Bone marrow mononuclear cell therapy led to alveolar-capillary membrane repair, improving lung mechanics in endotoxin-induced acute lung injury

The Emerging Role of Exosomes in the Treatment of Human Disorders With a Special Focus on Mesenchymal Stem Cells-Derived Exosomes

Extracellular vesicles (EVs) are produced by diverse eukaryotic and prokaryotic cells. They have prominent roles in the modulation of cell-cell communication, inflammation versus immunomodulation, carcinogenic processes, cell proliferation and differentiation, and tissue regeneration. These acellular vesicles are more promising than cellular methods because of the lower risk of tumor formation, autoimmune responses and toxic effects compared with cell therapy. Moreover, the small size and lower complexity of these vesicles compared with cells have made their production and storage easier than cellular methods. Exosomes originated from mesenchymal stem cells has also been introduced as therapeutic option for a number of human diseases. The current review aims at summarization of the role of EVs in the regenerative medicine with a focus on their therapeutic impacts in liver fibrosis, lung disorders, osteoarthritis, colitis, myocardial injury, spinal cord injury and retinal injury.

Application of Mesenchymal Stem Cells in Inflammatory and Fibrotic Diseases

Mesenchymal stem cells (MSCs) are multipotent stem cells that can be isolated from various tissues in the adult body. MSCs should be characterized by three criteria for regenerative medicine. MSCs must (1) adhere to plastic surfaces, (2) express specific surface antigens, and (3) differentiate into mesodermal lineages, including chondrocytes, osteoblasts, and adipocytes, in vitro. Interestingly, MSCs have immunomodulatory features and secrete trophic factors and immune receptors that regulate the microenvironment in host tissue. These specific and unique therapeutic properties make MSCs ideal as therapeutic agents in vivo. Specifically, pre-clinical and clinical investigators generated inflammatory and fibrotic diseases models, and then transplantation of MSCs into diseases models for therapeutic effects investigation. In this review, we characterize MSCs from various tissues and describe their applications for treating various inflammation and fibrotic diseases.

Mesenchymal stromal cells protect against vascular damage and depression-like behavior in mice surviving cerebral malaria

BACKGROUND

Malaria is one of the most critical global infectious diseases. Severe systemic inflammatory diseases, such as cerebral malaria, lead to the development of cognitive and behavioral alterations, such as learning disabilities and loss of memory capacity, as well as increased anxiety and depression. The consequences are profound and usually contribute to reduce the patient's quality of life. There are no therapies to treat the neurological sequelae of cerebral malaria. Mesenchymal stromal cells (MSCs) may be an alternative, since they have been used as therapy for neurodegenerative diseases and traumatic lesions of the central nervous system. So far, no study has investigated the effects of MSC therapy on the blood-brain barrier, leukocyte rolling and adherence in the brain, and depression like-behavior in experimental cerebral malaria.

METHODS

Male C57BL/6 mice were infected with Plasmodium berghei ANKA (PbA, 1 × 106 PbA-parasitized red blood cells, intraperitoneally). At day 6, PbA-infected animals received chloroquine (25 mg/kg orally for seven consecutive days) as the antimalarial treatment and were then randomized to receive MSCs (1 × 105 cells in 0.05 ml of saline/mouse) or saline (0.05 ml) intravenously. Parasitemia, clinical score, and survival rate were analyzed throughout the experiments. Evans blue assay was performed at 6, 7, and 15 days post-infection (dpi). Behavioral tests were performed at 5 and 15 dpi. Intravital microscopy experiments and brain-derived neurotrophic factor (BDNF) protein expression analyses were performed at 7 dpi, whereas inflammatory mediators were measured at 15 dpi. In vitro, endothelial cells were used to evaluate the effects of conditioned media derived from MSCs (CMMSC) on cell viability by lactate dehydrogenase (LDH) release.

RESULTS

PbA-infected mice presented increased parasitemia, adherent leukocytes, blood-brain barrier permeability, and reduced BDNF protein levels, as well as depression-like behavior. MSCs mitigated behavioral alterations, restored BDNF and transforming growth factor (TGF)-β protein levels, and reduced blood-brain barrier dysfunction and leukocyte adhesion in the brain microvasculature. In a cultured endothelial cell line stimulated with heme, CMMSC reduced LDH release, suggesting a paracrine mechanism of action.

CONCLUSION

A single dose of MSCs as adjuvant therapy protected against vascular damage and improved depression-like behavior in mice that survived experimental cerebral malaria.

Deconstructing tissue engineered trachea: Assessing the role of synthetic scaffolds, segmental replacement and cell seeding on graft performance

The ideal construct for tracheal replacement remains elusive in the management of long segment airway defects. Tissue engineered tracheal grafts (TETG) have been limited by the development of graft stenosis or collapse, infection, or lack of an epithelial lining. We applied a mouse model of orthotopic airway surgery to assess the impact of three critical barriers encountered in clinical applications: the scaffold, the extent of intervention, and the impact of cell seeding and characterized their impact on graft performance. First, synthetic tracheal scaffolds electrospun from polyethylene terephthalate / polyurethane (PET/PU) were orthotopically implanted in anterior tracheal defects of C57BL/6 mice. Scaffolds demonstrated complete coverage with ciliated respiratory epithelium by 2 weeks. Epithelial migration was accompanied by macrophage infiltration which persisted at long term (>6 weeks) time points. We then assessed the impact of segmental tracheal implantation using syngeneic trachea as a surrogate for the ideal tracheal replacement. Graft recovery involved local upregulation of epithelial progenitor populations and there was no evidence of graft stenosis or necrosis. Implantation of electrospun synthetic tracheal scaffold for segmental replacement resulted in respiratory distress and required euthanasia at an early time point. There was limited epithelial coverage of the scaffold with and without seeded bone marrow-derived mononuclear cells (BM-MNCs). We conclude that synthetic scaffolds support re-epithelialization in orthotopic patch implantation, syngeneic graft integration occurs with focal repair mechanisms, however epithelialization in segmental synthetic scaffolds is limited and is not influenced by cell seeding. STATEMENT OF SIGNIFICANCE: The life-threatening nature of long-segment tracheal defects has led to clinical use of tissue engineered tracheal grafts in the last decade for cases of compassionate use. However, the ideal tracheal reconstruction using tissue-engineered tracheal grafts (TETG) has not been clarified. We addressed the core challenges in tissue engineered tracheal replacement (re-epithelialization and graft patency) by defining the role of cell seeding with autologous bone marrow-derived mononuclear cells, the mechanism of respiratory epithelialization and proliferation, and the role of the inflammatory immune response in regeneration. This research will facilitate comprehensive understanding of cellular regeneration and neotissue formation on TETG, which will permit targeted therapies for accelerating re-epithelialization and attenuating stenosis in tissue engineered airway replacement.

Therapeutic potential of mesenchymal stem/stromal cell-derived secretome and vesicles for lung injury and disease

Introduction: The acute respiratory distress syndrome (ARDS) is a devastating clinical condition common in patients with respiratory failure. Based largely on numerous preclinical studies and recent Phase I/II clinical trials, administration of stem cells, specifically mesenchymal stem or stromal cells (MSC), as a therapeutic for acute lung injury (ALI) holds great promise. However, concern for the use of stem cells, specifically the risk of iatrogenic tumor formation, remains unresolved. Accumulating evidence now suggest that stem cell-derived conditioned medium (CM) and/or extracellular vesicles (EV) might constitute compelling alternatives.Areas covered: The current review focuses on the preclinical studies testing MSC CM and/or EV as treatment for ALI and other inflammatory lung diseases.Expert opinion: Clinical application of MSC or their secreted CM may be limited by the cost of growing enough cells, the logistic of MSC storage, and the lack of standardization of what constitutes MSC CM. However, the clinical application of MSC EV remains promising, primarily due to the ability of EV to maintain the functional phenotype of the parent cell as a therapeutic. However, utilization of MSC EV will also require large-scale production, the cost of which may be prohibitive unless the potency of the EV can be increased.

Transplantation of adipose-derived mesenchymal stem cells attenuates pulmonary fibrosis of silicosis via anti-inflammatory and anti-apoptosis effects in rats

Background

Silicosis has been topping the list of high-incidence occupational diseases in developing countries and cannot be completely cured. Recent advances in stem cell research have made possible the treatment of various diseases including lung fibrosis. The application of stem cell therapy in occupational diseases, in particular the use of adipose-derived mesenchymal stem cells (AD-MSCs) in treatment of silicosis, has not yet been reported. The aim of the study is to explore the intervening effect of silica-induced lung fibrosis in rats.

Methods

In this study, we investigated the anti-pulmonary fibrosis effects of the transplantation of AD-MSCs in rats in which lung fibrosis was induced by oral tracheal intubation with silica suspension. Twenty rats were divided into four groups: control group (n = 5), exposure group (n = 5), vehicle group (n = 5) and treatment group (n = 5). AD-MSCs were given to rats after exposure to silica for 24 h. Twenty-eight days after AD-MSC transplantation, we examined the organ coefficient, inflammatory cytokines, apoptosis, pathological and fibrotic changes in lung tissue.

Results

Results showed that exposure to silica for 28 days induced an increase of the lung coefficient with significant pulmonary fibrosis. Treatment with AD-MSC transplantation led to a remissive effect on pulmonary fibrosis. We found that after AD-MSC transplantation the inflammatory response decreased and Caspase-3 protein expression significantly decreased with a significant increase of the Bcl-2/Bax ratio.

Conclusions

Anti-inflammatory and anti-apoptosis of AD-MSCs may play important roles in their anti-pulmonary fibrosis effect. Our data suggest that transplantation of AD-MSCs holds promise for potential interference in the formation of silicosis through regulating inflammatory and apoptotic processes.

Effects of human umbilical cord blood mononuclear cells on respiratory system mechanics in a murine model of neonatal lung injury

BACKGROUND

Mononuclear cells (MNCs) have well-documented beneficial effects in a wide range of adult pulmonary diseases. The effects of human umbilical cord blood-derived MNCs on neonatal lung injury, highly relevant for potential autologous application in preterm newborns at risk for bronchopulmonary dysplasia (BPD), remain incompletely established. The aim of this study was to determine the long-term morphologic and functional effects of systemically delivered MNCs in a murine model of neonatal lung injury.

MATERIALS AND METHODS

MNCs from cryopreserved cord blood (1 × 10⁶ cells per pup) were given intravenously to newborn mice exposed to 90% O₂ from birth; controls received cord blood total nucleated cells (TNCs) or granular cells, or equal volume vehicle buffer (sham controls). In order to avoid immune rejection, we used SCID mice as recipients. Lung mechanics (flexiVent™), engraftment, growth, and alveolarization were evaluated eight weeks postinfusion.

RESULTS

Systemic MNC administration to hyperoxia-exposed newborn mice resulted in significant attenuation of methacholine-induced airway hyperreactivity, leading to reduction of central airway resistance to normoxic levels. These bronchial effects were associated with mild improvement of alveolarization, lung compliance, and elastance. TNCs had no effects on alveolar remodeling and were associated with worsened methacholine-induced bronchial hyperreactivity. Granular cell administration resulted in a marked morphologic and functional emphysematous phenotype, associated with high mortality. Pulmonary donor cell engraftment was sporadic in all groups.

CONCLUSIONS

These results suggest that cord blood MNCs may have a cell type-specific role in therapy of pulmonary conditions characterized by increased airway resistance, such as BPD and asthma. Future studies need to determine the active MNC subtype(s), their mechanisms of action, and optimal purification methods to minimize granular cell contamination.

De novo generation of adipocytes from circulating progenitor cells in mouse and human adipose tissue

White adipocytes in adults are typically derived from tissue resident mesenchymal progenitors. The recent identification of de novo production of adipocytes from bone marrow progenitor-derived cells in mice challenges this paradigm and indicates an alternative lineage specification that adipocytes exist. We hypothesized that alternative lineage specification of white adipocytes is also present in human adipose tissue. Bone marrow from transgenic mice in which luciferase expression is governed by the adipocyte-restricted adiponectin gene promoter was adoptively transferred to wild-type recipient mice. Light emission was quantitated in recipients by in vivo imaging and direct enzyme assay. Adipocytes were also obtained from human recipients of hematopoietic stem cell transplantation. DNA was isolated, and microsatellite polymorphisms were exploited to quantify donor/recipient chimerism. Luciferase emission was detected from major fat depots of transplanted mice. No light emission was observed from intestines, liver, or lungs. Up to 35% of adipocytes in humans were generated from donor marrow cells in the absence of cell fusion. Nontransplanted mice and stromal-vascular fraction samples were used as negative and positive controls for the mouse and human experiments, respectively. This study provides evidence for a nontissue resident origin of an adipocyte subpopulation in both mice and humans.

Mesenchymal stem cells for therapeutic applications in pulmonary medicine

INTRODUCTION

Mesenchymal stem cells (MSCs) of different biological sources are in Phase 1 clinical trials and are being considered for Phase 2 therapy of lung disorders, and lung (progenitor) cells derived from pluripotent stem cells (SCs) are under development in preclinical animal models.

SOURCES OF DATA

PubMed.gov and ClinicalTrials.gov.

AREAS OF AGREEMENT

There is consensus about the therapeutic potential of transplanted SCs, mainly MSCs, primarily involves paracrine 'bystander' effects that confer protection of the epithelial and endothelial linings of the lung caused by inflammation and/or fibrosis and lead to increased survival in animal models. Clinical trials of Phase 1 indicate safety and suggest that the efficacy of SC therapy in patients with various lung diseases will require a higher dosage than previously evaluated.

AREAS OF CONTROVERSY

A growing interest in the re-epithelialization and re-endothelialization of damaged lung tissue involves the putative pulmonary differentiation of exogenous MSCs. Currently, it is not clear whether or not the observed regeneration of distal airways/vasculature is derived from lung-resident and/or transplanted SCs.

GROWING POINTS

Important topics under investigation include optimization of the cell source with a decrease in cell population heterogeneity characterized by defined markers, route of delivery for effective treatment, potential dose and therapeutic protocol of SC application, development of quantitative assays and biomarkers of lung disease and repair, and the potential use of tissue engineered lung.

AREAS TIMELY FOR DEVELOPING RESEARCH

Ability of MSCs to differentiate into epithelial cells of the lung, use of autologous induced pluripotent SCs (iPSCs) derived from the patients, complete biochemical characterization of the secretome of SCs used for therapy, and the incorporation of simultaneous and/or subsequent treatment with drugs which also aid in lung repair and regeneration.

CAUTIONARY NOTE

Although safety of MSC-based cell therapy was proved in Phase 1, efficacy, long-term survival and preservation of lung respiratory function need to be further evaluated, cautioning against hastily translating SCs therapy from animal models of lung injury to clinical trials of patients with lung disorders.

Stem cells for respiratory failure

PURPOSE OF REVIEW

The prognosis of patients with respiratory failure in the ICU remains poor, while current therapeutic approaches are aimed at minimizing ventilator-induced lung injury. Stem cell-based therapies have the potential to transform respiratory failure treatment by achieving lung repair. The purpose of this article is to critically review the large body of clinical and experimental work performed with respect to the use of stem/progenitor cells in respiratory failure, and to discuss current challenges and future directions.

RECENT FINDINGS

Since the initial report of cell therapy for lung injury in 2005, numerous preclinical and clinical studies have been performed that support the ability of various stem cell populations to improve physiologic lung function and reduce inflammation in both infective and sterile acute respiratory distress syndrome. Nevertheless, many important issues (e.g., mechanism of action, long-term engraftment, optimal cell type, dose, route of administration) remain to be resolved.

SUMMARY

Cell-based therapeutics hold promise, particularly for acute respiratory distress syndrome, and early preclinical testing has been encouraging. To advance clinical testing of cell therapies in respiratory failure, and to help ensure that this approach will facilitate bench-to-bedside and bedside-to-bench discoveries, parallel paths of basic and clinical research are needed, including measures of cell therapy effectiveness in vivo and in vitro.

Cell-based therapy for acute organ injury: preclinical evidence and ongoing clinical trials using mesenchymal stem cells

Critically ill patients often suffer from multiple organ failures involving lung, kidney, liver, or brain. Genomic, proteomic, and metabolomic approaches highlight common injury mechanisms leading to acute organ failure. This underlines the need to focus on therapeutic strategies affecting multiple injury pathways. The use of adult stem cells such as mesenchymal stem or stromal cells (MSC) may represent a promising new therapeutic approach as increasing evidence shows that MSC can exert protective effects following injury through the release of promitotic, antiapoptotic, antiinflammatory, and immunomodulatory soluble factors. Furthermore, they can mitigate metabolomic and oxidative stress imbalance. In this work, the authors review the biological capabilities of MSC and the results of clinical trials using MSC as therapy in acute organ injuries. Although preliminary results are encouraging, more studies concerning safety and efficacy of MSC therapy are needed to determine their optimal clinical use. (ANESTHESIOLOGY 2014; 121:1099-121).

Cell-based therapies for the acute respiratory distress syndrome

PURPOSE OF REVIEW

Acute respiratory distress syndrome (ARDS) is a multifaceted lung disease with no current effective therapy. Many clinical trials using conventional pharmacologic therapies have failed, suggesting the need to examine alternative approaches. Thus, attention has focused on the therapeutic potential of cell-based therapies for ARDS, with promising results demonstrated in relevant preclinical disease models. We review data concerning the therapeutic promise of cell-based therapies for ARDS.

RECENT FINDINGS

Recent experimental studies provide further evidence for the potential of cell-based therapies in ARDS. A number of cell types, particularly mesenchymal stem/stromal cells (MSCs), bone marrow-derived mononuclear cells, endothelial progenitor cells, and embryonic stem cells have been demonstrated to reduce mortality and modulate the inflammatory and remodeling processes in relevant preclinical ARDS models. Multiple insights have emerged in regard to the mechanisms by which cell therapies - particularly MSCs - exert their effects, with evidence supporting direct cell-mediated and paracrine-mediated mechanisms of action. Diverse paracrine mechanisms exist, including the release of cytokines, growth factors (such as keratinocyte growth factor), and antimicrobial peptides, and transfer of cellular contents such as peptides, nucleic acids, and mitochondria via either microvesicular or direct cell-cell contact-mediated transfer.

SUMMARY

Cell-based therapies offer considerable promise for the treatment of ARDS. While MSC-based therapies are being rapidly advanced toward clinical testing, clear therapeutic potential exists for other cell types for ARDS. A greater understanding of current knowledge gaps should further enhance the therapeutic potential of cell-based therapies for ARDS.

Bone marrow-derived mononuclear cell therapy in sepsis-induced acute respiratory distress syndrome: different insults, different effects!

Acute respiratory distress syndrome (ARDS) is one of the devastating sequelae of sepsis, and so far no specific promising pharmacotherapies have been proven to decrease mortality from it. Stem cell therapy is a novel therapy that can promote earlier and more effective remodeling and repair of damaged lung tissue. Bone marrow-derived mononuclear cells are an alternative stem cell therapy that is safely and easily administered on the day of harvesting and yields benefits in acute disease processes like ARDS. In a recent issue of Stem Cell Research and Therapy, Maron-Gutierrez and colleagues demonstrated that the effects of transfused bone marrow-derived mononuclear cells on lung mechanics, inflammation and mortality might be different in different septic ARDS models due to different insults.

Infusion of bone marrow mononuclear cells reduces lung fibrosis but not inflammation in the late stages of murine silicosis

We hypothesized that infusion of bone marrow mononuclear cells (BMMCs) in the late stages of silica-induced damage would reduce the remodelling process in a murine model of silicosis. C57BL/6 mice were assigned to 2 groups. In the SIL group, mice were instilled with a silica particle suspension intratracheally. Control (C) mice received saline under the same protocol. On the 40th day, some of the animals from both groups were killed. The others were treated with either saline or BMMCs (1×10⁶cells) intravenously (C+BMMC and SIL+BMMC), and the mice were killed 70 days after the start of the protocol. In the mice in the SIL+BMMC group, collagen deposition, the presence of silica particles inside nodules, the presence of macrophages and cells reactive for inducible nitric oxide synthase were reduced. Lung parameters also improved. Beyond that, the total and differential cellularity of bronchoalveolar lavage fluid, immunoexpression of transforming growth factor-β, the number of T regulatory cells and apoptosis were increased. However, the presence of male donor cells in lung tissue was not observed using GFP+ cells (40d) or Y chromosome DNA (70d). Therefore, BMMC therapy in the late stages of experimental silicosis improved lung function by diminishing fibrosis but inflammatory cells persisted, which could be related to expansion of T regulatory cells, responsible for the beneficial effects of cell therapy.

The Th17 pathway in the peripheral lung microenvironment interacts with expression of collagen V in the late state of experimental pulmonary fibrosis

BACKGROUND

Myofibroblasts derived from fibroblasts in the pathogenesis of pulmonary fibrosis causes excessive and disordered deposition of matrix proteins, including collagen V, which can cause a Th17-mediated immune response and lead to apoptosis. However, whether the intrinsic ability of lung FBs to produce the matrix depends on their site-specific variations is not known.

AIM

To investigate the link between Th17 and collagen V that maintains pulmonary remodeling in the peripheral lung microenvironment during the late stage of experimental pulmonary fibrosis.

METHODS

Young male mice including wild Balb/c mice (BALB, n=10), wild C57 Black/6J mice (C57, n=10) and IL-17 receptor A knockout mice (KO, n=8), were sacrificed 21 days after treatment with bleomycin. Picrosirius red staining, immunohistochemistry for IL-17-related markers and "in situ" detection of apoptosis, immunofluorescence for collagen types I and V, primary cell cultures from tissue lung explants for RT-PCR and electron microscopy were used.

RESULTS

The peripheral deposition of extracellular matrix components by myofibroblasts during the late stage is maintained in C57 mice compared with that in Balb mice and is not changed in the absence of IL-17 receptor A; however, the absence of IL-17 receptor A induces overexpression of type V collagen, amplifies the peripheral expression of IL-17 and IL-17-related cytokines and reduces peripheral lung fibroblast apoptosis.

CONCLUSION

A positive feedback loop between the expression patterns of collagen V and IL-17 may coordinate the maintenance of peripheral collagen I in the absence of IL-17 receptor A in fibrosis-susceptible strains in a site-specific manner.

Effects of bone marrow-derived mononuclear cells from healthy or acute respiratory distress syndrome donors on recipient lung-injured mice

OBJECTIVE

The advantage of using autologous bone marrow-derived mononuclear cells to treat acute respiratory distress syndrome patients is to prevent immunological rejection. However, bone marrow-derived mononuclear cells may be altered by different acute respiratory distress syndrome etiologies, resulting in questionable efficacy and thus limited clinical application. We aimed to investigate the effects of bone marrow-derived mononuclear cells obtained from healthy and acute respiratory distress syndrome donors on pulmonary and extrapulmonary acute respiratory distress syndrome.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

University research laboratory.

SUBJECTS

Two hundred and twenty-five C57BL/6 mice.

INTERVENTIONS

Acute respiratory distress syndrome was induced by Escherichia coli lipopolysaccharide intratracheally (ARDSp) or intraperitoneally (ARDSexp). Control mice (Healthy) received saline solution intratracheally (Cp) or intraperitoneally (Cexp). After 24 hours, whole bone marrow cells were analyzed in vitro: 1) colony-forming unit-fibroblasts and 2) hematopoietic stem cells, neutrophils, T helper lymphocytes, B lymphocytes, and nonhematopoietic precursors. After cell characterization, all groups received saline or bone marrow-derived mononuclear cells (2 × 10), obtained from Cp, Cexp, ARDSp, and ARDSexp donor mice, IV, on day 1.

MEASUREMENTS AND MAIN RESULTS

On day 1, in ARDSp, different patterns of colony formation were found, with nonstromal cells (mainly neutrophils) predominating over fibroblastoid colonies. In ARDSexp, irregular colony-forming unit-fibroblasts morphology with dispersed proliferating colonies and a greater number of hematopoietic stem cells were observed. In ARDSp, colony-forming unit-fibroblasts count was higher but not measurable in ARDSexp. In ARDSp, monocytes and T lymphocytes were increased and hematopoietic precursor cells reduced, with no significant changes in ARDSexp. On day 7, bone marrow-derived mononuclear cells improved survival and attenuated changes in lung mechanics, alveolar collapse, inflammation, pulmonary fibrosis, and apoptosis in the lung and distal organs, regardless of donor type.

CONCLUSIONS

Bone marrow-derived mononuclear cells from ARDSp and ARDSexp donors showed different characteristics but were as effective as cells obtained from healthy donors in reducing inflammation and remodeling, suggesting the utility of autologous transplant of bone marrow-derived mononuclear cells in the clinical setting.

Stem cells, cell therapies, and bioengineering in lung biology and diseases. Comprehensive review of the recent literature 2010-2012

A conference, "Stem Cells and Cell Therapies in Lung Biology and Lung Diseases," was held July 25 to 28, 2011 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 and ex vivo bioengineering approaches for lung diseases. These are rapidly expanding areas of study that provide further insight into and challenge traditional views of 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, to discuss and debate current controversies, and to identify future research directions and opportunities for basic and translational research in cell-based therapies for lung diseases. The goal of this article, which accompanies the formal conference report, is to provide a comprehensive review of the published literature in lung regenerative medicine from the last conference report through December 2012.

Adult stem cells for acute lung injury: remaining questions and concerns

Acute lung injury (ALI) or acute respiratory distress syndrome remains a major cause of morbidity and mortality in hospitalized patients. The pathophysiology of ALI involves complex interactions between the inciting event, such as pneumonia, sepsis or aspiration, and the host immune response resulting in lung protein permeability, impaired resolution of pulmonary oedema, an intense inflammatory response in the injured alveolus and hypoxemia. In multiple preclinical studies, adult stem cells have been shown to be therapeutic due to both the ability to mitigate injury and inflammation through paracrine mechanisms and perhaps to regenerate tissue by virtue of their multi-potency. These characteristics have stimulated intensive research efforts to explore the possibility of using stem or progenitor cells for the treatment of lung injury. A variety of stem or progenitor cells have been isolated, characterized and tested experimentally in preclinical animal models of ALI. However, questions remain concerning the optimal dose, route and the adult stem or progenitor cell to use. Here, the current mechanisms underlying the therapeutic effect of stem cells in ALI as well as the questions that will arise as clinical trials for ALI are planned are reviewed.

Insult-dependent effect of bone marrow cell therapy on inflammatory response in a murine model of extrapulmonary acute respiratory distress syndrome

Introduction

Administration of bone marrow-derived cells produces beneficial effects in experimental extrapulmonary acute respiratory distress syndrome (ARDS). However, there are controversies regarding the effects of timing of cell administration and initial insult severity on inflammatory response. We evaluated the effects of bone marrow-derived mononuclear cells (BMDMC) in two models of extrapulmonary ARDS once lung morphofunctional changes had already been installed.

Methods

BALB/c mice received lipopolysaccharide (LPS) intraperitoneally (5 mg/kg in 0.5 ml saline) or underwent cecal ligation and puncture (CLP). Control mice received saline intraperitoneally (0.5 ml) or underwent sham surgery. At 24 hours, groups were further randomized to receive saline or BMDMC (2 × 10⁶) intravenously. Lung mechanics, histology, and humoral and cellular parameters of lung inflammation and remodeling were analyzed 1, 3 and 7 days after ARDS induction.

Results

BMDMC therapy led to improved survival in the CLP group, reduced lung elastance, alveolar collapse, tissue and bronchoalveolar lavage fluid cellularity, collagen fiber content, and interleukin-1β and increased chemokine (keratinocyte-derived chemokine and monocyte chemotactic protein-1) expression in lung tissue regardless of the experimental ARDS model. Intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 expression in lung tissue increased after cell therapy depending on the insult (LPS or CLP).

Conclusions

BMDMC therapy at day 1 successfully reduced lung inflammation and remodeling, thus contributing to improvement of lung mechanics in both extrapulmonary ARDS models. Nevertheless, the different inflammatory responses induced by LPS and CLP resulted in distinct effects of BMDMC therapy. These data may be useful in the clinical setting, as they suggest that the type of initial insult plays a key role in the outcome of treatment.

Mesenchymal stem cells in acute lung injury: are they ready for translational medicine?

Acute lung injury (ALI) is a severe clinical condition responsible for high mortality and the development of multiple organ dysfunctions, because of the lack of specific and effective therapies for ALI. Increasing evidence from pre-clinical studies supports preventive and therapeutic effects of mesenchymal stem cells (MSCs, also called mesenchymal stromal cells) in ALI/ARDS (acute respiratory distress syndrome). Therapeutic effects of MSCs were noticed in various delivery approaches (systemic, local, or other locations), multiple origins (bone marrow or other tissues), or different schedules of administrations (before or after the challenges). MSCs could reduce the over-production of inflammatory mediators, leucocyte infiltration, tissue injury and pulmonary failure, and produce a number of benefit factors through interaction with other cells in the process of lung tissue repair. Thus, it is necessary to establish guidelines, standard operating procedures and evaluation criteria for translating MSC-based therapies into clinical application for patients with ALI.

Paracrine effects and heterogeneity of marrow-derived stem/progenitor cells: relevance for the treatment of respiratory diseases

Stem cell-based treatment may represent a hope for the treatment of acute lung injury and pulmonary fibrosis, and other chronic lung diseases, such as cystic fibrosis, asthma and chronic obstructive pulmonary disease (COPD). It is well established in preclinical models that bone marrow-derived stem and progenitor cells exert beneficial effects on inflammation, immune responses and repairing of damage in virtually all lung-borne diseases. While it was initially thought that the positive outcome was due to a direct engraftment of these cells into the lung as endothelial and epithelial cells, paracrine factors are now considered the main mechanism through which stem and progenitor cells exert their therapeutic effect. This knowledge has led to the clinical use of marrow cells in pulmonary hypertension with endothelial progenitor cells (EPCs) and in COPD with mesenchymal stromal (stem) cells (MSCs). Bone marrow-derived stem cells, including hematopoietic stem/progenitor cells, MSCs, EPCs and fibrocytes, encompass a wide array of cell subsets with different capacities of engraftment and injured tissue-regenerating potential. The characterization/isolation of the stem cell subpopulations represents a major challenge to improve the efficacy of transplantation protocols used in regenerative medicine and applied to lung disorders.

Cell therapy demonstrates promise for acute respiratory distress syndrome - but which cell is best?

Acute respiratory distress syndrome (ARDS) constitutes a spectrum of increasingly severe acute respiratory failure and is the leading cause of death and disability in the critically ill. There are no therapies for ARDS, and management remains supportive. Cell therapy, particularly with allogeneic mesenchymal stem/stromal cells (MSCs), has emerged as a promising therapeutic strategy for ARDS, favorably modulating the immune response to reduce lung injury, while facilitating lung regeneration and repair. In this issue of the journal, Rojas and colleagues provide us with a rationale to consider autologous bone marrow-mononuclear cells as an alternative to MSCs for this devastating disease.

Bone marrow mononuclear cell therapy in experimental allergic asthma: intratracheal versus intravenous administration

We hypothesized that the route of administration would impact the beneficial effects of bone marrow-derived mononuclear cell (BMDMC) therapy on the remodelling process of asthma. C57BL/6 mice were randomly assigned to two main groups. In the OVA group, mice were sensitized and challenged with ovalbumin, while the control group received saline using the same protocol. Twenty-four hours before the first challenge, control and OVA animals were further randomized into three subgroups to receive saline (SAL), BMDMCs intravenously (2×10(6)), or BMDMCs intratracheally (2×10(6)). The following changes were induced by BMDMC therapy in OVA mice regardless of administration route: reduction in resistive and viscoelastic pressures, static elastance, eosinophil infiltration, collagen fibre content in airways and lung parenchyma; and reduction in the levels of interleukin (IL)-4, IL-13, transforming growth factor-β and vascular endothelial growth factor. In conclusion, BMDMC modulated inflammatory and remodelling processes regardless of administration route in this experimental model of allergic asthma.

Adipose lineage specification of bone marrow-derived myeloid cells

We have reported the production of white adipocytes in adipose tissue from hematopoietic progenitors arising from bone marrow. However, technical challenges have hindered detection of this adipocyte population by certain other laboratories. These disparate results highlight the need for sensitive and definitive techniques to identify bone marrow progenitor (BMP)-derived adipocytes. In these studies we exploited new models and methods to enhance detection of this adipocyte population. Here we showed that confocal microscopy with spectrum acquisition could effectively identify green fluorescent protein (GFP) positive BMP-derived adipocytes by matching their fluorescence spectrum to that of native GFP. Likewise, imaging flow cytometry made it possible to visualize intact unilocular and multilocular GFP-positive BMP-derived adipocytes and distinguished them from non-fluorescent adipocytes and cell debris in the cytometer flow stream. We also devised a strategy to detect marker genes in flow-enriched adipocytes from which stromal cells were excluded. This technique also proved to be an efficient means for detecting genetically labeled adipocytes and should be applicable to models in which marker gene expression is low or absent. Finally, in vivo imaging of mice transplanted with BM from adipocyte-targeted luciferase donors showed a time-dependent increase in luciferase activity, with the bulk of luciferase activity confined to adipocytes rather than stromal cells. These results confirmed and extended our previous reports and provided proof-of-principle for sensitive techniques and models for detection and study of these unique cells.

Monocytes control second-phase neutrophil emigration in established lipopolysaccharide-induced murine lung injury

RATIONALE

Acute lung injury (ALI) is an important cause of morbidity and mortality, with no currently effective pharmacological therapies. Neutrophils have been specifically implicated in the pathogenesis of ALI, and there has been significant research into the mechanisms of early neutrophil recruitment, but those controlling the later phases of neutrophil emigration that characterize disease are poorly understood.

OBJECTIVES

To determine the influence of peripheral blood monocytes (PBMs) in established ALI.

METHODS

In a murine model of LPS-induced ALI, three separate models of conditional monocyte ablation were used: systemic liposomal clodronate (sLC), inducible depletion using CD11b diphtheria toxin receptor (CD11b DTR) transgenic mice, and antibody-dependent ablation of CCR2(hi) monocytes.

MEASUREMENTS AND MAIN RESULTS

PBMs play a critical role in regulating neutrophil emigration in established murine LPS-induced lung injury. Gr1(hi) and Gr1(lo) PBM subpopulations contribute to this process. PBM depletion is associated with a significant reduction in measures of lung injury. The specificity of PBM depletion was demonstrated by replenishment studies in which the effects were reversed by systemic PBM infusion but not by systemic or local pulmonary infusion of mature macrophages or lymphocytes.

CONCLUSIONS

These results suggest that PBMs, or the mechanisms by which they influence pulmonary neutrophil emigration, could represent therapeutic targets in established ALI.

Protective effects of bone marrow mononuclear cell therapy on lung and heart in an elastase-induced emphysema model

We hypothesized that bone marrow-derived mononuclear cell (BMDMC) therapy protects the lung and consequently the heart in experimental elastase-induced emphysema. Twenty-four female C57BL/6 mice were intratracheally instilled with saline (C group) or porcine pancreatic elastase (E group) once a week during 4 weeks. C and E groups were randomized into subgroups receiving saline (SAL) or male BMDMCs (2 × 10(6), CELL) intravenously 3h after the first saline or elastase instillation. Compared to E-SAL group, E-CELL mice showed, at 5 weeks: lower mean linear intercept, neutrophil infiltration, elastolysis, collagen fiber deposition in alveolar septa and pulmonary vessel wall, lung cell apoptosis, right ventricle wall thickness and area, higher endothelial growth factor and insulin-like growth factor mRNA expressions in lung tissue, and reduced platelet-derived growth factor, transforming growth factor-β, and caspase-3 expressions. In conclusion, BMDMC therapy was effective at modulating the inflammatory and remodeling processes in the present model of elastase-induced emphysema.

Mechanisms of cellular therapy in respiratory diseases

PURPOSE

Stem cells present a variety of clinical implications in the lungs. According to their origin, these cells can be divided into embryonic and adult stem cells; however, due to the important ethical and safety limitations that are involved in the embryonic stem cell use, most studies have chosen to focus on adult stem cell therapy. This article aims to present and clarify the recent advances in the field of stem cell biology, as well as to highlight the effects of mesenchymal stem cell (MSC) therapy in the context of acute lung injury/acute respiratory distress syndrome and chronic disorders such as lung fibrosis and chronic obstructive pulmonary disease.

METHODS

For this purpose, we performed a critical review of adult stem cell therapies, covering the main clinical and experimental studies published in Pubmed databases in the past 11 years. Different characteristics were extracted from these articles, such as: the experimental model, strain, cellular type and administration route used as well as the positive or negative effects obtained.

RESULTS

There is evidence for beneficial effects of MSC on lung development, repair, and remodeling. The engraftment in the injured lung does not occur easily, but several studies report that paracrine factors can be effective in reducing inflammation and promoting tissue repair. MSC releases several growth factors and anti-inflammatory cytokines that regulate endothelial and epithelial permeability and reduce the severity of inflammation.

CONCLUSION

A better understanding of the mechanisms that control cell division and differentiation, as well as of their paracrine effects, is required to enable the optimal use of bone marrow-derived stem cell therapy to treat human respiratory diseases.

Bioreactor for the long-term culture of lung tissue

In this article we describe the design and validation of a bioreactor for the in vitro culture of whole rodent lung tissue. Many current systems only enable large segments of lung tissue to be studied ex vivo for up to a few hours in the laboratory. This limitation restricts the study of pulmonary biology in controlled laboratory settings, and also impacts the ability to reliably culture engineered lung tissues in the laboratory. Therefore, we designed, built, and validated a bioreactor intended to provide sufficient nutrient supply and mechanical stimulation to support cell survival and differentiation in cultured lung tissue. We also studied the effects of perfusion and ventilation on pulmonary cell survival and maintenance of cell differentiation state. The final bioreactor design described herein is capable of supporting the culture of whole native lung tissue for up to 1 week in the laboratory, and offers promise in the study of pulmonary biology and the development of engineered lung tissues in the laboratory.