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

Tissue regeneration as next-generation therapy for COPD--potential applications

COPD is a major cause of chronic morbidity and mortality worldwide, and there is a need to develop more effective therapeutic strategies to replace specialized treatment such as lung transplantation. Recent studies suggest that recognition of apoptotic lung epithelial or endothelial cells may result in growth factors to stimulate cell replacement, and defects in these processes may contribute to the pathogenesis of COPD. Furthermore, recent animal and human studies have revealed that tissue-specific stem cells and bone marrow-derived cells contribute to lung tissue regeneration and protection, and thus administration of exogenous stem/progenitor cells or humoral factors responsible for activation of endogenous stem/progenitor cells may be a potent next-generation therapy for COPD.

A new role of substance P as an injury-inducible messenger for mobilization of CD29(+) stromal-like cells

Tissue injury may create a specific microenvironment for inducing the systemic participation of stromal-like cells in the repair process. Here we show that substance P is an injury-inducible factor that acts early in the wound healing process to induce CD29(+) stromal-like cell mobilization. Likewise, mobilization of such cells also occurs in uninjured mice, rats and rabbits if substance P is intravenously injected. Upon further characterization these substance P-mobilized CD29(+) cells were found to be similar to stromal cells from a number of connective tissues, including bone marrow (that is, bone marrow stromal cells, or BMSCs). Both substance P injection and transfusion of autologously derived substance P-mobilized CD29(+) cells from uninjured rabbits accelerated wound healing in an alkali burn model. Also, epithelial engraftment of the transfused cells into the injured tissue occurred during the wound healing. Finally, using human BMSCs as a test population, we show that substance P stimulates transmigration, cell proliferation, activation of the extracellular signal-related kinases (Erk) 1 and 2 and nuclear translocation of beta-catenin in vitro. This finding highlights a previously undescribed function of substance P as a systemically acting messenger of injury and a mobilizer of CD29(+) stromal-like cells to participate in wound healing.

Prominin-1/CD133+ lung epithelial progenitors protect from bleomycin-induced pulmonary fibrosis

RATIONALE

The mouse model of bleomycin-induced lung injury offers an approach to study idiopathic pulmonary fibrosis, a progressive interstitial lung disease with poor prognosis. Progenitor cell-based treatment strategies might combine antiinflammatory effects and the capacity for tissue repair.

OBJECTIVES

To expand progenitor cells with reparative and regenerative capacities and to evaluate their protective effects on pulmonary fibrosis in vivo.

METHODS

Prominin-1/CD133(+) epithelial progenitor cells (PEPs) were expanded from adult mouse lungs after digestion and culture of distal airways. Lung fibrosis was induced in C57Bl/6 mice by instillation of bleomycin. Two hours later, animals were transplanted with PEPs. Inflammation and fibrosis were assessed by immunohistochemistry, bronchoalveolar lavage fluid differentials, and real-time polymerase chain reaction.

MEASUREMENTS AND MAIN RESULTS

PEPs expanded from mouse lungs were of bone marrow origin, coexpressed stem and hematopoietic cell markers, and differentiated in vitro into alveolar type II surfactant protein-C(+) epithelial cells. In bleomycin-challenged mice, intratracheally injected PEPs engrafted into the lungs and differentiated into type II pneumocytes. Furthermore, PEPs suppressed proinflammatory and profibrotic gene expression, prevented the recruitment of inflammatory cells, and protected bleomycin-challenged mice from pulmonary fibrosis. Mechanistically, the protective effect depended on upregulation of inducible nitric oxide synthase in PEPs and nitric oxide-mediated suppression of alveolar macrophage proliferation. Accordingly, PEPs from iNOS(-/-) but not iNOS(+/+) mice failed to protect from bleomycin-induced lung injury.

CONCLUSIONS

The combined antiinflammatory and regenerative capacity of bone marrow-derived pulmonary epithelial progenitors offers a promising approach for development of cell-based therapeutic strategies against pulmonary fibrosis.

TNF-alpha is required for the attraction of mesenchymal precursors to white adipose tissue in Ob/ob mice

Most adult tissues harbour a stem cell subpopulation (Mesenchymal Precursors or MPs) that represent a small proportion of the total cell number and have the potential to differentiate into several cell types within the mesenchymal lineage. In adipose tissue, adipocytes account for two-thirds of the total cell number. The remaining cells include blood and endothelial cells, along with adipocyte precursors (adipose MPs). Obesity is defined as an excess of body fat that frequently results in a significant impairment of health. The ob/ob mice bear a mutation in the ob gene that causes a deficiency in the hormone leptin and hence obesity. Here, we present evidence that ob/ob mice have a dramatic decrease in the resident MP pool of several tissues, including squeletal muscle, heart, lung and adipose tissue. Moreover, we show that that there is a migration of MP cells from distant organs, as well as homing of these cells to the adipose tissue mass of the ob/ob mice. We call this process adipotaxis. Once in the adipose tissue, migrant MPs undergoe adipose differentiation, giving rise to new differentiated adipocytes within the adipose mass. Finally, we provide evidence that adipotaxis is largely explained by the production of high levels of Tumor Necrosis Factor-alpha (TNF-α) within the ob/ob adipose tissue. The therapeutic implications for human obesity as well as for regenerative medicine are further discussed in this paper.

Effects of bone marrow and hepatocyte transplantation on liver injury

BACKGROUND

The therapeutic effects of bone marrow and hepatocyte transplantation were investigated regarding the treatment of retrorsine-partial hepatectomy-induced liver injury.

METHODS

Analbuminemic F344alb rats were given two doses of retrorsine 2 wk apart, followed 4 wk later by transplantation with F344 rat bone marrow cells or hepatocytes immediately after a two-thirds hepatectomy. The survival rate, liver regeneration rate, liver functions, albumin-positive hepatocytes, and normal albumin gene sequences in the liver and serum albumin levels were investigated in the recipients.

RESULTS

Although 65% retrorsine/partial hepatectomy-treated F344alb died between 1 and 11 d after the partial hepatectomy, only 27.5% of the animals died following bone marrow transplantation, and 50% with hepatocyte transplantation. Both bone marrow and hepatocyte transplantation ameliorated acute liver injury after a partial hepatectomy. Bone marrow transplantation yielded a very small increase in the number of albumin-positive hepatocytes in the liver, while hepatocyte transplantation resulted in massive replacement of the liver tissues by the donor hepatocytes associated with an elevation of serum albumin after an extended time.

CONCLUSIONS

Both bone marrow and hepatocyte transplantation could prevent acute hepatic injury, conceivably due to a paracrine mechanism.

Local irradiation not only induces homing of human mesenchymal stem cells at exposed sites but promotes their widespread engraftment to multiple organs: a study of their quantitative distribution after irradiation damage

Mesenchymal stem cells (MSCs) have been shown to migrate to various tissues. There is little information on the fate and potential therapeutic efficacy of the reinfusion of MSCs following total body irradiation (TBI). We addressed this question using human MSC (hMSCs) infused to nonobese diabetic/ severe combined immunodeficient (NOD/SCID) mice submitted to TBI. Further, we tested the impact of additional local irradiation (ALI) superimposed to TBI, as a model of accidental irradiation. NOD/SCID mice were transplanted with hM-SCs. Group 1 was not irradiated before receiving hMSC infusion. Group 2 received only TBI at a dose of 3.5 Gy, group 3 received local irradiation to the abdomen at a dose of 4.5 Gy in addition to TBI, and group 4 received local irradiation to the leg at 26.5 Gy in addition to TBI. Fifteen days after irradiation, quantitative and spatial distribution of the hMSCs were studied. Histological analysis of mouse tissues confirmed the presence of radio-induced lesions in the irradiated fields. Following their infusion into nonirradiated animals, hMSCs homed at a very low level to various tissues (lung, bone marrow, and muscles) and no significant engraftment was found in other organs. TBI induced an increase of engraftment levels of hMSCs in the brain, heart, bone marrow, and muscles. Abdominal irradiation (AI) as compared with leg irradiation (LI) increased hMSC engraftment in the exposed area (the gut, liver, and spleen). Hind LI as compared with AI increased hMSC engraftment in the exposed area (skin, quadriceps, and muscles). An increase of hMSC engraftment in organs outside the fields of the ALI was also observed. Conversely, following LI, hMSC engraftment was increased in the brain as compared with AI. This study shows that engraftment of hMSCs in NOD/ SCID mice with significantly increased in response to tissue injuries following TBI with or without ALI. ALI induced an increase of the level of engraftment at sites outside the local irradiation field, thus suggesting a distant (abscopal) effect of radiation damage. This work supports the use of MSCs to repair damaged normal tissues following accidental irradiation and possibly in patients submitted to radiotherapy.

Basic research and clinical applications of non-hematopoietic stem cells, 4-5 April 2008, Tubingen, Germany

From 4 to 5 April 2008, international experts met for the second time in Tubingen, Germany, to present and discuss the latest proceedings in research on non-hematopoietic stem cells (NHSC). This report presents issues of basic research including characterization, isolation, good manufacturing practice (GMP)-like production and imaging as well as clinical applications focusing on the regenerative and immunomodulatory capacities of NHSC.

Aging and lung injury repair: a role for bone marrow derived mesenchymal stem cells

The incidence of lung fibrosis increases with age. Aging is associated with modifications in the intracellular and extracellular environment including alteration of the extracellular matrix, imbalance of the redox state, accumulation of senescent cells and potential alteration of the recruitment of bone marrow mesenchymal stem cells. The combination of these senescence-related alterations in the lung and in bone marrow progenitor cells might be responsible of the higher susceptibility to lung fibrosis in elderly individuals. The understanding of these age related changes must be considered in the rationale for the development of therapeutic interventions to control lung injury and fibrosis.

Molecular trafficking mechanisms of multipotent mesenchymal stem cells derived from human bone marrow and placenta

We compared potential trafficking mechanisms used by human (h) multipotent mesenchymal stem cells (MSC) derived from bone marrow (bm) or placenta (p). Both hbmMSC and hpMSC expressed a broad range of cell surface adhesion molecules including beta1-integrins (CD29) and CD44. Array data showed that both hbmMSC and hpMSC expressed mRNA for the cell adhesion molecules CD54 (ICAM-1), E-cadherin, CD166 (ALCAM), CD56 (NCAM), CD106 (VCAM-1), CD49a, b, c, e and f (integrins alpha1, 2, 3, 4 and 6), integrin alpha11, CD51 (integrin alphaV), and CD29 (integrins beta1). Functional binding of hpMSC, but not hbmMSC to VCAM-1 was demonstrated using recombinant chimeric constructs. Neither bone marrow nor placental MSC expressed ligands to endothelial selectins such as PSGL-1 or sialyl Lewis X (sLe(x)) carbohydrates and neither were able to bind functionally to chimeric constructs of the endothelial selectins CD62E (E-selectin) and CD62P (P-selectin). Furthermore, MSC expressed a restricted range of transferases necessary for expression of sLe(x), with no detectable expression of fucosyl transferases IV or VII. Placental MSC, but not hbmMSC, expressed mRNA for the chemokine receptors CCR1 and CCR3, and both hbmMSC and hpMSC expressed mRNA for CCR7, CCR8, CCR10, CCR11, CXCR4 and CXCR6. Intracellular chemokine receptor protein expression of CCR1, CCR3, CXCR3, CXCR4 and CXCR6 was detected in both hbmMSC and hpMSC. Cell surface expression of chemokine receptors was much more restricted with only CXCR6 displaying a strong signal on hbmMSC and hpMSC. Although cell surface expression of CXCR4 was not detected, MSC migrated in response to its ligand, CXCL12 (SDF-1). Thus, hbmMSC and hpMSC have an almost identical profile for cell surface adhesion and chemokine receptor molecules at the mRNA and protein levels. However, at the functional level, hpMSC likely utilise VLA-4-mediated binding in a superior manner to hbmMSC and thus may have superior engraftment properties to hbmMSC in vivo.

Mesenchymal stem cells and skin wound repair and regeneration: possibilities and questions

Adult mesenchymal stem cells (MSCs) have the capacity for self-renewal and for differentiating into a variety of cells and tissues. They may leave their niche to migrate to remote tissues and play a critical role in wound repair and tissue regeneration. Because of their multipotency, easy isolation and culture, highly expansive potential, and immunosuppression properties, these cells may be an attractive therapeutic tool for regenerative medicine and tissue engineering. Several studies have indicated a contribution of MSCs to reconstituting skin in cutaneous wounds, but problems still need resolution before MSCs can be widely used clinically. This review focuses mainly on the benefits of MSCs in skin wound healing and tissue regeneration and on the questions that remain to be answered before MSCs can be used in clinical practice.

Paracrine mechanisms in adult stem cell signaling and therapy

Animal and preliminary human studies of adult cell therapy following acute myocardial infarction have shown an overall improvement of cardiac function. Myocardial and vascular regeneration have been initially proposed as mechanisms of stem cell action. However, in many cases, the frequency of stem cell engraftment and the number of newly generated cardiomyocytes and vascular cells, either by transdifferentiation or cell fusion, appear too low to explain the significant cardiac improvement described. Accordingly, we and others have advanced an alternative hypothesis: the transplanted stem cells release soluble factors that, acting in a paracrine fashion, contribute to cardiac repair and regeneration. Indeed, cytokines and growth factors can induce cytoprotection and neovascularization. It has also been postulated that paracrine factors may mediate endogenous regeneration via activation of resident cardiac stem cells. Furthermore, cardiac remodeling, contractility, and metabolism may also be influenced in a paracrine fashion. This article reviews the potential paracrine mechanisms involved in adult stem cell signaling and therapy.

Fate and effects of adult bone marrow cells in lungs of normoxic and hyperoxic newborn mice

Cell-based therapy in adult lung injury models is associated with highly variable donor cell engraftment and epithelial reconstitution. The role of marrow-derived cell therapy in neonatal lung injury is largely unknown. In this study, we determined the fate and effects of adult bone marrow cells in a model of neonatal lung injury. Wild-type mice placed in a normoxic or hyperoxic (95% O(2)) environment received bone marrow cells from animals expressing green fluorescent protein (GFP) at Postnatal Day (P)5. Controls received vehicle buffer. Lungs were analyzed between Post-Transplantation (TPX) Day 2 and Week 8. The volume of GFP-immunoreactive donor cells, monitored by stereologic volumetry, remained constant between Post-TPX Weeks 1 and 8 and was similar in normoxic and hyperoxia-exposed recipients. Virtually all marrow-derived cells showed colocalization of GFP and the pan-macrophage marker, F4/80, by double immunofluorescence studies. Epithelial transdifferentiation was not seen. Marrow cell administration had adverse effects on somatic growth and alveolarization in normoxic mice, while no effects were discerned in hyperoxia-exposed recipients. Reexposure of marrow-treated animals to hyperoxia at P66 resulted in significant expansion of the donor-derived macrophage population. In conclusion, intranasal administration of unfractionated bone marrow cells to newborn mice does not achieve epithelial reconstitution, but establishes persistent alveolar macrophage chimerism. The predominantly adverse effects of marrow treatment in newborn lungs are likely due to macrophage-associated paracrine effects. While this model and route of cell therapy may not achieve epithelial reconstitution, the role of selected stem cell populations and/or alternate routes of administration for cell-based therapy in injured newborn lungs deserve further investigation.

Potential of mesenchymal stem cells as immune therapy in solid-organ transplantation

Over the last decade, there has been a rising interest in the use of mesenchymal stem cells (MSCs) for clinical applications. This interest stems from the beneficial properties of MSCs, which include multi-lineage differentiation and immunosuppressive ability, suggesting there is a role for MSC therapy for tissue regeneration and in immunologic disease. Despite recent clinical trials investigating the use of MSCs in treating immune-mediated disease, their applicability in solid-organ transplantation is still unknown. In this review, we identified topics that are important when considering MSC therapy in clinical organ transplantation. Whereas, from other clinical studies, it would appear that administration of MSCs is safe, issues like dosing, timing, route of administration, and in particular the use of autologous or donor-derived MSCs may be of crucial importance for the functional outcome of MSCs treatment in organ transplantation. We discuss these topics and assess the feasibility of MSCs therapy in organ transplantation.

Mesenchymal progenitor cell research: limitations and recommendations

There is considerable interest in mesenchymal stem cell biology. This relates, in part, to the possibility that such cells could be used to replace tissues in degenerative diseases of mesenchyme. In this article, the current status of the field is discussed, highlighting technical and theoretical issues related to the identification, isolation, and characterization of these cells. Our focus is the endogenous noncirculating mesenchymal stem cell populations that normally reside in adult organs.

Hierarchical organization of lung progenitor cells: is there an adult lung tissue stem cell?

Dynamic changes to the developing lung endoderm during the process of lung development result in the establishment of functionally distinct epithelial compartments that vary both in their cellular composition and mechanisms contributing to their maintenance in adulthood. This focused review compares the hierarchical organization of cells within slowly and rapidly renewing tissues as a basis to better understand cellular and molecular mechanisms regulating epithelial maintenance and repair in the lung.

Exogenous administration of mesenchymal stem cells ameliorates dextran sulfate sodium-induced colitis via anti-inflammatory action in damaged tissue in rats

AIMS

Mesenchymal stem cells (MSCs) may modulate inflammatory responses resulting in improvement in inflammatory diseases, as well as tissue regeneration via cellular differentiation. We examined the therapeutic effects of exogenously administered MSCs in dextran sulfate sodium (DSS)-induced colitis in rats.

MAIN METHODS

Experimental colitis was produced in inbred male Lewis rats by administration of 4% DSS in drinking water for 7 days. MSCs (5x10(6) cells) which were isolated from whole marrow cells and cultured in an optimal medium for MSC outgrowth were administered to the treated rats via the tail vein on days 0, 2, and 4. On day 7, we evaluated colon length, histological changes, and colonic various mRNA expressions by RT-PCR. Localization of MSCs was evaluated using a green-fluorescent cell linker dye. To evaluate the anti-inflammatory action of MSCs, we assayed LPS-induced TNF-alpha secretion in a co-culture of MSCs and monocytes (THP-1 cells) using ELISA.

KEY FINDINGS

MSCs reduced in bloody stools, weight loss, colon shortening, and microscopic injuries. In the rectum of MSCs-treated rats, mRNA expression of TNF-alpha, IL-1beta, and COX-2 decreased to 40, 15, and 15% of their respective control levels. MSCs significantly suppressed mRNA expression of VEGF, HGF, and b-FGF to 40, 25, and 25% of their respective control levels. Green-fluorescent-labeled MSCs were found only within the lamina propria in inflamed regions. LPS-induced TNF-alpha secretion by THP-1 cells was significantly suppressed by co-culture with MSCs dose-dependently.

SIGNIFICANCE

We conclude that exogenous MSCs accumulated in inflamed tissues and ameliorated DSS-induced colitis via a local anti-inflammatory action.

Role of mesenchymal stromal cells in solid organ transplantation

Mesenchymal stromal cells (MSCs) originally isolated from bone marrow have been derived from almost every tissue in the body. These multipotent cells can be differentiated in vitro and in vivo into various cell types of mesenchymal origin, such as bone, fat, and cartilage. Furthermore, under some experimental conditions, these cells can differentiate into a wider variety of cell types. Upon systemic administration, ex vivo expanded MSCs preferentially home to damaged tissues and participate in regeneration processes through their diverse biological properties. In vitro and in vivo data suggest that MSCs have low inherent immunogenicity and modulate/suppress immunologic responses through interactions with different immune cells. Ease of isolation and ex vivo expansion of MSCs, combined with their intriguing differentiation and immunomodulatory potential, and their impressive record of safety in clinical trials make these cells prime candidates for cellular therapy. Mesenchymal stromal cells derived from bone marrow are currently being evaluated for a wide range of clinical applications including for treatment of immune dysregulation disorders such as acute graft-versus-host disease after allogeneic hematopoietic stem cell transplantation. In the future, MSCs might potentially provide novel therapeutic options for treatment/prevention of rejection and/or repair of organ allografts through their multifaceted properties.

Bone marrow-derived cells and stem cells in lung repair

Although it has been many years since publication of the first peer-reviewed studies showing that bone marrow (BM)-derived cells can become mature-appearing epithelial cells, we still know very little regarding the mechanisms, kinetics, cells, and potential clinical utility or pathology associated with this phenomenon. The initial discovery of BM-derived epithelial cells (BMDE) in the liver was published by Petersen and colleagues (Petersen BE, Bowen WC, Patrene KD, Mars WM, Sullivan AK, Murase N, Boggs SS, Greenberger JS, Goff JP. Bone marrow as a potential source of hepatic oval cells. Science 1999;284:1168-1170). Since that time, BMDE were identified in the skin, eye, GI tract, kidney, and the lung. Surprisingly, once several laboratories started to examine the effects of BM cells after tissue injury, BM-derived cells of different types were found to decrease tissue injury and enhance tissue repair, often without engraftment of marrow-derived epithelial cells. Thus, the potentially beneficial effects of BM-derived cells in some tissue microenvironments may be unrelated to differentiation into nonhematopoietic cell types. Here, I focus on recent findings from my laboratory as well as several other laboratories on the effects of BM cells on lung damage, and BMDE in the lung, including tracheal epithelial cells, bronchiolar epithelial cells, and type II pneumocytes in the alveoli. Potential mechanisms underlying the appearance of marrow-derived epithelial cells, and the role of tissue damage are discussed.

Therapeutic effects of bone marrow-derived mesenchymal stem cells engraftment on bleomycin-induced lung injury in rats

Previous studies have demonstrated that bone marrow-derived mesenchymal stem cell (MSC) engraftment attenuated lung injury in a model induced by bleomycin in mice. However, the mechanisms are not completely understood. The primary objective of the present study was to determine whether MSC engraftment can also protect lungs against bleomycin-induced injury in rats and to observe any beneficial effects of cytokines. Twelve hours after bleomycin (5 mg/kg) or phosphate-buffered saline was perfused into the trachea, 5x10(6) DAPI-labeled MSCs or DMEM-F12 were injected into the tail vein of rats. Two weeks later, MSCs labeled with DAPI were detected by pan-cytokeratin staining. The level of laminin and hyaluronan in bronchoalveolar lavage fluid was measured by radioimmunoassay. Collagen content in lung tissue was calculated by the hydroxyproline assay. TGF-beta1, PDGF-A, B, and IGF-I were measured by real-time PCR. It was observed that some MSCs positive for pan-cytokeratin staining, an indicator of alveolar epithelial cells, were present in injured lung tissue. Bleomycin injection increased the content of hydroxyproline in lung tissue, as well as laminin and hyaluronan in bronchoalveolar lavage fluid, markers for lung injury and fibrosis. However, these effects were attenuated by MSC treatment. Furthermore, the increased mRNA levels of TGF-beta1, PDGF-A, PDGF-B, and IGF-I following bleomycin injection were also significantly decreased by MSC treatment. These observations provided evidence that MSCs are still present in the lung 2 weeks after the initial MSC treatment in rats, as well as documented the beneficial effects of MSC engraftment against bleomycin-induced lung injury associated with changes in TGF-beta1, PDGF-A, PDGF-B, and IGF-I. These results may provide an experimental base for clinical therapy of pulmonary fibrosis in the future.

The paradoxical dynamism of marrow stem cells: considerations of stem cells, niches, and microvesicles

Marrow stem cell regulation represents a complex and flexible system. It has been assumed that the system was intrinsically hierarchical in nature, but recent data has indicated that at the progenitor/stem cell level the system may represent a continuum with reversible alterations in phenotype occurring as the stem cells transit cell cycle. Short and long-term engraftment, in vivo and in vitro differentiation, gene expression, and progenitor numbers have all been found to vary reversibly with cell cycle. In essence, the stem cells appear to show variable potential, probably based on transcription factor access, as they proceed through cell cycle. Another critical component of the stem cell regulation is the microenvironment, so-called niches. We propose that there are not just several unique niche cells, but a wide variety of niche cells which continually change phenotype to appropriately interact with the continuum of stem cell phenotypes. A third component of the regulatory system is microvesicle transfer of genetic information between cells. We have shown that marrow cells can express the genetic phenotype of pulmonary epithelial cells after microvesicle transfer from lung to marrow cells. Similar transfers of tissue specific mRNA occur between liver, brain, and heart to marrow cells. Thus, there would appear to be a continuous genetic modulation of cells through microvesicle transfer between cells. We propose that there is an interactive triangulated Venn diagram with continuously changing stem cells interacting with continuously changing areas of influence, both being modulated by transfer of genetic information by microvesicles.

Mesenchymal stem cells derived from human adipose tissues favor tumor cell growth in vivo

Mesenchymal stem cells (MSCs) have generated a great deal of interest in clinical situations, due principally to their potential use in regenerative medicine and tissue engineering applications. However, the therapeutic application of MSCs remains limited, unless the favorable effects of MSCs for tumor growth in vivo and the long-term safety of the clinical applications of MSCs can be understood more thoroughly. In this study, MSCs derived from human adipose tissues (hASCs) together with tumor cells were transplanted subcutaneously or intracranially into BALB/c nude mice to observe tumor outgrowth. The results indicated that hASCs with H460 or U87MG cells promoted tumor growth in nude mice. Our histopathological analyses indicated that the co-injection of tumor cells with hASCs exerted no influence on the formation of intratumoral vessels. Co-culture of tumor cells with hASCs or the addition of conditioned medium (CM) from hASCs effected an increase in the proliferation of H460 or U87MG cells. Co-injection of hASCs with tumor cells effected an increase in tumor cell viability in vivo, and also induced a reduction in apoptotic cell death. CM from hASCs inhibited hydrogen peroxide-induced cell death in H460 or U87MG cells. These findings indicated that MSCs could favor tumor growth in vivo. Thus, it is necessary to conduct a study concerning the long-term safety of this technique before MSCs can be used as therapeutic tools in regenerative medicine and tissue engineering.

Mesenchymal stem cells as vectors for lung disease

Stem cells divide asymmetrically, leading to self-renewal and the production of a daughter cell committed to differentiation. This property has engendered excitement as to the use of these cells for treatments. The majority of the work with stem cells has used the relatively accessible and well-characterized adult bone marrow stem cell compartment. Initially the focus of this research was on the potential for these stem cells to repair damaged organs by differentiating into epithelial cells to replace the injured areas. More recently it has become clear that engraftment of these stem cells as epithelial tissue is a rare event with perhaps limited clinical significance. Despite this, stem cells appear to have the ability to home to and be specifically recruited to areas of inflammation and injured tissues often characterized by excessive extracellular matrix deposition. As a consequence they are intimately involved in regions of physiological and pathological repair. Coupled with this, autologous hematopoietic stem cells, or the relatively immunoprivileged mesenchymal stem cells, can be expanded and engineered ex vivo and reintroduced without immunomodulation. The prospect of using such cells clinically as a cellular therapy holds much promise for many conditions and organ pathologies. Here we address the evidence for the incorporation of bone marrow stem cells into areas of stroma formation as a prelude to possible future treatment options for common lung diseases.

Time course of airway remodelling after an acute chlorine gas exposure in mice

Accidental chlorine (Cl2) gas inhalation is a common cause of acute airway injury. However, little is known about the kinetics of airway injury and repair after Cl2 exposure. We investigated the time course of airway epithelial damage and repair in mice after a single exposure to a high concentration of Cl2 gas. Mice were exposed to 800 ppm Cl2 gas for 5 minutes and studied from 12 hrs to 10 days post-exposure. The acute injury phase after Cl2 exposure (< or = 24 hrs post-exposure) was characterized by airway epithelial cell apoptosis (increased TUNEL staining) and sloughing, elevated protein in bronchoalveolar lavage fluid, and a modest increase in airway responses to methacholine. The repair phase after Cl2 exposure was characterized by increased airway epithelial cell proliferation, measured by immunoreactive proliferating cell nuclear antigen (PCNA), with maximal proliferation occurring 5 days after Cl2 exposure. At 10 days after Cl2 exposure the airway smooth muscle mass was increased relative to controls, suggestive of airway smooth muscle hyperplasia and there was evidence of airway fibrosis. No increase in goblet cells occurred at any time point. We conclude that a single exposure of mice to Cl2 gas causes acute changes in lung function, including pulmonary responsiveness to methacholine challenge, associated with airway damage, followed by subsequent repair and airway remodelling.

Murine mesenchymal stem cells exhibit a restricted repertoire of functional chemokine receptors: comparison with human

Mesenchymal stem cells (MSCs) are non-haematopoeitic, stromal cells that are capable of differentiating into mesenchymal tissues such as bone and cartilage. They are rare in bone marrow, but have the ability to expand many-fold in culture, and retain their growth and multi-lineage potential. The properties of MSCs make them ideal candidates for tissue engineering. It has been shown that MSCs, when transplanted systemically, can home to sites of injury, suggesting that MSCs possess migratory capacity; however, mechanisms underlying migration of these cells remain unclear. Chemokine receptors and their ligands play an important role in tissue-specific homing of leukocytes. Here we define the cell surface chemokine receptor repertoire of murine MSCs from bone marrow, with a view to determining their migratory activity. We also define the chemokine receptor repertoire of human MSCs from bone marrow as a comparison. We isolated murine MSCs from the long bones of Balb/c mice by density gradient centrifugation and adherent cell culture. Human MSCs were isolated from the bone marrow of patients undergoing hip replacement by density gradient centrifugation and adherent cell culture. The expression of chemokine receptors on the surface of MSCs was studied using flow cytometry. Primary murine MSCs expressed CCR6, CCR9, CXCR3 and CXCR6 on a large proportion of cells (73+/-11%, 44+/-25%, 55+/-18% and 96+/-2% respectively). Chemotaxis assays were used to verify functionality of these chemokine receptors. We have also demonstrated expression of these receptors on human MSCs, revealing some similarity in chemokine receptor expression between the two species. Consequently, these murine MSCs would be a useful model to further study the role of chemokine receptors in in vivo models of disease and injury, for example in recruitment of MSCs to inflamed tissues for repair or immunosuppression.

Anti-inflammatory effects of mesenchymal stem cells: novel concept for future therapies

BACKGROUND

Mesenchymal stem cells (MSC) are multipotent cells that can be isolated from the bone marrow and expanded in culture relatively easily. Culture-expanded MSC have been used in clinical settings to enhance hematopoietic stem cell engraftment in bone marrow transplant patients and in tissue regeneration therapy. More recently, the anti-inflammatory effects of MSC have generated a great deal of interest.

OBJECTIVE/METHODS

In this review we describe in vitro assays that have demonstrated how MSC regulate immune cell proliferation, differentiation and phenotype. We also highlight effector molecules produced by MSC that drive this function. In addition, we focus on animal models of lung injury, in which administration of MSC attenuates inflammation, and injury revealing a central role for MSC in mitigating pro-inflammatory networks and amplifying anti-inflammatory signals.

CONCLUSIONS

The discoveries described herein have contributed to the novel concept of MSC as a therapeutic modality in inflammatory diseases, including acute lung injury.

Retention of human bone marrow-derived cells in murine lungs following bleomycin-induced lung injury

We studied the capacity of adult human bone marrow-derived cells (BMDC) to incorporate into distal lung of immunodeficient mice following lung injury. Immunodeficient NOD/SCID and NOD/SCID/beta(2) microglobulin (beta(2)M)(null) mice were administered bleomycin (bleo) or saline intranasally. One, 2, 3 and 4 days after bleo or saline, human BMDC labeled with CellTracker Green CMFDA (5-chloromethylfluorescein diacetate) were infused intravenously. Retention of CMFDA(+) cells was maximal when delivered 4 days after bleo treatment. Seven days after bleo, <0.005% of enzymatically dispersed lung cells from NOD/SCID mice were CMFDA(+), which increased 10- to 100-fold in NOD/SCID/beta(2)M(null) mice. Preincubation of BMDC with Diprotin A, a reversible inhibitor of CD26 peptidase activity that enhances the stromal-derived factor-1 (SDF-1/CXCL12)/CXCR4 axis, resulted in a 30% increase in the percentage of CMFDA(+) cells retained in the lung. These data indicate that human BMDC can be identified in lungs of mice following injury, albeit at low levels, and this may be modestly enhanced by manipulation of the SDF-1/CXCR4 axis. Given the overall low number of human cells detected, methods to increase homing and retention of adult BMDC, and consideration of other stem cell populations, will likely be required to facilitate engraftment in the treatment of lung injury.

Points to Consider in Designing Mesenchymal Stem Cell-Based Clinical Trials

SUMMARY: Therapeutic applications of cells are likely to increase greatly in the future. Cell and cell-based gene therapy manufacturing facilities need to be purpose-designed and accredited by their national medicinal regulatory body. Production scientists need to work in close tandem with quality assurance and ethics committees to absolutely ensure the safety of new cellular products. In this review, we consider the need for preclinical safety and efficacy data, tissue source for manufacture of clinical grade human mesenchymal stem cells, aseptic tissue processing, indemnification, and the role of the national medicinal regulatory body in appropriate clinical trial design.

Multipotent Mesenchymal Stromal Cells for Autoimmune Diseases

SUMMARY: Multipotent mesenchymal stromal cells (MSC) are under consideration for the treatment of autoimmune disease (AD) based on their in vitro antiproliferative properties, efficacy in animal models, apparent low acute toxicity, and the early positive anecdotal outcomes in human acute graft versus host disease. Phase I/II clinical trials are under way in multiple sclerosis and Crohn's disease, and are being planned in systemic lupus erythematosus, systemic sclerosis, systemic vasculitis, and other AD. Open issues include: patient selection, disease stage and activity, MSC source and expansion, and long-term safety. Multidisciplinary groups including EULAR are collaborating to ensure maximal use of available resources to establish the place, if any, of MSC in the treatment of AD.

Cancer stem cells, endothelial progenitors, and mesenchymal stem cells: "seed and soil" theory revisited

Isolation of putative cancer stem cells (CSCs) in various tumors has generated much excitement among researchers who consider these cells the potential "culprits" behind resistance to conventional therapy. Both cancer and cardiovascular disease are believed to be stem cell disorders involving circulating endothelial progenitors (CEPs) and mesenchymal stem cells (MSCs). CD133 and CD44, markers of CSCs in many tumors, also enrich CEPs and MSCs, respectively. We propose an integrated tumorigenesis model that involves all three interdependent stem cell (CSC, CEP, MSC) compartments by revisiting the "seed and soil" model. Developing therapeutics that can effectively target CSCs and spare normal cardiovascular tissue will remain a challenge. Preliminary laboratory and clinical data on monitoring and targeting colon CSCs, using such a modeling system, are discussed.

Adult mesenchymal stromal stem cells for therapeutic applications

Mesenchymal stromal stem cells (MSC) can be found in almost any adult organ. They can be isolated and expanded within several weeks up to hundreds of millions of cells. The cell isolation based on the surface antigen expression may significantly enrich for the desired cell population and reduce the time required for cell expansion. MSC display a unique molecular signature which clearly discriminates them from other stem cell types. MSC can be differentiated into the cells of several lineages. Additionally, the unique biological properties of MSC are mediated by strong immunomodulatory activity and by paracrine mechanisms. Potential therapeutic applications of the cells require clinically compliant protocols for cell isolation and expansion. The therapeutic utility of MSC has been evaluated and found to be useful in several pre-clinical animal models as well as in clinical trials.

In search of the in vivo identity of mesenchymal stem cells

In spite of the advances in the knowledge of adult stem cells (ASCs) during the past few years, their natural activities in vivo are still poorly understood. Mesenchymal stem cells (MSCs), one of the most promising types of ASCs for cell-based therapies, are defined mainly by functional assays using cultured cells. Defining MSCs in vitro adds complexity to their study because the artificial conditions may introduce experimental artifacts. Inserting these results in the context of the organism is difficult because the exact location and functions of MSCs in vivo remain elusive; the identification of the MSC niche is necessary to validate results obtained in vitro and to further the knowledge of the physiological functions of this ASC. Here we show an analysis of the evidence suggesting a perivascular location for MSCs, correlating these cells with pericytes, and present a model in which the perivascular zone is the MSC niche in vivo, where local cues coordinate the transition to progenitor and mature cell phenotypes. This model proposes that MSCs stabilize blood vessels and contribute to tissue and immune system homeostasis under physiological conditions and assume a more active role in the repair of focal tissue injury. The establishment of the perivascular compartment as the MSC niche provides a basis for the rational design of additional in vivo therapeutic approaches. This view connects the MSC to the immune and vascular systems, emphasizing its role as a physiological integrator and its importance in tissue repair/regeneration.

Methods for studying stem cells: adult stem cells for lung repair

Recent progress in lung biology includes the description of a series of pulmonary stem and progenitor cells involved in homeostasis and regeneration of the respiratory system. Moreover, the contribution of extrapulmonary stem cells to healthy and pathological lung tissue has been observed and the developmental biology of such processes should provide important hints for understanding maintenance and repair of adult lung structure and function. Despite such remarkable advances, the phenotypic and especially the functional characterization of these stem and progenitor cells, and their derivatives, along with an understanding of the molecular cues and pathways underlying differentiation into specific respiratory lineages is still in its infancy. Accordingly, the role of endogenous and extrapulmonary stem cells in normal tissue repair and pathogenesis is still largely mysterious and added basic knowledge is required in order to explore their potential for novel regenerative therapies. This review provides an overview of the current state of the art in adult lung stem cell biology including technical aspects of isolation, characterization and differentiation, and a discussion of perspectives for future regenerative therapies.

Comparative study of mesenchymal stem cells from C57BL/10 and mdx mice

Background

Human mesenchymal stem cells (MSCs) have been studied and applied extensively because of their ability to self-renew and differentiate into various cell types. Since most human diseases models are murine, mouse MSCs should have been studied in detail. The mdx mouse – a Duchenne muscular dystrophy model – was produced by introducing a point mutation in the dystrophin gene. To understand the role of dystrophin in MSCs, we compared MSCs from mdx and C57BL/10 mice, focusing particularly on the aspects of light and electron microscopic morphology, immunophenotyping, and differentiation potential.

Results

Our study showed that at passage 10, mdx-MSCs exhibited increased heterochromatin, larger vacuoles, and more lysosomes under electron microscopy compared to C57BL/10-MSCs. C57BL/10-MSCs formed a few myotubes, while mdx-MSCs did not at the same passages. By passage 21, mdx-MSCs but not C57BL/10-MSCs had gradually lost their proliferative ability. In addition, a significant difference in the expression of CD34, not Sca-1 and CD11b, was observed between the MSCs from the 2 mice.

Conclusion

Our current study reveals that the MSCs from the 2 mice, namely, C57BL/10 and mdx, exhibit differences in proliferative and myogenic abilities. The results suggest that the changes in mouse MSC behavior may be influenced by lack of dystrophin protein in mdx mouse.

Hedgehog-mediated paracrine interaction between hepatic stellate cells and marrow-derived mesenchymal stem cells

During liver injury, bone marrow-derived mesenchymal stem cells (MSCs) can migrate and differentiate into hepatocytes. Hepatic stellate cell (SC) activation is a pivotal event in the development of liver fibrosis. Therefore, we hypothesized that SCs may play an important role in regulating MSC proliferation and differentiation through the paracrine signaling pathway. We demonstrate that MSCs and SCs both express hedgehog (Hh) pathway components, including its ligands, receptors, and target genes. Transwell co-cultures of SCs and MSCs showed that the SCs produced sonic hedgehog (Shh), which enhanced the proliferation and differentiation of MSCs. These findings demonstrate that SCs indirectly modulate the activity of MSCs in vitro via the Hh pathway, and provide a plausible explanation for the mechanisms of transplanted MSCs in the treatment of liver fibrosis.

Mesenchymal stem cells for treatment of steroid-resistant, severe, acute graft-versus-host disease: a phase II study

BACKGROUND

Severe graft-versus-host disease (GVHD) is a life-threatening complication after allogeneic transplantation with haemopoietic stem cells. Mesenchymal stem cells modulate immune responses in vitro and in vivo. We aimed to assess whether mesenchymal stem cells could ameliorate GVHD after haemopoietic-stem-cell transplantation.

METHODS

Patients with steroid-resistant, severe, acute GVHD were treated with mesenchymal stem cells, derived with the European Group for Blood and Marrow Transplantation ex-vivo expansion procedure, in a multicentre, phase II experimental study. We recorded response, transplantation-related deaths, and other adverse events for up to 60 months' follow-up from infusion of the cells.

FINDINGS

Between October, 2001, and January, 2007, 55 patients were treated. The median dose of bone-marrow derived mesenchymal stem cells was 1.4x10(6) (min-max range 0.4-9x10(6)) cells per kg bodyweight. 27 patients received one dose, 22 received two doses, and six three to five doses of cells obtained from HLA-identical sibling donors (n=5), haploidentical donors (n=18), and third-party HLA-mismatched donors (n=69). 30 patients had a complete response and nine showed improvement. No patients had side-effects during or immediately after infusions of mesenchymal stem cells. Response rate was not related to donor HLA-match. Three patients had recurrent malignant disease and one developed de-novo acute myeloid leukaemia of recipient origin. Complete responders had lower transplantation-related mortality 1 year after infusion than did patients with partial or no response (11 [37%] of 30 vs 18 [72%] of 25; p=0.002) and higher overall survival 2 years after haemopoietic-stem-cell transplantation (16 [53%] of 30 vs four [16%] of 25; p=0.018).

INTERPRETATION

Infusion of mesenchymal stem cells expanded in vitro, irrespective of the donor, might be an effective therapy for patients with steroid-resistant, acute GVHD.

Bone marrow-derived cells participate in stromal remodeling of the lung following acute bacterial pneumonia in mice

Bone marrow-derived cells (BMDC) have been shown to graft injured tissues, differentiate in specialized cells, and participate in repair. The importance of these processes in acute lung bacterial inflammation and development of fibrosis is unknown. The goal of this study was to investigate the temporal sequence and lineage commitment of BMDC in mouse lungs injured by bacterial pneumonia. We transplanted GFP-tagged BMDC into 5-Gy-irradiated C57BL/6 mice. After 3 months of recovery, mice were subjected to LD(50) intratracheal instillation of live E. coli (controls received saline) which produced pneumonia and subsequent areas of fibrosis. Lungs were investigated by immunohistology for up to 6 months. At the peak of lung inflammation, the predominant influx of BMDC were GFP(+) leukocytes. Postinflammatory foci of lung fibrosis were evident after 1-2 months. The fibrotic foci in lung stroma contained clusters of GFP(+) CD45(+) cells, GFP(+) vimentin-positive cells, and GFP(+) collagen I-positive fibroblasts. GFP(+) endothelial or epithelial cells were not identified. These data suggest that following 5-Gy irradiation and acute bacterial pneumonia, BMDC may temporarily participate in lung postinflammatory repair and stromal remodeling without long-term engraftment as specialized endothelial or epithelial cells.

Mesenchymal stem cell-based angiopoietin-1 gene therapy for acute lung injury induced by lipopolysaccharide in mice

Bone marrow-derived mesenchymal stem cells (MSCs) can serve as a vehicle for gene therapy. Angiopoietin-1 (Ang1) is a critical factor for endothelial survival and vascular stabilization via the inhibition of endothelial permeability and leukocyte-endothelium interactions. We hypothesized that MSC-based Ang1 gene therapy might be a potential therapeutic approach for lipopolysaccharide (LPS)-induced lung injury. MSCs were isolated from 6 week-old inbred male mice and transduced with the Ang1 gene, using a lentivirus vector. The MSCs showed no significant phenotypic changes after transduction. In the in vivo mouse model, the LPS-induced lung injury was markedly alleviated in the group treated with MSCs carrying Ang1 (MSCs-Ang1), compared with groups treated with MSCs or Ang1 alone. The expression of Ang1 protein in the recipient lungs was increased after MSCs-Ang1 administration. The histopathological and biochemical indices of LPS-induced lung injury were improved after MSCs-based Ang1 gene treatment. MSCs-Ang1 administration also reduced pulmonary vascular endothelial permeability and the recruitment of inflammatory cells into the lung. Cells of MSC origin could be detected in the recipient lungs for 2 weeks after injection with MSCs. These results suggest that MSCs and Ang1 have a synergistic role in the treatment of LPS-induced lung injury. MSC-based Ang1 gene therapy may be developed as a potential novel strategy for the treatment of acute lung injury.

Biologic characteristics of mesenchymal stromal cells and their clinical applications in pediatric patients

In the past few years, intensive research in the understanding of the biologic characteristics of the mesenchymal stromal cells has already led to some early clinical applications. The aim of this review is to summarize the latest information from basic science advances and the outcome of their use in clinical practice with a particular focus in pediatric patients. The minimum criteria required to identify mesenchymal stromal cells, their immunosuppressive-nonimmunogenic properties and their attribution in the treatment of graft-versus-host disease, in the acceleration of hematopoietic recovery, in tissue repair/tissue engineering and in the treatment of selected inherited disorders are discussed. Appropriate preclinical models, completion of ongoing and development of new clinical trials will establish the role of these cells in the treatment of both adult and pediatric patients.

Therapeutic potential of genetically modified mesenchymal stem cells

Bone marrow-derived mesenchymal stem cells (MSC) are multipotent adult stem cells of mesodermal origin localized within the bone marrow compartment. MSC possess multilineage property making them useful for a number of potential therapeutic applications. MSC can be isolated from the bone marrow, expanded in culture and genetically modified to serve as cell carriers for local or systemic therapy. Despite their ability to differentiate into osteoblasts, chondrocytes, adipocytes, myocytes and neuronal cells under appropriate stimuli, distinct molecular signals that guide migration of MSC to specific targets largely remain unknown. The pluripotent nature of MSC makes them ideal resources for regenerative medicine, graft-versus-host disease and autoimmune diseases. Despite their therapeutic potential in a variety of diseases, certain issues need to be critically addressed both in in vitro expansion of these cells without losing their stem cell properties, and the long-term fate of the transplanted MSC in vivo following ex vivo modifications. Finally, understanding of complex, multistep and multifactorial differentiation pathways from pluripotent stem cells to functional tissues will allow us to manipulate MSC for the formation of competent composite tissues in situ. The present article will provide comprehensive account of the characteristics of MSC, their isolation and culturing, multilineage properties and potential therapeutic applications.

Stem cells: an overview

Stem cells are specialized cells that possess a capacity to undergo self-renewal while at the same time having the ability to give rise to at least one or more differentiated or mature cell type. They therefore represent a fundamental cornerstone during the life of all vertebrates, playing central roles in the production of new and replacement cells for tissues during development and homeostasis, including repair following disease or injury. This unit is a review of stem cells, their roles in development, and their potentials as therapeutic agents.

Identification of surface markers for prospective isolation of human endometrial stromal colony-forming cells

BACKGROUND

Human endometrium is a highly regenerative tissue. We hypothesized that the source of endometrial stromal and vascular regeneration is a resident stromal stem/progenitor cell population. Putative human endometrial stromal stem/progenitor cells have been identified using clonal assays, a retrospective functional stem cell assay. Therefore, the aim of this study was to screen potential stem cell markers for the prospective isolation of human endometrial stromal stem/progenitor cells and to determine their capacity to identify colony-forming stromal cells.

METHODS

Single-cell suspensions of human endometrial stromal cells were sorted using fluorescence-activated cell sorting into positive and negative populations based on STRO-1, CD133, CD90 or CD146 expression for clonal assays. All markers were immunolocalized in human endometrium.

RESULTS

Small populations (2-9%) of human endometrial stromal cells expressed each of the markers. Only CD146(+) cells were enriched for colony-forming cells, and CD90(hi) cells showed a trend for greater enrichment compared with CD90(lo) cells. STRO-1 and CD146 were localized to perivascular cells of the endometrium. CD90 was strongly expressed by functionalis stroma and perivascular cells, but only weakly expressed in the basalis stroma. CD133 was expressed by epithelial cells of the endometrium, rather than by stroma or perivascular cells.

CONCLUSIONS

This study identified CD146 as a marker of colony-forming human endometrial stromal cells supporting the concept that human endometrium contains a population of candidate stromal stem/progenitor cells.