Modulation of adult mesenchymal stem cells activity by toll-like receptors: implications on therapeutic potential. Mediators Inflamm. 2010;2010:865601. [PMID: 20628526 PMCID: PMC2902124 DOI: 10.1155/2010/865601]

Macrophages after myocardial infarction: Mechanisms for repairing and potential as therapeutic approaches

Macrophages - one of the crucial immune cells, are recruited to the cardiac tissue by chemokines, cytokines and upregulated endothelial adhesion molecules after myocardial infarction (MI). During the course of inflammation in the cardiac tissue, necrotic cells and matrix debris is phagocytosed by M1 macrophages. During the resolution phase of cardiac inflammation, M2 macrophages promote cardiac recovery. Suppression or over expression of both the M1 and M2 macrophage subtypes significantly affect the reparation of infarction. Stem cells therapy, cytokine regulation and immune cells therapy are considered as effective interventions to regulate the phenotypic transformation of cardiac macrophages after MI. Intervention with macrophages in the myocardium has shown unique advantages. In this review, the mechanisms and role of macrophages in the development of MI are elaborated in detail, the promising therapeutic methods for regulating macrophage phenotypes, their limitations and possible future research directions are discussed.

Bioinspired injectable hydrogels for bone regeneration

The effective regeneration of bone/cartilage defects remains a significant clinical challenge, causing irreversible damage to millions annually.Conventional therapies such as autologous or artificial bone grafting often yield unsatisfactory outcomes, emphasizing the urgent need for innovative treatment methods. Biomaterial-based strategies, including hydrogels and active scaffolds, have shown potential in promoting bone/cartilage regeneration. Among them, injectable hydrogels have garnered substantial attention in recent years on account of their minimal invasiveness, shape adaptation, and controlled spatiotemporal release. This review systematically discusses the synthesis of injectable hydrogels, bioinspired approaches-covering microenvironment, structural, compositional, and bioactive component-inspired strategies-and their applications in various bone/cartilage disease models, highlighting bone/cartilage regeneration from an innovative perspective of bioinspired design. Taken together, bioinspired injectable hydrogels offer promising and feasible solutions for promoting bone/cartilage regeneration, ultimately laying the foundations for clinical applications. Furthermore, insights into further prospective directions for AI in injectable hydrogels screening and organoid construction are provided.

Evaluation of stem-cell therapies in companion animal disease models: a concise review (2015-2023)

Companion animals in veterinary medicine develop multiple naturally occurring diseases analogous to human conditions. We previously reported a comprehensive review on the feasibility, safety, and biologic activity of using novel stem cell therapies to treat a variety of inflammatory conditions in dogs and cats (2008-2015) [Hoffman AM, Dow SW. Concise review: stem cell trials using companion animal disease models. Stem Cells. 2016;34(7):1709-1729. https://doi.org/10.1002/stem.2377]. The purpose of this review is to provide an updated summary of current studies in companion animal disease models that have evaluated stem cell therapeutics that are relevant to human disease. Here we have reviewed the literature from 2015 to 2023 for publications on stem cell therapies that have been evaluated in companion animals, including dogs, cats, and horses. The review excluded case reports or studies performed in experimentally induced models of disease, studies involving cancer, or studies in purpose-bred laboratory species such as rodents. We identified 45 manuscripts meeting these criteria, an increase from 19 that were described in the previous review [Hoffman AM, Dow SW. Concise review: stem cell trials using companion animal disease models. Stem Cells. 2016;34(7):1709-1729. https://doi.org/10.1002/stem.2377]. The majority of studies were performed in dogs (n = 28), with additional studies in horses (n = 9) and cats (n = 8). Disease models included those related to musculoskeletal disease (osteoarthritis and tendon/ligament injury), neurologic disease (canine cognitive dysfunction, intervertebral disc disease, spinal cord injury) gingival/dental disease (gingivostomatitis), dermatologic disease (atopic dermatitis), chronic multi-drug resistant infections, ophthalmic disease (keratoconjunctivitis sicca, eosinophilic keratitis, immune-mediated keratitis), cardiopulmonary disease (asthma, degenerative valve disease, dilated cardiomyopathy), gastrointestinal disease (inflammatory bowel disease, chronic enteropathy), and renal disease (chronic kidney disease). The majority of studies reported beneficial responses to stem cell treatment, with the exception of those related to more chronic processes such as spinal cord injury and chronic kidney disease. However, it should also be noted that 22 studies were open-label, baseline-controlled trials and only 12 studies were randomized and controlled, making overall study interpretation difficult. As noted in the previous review, improved regulatory oversight and consistency in manufacturing of stem cell therapies are needed. Enhanced understanding of the temporal course of disease processes using advanced-omics approaches may further inform mechanisms of action and help define appropriate timing of interventions. Future directions of stem-cell-based therapies could include use of stem-cell-derived extracellular vesicles, or cell conditioning approaches to direct cells to specific pathways that are tailored to individual disease processes and stages of illness.

Anti-inflammatory and immunomodulatory effects of mesenchymal stem cell therapy on parasitic drug resistance

INTRODUCTION

The emergence of antiparasitic drug resistance poses a concerning threat to animals and humans. Mesenchymal Stem Cells (MSCs) have been widely used to treat infections in humans, pets, and livestock. Although this is an emerging field of study, the current review outlines possible mechanisms and examines potential synergism in combination therapies and the possible harmful effects of such an approach.

AREAS COVERED

The present study delved into the latest pre-clinical research on utilizing MSCs to treat parasitic infections. As per investigations, the introduction of MSCs to patients grappling with parasitic diseases like schistosomiasis, malaria, cystic echinococcosis, toxoplasmosis, leishmaniasis, and trypanosomiasis has shown a reduction in parasite prevalence. This intervention also alters the levels of both pro- and anti-inflammatory cytokines. Furthermore, the combined administration of MSCs and antiparasitic drugs has demonstrated enhanced efficacy in combating parasites and modulating the immune response.

EXPERT OPINION

Mesenchymal stem cells are a potential solution for addressing parasitic drug resistance. This is mainly because of their remarkable immunomodulatory abilities, which can potentially help combat parasites' resistance to drugs.

Emerging Strategies in Mesenchymal Stem Cell-Based Cardiovascular Therapeutics

Cardiovascular diseases continue to challenge global health, demanding innovative therapeutic solutions. This review delves into the transformative role of mesenchymal stem cells (MSCs) in advancing cardiovascular therapeutics. Beginning with a historical perspective, we trace the development of stem cell research related to cardiovascular diseases, highlighting foundational therapeutic approaches and the evolution of cell-based treatments. Recognizing the inherent challenges of MSC-based cardiovascular therapeutics, which range from understanding the pro-reparative activity of MSCs to tailoring patient-specific treatments, we emphasize the need to refine the pro-regenerative capacity of these cells. Crucially, our focus then shifts to the strategies of the fourth generation of cell-based therapies: leveraging the secretomic prowess of MSCs, particularly the role of extracellular vesicles; integrating biocompatible scaffolds and artificial sheets to amplify MSCs' potential; adopting three-dimensional ex vivo propagation tailored to specific tissue niches; harnessing the promise of genetic modifications for targeted tissue repair; and institutionalizing good manufacturing practice protocols to ensure therapeutic safety and efficacy. We conclude with reflections on these advancements, envisaging a future landscape redefined by MSCs in cardiovascular regeneration. This review offers both a consolidation of our current understanding and a view toward imminent therapeutic horizons.

Unraveling the Complexities of Toll-like Receptors: From Molecular Mechanisms to Clinical Applications

Toll-like receptors (TLRs) are vital components of the innate immune system, serving as the first line of defense against pathogens by recognizing a wide array of molecular patterns. This review summarizes the critical roles of TLRs in immune surveillance and disease pathogenesis, focusing on their structure, signaling pathways, and implications in various disorders. We discuss the molecular intricacies of TLRs, including their ligand specificity, signaling cascades, and the functional consequences of their activation. The involvement of TLRs in infectious diseases, autoimmunity, chronic inflammation, and cancer is explored, highlighting their potential as therapeutic targets. We also examine recent advancements in TLR research, such as the development of specific agonists and antagonists, and their application in immunotherapy and vaccine development. Furthermore, we address the challenges and controversies surrounding TLR research and outline future directions, including the integration of computational modeling and personalized medicine approaches. In conclusion, TLRs represent a promising frontier in medical research, with the potential to significantly impact the development of novel therapeutic strategies for a wide range of diseases.

Licensing effects of inflammatory factors and TLR ligands on the regenerative capacity of adipose-derived mesenchymal stem cells

Introduction: Adipose tissue-derived mesenchymal stem cells are promising contributors to regenerative medicine, exhibiting the ability to regenerate tissues and modulate the immune system, which is particularly beneficial for addressing chronic inflammatory ulcers and wounds. Despite their inherent capabilities, research suggests that pretreatment amplifies therapeutic effectiveness. Methods: Our experimental design exposed adipose-derived mesenchymal stem cells to six inflammatory factors for 24 h. We subsequently evaluated gene expression and proteome profile alterations and observed the wound closure rate post-treatment. Results: Specific pretreatments, such as IL-1β, notably demonstrated an accelerated wound-healing process. Analysis of gene and protein expression profiles revealed alterations in pathways associated with tissue regeneration. Discussion: This suggests that licensed cells exhibit potentially higher therapeutic efficiency than untreated cells, shedding light on optimizing regenerative strategies using adipose tissue-derived stem cells.

Preliminary evaluation of safety and migration of immune activated mesenchymal stromal cells administered by subconjunctival injection for equine recurrent uveitis

Introduction

Equine recurrent uveitis (ERU), an immune mediated disease characterized by repeated episodes of intra-ocular inflammation, affects 25% of horses in the USA and is the most common cause of glaucoma, cataracts, and blindness. Mesenchymal stromal cells (MSCs) have immunomodulatory properties, which are upregulated by preconditioning with toll-like receptor agonists. The objective was to evaluate safety and migration of TLR-3 agonist polyinosinic, polycytidylic acid (pIC)-activated MSCs injected subconjunctivally in healthy horses prior to clinical application in horses with ERU. We hypothesized that activated allogeneic MSCs injected subconjunctivally would not induce ocular or systemic inflammation and would remain in the conjunctiva for >14 days.

Methods

Bulbar subconjunctiva of two horses was injected with 10 × 106 pIC-activated (10 μg/mL, 2 h) GFP-labeled MSCs from one donor three times at two-week intervals. Vehicle (saline) control was injected in the contralateral conjunctiva. Horses received physical and ophthalmic exams [slit lamp biomicroscopy, rebound tonometry, fundic examination, and semiquantitative preclinical ocular toxicology scoring (SPOTS)] every 1-3 days. Systemic inflammation was assessed via CBC, fibrinogen, and serum amyloid A (SAA). Horses were euthanized 14 days following final injection. Full necropsy and histopathology were performed to examine ocular tissues and 36 systemic organs for MSC presence via IVIS Spectrum. Anti-GFP immunohistochemistry was performed on ocular tissues.

Results

No change in physical examinations was noted. Bloodwork revealed fibrinogen 100-300 mg/dL (ref 100-400) and SAA 0-25 μg/mL (ref 0-20). Ocular effects of the subjconjucntival injection were similar between MSC and control eyes on SPOTS grading system, with conjunctival hypermia, chemosis and ocular discharge noted bilaterally, which improved without intervention within 14 days. All other ocular parameters were unaffected throughout the study. Necropsy and histopathology revealed no evidence of systemic inflammation. Ocular histopathology was similar between MSC and control eyes. Fluorescent imaging analysis did not locate MSCs. Immunohistochemistry did not identify intact MSCs in the conjunctiva, but GFP-labeled cellular components were present in conjunctival phagocytic cells.

Discussion

Allogeneic pIC-activated conjunctival MSC injections were well tolerated. GFP-labeled tracking identified MSC components phagocytosed by immune cells subconjunctivally. This preliminary safety and tracking information is critical towards advancing immune conditioned cellular therapies to clinical trials in horses.

Exploring therapeutic avenues: mesenchymal stem/stromal cells and exosomes in confronting enigmatic biofilm-producing fungi

Fungal infections concomitant with biofilms can demonstrate an elevated capacity to withstand substantially higher concentrations of antifungal agents, contrasted with infectious diseases caused by planktonic cells. This inherent resilience intrinsic to biofilm-associated infections engenders a formidable impediment to effective therapeutic interventions. The different mechanisms that are associated with the intrinsic resistance of Candida species encompass drug sequestration by the matrix, drug efflux pumps, stress response cell density, and the presence of persister cells. These persisters, a subset of fungi capable of surviving hostile conditions, pose a remarkable challenge in clinical settings in virtue of their resistance to conventional antifungal therapies. Hence, an exigent imperative has arisen for the development of novel antifungal therapeutics with specific targeting capabilities focused on these pathogenic persisters. On a global scale, fungal persistence and their resistance within biofilms generate an urgent clinical need for investigating recently introduced therapeutic strategies. This review delves into the unique characteristics of Mesenchymal stem/stromal cells (MSCs) and their secreted exosomes, which notably exhibit immunomodulatory and regenerative properties. By comprehensively assessing the current literature and ongoing research in this field, this review sheds light on the plausible mechanisms by which MSCs and their exosomes can be harnessed to selectively target fungal persisters. Additionally, prospective approaches in the use of cell-based therapeutic modalities are examined, emphasizing the importance of further research to overcome the enigmatic fungal persistence.

The effect of TLR3 priming conditions on MSC immunosuppressive properties

BACKGROUND

Mesenchymal stromal cells (MSCs) have regenerative and immunomodulatory properties, making them suitable for cell therapy. Toll-like receptors (TLRs) in MSCs respond to viral load by secreting immunosuppressive or proinflammatory molecules. The expression of anti-inflammatory molecules in MSCs can be altered by the concentration and duration of exposure to the TLR3 ligand polyinosinic-polycytidylic acid (poly(I:C)). This study aimed to optimize the preconditioning of MSCs with poly(I:C) to increase immunosuppressive effects and to identify MSCs with activated TLR3 (prMSCs).

METHODS

Flow cytometry and histochemical staining were used to analyze MSCs for immunophenotype and differentiation potential. MSCs were exposed to poly(I:C) at 1 and 10 μg/mL for 1, 3, and 24 h, followed by determination of the expression of IDO1, WARS1, PD-L1, TSG-6, and PTGES2 and PGE2 secretion. MSCs and prMSCs were cocultured with intact (J-) and activated (J+) Jurkat T cells. The proportion of proliferating and apoptotic J+ and J- cells, IL-10 secretion, and IL-2 production after cocultivation with MSCs and prMSCs were measured. Liquid chromatography-mass spectrometry and bioinformatics analysis identified proteins linked to TLR3 activation in MSCs.

RESULTS

Poly(I:C) at 10 μg/mL during a 3-h incubation caused the highest expression of immunosuppression markers in MSCs. Activation of prMSCs caused a 18% decrease in proliferation and a one-third increase in apoptotic J+ cells compared to intact MSCs. Cocultures of prMSCs and Jurkat cells had increased IL-10 and decreased IL-2 in the conditioned medium. A proteomic study of MSCs and prMSCs identified 53 proteins with altered expression. Filtering the dataset with Gene Ontology and Reactome Pathway revealed that poly(I:C)-induced proteins activate the antiviral response. Protein‒protein interactions by String in prMSCs revealed that the antiviral response and IFN I signaling circuits were more active than in native MSCs. prMSCs expressed more cell adhesion proteins (ICAM-I and Galectin-3), PARP14, PSMB8, USP18, and GBP4, which may explain their anti-inflammatory effects on Jurkat cells.

CONCLUSIONS

TLR3 activation in MSCs is dependent on exposure time and poly(I:C) concentration. The maximum expression of immunosuppressive molecules was observed with 10 µg/mL poly(I:C) for 3-h preconditioning. This priming protocol for MSCs enhances the immunosuppressive effects of prMSCs on T cells.

Toll-like receptor expression profile of stem/progenitor cells from human exfoliated deciduous teeth

BACKGROUND

Stem/progenitor cells from human exfoliated deciduous teeth (SHED) show remarkable pluripotent, regenerative, and immunological capacities. During in vivo regenerative processes, there could be the presence of SHED in the surrounding inflammatory microenvironment, through toll-like receptors (TLRs).

AIM

The aim of this paper was to present a characteristic TLR expression profile on SHED for the first time.

DESIGN

Cells were harvested from extracted primary teeth (n = 10), anti-STRO-1 immunomagnetically sorted and cultivated, through colony-forming units (CFUs). SHED were examined for mesenchymal stem/progenitor cell traits, including the expression of clusters of differentiation (CDs) 14, 34, 45, 73, 90, 105, and 146, and their multilineage differentiation aptitude. TLRs 1-10 expression was investigated for SHED in uninflamed and inflamed (25 ng/mL IL-1β, 103 U/mL IFN-γ, 50 ng/mL TNF-α, and 3 × 103  U/mL IFN-α; SHED-i) microenvironmental conditions.

RESULTS

SHED were negative for CDs 14, 34, and 45, but were positive for CDs 73, 90, 105, and 146, and demonstrated characteristic multilineage differentiation. In an uninflamed microenvironment, SHED expressed TLRs 1, 2, 3, 4, 6, 8, 9, and 10. The inflammatory microenvironment downregulated TLR7 significantly on gene level and upregulated TLR8 on gene and protein levels (p < .05; Wilcoxon signed-rank test).

CONCLUSION

There appears to be a unique TLR expression profile on SHED, which could modulate their immunological and regenerative abilities in oral tissue engineering approaches.

Immune Privileges as a Result of Mutual Regulation of Immune and Stem Systems

Immune privileges of cancer stem cells is a well-known and widely studied problem, as presence of such cells in tumors is associated with refractoriness, recurrence, and metastasis. Accumulating evidence also suggests presence of immune privileges in non-pathological stem cells in addition to their other defense mechanisms against damaging factors. This similarity between pathological and normal stem cells raises the question of why stem cells have such a potentially dangerous property. Regulation of vital processes of autoimmunity control and regeneration realized through interactions between immune cells, stem cells, and their microenvironment are reviewed in this work as causes of formation of the stem cell immune privilege. Deep mutual integration between regulations of stem and immune cells is noted. Considering diversity and complexity of mutual regulation of stem cells, their microenvironment, and immune system, I suggest the term "stem system".

Host and Pathogen-Directed Therapies against Microbial Infections Using Exosome- and Antimicrobial Peptide-derived Stem Cells with a Special look at Pulmonary Infections and Sepsis

Microbial diseases are a great threat to global health and cause considerable mortality and extensive economic losses each year. The medications for treating this group of diseases (antibiotics, antiviral, antifungal drugs, etc.) directly attack the pathogenic agents by recognizing the target molecules. However, it is necessary to note that excessive use of any of these drugs can lead to an increase in microbial resistance and infectious diseases. New therapeutic methods have been studied recently using emerging drugs such as mesenchymal stem cell-derived exosomes (MSC-Exos) and antimicrobial peptides (AMPs), which act based on two completely different strategies against pathogens including Host-Directed Therapy (HDT) and Pathogen-Directed Therapy (PDT), respectively. In the PDT approach, AMPs interact directly with pathogens to interrupt their intrusion, survival, and proliferation. These drugs interact directly with the cell membrane or intracellular components of pathogens and cause the death of pathogens or inhibit their replication. The mechanism of action of MSC-Exos in HDT is based on immunomodulation and regulation, promotion of tissue regeneration, and reduced host toxicity. This review studies the potential of mesenchymal stem cell-derived exosomes/ATPs therapeutic properties against microbial infectious diseases especially pulmonary infections and sepsis.

Human umbilical cord mesenchymal stem cells in diabetes mellitus and its complications: applications and research advances

Diabetes mellitus and its complications pose a major threat to global health and affect the quality of life and life expectancy of patients. Currently, the application of traditional therapeutic drugs for diabetes mellitus has great limitations and can only temporarily control blood glucose but not fundamentally cure it. Mesenchymal stem cells, as pluripotent stromal cells, have multidirectional differentiation potential, high self-renewal, immune regulation, and low immunogenicity, which provide a new idea and possible development direction for diabetes mellitus treatment. Regenerative medicine with mesenchymal stem cells treatment as the core treatment will become another treatment option for diabetes mellitus after traditional treatment. Recently, human umbilical cord mesenchymal stem cells have been widely used in basic and clinical research on diabetes mellitus and its complications because of their abundance, low ethical controversy, low risk of infection, and high proliferation and differentiation ability. This paper reviews the therapeutic role and mechanism of human umbilical cord mesenchymal stem cells in diabetes mellitus and its complications and highlights the challenges faced by the clinical application of human umbilical cord mesenchymal stem cells to provide a more theoretical basis for the application of human umbilical cord mesenchymal stem cells in diabetes mellitus patients.

Logical modelling of myelofibrotic microenvironment predicts dysregulated progenitor stem cell crosstalk

Primary myelofibrosis is an untreatable age-related disorder of haematopoiesis in which a break in the crosstalk between progenitor Haematopoietic Stem Cells (HSCs) and neighbouring mesenchymal stem cells causes HSCs to rapidly proliferate and migrate out of the bone marrow. Around 90% of patients harbour mutations in driver genes that all converge to overactivate haematopoietic JAK-STAT signalling, which is thought to be critical for disease progression, as well as microenvironment modification induced by chronic inflammation. The trigger to the initial event is unknown but dysregulated thrombopoietin (TPO) and Toll-Like Receptor (TLR) signalling are hypothesised to initiate chronic inflammation which then disrupts stem cell crosstalk. Using a systems biology approach, we have constructed an intercellular logical model that captures JAK-STAT signalling and key crosstalk channels between haematopoietic and mesenchymal stem cells. The aim of the model is to decipher how TPO and TLR stimulation can perturb the bone marrow microenvironment and dysregulate stem cell crosstalk. The model predicted conditions in which the disease was averted and established for both wildtype and ectopically JAK mutated simulations. The presence of TPO and TLR are both required to disturb stem cell crosstalk and result in the disease for wildtype. TLR signalling alone was sufficient to perturb the crosstalk and drive disease progression for JAK mutated simulations. Furthermore, the model predicts probabilities of disease onset for wildtype simulations that match clinical data. These predictions might explain why patients who test negative for the JAK mutation can still be diagnosed with PMF, in which continual exposure to TPO and TLR receptor activation may trigger the initial inflammatory event that perturbs the bone marrow microenvironment and induce disease onset.

Can mesenchymal stem/stromal cells and their secretomes combat bacterial persisters?

The increasing number of life-threatening infections caused by persister bacteria is associated with various issues, including antimicrobial resistance and biofilm formation. Infections due to persister cells are often difficult to suppress without the use of last-resort antibiotics. Throughout the world, bacterial persistence and resistance create an unmet clinical demand for the exploration of newly introduced therapeutic approaches. Mesenchymal stem / stromal cells (MSCs) have an antimicrobial activity to protect against bacterial infections, including those caused by bacterial persisters. MSCs have substantial potential to secrete antimicrobial peptides (AMPs), including cathelicidin, beta-defensins, lipocalin-2, hepcidin, indoleamine 2,3-dioxygenase (IDO), cysteine proteases, and inducible nitric oxide synthases (iNOS). MSCs possess the potential to contribute to innate immunity by regulating the immune response. Recently, MSCs and their secreted components have been reported to improve antimicrobial activity. Bactericidal activity by MSCs and their secretomes has been shown to be mediated in part by the secretion of AMPs. Even though they were discovered more than 80 years ago, therapeutic options for persisters are restricted, and there is an urgent need for alternative treatment regimens. Hence, this review intends to critically assess the current literature on the effects of MSCs and their secretomes on persister bacteria. MSCs and their secretome-based therapies could be preferred as an up-and-coming approach to reinforce the antimicrobial efficiency in persister infections.

Effect of Inflammatory Microenvironment on the Regenerative Capacity of Adipose-Derived Mesenchymal Stem Cells

Adipose-derived mesenchymal stem cells are increasingly being used in regenerative medicine as cell therapy targets, including in the treatment of burns and ulcers. The regenerative potential of AD-MSCs and some of their immunological properties are known from in vitro studies; however, in clinical applications, cells are used in non-ideal conditions and can behave differently in inflammatory environments, affecting the efficacy and outcome of therapy. Our aim was to investigate and map the pathways that the inflammatory microenvironment can induce in these cells. High-throughput gene expression assays were performed on AD-MSCs activated with LPS and TNFα. Analysis of RNA-Seq data showed that control, LPS-treated and TNFα-treated samples exhibited distinct gene expression patterns. LPS treatment increased the expression of 926 genes and decreased the expression of 770 genes involved in cell division, DNA repair, the cell cycle, and several metabolic processes. TNFα treatment increased the expression of 174 genes and decreased the expression of 383 genes, which are related to cell division, the immune response, cell proliferation, and differentiation. We also map the biological pathways by further investigating the most altered genes using the Gene Ontology and KEGG databases. Secreted cytokines, which are important in the immunological response, were also examined at the protein level, and a functional assay was performed to assess wound healing. Activated AD-MSC increased the secretion of IL-6, IL-8 and CXCL-10, and also the closure of wounds. AD-MSCs presented accelerated wound healing under inflammation conditions, suggesting that we could use this cell in clinical application.

In vitro effects of monophosphoryl lipid A and Poly I:C combination on equine cells

BACKGROUND

Toll-like receptor (TLR) agonists have been used as adjuvants to modulate immune responses in both animals and humans.

OBJECTIVES

The objective of this study was to evaluate the combined effects of the TLR 4 agonist monophosphoryl lipid A (MPL) and the TLR 3 agonist polyinosinic:polycytidylic acid (Poly I:C) on equine peripheral blood mononuclear cells (PBMCs), monocyte-derived dendritic cells (MoDCs), and bone marrow-derived mesenchymal stromal cells (BM-MSCs).

METHODS

The PBMCs, MoDCs, and BM-MSCs collected from three mixed breed horses were treated with MPL, Poly I:C, and their combination. The mRNA expression of interferon gamma (IFN-γ), interleukin (IL)-1β, IL-4, IL-6, IL-8, IL-12p40, tumor necrosis factor alpha (TNF-α), vascular endothelial growth factor (VEGF), and monocyte chemoattractant protein-1 (MCP-1) was determined using real-time polymerase chain reaction.

RESULTS

The combination of MPL and Poly I:C significantly upregulated immunomodulatory responses in equine cells/ without cytotoxicity. The combination induced greater mRNA expression of pro-inflammatory cytokines IFN-γ and IL-6 than MPL or Poly I:C stimulation alone in PBMCs. In addition, the combination induced significantly higher mRNA expression of IL-1β, IL-6, and IL-12p40 in MoDCs, and IL-8, MCP-1, and VEGF in BM-MSCs compared to stimulation with a single TLR agonist.

CONCLUSIONS

The combination of MPL and Poly I:C can be used as a potential adjuvant candidate for vaccines to aid in preventing infectious diseases in horses.

Evaluation of human adipose-derived mesenchymal stromal cell Toll-like receptor priming and effects on interaction with prostate cancer cells

BACKGROUND AIMS

Mesenchymal stromal cells (MSCs) are a multipotent cell population of clinical interest because of their ability to migrate to injury and tumor sites, where they may participate in tissue repair and modulation of immune response. Although the processes regulating MSC function are incompletely understood, it has been shown that stimulation of Toll-like receptors (TLRs) can alter MSC activity. More specifically, it has been reported that human bone marrow-derived MSCs can be "polarized" by TLR priming into contrasting immunomodulatory functions, with opposite (supportive or suppressive) roles in tumor progression and inflammation. Adipose-derived MSCs (ASCs) represent a promising alternative MSC subpopulation for therapeutic development because of their relative ease of isolation and higher abundance compared with their bone marrow-derived counterparts; however, the polarization of ASCs remains unreported.

METHODS

In this study, we evaluated the phenotypic and functional consequences of short-term, low-level stimulation of ASCs with TLR3 and TLR4 agonists.

RESULTS

In these assays, we identified transient gene expression changes resembling the reported pro-inflammatory and anti-inflammatory MSC phenotypes. Furthermore, these priming strategies led to changes in the functional properties of ASCs, affecting their ability to migrate and modulate immune-mediated responses to prostate cancer cells in vitro.

CONCLUSIONS

TLR3 stimulation significantly decreased ASC migration, and TLR4 stimulation increased ASC immune-mediated killing potential against prostate cancer cells.

Immune Activated Cellular Therapy for Drug Resistant Infections: Rationale, Mechanisms, and Implications for Veterinary Medicine

Antimicrobial resistance and biofilm formation both present challenges to treatment of bacterial infections with conventional antibiotic therapy and serve as the impetus for development of improved therapeutic approaches. Mesenchymal stromal cell (MSC) therapy exerts an antimicrobial effect as demonstrated in multiple acute bacterial infection models. This effect can be enhanced by pre-conditioning the MSC with Toll or Nod-like receptor stimulation, termed activated cellular therapy (ACT). The purpose of this review is to summarize the current literature on mechanisms of antimicrobial activity of MSC with emphasis on enhanced effects through receptor agonism, and data supporting use of ACT in treatment of bacterial infections in veterinary species including dogs, cats, and horses with implications for further treatment applications. This review will advance the field's understanding of the use of activated antimicrobial cellular therapy to treat infection, including mechanisms of action and potential therapeutic applications.

MSCs vs. iPSCs: Potential in therapeutic applications

Over the past 2 decades, mesenchymal stem cells (MSCs) have attracted a lot of interest as a unique therapeutic approach for a variety of diseases. MSCs are capable of self-renewal and multilineage differentiation capacity, immunomodulatory, and anti-inflammatory properties allowing it to play a role in regenerative medicine. Furthermore, MSCs are low in tumorigenicity and immune privileged, which permits the use of allogeneic MSCs for therapies that eliminate the need to collect MSCs directly from patients. Induced pluripotent stem cells (iPSCs) can be generated from adult cells through gene reprogramming with ectopic expression of specific pluripotency factors. Advancement in iPS technology avoids the destruction of embryos to make pluripotent cells, making it free of ethical concerns. iPSCs can self-renew and develop into a plethora of specialized cells making it a useful resource for regenerative medicine as they may be created from any human source. MSCs have also been used to treat individuals infected with the SARS-CoV-2 virus. MSCs have undergone more clinical trials than iPSCs due to high tumorigenicity, which can trigger oncogenic transformation. In this review, we discussed the overview of mesenchymal stem cells and induced pluripotent stem cells. We briefly present therapeutic approaches and COVID-19-related diseases using MSCs and iPSCs.

Dental-Pulp Stem Cells as a Therapeutic Strategy for Ischemic Stroke

Regenerative medicine aims to restore human functions by regenerating organs and tissues using stem cells or living tissues for the treatment of organ and tissue defects or dysfunction. Clinical trials investigating the treatment of cerebral infarction using mesenchymal stem cells, a type of somatic stem cell therapy, are underway. The development and production of regenerative medicines using somatic stem cells is expected to contribute to the treatment of cerebral infarction, a central nervous system disease for which there is no effective treatment. Numerous experimental studies have shown that cellular therapy, including the use of human dental pulp stem cells, is an attractive strategy for patients with ischemic brain injury. This review describes the basic research, therapeutic mechanism, clinical trials, and future prospects for dental pulp stem cell therapy, which is being investigated in Japan in first-in-human clinical trials for the treatment of patients with acute cerebral ischemia.

Potential of Mesenchymal Stem Cell-Derived Exosomes as a Novel Treatment for Female Infertility Caused by Bacterial Infections

Neisseria gonorrhoeae and Chlamydia trachomatis are the most common causes of bacterial sexually transmitted diseases (STDs) with complications in women, including pelvic inflammatory disease (PID), ectopic pregnancy, and infertility. The main concern with these infections is that 70% of infected women are asymptomatic and these infections ascend to the upper female reproductive tract (FRT). Primary infection in epithelial cells creates a cascade of events that leads to secretion of pro-inflammatory cytokines that stimulate innate immunity. Production of various cytokines is damaging to mucosal barriers, and tissue destruction leads to ciliated epithelial destruction that is associated with tubal scarring and ultimately provides the conditions for infertility. Mesenchymal stem cells (MSCs) are known as tissue specific stem cells with limited self-renewal capacity and the ability to repair damaged tissues in a variety of pathological conditions due to their multipotential differentiation capacity. Moreover, MSCs secrete exosomes that contain bioactive factors such as proteins, lipids, chemokines, enzymes, cytokines, and immunomodulatory factors which have therapeutic properties to enhance recovery activity and modulate immune responses. Experimental studies have shown that local and systemic treatment of MSC-derived exosomes (MSC-Exos) suppresses the destructive immune response due to the delivery of immunomodulatory proteins. Interestingly, some recent data have indicated that MSC-Exos display strong antimicrobial effects, by the secretion of antimicrobial peptides and proteins (AMPs), and increase bacterial clearance by enhancing the phagocytic activity of host immune cells. Considering MSC-Exos can secrete different bioactive factors that can modulate the immune system and prevent infection, exosome therapy is considered as a new therapeutic method in the treatment of inflammatory and microbial diseases. Here we intend to review the possible application of MSC-Exos in female reproductive system bacterial diseases.

Regulation of pathophysiological and tissue regenerative functions of MSCs mediated via the WNT signaling pathway (Review)

Tissues have remarkable natural capabilities to regenerate for the purpose of physiological turnover and repair of damage. Adult mesenchymal stem cells (MSCs) are well known for their unique self-renewal ability, pluripotency, homing potential, paracrine effects and immunomodulation. Advanced research of the unique properties of MSCs have opened up new horizons for tissue regenerative therapies. However, certain drawbacks of the application of MSCs, such as the low survival rate of transplanted MSCs, unsatisfactory efficiency and even failure to regenerate under an unbalanced microenvironment, are concerning with regards to their wider therapeutic applications. The activity of stem cells is mainly regulated by the anatomical niche; where they are placed during their clinical and therapeutic applications. Crosstalk between various niche signals maintains MSCs in homeostasis, in which the WNT signaling pathway plays vital roles. Several external or internal stimuli have been reported to interrupt the normal bioactivity of stem cells. The irreversible tissue loss that occurs during infection at the site of tissue grafting suggests an inhibitory effect mediated by microbial infections within MSC niches. In addition, MSC-seeded tissue engineering success is difficult in various tissues, when sites of injury are under the effects of a severe infection despite the immunomodulatory properties of MSCs. In the present review, the current understanding of the way in which WNT signaling regulates MSC activity modification under physiological and pathological conditions was summarized. An effort was also made to illustrate parts of the underlying mechanism, including the inflammatory factors and their interactions with the regulatory WNT signaling pathway, aiming to promote the clinical translation of MSC-based therapy.

Transcriptional Profile of Cytokines, Regulatory Mediators and TLR in Mesenchymal Stromal Cells after Inflammatory Signaling and Cell-Passaging

Adult human subcutaneous adipose tissue (AT) harbors a rich population of mesenchymal stromal cells (MSCs) that are of interest for tissue repair. For this purpose, it is of utmost importance to determine the response of AT-MSCs to proliferative and inflammatory signals within the damaged tissue. We have characterized the transcriptional profile of cytokines, regulatory mediators and Toll-like receptors (TLR) relevant to the response of MSCs. AT-MSCs constitutively present a distinct profile for each gene and differentially responded to inflammation and cell-passaging. Inflammation leads to an upregulation of IL-6, IL-8, IL-1β, TNFα and CCL5 cytokine expression. Inflammation and cell-passaging increased the expression of HGF, IDO1, PTGS1, PTGS2 and TGFβ. The expression of the TLR pattern was differentially modulated with TLR 1, 2, 3, 4, 9 and 10 being increased, whereas TLR 5 and 6 downregulated. Functional enrichment analysis demonstrated a complex interplay between cytokines, TLR and regulatory mediators central for tissue repair. This profiling highlights that following a combination of inflammatory and proliferative signals, the sensitivity and responsive capacity of AT-MSCs may be significantly modified. Understanding these transcriptional changes may help the development of novel therapeutic approaches.

Toll-like receptor activation of equine mesenchymal stromal cells to enhance antibacterial activity and immunomodulatory cytokine secretion

OBJECTIVE

To evaluate effects of Toll-like and nucleotide-binding oligomerization domain (NOD)-like receptor (TLR, NLR) ligand stimulation of equine mesenchymal stromal cells (MSCs) on antibacterial and immunomodulatory properties in vitro.

STUDY DESIGN

Controlled laboratory study.

SAMPLE POPULATION

Equine bone-marrow-derived MSCs (three horses).

METHODS

MSCs were stimulated with TLR (polyinosinic:polycytidylic acid [pIC] and lipopolysaccharide [LPS]) and NLR agonists (γ-d-Glu-mDAP [IE-DAP]) for 2 h, and plated at 1 × 10⁵ cells/well 24 h. MSC-conditioned media (MSC-CM) were collected and assessed for antimicrobial peptide cathelicidin/LL-37 production, bactericidal action against multidrug-resistant planktonic and biofilm Staphylococcus aureus and neutrophil phagocytosis. Bacterial growth was measured by plating bacteria and counting viable colonies, reading culture absorbance, and live-dead staining with confocal microscopy imaging. Following initial comparison of activating stimuli, TLR3-agonist pIC protocols (cell density during activation and plating, culture time, %serum) were further optimized for bactericidal activity and secretion of interleukin-8 (IL-8), monocyte-chemoattractant-protein (MCP-1), and cathelicidin/LL37.

RESULTS

MSCs stimulation with pIC (p = .004) and IE-DAP (p = .03) promoted increased bactericidal activity, evidenced by reduced viable planktonic colony counts. PIC stimulation (2 × 10⁶ cells/ml, 2 h, 10 μg/ml) further suppressed biofilm formation (p = .001), enhanced neutrophil bacterial phagocytosis (p = .009), increased MCP-1 secretion (p < .0001), and enhanced cathelicidin/LL-37 production, which was apparent when serum concentration in media was reduced to 1% (p = .01) and 2.5% (p = .05).

CONCLUSION

TLR-3 pIC MSCs activation was most effective to enhance antibacterial and cytokine responses, which were affected by serum reduction.

CLINICAL SIGNIFICANCE

In vitro TLR-3 activation of equine MSCs tested here may be a strategy to improve antibacterial properties of MSCs to treat antibiotic-resistant infections.

Translational Animal Models Provide Insight Into Mesenchymal Stromal Cell (MSC) Secretome Therapy

The therapeutic potential of the mesenchymal stromal cell (MSC) secretome, consisting of all molecules secreted by MSCs, is intensively studied. MSCs can be readily isolated, expanded, and manipulated in culture, and few people argue with the ethics of their collection. Despite promising pre-clinical studies, most MSC secretome-based therapies have not been implemented in human medicine, in part because the complexity of bioactive factors secreted by MSCs is not completely understood. In addition, the MSC secretome is variable, influenced by individual donor, tissue source of origin, culture conditions, and passage. An increased understanding of the factors that make up the secretome and the ability to manipulate MSCs to consistently secrete factors of biologic importance will improve MSC therapy. To aid in this goal, we can draw from the wealth of information available on secreted factors from MSC isolated from veterinary species. These translational animal models will inspire efforts to move human MSC secretome therapy from bench to bedside.

Human umbilical cord mesenchymal stem cells attenuate podocyte injury under high glucose via TLR2 and TLR4 signaling

AIMS

This research aimed to investigate the effects of high glucose (HG) on the innate immunity of podocytes and diabetic nephropathy (DN) mice via Toll like receptor (TLR) signaling, and explore the protective effectsof human umbilical cord mesenchymal stem cells (HUC-MSCs) on this process.

METHODS

HUC-MSCs obtained from human umbilical cord were cocultured with podocytes and transplanted into DN mice. Flow cytometry, CCK-8assay, ELISA, western blot analysis, periodicacid-schiff, masson, immunohistochemistry and immunofluorescence staining was used to detect the inflammation, TLR signaling, physical, biochemical and morphological parameters in podocytes and DN mice.

RESULTS

HG reduced the viability of podocytes, activated TLR2 and TLR4 signaling pathway and increased the expression of inflammatory cytokines such as IL-6, IL-1β, TNF-α, and MCP-1 in podocytes and DN mice. However, HUC-MSCs decreased the inflammation and restrained the TLR signaling pathway caused by HG in vitro and in vivo. Furthermore the rhHGF decreased the expression of TLR2 and TLR4 while the blockade of HGF increased the expression of TLR2 and TLR4 in podocytes.

CONCLUSIONS

HUC-MSCs have benefits to the podocytes under HG and the progression of DN by inhibiting TLR signaling pathway and depressing the inflammation. HUC-MSCs may be a therapeutic strategy for treating patients with DN.

Critical roles of TLRs on the polarization of mesenchymal stem cells for cell therapy of viral infections: a notice for COVID-19 treatment

Mesenchymal stem cells (MSCs), as one of the leading cell-based therapy, have provided a strong link between clinical investigation and basic research. MSCs have been successfully employed in treating graft versus host disease (GvHD), autoimmune disease, and several other diseases, particularly with high immune activity. Recently, MSCs have attracted attention to treating untreatable viral infections such as severe coronavirus disease 2019 (COVID-19). Given that the Toll-like receptors (TLRs) are directly able to detect internal and external hazard signals, and their stimulation has an intense effect on the ability to grow, differentiate, migrate, and maintain MSCs, it seems stimulation of these receptors can have a direct impact on the interaction of MSCs and immune cells, altering the ability to modify immune system responses. Hence, this mini-review focused on TLRs’ critical roles in the polarization of MSCs for developing MSC-based therapy in viral infections. Consequently, according to the literature review, a polarization process, mediated by TLRs concerning anti-inflammatory and proinflammatory phenotype, may be considered for MSC-therapy against viral infections.

Immunomodulatory effects of mesenchymal stem cells for the treatment of cardiac allograft rejection

Heart transplantation continues to be the gold standard clinical intervention to treat patients with end-stage heart failure. However, there are major complications associated with this surgical procedure that reduce the survival prognosis of heart transplant patients, including allograft rejection, malignancies, infections, and other complications that arise from the use of broad-spectrum immunosuppression drugs. Recent studies have demonstrated the use of mesenchymal stem cells (MSCs) against allotransplantation rejection in both in vitro and in vivo settings due to their immunomodulatory properties. Therefore, utilization of MSCs provides new and exciting strategies to improve heart transplantation and potentially reduce the use of broad-spectrum immunosuppression drugs while alleviating allograft rejection. In this review, we will discuss the current research on the mechanisms of cardiac allograft rejection, the physiological and immunological characteristics of MSCs, the effects of MSCs on the immune system, and immunomodulation of heart transplantation by MSCs.

Mesenchymal Stem Cell-Mediated Immuno-Modulatory and Anti- Inflammatory Mechanisms in Immune and Allergic Disorders

Background: Mesenchymal Stem Cells (MSCs) are present in almost all the tissues of the body and act as the backbone of the internal tissue homeostasis. Among their various characteristic features, immuno-modulatory and/ anti-inflammatory properties play an important role in therapeutics.

Objective: The current topic focuses on the characterization and immuno-modulatory and/ anti-inflammatory properties of MSCs. To present and discuss the current status of MSCs immuno-modulatory properties.

Methods: Available literature on MSCs properties and patents have been detailed, critically interpreted, and discussed based upon available literature. The main focus has been on their characteristic immuno-modulatory and anti-inflammatory properties though some of the basic characterization markers have also been detailed. The databases searched for the literature include PubMed, Med Line, PubMed Central, Science Direct and a few other scientific databases.

Results: MSCs are present in a very limited concentration in the tissues, and as such their culture expansion becomes imperative. MSCs immuno-modulatory and anti-inflammatory roles are achieved through direct cell-cell contact and / by the release of certain factors. Such properties are controlled by micro-environment upon which currently very limited control can be exerted. Besides, further insights in the xeno-protein free culture media as against the fetal bovine serum is required.

Conclusion: MSCs have been well-isolated, cultured and characterized from numerous tissues of the body. The majority of the studies have shown MSCs as immuno-compromised with immunomodulatory and / or anti-inflammatory properties except some of the latest studies that have failed to achieve the desired results and thus, demand further research. Further research is required in the area to translate the results into clinical application.

Mesenchymal stem cells: amazing remedies for bone and cartilage defects

Skeletal disorders are among the leading debilitating factors affecting millions of people worldwide. The use of stem cells for tissue repair has raised many promises in various medical fields, including skeletal disorders. Mesenchymal stem cells (MSCs) are multipotent stromal cells with mesodermal and neural crest origin. These cells are one of the most attractive candidates in regenerative medicine, and their use could be helpful in repairing and regeneration of skeletal disorders through several mechanisms including homing, angiogenesis, differentiation, and response to inflammatory condition. The most widely studied sources of MSCs are bone marrow (BM), adipose tissue, muscle, umbilical cord (UC), umbilical cord blood (UCB), placenta (PL), Wharton's jelly (WJ), and amniotic fluid. These cells are capable of differentiating into osteoblasts, chondrocytes, adipocytes, and myocytes in vitro. MSCs obtained from various sources have diverse capabilities of secreting many different cytokines, growth factors, and chemokines. It is believed that the salutary effects of MSCs from different sources are not alike in terms of repairing or reformation of injured skeletal tissues. Accordingly, differential identification of MSCs' secretome enables us to make optimal choices in skeletal disorders considering various sources. This review discusses and compares the therapeutic abilities of MSCs from different sources for bone and cartilage diseases.

Role of Curcuminoids and Tricalcium Phosphate Ceramic in Rat Spinal Fusion

Despite considerable research effort, there is a significant need for safe agents that stimulate bone formation. Treatment of large or complex bone defects remains a challenge. Implantation of small molecule-induced human bone marrow-derived mesenchymal stromal cells (hBMSCs) on an appropriate tricalcium phosphate (TCP) scaffold offers a robust system for noninvasive therapy for spinal fusion. To show the efficacy of this approach, we identified a small molecule curcuminoid that when combined with TCP ceramic in the presence of hBMSCs selectively induced growth of bone cells: after 8- or 25-day incubations, alkaline phosphatase was elevated. Treatment of hBMSCs with curcuminoid 1 and TCP ceramic increased osteogenic target gene expression (i.e., Runx2, BMP2, Osteopontin, and Osteocalcin) over time. In the presence of curcuminoid 1 and TCP ceramic, osteogenesis of hBMSCs, including proliferation, differentiation, and mineralization, was observed. No evidence of chondrogenic or adipogenic potential using this protocol was observed. Transplantation of curcuminoid 1-treated hBMSC/TCP mixtures into the spine of immunodeficient rats showed that it achieved spinal fusion and provided greater stability of the spinal column than untreated hBMSC-TCP implants or TCP alone implants. On the basis of histological analysis, greater bone formation was associated with curcuminoid 1-treated hBMSC implants manifested as contiguous growth plates with extensive hematopoietic territories. Stimulation of hBMSCs by administration of small molecule curcuminoid 1 in the presence of TCP ceramic afforded an effective noninvasive strategy that increased spinal fusion repair and provided greater stability of the spinal column after 8 weeks in immunodeficient rats. Impact statement Bone defects only slowly regenerate themselves in humans. Current procedures to restore spinal defects are not always effective. Some have side effects. In this article, a new method to produce bone growth within 8 weeks in rats is presented. In the presence of tricalcium phosphate ceramic, curcuminoid-1 small molecule-stimulated human bone marrow-derived mesenchymal stromal cells showed robust bone cell growth in vitro. Transplantation of this mixture into the spine showed efficient spinal fusion in rats. The approach presented herein provides an efficient biocompatible scaffold for delivery of a potentially clinically useful system that could be applicable in patients.

Toll-like Receptor Expression Profile of Human Stem/Progenitor Cells Form the Apical Papilla

INTRODUCTION

Stem/progenitor cells from the apical papilla (SCAPs) demonstrate remarkable regenerative and immunomodulatory properties. During their regenerative events, SCAPs, similar to other stem/progenitor cells, could interact with their local inflammatory microenvironment via their expressed toll-like receptors (TLRs). The present study aimed to describe for the first time the unique TLR expression profile of SCAPs.

METHODS

Cells were isolated from the apical papilla of extracted wisdom teeth (n = 8), STRO-1 immunomagnetically sorted, and cultured to obtain single colony-forming units. The expression of CD14, 34, 45, 73, 90, and 105 were characterized on the SCAPs, and their multilineage differentiation potential was examined to prove their multipotent aptitude. After their incubation in basic or inflammatory medium (25 ng/mL interleukin 1 beta, 10³ U/mL interferon gamma, 50 ng/mL tumor necrosis factor alpha, and 3 × 10³ U/mL interferon alpha), a TLR expression profile for SCAPs under uninflamed as well as inflamed conditions was respectively generated.

RESULTS

SCAPs demonstrated all predefined stem/progenitor cell characteristics. In basic medium, SCAPs expressed TLRs 1-10. The inflammatory microenvironment up-regulated the expression of TLR1, TLR2, TLR4, TLR5, TLR6, and TLR9 and down-regulated the expression of TLR3, TLR7, TLR8, and TLR10 in SCAPs under the inflamed condition.

CONCLUSIONS

The present study defines for the first time a distinctive TLR expression profile for SCAPs under uninflamed and inflamed conditions. This profile could greatly impact SCAP responsiveness to their inflammatory microenvironmental agents under regenerative conditions in vivo.

Potential methods for improving the efficacy of mesenchymal stem cells in the treatment of inflammatory bowel diseases

Inflammatory bowel diseases (IBD) are a group of chronic recurrent gastrointestinal inflammatory diseases, including ulcerative colitis (UC), Crohn's disease (CD) and IBD unclassified. The pathogenesis may be related to the mucosal immune dysfunction in genetically susceptible hosts affected by environmental factors. Current therapeutic agents mainly include aminosalicylates, corticosteroids, immunosuppressive drugs and novel biological agents. The purpose of treatment is to suppress inflammation and prevent irreversible structural damage. However, long-term application of these drugs may lead to multiple adverse effects and is not always effective. Mesenchymal stem cells (MSCs) are multipotent progenitors with low immunogenicity, which can be obtained and expanded easily. They play an important role in regulating immune responses and repairing damaged tissues in vivo. Therefore, MSCs are considered to be a promising option for the treatment of IBD. Nonetheless, there are many factors that can reduce the efficacy of MSCs, such as gradual deterioration of functional stem cells with age, low recruitment and persistence in vivo and different routes of administration. In recent years, researchers have been able to improve the efficacy of MSCs by pretreatment, genetic modification or co-application with other substances, as well as using different tissue-derived cells, administration methods or doses. This article reviews these methods to provide references for more effective application of MSCs in the treatment of IBD in the future.

Medicinal signaling cells: A potential antimicrobial drug store

Medicinal signaling cells (MSCs) are multipotent cells derived from mammalian bone marrow and periosteum that can be extended in culture. They can keep their ability in vitro to form a variety of mesodermal phenotypes and tissues. Over recent years, there has been great attention over MSCs since they can impact the organ transplantation as well as autoimmune and bacterial diseases. MSCs can secrete different bioactive factors such as growth factors, antimicrobial peptides/proteins and cytokines that can suppress the immune system and prevent infection via direct and indirect mechanisms. Moreover, MSCs are able to increase bacterial clearance in sepsis models by producing antimicrobial peptides such as defensins, cathelicidins, lipocalin and hepcidin. It is the aim of the present review to focus on the antibacterial effector functions of MSCs and their mechanisms of action against the pathogenic microbes.

Mesenchymal stem cells: a promising way in therapies of graft-versus-host disease

It is well acknowledged that allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an effective treatment for numerous malignant blood diseases, which has also been applied to autoimmune diseases for more than a decade. Whereas graft-versus-host disease (GVHD) occurs after allogeneic hematopoietic stem cell transplantation (allo-HSCT) as a common serious complication, seriously affecting the efficacy of transplantation. Mesenchymal stem cells (MSCs) derived from a wealth of sources can easily isolate and expand with low immunogenicity. MSCs also have paracrine and immune regulatory functions, leading to a broad application prospect in treatment and tissue engineering. This review focuses on immunoregulatory function of MSCs, factors affecting mesenchymal stem cells to exert immunosuppressive effects, clinical application of MSCs in GVHD and researches on MSC-derived extracellular vesicles (EVs). The latest research progress on MSC in related fields is reviewed as well. The relevant literature from PubMed databases is reviewed in this article.

Allogeneic mesenchymal stem cells and growth factors in gel scaffold repair osteochondral defect in rabbit

Aim: An attempt was made to improve osteochondral healing with allogeneic mesenchymal stem cells (MSCs) along with certain growth factors. Materials & methods: Induced knee osteochondral defects were filled as: phosphate buffer saline (group A); MSCs in collagen gel (group B); group B plus insulin like growth factor-1 (group C); group C plus transforming growth factor β-1 (group D). Results: Gross and scanning electron microscopy showed superior morphology and surface architecture of the healed tissue in groups D and C. Histologically, group D revealed hyaline cartilage characteristic features followed in order by group C and group B. In all treatment groups, chondrogenic matrix, collagen II2B (col II 2B) and aggrecan were secreted. Conclusion: Combined use of MSCs and growth factors could accelerate osteochondral healing.

Imiquimod Acts Synergistically with BMP9 through the Notch Pathway as an Osteoinductive Agent In Vitro

BACKGROUND

Autologous bone grafts used for surgical reconstruction are limited by infection or insufficient supply of host material. Experimental agents that promote differentiation of stem cells into mature bone are currently being studied for future use in the repair of bone defects. The authors hypothesized that imiquimod, a synthetic immune response modifier, increases Notch pathway gene expression and acts synergistically with bone morphogenetic protein (BMP) 9 to induce differentiation of mesenchymal stem cells toward an osteogenic phenotype.

METHODS

Alkaline phosphatase activity was used to assess the osteogenic potential of cultured mouse immortalized multipotent adipose-derived cells (iMADs) treated with 0, 4, 6, and 8 μg/ml of imiquimod with and without BMP9. Adenoviral vectors expressing human BMP9 and a dominant-negative mutant of mouse Notch1 were used to assess BMP9 and Notch blockade on osteogenic activity, respectively. Expression of Notch signaling mediators and osteogenic markers were assayed by quantitative polymerase chain reaction. Alizarin red staining was used to assess the synergism between BMP9 and imiquimod.

RESULTS

Imiquimod exposure enhanced osteogenic differentiation of iMADs by 2.8-fold (p < 0.001) and potentiated BMP9-induced osteogenic differentiation of iMADs by 1.6-fold (p < 0.001), shown by increased alkaline phosphatase activity and augmented matrix mineralization. Quantitative-real time polymerase chain reaction analysis demonstrated that imiquimod induced the expression of downstream genes (p < 0.01) of the Notch signaling pathway Hey1, Hey2, and Hes1, by increases of 9.7-, 22-, and 2.7-fold, respectively.

CONCLUSIONS

These findings identify a novel role for imiquimod to shift mesenchymal stem cells toward an osteogenic phenotype. Imiquimod may be useful clinically when scaffolds are applied to treat bone defects.

Immunomodulatory role of mesenchymal stem cells in Alzheimer's disease

Alzheimer's disease (AD) is one of the most common causes of dementia and is characterized by gradual loss in memory, language, and cognitive function. The hallmarks of AD include extracellular amyloid deposition, intracellular neuronal fiber entanglement, and neuronal loss. Despite strenuous efforts toward improvement of AD, there remains a lack of effective treatment and current pharmaceutical therapies only alleviate the symptoms for a short period of time. Interestingly, some progress has been achieved in treatment of AD based on mesenchymal stem cell (MSC) transplantation in recent years. MSC transplantation, as a rising therapy, is used as an intervention in AD, because of the enormous potential of MSCs, including differentiation potency, immunoregulatory function, and no immunological rejection. Although numerous strategies have focused on the use of MSCs to replace apoptotic or degenerating neurons, recent studies have implied that MSC-immunoregulation, which modulates the activity state of microglia or astrocytes and mediates neuroinflammation via several transcription factors (NFs) signaling pathways, may act as a major mechanism for the therapeutic efficacy of MSC and be responsible for some of the satisfactory results. In this review, we will focus on the role of MSC-immunoregulation in MSC-based therapy for AD.

Priming TLR3 and TLR4 in human adipose- and olfactory mucosa-derived mesenchymal stromal cells and comparison of their cytokine secretions

Mesenchymal stromal cells (MSCs) have potent immunomodulatory abilities to regulate most of the immune cells. Not only the tissue origin of MSCs can affect their functions, but also their microenvironment can strongly influence their biology, particularly through toll-like receptors (TLR)/ligands interaction. In the present study, we compared MSCs derived from two different sources, i.e. human olfactory ecto-mesenchymal stem cells (OE-MSCs) and adipose tissue (AT-MSCs), in terms of their immunosuppressive effects before and after TLR3 and TLR4 stimulation through low-level and short-term TLR-priming protocol. After isolation and characterization of OE-MSCs and AT-MSCs, flow cytometry analyses were used to assess the expression of TLR3, TLR4 by MSCs. Secretion and expression levels of immune-related genes were analyzed using ELISA and RT-qPCR techniques. Based on the results, the proliferation potential of OE-MSCs was significantly higher than that of AT-MSCs. The gene expression and also protein levels of both TLR3 and TLR4 were significantly higher in OE-MSCs, compared to AT-MSCs. Among the examined cytokines and chemokines, OE-MSCs exhibited significantly higher levels of CCL5, IL-8, and TGF-β production, in comparison with AT-MSCs. However, IL-6 secretion by AT-MSCs was considerably more than that by OE-MSCs. OE-MSCs were only affected by the TLR4 ligand, and IL-8 and IL-6 production levels increased after LPS treatment. However, only IL-8 significantly increased after adding LPS or Poly (I:C) to the AT-MSC media. According to the obtained data, OE-MSCs exhibited a higher proliferative potential and greater expression levels of TLR3 and TLR4 genes, compared to AT-MSCs. However, unlike AT-MSCs, the expression of TLR3 by OE-MSCs was nonfunctional. Finally, based on our findings, OE-MSCs have a stronger secretion of immunosuppressive cytokines both before and after LPS or PIC treatment, compared to AT-MSCs.

The Immunomodulatory Properties of the Human Amnion-Derived Mesenchymal Stromal/Stem Cells Are Induced by INF-γ Produced by Activated Lymphomonocytes and Are Mediated by Cell-To-Cell Contact and Soluble Factors

Human mesenchymal stromal/stem cells (MSCs), being immunoprivileged and having immunomodulatory ability, represent a promising tool to be applied in the field of regenerative medicine. Based on numerous in vitro evidences, the immunological effects of MSCs on immune cells could depend on different mechanisms as cell-to-cell contact and paracrine signals. Furthermore, recent studies have shown that the immunomodulatory activity of MSCs is initiated by activated immune cells; thus, their interaction represents a potential homeostatic mechanism by which MSCs regulate the immune response. MSCs also release exosomes able to give different effects, in a paracrine manner, by influencing inflammatory processes. In this study, we aimed to establish the potential role of human amnion-derived MSCs (hAMSCs), in immunomodulation. We found that the immunosuppressive properties of hAMSCs are not constitutive, but require "supportive signals" capable of promoting these properties. Indeed, we observed that hAMSCs alone are not able to produce an adequate amount of soluble immunomodulatory factors. Here, we studied, in depth, the strong immunomodulatory licensing signal deriving from the direct interaction between hAMSCs and stimulated peripheral blood mononuclear cells. We found that the immunomodulatory effect of hAMSCs also depends on cell-to-cell contact through the contribution of the PDL-1/PD-1 axis. We then investigated the IFN-γ priming of hAMSCs (γ-hAMSCs), which induce the increase of PDL-1 expression, high production of IDO, and upregulation of different immunomodulatory exosome-derived miRNAs. Our miRNA-target network analysis revealed that nine of the deregulated miRNAs are involved in the regulation of key proteins that control both T cell activation/anergy and monocyte differentiation pathways. Finally, we observed that γ-hAMSCs induce in monocytes both M2-like phenotype and the increase of IL-10 production. The extensive implications of MSCs in modulating different aspects of the immune system make these cells attractive candidates to be employed in therapeutic application in immune-based diseases. For these reasons, we aimed, with this study, to shed light on the potential of hAMSCs, and how they could become a useful tool for treating different inflammatory diseases, including end-stage pathologies or adverse effects in transplanted patients.

Convergence of Cell Pharmacology and Drug Delivery

Cellular therapy is enabling new approaches to tackle significant unmet needs in areas such as regenerative medicine and immunotherapy. The pharmacology of cell therapeutics becomes of critical importance to assure that these new drugs work reproducibly and effectively. Cell pharmacology can benefit from adapting principles of classical molecular drug pharmacokinetics (PK) and pharmacodynamics (PD) to quantitatively understand rate-limiting constraints of cell fate after administration. Future innovations focused on improvements in drug delivery using a PK/PD perspective can aid in designing a cell therapeutic product to overcome any pharmacological barriers for a given disease application. Herein, we present a perspective on the development of an ex vivo mesenchymal stromal therapeutic using a PK/PD framework and also present examples of general cell engineering techniques that implicitly influence the PK/PD curve by genetically modifying cells to regulate their in vivo duration, biodistribution, and activity. Stem Cells Translational Medicine 2019;8:874&879.

A Novel Virtue in Stem Cell Research: Exosomes and Their Role in Differentiation

In the past decade a number of different stem cell types have entered the clinical applications increasingly as a therapeutic option, due to their tissue maintenance capacity at the site where they localize. Although it was initially thought that conferral of resilience to damaged tissue largely depends on the stem cells themselves through orchestration of signaling among the local epithelial and immune systems at the injury site, recent findings point out that the remarkable regenerative capacity of stem cells is rather due to their nanovesicular products that emerge as the new active players of tissue repair processes. Among these extracellular vesicles exosomes generated particularly by stem cells have been receiving a substantial interest both in the fields of stem cell biology and extracellular vesicles. In this chapter fundamental facts about stem cell biology, biogenesis of extracellular vesicles and exosomes, their structure, and function are summarized. Moreover, properties of both tumor-derived exosomes as well as those derived from stem cells are discussed relatively in-depth in terms of their influence on proximal and distal tissue physiology. Last but not the least, among countless studies in an exploding field, we summarize those that attempt to unravel the complex signaling networks through which stem cell-derived exosomes alter the fate of differentiating stem cells as well as the molecular make-up of exosomes released from differentiating stem cells by conducting thorough proteomic and genomic analyses with the ultimate goal of identifying effector gene products mediating exosomal cues in stem cell biology.

Forkhead box O1 (FOXO1) controls the migratory response of Toll-like receptor (TLR3)-stimulated human mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) can potently regulate the functions of immune cells and are being investigated for the management of inflammatory diseases. Toll-like receptor 3 (TLR3)-stimulated human MSCs (hMSCs) exhibit increased migration and chemotaxis within and toward damaged tissues. However, the regulatory mechanisms underlying these migratory activities are unclear. Therefore, we analyzed the migration capability and gene expression profiles of TLR3-stimulated hMSCs using RNA-Seq, wound healing, and transwell cell migration assay. Along with increased cell migration, the TLR3 stimulation also increased the expression of cytokines, chemokines, and cell migration-related genes. The promoter regions of the latter showed an enrichment of putative motifs for binding the transcription factors forkhead box O1 (FOXO1), FOXO3, NF-κB (NF-κB1), and RELA proto-oncogene and NF-κB subunit. Of note, FOXO1 inhibition by the FOXO1-selective inhibitor AS1842856 significantly reduced both migration and the expression of migration-related genes. In summary, our results indicate that TLR3 stimulation induces hMSC migration through the expression of FOXO1-activated genes.

The periodontal stem/progenitor cell inflammatory-regenerative cross talk: A new perspective

Adult multipotent stem/progenitor cells, with remarkable regenerative potential, have been isolated from various components of the human periodontium. These multipotent stem/progenitor cells include the periodontal ligament stem/progenitor cells (PDLSCs), stem cells from the apical papilla (SCAP), the gingival mesenchymal stem/progenitor cells (G-MSCs), and the alveolar bone proper stem/progenitor cells (AB-MSCs). Whereas inflammation is regarded as the reason for tissue damage, it also remains a fundamental step of any early healing process. In performing their periodontal tissue regenerative/reparative activity, periodontal stem/progenitor cells interact with their surrounding inflammatory micro-environmental, through their expressed receptors, which could influence their fate and the outcome of any periodontal stem/progenitor cell-mediated reparative/regenerative activity. The present review discusses the current understanding about the interaction of periodontal stem/progenitor cells with their surrounding inflammatory micro-environment, elaborates on the inflammatory factors influencing their stemness, proliferation, migration/homing, differentiation, and immunomodulatory attributes, the possible underlying intracellular mechanisms, as well as their proposed relationship to the canonical and noncanonical Wnt pathways.

Current understanding of the immunosuppressive properties of mesenchymal stromal cells

Several studies have demonstrated the anti-inflammatory potential of mesenchymal stromal cells (MSCs) isolated from bone marrow, adipose tissue, placenta, and other sources. Nevertheless, MSCs may also induce immunosuppression when administered systemically or directly to injured environments, as shown in different preclinical disease models. MSCs express certain receptors, including toll-like receptors and the aryl-hydrocarbon receptor, that are activated by the surrounding environment, thus leading to modulation of their immunosuppressive activity. Once MSCs are activated, they can affect a wide range of immune cells (e.g., neutrophils, monocytes/macrophages, dendritic cells, natural killer cells, T and B lymphocytes), a phenomenon that has been correlated to secretion of several mediators (e.g., indolamine 2,3-dioxygenase, galectins, prostaglandin E₂, nitric oxide, and damage- and pathogen-associated molecular patterns) and stimulation of certain signaling pathways (e.g., protein kinase R, signal transducer and activator of transcription-1, nuclear factor-κB). Additionally, MSC manipulation and culture conditions, as well as the number of passages, duration of cryopreservation, and O₂ content available, can significantly affect the immunosuppressive properties of MSCs. This review sheds light on current knowledge regarding the mechanisms by which MSCs exert immunosuppressive effects both in vitro and in vivo, focusing on the receptors expressed by MSCs, the correlation between soluble factors secreted by MSCs and their immunosuppressive effects, and interactions between MSCs and immune cells.