Extracellular Vesicles from Interferon-γ-primed Human Umbilical Cord Mesenchymal Stromal Cells Reduce Escherichia coli-induced Acute Lung Injury in Rats

Therapeutic Efficacy of Interferon-Gamma and Hypoxia-Primed Mesenchymal Stromal Cells and Their Extracellular Vesicles: Underlying Mechanisms and Potentials in Clinical Translation

Multipotent mesenchymal stromal cells (MSCs) hold promises for cell therapy and tissue engineering due to their self-renewal and differentiation abilities, along with immunomodulatory properties and trophic factor secretion. Extracellular vesicles (EVs) from MSCs offer similar therapeutic effects. However, MSCs are heterogeneous and lead to variable outcomes. In vitro priming enhances MSC performance, improving immunomodulation, angiogenesis, proliferation, and tissue regeneration. Various stimuli, such as cytokines, growth factors, and oxygen tension, can prime MSCs. Two classical priming methods, interferon-gamma (IFN-γ) and hypoxia, enhance MSC immunomodulation, although standardized protocols are lacking. This review discusses priming protocols, highlighting the most commonly used concentrations and durations, along with mechanisms and in vivo therapeutics effects of primed MSCs and their EVs. The feasibility of up-scaling their production was also discussed. The review concluded that priming with IFN-γ or hypoxia (alone or in combination with other factors) boosted the immunomodulation capability of MSCs and their EVs, primarily via the JAK/STAT and PI3K/AKT and Leptin/JAK/STAT and TGF-β/Smad signalling pathways, respectively. Incorporating priming in MSC and EV production enables translation into cell-based or cell-free therapies for various disorders.

Stem Cell Extracellular Vesicles as Anti-SARS-CoV-2 Immunomodulatory Therapeutics: A Systematic Review of Clinical and Preclinical Studies

BACKGROUND

COVID-19 rapidly escalated into a worldwide pandemic with elevated infectivity even from asymptomatic patients. Complications can lead to severe pneumonia and acute respiratory distress syndrome (ARDS), which are the main contributors to death. Because of their regenerative and immunomodulatory capacities, stem cells and their derived extracellular vesicles (EVs) are perceived as promising therapies against severe pulmonary conditions, including those associated with COVID-19. Herein, we evaluate the safety and efficacy of stem cell EVs in treating COVID-19 and complicating pneumonia, acute lung injury, and ARDS. We also cover relevant preclinical studies to recapitulate the current progress in stem cell EV-based therapy.

METHODS

Using PubMed, Cochrane Central Register of Controlled Trials, Scopus, and Web of Science, we searched for all English-language published studies (2000-2023) that used stem cell EVs as a therapy for COVID-19, ARDS, or pneumonia. The risk of bias (ROB) was assessed for all studies.

RESULTS

Forty-eight studies met our inclusion criteria. Various-sized EVs derived from different types of stem cells were reported as a potentially safe and effective therapy to attenuate the cytokine storm induced by COVID-19. EVs alleviated inflammation and regenerated the alveolar epithelium by decreasing apoptosis, proinflammatory cytokines, neutrophil infiltration, and M2 macrophage polarization. They also prevented fibrin production and promoted the production of anti-inflammatory cytokines and endothelial cell junction proteins.

CONCLUSION

Similar to their parental cells, stem cell EVs mediate lung tissue regeneration by targeting multiple pathways and thus hold promise in promoting the recovery of COVID-19 patients and improving the survival rate of severely affected patients.

Manufacturing, quality control, and GLP-grade preclinical study of nebulized allogenic adipose mesenchymal stromal cells-derived extracellular vesicles

BACKGROUND

Human adipose stromal cells-derived extracellular vesicles (haMSC-EVs) have been shown to alleviate inflammation in acute lung injury (ALI) animal models. However, there are few systemic studies on clinical-grade haMSC-EVs. Our study aimed to investigate the manufacturing, quality control (QC) and preclinical safety of clinical-grade haMSC-EVs.

METHODS

haMSC-EVs were isolated from the conditioned medium of human adipose MSCs incubated in 2D containers. Purification was performed by PEG precipitation and differential centrifugation. Characterizations were conducted by nanoparticle tracking analysis, transmission electron microscopy (TEM), Western blotting, nanoflow cytometry analysis, and the TNF-α inhibition ratio of macrophage [after stimulated by lipopolysaccharide (LPS)]. RNA-seq and proteomic analysis with liquid chromatography tandem mass spectrometry (LC-MS/MS) were used to inspect the lot-to-lot consistency of the EV products. Repeated toxicity was evaluated in rats after administration using trace liquid endotracheal nebulizers for 28 days, and respiratory toxicity was evaluated 24 h after the first administration. In vivo therapeutic effects were assessed in an LPS-induced ALI/ acute respiratory distress syndrome (ARDS) rat model.

RESULTS

The quality criteria have been standardized. In a stability study, haMSC-EVs were found to remain stable after 6 months of storage at - 80°C, 3 months at - 20 °C, and 6 h at room temperature. The microRNA profile and proteome of haMSC-EVs demonstrated suitable lot-to-lot consistency, further suggesting the stability of the production processes. Intratracheally administered 1.5 × 108 particles/rat/day for four weeks elicited no significant toxicity in rats. In LPS-induced ALI/ARDS model rats, intratracheally administered haMSC-EVs alleviated lung injury, possibly by reducing the serum level of inflammatory factors.

CONCLUSION

haMSC-EVs, as an off-shelf drug, have suitable stability and lot-to-lot consistency. Intratracheally administered haMSC-EVs demonstrated excellent safety at the tested dosages in systematic preclinical toxicity studies. Intratracheally administered haMSC-EVs improved the lung function and exerted anti-inflammatory effects on LPS-induced ALI/ARDS model rats.

The efficacy of extracellular vesicles for acute lung injury in preclinical animal models: a meta-analysis

BACKGROUND

With the increasing research on extracellular vesicles (EVs), EVs have received widespread attention as biodiagnostic markers and therapeutic agents for a variety of diseases. Stem cell-derived EVs have also been recognized as a new viable therapy for acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). To assess their efficacy, we conducted a meta-analysis of existing preclinical experimental animal models of EVs for ALI treatment.

METHODS

The database was systematically interrogated for pertinent data encompassing the period from January 2010 to April 2022 concerning interventions involving extracellular vesicles (EVs) in animal models of acute lung injury (ALI). The lung injury score was selected as the primary outcome measure for statistical analysis. Meta-analyses were executed utilizing RevMan 5.3 and State15.1 software tools.

RESULTS

The meta-analyses comprised 31 studies, exclusively involving animal models of acute lung injury (ALI), categorized into two cohorts based on the presence or absence of extracellular vesicle (EV) intervention. The statistical outcomes from these two study groups revealed a significant reduction in lung injury scores with the administration of stem and progenitor cell-derived EVs (SMD = -3.63, 95% CI [-4.97, -2.30], P < 0.05). Conversely, non-stem cell-derived EVs were associated with an elevation in lung injury scores (SMD = -4.34, 95% CI [3.04, 5.63], P < 0.05). EVs originating from stem and progenitor cells demonstrated mitigating effects on alveolar neutrophil infiltration, white blood cell counts, total cell counts in bronchoalveolar lavage fluid (BALF), lung wet-to-dry weight ratios (W/D), and total protein in BALF. Furthermore, pro-inflammatory mediators exhibited down-regulation, while anti-inflammatory mediators demonstrated up-regulation. Conversely, non-stem cell-derived EVs exacerbated lung injury.

CONCLUSION

In preclinical animal models of acute lung injury (ALI), the administration of extracellular vesicles (EVs) originating from stem and progenitor cells demonstrably enhances pulmonary function. This ameliorative effect is attributed to the mitigation of pulmonary vascular permeability and the modulation of immune homeostasis, collectively impeding the progression of inflammation. In stark contrast, the utilization of EVs derived from non-stem progenitor cells exacerbates the extent of lung injury. These findings substantiate the potential utility of EVs as a novel therapeutic avenue for addressing acute lung injury.

Therapeutic utility of human umbilical cord-derived mesenchymal stem cells-based approaches in pulmonary diseases: Recent advancements and prospects

Pulmonary diseases across all ages threaten millions of people and have emerged as one of the major public health issues worldwide. For diverse disease conditions, the currently available approaches are focused on alleviating clinical symptoms and delaying disease progression but have not shown significant therapeutic effects in patients with lung diseases. Human umbilical cord-derived mesenchymal stem cells (UC-MSCs) isolated from the human UC have the capacity for self-renewal and multilineage differentiation. Moreover, in recent years, these cells have been demonstrated to have unique advantages in the treatment of lung diseases. We searched the Public Clinical Trial Database and found 55 clinical trials involving UC-MSC therapy for pulmonary diseases, including coronavirus disease 2019, acute respiratory distress syndrome, bronchopulmonary dysplasia, chronic obstructive pulmonary disease, and pulmonary fibrosis. In this review, we summarize the characteristics of these registered clinical trials and relevant published results and explore in depth the challenges and opportunitiesfaced in clinical application. Moreover, the underlying molecular mechanisms involved in UC-MSC-based therapy for pulmonary diseases are also analyzed in depth. In brief, this comprehensive review and detailed analysis of these clinical trials can be expected to provide a scientific reference for future large-scale clinical application.

Extracellular vesicles secreted by primary human bronchial epithelial cells reduce Pseudomonas aeruginosa burden and inflammation in cystic fibrosis mouse lung

Cystic fibrosis (CF) results in a reduction in the volume of airway surface liquid, increased accumulation of viscous mucus, persistent antibiotic-resistant lung infections that cause chronic inflammation, and a decline in lung function. More than 50% of adults with CF are chronically colonized by Pseudomonas aeruginosa (P. aeruginosa), the primary reason for morbidity and mortality in people with CF (pwCF). Although highly effective modulator therapy (HEMT) is an important part of disease management in CF, HEMT does not eliminate P. aeruginosa or lung inflammation. Thus, new treatments are required to reduce lung infection and inflammation in CF. In a previous in vitro study, we demonstrated that primary human bronchial epithelial cells (HBECs) secrete extracellular vesicles (EVs) that block the ability of P. aeruginosa to form biofilms by reducing the abundance of several proteins necessary for biofilm formation as well as enhancing the sensitivity of P. aeruginosa to β-lactam antibiotics. In this study, using a CF mouse model of P. aeruginosa infection, we demonstrate that intratracheal administration of EVs secreted by HBEC reduced P. aeruginosa lung burden and several proinflammatory cytokines including IFN-γ, TNF-α, and MIP-1β in bronchoalveolar lavage fluid (BALF), even in the absence of antibiotics. Moreover, EVs decreased neutrophils in BALF. Thus, EVs secreted by HBEC reduce the lung burden of P. aeruginosa, decrease inflammation, and reduce neutrophils in a CF mouse model. These results suggest that HBEC via the secretion of EVs may play an important role in the immune response to P. aeruginosa lung infection.NEW & NOTEWORTHY Our findings show that extracellular vesicles secreted by primary human bronchial epithelial cells significantly reduce Pseudomonas aeruginosa burden, inflammation, and weight loss in a cystic fibrosis mouse model of infection.

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.

Apoptotic bodies inhibit inflammation by PDL1-PD1-mediated macrophage metabolic reprogramming

Apoptosis triggers immunoregulation to prevent and suppress inflammation and autoimmunity. However, the mechanism by which apoptotic cells modulate immune responses remains largely elusive. In the context of allogeneic mesenchymal stem cells (MSCs) transplantation, long-term immunoregulation is observed in the host despite the short survive of the injected MSCs. In this study, utilizing a mouse model of acute lung injury (ALI), we demonstrate that apoptotic bodies (ABs) released by transplanted human umbilical cord MSCs (UC-MSCs) convert the macrophages from a pro-inflammatory to an anti-inflammatory state, thereby ameliorating the disease. Mechanistically, we identify the expression of programmed cell death 1 ligand 1 (PDL1) on the membrane of UC-MSCs-derived ABs, which interacts with programmed cell death protein 1 (PD1) on host macrophages. This interaction leads to the reprogramming of macrophage metabolism, shifting from glycolysis to mitochondrial oxidative phosphorylation via the Erk-dependent pathway in ALI. Importantly, we have reproduced the PDL1-PD1 effects of ABs on metabolic switch using alveolar macrophages from patients with ALI, suggesting the potential clinical implications of developing therapeutic strategies for the patients.

Stem cell-based therapy for COVID-19

While The World Health Organization (WHO) has announced that COVID-19 is no longer a public health emergency of international concern(PHEIC), the risk of reinfection and new emerging variants still makes it crucial to study and work towards the prevention of COVID-19. Stem cell and stem cell-like derivatives have shown some promising results in clinical trials and preclinical studies as an alternative treatment option for the pulmonary illnesses caused by the COVID-19 and can be used as a potential vaccine. In this review, we will systematically summarize the pathophysiological process and potential mechanisms underlying stem cell-based therapy in COVID-19, and the registered COVID-19 clinical trials, and engineered extracellular vesicle as a potential vaccine for preventing COVID-19.

Mesenchymal stromal/stem cells and bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a common complication in preterm infants, leading to chronic respiratory disease. There has been an improvement in perinatal care, but many infants still suffer from impaired branching morphogenesis, alveolarization, and pulmonary capillary formation, causing lung function impairments and BPD. There is an increased risk of respiratory infections, pulmonary hypertension, and neurodevelopmental delays in infants with BPD, all of which can lead to long-term morbidity and mortality. Unfortunately, treatment options for Bronchopulmonary dysplasia are limited. A growing body of evidence indicates that mesenchymal stromal/stem cells (MSCs) can treat various lung diseases in regenerative medicine. MSCs are multipotent cells that can differentiate into multiple cell types, including lung cells, and possess immunomodulatory, anti-inflammatory, antioxidative stress, and regenerative properties. MSCs are regulated by mitochondrial function, as well as oxidant stress responses. Maintaining mitochondrial homeostasis will likely be key for MSCs to stimulate proper lung development and regeneration in Bronchopulmonary dysplasia. In recent years, MSCs have demonstrated promising results in treating and preventing bronchopulmonary dysplasia. Studies have shown that MSC therapy can reduce inflammation, mitochondrial impairment, lung injury, and fibrosis. In light of this, MSCs have emerged as a potential therapeutic option for treating Bronchopulmonary dysplasia. The article explores the role of MSCs in lung development and disease, summarizes MSC therapy's effectiveness in treating Bronchopulmonary dysplasia, and delves into the mechanisms behind this treatment.

Cell culture-derived extracellular vesicles: Considerations for reporting cell culturing parameters

Cell culture-conditioned medium (CCM) is a valuable source of extracellular vesicles (EVs) for basic scientific, therapeutic and diagnostic applications. Cell culturing parameters affect the biochemical composition, release and possibly the function of CCM-derived EVs (CCM-EV). The CCM-EV task force of the Rigor and Standardization Subcommittee of the International Society for Extracellular Vesicles aims to identify relevant cell culturing parameters, describe their effects based on current knowledge, recommend reporting parameters and identify outstanding questions. While some recommendations are valid for all cell types, cell-specific recommendations may need to be established for non-mammalian sources, such as bacteria, yeast and plant cells. Current progress towards these goals is summarized in this perspective paper, along with a checklist to facilitate transparent reporting of cell culturing parameters to improve the reproducibility of CCM-EV research.

Biodistribution of mesenchymal stromal cell-derived extracellular vesicles administered during acute lung injury

BACKGROUND

Mesenchymal stromal cell-derived extracellular vesicles (MSC-EVs) are a promising cell-free therapy for acute lung injury (ALI). To date, no studies have investigated their biodistribution in ALI or discerned the timing of administration for maximal lung targeting, which are crucial considerations for clinical translation. Our study aimed to characterize a mouse model of ALI and establish the distribution kinetics and optimal timing of MSC-EV delivery during lung injury.

METHODS

MSC-EVs were isolated by ultracentrifugation alone (U/C) or tangential flow filtration with ultracentrifugation (TFF-U/C) and characterized by nanoparticle tracking analysis and western blot. A lipopolysaccharide (LPS)-induced mouse model of ALI was established to study the inflammatory response over 72 h. ALI was assessed by histological lung injury score, bronchoalveolar lavage fluid cell count and inflammatory cytokines. For biodistribution studies, ALI mice were intravenously administered fluorescently labeled MSC-EVs to determine the optimal timing of administration and organ-specific biodistribution. Live in vivo and ex vivo fluorescence imaging was conducted at various timepoints post-EV injection.

RESULTS

EVs isolated by either ultracentrifugation alone or TFF-U/C displayed comparable size distribution (~ 50-350 nm) and EV marker expression (CD63/81). TFF-U/C generated a 5.4-fold higher particle concentration and 3.9-fold higher total protein when compared to ultracentrifugation alone. From the inflammatory time-course study, cell count and IL-1β peaked in bronchoalveolar lavage fluid at 24 h after ALI induction. MSC-EVs delivered at 24 h (as opposed to 0.5 h, 5 h or 10 h) after disease induction resulted in a 2.7-4.4-fold higher lung uptake of EVs. Biodistribution studies comparing organ-specific MSC-EV uptake showed progressive lung accumulation up to 48 h post-delivery (threefold higher than the spleen/liver), with a decline at 72 h. Importantly, lung EV fluorescence at 48 h in ALI mice was significantly elevated as compared to control mice. The lung tropism of MSC-EVs was further validated as therapeutically inert EVs derived from HEK293T cells accumulated mainly to the spleen and liver with a 5.5-fold lower distribution to the lungs as compared to MSC-EVs.

CONCLUSION

MSC-EVs exhibit maximal lung accumulation when administered during heightened inflammation at 24 h after ALI induction. This lung tropism suggests that MSC-EVs may serve as a practical rescue treatment for acute inflammatory respiratory conditions.

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.

Bioengineered extracellular vesicles: future of precision medicine for sepsis

Sepsis is a syndromic response to infection and is frequently a final common pathway to death from many infectious diseases worldwide. The complexity and high heterogeneity of sepsis hinder the possibility to treat all patients with the same protocol, requiring personalized management. The versatility of extracellular vesicles (EVs) and their contribution to sepsis progression bring along promises for one-to-one tailoring sepsis treatment and diagnosis. In this article, we critically review the endogenous role of EVs in sepsis progression and how current advancements have improved EVs-based therapies toward their translational future clinical application, with innovative strategies to enhance EVs effect. More complex approaches, including hybrid and fully synthetic nanocarriers that mimic EVs, are also discussed. Several pre-clinical and clinical studies are examined through the review to offer a general outlook of the current and future perspectives of EV-based sepsis diagnosis and treatment.

Key Role of Mesenchymal Stromal Cell Interaction with Macrophages in Promoting Repair of Lung Injury

Lung macrophages (Mφs) are essential for pulmonary innate immunity and host defense due to their dynamic polarization and phenotype shifts. Mesenchymal stromal cells (MSCs) have secretory, immunomodulatory, and tissue-reparative properties and have shown promise in acute and chronic inflammatory lung diseases and in COVID-19. Many beneficial effects of MSCs are mediated through their interaction with resident alveolar and pulmonary interstitial Mφs. Bidirectional MSC-Mφ communication is achieved through direct contact, soluble factor secretion/activation, and organelle transfer. The lung microenvironment facilitates MSC secretion of factors that result in Mφ polarization towards an immunosuppressive M2-like phenotype for the restoration of tissue homeostasis. M2-like Mφ in turn can affect the MSC immune regulatory function in MSC engraftment and tissue reparatory effects. This review article highlights the mechanisms of crosstalk between MSCs and Mφs and the potential role of their interaction in lung repair in inflammatory lung diseases.

Dual Role of Extracellular Vesicles in Sepsis-Associated Kidney and Lung Injury

Extracellular vesicles form a complex intercellular communication network, shuttling a variety of proteins, lipids, and nucleic acids, including regulatory RNAs, such as microRNAs. Transfer of these molecules to target cells allows for the modulation of sets of genes and mediates multiple paracrine and endocrine actions. EVs exert broad pro-inflammatory, pro-oxidant, and pro-apoptotic effects in sepsis, mediating microvascular dysfunction and multiple organ damage. This deleterious role is well documented in sepsis-associated acute kidney injury and acute respiratory distress syndrome. On the other hand, protective effects of stem cell-derived extracellular vesicles have been reported in experimental models of sepsis. Stem cell-derived extracellular vesicles recapitulate beneficial cytoprotective, regenerative, and immunomodulatory properties of parental cells and have shown therapeutic effects in experimental models of sepsis with kidney and lung involvement. Extracellular vesicles are also likely to play a role in deranged kidney-lung crosstalk, a hallmark of sepsis, and may be key to a better understanding of shared mechanisms underlying multiple organ dysfunction. In this review, we analyze the state-of-the-art knowledge on the dual role of EVs in sepsis-associated kidney/lung injury and repair. PubMed library was searched from inception to July 2022, using a combination of medical subject headings (MeSH) and keywords related to EVs, sepsis, acute kidney injury (AKI), acute lung injury (ALI), and acute respiratory distress syndrome (ARDS). Key findings are summarized into two sections on detrimental and beneficial mechanisms of actions of EVs in kidney and lung injury, respectively. The role of EVs in kidney-lung crosstalk is then outlined. Efforts to expand knowledge on EVs may pave the way to employ them as prognostic biomarkers or therapeutic targets to prevent or reduce organ damage in sepsis.

Extracellular Vesicles Derived from Mesenchymal Stem Cells: A Potential Biodrug for Acute Respiratory Distress Syndrome Treatment

Acute respiratory distress syndrome (ARDS) is a severe respiratory disease associated with high morbidity and mortality in the clinic. In the face of limited treatment options for ARDS, extracellular vesicles derived from mesenchymal stem cells (MSC-EVs) have recently shown promise. They regulate levels of growth factors, cytokines, and other internal therapeutic molecules. The possible therapeutic mechanisms of MSC-EVs include anti-inflammatory, cell injury repair, alveolar fluid clearance, and microbe clearance. The potent therapeutic ability and biocompatibility of MSC-EVs have enabled them as an alternative option to ameliorate ARDS. In this review, recent advances, therapeutic mechanisms, advantages and limitations, as well as improvements of using MSC-EVs to treat ARDS are summarized. This review is expected to provide a brief view of the potential applications of MSC-EVs as novel biodrugs to treat ARDS.

Delivery of Stem Cell Secretome for Therapeutic Applications

Intensive studies on stem cell therapy reveal that benefits of stem cells attribute to the paracrine effects. Hence, direct delivery of stem cell secretome to the injured site shows the comparative therapeutic efficacy of living cells while avoiding the potential limitations. However, conventional systemic administration of stem cell secretome often leads to rapid clearance in vivo. Therefore, a variety of different biomaterials are developed for sustained and controllable delivery of stem cell secretome to improve therapeutic efficiency. In this review, we first introduce current approaches for the preparation and characterization of stem cell secretome as well as strategies to improve their therapeutic efficacy and production. The up-to-date delivery platforms are also summarized, including nanoparticles, injectable hydrogels, microneedles, and scaffold patches. Meanwhile, we discuss the underlying therapeutic mechanism of stem cell secretome for the treatment of various diseases. In the end, future opportunities and challenges are proposed.

Mesenchymal Stromal/Stem Cells and Their Products as a Therapeutic Tool to Advance Lung Transplantation

Lung transplantation (LTx) has become the gold standard treatment for end-stage respiratory failure. Recently, extended lung donor criteria have been applied to decrease the mortality rate of patients on the waiting list. Moreover, ex vivo lung perfusion (EVLP) has been used to improve the number/quality of previously unacceptable lungs. Despite the above-mentioned progress, the morbidity/mortality of LTx remains high compared to other solid organ transplants. Lungs are particularly susceptible to ischemia-reperfusion injury, which can lead to graft dysfunction. Therefore, the success of LTx is related to the quality/function of the graft, and EVLP represents an opportunity to protect/regenerate the lungs before transplantation. Increasing evidence supports the use of mesenchymal stromal/stem cells (MSCs) as a therapeutic strategy to improve EVLP. The therapeutic properties of MSC are partially mediated by secreted factors. Hence, the strategy of lung perfusion with MSCs and/or their products pave the way for a new innovative approach that further increases the potential for the use of EVLP. This article provides an overview of experimental, preclinical and clinical studies supporting the application of MSCs to improve EVLP, the ultimate goal being efficient organ reconditioning in order to expand the donor lung pool and to improve transplant outcomes.

Human Amnion-Derived Mesenchymal Stromal Cells: A New Potential Treatment for Carbapenem-Resistant Enterobacterales in Decompensated Cirrhosis

BACKGROUND

Spontaneous bacterial peritonitis (SBP) is a severe and often fatal infection in patients with decompensated cirrhosis and ascites. The only cure for SBP is antibiotic therapy, but the emerging problem of bacterial resistance requires novel therapeutic strategies. Human amniotic mesenchymal stromal cells (hA-MSCs) possess immunomodulatory and anti-inflammatory properties that can be harnessed as a therapy in such a context.

METHODS

An in vitro applications of hA-MSCs in ascitic fluid (AF) of cirrhotic patients, subsequently infected with carbapenem-resistant Enterobacterales, was performed. We evaluated the effects of hA-MSCs on bacterial load, innate immunity factors, and macrophage phenotypic expression.

RESULTS

hA-MSCs added to AF significantly reduce the proliferation of both bacterial strains at 24 h and diversely affect M1 and M2 polarization, C3a complement protein, and ficolin 3 concentrations during the course of infection, in a bacterial strain-dependent fashion.

CONCLUSION

This study shows the potential usefulness of hA-MSC in treating ascites infected with carbapenem-resistant bacteria and lays the foundation to further investigate antibacterial and anti-inflammatory roles of hA-MSC in in vivo models.

Mesenchymal Stem Cell-Derived Exosome Therapy of Microbial Diseases: From Bench to Bed

Microbial diseases are a global health threat, leading to tremendous casualties and economic losses. The strategy to treat microbial diseases falls into two broad categories: pathogen-directed therapy (PDT) and host-directed therapy (HDT). As the typical PDT, antibiotics or antiviral drugs directly attack bacteria or viruses through discerning specific molecules. However, drug abuse could result in antimicrobial resistance and increase infectious disease morbidity. Recently, the exosome therapy, as a HDT, has attracted extensive attentions for its potential in limiting infectious complications and targeted drug delivery. Mesenchymal stem cell-derived exosomes (MSC-Exos) are the most broadly investigated. In this review, we mainly focus on the development and recent advances of the application of MSC-Exos on microbial diseases. The review starts with the difficulties and current strategies in antimicrobial treatments, followed by a comprehensive overview of exosomes in aspect of isolation, identification, contents, and applications. Then, the underlying mechanisms of the MSC-Exo therapy in microbial diseases are discussed in depth, mainly including immunomodulation, repression of excessive inflammation, and promotion of tissue regeneration. In addition, we highlight the latest progress in the clinical translation of the MSC-Exo therapy, by summarizing related clinical trials, routes of administration, and exosome modifications. This review will provide fundamental insights and future perspectives on MSC-Exo therapy in microbial diseases from bench to bedside.

Current Status and Future Perspectives on Machine Perfusion: A Treatment Platform to Restore and Regenerate Injured Lungs Using Cell and Cytokine Adsorption Therapy

Since its advent in the 1990′s, ex vivo lung perfusion (EVLP) has been studied and implemented as a tool to evaluate the quality of a donor organ prior to transplantation. It provides an invaluable window of opportunity for therapeutic intervention to render marginal lungs viable for transplantation. This ultimately aligns with the need of the lung transplant field to increase the number of available donor organs given critical shortages. As transplantation is the only option for patients with end-stage lung disease, advancements in technology are needed to decrease wait-list time and mortality. This review summarizes the results from the application of EVLP as a therapeutic intervention and focuses on the use of the platform with regard to cell therapies, cell product therapies, and cytokine filtration among other technologies. This review will summarize both the clinical and translational science being conducted in these aspects and will highlight the opportunities for EVLP to be developed as a powerful tool to increase the donor lung supply.

Extracellular Vesicles and Alveolar Epithelial-Capillary Barrier Disruption in Acute Respiratory Distress Syndrome: Pathophysiological Role and Therapeutic Potential

Extracellular vesicles (EVs) mediate intercellular communication by transferring genetic material, proteins and organelles between different cells types in both health and disease. Recent evidence suggests that these vesicles, more than simply diagnostic markers, are key mediators of the pathophysiology of acute respiratory distress syndrome (ARDS) and other lung diseases. In this review, we will discuss the contribution of EVs released by pulmonary structural cells (alveolar epithelial and endothelial cells) and immune cells in these diseases, with particular attention to their ability to modulate inflammation and alveolar-capillary barrier disruption, a hallmark of ARDS. EVs also offer a unique opportunity to develop new therapeutics for the treatment of ARDS. Evidences supporting the ability of stem cell-derived EVs to attenuate the lung injury and ongoing strategies to improve their therapeutic potential are also discussed.

Mechanism and Potential of Extracellular Vesicles Derived From Mesenchymal Stem Cells for the Treatment of Infectious Diseases

Extracellular vesicles (EVs) are nano-sized membrane vesicles secreted by cells. EVs serve as a mediator for cell-to-cell communication by regulating the exchange of genetic materials and proteins between the donor and surrounding cells. Current studies have explored the therapeutic value of mesenchymal stem cells-derived EVs (MSC-EVs) for the treatment of infectious diseases extensively. MSC-EVs can eliminate the pathogen, regulate immunity, and repair tissue injury in contagious diseases through the secretion of antimicrobial factors, inhibiting the replication of pathogens and activating the phagocytic function of macrophages. MSC-EVs can also repair tissue damage associated with the infection by upregulating the levels of anti-inflammatory factors, downregulating the pro-inflammatory factors, and participating in the regulation of cellular biological behaviors. The purpose of this mini-review is to discuss in detail the various mechanisms of MSC-EV treatment for infectious diseases including respiratory infections, sepsis, and intestinal infections, as well as challenges for implementing MSC-EVs from bench to bedside.

IFN-Gamma and TNF-Alpha as a Priming Strategy to Enhance the Immunomodulatory Capacity of Secretomes from Menstrual Blood-Derived Stromal Cells

Mesenchymal stromal cells isolated from menstrual blood (MenSCs) exhibit a potent pro-angiogenic and immunomodulatory capacity. Their therapeutic effect is mediated by paracrine mediators released by their secretomes. In this work, we aimed to evaluate the effect of a specific priming condition on the phenotype and secretome content of MenSCs. Our results revealed that the optimal condition for priming MenSCs was the combination of interferon gamma (IFNγ) and tumor necrosis factor alpha (TNFα) that produced a synergistic and additive effect on IDO1 release and immune-related molecule expression. The analyses of MenSC-derived secretomes after IFNγ and TNFα priming also revealed an increase in EV release and in the differentially expressed miRNAs involved in the immune response and inflammation. Proliferation assays on lymphocyte subsets demonstrated a decrease in CD4+ T cells and CD8+ T cells co-cultured with secretomes, especially in the lymphocytes co-cultured with secretomes from primed cells. Additionally, the expression of immune checkpoints (PD-1 and CTLA-4) was increased in the CD4+ T cells co-cultured with MenSC-derived secretomes. These findings demonstrate that the combination of IFNγ and TNFα represents an excellent priming strategy to enhance the immunomodulatory capacity of MenSCs. Moreover, the secretome derived from primed MenSCs may be postulated as a therapeutic option for the regulation of adverse inflammatory reactions.

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.

Mesenchymal Stromal Cell Secretome for the Treatment of Immune-Mediated Inflammatory Diseases: Latest Trends in Isolation, Content Optimization and Delivery Avenues

Considering the high prevalence and the complex pharmacological management of immune-mediated inflammatory diseases (IMIDs), the search for new therapeutic approaches for their treatment is vital. Although the immunomodulatory and anti-inflammatory effects of mesenchymal stromal cells (MSCs) have been extensively studied as a potential therapy in this field, direct MSC implantation presents some limitations that could slow down the clinical translation. Since the beneficial effects of MSCs have been mainly attributed to their ability to secrete a plethora of bioactive factors, their secretome has been proposed as a new and promising pathway for the treatment of IMIDs. Formed from soluble factors and extracellular vesicles (EVs), the MSC-derived secretome has been proven to elicit immunomodulatory effects that control the inflammatory processes that occur in IMIDs. This article aims to review the available knowledge on the MSC secretome, evaluating the advances in this field in terms of its composition, production and application, as well as analyzing the pending challenges in the field. Moreover, the latest research involving secretome administration in IMIDs is discussed to provide an updated state-of-the-art for this field. Finally, novel secretome delivery alternatives are reviewed, paying special attention to hydrogel encapsulation as one of the most convenient and promising strategies.

Lung Fibrosis Is Improved by Extracellular Vesicles from IFNγ-Primed Mesenchymal Stromal Cells in Murine Systemic Sclerosis

BACKGROUND

Systemic sclerosis (SSc) is a severe autoimmune disease for which mesenchymal stromal cells (MSCs)-based therapy was reported to reduce SSc-related symptoms in pre-clinical studies. Recently, extracellular vesicles released by MSCs (MSC-EVs) were shown to mediate most of their therapeutic effect. Here, we aimed at improving their efficacy by increasing the MSC-EV dose or by IFNγ-priming of MSCs.

METHODS

small size (ssEVs) and large size EVs (lsEVs) were recovered from murine MSCs that were pre-activated using 1 or 20 ng/mL of IFNγ. In the HOCl-induced model of SSc, mice were treated with EVs at day 21 and sacrificed at day 42. Lung and skin samples were collected for histological and molecular analyses.

RESULTS

increasing the dose of MSC-EVs did not add benefit to the dose previously reported to be efficient in SSc. By contrast, IFNγ pre-activation improved MSC-EVs-based treatment, essentially in the lungs. Low doses of IFNγ decreased the expression of fibrotic markers, while high doses improved remodeling and anti-inflammatory markers. IFNγ pre-activation upregulated iNos, IL1ra and Il6 in MSCs and ssEVs and the PGE2 protein in lsEVs.

CONCLUSION

IFNγ-pre-activation improved the therapeutic effect of MSC-EVs preferentially in the lungs of SSc mice by modulating anti-inflammatory and anti-fibrotic markers.

Mesenchymal stromal cell extracellular vesicles as therapy for acute and chronic respiratory diseases: A meta-analysis

Preclinical studies suggest mesenchymal stromal cell extracellular vesicles (MSC-EVs) reduce inflammation and improve organ function in lung diseases; however, an objective analysis of all available data is needed prior to translation. Using rigorous meta-research methods, we determined the effectiveness of MSC-EVs for preclinical respiratory diseases and identified experimental conditions that may further refine this therapy. A systematic search of MEDLINE/Embase identified 1167 records. After screening, 52 articles were included for data extraction and evaluated for risk of bias and quality of reporting in study design. A random effects meta-analysis was conducted for acute lung injury (ALI; N = 23), bronchopulmonary dysplasia (BPD; N = 8) and pulmonary arterial hypertension (PAH; N = 7). Subgroup analyses identified EV methods/characteristics that may be associated with improved efficacy. Data is presented as standardized mean differences (SMD) or risk ratios (RR) with 95% confidence intervals (CI). For ALI, MSC-EVs markedly reduced lung injury (SMD -4.33, CI -5.73 to -2.92), vascular permeability (SMD -2.43, CI -3.05 to -1.82), and mortality (RR 0.39, CI 0.22 to 0.68). Small EVs were more consistently effective than large EVs whereas no differences were observed between tissue sources, immunocompatibility or isolation techniques. For BPD, alveolarization was improved by MSC-EVs (SMD -1.45, CI -2.08 to -0.82) with small EVs more consistently beneficial then small/large EVs. In PAH, right ventricular systolic pressure (SMD -4.16, CI -5.68 to -2.64) and hypertrophy (SMD -2.80, CI -3.68 to -1.91) were significantly attenuated by EVs. In BPD and PAH, EVs isolated by ultracentrifugation demonstrated therapeutic benefit whereas tangential flow filtration (N = 2) displayed minimal efficacy. Lastly, risk of bias and quality of reporting for experimental design were consistently unclear across all studies. Our findings demonstrate clear potential of MSC-EVs to be developed as therapy for acute and chronic lung diseases. However, greater transparency in research design and direct comparisons of isolation technique and EV subtypes are needed to generate robust evidence to guide clinical translation. Protocol Registration: PROSPERO CRD42020145334.

Nanomedicine for acute respiratory distress syndrome: The latest application, targeting strategy, and rational design

Acute respiratory distress syndrome (ARDS) is characterized by the severe inflammation and destruction of the lung air-blood barrier, leading to irreversible and substantial respiratory function damage. Patients with coronavirus disease 2019 (COVID-19) have been encountered with a high risk of ARDS, underscoring the urgency for exploiting effective therapy. However, proper medications for ARDS are still lacking due to poor pharmacokinetics, non-specific side effects, inability to surmount pulmonary barrier, and inadequate management of heterogeneity. The increased lung permeability in the pathological environment of ARDS may contribute to nanoparticle-mediated passive targeting delivery. Nanomedicine has demonstrated unique advantages in solving the dilemma of ARDS drug therapy, which can address the shortcomings and limitations of traditional anti-inflammatory or antioxidant drug treatment. Through passive, active, or physicochemical targeting, nanocarriers can interact with lung epithelium/endothelium and inflammatory cells to reverse abnormal changes and restore homeostasis of the pulmonary environment, thereby showing good therapeutic activity and reduced toxicity. This article reviews the latest applications of nanomedicine in pre-clinical ARDS therapy, highlights the strategies for targeted treatment of lung inflammation, presents the innovative drug delivery systems, and provides inspiration for strengthening the therapeutic effect of nanomedicine-based treatment.

Mesenchymal Stem Cell-Derived Exosomes for COVID-19 Therapy, Preclinical and Clinical Evidence

Since the emergence of the novel coronavirus, named COVID-19, researchers are looking for a treatment to stop the devastating pandemic. During these efforts, mesenchymal stem cells (MSCs), the potential next generation of therapeutic methods with wide application for diseases, have successfully controlled cytokine storm following the virus infection. However, the use of MSCs has been limited due to the ethical issues, immunogenicity, and genetic modifications. Therefore, exosomes were introduced as a suitable substitute for the MSCs. In the case of COVID-19 treatment, both MSCs and exosomes exert their beneficial effect mainly through the management of the cytokine storm. This study provided the underlying mechanisms for the effect of exosomes on COVID-19 treatment and presented several preclinical and clinical studies of exosomes for COVID-19 treatment.

Mesenchymal Stem Cell-Derived Exosomes as an Emerging Paradigm for Regenerative Therapy and Nano-Medicine: A Comprehensive Review

Mesenchymal Stem Cells are potent therapeutic candidates in the field of regenerative medicine, owing to their immunomodulatory and differentiation potential. However, several complications come with their translational application like viability, duration, and degree of expansion, long-term storage, and high maintenance cost. Therefore, drawbacks of cell-based therapy can be overcome by a novel therapeutic modality emerging in translational research and application, i.e., exosomes. These small vesicles derived from mesenchymal stem cells are emerging as new avenues in the field of nano-medicine. These nano-vesicles have caught the attention of researchers with their potency as regenerative medicine both in nanotherapeutics and drug delivery systems. In this review, we discuss the current knowledge in the biology and handling of exosomes, with their limitations and future applications. Additionally, we highlight current perspectives that primarily focus on their effect on various diseases and their potential as a drug delivery vehicle.

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.

Therapeutic Potential of Extracellular Vesicles for Sepsis Treatment

Sepsis is a deadly condition lacking a specific treatment despite decades of research. This has prompted the exploration of new approaches, with extracellular vesicles (EVs) emerging as a focal area. EVs are nanosized, cell-derived particles that transport bioactive components (i.e., proteins, DNA, and RNA) between cells, enabling both normal physiological functions and disease progression depending on context. In particular, EVs have been identified as critical mediators of sepsis pathophysiology. However, EVs are also thought to constitute the biologically active component of cell-based therapies and have demonstrated anti-inflammatory, anti-apoptotic, and immunomodulatory effects in sepsis models. The dual nature of EVs in sepsis is explored here, discussing their endogenous roles and highlighting their therapeutic properties and potential. Related to the latter component, prior studies involving EVs from mesenchymal stem/stromal cells (MSCs) and other sources are discussed and emerging producer cells that could play important roles in future EV-based sepsis therapies are identified. Further, how methodologies could impact therapeutic development toward sepsis treatment to enhance and control EV potency is described.

Plasma extracellular vesicle delivery of miR-210-3p by targeting ATG7 to promote sepsis-induced acute lung injury by regulating autophagy and activating inflammation

Extracellular vesicles (EVs) can be used for intercellular communication by facilitating the transfer of miRNAs from one cell to a recipient cell. MicroRNA (miR)-210-3p is released into the blood during sepsis, inducing cytokine production and promoting leukocyte migration. Thus, the current study aimed to elucidate the role of plasma EVs in delivering miR-210-3p in sepsis-induced acute lung injury (ALI). Plasma EVs were isolated from septic patients, after which the expression of various inflammatory factors was measured using enzyme-linked immunosorbent assay. Cell viability and apoptosis were measured via cell counting kit-8 and flow cytometry. Transendothelial resistance and fluorescein isothiocyanate fluorescence were used to measure endothelial cell permeability. Matrigel was used to examine the tubulogenesis of endothelial cells. The targeting relationship between miR-210-3p and ATG7 was assessed by dual-luciferase reporter assays. The expression of ATG7 and autophagy-related genes was determined to examine autophagic activation. A sepsis mouse model was established by cecal ligation and puncture (CLP)-induced surgery. The level of miR-210-3p was highly enriched in septic EVs. MiR-210-3p enhanced THP-1 macrophage inflammation, BEAS-2B cell apoptosis, and HLMVEC permeability while inhibiting angiogenesis and cellular activity. MiR-210-3p overexpression reduced ATG7 and LC3II/LC3I expression and increased P62 expression. Improvements in vascular density and autophagosome formation, increased ATG7 expression, and changes in the ratio of LC3II/LC3I were detected, as well as reduced P62 expression, in adenovirus-anti-miR-210-3p treated mice after CLP injury. Taken together, the key findings of the current study demonstrate that plasma EVs carrying miR-210-3p target ATG7 to regulate autophagy and inflammatory activation in a sepsis-induced ALI model.

Mesenchymal stromal cell extracellular vesicles rescue mitochondrial dysfunction and improve barrier integrity in clinically relevant models of ARDS

Alveolar epithelial–capillary barrier disruption is a hallmark of acute respiratory distress syndrome (ARDS). Contribution of mitochondrial dysfunction to the compromised alveolar-capillary barrier in ARDS remains unclear. Mesenchymal stromal cells-derived extracellular vesicles (MSC-EVs) are considered as a cell-free therapy for ARDS. Mitochondrial transfer was shown to be important for the therapeutic effects of MSCs and MSC-EVs. Here we investigated the contribution of mitochondrial dysfunction to the injury of alveolar epithelial and endothelial barriers in ARDS and the ability of MSC-EVs to modulate alveolar–capillary barrier integrity through mitochondrial transfer.

Primary human small airway epithelial and pulmonary microvascular endothelial cells and human precision cut lung slices (PCLSs) were stimulated with endotoxin or plasma samples from patients with ARDS and treated with MSC-EVs, barrier properties and mitochondrial functions were evaluated. Lipopolysaccharide (LPS)-injured mice were treated with MSC-EVs and degree of lung injury and mitochondrial respiration of the lung tissue were assessed.

Inflammatory stimulation resulted in increased permeability coupled with pronounced mitochondrial dysfunction in both types of primary cells and PCLSs. Extracellular vesicles derived from normal MSCs restored barrier integrity and normal levels of oxidative phosphorylation while an extracellular vesicles preparation which did not contain mitochondria was not effective. In vivo, presence of mitochondria was critical for extracellular vesicles ability to reduce lung injury and restore mitochondrial respiration in the lung tissue.

In the ARDS environment, MSC-EVs improve alveolar–capillary barrier properties through restoration of mitochondrial functions at least partially via mitochondrial transfer.

This study demonstrates that mitochondrial dysfunction is an important mechanism of ARDS pathogenesis. Mitochondrial transfer is crucial for the ability of MSC extracellular vesicles to restore integrity of the alveolar–capillary barrier.https://bit.ly/2JuqoCY

Review of the potential of mesenchymal stem cells for the treatment of infectious diseases

The therapeutic value of mesenchymal stem cells (MSCs) for the treatment of infectious diseases and the repair of disease-induced tissue damage has been explored extensively. MSCs inhibit inflammation, reduce pathogen load and tissue damage encountered during infectious diseases through the secretion of antimicrobial factors for pathogen clearance and they phagocytose certain bacteria themselves. MSCs dampen tissue damage during infection by downregulating the levels of pro-inflammatory cytokines, and inhibiting the excessive recruitment of neutrophils and proliferation of T cells at the site of injury. MSCs aid in the regeneration of damaged tissue by differentiating into the damaged cell types or by releasing paracrine factors that direct tissue regeneration, differentiation, and wound healing. In this review, we discuss in detail the various mechanisms by which MSCs help combat pathogens, tissue damage associated with infectious diseases, and challenges in utilizing MSCs for therapy.

Harnessing the ECM Microenvironment to Ameliorate Mesenchymal Stromal Cell-Based Therapy in Chronic Lung Diseases

It is known that the cell environment such as biomechanical properties and extracellular matrix (ECM) composition dictate cell behaviour including migration, proliferation, and differentiation. Important constituents of the microenvironment, including ECM molecules such as proteoglycans and glycosaminoglycans (GAGs), determine events in both embryogenesis and repair of the adult lung. Mesenchymal stromal/stem cells (MSC) have been shown to have immunomodulatory properties and may be potent actors regulating tissue remodelling and regenerative cell responses upon lung injury. Using MSC in cell-based therapy holds promise for treatment of chronic lung diseases such as idiopathic pulmonary fibrosis (IPF) and chronic obstructive pulmonary disease (COPD). However, so far clinical trials with MSCs in COPD have not had a significant impact on disease amelioration nor on IPF, where low cell survival rate and pulmonary retention time are major hurdles to overcome. Research shows that the microenvironment has a profound impact on transplanted MSCs. In our studies on acellular lung tissue slices (lung scaffolds) from IPF patients versus healthy individuals, we see a profound effect on cellular activity, where healthy cells cultured in diseased lung scaffolds adapt and produce proteins further promoting a diseased environment, whereas cells on healthy scaffolds sustain a healthy proteomic profile. Therefore, modulating the environmental context for cell-based therapy may be a potent way to improve treatment using MSCs. In this review, we will describe the importance of the microenvironment for cell-based therapy in chronic lung diseases, how MSC-ECM interactions can affect therapeutic output and describe current progress in the field of cell-based therapy.

Intra-vital imaging of mesenchymal stromal cell kinetics in the pulmonary vasculature during infection

Mesenchymal stem/stromal cells (MSCs) have demonstrated efficacy in pre-clinical models of inflammation and tissue injury, including in models of lung injury and infection. Rolling, adhesion and transmigration of MSCs appears to play a role during MSC kinetics in the systemic vasculature. However, a large proportion of MSCs become entrapped within the lungs after intravenous administration, while the initial kinetics and the site of arrest of MSCs in the pulmonary vasculature are unknown. We examined the kinetics of intravascularly administered MSCs in the pulmonary vasculature using a microfluidic system in vitro and intra-vital microscopy of intact mouse lung. In vitro, MSCs bound to endothelium under static conditions but not under laminar flow. VCAM-1 antibodies did not affect MSC binding. Intravital microscopy demonstrated MSC arrest at pulmonary micro-vessel bifurcations due to size obstruction. Retention of MSCs in the pulmonary microvasculature was increased in Escherichia coli-infected animals. Trapped MSCs deformed over time and appeared to release microvesicles. Labelled MSCs retained therapeutic efficacy against pneumonia. Our results suggest that MSCs are physically obstructed in pulmonary vasculature and do not display properties of rolling/adhesion, while retention of MSCs in the infected lung may require receptor interaction.

'Primed' Mesenchymal Stem Cells: a Potential Novel Therapeutic for COVID19 Patients

The COVID19 pandemic, designated as a public health crisis by the World Health Organization (WHO), is rapidly spreading around the world impacting the health and economy of almost all the countries. The data of hospitalized COVID19 patients, especially those with serious illness, indicate the involvement of immunopathological complications. As no effective treatment is currently available, we propose ‘Primed’ Mesenchymal Stem Cells (MSCs) as a therapeutic alternative to tackle devastating epidemic. The individual response to MSCs treatment is heterogeneous. During the treatment of infectious pathology, the effectiveness of the treatment may vary based on the disease scenario. Interestingly, when transplanted in vivo, MSCs are governed by the locally regulated microenvironment, suggesting that the restorative variability could be tailored by choosing a priming regimen to specifically correct a given pathology. Therefore, in our opinion, the priming of MSCs could be a novel approach to improve the responses of COVID19 patients.

Mesenchymal Stromal Cell-Derived Extracellular Vesicles in Lung Diseases: Current Status and Perspectives

Extracellular vesicles (EVs) have emerged as a potential therapy for several diseases. These plasma membrane-derived fragments are released constitutively by virtually all cell types-including mesenchymal stromal cells (MSCs)-under stimulation or following cell-to-cell interaction, which leads to activation or inhibition of distinct signaling pathways. Based on their size, intracellular origin, and secretion pathway, EVs have been grouped into three main populations: exosomes, microvesicles (or microparticles), and apoptotic bodies. Several molecules can be found inside MSC-derived EVs, including proteins, lipids, mRNA, microRNAs, DNAs, as well as organelles that can be transferred to damaged recipient cells, thus contributing to the reparative process and promoting relevant anti-inflammatory/resolutive actions. Indeed, the paracrine/endocrine actions induced by MSC-derived EVs have demonstrated therapeutic potential to mitigate or even reverse tissue damage, thus raising interest in the regenerative medicine field, particularly for lung diseases. In this review, we summarize the main features of EVs and the current understanding of the mechanisms of action of MSC-derived EVs in several lung diseases, such as chronic obstructive pulmonary disease (COPD), pulmonary infections [including coronavirus disease 2019 (COVID-19)], asthma, acute respiratory distress syndrome (ARDS), idiopathic pulmonary fibrosis (IPF), and cystic fibrosis (CF), among others. Finally, we list a number of limitations associated with this therapeutic strategy that must be overcome in order to translate effective EV-based therapies into clinical practice.

Therapeutic Application of Exosomes in Inflammatory Diseases

Immunomodulation is on the cusp of being an important therapy for treating many diseases, due to the significant role of the immune system in defending the human body. Although the immune system is an essential defense system, overactivity can result in diverse sicknesses such as inflammation and autoimmune disease. Exosomes are emerging as a state-of-the-art therapeutic strategy for treating an overactive immune system. Thus, in this review, we will thoroughly review therapeutic applications of exosomes in various inflammatory and autoimmune diseases. Finally, issues for an outlook to the future of exosomal therapy will be introduced.

Perinatal Cells: A Promising COVID-19 Therapy?

The COVID-19 pandemic has become a priority in the health systems of all nations worldwide. In fact, there are currently no specific drugs or preventive treatments such as vaccines. The numerous therapies available today aim to counteract the symptoms caused by the viral infection that in some subjects can evolve causing acute respiratory distress syndromes (ARDS) with consequent admission to intensive care unit. The exacerbated response of the immune system, through cytokine storm, causes extensive damage to the lung tissue, with the formation of edema, fibrotic tissues and susceptibility to opportunistic infections. The inflammatory picture is also aggravated by disseminated intravascular coagulation which worsens the damage not only to the respiratory system, but also to other organs. In this context, perinatal cells represent a valid strategy thanks to their strong immunomodulatory potential, their safety profile, the ability to reduce fibrosis and stimulate reparative processes. Furthermore, perinatal cells exert antibacterial and antiviral actions. This review therefore provides an overview of the characteristics of perinatal cells with a particular focus on the beneficial effects that they could have in patients with COVID-19, and more specifically for their potential use in the treatment of ARDS and sepsis.

How severe RNA virus infections such as SARS-CoV-2 disrupt tissue and organ barriers—Reconstitution by mesenchymal stem cell-derived exosomes

The host tissue barriers arrange numerous lines of resistance to influx and cell-to-cell spread of pathogenic viruses. However, the highly virulent pathogens are equipped with diverse molecular mechanisms that can subvert the host countermeasures and/or exaggerate the host cell responses to toxic levels leading to severe illnesses. In his review, we discuss the immune-mediated pathogenesis of COVID-19 disease induced by the SARS-Cov-2 coronavirus. SARS-Cov-2 primarily infects type II alveolar epithelial cells. These cells are highly abundant with the ACE2 receptor protein, which occurs to be counterpart of the viral Spike protein and thus facilitates internalization of the virus. Following infection onset, the rapid clinical deterioration occurs about in a week suggesting that the respiratory failure in COVID-19 could result from a unique pattern of immune impairment characterized by severe Cytokine Release Syndrome (known as cytokine storm) leading to macrophage activation syndrome. In addition, the SARS-Cov-2 infection can induce a profound depletion of CD4 lymphocytes, CD19 lymphocytes, and natural killer cells, i.e., all major guardians cell components of the host immune barrier. However, while the numbers of that cells decline in the sequelae of the disease, the presence of persistent hyper-inflammation driving progressive tissue injury, suggests that the deteriorating impact of the systemic reactive responses can be more significant than the virus-induced cytopathic effects on the immunocompetent cells. In this respect, the authors discuss the emerging evidence of beneficial effects of administration of exosomes derived from mesenchymal stem cells—another sentinel-type cells—in management of the hyper-inflammatory response to SARS-CoV-2. Moreover, they also discuss the exosomes-originated mechanisms, which sustain regeneration of the damaged pulmonary lining cells and the vascular endothelial cells in various organs, including the brain.

Emerging cellular and pharmacologic therapies for acute respiratory distress syndrome

PURPOSE OF REVIEW

Advances in our understanding of the pathophysiology and biology of ARDS has identified a number of promising cellular and pharmacological therapies. These emerging therapeutics can modulate the immune response, reduce epithelial injury, target endothelial and vascular dysfunction, have anticoagulant effects, and enhance ARDS resolution.

RECENT FINDINGS

Mesenchymal stromal cell therapy shows promise in earlier phase clinical testing, whereas a number of issues regarding clinical translation, such as donor and effect variability, are currently being optimized to enable larger scale clinical trials. Furthermore, a number of promising mesenchymal stromal cell therapy clinical studies for COVID-19-induced ARDS are underway. Recent studies provide support for several emerging ARDS pharmacotherapies, including steroids, statins, vitamins, anticoagulants, interferons, and carbon monoxide. The history of unsuccessful clinical trials of potential therapies highlights the challenges to successful translation for this heterogeneous clinical syndrome. Given this, attention has focused on the potential to identify biologically homogenous subtypes within ARDS, to enable us to target more specific therapies, i.e. 'precision medicines'.

SUMMARY

Mesenchymal stromal cells, steroids, statins, vitamins, anticoagulants, interferons and carbon monoxide have therapeutic promise for ARDS. Identifying ARDS sub-populations most likely to benefit from targeted therapies may facilitate future advances.

Mesenchymal stromal cells for acute respiratory distress syndrome (ARDS), sepsis, and COVID-19 infection: optimizing the therapeutic potential

Introduction: Mesenchymal stromal (stem) cell (MSC) therapies are emerging as a promising therapeutic intervention in patients with Acute Respiratory Distress Syndrome (ARDS) and sepsis due to their reparative, immunomodulatory, and antimicrobial properties.Areas covered: This review provides an overview of Mesenchymal stromal cells (MSCs) and their mechanisms of effect in ARDS and sepsis. The preclinical and clinical evidence to support MSC therapy in ARDS and sepsis is discussed. The potential for MSC therapy in COVID-19 ARDS is discussed with insights from respiratory viral models and early clinical reports of MSC therapy in COVID-19. Strategies to optimize the therapeutic potential of MSCs in ARDS and sepsis are considered including preconditioning, altered gene expression, and alternative cell-free MSC-derived products, such as extracellular vesicles and conditioned medium.Expert opinion: MSC products present considerable therapeutic promise for ARDS and sepsis. Preclinical investigations report significant benefits and early phase clinical studies have not highlighted safety concerns. Optimization of MSC function in preclinical models of ARDS and sepsis has enhanced their beneficial effects. MSC-derived products, as cell-free alternatives, may provide further advantages in this field. These strategies present opportunity for the clinical development of MSCs and MSC-derived products with enhanced therapeutic efficacy.

The efficacy of mesenchymal stromal cell-derived therapies for acute respiratory distress syndrome-a meta-analysis of preclinical trials

Background

The investigation of mesenchymal stromal cell (MSC)-conditioned medium or extracellular vesicles (exosomes or microvesicles) as a remedy for acute lung injury (ALI) or acute respiratory distress syndrome (ARDS) has become a fast-growing field in recent years. Our purpose was to conduct a meta-analysis to investigate the efficacy of MSC-derived therapies (MDTs) for ALI/ARDS in animal models.

Methods

A meta-analysis of MDTs for ALI/ARDS in animal trials was performed. PubMed and EMBASE were searched to screen relevant preclinical trials with a predetermined search strategy.

Results

A total of 17 studies that compared MDT with the ALI control group were included in our study. The pooled result derived from the comparison of the two groups suggested that MDT could significantly reduce the lung injury score (standardized mean difference (SMD) = − 4.02, 95% CI [− 5.28, − 2.23], P < 0.0001) and improve animal survival (OR = − 6.45, 95% CI [2.78, 14.97], P < 0.0001). MDT mitigated the infiltration of neutrophils in alveoli (SMD = − 3.38, 95% CI [− 4.58, − 2.18], P < 0.00001). MDT also reduced the wet-dry weight ratio of the lung (SMD = − 2.34, 95% CI [− 3.42, − 1.26], P < 0.0001) and the total protein in BALF (SMD = − 2.23, 95% CI [− 3.07, − 1.40], P < 0.00001). Furthermore, MDT was found to downregulate proinflammatory mediators such as IL-1, IL-6 and TNF-a and to upregulate anti-inflammatory mediators such as IL-10.

Conclusion

MDT reduces lung injury and improves survival in animal ARDS models since it can ameliorate lung permeability, decrease inflammatory cell infiltration, downregulate proinflammatory mediators, and upregulate anti-inflammatory mediators. However, more animal studies and human trials are needed for further investigation.

Potential application of mesenchymal stem cells and their exosomes in lung injury: an emerging therapeutic option for COVID-19 patients

The COVID-19 pandemic has negatively impacted the global public health and the international economy; therefore, there is an urgent need for an effective therapy to treat COVID-19 patients. Mesenchymal stem cells (MSCs) have been proposed as an emerging therapeutic option for the SARS-CoV-2 infection. Recently, numerous clinical trials have been registered to examine the safety and efficacy of different types of MSCs and their exosomes for treating COVID-19 patients, with less published data on the mechanism of action. Although there is no approved effective therapy for COVID-19 as of yet, MSC therapies showed an improvement in the treatment of some COVID-19 patients. MSC’s therapeutic effect is displayed in their ability to reduce the cytokine storm, enhance alveolar fluid clearance, and promote epithelial and endothelial recovery; however, the safest and most effective route of MSC delivery remains unclear. The use of poorly characterized MSC products remains one of the most significant drawbacks of MSC-based therapy, which could theoretically promote the risk for thromboembolism. Optimizing the clinical-grade production of MSCs and establishing a consensus on registered clinical trials based on cell-product characterization and mode of delivery would aid in laying the foundation for a safe and effective therapy in COVID-19. In this review, we shed light on the mechanistic view of MSC therapeutic role based on preclinical and clinical studies on acute lung injury and ARDS; therefore, offering a unique correlation and applicability in COVID-19 patients. We further highlight the challenges and opportunities in the use of MSC-based therapy.