtain MPC from bone marrow, cord and peripheral blood and their transplantability support the impact that the use of MPC will have in clinical settings. However, a number of fundamental questions about the cellular and molecular biology of MPC still need to be resolved before these cells can be used for safe and effective cell and gene therapies intended to replace, repair or enhance the physiological function of the mesenchymal and/or hematopoietic systems.

Adult bone marrow stromal cells differentiate into neural cells in vitro

Bone marrow stromal cells (BMSC) normally give rise to bone, cartilage, and mesenchymal cells. Recently, bone marrow cells have been shown to have the capacity to differentiate into myocytes, hepatocytes, and glial cells. We now demonstrate that human and mouse BMSC can be induced to differentiate into neural cells under experimental cell culture conditions. BMSC cultured in the presence of EGF or BDNF expressed the protein and mRNA for nestin, a marker of neural precursors. These cultures also expressed glial fibrillary acidic protein (GFAP) and neuron-specific nuclear protein (NeuN). When labeled human or mouse BMSC were cultured with rat fetal mesencephalic or striatal cells, a small proportion of BMSC-derived cells differentiated into neuron-like cells expressing NeuN and glial cells expressing GFAP.

Liver from bone marrow in humans

It has been shown in animal models that hepatocytes and cholangiocytes can derive from bone marrow cells. We have investigated whether such a process occurs in humans. Archival autopsy and biopsy liver specimens were obtained from 2 female recipients of therapeutic bone marrow transplantations with male donors and from 4 male recipients of orthotopic liver transplantations from female donors. Immunohistochemical staining with monoclonal antibody CAM5.2, specific for cytokeratins 8, 18, and 19, gave typical strong staining of hepatocytes, cholangiocytes, and ductular reactions in all tissues, to the exclusion of all nonepithelial cells. Slides were systematically photographed and then restained by fluorescence in situ hybridization (FISH) for X and Y chromosomes. Using morphologic criteria, field-by-field comparison of the fluorescent images with the prior photomicrographs, and persistence of the diaminiobenzidene (DAB) stain through the FISH protease digestion, Y-positive hepatocytes and cholangiocytes could be identified in male control liver tissue and in all study specimens. Cell counts were adjusted based on the number of Y-positive cells in the male control liver to correct for partial sampling of nuclei in the 3-micron thin tissue sections. Adjusted Y-positive hepatocyte and cholangiocyte engraftment ranged from 4% to 43% and from 4% to 38%, respectively, in study specimens, with the peak values being found in a case of fibrosing cholestatic recurrent hepatitis C in one of the liver transplant recipients. We therefore show that in humans, hepatocytes and cholangiocytes can be derived from extrahepatic circulating stem cells, probably of bone marrow origin, and such "transdifferentiation can replenish large numbers of hepatic parenchymal cells.

Generalized potential of adult neural stem cells

The differentiation potential of stem cells in tissues of the adult has been thought to be limited to cell lineages present in the organ from which they were derived, but there is evidence that some stem cells may have a broader differentiation repertoire. We show here that neural stem cells from the adult mouse brain can contribute to the formation of chimeric chick and mouse embryos and give rise to cells of all germ layers. This demonstrates that an adult neural stem cell has a very broad developmental capacity and may potentially be used to generate a variety of cell types for transplantation in different diseases.

Human bone marrow stromal cell: coexpression of markers specific for multiple mesenchymal cell lineages

The role of hematopoietic stem cells in blood cell development is reasonably understood, whereas the identity and the function of bone marrow stromal cells are much less clear. Using stromal cells in bone marrow cultures of the Dexter type, a favorite medium for the study of hematopoiesis, we show that stromal cells actually represent a unique cell type. Conventional wisdom has held that stromal cells in Dexter cultures comprise a mixture of macrophages, hematopoietic cells, adipocytes, osteoblasts, fibroblasts, muscle cells, and endothelial cells. Our findings demonstrate that Dexter cultures consist of three cell types: macrophages ( approximately 35%), hematopoietic cells ( approximately 5%), and nonhematopoietic cells ( approximately 60%). We have purified the nonhematopoietic cells free of macrophages and hematopoietic cells to produce compelling evidence that they in fact represent a single cell type (multidifferentiated mesenchymal progenitor cell, MPC) which coexpresses genes specific for various mesenchymal cell lineages including adipocytes, osteoblasts, fibroblasts, and muscle cells. We further show that these multi- or pluridifferentiated MPCs are capable of supporting hematopoiesis by demonstrating the expression of several hematopoietic growth factors and extracellular matrix receptors including G-CSF, SCF, VCAM-1, ICAM-1, and ALCAM. Since the MPCs can be easily purified to near homogeneity (95%), they can be of value in enhancing engraftment of hematopoietic stem cells. Also, this new understanding of bone marrow stromal cells as "one cell with many different faces" promises to advance our knowledge of regulatory cellular interactions within bone marrow.

Rapid expansion of recycling stem cells in cultures of plastic-adherent cells from human bone marrow

Cultures of plastic-adherent cells from bone marrow have attracted interest because of their ability to support growth of hematopoietic stem cells, their multipotentiality for differentiation, and their possible use for cell and gene therapy. Here we found that the cells grew most rapidly when they were initially plated at low densities (1.5 or 3.0 cells/cm(2)) to generate single-cell derived colonies. The cultures displayed a lag phase of about 5 days, a log phase of rapid growth of about 5 days, and then a stationary phase. FACS analysis demonstrated that stationary cultures contained a major population of large and moderately granular cells and a minor population of small and agranular cells here referred to as recycling stem cells or RS-1 cells. During the lag phase, the RS-1 cells gave rise to a new population of small and densely granular cells (RS-2 cells). During the late log phase, the RS-2 cells decreased in number and regenerated the pool of RS-1 cells found in stationary cultures. In repeated passages in which the cells were plated at low density, they were amplified about 10(9)-fold in 6 wk. The cells retained their ability to generate single-cell derived colonies and therefore apparently retained their multipotentiality for differentiation.

Rapid expansion of recycling stem cells in cultures of plastic-adherent cells from human bone marrow

Cultures of plastic-adherent cells from bone marrow have attracted interest because of their ability to support growth of hematopoietic stem cells, their multipotentiality for differentiation, and their possible use for cell and gene therapy. Here we found that the cells grew most rapidly when they were initially plated at low densities (1.5 or 3.0 cells/cm(2)) to generate single-cell derived colonies. The cultures displayed a lag phase of about 5 days, a log phase of rapid growth of about 5 days, and then a stationary phase. FACS analysis demonstrated that stationary cultures contained a major population of large and moderately granular cells and a minor population of small and agranular cells here referred to as recycling stem cells or RS-1 cells. During the lag phase, the RS-1 cells gave rise to a new population of small and densely granular cells (RS-2 cells). During the late log phase, the RS-2 cells decreased in number and regenerated the pool of RS-1 cells found in stationary cultures. In repeated passages in which the cells were plated at low density, they were amplified about 10(9)-fold in 6 wk. The cells retained their ability to generate single-cell derived colonies and therefore apparently retained their multipotentiality for differentiation.

Why stem cells?

Stem cells are viewed from the perspectives of their function, evolution, development, and cause. Counterintuitively, most stem cells may arise late in development, to act principally in tissue renewal, thus ensuring an organism's long-term survival. Surprisingly, recent reports suggest that tissue-specific adult stem cells have the potential to contribute to replenishment of multiple adult tissues.

Mammalian neural stem cells

Neural stem cells exist not only in the developing mammalian nervous system but also in the adult nervous system of all mammalian organisms, including humans. Neural stem cells can also be derived from more primitive embryonic stem cells. The location of the adult stem cells and the brain regions to which their progeny migrate in order to differentiate remain unresolved, although the number of viable locations is limited in the adult. The mechanisms that regulate endogenous stem cells are poorly understood. Potential uses of stem cells in repair include transplantation to repair missing cells and the activation of endogenous cells to provide "self-repair. " Before the full potential of neural stem cells can be realized, we need to learn what controls their proliferation, as well as the various pathways of differentiation available to their daughter cells.