Tropism of avian influenza A (H5N1) virus to mesenchymal stem cells and CD34+ hematopoietic stem cells. PLoS One. 2013;8:e81805. [PMID: 24339969 PMCID: PMC3858287 DOI: 10.1371/journal.pone.0081805]

Deciphering avian hematopoietic stem cells by surface marker screening and gene expression profiling

BACKGROUND

Avian species have played a pivotal role in developmental hematopoiesis research, leading to numerous critical discoveries. Avian influenza, particularly the H5N1 strain, poses a significant threat to poultry and has zoonotic potential for humans. Infections often result in abnormal hematologic profiles, highlighting the complex interplay between avian diseases and hematopoiesis. Many avian diseases can suppress immune cells in the bone marrow (BM), impacting immune responses. Studying hematopoietic stem cells (HSCs) in avian BM is crucial for understanding these processes and developing effective vaccines and protection strategies for both avian and human health.

METHODS

This study adapted methods from mouse studies to isolate avian HSCs as Lineage-negative (Lin-) cells. These isolated cells were further identified as Lin-Sca1+c-Kit+ (LSK) and were found to be more prevalent than in control groups. RT-PCR analyses were conducted, showing that genes like MEIS1 and TSC1 were upregulated, while SIRT1, FOXO1, and AHR were downregulated in these stem cells. Screening for LSK markers revealed ten unique surface antigens in the Sca1+c-Kit+ cell populations, including highly enriched antigens such as CD178, CD227, and CD184. Additionally, studies on quail HSCs demonstrated that similar labeling techniques were effective in quail BM.

RESULTS

The research demonstrated that the identification of avian HSC-specific surface antigens provides valuable insights into the pathogenesis of avian influenza and other diseases, enhancing our understanding of how these diseases suppress HSC function. Notably, the upregulation of MEIS1 and TSC1 genes in LSK cells underscores their critical roles in regulating hematopoietic processes. Conversely, the downregulation of SIRT1, FOXO1, and AHR genes provides important clues about their roles in differentiation and immune response mechanisms.

DISCUSSION

The findings of this study deepen our understanding of the effects of avian diseases on the immune system by identifying surface markers specific to avian HSCs. The suppression of HSC function by pathogens such as influenza highlights the importance of understanding these cells in developing targeted vaccines. These results represent a significant step towards improving global health security by mitigating risks associated with avian pathogens.

Mesenchymal stem cell therapy in diabetic foot ulcer: An updated comprehensive review

Background

Diabetes has evolved into a worldwide public health issue. One of the most serious complications of diabetes is diabetic foot ulcer (DFU), which frequently creates a significant financial strain on patients and lowers their quality of life. Up until now, there has been no curative therapy for DFU, only symptomatic relief or an interruption in the disease's progression. Recent studies have focused attention on mesenchymal stem cells (MSCs), which provide innovative and potential treatment candidates for several illnesses as they can differentiate into various cell types. They are mostly extracted from the placenta, adipose tissue, umbilical cord (UC), and bone marrow (BM). Regardless of their origin, they show comparable features and small deviations. Our goal is to investigate MSCs' therapeutic effects, application obstacles, and patient benefit strategies for DFU therapy.

Methodology

A comprehensive search was conducted using specific keywords relating to DFU, MSCs, and connected topics in the databases of Medline, Scopus, Web of Science, and PubMed. The main focus of the selection criteria was on English-language literature that explored the relationship between DFU, MSCs, and related factors.

Results and Discussion

Numerous studies are being conducted and have demonstrated that MSCs can induce re-epithelialization and angiogenesis, decrease inflammation, contribute to immunological modulation, and subsequently promote DFU healing, making them a promising approach to treating DFU. This review article provides a general snapshot of DFU (including clinical presentation, risk factors and etiopathogenesis, and conventional treatment) and discusses the clinical progress of MSCs in the management of DFU, taking into consideration the side effects and challenges during the application of MSCs and how to overcome these challenges to achieve maximum benefits.

Conclusion

The incorporation of MSCs in the management of DFU highlights their potential as a feasible therapeutic strategy. Establishing a comprehensive understanding of the complex relationship between DFU pathophysiology, MSC therapies, and related obstacles is essential for optimizing therapy outcomes and maximizing patient benefits.

Adoptive cell therapy for high grade gliomas using simultaneous temozolomide and intracranial mgmt-modified γδ t cells following standard post-resection chemotherapy and radiotherapy: current strategy and future directions

Cellular therapies, including chimeric antigen receptor T cell therapies (CAR-T), while generally successful in hematologic malignancies, face substantial challenges against solid tumors such as glioblastoma (GBM) due to rapid growth, antigen heterogeneity, and inadequate depth of response to cytoreductive and immune therapies, We have previously shown that GBM constitutively express stress associated NKG2D ligands (NKG2DL) recognized by gamma delta (γδ) T cells, a minor lymphocyte subset that innately recognize target molecules via the γδ T cell receptor (TCR), NKG2D, and multiple other mechanisms. Given that NKG2DL expression is often insufficient on GBM cells to elicit a meaningful response to γδ T cell immunotherapy, we then demonstrated that NKG2DL expression can be transiently upregulated by activation of the DNA damage response (DDR) pathway using alkylating agents such as Temozolomide (TMZ). TMZ, however, is also toxic to γδ T cells. Using a p140K/MGMT lentivector, which confers resistance to TMZ by expression of O(6)-methylguanine-DNA-methyltransferase (MGMT), we genetically engineered γδ T cells that maintain full effector function in the presence of therapeutic doses of TMZ. We then validated a therapeutic system that we termed Drug Resistance Immunotherapy (DRI) that combines a standard regimen of TMZ concomitantly with simultaneous intracranial infusion of TMZ-resistant γδ T cells in a first-in-human Phase I clinical trial (NCT04165941). This manuscript will discuss DRI as a rational therapeutic approach to newly diagnosed GBM and the importance of repeated administration of DRI in combination with the standard-of-care Stupp regimen in patients with stable minimal residual disease.

Investigational Use of Mesenchymal Stem/Stromal Cells and Their Secretome as Add-On Therapy in Severe Respiratory Virus Infections: Challenges and Perspectives

Serious manifestations of respiratory virus infections such as influenza and coronavirus disease 2019 (COVID-19) are associated with a dysregulated immune response and systemic inflammation. Treating the immunological/inflammatory dysfunction with glucocorticoids, Janus kinase inhibitors, and monoclonal antibodies against the interleukin-6 receptor has significantly reduced the risk of respiratory failure and death in hospitalized patients with severe COVID-19, but the proportion of those requiring invasive mechanical ventilation (IMV) and dying because of respiratory failure remains elevated. Treatment of severe influenza-associated pneumonia and acute respiratory distress syndrome (ARDS) with available immunomodulators and anti-inflammatory compounds is still not recommended. New therapies are therefore needed to reduce the use of IMV and the risk of death in hospitalized patients with rapidly increasing oxygen demand and systemic inflammation who do not respond to the current standard of care. This paper provides a critical assessment of the published clinical trials that have tested the investigational use of intravenously administered allogeneic mesenchymal stem/stromal cells (MSCs) and MSC-derived secretome with putative immunomodulatory/antiinflammatory/regenerative properties as add-on therapy to improve the outcome of these patients. Increased survival rates are reported in 5 of 12 placebo-controlled or open-label comparative trials involving patients with severe and critical COVID-19 and in the only study concerning patients with influenza-associated ARDS. Results are encouraging but inconclusive for the following reasons: small number of patients tested in each trial; differences in concomitant treatments and respiratory support; imbalances between study arms; differences in MSC source, MSC-derived product, dosing and starting time of the investigational therapy; insufficient/inappropriate reporting of clinical data. Solutions are proposed for improving the clinical development plan, with the aim of facilitating regulatory approval of the MSC-based investigational therapy for life-threatening respiratory virus infections in the future. Major issues are the absence of a biomarker predicting responsiveness to MSCs and MSC-derived secretome and the lack of pharmacoeconomic evaluations.

Histoplasma capsulatum modulates the immune response, affects proliferation and differentiation, and induces apoptosis of mesenchymal stromal cells

Mesenchymal stromal cells (MSC) have been widely used not only for tissue regeneration but also for the treatment of various diseases; however, it has been shown that infection of MSCs by different pathogens can attenuate their intrinsic immunomodulatory properties, affecting the proliferation and differentiation of these cells. Currently, the mechanisms by which MSCs respond to pathogen invasion are poorly understood. Therefore, the objective of the present study was to determine if the infection of bone marrow-derived MSCs, with yeasts of the pathogenic fungus Histoplasma capsulatum affects the activation, differentiation and/or proliferation of the MSCs. The results indicate that MSCs have the ability to phagocytose H. capsulatum yeasts but do not exert a notable antifungal effect. On the contrary, the infection of the MSCs with this fungal pathogen not only modulates the expression of inflammatory mediators by a mechanism dependent on TLR2, TLR4 and Dectin-1 but also affects the viability and differentiation capacity of the MSCs. These findings suggest that infection of MSCs by H. capsulatum could not only affect haematopoiesis but also modulate the immune response in the infected host and, furthermore, these MSCs could provide a niche for the fungus, allowing it to persist and evade the immune response of the host.

Adverse events, side effects and complications in mesenchymal stromal cell-based therapies

Numerous clinical studies have shown a wide clinical potential of mesenchymal stromal cells (MSCs) application. However, recent experience has accumulated numerous reports of adverse events and side effects associated with MSCs therapy. Furthermore, the strategies and methods of MSCs therapy did not change significantly in recent decades despite the clinical impact and awareness of potential complications. An extended understanding of limitations could lead to a wider clinical implementation of safe cell therapies and avoid harmful approaches. Therefore, our objective was to summarize the possible negative effects observed during MSCs-based therapies. We were also aimed to discuss the risks caused by weaknesses in cell processing, including isolation, culturing, and storage. Cell processing and cell culture could dramatically influence cell population profile, change protein expression and cell differentiation paving the way for future negative effects. Long-term cell culture led to accumulation of chromosomal abnormalities. Overdosed antibiotics in culture media enhanced the risk of mycoplasma contamination. Clinical trials reported thromboembolism and fibrosis as the most common adverse events of MSCs therapy. Their delayed manifestation generally depends on the patient's individual phenotype and requires specific awareness during the clinical trials with obligatory inclusion in the patient' informed consents. Finally we prepared the safety checklist, recommended for clinical specialists before administration or planning of MSCs therapy.

Perivascular Mesenchymal Stem/Stromal Cells, an Immune Privileged Niche for Viruses?

Mesenchymal stem cells (MSCs) play a critical role in response to stress such as infection. They initiate the removal of cell debris, exert major immunoregulatory activities, control pathogens, and lead to a remodeling/scarring phase. Thus, host-derived ‘danger’ factors released from damaged/infected cells (called alarmins, e.g., HMGB1, ATP, DNA) as well as pathogen-associated molecular patterns (LPS, single strand RNA) can activate MSCs located in the parenchyma and around vessels to upregulate the expression of growth factors and chemoattractant molecules that influence immune cell recruitment and stem cell mobilization. MSC, in an ultimate contribution to tissue repair, may also directly trans- or de-differentiate into specific cellular phenotypes such as osteoblasts, chondrocytes, lipofibroblasts, myofibroblasts, Schwann cells, and they may somehow recapitulate their neural crest embryonic origin. Failure to terminate such repair processes induces pathological scarring, termed fibrosis, or vascular calcification. Interestingly, many viruses and particularly those associated to chronic infection and inflammation may hijack and polarize MSC’s immune regulatory activities. Several reports argue that MSC may constitute immune privileged sanctuaries for viruses and contributing to long-lasting effects posing infectious challenges, such as viruses rebounding in immunocompromised patients or following regenerative medicine therapies using MSC. We will herein review the capacity of several viruses not only to infect but also to polarize directly or indirectly the functions of MSC (immunoregulation, differentiation potential, and tissue repair) in clinical settings.

Current Status of Cell-Based Therapies for COVID-19: Evidence From Mesenchymal Stromal Cells in Sepsis and ARDS

The severe respiratory consequences of the coronavirus disease 2019 (COVID-19) pandemic have prompted the urgent need for novel therapies. Cell-based therapies, primarily using mesenchymal stromal cells (MSCs), have demonstrated safety and potential efficacy in the treatment of critical illness, particularly sepsis and acute respiratory distress syndrome (ARDS). However, there are limited preclinical data for MSCs in COVID-19. Recent studies have shown that MSCs could decrease inflammation, improve lung permeability, enhance microbe and alveolar fluid clearance, and promote lung epithelial and endothelial repair. In addition, MSC-based therapy has shown promising effects in preclinical studies and phase 1 clinical trials in sepsis and ARDS. Here, we review recent advances related to MSC-based therapy in the context of sepsis and ARDS and evaluate the potential value of MSCs as a therapeutic strategy for COVID-19.

Alveolar-like Macrophages Attenuate Respiratory Syncytial Virus Infection

Respiratory Syncytial Virus (RSV) is the leading cause of acute lower respiratory infections in young children and infection has been linked to the development of persistent lung disease in the form of wheezing and asthma. Despite substantial research efforts, there are no RSV vaccines currently available and an effective monoclonal antibody targeting the RSV fusion protein (palivizumab) is of limited general use given the associated expense. Therefore, the development of novel approaches to prevent RSV infection is highly desirable to improve pediatric health globally. We have developed a method to generate alveolar-like macrophages (ALMs) from pluripotent stem cells. These ALMs have shown potential to promote airway innate immunity and tissue repair and so we hypothesized that ALMs could be used as a strategy to prevent RSV infection. Here, we demonstrate that ALMs are not productively infected by RSV and prevent the infection of epithelial cells. Prevention of epithelial infection was mediated by two different mechanisms: phagocytosis of RSV particles and release of an antiviral soluble factor different from type I interferon. Furthermore, intratracheal administration of ALMs protected mice from subsequent virus-induced weight loss and decreased lung viral titres and inflammation, indicating that ALMs can impair the pathogenesis of RSV infection. Our results support a prophylactic role for ALMs in the setting of RSV infection and warrant further studies on stem cell-derived ALMs as a novel cell-based therapy for pulmonary viral infections.

Mesenchymal stromal/stem cells (MSCs) and MSC-derived extracellular vesicles in COVID-19-induced ARDS: Mechanisms of action, research progress, challenges, and opportunities

In late 2019, a novel coronavirus (SARS-CoV-2) emerged in Wuhan city, Hubei province, China. Rapidly escalated into a worldwide pandemic, it has caused an unprecedented and devastating situation on the global public health and society economy. The severity of recent coronavirus disease, abbreviated to COVID-19, seems to be mostly associated with the patients' immune response. In this vein, mesenchymal stromal/stem cells (MSCs) have been suggested as a worth-considering option against COVID-19 as their therapeutic properties are mainly displayed in immunomodulation and anti-inflammatory effects. Indeed, administration of MSCs can attenuate cytokine storm and enhance alveolar fluid clearance, endothelial recovery, and anti-fibrotic regeneration. Despite advantages attributed to MSCs application in lung injuries, there are still several issues __foremost probability of malignant transformation and incidence of MSCs-related coagulopathy__ which should be resolved for the successful application of MSC therapy in COVID-19. In the present study, we review the historical evidence of successful use of MSCs and MSC-derived extracellular vesicles (EVs) in the treatment of acute respiratory distress syndrome (ARDS). We also take a look at MSCs mechanisms of action in the treatment of viral infections, and then through studying both the dark and bright sides of this approach, we provide a thorough discussion if MSC therapy might be a promising therapeutic approach in COVID-19 patients.

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.

Fundamental and Advanced Therapies, Vaccine Development against SARS-CoV-2

Coronavirus disease (COVID-19) caused by the SARS-CoV-2 virus has been affecting the world since the end of 2019. The severity of the disease can range from an asymptomatic or mild course to acute respiratory distress syndrome (ARDS) with respiratory failure, which may lead to death. Since the outbreak of the pandemic, scientists around the world have been studying the genome and molecular mechanisms of SARS-CoV-2 infection to develop effective therapies and prevention. In this review, we summarize the progressive development of various treatments and vaccines as they have emerged, a year after the outbreak of the pandemic. Initially for COVID-19, patients were recommended drugs with presumed antiviral, anti-inflammatory, and antimicrobial effects that were previously used to treat other diseases. Thereafter, therapeutic interventions were supplemented with promising approaches based on antibodies, peptides, and stem cells. However, licensed COVID-19 vaccines remain the most effective weapon in combating the pandemic. While there is an enormous effort to enhance the vaccination rate to increase the entire population immunity, the production and delivery of vaccines is becoming limited in several countries. In this regard, there are new challenges needing to be addressed by combining non-pharmacological intervention with effective therapies until vaccination is accessible to all.

The Effect of Proinflammatory Cytokines on the Proliferation, Migration and Secretory Activity of Mesenchymal Stem/Stromal Cells (WJ-MSCs) under 5% O2 and 21% O2 Culture Conditions

Treatment with Mesenchymal Stem/Stromal Cells (MSCs) in clinical trials is becoming one of the most-popular and fast-developing branches of modern regenerative medicine, as it is still in an experimental phase. The cross-section of diseases to which these cells are applied is very wide, ranging from degenerative diseases, through autoimmune processes and to acute inflammatory diseases, e.g., viral infections. Indeed, now that first clinical trials applying MSCs against COVID-19 have started, important questions concern not only the therapeutic properties of MSCs, but also the changes that might occur in the cell features as a response to the "cytokine storm" present in the acute phase of an infection and capable of posing a risk to a patient. The aim of our study was thus to assess changes potentially occurring in the biology of MSCs in the active inflammatory environment, e.g., in regards to the cell cycle, cell migration and secretory capacity. The study using MSCs derived from Wharton's jelly (WJ-MSCs) was conducted under two aerobic conditions: 21% O2 vs. 5% O2, since oxygen concentration is one of the key factors in inflammation. Under both oxygen conditions cells were exposed to proinflammatory cytokines involved significantly in acute inflammation, i.e., IFNγ, TNFα and IL-1β at different concentrations. Regardless of the aerobic conditions, WJ-MSCs in the inflammatory environment do not lose features typical for mesenchymal cells, and their proliferation dynamic remains unchanged. Sudden fluctuations in proliferation, the early indicator of potential genetic disturbance, were not observed, while the cells' migration activity increased. The presence of pro-inflammatory factors was also found to increase the secretion of such anti-inflammatory cytokines as IL-4 and IL-10. It is concluded that the inflammatory milieu in vitro does not cause phenotype changes or give rise to proliferation disruption of WJ-MSCs, and nor does it inhibit the secretory properties providing for their use against acute inflammation.

Immunopathological similarities between COVID-19 and influenza: Investigating the consequences of Co-infection

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been a global public health emergency since December 2019, and so far, more than 980,000 people (until September 24, 2020) around the world have died. SARS-CoV-2 mimics the influenza virus regarding methods and modes of transmission, clinical features, related immune responses, and seasonal coincidence. Accordingly, co-infection by these viruses is imaginable because some studies have reported several cases with SARS-CoV-2 and influenza virus co-infection. Given the importance of the mentioned co-infection and the coming influenza season, it is essential to recognize the similarities and differences between the symptoms, immunopathogenesis and treatment of SARS-CoV-2 and influenza virus. Therefore, we reviewed the virology, clinical features, and immunopathogenesis of both influenza virus and SARS-CoV-2 and evaluated outcomes in cases with SARS-CoV-2 and influenza virus co-infection.

Human mesenchymal stromal cells do not express ACE2 and TMPRSS2 and are not permissive to SARS-CoV-2 infection

Anti‐inflammatory and immune‐modulatory therapies have been proposed for the treatment of COVID‐19 and its most serious complications. Among others, the use of mesenchymal stromal cells (MSCs) is under investigation given their well‐documented anti‐inflammatory and immunomodulatory properties. However, some critical issues regarding the possibility that MSCs could be infected by the virus have been raised. Angiotensin‐converting enzyme 2 (ACE2) and type II transmembrane serine protease (TMPRSS2) are the main host cell factors for the severe acute respiratory syndrome‐coronavirus 2 (SARS‐CoV‐2), entry, but so far it is unclear if human MSCs do or do not express these two proteins. To elucidate these important aspects, we evaluated if human MSCs from both fetal and adult tissues constitutively express ACE2 and TMPRSS2 and, most importantly, if they can be infected by SARS‐CoV‐2. We evaluated human MSCs derived from amnios, cord blood, cord tissue, adipose tissue, and bone marrow. ACE2 and TMPRSS2 were expressed by the SARS‐CoV‐2‐permissive human pulmonary Calu‐3 cell line but not by all the MSCs tested. MSCs were then exposed to SARS‐CoV‐2 wild strain without evidence of cytopathic effect. Moreover, we also excluded that the MSCs could be infected without showing lytic effects since their conditioned medium after SARS‐CoV‐2 exposure did not contain viral particles. Our data, demonstrating that MSCs derived from different human tissues are not permissive to SARS‐CoV‐2 infection, support the safety of MSCs as potential therapy for COVID‐19.

Mesenchymal Stromal Cell-Based Therapy: A Promising Approach for Severe COVID-19

During the outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), many critically ill patients died of severe pneumonia, acute respiratory distress syndrome (ARDS), or multiple organ dysfunction syndrome. To date, no specific treatments have been proven to be effective for coronavirus disease 2019 (COVID-19). In the animal models and clinical applications, mesenchymal stromal/stem cells (MSCs) have been shown safety and efficacy for the treatment of respiratory virus infection through their abilities of differentiation and immunomodulation. Besides, possessing several advantages of MSC-derived extracellular vesicles (EVs) over MSCs, EV-based therapy also holds potential therapeutic effects in respiratory virus infection. In this review, we summarized the basic characteristics and mechanisms of COVID-19 and MSCs, outlined some preclinical and clinical studies of MSCs or MSC-EVs for respiratory virus infection such as influenza virus and SARS-CoV-2, shed light on the common problems that we should overcome to translate MSC therapy into clinical application, and discussed some safe issues related to the use of MSCs.

Current status of mesenchymal stem cell therapy for immune/inflammatory lung disorders: Gleaning insights for possible use in COVID-19

The broad immunomodulatory properties of human mesenchymal stem cells (MSCs) have allowed for wide application in regenerative medicine as well as immune/inflammatory diseases, including unmatched allogeneic use. The novel coronavirus disease COVID‐19 has unleashed a pandemic in record time accompanied by an alarming mortality rate mainly due to pulmonary injury and acute respiratory distress syndrome. Because there are no effective preventive or curative therapies currently, MSC therapy (MSCT) has emerged as a possible candidate despite the lack of preclinical data of MSCs for COVID‐19. Interestingly, MSCT preclinical data specifically on immune/inflammatory disorders of the lungs were among the earliest to be reported in 2003, with the first clinical use of MSCT for graft‐vs‐host disease reported in 2004. Since these first reports, preclinical data showing beneficial effects of MSC immunomodulation have accumulated substantially, and as a consequence, over a third of MSCT clinical trials now target immune/inflammatory diseases. There is much preclinical evidence for MSCT in noninfectious—including chronic obstructive pulmonary disease, asthma, and idiopathic pulmonary fibrosis—as well as infectious bacterial immune/inflammatory lung disorders, with data generally demonstrating therapeutic effects; however, for infectious viral pulmonary conditions, the preclinical evidence is more scarce with some inconsistent outcomes. In this article, we review the mechanistic evidence for clinical use of MSCs in pulmonary immune/inflammatory disorders, and survey the ongoing clinical trials—including for COVID‐19—of MSCT for these diseases, with some perspectives and comment on MSCT for COVID‐19.

Current status of cell-based therapies for respiratory virus infections: applicability to COVID-19

The severe respiratory consequences of the coronavirus disease 2019 (COVID-19) pandemic have prompted urgent need for novel therapies. Cell-based approaches, primarily using mesenchymal stem (stromal) cells (MSCs), have demonstrated safety and possible efficacy in patients with acute respiratory distress syndrome (ARDS), although they are not yet well studied in respiratory virus-induced ARDS. Limited pre-clinical data suggest that systemic MSC administration can significantly reduce respiratory virus (influenza strains H5N1 and H9N2)-induced lung injury; however, there are no available data in models of coronavirus respiratory infection.There is a rapidly increasing number of clinical investigations of cell-based therapy approaches for COVID-19. These utilise a range of different cell sources, doses, dosing strategies and targeted patient populations. To provide a rational strategy to maximise potential therapeutic use, it is critically important to understand the relevant pre-clinical studies and postulated mechanisms of MSC actions in respiratory virus-induced lung injuries. This review presents these, along with consideration of current clinical investigations.

Mesenchymal stem cell-derived extracellular vesicles attenuate influenza virus-induced acute lung injury in a pig model

BACKGROUND

Mesenchymal stem (stromal) cells (MSCs) mediate their immunoregulatory and tissue repair functions by secreting paracrine factors, including extracellular vesicles (EVs). In several animal models of human diseases, MSC-EVs mimic the beneficial effects of MSCs. Influenza viruses cause annual outbreaks of acute respiratory illness resulting in significant mortality and morbidity. Influenza viruses constantly evolve, thus generating drug-resistant strains and rendering current vaccines less effective against the newly generated strains. Therefore, new therapies that can control virus replication and the inflammatory response of the host are needed. The objective of this study was to examine if MSC-EV treatment can attenuate influenza virus-induced acute lung injury in a preclinical model.

METHODS

We isolated EVs from swine bone marrow-derived MSCs. Morphology of MSC-EVs was determined by electron microscopy and expression of mesenchymal markers was examined by flow cytometry. Next, we examined the anti-influenza activity of MSC-EVs in vitro in lung epithelial cells and anti-viral and immunomodulatory properties in vivo in a pig model of influenza virus.

RESULTS

MSC-EVs were isolated from MSC-conditioned medium by ultracentrifugation. MSC-EVs were round-shaped and, similarly to MSCs, expressed mesenchymal markers and lacked the expression of swine leukocyte antigens I and II. Incubation of PKH-26-labeled EVs with lung epithelial cells revealed that MSC-EVs incorporated into the epithelial cells. Next, we examined the anti-influenza and anti-inflammatory properties of MSC-EVs. MSC-EVs inhibited the hemagglutination activity of avian, swine, and human influenza viruses at concentrations of 1.25-5 μg/ml. MSC-EVs inhibited influenza virus replication and virus-induced apoptosis in lung epithelial cells. The anti-influenza activity of MSC-EVs was due to transfer of RNAs from EVs to epithelial cells since pre-incubation of MSC-EVs with RNase enzyme abrogated the anti-influenza activity of MSC-EVs. In a pig model of influenza virus, intratracheal administration of MSC-EVs 12 h after influenza virus infection significantly reduced virus shedding in the nasal swabs, influenza virus replication in the lungs, and virus-induced production of proinflammatory cytokines in the lungs of influenza-infected pigs. The histopathological findings revealed that MSC-EVs alleviated influenza virus-induced lung lesions in pigs.

CONCLUSIONS

Our data demonstrated in a relevant preclinical large animal model of influenza virus that MSC-EVs possessed anti-influenza and anti-inflammatory properties and that EVs may be used as cell-free therapy for influenza in humans.

The activation of B cells enhances DC-SIGN expression and promotes susceptibility of B cells to HPAI H5N1 infection

The interplay between highly pathogenic avian influenza (HPAI) H5N1 virus and immune cells has been extensively studied for years, as host immune components are thought to play significant roles in promoting the systemic spread of the virus and responsible for cytokine storm. Previous studies suggested that the interaction of B cells and monocytes could promote HPAI H5N1 infection by enhancing avian influenza virus receptor expression. In this study, we further investigate the relationship between the HPAI H5N1 virus, activated B cells, and DC-SIGN expression. DC-SIGN has been described as an important factor for mediating various types of viral infection. Here, we first demonstrate that HPAI H5N1 infection could induce an activation of B cells, which was associated with DC-SIGN expression. Using CD40L and recombinant IL-4 for B cell stimulation, we determined that DC-SIGN expressed on activated B cells was able to enhance its susceptibility to HPAI H5N1 infection. Our findings uncover the interplay between this H5N1 virus and B cells and provide important information in understanding how the virus overcomes our immune system, contributing to its unusual immunopathogenesis.

Neuraminidase of Influenza A Virus Binds Lysosome-Associated Membrane Proteins Directly and Induces Lysosome Rupture

As a recycling center, lysosomes are filled with numerous acid hydrolase enzymes that break down waste materials and invading pathogens. Recently, lysosomal cell death has been defined as "lysosomal membrane permeabilization and the consequent leakage of lysosome contents into cytosol." Here, we show that the neuraminidase (NA) of H5N1 influenza A virus markedly deglycosylates and degrades lysosome-associated membrane proteins (LAMPs; the most abundant membrane proteins of lysosome), which induces lysosomal rupture, and finally leads to cell death of alveolar epithelial carcinoma A549 cells and human tracheal epithelial cells. The NA inhibitors peramivir and zanamivir could effectively block the deglycosylation of LAMPs, inhibit the virus cell entry, and prevent cell death induced by the H5N1 influenza virus. The NA of seasonal H1N1 virus, however, does not share these characteristics. Our findings not only reveal a novel role of NA in the early stage of the H5N1 influenza virus life cycle but also elucidate the molecular mechanism of lysosomal rupture crucial for influenza virus induced cell death.

IMPORTANCE

The integrity of lysosomes is vital for maintaining cell homeostasis, cellular defense and clearance of invading pathogens. This study shows that the H5N1 influenza virus could induce lysosomal rupture through deglycosylating lysosome-associated membrane proteins (LAMPs) mediated by the neuraminidase activity of NA protein. NA inhibitors such as peramivir and zanamivir could inhibit the deglycosylation of LAMPs and protect lysosomes, which also further interferes with the H5N1 influenza virus infection at early stage of life cycle. This work is significant because it presents new concepts for NA's function, as well as for influenza inhibitors' mechanism of action, and could partially explain the high mortality and high viral load after H5N1 virus infection in human beings and why NA inhibitors have more potent therapeutic effects for lethal avian influenza virus infections at early stage.

Influenza lung injury: mechanisms and therapeutic opportunities

In this Perspectives, we discuss some recent developments in the pathogenesis of acute lung injury following influenza infection, with an emphasis on promising therapeutic leads. Damage to the alveolar-capillary barrier has been quantified in mice, and agents have been identified that can help to preserve barrier integrity, such as vasculotide, angiopoietin-like 4 neutralization, and sphingosine 1-phosphate mimics. Results from studies using mesenchymal stem cells have been disappointing, despite promising data in other types of lung injury. The roles of fatty acid binding protein 5, prostaglandin E2, and the interplay between IFN-γ and STAT1 in epithelial signaling during infection have been addressed in vitro. Finally, we discuss the role of autophagy in inflammatory cytokine production and the viral life cycle and the opportunities this presents for intervention.

Tropism and Induction of Cytokines in Human Embryonic-Stem Cells-Derived Neural Progenitors upon Inoculation with Highly- Pathogenic Avian H5N1 Influenza Virus

Central nervous system (CNS) dysfunction caused by neurovirulent influenza viruses is a dreaded complication of infection, and may play a role in some neurodegenerative conditions, such as Parkinson-like diseases and encephalitis lethargica. Although CNS infection by highly pathogenic H5N1 virus has been demonstrated, it is unknown whether H5N1 infects neural progenitor cells, nor whether such infection plays a role in the neuroinflammation and neurodegeneration. To pursue this question, we infected human neural progenitor cells (hNPCs) differentiated from human embryonic stem cells in vitro with H5N1 virus, and studied the resulting cytopathology, cytokine expression, and genes involved in the differentiation. Human embryonic stem cells (BG01) were maintained and differentiated into the neural progenitors, and then infected by H5N1 virus (A/Chicken/Thailand/CUK2/04) at a multiplicity of infection of 1. At 6, 24, 48, and 72 hours post-infection (hpi), cytopathic effects were observed. Then cells were characterized by immunofluorescence and electron microscopy, supernatants quantified for virus titers, and sampled cells studied for candidate genes.The hNPCs were susceptible to H5N1 virus infection as determined by morphological observation and immunofluorescence. The infection was characterized by a significant up-regulation of TNF-α gene expression, while expressions of IFN-α2, IFN-β1, IFN-γ and IL-6 remained unchanged compared to mock-infected controls. Moreover, H5N1 infection did not appear to alter expression of neuronal and astrocytic markers of hNPCs, such as β-III tubulin and GFAP, respectively. The results indicate that hNPCs support H5N1 virus infection and may play a role in the neuroinflammation during acute viral encephalitis.

Mesenchymal Stromal Cells and Viral Infection

Mesenchymal Stromal Cells (MSCs) are a subset of nonhematopoietic adult stem cells, readily isolated from various tissues and easily culture-expanded ex vivo. Intensive studies of the immune modulation and tissue regeneration over the past few years have demonstrated the great potential of MSCs for the prevention and treatment of steroid-resistant acute graft-versus-host disease (GvHD), immune-related disorders, and viral diseases. In immunocompromised individuals, the immunomodulatory activities of MSCs have raised safety concerns regarding the greater risk of primary viral infection and viral reactivation, which is a major cause of mortality after allogeneic transplantation. Moreover, high susceptibilities of MSCs to viral infections in vitro could reflect the destructive outcomes that might impair the clinical efficacy of MSCs infusion. However, the interplay between MSCs and virus is like a double-edge sword, and it also provides beneficial effects such as allowing the proliferation and function of antiviral specific effector cells instead of suppressing them, serving as an ideal tool for study of viral pathogenesis, and protecting hosts against viral challenge by using the antimicrobial activity. Here, we therefore review favorable and unfavorable consequences of MSCs and virus interaction with the highlight of safety and efficacy for applying MSCs as cell therapy.