Healthy versus inflamed lung environments differentially affect mesenchymal stromal cells

The impact of the inflammatory pulmonary microenvironment on the behavior and function of mesenchymal stromal cells

INTRODUCTION

Acute respiratory distress syndrome is characterized by the dysregulation and activation of several inflammatory pathways which lead to widespread inflammation in the lungs. Presently, direct therapy is unavailable and the use of mesenchymal stromal cells as a direct therapy has been proposed, as early-phase studies have shown promise.

AREAS COVERED

MSCs exert various therapeutic effects on the inflammatory microenvironment, such as anti-microbial effects, restoration of the alveolar-capillary barrier, and exuding various anti-inflammatory effects. However, to exert these effects MSCs need to be submitted to specific external stimuli which can affect their immunomodulation, survival, migration and metabolic state. This review references several articles found through targeted searches in PubMed [Accessed between November 2024 and March 2025], for key terms such as 'mesenchymal stromal cells', 'inflammatory microenvironment', anti-inflammatory', 'metabolism', and 'immunomodulation'.

EXPERT OPINION

The advancement of MSCs therapy in the treatment of ARDS has not progressed as effectively as one might have anticipated. Several clinical findings have established patient subgroups based on inflammatory cytokine profiles and severity of ARDS. This variation in patients may influence the clinical efficacy of MSCs and instead of concluding that MSCs therapy is not worth pursuing, more research is needed to develop an appropriate therapy.

Extracellular Vesicles Derived from Mesenchymal Stromal Cells Reduce Pseudomonas aeruginosa Lung Infection and Inflammation in Mice

The World Health Organization and the U.S. Centers for Disease Control and Prevention have reported that antibiotic resistant infections with Pseudomonas aeruginosa present a significant health risk world-wide. In the genetic disease Cystic Fibrosis (CF), chronic antibiotic resistant Pseudomonas lung infections and persistent inflammation remain the leading causes of morbidity and mortality. While highly effective modulator therapy (HEMT) dramatically improves lung function in CF, they fail to eradicate chronic infections or eliminate the associated hyperinflammatory state. Thus, there is an urgent need for innovative therapies that can simultaneously eliminate antibiotic resistant P. aeruginosa lung infection and the attendant hyperinflammatory lung environment. Mesenchymal stromal cell-derived extracellular vesicles (MSC EVs) represent a promising solution, offering potent anti-inflammatory, immunomodulatory, and antimicrobial properties while being safe and non-toxic. This study demonstrates using a CF mouse model of infection that MSC EVs reduce acute P. aeruginosa lung infection and inflammation. MSC EVs reduced Pseudomonas burden, immune cell infiltration, and pro-inflammatory cytokine levels. As the first investigation of MSC EVs in CF, this research underscores the dual effects of MSC EVs; mitigating inflammation and reducing bacterial burden. These findings mark an important advancement in antimicrobial therapy, addressing the unmet need for reducing antibiotic resistant infections and hyperinflammation for people with CF as well as the multitude of others with chronic, antibiotic resistant P. aeruginosa lung infections.

GRAPHICAL ABSTRACT

NEW AND NOTEWORTHY

This is the first study demonstrating the ability of Mesenchymal Stromal Cell Extracellular Vesicles (MSC EVs) to reduce Pseudomonas aeruginosa burden and inflammation in a CF mouse model of infection.

Proinflammatory cytokines sensitise mesenchymal stromal cells to apoptosis

Mesenchymal stromal cells (MSCs) exert broad therapeutic effects across a range of inflammatory diseases. Their mechanism of action has largely been attributed to paracrine signalling, orchestrated by an array of factors produced by MSCs that are collectively termed the "secretome". Strategies to enhance the release of these soluble factors by pre-exposure to inflammatory cytokines, a concept known as "licensing", is thought to provide a means of enhancing MSC efficacy. Yet, recent evidence shows that intravenously infused MSCs entrapped within the lungs undergo apoptosis, and their subsequent clearance by host phagocytes is essential for their therapeutic efficacy. We therefore sought to clarify the mechanisms governing regulated cell death in MSCs and how exposure to inflammatory cytokines impacts this process. Our results show that MSCs are relatively resistant to cell death induced via the extrinsic pathway of apoptosis, as well as stimuli that induce necroptosis, a form of regulated inflammatory cell death. Instead, efficient killing of MSCs required triggering of the mitochondrial pathway of apoptosis, via inhibition of the pro-survival proteins MCL-1 and BCL-XL. Apoptotic bodies were readily released by MSCs during cell disassembly, a process that was inhibited in vitro and in vivo when the apoptotic effectors BAK and BAX were genetically deleted. Licensing of MSCs by pre-exposure to the inflammatory cytokines TNF and IFN-γ increased the sensitivity of MSCs to intrinsic apoptosis in vitro and accelerated their in vivo clearance by host cells within the lungs after intravenous infusion. Taken together, our study demonstrates that inflammatory "licensing" of MSCs facilitates cell death by increasing their sensitivity to triggers of the intrinsic pathway of apoptosis and accelerating the kinetics of apoptotic cell disassembly.

Human mesenchymal stem cell therapy: Potential advances for reducing cystic fibrosis infection and organ inflammation

Innovation in cystic fibrosis (CF) supportive care, including implementing new antimicrobial agents, improved physiotherapy, and highly effective modulators therapy, has advanced patient survival into the 4th and 5th decades of life. However, even with these remarkable improvements in therapy, CF patients continue to suffer from pulmonary infection and other visceral organ complications associated with long-term deficient cystic fibrosis transmembrane conductance regulator (CFTR) expression. Human mesenchymal stem cells (MSCs) have been utilized in tissue engineering based upon their capacity to provide structural components of mesenchymal tissues. An alternative role of MSCs, however is their versatile utilization as cell-based infusion powerhouses due to the unique capacity to deliver milieu specific soluble biologic factors, promoting immune supportive antimicrobial and anti-inflammatory potency. MSCs derived from umbilical cord blood, bone marrow, adipose and other tissues can be expanded in ex vivo using good manufacturing procedure facilities for a safe, unique therapeutic to reduce and limit CF infection and facilitate the resolution of multi-organ inflammation. In our efforts, we conducted extensive preclinical development and validation of an allogeneic derived bone marrow derived MSC product in preparation for a clinical trial in CF. In this process, potency models were developed to ensure the functional capacity of the MSC product to provide clinical benefit. In vitro, murine in vivo and patient tissue ex vivo potency models were utilized to follow MSC anti-infective and anti-inflammatory potency associated with the CFTR deficient environment. We showed in our "First in CF" clinical trial that the allogeneic MSCs obtained from healthy volunteer bone marrow samples were safe. The advent of improved CF care measures and exciting new small molecules has changed the survival and morbidity phenotype of patients with CF, however, there are CF patients who cannot tolerate or have genotypes that are non-responsive to modulators. Additionally, even with the small molecule therapy, CF patients are living longer, but without genetic correction, with the CF disease manifestation aggravated by the continuance of pre-existing CFTR-associated clinical issues such as ongoing inflammation. MSCs secrete bio-active factors that enhance and protect tissue function and can promote "self-immune" regulation. These properties can provide therapeutic support for the traditional and changing face of CF disease clinical complications. Further, MSC-derived bio-active factors can directly mitigate colonizing pathogens' survival by producing antimicrobial peptides (AMPs) which change the pathogen surface and increase host recognition, elimination, and sensitivity to antibiotics. Herein, we review the potential of MSC therapeutics for treating many facets of CF, emphasizing the potential for providing great additive therapeutics for managing morbidity and quality of life.

The ARDS microenvironment enhances MSC-induced repair via VEGF in experimental acute lung inflammation

Clinical trials investigating the potential of mesenchymal stromal cells (MSCs) for the treatment of inflammatory diseases, such as acute respiratory distress syndrome (ARDS), have been disappointing, with less than 50% of patients responding to treatment. Licensed MSCs show enhanced therapeutic efficacy in response to cytokine-mediated activation signals. There are two distinct sub-phenotypes of ARDS: hypo- and hyper-inflammatory. We hypothesized that pre-licensing MSCs in a hyper-inflammatory ARDS environment would enhance their therapeutic efficacy in acute lung inflammation (ALI). Serum samples from patients with ARDS were segregated into hypo- and hyper-inflammatory categories based on interleukin (IL)-6 levels. MSCs were licensed with pooled serum from patients with hypo- or hyper-inflammatory ARDS or healthy serum controls. Our findings show that hyper-inflammatory ARDS pre-licensed MSC conditioned medium (MSC-CMHyper) led to a significant enrichment in tight junction expression and enhanced barrier integrity in lung epithelial cells in vitro and in vivo in a vascular endothelial growth factor (VEGF)-dependent manner. Importantly, while both MSC-CMHypo and MSC-CMHyper significantly reduced IL-6 and tumor necrosis factor alpha (TNF-α) levels in the bronchoalveolar lavage fluid (BALF) of lipopolysaccharide (LPS)-induced ALI mice, only MSC-CMHyper significantly reduced lung permeability and overall clinical outcomes including weight loss and clinical score. Thus, the hypo- and hyper-inflammatory ARDS environments may differentially influence MSC cytoprotective and immunomodulatory functions.

The Effects of the Pneumonia Lung Microenvironment on MSC Function

BACKGROUND

Despite promise in preclinical models of acute respiratory distress syndrome (ARDS), mesenchymal stem cells (MSC) have failed to translate to therapeutic benefit in clinical trials. The MSC is a live cell medicine and interacts with the patient's disease state. Here, we explored this interaction, seeking to devise strategies to enhance MSC therapeutic function.

METHODS

Human bone-marrow-derived MSCs were exposed to lung homogenate from healthy and E. coli-induced ARDS rat models. Apoptosis and functional assays of the MSCs were performed.

RESULTS

The ARDS model showed reduced arterial oxygenation, decreased lung compliance and an inflammatory microenvironment compared to controls. MSCs underwent more apoptosis after stimulation by lung homogenate from controls compared to E. coli, which may explain why MSCs persist longer in ARDS subjects after administration. Changes in expression of cell surface markers and cytokines were associated with lung homogenate from different groups. The anti-microbial effects of MSCs did not change with the stimulation. Moreover, the conditioned media from lung-homogenate-stimulated MSCs inhibited T-cell proliferation.

CONCLUSIONS

These findings suggest that the ARDS microenvironment plays an important role in the MSC's therapeutic mechanism of action, and changes can inform strategies to modulate MSC-based cell therapy for ARDS.

Endothelial cell-derived extracellular vesicles modulate the therapeutic efficacy of mesenchymal stem cells through IDH2/TET pathway in ARDS

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a severe and fatal disease. Although mesenchymal stem cell (MSC)-based therapy has shown remarkable efficacy in treating ARDS in animal experiments, clinical outcomes have been unsatisfactory, which may be attributed to the influence of the lung microenvironment during MSC administration. Extracellular vesicles (EVs) derived from endothelial cells (EC-EVs) are important components of the lung microenvironment and play a crucial role in ARDS. However, the effect of EC-EVs on MSC therapy is still unclear. In this study, we established lipopolysaccharide (LPS) - induced acute lung injury model to evaluate the impact of EC-EVs on the reparative effects of bone marrow-derived MSC (BM-MSC) transplantation on lung injury and to unravel the underlying mechanisms.

METHODS

EVs were isolated from bronchoalveolar lavage fluid of mice with LPS - induced acute lung injury and patients with ARDS using ultracentrifugation. and the changes of EC-EVs were analysed using nanoflow cytometry analysis. In vitro assays were performed to establish the impact of EC-EVs on MSC functions, including cell viability and migration, while in vivo studies were performed to validate the therapeutic effect of EC-EVs on MSCs. RNA-Seq analysis, small interfering RNA (siRNA), and a recombinant lentivirus were used to investigate the underlying mechanisms.

RESULTS

Compared with that in non-ARDS patients, the quantity of EC-EVs in the lung microenvironment was significantly greater in patients with ARDS. EVs derived from lipopolysaccharide-stimulated endothelial cells (LPS-EVs) significantly decreased the viability and migration of BM-MSCs. Furthermore, engrafting BM-MSCs pretreated with LPS-EVs promoted the release of inflammatory cytokines and increased pulmonary microvascular permeability, aggravating lung injury. Mechanistically, LPS-EVs reduced the expression level of isocitrate dehydrogenase 2 (IDH2), which catalyses the formation of α-ketoglutarate (α-KG), an intermediate product of the tricarboxylic acid (TCA) cycle, in BM-MSCs. α-KG is a cofactor for ten-eleven translocation (TET) enzymes, which catalyse DNA hydroxymethylation in BM-MSCs.

CONCLUSIONS

This study revealed that EC-EVs in the lung microenvironment during ARDS can affect the therapeutic efficacy of BM-MSCs through the IDH2/TET pathway, providing potential strategies for improving the therapeutic efficacy of MSC-based therapy in the clinic.

Tiny Guides, Big Impact: Focus on the Opportunities and Challenges of miR-Based Treatments for ARDS

Acute Respiratory Distress Syndrome (ARDS) is characterized by lung inflammation and increased membrane permeability, which represents the leading cause of mortality in ICUs. Mechanical ventilation strategies are at the forefront of supportive approaches for ARDS. Recently, an increasing understanding of RNA biology, function, and regulation, as well as the success of RNA vaccines, has spurred enthusiasm for the emergence of novel RNA-based therapeutics. The most common types of RNA seen in development are silencing (si)RNAs, antisense oligonucleotide therapy (ASO), and messenger (m)RNAs that collectively account for 80% of the RNA therapeutics pipeline. These three RNA platforms are the most mature, with approved products and demonstrated commercial success. Most recently, miRNAs have emerged as pivotal regulators of gene expression. Their dysregulation in various clinical conditions offers insights into ARDS pathogenesis and offers the innovative possibility of using microRNAs as targeted therapy. This review synthesizes the current state of the literature to contextualize the therapeutic potential of miRNA modulation. It considers the potential for miR-based therapeutics as a nuanced approach that incorporates the complexity of ARDS pathophysiology and the multifaceted nature of miRNA interactions.

Biomass-related PM2.5 induced inflammatory microenvironment via IL-17F/IL-17RC axis

Biomass exposure is a significant environmental risk factor for COPD, but the underlying mechanisms have not yet been fully elucidated. Inflammatory microenvironment has been shown to drive the development of many chronic diseases. Pollution exposure can cause increased levels of inflammatory factors in the lungs, leading to an inflammatory microenvironment which is prevalent in COPD. Our findings revealed that IL-17F was elevated in COPD, while exposure to biomass led to increased expression of IL-17F in both alveolar epithelial and macrophage cells in mice. Blocking IL-17F could alleviate the lung inflammation induced by seven days of biomass exposure in mice. We employed a transwell co-culture system to simulate the microenvironment and investigate the interactions between MLE-12 and MH-S cells. We demonstrated that anti-IL-17F antibody attenuated the inflammatory responses induced by BRPM2.5 in MLE-12 and MH-S co-cultured with BRPM2.5-MLE-12, which reduced inflammatory changes in microenvironment. We found that IL-17RC, an important receptor for IL-17F, played a key role in the interactions. Knockout of IL-17RC in MH-S resulted in inhibited IL-17F signaling and attenuated inflammatory response after MH-S co-culture with BRPM2.5-MLE-12. Our investigation suggests that BRPM2.5 induces lung epithelial-macrophage interactions via IL-17F/IL-17RC axis regulating the inflammatory response. These results may provide a novel strategy for effective prevention and treatment of biomass-related COPD.

The MSC-EV-microRNAome: A Perspective on Therapeutic Mechanisms of Action in Sepsis and ARDS

Mesenchymal stromal cells (MSCs) and MSC-derived extracellular vesicles (EVs) have emerged as innovative therapeutic agents for the treatment of sepsis and acute respiratory distress syndrome (ARDS). Although their potential remains undisputed in pre-clinical models, this has yet to be translated to the clinic. In this review, we focused on the role of microRNAs contained in MSC-derived EVs, the EV microRNAome, and their potential contribution to therapeutic mechanisms of action. The evidence that miRNA transfer in MSC-derived EVs has a role in the overall therapeutic effects is compelling. However, several questions remain regarding how to reconcile the stochiometric issue of the low copy numbers of the miRNAs present in the EV particles, how different miRNAs delivered simultaneously interact with their targets within recipient cells, and the best miRNA or combination of miRNAs to use as therapy, potency markers, and biomarkers of efficacy in the clinic. Here, we offer a molecular genetics and systems biology perspective on the function of EV microRNAs, their contribution to mechanisms of action, and their therapeutic potential.

Human macrophage migration inhibitory factor potentiates mesenchymal stromal cell efficacy in a clinically relevant model of allergic asthma

Current asthma therapies focus on reducing symptoms but fail to restore existing structural damage. Mesenchymal stromal cell (MSC) administration can ameliorate airway inflammation and reverse airway remodeling. However, differences in patient disease microenvironments seem to influence MSC therapeutic effects. A polymorphic CATT tetranucleotide repeat at position 794 of the human macrophage migration inhibitory factor (hMIF) gene has been associated with increased susceptibility to and severity of asthma. We investigated the efficacy of human MSCs in high- vs. low-hMIF environments and the impact of MIF pre-licensing of MSCs using humanized MIF mice in a clinically relevant house dust mite (HDM) model of allergic asthma. MSCs significantly attenuated airway inflammation and airway remodeling in high-MIF-expressing CATT7 mice but not in CATT5 or wild-type littermates. Differences in efficacy were correlated with increased MSC retention in the lungs of CATT7 mice. MIF licensing potentiated MSC anti-inflammatory effects at a previously ineffective dose. Mechanistically, MIF binding to CD74 expressed on MSCs leads to upregulation of cyclooxygenase 2 (COX-2) expression. Blockade of CD74 or COX-2 function in MSCs prior to administration attenuated the efficacy of MIF-licensed MSCs in vivo. These findings suggest that MSC administration may be more efficacious in severe asthma patients with high MIF genotypes (CATT6/7/8).

Apoptotic Vesicles of MSCs: The Natural Therapeutic Agents and Bio-Vehicles for Targeting Drug Delivery

Mesenchymal stem cell (MSC)-based therapies are increasingly recognized as promising cellular therapeutics and show the ability to treat various diseases. However, the underlying mechanism is not fully elucidated. Some recent studies have shown an unexpected result whereby MSCs undergo rapid apoptosis following administration but still exert therapeutic effects in some disease treatments. Such a therapeutic mechanism is believed to associate with the released apoptotic vesicles from apoptotic MSCs (MSC-ApoVs). This finding inspires a novel therapeutic strategy for using MSC-ApoVs for disease treatment. The present review aims to summarize the biogenesis, physiological functions, therapeutic potentials, and related mechanisms of apoptotic vesicles in MSC-based therapy. In addition, the potential applications of MSC-ApoVs as natural therapeutic agents and natural drug delivery vehicles are proposed and highlighted. The present review is hoped to provide a general understanding of MSC-ApoVs in disease treatment and inspire potential applications in targeted drug delivery.

Functional enhancement strategies to potentiate the therapeutic properties of mesenchymal stromal cells for respiratory diseases

Respiratory diseases remain a major health concern worldwide because they subject patients to considerable financial and psychosocial burdens and result in a high rate of morbidity and mortality. Although significant progress has been made in understanding the underlying pathologic mechanisms of severe respiratory diseases, most therapies are supportive, aiming to mitigate symptoms and slow down their progressive course but cannot improve lung function or reverse tissue remodeling. Mesenchymal stromal cells (MSCs) are at the forefront of the regenerative medicine field due to their unique biomedical potential in promoting immunomodulation, anti-inflammatory, anti-apoptotic and antimicrobial activities, and tissue repair in various experimental models. However, despite several years of preclinical research on MSCs, therapeutic outcomes have fallen far short in early-stage clinical trials for respiratory diseases. This limited efficacy has been associated with several factors, such as reduced MSC homing, survival, and infusion in the late course of lung disease. Accordingly, genetic engineering and preconditioning methods have emerged as functional enhancement strategies to potentiate the therapeutic actions of MSCs and thus achieve better clinical outcomes. This narrative review describes various strategies that have been investigated in the experimental setting to functionally potentiate the therapeutic properties of MSCs for respiratory diseases. These include changes in culture conditions, exposure of MSCs to inflammatory environments, pharmacological agents or other substances, and genetic manipulation for enhanced and sustained expression of genes of interest. Future directions and challenges in efficiently translating MSC research into clinical practice are discussed.

Early Stage Professionals Committee Proceedings from the International Society for Cell & Gene Therapy 2022 Annual Meeting

In this Committee Proceedings, representatives from the Early Stage Professional (ESP) committee highlight the innovative discoveries and key take-aways from oral presentations at the 2022 International Society for Cell and Gene Therapy (ISCT) Annual Meeting that cover the following subject categories: Immunotherapy, Exosomes and Extracellular Vesicles, HSC/Progenitor Cells and Engineering, Mesenchymal Stromal Cells, and ISCT Late-Breaking Abstracts.

What is the need and why is it time for innovative models for understanding lung repair and regeneration?

Advances in tissue engineering continue at a rapid pace and have provided novel methodologies and insights into normal cell and tissue homeostasis, disease pathogenesis, and new potential therapeutic strategies. The evolution of new techniques has particularly invigorated the field and span a range from novel organ and organoid technologies to increasingly sophisticated imaging modalities. This is particularly relevant for the field of lung biology and diseases as many lung diseases, including chronic obstructive pulmonary disease (COPD) and idiopathic fibrosis (IPF), among others, remain incurable with significant morbidity and mortality. Advances in lung regenerative medicine and engineering also offer new potential avenues for critical illnesses such as the acute respiratory distress syndrome (ARDS) which also continue to have significant morbidity and mortality. In this review, an overview of lung regenerative medicine with focus on current status of both structural and functional repair will be presented. This will serve as a platform for surveying innovative models and techniques for study, highlighting the need and timeliness for these approaches.

Nestin prevents mesenchymal stromal cells from apoptosis in LPS-induced lung injury via inhibition of unfolded protein response sensor IRE1α

The clinical applications of MSC therapy have been intensely investigated in acute respiratory distress syndrome. However, clinical studies have fallen short of expectations despite encouraging preclinical results. One of the key problems is that transplanted stem cells can hardly survive in the harsh inflammatory environment. Prolonging the survival of transplanted MSCs might be a promising strategy to enhance the therapeutic efficacy of MSC therapy. Here, we identified Nestin, a class VI intermediate filament, as a positive regulator of MSC survival in the inflammatory microenvironment. We showed that Nestin knockout led to a significant increase of MSC apoptosis, which hampered the therapeutic effects in an LPS-induced lung injury model. Mechanistically, Nestin knockout induced a significant elevation of endoplasmic reticulum (ER) stress level. Further investigations showed that Nestin could bind to IRE1α and inhibit ER stress-induced apoptosis under stress. Furthermore, pretreatment with IRE1α inhibitor 4μ8C improved MSC survival and improved therapeutic effect. Our data suggests that Nestin enhances stem cell survival after transplantation by inhibiting ER stress-induced apoptosis, improving protection, and repair of the lung inflammatory injury.

MSCs interaction with the host lung microenvironment: An overlooked aspect?

Mesenchymal stromal cells (MSCs) were identified more than 50 years ago, and research advances have promoted the translation of pre-clinical studies into clinical settings in several diseases. However, we are only starting to uncover the local factors that regulate cell phenotype, cell function, and cell viability across tissues following administration in different diseases. Advances in pre-clinical and translational studies suggest that the host environment, especially inflammatory active environments, plays a significant role in directing the infused MSCs towards different phenotypes with different functions. This can significantly effect their therapeutic efficacy. One way to study this interaction between the host environment and the infused cells is to expose MSCs ex vivo to patient samples such as serum or bronchoalveolar lavage fluid. Using this approach, it has been demonstrated that MSCs are very sensitive to different host factors such as pathogens, inflammatory cytokines, and extra cellular matrix properties. By understanding how different local host factors effect MSC function it will open possibilities to select specific patient sub-groups that are more likely to respond to this type of treatment and will also open possibilities to prime the local host environment to increase viability and to enrich for a specific MSC phenotype. Here, we aim to review the current understanding of the interaction of MSCs with the host microenvironment. To narrow the scope of this mini review, the focus will be on the pulmonary microenvironment, with a specific focus on the diseases acute respiratory distress syndrome (ARDS) and cystic fibrosis (CF).

Therapeutic Benefits of Mesenchymal Stem Cells in Acute Respiratory Distress Syndrome: Potential Mechanisms and Challenges

Acute respiratory distress syndrome (ARDS) presents as a form of acute respiratory failure resulting from non-cardiogenic pulmonary edema due to excessive alveolocapillary permeability, which may be pulmonary or systemic in origin. In the last 3 years, the coronavirus disease 2019 pandemic has resulted in an increase in ARDS cases and highlighted the challenges associated with this syndrome, as well as the unacceptably high mortality rates and lack of effective treatments. Currently, clinical treatment remains primarily supportive, including mechanical ventilation and drug-based therapy. Mesenchymal stem cell (MSC) therapies are emerging as a promising intervention in patients with ARDS and have promising therapeutic effects and safety. The therapeutic mechanisms include modifying the immune response and assisting with tissue repair. This review provides an overview of the general properties of MSCs and outlines their role in mitigating lung injury and promoting tissue repair in ARDS. Finally, we summarize the current challenges in the study of translational MSC research and identify avenues by which the discipline may progress in the coming years.

Mesenchymal stromal cells-derived extracellular vesicles reprogramme macrophages in ARDS models through the miR-181a-5p-PTEN-pSTAT5-SOCS1 axis

RATIONALE

A better understanding of the mechanism of action of mesenchymal stromal cells (MSCs) and their extracellular vesicles (EVs) is needed to support their use as novel therapies for acute respiratory distress syndrome (ARDS). Macrophages are important mediators of ARDS inflammatory response. Suppressor of cytokine signalling (SOCS) proteins are key regulators of the macrophage phenotype switch. We therefore investigated whether SOCS proteins are involved in mediation of the MSC effect on human macrophage reprogramming.

METHODS

Human monocyte-derived macrophages (MDMs) were stimulated with lipopolysaccharide (LPS) or plasma samples from patients with ARDS (these samples were previously classified into hypo-inflammatory and hyper-inflammatory phenotype) and treated with MSC conditioned medium (CM) or EVs. Protein expression was measured by Western blot. EV micro RNA (miRNA) content was determined by miRNA sequencing. In vivo: LPS-injured C57BL/6 mice were given EVs isolated from MSCs in which miR-181a had been silenced by miRNA inhibitor or overexpressed using miRNA mimic.

RESULTS

EVs were the key component of MSC CM responsible for anti-inflammatory modulation of human macrophages. EVs significantly reduced secretion of tumour necrosis factor-α and interleukin-8 by LPS-stimulated or ARDS plasma-stimulated MDMs and this was dependent on SOCS1. Transfer of miR-181a in EVs downregulated phosphatase and tensin homolog (PTEN) and subsequently activated phosphorylated signal transducer and activator of transcription 5 (pSTAT5) leading to upregulation of SOCS1 in macrophages. In vivo, EVs alleviated lung injury and upregulated pSTAT5 and SOCS1 expression in alveolar macrophages in a miR181-dependent manner. Overexpression of miR-181a in MSCs significantly enhanced therapeutic efficacy of EVs in this model.

CONCLUSION

miR-181a-PTEN-pSTAT5-SOCS1 axis is a novel pathway responsible for immunomodulatory effect of MSC EVs in ARDS.

Anti-Inflammatory and Anti-Fibrotic Effect of Immortalized Mesenchymal-Stem-Cell-Derived Conditioned Medium on Human Lung Myofibroblasts and Epithelial Cells

Idiopathic pulmonary fibrosis (IPF) is caused by progressive lung tissue impairment due to extended chronic fibrosis, and it has no known effective treatment. The use of conditioned media (CM) from an immortalized human adipose mesenchymal stem cell line could be a promising therapeutic strategy, as it can reduce both fibrotic and inflammatory responses. We aimed to investigate the anti-inflammatory and anti-fibrotic effect of CM on human pulmonary subepithelial myofibroblasts (hPSM) and on A549 pulmonary epithelial cells, treated with pro-inflammatory or pro-fibrotic mediators. CM inhibited the proinflammatory cytokine-induced mRNA and protein production of various chemokines in both hPSMs and A549 cells. It also downregulated the mRNA expression of IL-1α, but upregulated IL-1β and IL-6 mRNA production in both cell types. CM downregulated the pro-fibrotic-induced mRNA expression of collagen Type III and the migration rate of hPSMs, but upregulated fibronectin mRNA production and the total protein collagen secretion. CM's direct effect on the chemotaxis and cell recruitment of immune-associated cells, and its indirect effect on fibrosis through the significant decrease in the migration capacity of hPSMs, makes it a plausible candidate for further development towards a therapeutic treatment for IPF.

Mesenchymal stem/stromal cell-based therapies for severe viral pneumonia: therapeutic potential and challenges

Severe viral pneumonia is a significant cause of morbidity and mortality globally, whether due to outbreaks of endemic viruses, periodic viral epidemics, or the rarer but devastating global viral pandemics. While limited anti-viral therapies exist, there is a paucity of direct therapies to directly attenuate viral pneumonia-induced lung injury, and management therefore remains largely supportive. Mesenchymal stromal/stem cells (MSCs) are receiving considerable attention as a cytotherapeutic for viral pneumonia. Several properties of MSCs position them as a promising therapeutic strategy for viral pneumonia-induced lung injury as demonstrated in pre-clinical studies in relevant models. More recently, early phase clinical studies have demonstrated a reassuring safety profile of these cells. These investigations have taken on an added importance and urgency during the COVID-19 pandemic, with multiple trials in progress across the globe. In parallel with clinical translation, strategies are being investigated to enhance the therapeutic potential of these cells in vivo, with different MSC tissue sources, specific cellular products including cell-free options, and strategies to ‘licence’ or ‘pre-activate’ these cells, all being explored. This review will assess the therapeutic potential of MSC-based therapies for severe viral pneumonia. It will describe the aetiology and epidemiology of severe viral pneumonia, describe current therapeutic approaches, and examine the data suggesting therapeutic potential of MSCs for severe viral pneumonia in pre-clinical and clinical studies. The challenges and opportunities for MSC-based therapies will then be considered.

The Inflammatory Lung Microenvironment; a Key Mediator in MSC Licensing

Recent clinical trials of mesenchymal stromal cell (MSC) therapy for various inflammatory conditions have highlighted the significant benefit to patients who respond to MSC administration. Thus, there is strong interest in investigating MSC therapy in acute inflammatory lung conditions, such as acute respiratory distress syndrome (ARDS). Unfortunately, not all patients respond, and evidence now suggests that the differential disease microenvironment present across patients and sub-phenotypes of disease or across disease severities influences MSC licensing, function and therapeutic efficacy. Here, we discuss the importance of licensing MSCs and the need to better understand how the disease microenvironment influences MSC activation and therapeutic actions, in addition to the need for a patient-stratification approach.

Effect of mesenchymal stromal cell infusions on lung function in COPD patients with high CRP levels

Background

We previously reported a Phase 1/2 randomized placebo-controlled trial of systemic administration of bone marrow-derived allogeneic MSCs (remestemcel-L) in COPD. While safety profile was good, no functional efficacy was observed. However, in view of growing recognition of effects of inflammatory environments on MSC actions we conducted a post-hoc analysis with stratification by baseline levels of a circulating inflammatory marker, C-reactive protein (CRP) to determine the effects of MSC administration in COPD patients with varying circulating CRP levels.

Methods

Time course of lung function, exercise performance, patient reported responses, and exacerbation frequency following four monthly infusions of remestemcel-L vs. placebo were re-assessed in subgroups based on baseline circulating CRP levels.

Results

In COPD patients with baseline CRP ≥ 4 mg/L, compared to COPD patients receiving placebo (N = 17), those treated with remestemcel-L (N = 12), demonstrated significant improvements from baseline in forced expiratory volume in one second, forced vital capacity, and six minute walk distance at 120 days with treatment differences evident as early as 10 days after the first infusion. Significant although smaller benefits were also detected in those with CRP levels ≥ 2 or ≥ 3 mg/L. These improvements persisted variably over the 2-year observational period. No significant benefits were observed in patient reported responses or number of COPD exacerbations between treatment groups.

Conclusion

In an inflammatory environment, defined by elevated circulating CRP, remestemcel-L administration yielded at least transient meaningful pulmonary and functional improvements. These findings warrant further investigation of potential MSC-based therapies in COPD and other inflammatory pulmonary diseases.

Trial registration: Clinicaltrials.gov NCT00683722.