Lung resident mesenchymal stem cells isolated from human lung allografts inhibit T cell proliferation via a soluble mediator

Chimerism of bone marrow mesenchymal stem/stromal cells in allogeneic hematopoietic cell transplantation: is it clinically relevant?

Multipotent mesenchymal stem/stromal cells (MSCs) have been extensively used as a transplantable cell source for regenerative medicine and immunomodulatory therapy. Specifically in allogeneic hematopoietic stem cell transplantation (HSCT), co-transplantation or post-transplant infusion of MSCs derived from bone marrow (BM) of non-self donors has been implicated in accelerating hematopoietic recovery, ameliorating graft-vs.-host disease, and promoting tissue regeneration. However, irrespective of the use of MSC co-administration, post-transplant chimerism of BM-derived MSCs after allogeneic HSCT has been reported to remain of host origin, suggesting that the infused donor MSCs are immunologically rejected or not capable of long-term engraftment in the host microenvironment. Also, hematopoietic cell allografts currently used for HSCT do not seem to contain sufficient amount of MSCs or their precursors to reconstitute host BM microenvironment. Since the toxic conditioning employed in allo-HSCT may impair the function of host MSCs to maintain hematopoietic/regenerative stem cell niches and to provide a local immunomodulatory milieu, we propose that new directions for enhancing immunohematopoietic reconstitution and tissue repair after allogeneic HSCT include the development of strategies to support functional replenishment of residual host MSCs or to support more efficient engraftment of infused donor MSCs. Future areas of research should include in vivo tracking of infused MSCs and detection of their microchimeric presence in extra-marrow sites as well as in BM.

Identification and isolation of small CD44-negative mesenchymal stem/progenitor cells from human bone marrow using elutriation and polychromatic flow cytometry

The method of isolation of bone marrow (BM) mesenchymal stem/stromal cells (MSCs) is a limiting factor in their study and therapeutic use. MSCs are typically expanded from BM cells selected on the basis of their adherence to plastic, which results in a heterogeneous population of cells. Prospective identification of the antigenic profile of the MSC population(s) in BM that gives rise to cells with MSC activity in vitro would allow the preparation of very pure populations of MSCs for research or clinical use. To address this issue, we used polychromatic flow cytometry and counterflow centrifugal elutriation to identify a phenotypically distinct population of mesenchymal stem/progenitor cells (MSPCs) within human BM. The MSPC activity resided within a population of rare, small CD45⁻CD73⁺CD90⁺CD105⁺ cells that lack CD44, an antigen that is highly expressed on culture-expanded MSCs. In culture, these MSPCs adhere to plastic, rapidly proliferate, and acquire CD44 expression. They form colony forming units-fibroblast and are able to differentiate into osteoblasts, chondrocytes, and adipocytes under defined in vitro conditions. Their acquired expression of CD44 can be partially downregulated by treatment with recombinant human granulocyte-colony stimulating factor, a response not found in BM-MSCs derived from conventional plastic adherence methods. These observations indicate that MSPCs within human BM are rare, small CD45⁻CD73⁺CD90⁺CD105⁺ cells that lack expression of CD44. These MSPCs give rise to MSCs that have phenotypic and functional properties that are distinct from those of BM-MSCs purified by plastic adherence.

Therapeutic implications of mesenchymal stem cells in acute lung injury/acute respiratory distress syndrome

Acute lung injury (ALI), and its more severe form, acute respiratory distress syndrome (ARDS), are syndromes of acute hypoxemic respiratory failure resulting from a variety of direct and indirect injuries to the gas exchange parenchyma of the lungs. Current treatment of ALI/ARDS is primarily supportive, with lung protective ventilation and fluid conserving strategies. Despite improvement in these strategies, recent data indicate that the mortality of ALI/ARDS is still as high as 30 to 50%. Thus, there is a need for innovative therapies to further improve clinical outcomes of ALI/ARDS. Recent studies involving the administration of mesenchymal stem cells (MSCs) for the treatment of experimental ALI/ARDS have shown promising results. This review focuses on existing studies that have tested the use of MSCs in models of ALI/ARDS, and the potential mechanisms underlying their therapeutic effects.

Lung transplantation

Lung transplantation may be the only intervention that can prolong survival and improve quality of life for those individuals with advanced lung disease who are acceptable candidates for the procedure. However, these candidates may be extremely ill and require ventilator and/or circulatory support as a bridge to transplantation, and lung transplantation recipients are at risk of numerous post-transplant complications that include surgical complications, primary graft dysfunction, acute rejection, opportunistic infection, and chronic lung allograft dysfunction (CLAD), which may be caused by chronic rejection. Many advances in pre- and post-transplant management have led to improved outcomes over the past decade. These include the creation of sound guidelines for candidate selection, improved surgical techniques, advances in donor lung preservation, an improving ability to suppress and treat allograft rejection, the development of prophylaxis protocols to decrease the incidence of opportunistic infection, more effective therapies for treating infectious complications, and the development of novel therapies to treat and manage CLAD. A major obstacle to prolonged survival beyond the early post-operative time period is the development of bronchiolitis obliterans syndrome (BOS), which is the most common form of CLAD. This manuscript discusses recent and evolving advances in the field of lung transplantation.

Mesenchymal stem cells tune the development of monocyte-derived dendritic cells toward a myeloid-derived suppressive phenotype through growth-regulated oncogene chemokines

Mesenchymal stem/stromal cells (MSCs) are promising potential candidates for the treatment of immunological diseases because of their immunosuppressive functions. However, the molecular mechanisms that mediate MSCs' immunosuppressive activity remain elusive. In this article, we report for the first time, to our knowledge, that secreted growth-regulated oncogene (GRO) chemokines, specifically GRO-γ, in human MSC-conditioned media have an effect on the differentiation and the function of human monocyte-derived dendritic cells. The monocyte-derived dendritic cells were driven toward a myeloid-derived suppressor cell (MDSC)-like phenotype by the GRO chemokines. GRO-γ-treated MDSCs had a tolerogenic phenotype that was characterized by an increase in the secretion of IL-10 and IL-4, and a reduction in the production of IL-12 and IFN-γ. We have also shown that the mRNA expression levels of the arginase-1 and inducible NO synthase genes, which characterize MDSCs, were upregulated by GRO-γ-primed mouse bone marrow cells. In addition, the ability of GRO-γ-treated bone marrow-derived dendritic cells to stimulate the OVA-specific CD8(+) T (OT-1) cell proliferation and the cytokine production of IFN-γ and TNF-α were significantly decreased in vivo. Our findings allow a greater understanding of how MDSCs can be generated and offer new perspectives to exploit the potential of MDSCs for alternative approaches to treat chronic inflammation and autoimmunity, as well as for the prevention of transplant rejection.

Ischemia-reperfusion injury: beneficial effects of mesenchymal stromal cells

PURPOSE OF REVIEW

Organ transplantation and other major surgeries are impacted by ischemia-reperfusion injury (IRI). Mesenchymal stromal cells (MSCs) recently became an attractive alternative therapeutic tool to combat IRI. The present review highlights the effects of MSCs in the preclinical animal models of IRI and clinical trials, and explains their potential modes of action based on the pathophysiological IRI cascade.

RECENT FINDINGS

The application of MSCs in animal models of IRI show anti-inflammatory and anti-apoptotic effects, particularly for damage to the kidneys, heart and lungs. The mechanism of MSC action remains unclear, but may involve paracrine factors which could include the transfer of microvesicles, RNA or mitochondria. Although few clinical trials have reached completion, adverse effects appear minimal.

SUMMARY

MSCs show promise in protecting against IRI-induced damage. They appear to help recovery mainly by affecting the levels of inflammation and apoptosis during the organ repair process. In addition, they may mediate immunomodulatory effects on the innate and adaptive immune processes triggered during reperfusion and reduce fibrosis. Success in preclinical animal models has led to the initiation of ongoing clinical trials.

Stemming the Degeneration: IVD Stem Cells and Stem Cell Regenerative Therapy for Degenerative Disc Disease

The intervertebral disc (IVD) is immensely important for the integrity of vertebral column function. The highly specialized IVD functions to confer flexibility and tensile strength to the spine and endures various types of biomechanical force. Degenerative disc disease (DDD) is a prevalent musculoskeletal disorder and is the major cause of low back pain and includes the more severe degenerative lumbar scoliosis, disc herniation and spinal stenosis. DDD is a multifactorial disorder whereby an imbalance of anabolic and catabolic factors, or alterations to cellular composition, or biophysical stimuli and genetic background can all play a role in its genesis. However, our comprehension of IVD formation and theetiology of disc degeneration (DD) are far from being complete, hampering efforts to formulate appropriate therapies to tackle DD. Knowledge of the stem cells and various techniques to manipulate and direct them to particular fates have been promising in adopting a stem-cell based regenerative approach to DD. Moreover, new evidence on the residence of stem/progenitor cells within particular IVD niches has emerged holding promise for future therapeutic applications. Existing issues pertaining to current therapeutic approaches are also covered in this review.

Mesenchymal stem cell: keystone of the hematopoietic stem cell niche and a stepping-stone for regenerative medicine

Mesenchymal stem cells (MSCs) are self-renewing precursor cells that can differentiate into bone, fat, cartilage, and stromal cells of the bone marrow. Recent studies suggest that MSCs themselves are critical for forming a niche that maintains hematopoietic stem cells (HSCs). The ease by which human MSC-like and stromal progenitor cells can be isolated from the bone marrow and other tissues has led to the rapid development of clinical investigations exploring their anti-inflammatory properties, tissue preservation capabilities, and regenerative potential. However, the identity of genuine MSCs and their specific contributions to these various beneficial effects have remained enigmatic. In this article, we examine the definition of MSCs and discuss the importance of rigorously characterizing their stem cell activity. We review their role and that of other putative niche constituents in the regulation of bone marrow HSCs. Additionally, how MSCs and their stromal progeny alter immune function is discussed, as well as potential therapeutic implications.

Introduction to stem cells and regenerative medicine

Stem cells are a population of undifferentiated cells characterized by the ability to extensively proliferate (self-renewal), usually arise from a single cell (clonal), and differentiate into different types of cells and tissue (potent). There are several sources of stem cells with varying potencies. Pluripotent cells are embryonic stem cells derived from the inner cell mass of the embryo and induced pluripotent cells are formed following reprogramming of somatic cells. Pluripotent cells can differentiate into tissue from all 3 germ layers (endoderm, mesoderm, and ectoderm). Multipotent stem cells may differentiate into tissue derived from a single germ layer such as mesenchymal stem cells which form adipose tissue, bone, and cartilage. Tissue-resident stem cells are oligopotent since they can form terminally differentiated cells of a specific tissue. Stem cells can be used in cellular therapy to replace damaged cells or to regenerate organs. In addition, stem cells have expanded our understanding of development as well as the pathogenesis of disease. Disease-specific cell lines can also be propagated and used in drug development. Despite the significant advances in stem cell biology, issues such as ethical controversies with embryonic stem cells, tumor formation, and rejection limit their utility. However, many of these limitations are being bypassed and this could lead to major advances in the management of disease. This review is an introduction to the world of stem cells and discusses their definition, origin, and classification, as well as applications of these cells in regenerative medicine.

Mesenchymal stem cells support proliferation and terminal differentiation of B cells

BACKGROUND

Mesenchymal stem cells (MSC) play important roles in modulating the activities of T lymphocytes, dendritic cells and natural killer cells. These immunoregulatory properties of MSC suggest their therapeutic potential in autoimmune diseases. However, the effects of MSC on B cells are still poorly understood. The present study was designed to investigate the interaction between MSC and B cells both in vitro and in vivo, and to determine the possible mechanism of action.

DESIGN AND METHOD

The effect of human umbilical cord mesenchymal stem cells (UC-MSC) on proliferation and differentiation of B-cells were characterized in vitro, and we also tested the immunoregulatory properties of mouse bone marrow MSC (BM-MSC) on T cell dependent and independent antibody production in vivo in mice.

RESULTS

Treatment with human UC-MSC resulted in an increase of proliferation, differentiation of B cells into plasma cells and production of antibodies in vitro. Mouse BM-MSC significantly enhanced T cell dependent and independent antibodies production in vivo in mice. PGE2 partially mediated the immunosuppressive activity of human UC-MSC but IL-6 did not regulate this activity.

CONCLUSION

MSC promote proliferation and differentiation of B cells in vitro and in vivo partially through PGE2 but not IL-6.

Stem cell conditioned medium improves acute lung injury in mice: in vivo evidence for stem cell paracrine action

Mortality and morbidity of acute lung injury and acute respiratory distress syndrome remain high because of the lack of pharmacological therapies to prevent injury or promote repair. Mesenchymal stem cells (MSCs) prevent lung injury in various experimental models, despite a low proportion of donor-derived cell engraftment, suggesting that MSCs exert their beneficial effects via paracrine mechanisms. We hypothesized that soluble factors secreted by MSCs promote the resolution of lung injury in part by modulating alveolar macrophage (AM) function. We tested the therapeutic effect of MSC-derived conditioned medium (CdM) compared with whole MSCs, lung fibroblasts, and fibroblast-CdM. Intratracheal MSCs and MSC-CdM significantly attenuated lipopolysaccharide (LPS)-induced lung neutrophil influx, lung edema, and lung injury as assessed by an established lung injury score. MSC-CdM increased arginase-1 activity and Ym1 expression in LPS-exposed AMs. In vivo, AMs from LPS-MSC and LPS-MSC CdM lungs had enhanced expression of Ym1 and decreased expression of inducible nitric oxide synthase compared with untreated LPS mice. This suggests that MSC-CdM promotes alternative macrophage activation to an M2 "healer" phenotype. Comparative multiplex analysis of MSC- and fibroblast-CdM demonstrated that MSC-CdM contained several factors that may confer therapeutic benefit, including insulin-like growth factor I (IGF-I). Recombinant IGF-I partially reproduced the lung protective effect of MSC-CdM. In summary, MSCs act through a paracrine activity. MSC-CdM promotes the resolution of LPS-induced lung injury by attenuating lung inflammation and promoting a wound healing/anti-inflammatory M2 macrophage phenotype in part via IGF-I.

Mesenchymal stem cell secreted vesicles provide novel opportunities in (stem) cell-free therapy

Mesenchymal stem cells (MSCs) are adult multipotent cells that give rise to various cell types of the mesodermal germ layer. MSCs are of great interest in the field of regenerative medicine and cancer therapy because of their unique ability to home to damaged and cancerous tissue. These cells also regulate the immune response and contribute to reparative processes in different pathological conditions, including musculoskeletal and cardiovascular diseases. The use of MSCs for tissue repair was initially based on the hypothesis that these cells home to and differentiate within the injured tissue into specialized cells. However, it now appears that only a small proportion of transplanted MSCs actually integrate and survive in host tissues. Thus, the predominant mechanism by which MSCs participate in tissue repair seems to be related to their paracrine activity. Indeed, MSCs provide the microenvironment with a multitude of trophic and survival signals including growth factors and cytokines. Recent discoveries suggest that lipid microvesicles released by MSCs may also be important in the physiological function of these cells. Over the past few years the biological relevance of micro- and nano-vesicles released by cells in intercellular communication has been established. Alongside the conventional mediators of cell secretome, these sophisticated nanovesicles transfer proteins, lipids and, most importantly, various forms of RNAs to neighboring cells, thereby mediating a variety of biological responses. The physiological role of MSC-derived vesicles (MSC-MVs) is currently not well understood. Nevertheless, encouraging results indicate that MSC-MVs have similar protective and reparative properties as their cellular counterparts in tissue repair and possibly anti-cancer therapy. Thus, MSC-MVs represent a promising opportunity to develop novel cell-free therapy approaches that might overcome the obstacles and risks associated with the use of native or engineered stem cells.

Intravenous mesenchymal stem cells prevented rejection of allogeneic corneal transplants by aborting the early inflammatory response

Mesenchymal stem/progenitor cells (MSCs) were reported to enhance the survival of cellular and organ transplants. However, their mode of action was not established. We here used a mouse model of corneal allotransplantation and demonstrated that peri-transplant intravenous (i.v.) infusion of human MSCs (hMSCs) decreased the early surgically induced inflammation and reduced the activation of antigen-presenting cells (APCs) in the cornea and draining lymph nodes (DLNs). Subsequently, immune rejection was decreased, and allograft survival was prolonged. Quantitative assays for human GAPDH revealed that <10 hMSCs out of 1 × 10(6) injected cells were recovered in the cornea 10 hours to 28 days after i.v. infusion. Most of hMSCs were trapped in lungs where they were activated to increase expression of the gene for a multifunctional anti-inflammatory protein tumor necrosis factor-α stimulated gene/protein 6 (TSG-6). i.v. hMSCs with a knockdown of TSG-6 did not suppress the early inflammation and failed to prolong the allograft survival. Also, i.v. infusion of recombinant TSG-6 reproduced the effects of hMSCs. Results suggest that hMSCs improve the survival of corneal allografts without engraftment and primarily by secreting TSG-6 that acts by aborting early inflammatory responses. The same mechanism may explain previous reports that MSCs decrease rejection of other organ transplants.

Osteogenic differentiated periodontal ligament stem cells maintain their immunomodulatory capacity

Periodontal ligament stem cells (PDLSCs) have great potential for regenerating periodontal ligament tissue, which is involved in attaching teeth to the underlying alveolar bone. Recently, PDLSCs were characterized as having both low immunogenicity and profound immunomodulation abilities. Further, transplanted PDLSCs differentiate into osteoblasts in vivo. In the present study, we investigated the immunological characteristics of osteogenic differentiated PDLSCs. We found that PDLSCs expressed mesenchymal stem cells markers, including STRO-1 and CD146, but were negative for CD14, CD34 and CD45. RT-PCR indicated that NCAM1, MSX1 and S100A4 were expressed in PDLSCs. The cells underwent osteogenic and adipogenic differentiation when cultured in defined medium. Osteogenic differentiated PDLSCs failed to stimulate allogeneic T cell proliferation and suppressed phytohaemagglutinin-triggered T cell proliferation. Indomethacin, an inhibitor of prostaglandin E2 (PGE2) production, restored the T cell proliferation inhibited by osteogenic differentiated PDLSCs. These data confirm that osteogenic differentiated PDLSCs have low immunogenicity and demonstrate that they suppress T cell proliferation in vitro through secretion of PGE2.

Mesenchymal stem cell therapy for attenuation of scar formation during wound healing

Scars are a consequence of cutaneous wound healing that can be both unsightly and detrimental to the function of the tissue. Scar tissue is generated by excessive deposition of extracellular matrix tissue by wound healing fibroblasts and myofibroblasts, and although it is inferior to the uninjured skin, it is able to restore integrity to the boundary between the body and its environment. Scarring is not a necessary process to repair the dermal tissues. Rather, scar tissue forms due to specific mechanisms that occur during the adult wound healing process and are modulated primarily by the inflammatory response at the site of injury. Adult tissue-derived mesenchymal stem cells, which participate in normal wound healing, are trophic mediators of tissue repair. These cells participate in attenuating inflammation in the wound and reprogramming the resident immune and wound healing cells to favor tissue regeneration and inhibit fibrotic tissue formation. As a result, these cells have been considered and tested as a likely candidate for a cellular therapy to promote scar-less wound healing. This review identifies specific mechanisms by which mesenchymal stem cells can limit tissue fibrosis and summarizes recent in vivo studies where these cells have been used successfully to limit scar formation.

Human gingiva-derived mesenchymal stromal cells attenuate contact hypersensitivity via prostaglandin E2-dependent mechanisms

The immunomodulatory and anti-inflammatory functions of mesenchymal stromal cells (MSCs) have been demonstrated in several autoimmune/inflammatory disease models, but their contribution to the mitigation of contact hypersensitivity (CHS) remains unclear. Here, we report a new immunological approach using human gingiva-derived MSCs (GMSCs) to desensitize and suppress CHS and the underlying mechanisms. Our results showed that systemic infusion of GMSCs before the sensitization and challenge phase dramatically suppress CHS, manifested as a decreased infiltration of dendritic cells (DCs), CD8(+) T cells, T(H)-17 and mast cells (MCs), a suppression of a variety of inflammatory cytokines, and a reciprocal increased infiltration of regulatory T cells and expression of IL-10 at the regional lymph nodes and the allergic contact areas. The GMSC-mediated immunosuppressive effects and mitigation of CHS were significantly abrogated on pretreatment with indomethacin, an inhibitor of cyclooxygenases. Under coculture condition of direct cell-cell contact or via transwell system, GMSCs were capable of direct suppression of differentiation of DCs and phorbol 12-myristate 13-acetate-stimulated activation of MCs, whereas the inhibitory effects were attenuated by indomethacin. Mechanistically, GMSC-induced blockage of de novo synthesis of proinflammatory cytokines by MCs is mediated partly by the tumor necrosis factor-alpha/prostaglandin E(2) (PGE(2)) feedback axis. These results demonstrate that GMSCs are capable of desensitizing allergic contact dermatitis via PGE(2)-dependent mechanisms.

Comparison of epithelial differentiation and immune regulatory properties of mesenchymal stromal cells derived from human lung and bone marrow

Mesenchymal stromal cells (MSCs) reside in many organs including lung, as shown by their isolation from fetal lung tissues, bronchial stromal compartment, bronchial-alveolar lavage and transplanted lung tissues. It is still controversial whether lung MSCs can undergo mesenchymal-to-epithelial-transition (MET) and possess immune regulatory properties. To this aim, we isolated, expanded and characterized MSCs from normal adult human lung (lung-hMSCs) and compared with human bone marrow-derived MSCs (BM-hMSCs). Our results show that lung-MSCs reside at the perivascular level and do not significantly differ from BM-hMSCs in terms of immunophenotype, stemness gene profile, mesodermal differentiation potential and modulation of T, B and NK cells. However, lung-hMSCs express higher basal level of the stemness-related marker nestin and show, following in vitro treatment with retinoic acid, higher epithelial cell polarization, which is anyway partial when compared to a control epithelial bronchial cell line. Although these results question the real capability of acquiring epithelial functions by MSCs and the feasibility of MSC-based therapeutic approaches to regenerate damaged lung tissues, the characterization of this lung-hMSC population may be useful to study the involvement of stromal cell compartment in lung diseases in which MET plays a role, such as in chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis.

Role of PGE2 in asthma and nonasthmatic eosinophilic bronchitis

Eosinophilic bronchitis is a common cause of chronic cough, which like asthma is characterized by sputum eosinophilia, but unlike asthma there is no variable airflow obstruction or airway hyperresponsiveness. Several studies suggest that prostaglandins may play an important role in orchestrating interactions between different cells in several inflammatory diseases such as asthma. PGE₂ is important because of the multiplicity of its effects on immune response in respiratory diseases; however, respiratory system appears to be unique in that PGE₂ has beneficial effects. We described that the difference in airway function observed in patients with eosinophilic bronchitis and asthma could be due to differences in PGE₂ production. PGE₂ present in induced sputum supernatant from NAEB patients decreases BSMC proliferation, probably due to simultaneous stimulation of EP2 and EP4 receptors with inhibitory activity. This protective effect of PGE₂ may not only be the result of a direct action exerted on airway smooth-muscle proliferation but may also be attributable to the other anti-inflammatory actions.

Stem cells and regenerative medicine in lung biology and diseases

A number of novel approaches for repair and regeneration of injured lung have developed over the past several years. These include a better understanding of endogenous stem and progenitor cells in the lung that can function in reparative capacity as well as extensive exploration of the potential efficacy of administering exogenous stem or progenitor cells to function in lung repair. Recent advances in ex vivo lung engineering have also been increasingly applied to the lung. The current status of these approaches as well as initial clinical trials of cell therapies for lung diseases are reviewed below.

Prostaglandin E2 as an inhibitory modulator of fibrogenesis in human lung allografts

RATIONALE

Donor mesenchymal stromal/stem cell (MSC) expansion and fibrotic differentiation is associated with development of bronchiolitis obliterans syndrome (BOS) in human lung allografts. However, the regulators of fibrotic differentiation of these resident mesenchymal cells are not well understood.

OBJECTIVES

This study examines the role of endogenous and exogenous prostaglandin (PG)E2 as a modulator of fibrotic differentiation of human lung allograft-derived MSCs.

METHODS

Effect of PGE2 on proliferation, collagen secretion, and α-smooth muscle actin (α-SMA) expression was assessed in lung-resident MSCs (LR-MSCs) derived from patients with and without BOS. The response pathway involved was elucidated by use of specific agonists and antagonists.

MEASUREMENT AND MAIN RESULTS

PGE2 treatment of LR-MSCs derived from normal lung allografts significantly inhibited their proliferation, collagen secretion, and α-SMA expression. On the basis of pharmacologic and small-interfering RNA approaches, a PGE2/E prostanoid (EP)2/adenylate cyclase pathway was implicated in these suppressive effects. Stimulation of endogenous PGE2 secretion by IL-1β was associated with amelioration of their myofibroblast differentiation in vitro, whereas its inhibition by indomethacin augmented α-SMA expression. LR-MSCs from patients with BOS secreted significantly less PGE2 than non-BOS LR-MSCs. Furthermore, BOS LR-MSCs were found to be defective in their ability to induce cyclooxygenase-2, and therefore unable to up-regulate PGE2 synthesis in response to IL-1β. BOS LR-MSCs also demonstrated resistance to the inhibitory actions of PGE2 in association with a reduction in the EP2/EP1 ratio.

CONCLUSIONS

These data identify the PGE2 axis as an important autocrine-paracrine brake on fibrotic differentiation of LR-MSCs, a failure of which is associated with BOS.

Concise review: clinical translation of wound healing therapies based on mesenchymal stem cells

There is enormous worldwide demand for therapies to promote the efficient resolution of hard-to-heal wounds with minimal appearance of scarring. Recent in vitro studies with mesenchymal stem cells (MSCs) have identified numerous mechanisms by which these cells can promote the process of wound healing, and there is significant interest in the clinical translation of an MSC-based therapy to promote dermal regeneration. This review provides a systematic analysis of recent preclinical and clinical research to evaluate the use of MSCs in wound healing applications. These in vivo studies provide overwhelming evidence that MSCs can accelerate wound closure by modulating the inflammatory environment, promoting the formation of a well-vascularized granulation matrix, encouraging the migration of keratinocytes, and inhibiting apoptosis of wound healing cells. The trophic effects of MSC therapy also appear to augment wound healing in diabetic tissues, thereby preventing the formation of nonhealing ulcers. Finally, a number of delivery systems have been evaluated and indicate that MSCs could be the basis of a versatile therapy to fulfill the clinical needs for dermal regeneration. However, despite the apparent advantages of MSC-based therapies, there have been only limited clinical investigations of this type of therapy in humans. Thus, our review concludes with a discussion of the translational barriers that are limiting the widespread clinical use of MSCs to enhance wound healing.

Mesenchymal stromal cells from neonatal tracheal aspirates demonstrate a pattern of lung-specific gene expression

We have previously isolated mesenchymal stromal cells (MSCs) from the tracheal aspirates of premature neonates with respiratory distress. Although isolation of MSCs correlates with the development of bronchopulmonary dysplasia, the physiologic role of these cells remains unclear. To address this, we further characterized the cells, focusing on the issues of gene expression, origin, and cytokine expression. Microarray comparison of early passage neonatal lung MSC gene expression to cord blood MSCs and human fetal and neonatal lung fibroblast lines demonstrated that the neonatal lung MSCs differentially expressed 971 gene probes compared with cord blood MSCs, including the transcription factors Tbx2, Tbx3, Wnt5a, FoxF1, and Gli2, each of which has been associated with lung development. Compared with lung fibroblasts, 710 gene probe transcripts were differentially expressed by the lung MSCs, including IL-6 and IL-8/CXCL8. Differential chemokine expression was confirmed by protein analysis. Further, neonatal lung MSCs exhibited a pattern of Hox gene expression distinct from cord blood MSCs but similar to human fetal lung fibroblasts, consistent with a lung origin. On the other hand, limiting dilution analysis showed that fetal lung fibroblasts form colonies at a significantly lower rate than MSCs, and fibroblasts failed to undergo differentiation along adipogenic, osteogenic, and chondrogenic lineages. In conclusion, MSCs isolated from neonatal tracheal aspirates demonstrate a pattern of lung-specific gene expression, are distinct from lung fibroblasts, and secrete pro-inflammatory cytokines.

Resident tissue-specific mesenchymal progenitor cells contribute to fibrogenesis in human lung allografts

Fibrotic obliteration of the small airways leading to progressive airflow obstruction, termed bronchiolitis obliterans syndrome (BOS), is the major cause of poor outcomes after lung transplantation. We recently demonstrated that a donor-derived population of multipotent mesenchymal stem cells (MSCs) can be isolated from the bronchoalveolar lavage (BAL) fluid of human lung transplant recipients. Herein, we study the organ specificity of these cells and investigate the role of local mesenchymal progenitors in fibrogenesis after lung transplantation. We demonstrate that human lung allograft-derived MSCs uniquely express embryonic lung mesenchyme-associated transcription factors with a 35,000-fold higher expression of forkhead/winged helix transcription factor forkhead box (FOXF1) noted in lung compared with bone marrow MSCs. Fibrotic differentiation of MSCs isolated from normal lung allografts was noted in the presence of profibrotic mediators associated with BOS, including transforming growth factor-β and IL-13. MSCs isolated from patients with BOS demonstrated increased expression of α-SMA and collagen I when compared with non-BOS controls, consistent with a stable in vivo fibrotic phenotype. FOXF1 mRNA expression in the BAL cell pellet correlated with the number of MSCs in the BAL fluid, and myofibroblasts present in the fibrotic lesions expressed FOXF1 by in situ hybridization. These data suggest a key role for local tissue-specific, organ-resident, mesenchymal precursors in the fibrogenic processes in human adult lungs.

Endothelin-1 governs proliferation and migration of bronchoalveolar lavage-derived lung mesenchymal stem cells in bronchiolitis obliterans syndrome

BACKGROUND

Bronchiolitis obliterans syndrome (BOS) has an incidence of 57% at 5 years after lung transplantation, accounts for 30% of all deaths 3 years posttransplant and because treatment options are extremely limited, it constitutes a significant health care problem. Adult mesenchymal stem cells (MSCs) play a role in lung turnover; however, their role in BOS remains unknown.

METHODS

MSCs were isolated from bronchoalveolar lavage (BAL) in 101 lung allograft recipients. BAL was screened by protein array and MSCs were analyzed by real-time polymerase chain reaction, proliferation, migration, and enzyme linked immunosorbent assays.

RESULTS

Multipotent MSCs were isolated from BAL of lung recipients independent of BOS presence. However, MSCs from BOS patients proliferated at higher rates (P<0.001) and were associated with higher α-smooth muscle actin (P = 0.03) but lower surfactant protein B (P = 0.02) compared with those from no-BOS patients. Histological analysis revealed that MSCs are abundant in lung tissue of BOS patients. MSCs from BOS patients produced higher endothelin-1 (ET-1) amounts (P<0.001) compared with those from no-BOS; and ET-1 stimulated whereas ET-1 blockade suppressed MSC proliferation, migration, and differentiation.

CONCLUSIONS

These results indicate that MSCs are associated with BOS and are governed by ET-1. Targeting MSCs by ET-1 blockade might be useful in BOS treatment.

Mesenchymal stem cell like (MSCl) cells generated from human embryonic stem cells support pluripotent cell growth

Mesenchymal stem cell like (MSCl) cells were generated from human embryonic stem cells (hESC) through embryoid body formation, and isolated by adherence to plastic surface. MSCl cell lines could be propagated without changes in morphological or functional characteristics for more than 15 passages. These cells, as well as their fluorescent protein expressing stable derivatives, efficiently supported the growth of undifferentiated human embryonic stem cells as feeder cells. The MSCl cells did not express the embryonic (Oct4, Nanog, ABCG2, PODXL, or SSEA4), or hematopoietic (CD34, CD45, CD14, CD133, HLA-DR) stem cell markers, while were positive for the characteristic cell surface markers of MSCs (CD44, CD73, CD90, CD105). MSCl cells could be differentiated toward osteogenic, chondrogenic or adipogenic directions and exhibited significant inhibition of mitogen-activated lymphocyte proliferation, and thus presented immunosuppressive features. We suggest that cultured MSCl cells can properly model human MSCs and be applied as efficient feeders in hESC cultures.

Concise review: Mesenchymal stem cells for acute lung injury: role of paracrine soluble factors

Morbidity and mortality have declined only modestly in patients with clinical acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), despite extensive research into the pathophysiology. Current treatment remains primarily supportive with lung-protective ventilation and a fluid conservative strategy. Pharmacologic therapies that reduce the severity of lung injury in preclinical models have not yet been translated to effective clinical treatment options. Consequently, further research in translational therapies is needed. Cell-based therapy with mesenchymal stem cells (MSCs) is one attractive new therapeutic approach. MSCs have the capacity to secrete multiple paracrine factors that can regulate endothelial and epithelial permeability, decrease inflammation, enhance tissue repair, and inhibit bacterial growth. This review will focus on recent studies, which support the potential therapeutic use of MSCs in ALI/ARDS, with an emphasis on the role of paracrine soluble factors.

Airway delivery of soluble factors from plastic-adherent bone marrow cells prevents murine asthma

Asthma affects an estimated 300 million people worldwide and accounts for 1 of 250 deaths and 15 million disability-adjusted life years lost annually. Plastic-adherent bone marrow-derived cell (BMC) administration holds therapeutic promise in regenerative medicine. However, given the low cell engraftment in target organs, including the lung, cell replacement cannot solely account for the reported therapeutic benefits. This suggests that BMCs may act by secreting soluble factors. BMCs also possess antiinflammatory and immunomodulatory properties and may therefore be beneficial for asthma. Our objective was to investigate the therapeutic potential of BMC-secreted factors in murine asthma. In a model of acute and chronic asthma, intranasal instillation of BMC conditioned medium (CdM) prevented airway hyperresponsiveness (AHR) and inflammation. In the chronic asthma model, CdM prevented airway smooth muscle thickening and peribronchial inflammation while restoring blunted salbutamol-induced bronchodilation. CdM reduced lung levels of the T(H)2 inflammatory cytokines IL-4 and IL-13 and increased levels of IL-10. CdM up-regulated an IL-10-induced and IL-10-secreting subset of T regulatory lymphocytes and promoted IL-10 expression by lung macrophages. Adiponectin (APN), an antiinflammatory adipokine found in CdM, prevented AHR, airway smooth muscle thickening, and peribronchial inflammation, whereas the effect of CdM in which APN was neutralized or from APN knock-out mice was attenuated compared with wild-type CdM. Our study provides evidence that BMC-derived soluble factors prevent murine asthma and suggests APN as one of the protective factors. Further identification of BMC-derived factors may hold promise for novel approaches in the treatment of asthma.

Lung-derived mesenchymal stromal cell post-transplantation survival, persistence, paracrine expression, and repair of elastase-injured lung

While multipotent mesenchymal stromal cells have been recently isolated from adult lung (L-MSCs), there is very limited data on their biological properties and therapeutic potential in vivo. How L-MSCs compare with bone marrow-derived MSCs (BM-MSCs) is also unclear. In this study, we characterized L-MSC phenotype, clonogenicity, and differentiation potential, and compared L-MSCs to BM-MSCs in vivo survival, retention, paracrine gene expression, and repair or elastase injury after transplantation. L-MSCs were highly clonogenic, frequently expressed aldehyde dehydrogenase activity, and differentiated into osteocytes, chondrocytes, adipocytes, myofibroblasts, and smooth muscle cells. After intravenous injection (2 h), L-MSCs showed greater survival than BM-MSCs; similarly, L-MSCs were significantly more resistant than BM-MSCs to anchorage independent culture (4 h) in vitro. Long after transplantation (4 or 32 days), a significantly higher number of CD45(neg) L-MSCs were retained than BM-MSCs. By flow cytometry, L-MSCs expressed more intercellular adhesion molecule-1 (ICAM-1), platelet derived growth factor receptor alpha (PDGFRα), and integrin α2 than BM-MSCs; these proteins were found to modulate endothelial adherence, directional migration, and migration across Matrigel in L-MSCs. Further, L-MSCs with low ICAM-1 showed poorer lung retention and higher phagocytosis in vivo. Compared with BM-MSCs, L-MSCs expressed higher levels of several transcripts (e.g., Ccl2, Cxcl2, Cxcl10, IL-6, IL-11, Hgf, and Igf2) in vitro, although gene expression in vivo was increased by L-MSCs and BM-MSCs equivalently. Accordingly, both L-MSCs and BM-MSCs reduced elastase injury to the same extent. This study demonstrates that tissue-specific L-MSCs possess mechanisms that enhance their lung retention after intravenous transplantation, and produce substantial healing of elastase injury comparable to BM-MSCs.

Stem cells and cell therapies in lung biology and lung diseases

The University of Vermont College of Medicine and the Vermont Lung Center, with support of the National Heart, Lung, and Blood Institute (NHLBI), the Alpha-1 Foundation, the American Thoracic Society, the Emory Center for Respiratory Health,the Lymphangioleiomyomatosis (LAM) Treatment Alliance,and the Pulmonary Fibrosis Foundation, convened a workshop,‘‘Stem Cells and Cell Therapies in Lung Biology and Lung Diseases,’’ held July 26-29, 2009 at the University of Vermont,to review the current understanding of the role of stem and progenitor cells in lung repair after injury and to review the current status of cell therapy approaches for lung diseases. These are rapidly expanding areas of study that provide further insight into and challenge traditional views of the mechanisms of lung repair after injury and pathogenesis of several lung diseases. The goals of the conference were to summarize the current state of the field, discuss and debate current controversies, and identify future research directions and opportunities for both basic and translational research in cell-based therapies for lung diseases.

The pathology of bleomycin-induced fibrosis is associated with loss of resident lung mesenchymal stem cells that regulate effector T-cell proliferation

Tissue-resident mesenchymal stem cells (MSCs) are important regulators of tissue repair or regeneration, fibrosis, inflammation, angiogenesis, and tumor formation. Here, we define a population of resident lung MSCs (luMSCs) that function to regulate the severity of bleomycin injury via modulation of the T-cell response. Bleomycin-induced loss of these endogenous luMSCs and elicited fibrosis (pulmonary fibrosis), inflammation, and pulmonary arterial hypertension (PAH). Replacement of resident stem cells by administration of isolated luMSCs attenuated the bleomycin-associated pathology and mitigated the development of PAH. In addition, luMSC modulated a decrease in numbers of lymphocytes and granulocytes in bronchoalveolar fluid and demonstrated an inhibition of effector T-cell proliferation in vitro. Global gene expression analysis indicated that the luMSCs are a unique stromal population differing from lung fibroblasts in terms of proinflammatory mediators and profibrotic pathways. Our results demonstrate that luMSCs function to protect lung integrity after injury; however, when endogenous MSCs are lost, this function is compromised illustrating the importance of this novel population during lung injury. The definition of this population in vivo in both murine and human pulmonary tissue facilitates the development of a therapeutic strategy directed at the rescue of endogenous cells to facilitate lung repair during injury.

Characterization of immortalized mesenchymal stem cells derived from foetal porcine pancreas

Islet replacement therapy is limited by shortage of donor islet cells. Usage of islet cells derived from porcine pancreatic stem cells (PSCs) is currently viewed as the most promising alternative for human islet transplantation. However, PSCs are rare and have a finite proliferative lifespan. In this study, we isolated and established an immortalized mesenchymal stem cell (MSC) line derived from foetal porcine pancreas, by transfecting human telomerase reverse transcriptase (hTERT) and called these immortalized pancreatic mesenchymal stem cells (iPMSCs). The iPMSCs have been cultured for more than 80 passages and have capacity to differentiate into neurons, cardiomyocytes, germ cells and islet-like cells, analysed by morphology, RT-PCR, western blotting, immunofluorescence, immunocytochemistry and transplantation assay. Islets derived from iPMSCs reversed hyperglycaemia in streptozotocin-induced diabetic mice and secreted insulin and C-peptide in vitro. These results demonstrated that iPMSCs might provide unlimited resources for islet replacement therapy and models for functional cell differentiation.

Perivascular cells as mesenchymal stem cells

IMPORTANCE OF THE FIELD

Mesenchymal stem cells are multipotent adult stem cell populations that have broad differentiation plasticity and immunosuppressive potential that render them of great importance in cell-based therapies. They are identified by in vitro characteristics based on their differentiation potential for clinical approaches while their biological properties and in vivo identities are often less understood.

AREAS COVERED IN THIS REVIEW

Recent research carried out in the last decade on mesenchymal stem cell biology suggests that mesenchymal stem cells from various tissues reside in a perivascular location and these can be identified as pericytes that function as mural cells in microvessels.

WHAT THE READER WILL GAIN

This review covers recent progress on understanding the link between pericytes and mesenchymal stem cells discussing specific points such as response to injury and tissue-specific functions.

TAKE HOME MESSAGE

Despite a long and controversial history, there is a growing acceptance that perivascular cells are connected with mesenchymal stem cells, all that is really lacking is genetic evidence to show differentiation of pericytes into different cells types.

Mycoplasma contamination revisited: mesenchymal stromal cells harboring Mycoplasma hyorhinis potently inhibit lymphocyte proliferation in vitro

Background

Mesenchymal stromal cells (MSC) have important immunomodulatory effects that can be exploited in the clinical setting, e.g. in patients suffering from graft-versus-host disease after allogeneic stem cell transplantation. In an experimental animal model, cultures of rat T lymphocytes were stimulated in vitro either with the mitogen Concanavalin A or with irradiated allogeneic cells in mixed lymphocyte reactions, the latter to simulate allo-immunogenic activation of transplanted T cells in vivo. This study investigated the inhibitory effects of rat bone marrow-derived MSC subsequently found to be infected with a common mycoplasma species (Mycoplasma hyorhinis) on T cell activation in vitro and experimental graft-versus-host disease in vivo.

Principal Findings

We found that M. hyorhinis infection increased the anti-proliferative effect of MSC dramatically, as measured by both radiometric and fluorimetric methods. Inhibition could not be explained solely by the well-known ability of mycoplasmas to degrade tritiated thymidine, but likely was the result of rapid dissemination of M. hyorhinis in the lymphocyte culture.

Conclusions

This study demonstrates the potent inhibitory effect exerted by M. hyorhinis in standard lymphocyte proliferation assays in vitro. MSC are efficient vectors of mycoplasma infection, emphasizing the importance of monitoring cell cultures for contamination.

Mesenchymal stromal cells in bronchoalveolar lavage as predictors of bronchiolitis obliterans syndrome

RATIONALE

Bronchoalveolar lavage fluid (BAL) from human lung allografts demonstrates the presence of a multipotent mesenchymal stromal cell population. However, the clinical relevance of this novel cellular component of BAL and its association with bronchiolitis obliterans syndrome (BOS), a disease marked by progressive airflow limitation secondary to fibrotic obliteration of the small airways, remains to be determined.

OBJECTIVES

In this study we investigate the association of number of mesenchymal stromal cells in BAL with development of BOS in human lung transplant recipients.

METHODS

Mesenchymal colony-forming units (CFUs) were quantitated in a cohort of 405 BAL samples obtained from 162 lung transplant recipients. Poisson generalized estimating equations were used to determine the predictors of BAL mesenchymal CFU count.

MEASUREMENTS AND MAIN RESULTS

Higher CFU counts were noted early post-transplantation; time from transplant to BAL of greater than 3 months predicted 0.4-fold lower CFU counts (P = 0.0001). BOS diagnosis less than or equal to 365 days before BAL was associated with a 2.11-fold higher CFU count (P = 0.02). There were 2.62- and 2.70-fold higher CFU counts noted in the presence of histologic diagnosis of bronchiolitis obliterans (P = 0.05) and organizing pneumonia (0.0003), respectively. In BAL samples obtained from BOS-free patients greater than 6 months post-transplantation (n = 173), higher mesenchymal CFU counts (≥10) significantly predicted BOS onset in both univariate (hazard ratio, 5.61; 95% CI, 3.03-10.38; P < 0.0001) and multivariate (hazard ratio, 5.02; 95% CI, 2.40-10.51; P < 0.0001) Cox regression analysis.

CONCLUSIONS

Measurement of mesenchymal CFUs in the BAL provides predictive information regarding future BOS onset.

Relevance of the mevalonate biosynthetic pathway in the regulation of bone marrow mesenchymal stromal cell-mediated effects on T-cell proliferation and B-cell survival

BACKGROUND

Bone marrow mesenchymal stromal cells can suppress T-lymphocyte proliferation but promote survival of normal and malignant B cells, thus representing a possible target for new therapeutic schemes. Here we defined the effects of cholesterol synthesis inhibitors on the interaction between these mesenchymal stromal cells and T or B lymphocytes.

DESIGN AND METHODS

We exposed mesenchymal stromal cells to inhibitors, such as fluvastatin, of the 3-hydroxy-3-methylglutaryl-coenzyme A reductase, responsible for the synthesis of mevalonate, the precursor of cholesterol. Also, these cells were treated with manumycin A, a farnesyl transferase inhibitor which blocks the mevalonate-dependent isoprenylation of small guanosin triphosphate binding proteins. First, mesenchymal stromal cell morphology, cytoskeleton assembly, cell cycle, survival and cytokine production were evaluated. Then, these cells were co-cultured with either T or B lymphocytes and we analyzed: 1) the inhibition of T-cell proliferation to mitogenic stimuli; 2) B-cell survival.

RESULTS

Fluvastatin altered the assembly of actin microfilaments, inactivated RhoA guanosin triphosphate binding protein, inhibited the S-phase of the cell cycle, induced apoptosis in a small fraction of cells but preserved cytokine production. Preincubation of mesenchymal stromal cells with fluvastatin, or manumycin A, down-regulated the expression of adhesion molecules, reduced cell-to-cell interactions and prevented the inhibition exerted by these stromal cells on CD3/T-cell receptor-induced lymphocyte proliferation. Mevalonic acid could revert morphological, phenotypic and functional effects of fluvastatin. Finally, fluvastatin significantly reduced the mesenchymal stromal cells-mediated rescue of B cells in the presence of dexamethasone, although it did not function in the absence of corticosteroids.

CONCLUSIONS

Fluvastatin-mediated effects on bone marrow mesenchymal stromal cells were conceivably due to the inhibition of isoprenylation of small guanosin triphosphate binding proteins, occurring for the lack of mevalonate. Altogether these findings suggest that drugs acting on the mevalonate biosynthetic pathway can regulate mesenchymal stromal cell-induced T-cell suppression and B-lymphocyte survival.

Ovalbumin sensitization and challenge increases the number of lung cells possessing a mesenchymal stromal cell phenotype

Background

Recent studies have indicated the presence of multipotent mesenchymal stromal cells (MSCs) in human lung diseases. Excess airway smooth muscle, myofibroblasts and activated fibroblasts have each been noted in asthma, suggesting that mesenchymal progenitor cells play a role in asthma pathogenesis. We therefore sought to determine whether MSCs are present in the lungs of ovalbumin (OVA)-sensitized and challenged mice, a model of allergic airways disease.

Methods

Balb/c mice were sensitized and challenged with PBS or OVA over a 25 day period. Flow cytometry as well as colony forming and differentiation potential were used to analyze the emergence of MSCs along with gene expression studies using immunochemical analyses, quantitative polymerase chain reaction (qPCR), and gene expression beadchips.

Results

A CD45-negative subset of cells expressed Stro-1, Sca-1, CD73 and CD105. Selection for these markers and negative selection against CD45 yielded a population of cells capable of adipogenic, osteogenic and chondrogenic differentiation. Lungs from OVA-treated mice demonstrated a greater average colony forming unit-fibroblast (CFU-F) than control mice. Sorted cells differed from unsorted lung adherent cells, exhibiting a pattern of gene expression nearly identical to bone marrow-derived sorted cells. Finally, cells isolated from the bronchoalveolar lavage of a human asthma patient showed identical patterns of cell surface markers and differentiation potential.

Conclusions

In summary, allergen sensitization and challenge is accompanied by an increase of MSCs resident in the lungs that may regulate inflammatory and fibrotic responses.

Human mesenchymal stem cells suppress chronic airway inflammation in the murine ovalbumin asthma model

Allogeneic human mesenchymal stem cells (hMSCs) introduced intravenously can have profound anti-inflammatory activity resulting in suppression of graft vs. host disease as well as regenerative events in the case of stroke, infarct, spinal cord injury, meniscus regeneration, tendinitis, acute renal failure, and heart disease in human and animal models of these diseases. hMSCs produce bioactive factors that provide molecular cuing for: 1) immunosuppression of T cells; 2) antiscarring; 3) angiogenesis; 4) antiapoptosis; and 5) regeneration (i.e., mitotic for host-derived progenitor cells). Studies have shown that hMSCs have profound effects on the immune system and are well-tolerated and therapeutically active in immunocompetent rodent models of multiple sclerosis and stroke. Furthermore, intravenous administration of MSCs results in pulmonary localization. Asthma is a major debilitating pulmonary disease that impacts in excess of 150 million people in the world with uncontrolled asthma potentially leading to death. In addition, the socioeconomic impact of asthma-associated illnesses at the pediatric and adult level are in the millions of dollars in healthcare costs and lost days of work. hMSCs may provide a viable multiaction therapeutic for this inflammatory lung disease by secreting bioactive factors or directing cellular activity. Our studies show the effectiveness and specificity of the hMSCs on decreasing chronic airway inflammation associated with the murine ovalbumin model of asthma. In addition, the results from these studies verify the in vivo immunoeffectiveness of hMSCs in rodents and support the potential therapeutic use of hMSCs for the treatment of airway inflammation associated with chronic asthma.

Mesenchymal stem cells: Mechanisms of immunomodulation and homing

Mesenchymal stem cell (MSC) transplantation has been explored as a new clinical approach to repair injured tissue. A growing corpus of studies have highlighted two important aspects of MSC therapy: 1) MSCs can modulate T-cell-mediated immunological responses, and (2) systemically administered MSCs home to sites of ischemia or injury. In this review, we describe the known mechanisms of immunomodulation and homing of MSCs. First, we examine the low immunogenicity of MSCs and their antigen presentation capabilities. Next, we discuss the paracrine interactions between MSCs and innate [dendritic cells (DC)] and adaptive immune cells (T lymphocytes) with a focus on prostaglandin E(2) (PGE(2)), indoleamine 2,3-dioxygenase (IDO), and toll-like receptor (TLR) signaling pathways. We transition to outline the steps of activation, rolling/adhesion, and transmigration of MSCs into target tissues during inflammatory or ischemic conditions. These aspects of MSC grafts--immunomodulation and homing--are contextualized to understand a reported side effect of MSC therapy, cancer development.

CD14+ monocytes promote the immunosuppressive effect of human umbilical cord matrix stem cells

Here, the effect of CD14(+) monocytes on human umbilical cord matrix stem cell (hUC-MSC)-mediated immunosuppression was studied in vitro. hUC-MSCs exerted a potent inhibitory effect on the proliferation and interferon-gamma (IFN-gamma) secretion capacities of CD4(+) and CD8(+) T cells in response to anti-CD3/CD28 stimulation. Transwell co-culture system revealed that the suppressive effect was primarily mediated by soluble factors. Addition of prostaglandin synthesis inhibitors (indomethacin or NS-398) almost completely abrogated the immunosuppression activity of hUC-MSCs, identifying prostaglandin E(2) (PGE(2)) as an important soluble mediator. CD14(+) monocytes were found to be able to enhance significantly the immunosuppressive effect of hUC-MSCs in a dose-dependent fashion. Moreover, the inflammatory cytokine IL-1beta, either exogenously added or produced by CD14(+) monocytes in culture, could trigger expression of high levels of PGE(2) by hUC-MSCs, whereas inclusion of the IL-1 receptor antagonist (IL-1RA) in the culture down-regulated not only PGE(2) expression, but also reversed the promotional effect of CD14(+) monocytes and partially restored CD4(+) and CD8(+) T cell proliferation and IFN-gamma secretion. Our data demonstrate an important role of monocytes in the hUC-MSC-induced immunomodulation, which may have important implications in future efforts to explore the clinical potentials of hUC-MSCs.

Isolation and characterization of chicken lung mesenchymal stromal cells and their susceptibility to avian influenza virus

In this study, we isolated and characterized mesenchymal stromal cells (MSCs) from the lungs of 1- to 2-week-old chickens. Microscopically, the cultured cells showed fibroblast-like morphology. Phenotypically these cells expressed CD44, CD90, CD105 and the transcription factor PouV, which has been shown to be critical for stem cell self-renewal and pluripotency. The multipotency of chicken MSCs was demonstrated by their ability to undergo adipogenic and osteogenic differentiation. Like chicken bone marrow MSCs and mammalian MSCs, chicken lung MSCs had immunoregulatory activity and profoundly suppressed the proliferative capacity of T cells in response to a mitogenic stimulus. Next, we examined the susceptibility of these cells to H1N1 and H9N5 avian influenza (AI) viruses. The lung MSCs were shown to express known influenza virus alpha-2,3 and alpha-2,6 sialic acid receptors and to support replication of both the avian H1N1 and avian H9N5 influenza strains. Viral infection of MSCs resulted in cell lysis and cytokine and chemokine production. Further characterization of lung MSCs in chicken and other mammalian species may help in understanding the pathogenesis of infectious and non-infectious lung diseases and the mechanisms of lung injury repair.