Mesenchymal Stem Cell-Derived Interleukin 1 Receptor Antagonist Promotes Macrophage Polarization and Inhibits B Cell Differentiation

Induction of M2 Macrophages Prevents Bone Loss in Murine Periodontitis Models

Periodontitis is characterized by the progressive destruction of tooth-supporting alveolar bone, which is mainly caused by chronic inflammation in response to persistent bacterial insult. It has recently become clear that the pathogenesis of periodontitis is associated with a high ratio of proinflammatory M1 (classically activated) macrophages to anti-inflammatory M2 (alternatively activated). To decrease the inflammatory activity, we locally delivered the C-C motif chemokine ligand 2 (CCL2) using controlled-release microparticles (MPs). CCL2 is known to promote chemotaxis of M0 or M2 phenotype macrophages to the inflamed site and induce M2 phenotype polarization locally. Our in vitro data showed that CCL2 increased the number of M2 phenotype macrophages, decreased TNF-α secretion, and enhanced chemotaxis of RAW264.7 cells toward CCL2 MPs. Moreover, we induced periodontal disease in 2 animal models through inoculation of Porphyromonas gingivalis and ligature around the murine molar. Micro-computed tomography analysis showed significant reduction of alveolar bone loss in the CCL2 MP treatment group when compared with a blank MP group and a no-treatment periodontitis group in both models. Immunohistologic analysis showed a significant increase in the M2 phenotype subset and a decrease in the M1 phenotype subset in the CCL2 MP group of the P. gingivalis-induced model. Also, in both models, tartrate-resistant acidic phosphatase staining showed significantly fewer numbers of osteoclasts in the CCL2 MP group in alveolar bone area. Moreover, quantitative polymerase chain reaction results showed a significant increase in IL-1RA (interleukin 1 receptor antagonist) mRNA expression and a decrease in RANKL (receptor activator of nuclear factor kappa-Β ligand) mRNA expression in the CCL2 MP group in the ligature model. In summary, manipulation of endogenous M2 phenotype macrophages with CCL2 MPs decreased the M1 phenotype:M2 phenotype ratio and prevented alveolar bone loss in mouse periodontitis models. The delivery of CCL2 MPs provides a novel approach to treat periodontal disease.

Mesenchymal Stem Cells in Primary Sjögren's Syndrome: Prospective and Challenges

Primary Sjögren's syndrome (pSS) is a chronic systemic inflammatory autoimmune disease characterized by lymphocytic infiltrates in exocrine glands. Current approaches do not control harmful autoimmune attacks or prevent irreversible damage and have considerable side effects. Mesenchymal stem cells (MSCs) have been effective in the treatment of several autoimmune diseases. The objective of this review is to illustrate the potential therapeutic role of MSCs in pSS. We summarize the recent advances in what is known about their immunomodulatory function and therapeutic applications in pSS. MSC transfusion can suppress autoimmunity and restore salivary gland secretory function in mouse models and patients with pSS by inducing regulatory T cells, suppressing Th1, Th17, and T follicular helper cell responses. In addition, MSCs can differentiate into salivary epithelial cells, presenting an option as a suitable alternative treatment. We also discuss current bioengineering methods which improve functions of MSCs for pSS. However, there remain many challenges to overcome before their wide clinical application.

Regulation of decellularized tissue remodeling via scaffold-mediated lentiviral delivery in anatomically-shaped osteochondral constructs

Cartilage-derived matrix (CDM) has emerged as a promising scaffold material for tissue engineering of cartilage and bone due to its native chondroinductive capacity and its ability to support endochondral ossification. Because it consists of native tissue, CDM can undergo cellular remodeling, which can promote integration with host tissue and enables it to be degraded and replaced by neotissue over time. However, enzymatic degradation of decellularized tissues can occur unpredictably and may not allow sufficient time for mechanically competent tissue to form, especially in the harsh inflammatory environment of a diseased joint. The goal of the current study was to engineer cartilage and bone constructs with the ability to inhibit aberrant inflammatory processes caused by the cytokine interleukin-1 (IL-1), through scaffold-mediated delivery of lentiviral particles containing a doxycycline-inducible IL-1 receptor antagonist (IL-1Ra) transgene on anatomically-shaped CDM constructs. Additionally, scaffold-mediated lentiviral gene delivery was used to facilitate spatial organization of simultaneous chondrogenic and osteogenic differentiation via site-specific transduction of a single mesenchymal stem cell (MSC) population to overexpress either chondrogenic, transforming growth factor-beta 3 (TGF-β3), or osteogenic, bone morphogenetic protein-2 (BMP-2), transgenes. Controlled induction of IL-1Ra expression protected CDM hemispheres from inflammation-mediated degradation, and supported robust bone and cartilage tissue formation even in the presence of IL-1. In the absence of inflammatory stimuli, controlled cellular remodeling was exploited as a mechanism for fusing concentric CDM hemispheres overexpressing BMP-2 and TGF-β3 into a single bi-layered osteochondral construct. Our findings demonstrate that site-specific delivery of inducible and tunable transgenes confers spatial and temporal control over both CDM scaffold remodeling and neotissue composition. Furthermore, these constructs provide a microphysiological in vitro joint organoid model with site-specific, tunable, and inducible protein delivery systems for examining the spatiotemporal response to pro-anabolic and/or inflammatory signaling across the osteochondral interface.

The Reparative Abilities of Menstrual Stem Cells Modulate the Wound Matrix Signals and Improve Cutaneous Regeneration

Considerable advances have been made toward understanding the cellular and molecular mechanism of wound healing, however, treatments for chronic wounds remain elusive. Emerging concepts utilizing mesenchymal stem cells (MSCs) from umbilical cord, adipose tissue and bone marrow have shown therapeutical advantages for wound healing. Based on this positive outcome, efforts to determine the optimal sources for MSCs are required in order to improve their migratory, angiogenic, immunomodulatory, and reparative abilities. An alternative source suitable for repetitive, non-invasive collection of MSCs is from the menstrual fluid (MenSCs), displaying a major practical advantage over other sources. This study aims to compare the biological functions and the transcriptomic pattern of MenSCs with umbilical cord MSCs in conditions resembling the wound microenvironment. Consequently, we correlate the specific gene expression signature from MenSCs with changes of the wound matrix signals in vivo. The direct comparison revealed a superior clonogenic and migratory potential of MenSCs as well as a beneficial effect of their secretome on human dermal fibroblast migration in vitro. Furthermore, MenSCs showed increased immunomodulatory properties, inhibiting T-cell proliferation in co-culture. We further, investigated the expression of selected genes involved in wound repair (growth factors, cytokines, chemokines, AMPs, MMPs) and found considerably higher expression levels in MenSCs (ANGPT1 1.5-fold; PDGFA 1.8-fold; PDGFB 791-fold; MMP3 21.6-fold; ELN 13.4-fold; and MMP10 9.2-fold). This difference became more pronounced under a pro-inflammatory stimulation, resembling wound bed conditions. Locally applied in a murine excisional wound splinting model, MenSCs showed a significantly improved wound closure after 14 days, as well as enhanced neovascularization, compared to the untreated group. Interestingly, analysis of excised wound tissue revealed a significantly higher expression of VEGF (1.42-fold) among other factors, translating an important conversion of the matrix signals in the wound site. Furthermore, histological analysis of the wound tissue from MenSCs-treated group displayed a more mature robust vascular network and a genuinely higher collagen content confirming the pro-angiogenic and reparative effect of MenSCs treatment. In conclusion, the superior clonogenicity, immunosuppressive and migration potential in combination with specific paracrine signature of MenSCs, resulted in an enhanced wound healing and cutaneous regeneration process.

IL17/IL17RA as a Novel Signaling Axis Driving Mesenchymal Stem Cell Therapeutic Function in Experimental Autoimmune Encephalomyelitis

The therapeutic effect of mesenchymal stem cells (MSCs) in multiple sclerosis (MS) and the experimental autoimmune encephalomyelitis (EAE) model has been well described. This effect is, in part, mediated through the inhibition of IL17-producing cells and the generation of regulatory T cells. While proinflammatory cytokines such as IFNγ, TNFα, and IL1β have been shown to enhance MSCs immunosuppressive function, the role of IL17 remains poorly elucidated. The aim of this study was, therefore, to investigate the role of the IL17/IL17R pathway on MSCs immunoregulatory effects focusing on Th17 cell generation in vitro and on Th17-mediated EAE pathogenesis in vivo. In vitro, we showed that the immunosuppressive effect of MSCs on Th17 cell proliferation and differentiation is partially dependent on IL17RA expression. This was associated with a reduced expression level of MSCs immunosuppressive mediators such as VCAM1, ICAM1, and PD-L1 in IL17RA^-/- MSCs as compared to wild-type (WT) MSCs. In the EAE model, we demonstrated that while WT MSCs significantly reduced the clinical scores of the disease, IL17RA^-/- MSCs injected mice exhibited a clinical worsening of the disease. The disability of IL17RA^-/- MSCs to reduce the progression of the disease paralleled the inability of these cells to reduce the frequency of Th17 cells in the draining lymph node of the mice as compared to WT MSCs. Moreover, we showed that the therapeutic effect of MSCs was correlated with the generation of classical Treg bearing the CD4⁺CD25⁺Foxp3⁺ signature in an IL17RA-dependent manner. Our findings reveal a novel role of IL17RA on MSCs immunosuppressive and therapeutic potential in EAE and suggest that the modulation of IL17RA in MSCs could represent a novel method to enhance their therapeutic effect in MS.

The Fas/Fap-1/Cav-1 complex regulates IL-1RA secretion in mesenchymal stem cells to accelerate wound healing

Mesenchymal stem cells (MSCs) are capable of secreting exosomes, extracellular vesicles, and cytokines to regulate cell and tissue homeostasis. However, it is unknown whether MSCs use a specific exocytotic fusion mechanism to secrete exosomes and cytokines. We show that Fas binds with Fas-associated phosphatase-1 (Fap-1) and caveolin-1 (Cav-1) to activate a common soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein receptor (SNARE)-mediated membrane fusion mechanism to release small extracellular vesicles (sEVs) in MSCs. Moreover, we reveal that MSCs produce and secrete interleukin-1 receptor antagonist (IL-1RA) associated with sEVs to maintain rapid wound healing in the gingiva via the Fas/Fap-1/Cav-1 cascade. Tumor necrosis factor-α (TNF-α) serves as an activator to up-regulate Fas and Fap-1 expression via the nuclear factor κB pathway to promote IL-1RA release. This study identifies a previously unknown Fas/Fap-1/Cav-1 axis that regulates SNARE-mediated sEV and IL-1RA secretion in stem cells, which contributes to accelerated wound healing.

Intra-articular Injections of Platelet-Rich Plasma Releasate Reduce Pain and Synovial Inflammation in a Mouse Model of Osteoarthritis

BACKGROUND

Osteoarthritis (OA) is a degenerative joint disease leading to pain and disability for which no curative treatment exists. A promising biological treatment for OA is intra-articular administration of platelet-rich plasma (PRP). PRP injections in OA joints can relieve pain, although the exact working mechanism is unclear.

PURPOSE

To examine the effects of PRP releasate (PRPr) on pain, cartilage damage, and synovial inflammation in a mouse OA model.

STUDY DESIGN

Controlled laboratory study.

METHODS

OA was induced unilaterally in the knees of male mice (n = 36) by 2 intra-articular injections of collagenase at days -7 and -5. At day 0, pain was measured by registering weight distribution on the hindlimbs, after which mice were randomly divided into 2 groups. Mice received 3 intra-articular injections of PRP or saline in the affected knee. Seven mice per group were euthanized at day 5 for assessment of early synovial inflammation and cartilage damage. Pain in the remaining mice was registered for a total of 3 weeks. These mice were euthanized at day 21 for assessment of cartilage damage and synovial inflammation on histological evaluation. Antibodies against iNOS, CD163, and CD206 were used to identify different subtypes of macrophages in the synovial membrane.

RESULTS

Mice in the PRPr group increased the distribution of weight on the affected joint in 2 consecutive weeks after the start of the treatment ( P < .05), whereas mice in the saline group did not. At day 21, PRPr-injected knees had a thinner synovial membrane ( P < .05) and a trend toward less cartilage damage in the lateral joint compartment ( P = .053) than saline-injected knees. OA knees treated with saline showed less anti-inflammatory (CD206+ and CD163+) cells at day 5 than healthy knees, an observation that was not made in the PRPr-treated group. A higher level of pain at day 7 was associated with a thicker synovial membrane at day 21. The presence of CD206+ cells was negatively associated with synovial membrane thickness.

CONCLUSION

In a murine OA model, multiple PRPr injections reduced pain and synovial thickness, possibly through modulation of macrophage subtypes.

CLINICAL RELEVANCE

PRPr injections in early OA or shortly after joint trauma can reduce pain and synovial inflammation and may inhibit OA development in patients.

Mesenchymal stem cells ameliorate experimental arthritis via expression of interleukin-1 receptor antagonist

Human bone marrow-derived mesenchymal stem cells (MSCs) have been observed to inhibit arthritis in experimental animal models such as collagen-induced arthritis. However, the exact anti-inflammatory mechanisms remain poorly understood. Interleukin-1 receptor antagonist (IL-1Ra) is an anti-inflammatory cytokine produced by immune and stromal cells. We postulated that MSCs could produce IL-1Ra and attenuate experimental arthritis. In this study, 5x106 MSCs were injected into the peritoneal cavity of IL-1Ra knockout (IL-1RaKO) mice. MSCs reduced the severity of the arthritis by histology and decreased pro-inflammatory cytokine levels in IL-1RaKO mice. The ratio of splenic T helper 17 (Th17) cells to regulatory T cells (Treg) was significantly decreased in MSC-injected IL-1RaKO mice. Purified splenic CD4+ T cells from mice in each of the treatment groups were cultured under Th17 polarizing conditions and analyzed by flow cytometry. Less expansion of the Th17 population was observed in the MSC-treated group. Interestingly, MSCs expressed inducible IL-1Ra against inflammatory environmental stimuli. Human recombinant IL-1Ra could suppress Th17 cells differentiation under Th17 polarizing conditions. These results indicate that IL-1Ra expressed by MSCs can inhibit Th17 polarization and decrease the immune response in IL-1RaKO mice. Therefore, MSC-derived IL-1Ra may inhibit inflammation in IL-1RaKO mice via effects on Th17 differentiation.

Anti-inflammatory Effects of Oct4/Sox2-overexpressing Human Adipose Tissue-derived Mesenchymal Stem Cells

BACKGROUND/AIM

The transcription factors Oct4 and Sox2 enhance the proliferation and pluripotency of human adipose tissue-derived mesenchymal stem cells (hAT-MSCs); however, the anti-inflammatory effects of Oct4- and Sox2-overexpressing hAT-MSCs (Oct4/Sox2-hAT-MSCs) are unclear. Here, we evaluated the anti-inflammatory effects of Oct4/Sox2-hAT-MSCs in vitro and in vivo.

MATERIALS AND METHODS

Supernatants from green-fluorescent protein (GFP)- and Oct4/Sox2-hAT-MSCs were used to treat lipopolysaccharide (LPS)-stimulated RAW264.7 cells and inflammatory cytokine expression was determined. In LPS-induced mice, GFP- and Oct4/Sox2-hAT-MSCs were injected intraperitoneally and survival rates, as well as sickness scores of mice, were monitored.

RESULTS

Decreased expression of pro-inflammatory cytokines was observed in Oct4/Sox2-hAT-MSC supernatant-exposed RAW264.7 cells compared to that in GFP-hAT-MSC supernatant-exposed RAW264.7 cells. The sickness score was reduced to 34.9% and the survival rate was increased by 11.1% in Oct4/Sox2-hAT-MSC-injected mice compared to that in GFP-hAT-MSC-injected mice.

CONCLUSION

Our findings provide important insights into the development of therapies utilizing Oct4/Sox2-hAT-MSCs in inflammatory diseases.

Mesenchymal stem cells-derived exosomes are more immunosuppressive than microparticles in inflammatory arthritis

Objectives: Mesenchymal stem cells (MSCs) release extracellular vesicles (EVs) that display a therapeutic effect in inflammatory disease models. Although MSCs can prevent arthritis, the role of MSCs-derived EVs has never been reported in rheumatoid arthritis. This prompted us to compare the function of exosomes (Exos) and microparticles (MPs) isolated from MSCs and investigate their immunomodulatory function in arthritis.

Methods: MSCs-derived Exos and MPs were isolated by differential ultracentrifugation. Immunosuppressive effects of MPs or Exos were investigated on T and B lymphocytes in vitro and in the Delayed-Type Hypersensitivity (DTH) and Collagen-Induced Arthritis (CIA) models.

Results: Exos and MPs from MSCs inhibited T lymphocyte proliferation in a dose-dependent manner and decreased the percentage of CD4⁺ and CD8⁺ T cell subsets. Interestingly, Exos increased Treg cell populations while parental MSCs did not. Conversely, plasmablast differentiation was reduced to a similar extent by MSCs, Exos or MPs. IFN-γ priming of MSCs before vesicles isolation did not influence the immunomodulatory function of isolated Exos or MPs. In DTH, we observed a dose-dependent anti-inflammatory effect of MPs and Exos, while in the CIA model, Exos efficiently decreased clinical signs of inflammation. The beneficial effect of Exos was associated with fewer plasmablasts and more Breg-like cells in lymph nodes.

Conclusions: Both MSCs-derived MPs and Exos exerted an anti-inflammatory role on T and B lymphocytes independently of MSCs priming. However, Exos were more efficient in suppressing inflammation in vivo. Our work is the first demonstration of the therapeutic potential of MSCs-derived EVs in inflammatory arthritis.

Effect of bone marrow mesenchymal stem cells on the polarization of macrophages

Inflammation is a defensive response in the living tissue of the vascular system that acts against damage factors and involves various types of immune cells, including macrophages, neutrophils, endothelial cells and other associated immune molecules. If the release of inflammatory mediators is excessive, systemic inflammatory response syndrome may develop. Sepsis is the most common complication of severe burns and is a systemic inflammatory response syndrome that is caused by infectious factors and is capable of leading to multiple organ dysfunction and potentially death. Research concerning the mechanism and treatment of sepsis is crucial. Macrophages are an important type of immune cell that remove invasive pathogens and are involved in innate and adaptive immune responses. It has been previously reported that bone marrow mesenchymal stem cells (BMSCs) affect macrophages by regulating immunity. The present study aimed to investigate the effect of BMSCs on macrophage polarization in vivo and in vitro, in addition to the potential therapeutic effect of these cells on experimental sepsis. BMSCs and peritoneal macrophages were isolated from Sprague‑Dawley rats and co‑cultured overnight as a mixed culture or Transwell system, and subsequently stimulated with 100 ng/ml lipopolysaccharide (LPS). After 12 h, the medium was replaced with normal complete medium for various durations and supernatants were collected to extract proteins and cells for ELISA, western blot and flow cytometry analysis to investigate different aspects of macrophages. Sepsis was induced in Sprague‑Dawley rats by injection of LPS (5 mg/kg), followed by tail vein injection of BMSCs or PBS 1 h later. After 6, 12, 24 and 48 h, lung tissues were harvested for pathological observation and peritoneal macrophages were collected for flow cytometry analysis to assess the expression of markers, including cluster of differentiation (CD)68 (used for gating), CD11c and CD206. The results demonstrated that, in the culture medium, LPS stimulation increased the expression of CD11c in macrophages, and the levels of tumor necrosis factor‑α and inducible nitric oxide synthase were also increased. By contrast, in macrophages treated with BMSCs directly, the expression of CD11c was reduced compared with the LPS‑stimulated macrophage alone group. However, the secretion of interleukin‑10, transforming growth factor‑β and arginase‑1 was increased in the direct co‑culture group, compared with the LPS‑stimulated macrophage alone group. BMSCs reduced the inflammation in lung tissues and inhibited macrophage expression of CD11c in the rat model of sepsis. The results of the present study demonstrated that BMSCs co‑cultured with macrophages directly inhibited macrophage differentiation into the M1 phenotype and reduced inflammation in macrophages stimulated by LPS. In vivo, BMSCs decreased the expression of CD11c in peritoneal macrophages and reduced the pathological inflammatory response in the lungs. The findings of the present study demonstrated that BMSCs may reduce the extent of the systemic inflammatory response, which may contribute to the development for a novel type of treatment for sepsis in the future.

Gilz-Activin A as a Novel Signaling Axis Orchestrating Mesenchymal Stem Cell and Th17 Cell Interplay

Mesenchymal stem cells (MSC) are highly immunosuppressive cells able to reduce chronic inflammation through the active release of mediators. Recently, we showed that glucocorticoid-induced leucine zipper (Gilz) expression by MSC is involved in their therapeutic effect by promoting the generation of regulatory T cells. However, the mechanisms underlying this pivotal role of Gilz remain elusive.

Methods and Results In this study, we have uncovered evidence that Gilz modulates the phenotype and function of Th1 and Th17 cells likely by upregulating the level of Activin A and NO₂ secreted by MSC. Adoptive transfer experiments sustained this Gilz-dependent suppressive effect of MSC on Th1 and Th17 cell functions. In immunoregulatory MSC, obtained by priming with IFN-γ and TNF-α, Gilz was translocated to the nucleus and bound to the promoters of inos and Activin βA to induce their expression. The increased expression of Activin A directly impacted on Th17 cells fate by repressing their differentiation program through the activation of Smad3/2 and enhancing IL-10 production.

Conclusion Our results reveal how Gilz controls inos and Activin βA gene expression to ultimately assign immunoregulatory status to MSC able to repress the pathogenic Th17 cell differentiation program and uncover Activin A as a novel mediator of MSC in this process.

Tissue regeneration: The crosstalk between mesenchymal stem cells and immune response

Mesenchymal stem cells (MSCs) exist in almost all tissues with the capability to differentiate into several different cell types and hold great promise in tissue repairs in a cell replacement manner. The study of the bidirectional regulation between MSCs and immune response has ushered an age of rethinking of tissue regeneration in the process of stem cell-based tissue repairs. By sensing damaged signals, both endogenous and exogenous MSCs migrate to the damaged site where they involve in the reconstitution of the immune microenvironment and empower tissue stem/progenitor cells and other resident cells, whereby facilitate tissue repairs. This MSC-based therapeutic manner is conferred as cell empowerment. In this process, MSCs have been found to exert extensive immunosuppression on both innate and adaptive immune response, while such regulation needs to be licensed by inflammation. More importantly, the immunoregulation of MSCs is highly plastic, especially in the context of pathological microenvironment. Understanding the immunoregulatory properties of MSCs is necessary for appropriate application of MSCs. Here we review the current studies on the crosstalk of MSCs and immune response in disease pathogenesis and therapy.

Mesenchymal stem cells derived exosomes and microparticles protect cartilage and bone from degradation in osteoarthritis

Mesenchymal stem or stromal cells (MSCs) exert chondroprotective effects in preclinical models of osteoarthritis (OA). Most of their therapeutic effects are mediated via soluble mediators, which can be conveyed within extracellular vesicles (EVs). The objective of the study was to compare the respective role of exosomes (Exos) or microvesicles/microparticles (MPs) in OA. MPs and Exos were isolated from bone marrow murine BM-MSCs through differential centrifugation. Effect of MPs or Exos was evaluated on OA-like murine chondrocytes and chondroprotection was quantified by RT-qPCR. In OA-like chondrocytes, BM-MSC-derived MPs and Exos could reinduce the expression of chondrocyte markers (type II collagen, aggrecan) while inhibiting catabolic (MMP-13, ADAMTS5) and inflammatory (iNOS) markers. Exos and MPs were also shown to protect chondrocytes from apoptosis and to inhibit macrophage activation. In vivo, Exos or MPs were injected in the collagenase-induced OA (CIOA) model and histomorphometric analyses of joints were performed by µCT and confocal laser microscopy. BM-MSCs, MPs and Exos equally protected mice from joint damage. In conclusion, MPs and Exos exerted similar chondroprotective and anti-inflammatory function in vitro and protected mice from developing OA in vivo, suggesting that either Exos or MPs reproduced the main therapeutic effect of BM-MSCs.

Impaired Function of Bone Marrow Mesenchymal Stem Cells from Immune Thrombocytopenia Patients in Inducing Regulatory Dendritic Cell Differentiation Through the Notch-1/Jagged-1 Signaling Pathway

Immune thrombocytopenia (ITP) is an autoimmune disease in which dendritic cells (DCs) play a crucial role in the breakdown of self-tolerance. Studies have identified the function of mesenchymal stem cells (MSCs) in promoting the development of regulatory DCs (regDCs). Our previous work revealed that MSCs in ITP exerted senescence, apoptosis, and impaired immunosuppressive effects on T and B cells. However, it is unclear whether the effects of MSCs on regDC induction are altered in ITP. Our data demonstrated that MSCs in ITP were impaired in inhibiting CD1a⁺ DC and CD14⁺ DC differentiation from CD34⁺ hematopoietic progenitor cells (CD34⁺ HPCs). DCs differentiated with MSCs in ITP exhibited an increased expression of costimulatory molecules CD80/CD86 and secretion of proinflammatory interleukin-12 (IL-12). Accordingly, the tolerogenic characteristics were deficient in DCs induced by MSCs in ITP. DCs differentiated with MSCs in ITP exhibited an impaired ability to inhibit CD3⁺ T cell proliferation, to suppress T helper (Th)1 cell differentiation, and to induce anergic and regulatory T cells (Tregs). The expression of Notch signaling components was measured in MSCs in ITP. Reduced expression of the ligand Jagged-1, the receptor Notch-1 intracellular domain (NICD-1), and the target gene Hes-1 was identified in MSCs in ITP. The addition of biologically active Jagged-1 to CD34⁺ HPCs was observed to promote regDC differentiation. When cultured on Jagged-1-coated plates, MSCs in ITP showed an enhancement of the Notch-1 pathway activation, Jagged-1 expression, and the function in inducing regDCs. Pretreatment with all-trans retinoic acid (ATRA) was found to partially restore the capacity of MSCs in both ITP patients and healthy controls in inducing CD34⁺-derived regDCs. Our data elucidated that MSCs in ITP were impaired in inducing CD34⁺-regDCs, associated with the Notch-1/Jagged-1 signaling pathway. ATRA could partially correct the impairment of MSCs, suggesting that ATRA could serve as a potential therapeutic alternative for ITP.

The role of secreted factors in stem cells-mediated immune regulation

Stem cells are characterized by self-renew and multipotent differentiation abilities. Besides their roles in cell compensation, stem cells are also rich sources of growth factors, cytokines, chemokines, micro-RNAs and exosomes and serve as drug stores to maintain tissue homeostasis. Recent studies have revealed that the secretome of stem cells is regulated by the local inflammatory cues and highlighted the roles of these secretory factors in stem cell based therapies. Importantly, stem cell conditioned medium, in the absence of stem cell engraftment, have shown efficiency in treating diseases involves immune disorders. In this review, we summarize the recent advances in understanding the regulatory effects of stem cells secreted factors on different immune cells including macrophages, dendritic cells, neutrophils, NK cells, T cells, and B cells. We also discuss how stem cells released factors participate in the initiation, maintenance and resolution of inflammation. The in depth understanding of interaction between stem cells secreted factors and immune system would lead to new strategies to restore tissue homeostasis and improve the efficiency of stem cell therapies.

Mesenchymal Stem Cells Direct the Immunological Fate of Macrophages

Mesenchymal stem cells (MSC) are multipotent stem cells with a broad well-described immunosuppressive potential. They are able to modulate both the innate and the adaptive immune response. Particularly, MSC are able to regulate the phenotype and function of macrophages that are critical for different biological processes including wound healing, inflammation, pathogenesis of several autoimmune diseases, and tumor growth. These multifunctional roles of macrophages are due to their high plasticity, which enable them to adopt different phenotypes such as a pro-inflammatory M1 and anti-inflammatory M2 phenotype. MSC promote macrophage differentiation toward an M2-like phenotype with a high tissue remodeling potential and anti-inflammatory activity but also a pro-tumorigenic function. MSC regulatory effect on macrophages is mediated through the secretion of different immunomodulatory molecules such as PGE₂, IL1RA, and IL-6. Moreover, the presence of macrophages in damaged tissue and inflammation is essential for MSC to exert their therapeutic function. In this chapter, we discuss how the interplay between macrophages and MSC mutually modulates their phenotypes and functions, orchestrates tissue repair, and controls inflammation during autoimmunity and tumor growth.

Is macrophage polarization important in rheumatoid arthritis?

Macrophages are myeloid immune cells which are strategically positioned throughout the body, where they engulf and degrade debris, dead cells, and foreign substances, and coordinating the inflammatory processes. Macrophages can be divided into two extreme subsets, classical activation (M1), and alternatively activation (M2). The symptoms and signs of rheumatoid arthritis (RA) would exacerbate with the increase in pro-inflammatory cytokines, whereas anti-inflammatory cytokines will alleviate the symptoms and signs of RA. This review, mainly discusses the effects of Notch, JNK and ERK signaling pathways on the regulation of macrophage polarization, and the effects of pro-inflammatory factors and/or anti-inflammatory cytokines produced by polarized macrophages in RA. Also, we will make an attempt to find out the importance of macrophage polarization in RA treatment as a drug target.

Mesenchymal stem cells and their immunosuppressive role in transplantation tolerance

Since they were first described, mesenchymal stem cells (MSCs) have been shown to have important effector mechanisms and the potential for use in cell therapy. A great deal of research has been focused on unveiling how MSCs contribute to anti-inflammatory responses, including describing several cell populations involved and identifying soluble and other effector molecules. In this review, we discuss some of the contemporary evidence for use of MSCs in the field of immune tolerance, with a special emphasis on transplantation. Although considerable effort has been devoted to understanding the biological function of MSCs, additional resources are required to clarify the mechanisms of their induction of immune tolerance, which will undoubtedly lead to improved clinical outcomes for MSC-based therapies.

Interactions between mesenchymal stem cells and the immune system

In addition to being multi-potent, mesenchymal stem cells (MSCs) possess immunomodulatory functions that have been investigated as potential treatments in various immune disorders. MSCs can robustly interact with cells of the innate and adaptive immune systems, either through direct cell-cell contact or through their secretome. In this review, we discuss current findings regarding the interplay between MSCs and different immune cell subsets. We also draw attention to the mechanisms involved.

Cytokine treatment optimises the immunotherapeutic effects of umbilical cord-derived MSC for treatment of inflammatory liver disease

BACKGROUND

Mesenchymal stromal cells (MSC) possess immunomodulatory properties and low immunogenicity, both crucial properties for their development into an effective cellular immunotherapy. They have shown benefit in clinical trials targeting liver diseases; however the efficacy of MSC therapy will benefit from improvement of the immunomodulatory and immunogenic properties of MSC.

METHODS

MSC derived from human umbilical cords (ucMSC) were treated for 3 days in vitro with various inflammatory factors, interleukins, vitamins and serum deprivation. Their immunogenicity and immunomodulatory capacity were examined by gene-expression analysis, surface-marker expressions, IDO activity, PGE₂ secretion and inhibition of T cell proliferation and IFNγ production. Furthermore, their activation of NK cell cytotoxicity was investigated via CD107a expression on NK cells. The immunomodulatory capacity, biodistribution and survival of pre-treated ucMSC were investigated in a CCl₄-induced liver disease mouse model. In addition, capacity of pre-treated MSC to ameliorate liver inflammation was examined in an ex vivo liver inflammation co-culture model.

RESULTS

IFN-γ and a multiple cytokine cocktail (MC) consisting of IFN-γ, TGFβ and retinoic acid upregulated the expression of immunomodulatory factor PD-L1 and IDO activity. Subsequently, both treatments enhanced the capacity of ucMSC to inhibit CD4 and CD8 T cell proliferation and IFN-γ production. The susceptibility of ucMSC for NK cell lysis was decreased by IFN-β, TGFβ and MC treatment. In vivo, no immunomodulation was observed by the ucMSC. Four hours after intravenous infusion in mice with CCl₄-induced inflammatory liver injury, the majority of ucMSC were trapped in the lungs. Rapid clearance of ucMSC(VitB₆), ucMSC(Starv + VitB₆) and ucMSC(MC) and altered bio-distribution of ucMSC(TGFβ) compared to untreated ucMSC was observed. In the ex vivo co-culture system with inflammatory liver slices ucMSC(MC) showed significantly enhanced modulatory capacity compared to untreated ucMSC.

CONCLUSIONS

The present study demonstrates the responsiveness of ucMSC to in vitro optimisation treatment. The observed improvements in immunomodulatory capacity as well as immunogenicity after MC treatment may improve the efficacy of ucMSC as immunotherapy targeted towards liver inflammation.

Pathogenic or Therapeutic Extracellular Vesicles in Rheumatic Diseases: Role of Mesenchymal Stem Cell-Derived Vesicles

Extracellular vesicles (EVs) are important mediators of cell-to-cell communication pathways via the transport of proteins, mRNA, miRNA and lipids. There are three main types of EVs, exosomes, microparticles and apoptotic bodies, which are classified according to their size and biogenesis. EVs are secreted by all cell types and their function reproduces that of the parental cell. They are involved in many biological processes that regulate tissue homeostasis and physiopathology of diseases. In rheumatic diseases, namely osteoarthritis (OA) and rheumatoid arthritis (RA), EVs have been isolated from synovial fluid and shown to play pathogenic roles contributing to progression of both diseases. By contrast, EVs may have therapeutic effect via the delivery of molecules that may stop disease evolution. In particular, EVs derived from mesenchymal stem cells (MSCs) reproduce the main functions of the parental cells and therefore represent the ideal type of EVs for modulating the course of either disease. The aim of this review is to discuss the role of EVs in OA and RA focusing on their potential pathogenic effect and possible therapeutic options. Special attention is given to MSCs and MSC-derived EVs for modulating OA and RA progression with the perspective of developing innovative therapeutic strategies.

Adipose derived stem cells for regenerative therapy in osteoarticular diseases

In the recent years, adipose derived stem cells (ASCs) led to significant findings in the field of regenerative therapy. ASCs have various biological properties and capacity as differentiation in three lineages (chondrocytes, osteocytes and adipocytes) or immunomodulation by releasing paracrine factors. Osteoarthritis (OA) is the most frequent osteoarticular disease characterized by none curative treatment. We reviewed all current data on the proof of concept of ASCs in OA pathophysiology as well as an inventory of ASC promising cell therapy in OA.

The influence of macrophages on mesenchymal stromal cell therapy: passive or aggressive agents?

Mesenchymal stromal cells (MSC) have emerged as promising cell therapies for multiple conditions based on demonstrations of their potent immunomodulatory and regenerative capacities in models of inflammatory disease. Understanding the effects of MSC on T cells has dominated the majority of work carried out in this field to date; recently, however, a number of studies have shown that the therapeutic effect of MSC requires the presence of macrophages. It is timely to review the mechanisms and manner by which MSC modulate macrophage populations in order to design more effective MSC therapies and clinical studies. A complex cross-talk exists through which MSC and macrophages communicate, a communication that is not controlled exclusively by MSC. Here, we examine the evidence that suggests that MSC not only respond to inflammatory macrophages and adjust their secretome accordingly, but also that macrophages respond to encounters with MSC, creating a feedback loop which contributes to the immune regulation observed following MSC therapy. Future studies examining the effects of MSC on macrophages should consider the antagonistic role that macrophages play in this exchange.

Biodistribution and Immunogenicity of Allogeneic Mesenchymal Stem Cells in a Rat Model of Intraarticular Chondrocyte Xenotransplantation

Xenogeneic chondrocytes and allogeneic mesenchymal stem cells (MSC) are considered a potential source of cells for articular cartilage repair. We here assessed the immune response triggered by xenogeneic chondrocytes when injected intraarticularly, as well as the immunoregulatory effect of allogeneic bone marrow-derived MSC after systemic administration. To this end, a discordant xenotransplantation model was established by injecting three million porcine articular chondrocytes (PAC) into the femorotibial joint of Lewis rats and monitoring the immune response. First, the fate of MSC injected using various routes was monitored in an in vivo imaging system. The biodistribution revealed a dependency on the injection route with MSC injected intravenously (i.v.) succumbing early after 24 h and MSC injected intraperitoneally (i.p.) lasting locally for at least 5 days. Importantly, no migration of MSC to the joint was detected in rats previously injected with PAC. MSC were then administered either i.v. 1 week before PAC injection or i.p. 3 weeks after to assess their immunomodulatory function on humoral and adaptive immune parameters. Anti-PAC IgM and IgG responses were detected in all PAC-injected rats with a peak at week 2 postinjection and reactivity remaining above baseline levels by week 18. IgG2a and IgG2b were the predominant and long-lasting IgG subtypes. By contrast, no anti-MSC antibody response was detected in the cohort injected with MSC only, but infusion of MSC before PAC injection temporarily augmented the anti-PAC antibody response. Consistent with a cellular immune response to PAC in PAC-injected rats, cytokine/chemokine profiling in serum by antibody array revealed a distinct pattern relative to controls characterized by elevation of multiple markers at week 2, as well as increases in proliferation in draining lymph nodes. Notably, systemic administration of allogeneic MSC under the described conditions did not diminish the immune response. IL-2 measurements in cocultures of rat peripheral blood lymphocytes with PAC indicated that PAC injection induced some T-cell hyporesponsiveness that was not enhanced in the cohorts additionally receiving MSC. Thus, PAC injected intraarticularly in Lewis rats induced a cellular and humoral immune response that was not counteracted by the systemic administration of allogeneic MSC under the described conditions.

Immunomodulatory effects of bone marrow mesenchymal stem cells overexpressing heme oxygenase-1: Protective effects on acute rejection following reduced-size liver transplantation in a rat model

Here we explore the T-lymphocyte suppressive and immunomodulatory effects of bone marrow mesenchymal stem cells (BMMSCs) overexpressing heme oxygenase-1 (HO-1) on acute rejection following reduced-size liver transplantation (RLT) in a rat model. The proliferation activity, cell cycle progression, secretion of proinflammatory cytokines, expression of CD25 and CD71 in lymphocytes, and activity of NK cells were found to be significantly lowered, and the proportion of regulatory T cells (Tregs) was found to be increased relative to BMMSCs when Adv-HO-1/BMMSCs were co-cultured with Con A ex vivo; secretion of anti-inflammatory cytokines was significantly higher. When treated with saline, BMMSCs or Adv-HO-1/BMMSCs, post-transplantation rats receiving Adv-HO-1/BMMSCs showed better median survival time, lower rejection activity index, higher anti-inflammatory cytokine levels, lower proinflammatory cytokine levels, more peripheral Tregs, and lower natural killer cell viability. These results suggest that HO-1 enhanced and prolonged the effects of BMMSCs on acute rejection following RLT, with immunomodulatory effects in which adaptive and innate immunity, as well as paracrine signaling, may play important roles.

Human umbilical cord blood-stem cells direct macrophage polarization and block inflammasome activation to alleviate rheumatoid arthritis

Rheumatoid arthritis (RA) is a long-lasting intractable autoimmune disorder, which has become a substantial public health problem. Despite widespread use of biologic drugs, there have been uncertainties in efficacy and long-term safety. Mesenchymal stem cells (MSCs) have been suggested as a promising alternative for the treatment of RA because of their immunomodulatory properties. However, the precise mechanisms of MSCs on RA-related immune cells are not fully elucidated. The aim of this study was to investigate the therapeutic potential of human umbilical cord blood-derived MSCs (hUCB-MSCs) as a new therapeutic strategy for patients with RA and to explore the mechanisms underlying hUCB-MSC-mediated immunomodulation. Mice with collagen-induced arthritis (CIA) were administered with hUCB-MSCs after the onset of disease, and therapeutic efficacy was assessed. Systemic delivery of hUCB-MSCs significantly ameliorated the severity of CIA to a similar extent observed in the etanercept-treated group. hUCB-MSCs exerted this therapeutic effect by regulating macrophage function. To verify the regulatory effects of hUCB-MSCs on macrophages, macrophages were co-cultured with hUCB-MSCs. The tumor necrosis factor (TNF)-α-mediated activation of cyclooxygenase-2 and TNF-stimulated gene/protein 6 in hUCB-MSCs polarized naive macrophages toward an M2 phenotype. In addition, hUCB-MSCs down-regulated the activation of nucleotide-binding domain and leucine-rich repeat pyrin 3 inflammasome via a paracrine loop of interleukin-1β signaling. These immune-balancing effects of hUCB-MSCs were reproducible in co-culture experiments using peripheral blood mononuclear cells from patients with active RA. hUCB-MSCs can simultaneously regulate multiple cytokine pathways in response to pro-inflammatory cytokines elevated in RA microenvironment, suggesting that treatment with hUCB-MSCs could be an attractive candidate for patients with treatment-refractory RA.

PPARβ/δ: A master regulator of mesenchymal stem cell functions

Peroxisome proliferator-activated receptors (PPARs) have emerged as key regulators of physiological and immunological processes. Recently, one of their members PPARβ/δ has been identified as major player in the maintenance of bone homeostasis, by promoting Wnt signalling activity in osteoblast and mesenchymal stem cells (MSC). PPARβ/δ not only controls the fate of MSC but also regulates their immunosuppressive properties by directly modulating their NF-κB activity. In this review, we discuss how the regulation of PPARβ/δ provides an innovative strategy for an optimisation of MSC-based therapy.

Mesenchymal Stem Cells Regulate the Innate and Adaptive Immune Responses Dampening Arthritis Progression

Mesenchymal stem cells (MSCs) are multipotent stem cells that are able to immunomodulate cells from both the innate and the adaptive immune systems promoting an anti-inflammatory environment. During the last decade, MSCs have been intensively studied in vitro and in vivo in experimental animal model of autoimmune and inflammatory disorders. Based on these studies, MSCs are currently widely used for the treatment of autoimmune diseases such as rheumatoid arthritis (RA) characterized by complex deregulation of the immune systems. However, the therapeutic properties of MSCs in arthritis are still controverted. These controversies might be due to the diversity of MSC sources and isolation protocols used, the time, the route and dose of MSC administration, the variety of the mechanisms involved in the MSCs suppressive effects, and the complexity of arthritis pathogenesis. In this review, we discuss the role of the interactions between MSCs and the different immune cells associated with arthritis pathogenesis and the possible means described in the literature that could enhance MSCs therapeutic potential counteracting arthritis development and progression.

Mesenchymal stromal/stem cells in drug therapy: New perspective

Mesenchymal stromal/stem cells (MSC) have emerged as a class of cells suitable for cellular delivery of nanoparticles, drugs and micro-RNA cargo for targeted treatments such as tumor and other protective mechanisms. The special properties of MSC underscore the current use for various clinical applications. Examples of applications include but are not limited to regenerative medicine, immune disorders and anti-cancer therapies. In recent years, there has been intense research in modifying MSC to achieve targeted and efficient clinical outcomes. This review discusses effects of MSC in an inflammatory microenvironment and then explains how these properties could be important to the overall application of MSC in cell therapy. The article also advises caution in the application of these cells because of their role in tumorigenesis. The review stresses the use of MSC as vehicles for drug delivery and discusses the accompanying challenges, based on the influence of the microenvironment on MSC.

Human Mesenchymal Stem Cells Impact Th17 and Th1 Responses Through a Prostaglandin E2 and Myeloid-Dependent Mechanism

: Human mesenchymal stem cells (hMSCs) are being increasingly pursued as potential therapies for immune-mediated conditions, including multiple sclerosis. Although they can suppress human Th1 responses, they reportedly can reciprocally enhance human Th17 responses. Here, we investigated the mechanisms underlying the capacity of hMSCs to modulate human Th1 and Th17 responses. Human adult bone marrow-derived MSCs were isolated, and their purity and differentiation capacity were confirmed. Human venous peripheral blood mononuclear cells (PBMC) were activated, alone, together with hMSC, or in the presence of hMSC-derived supernatants (sups). Cytokine expression by CD4+ T-cell subsets (intracellular staining by fluorescence-activated cell sorting) and secreted cytokines (enzyme-linked immunosorbent assay) were then quantified. The contribution of prostaglandin E2 (PGE2) as well as of myeloid cells to the hMSC-mediated regulation of T-cell responses was investigated by selective depletion of PGE2 from the hMSC sups (anti-PGE2 beads) and by the selective removal of CD14+ cells from the PBMC (magnetic-activated cell sorting separation). Human MSC-secreted products could reciprocally induce interleukin-17 expression while decreasing interferon-γ expression by human CD4+ T cells, both in coculture and through soluble products. Pre-exposure of hMSCs to IL-1β accentuated their capacity to reciprocally regulate Th1 and Th17 responses. Human MSCs secreted high levels of PGE2, which correlated with their capacity to regulate the T-cell responses. Selective removal of PGE2 from the hMSC supernatants abrogated the impact of hMSC on the T cells. Selective removal of CD14+ cells from the PBMCs also limited the capacity of hMSC-secreted PGE2 to affect T-cell responses. Our discovery of a novel PGE2-dependent and myeloid cell-mediated mechanism by which human MSCs can reciprocally induce human Th17 while suppressing Th1 responses has implications for the use of, as well as monitoring of, MSCs as a potential therapeutic for patients with multiple sclerosis and other immune-mediated diseases.

SIGNIFICANCE

Although animal studies have generated a growing interest in the anti-inflammatory potential of mesenchymal stem cells (MSCs) for the treatment of autoimmune diseases, MSCs possess the capacity to both limit and promote immune responses. Yet relatively little is known about human-MSC modulation of human disease-implicated T-cell responses, or the mechanisms underlying such modulation. The current study reveals a novel prostaglandin E2-dependent and myeloid cell-mediated mechanism by which human MSCs can reciprocally regulate human Th17 and Th1 responses, with implications for the use of MSCs as a potential therapeutic for patients with multiple sclerosis and other immune-mediated diseases.

Mesenchymal Stem and Progenitor Cells in Normal and Dysplastic Hematopoiesis-Masters of Survival and Clonality?

Myelodysplastic syndromes (MDS) are malignant hematopoietic stem cell disorders that have the capacity to progress to acute myeloid leukemia (AML). Accumulating evidence suggests that the altered bone marrow (BM) microenvironment in general, and in particular the components of the stem cell niche, including mesenchymal stem cells (MSCs) and their progeny, play a pivotal role in the evolution and propagation of MDS. We here present an overview of the role of MSCs in the pathogenesis of MDS, with emphasis on cellular interactions in the BM microenvironment and related stem cell niche concepts. MSCs have potent immunomodulatory capacities and communicate with diverse immune cells, but also interact with various other cellular components of the microenvironment as well as with normal and leukemic stem and progenitor cells. Moreover, compared to normal MSCs, MSCs in MDS and AML often exhibit altered gene expression profiles, an aberrant phenotype, and abnormal functional properties. These alterations supposedly contribute to the “reprogramming” of the stem cell niche into a disease-permissive microenvironment where an altered immune system, abnormal stem cell niche interactions, and an impaired growth control lead to disease progression. The current article also reviews molecular targets that play a role in such cellular interactions and possibilities to interfere with abnormal stem cell niche interactions by using specific targeted drugs.