CD73 Pathway Contributes to the Immunosuppressive Ability of Mesenchymal Stem Cells in Intraocular Autoimmune Responses

Mesenchymal stem cell based therapies for uveitis: a systematic review of preclinical studies

Cell therapy has shown promising results for treating uveitis in preclinical studies. As the field continues to grow towards clinical translation, it is important to review and critically appraise existing studies. Herein, we analysed and critically appraised all preclinical studies using cell therapy or cell derived extracellular vesicles (EVs) for uveitis, and provided insight into mechanisms regulating ocular inflammation. We used PubMed, Medline, and Embase to search for preclinical studies examining stem cell therapy (e.g., mesenchymal stem cells [MSC]) and secreted EVs. All included studies were assessed for quality using the SYstematic Review Center for Laboratory animal Experimentation (SYRCLE) checklist. Sixteen preclinical studies from 2011 to 2022 were analysed and included in this review of which 75% (n = 12) focused only on cell therapy, 18.7% (n = 3) studies focused on EVs, and 6.3% (n = 1) study focused on both cells and EVs. MSCs were the most common type of cells used in preclinical studies (n = 15) and EVs were commonly isolated from MSCs (n = 3). Overall, both MSCs and EVs showed improvements in ocular inflammation (seen on fundoscopy/slit lamp and histology) and electroretinogram outcomes. Overall, MSC and MSC-derived EVs shown great potential as therapeutic agents for treating uveitis. Unfortunately, small sample size, risk of selection/performance bias, and lack of standardized cell harvesting or delivery protocols are some factors which limits clinical translation. Large scaled, randomized preclinical studies are required to understand the full potential of MSCs for treating uveitis.

IFN-γ-Preconditioned Human Gingival-Derived Mesenchymal Stromal Cells Inhibit Plasmacytoid Dendritic Cells via Adenosine

Plasmacytoid dendritic cells (pDCs) are vital players in antiviral immune responses because of their high levels of IFN-α secretion. However, this attribute has also implicated them as critical factors behind the immunopathogenesis of inflammatory diseases, and no currently available therapy can efficiently inhibit pDCs' aberrant activation. Mesenchymal stromal cells (MSCs) possess stromal immunomodulatory functionality, regulating immune cell activation through several mechanisms, including the adenosinergic (CD39/CD73/adenosine) pathway. The IFN-γ preconditioning of bone marrow MSCs improves their inhibitory properties for therapy applications; however, isolating human gingival tissue-derived MSCs (hGMSCs) is more accessible. These cells have shown better immunomodulatory effects, yet the outcome of IFN-γ preconditioning and its impact on the adenosinergic pathway has not been evaluated. This study first validated the immunoregulatory properties of primary-cultured hGMSCs, and the results showed that IFN-γ preconditioning strengthens CD39/CD73 coexpression, adenosine production, and the regulatory properties of hGMSC, which were confirmed by describing for the first time their ability to reduce pDC activation and their IFN-α secretion and to increase the frequency of CD73+ pDC. In addition, when CD73's enzymatic activity was neutralized in hGMSCs, adenosine production and the IFN-γ preconditioning effect were restrained. This evidence might be applied to design hGMSCs- and adenosine-based immunotherapeutic strategies for treating inflammatory disorders that are associated with pDC overactivation.

A novel role of CD73-IFNγ signalling axis in human mesenchymal stromal cell mediated inflammatory macrophage suppression

Introduction

Immunomodulation is the predominant mechanism via which Mesenchymal stromal cells (MSCs) mediate their therapeutic benefits. However, inconsistent success in numerous clinical trials warrants a better understating of the molecular mechanisms regulating their immunomodulatory properties. CD73, an ecto-5'-nucleotidase is abundantly expressed by MSCs, however its precise role in regulating their immunomodulatory properties is still elusive. The present study explored the role of CD73 in Interferon-gamma (IFNγ) sensing and in turn their ability to suppress "inflammatory" M1 macrophages.

Materials and methods

CD73 knockdown MSCs (CD73-KDN) were initially assessed for expression of immunoregulatory molecules and IFNγ sensing ability by analysing expression of IFNγ signalling downstream targets such as pSTAT-1, Interferon-Stimulated Genes (ISG) and Indoleamine 2,3-dioxygnease (IDO), a prototypic IFNγ-induced immunomodulator. Next CD73-KDN MSCs were co-cultured with inflammatory M1 macrophages and evaluated for their ability to suppress them. To delineate the contributory role of CD73 and IFNγ signalling downstream target IDO, they were overexpressed independently in CD73-KDN MSCs and re-evaluated for their ability to suppress M1 macrophages.

Results

CD73-KDN MSCs exhibited reduced expression of immunoregulatory molecules and were refractory to IFNγ signalling as indicated by attenuated expression of pSTAT-1, Interferon-Stimulated Genes (ISG) and Indoleamine 2,3-dioxygnease (IDO) upon IFNγ exposure. Since sensing of inflammation is critical for MSC mediated immunomodulation, CD73-KDN MSCs were functionally evaluated for their ability to immune-modulate "inflammatory" M1 macrophages wherein they failed to suppress M1 macrophages. Interestingly, ectopic expression of either CD73 or IFNγ signalling target IDO1 in CD73-KDN MSCs restored their ability to suppress M1 macrophages, establishing the importance of CD73-IFNγ signalling axis in MSC-mediated inflammatory macrophage suppression.

Conclusion

The present study uncovers the unexplored role of CD73-IFNγ axis in MSC-mediated M1 macrophage suppression. MSC-educated macrophages are the actual immune-modulators at MSC transplant sites, thus CD73 can serve as a key immune-potency marker for benchmarking therapeutically relevant MSCs.

Enhanced immunosuppressive capability of mesenchymal stem cell-derived small extracellular vesicles with high expression of CD73 in experimental autoimmune uveitis

BACKGROUND

Autoimmune uveitis is an inflammatory disease triggered by an aberrant immune response. Mesenchymal stem cell-derived small extracellular vesicles (MSC-sEVs) are emerging as potential therapeutic agents for this condition. CD73, an ectoenzyme present on MSC-sEVs, is involved in mitigating inflammation by converting extracellular adenosine monophosphate into adenosine. We hypothesize that the inhibitory effect of MSC-sEVs on experimental autoimmune uveitis (EAU) could be partially attributed to the surface expression of CD73.

METHODS

To investigate novel therapeutic approaches for autoimmune uveitis, we performed lentiviral transduction to overexpress CD73 on the surface of MSC-sEVs, yielding CD73-enriched MSC-sEVs (sEVs-CD73). Mice with interphotoreceptor retinoid-binding protein (IRBP)-induced EAU were grouped randomly and treated with 50 µg MSC-sEVs, vector infected MSC-sEVs, sEVs-CD73 or PBS via single tail vein injection. We evaluated the clinical and histological features of the induced mice and analyzed the proportion and functional capabilities of T helper cells. Furthermore, T-cells were co-cultured with various MSC-sEVs in vitro, and we quantified the resulting inflammatory response to assess the potential therapeutic benefits of sEVs-CD73.

RESULTS

Compared to MSC-sEVs, sEVs-CD73 significantly alleviates EAU, leading to reduced inflammation and diminished tissue damage. Treatment with sEVs-CD73 results in a decreased proportion of Th1 cells in the spleen, draining lymph nodes, and eyes, accompanied by an increased proportion of regulatory T-cells (Treg cells). In vitro assays further reveal that sEVs-CD73 inhibits T-cell proliferation, suppresses Th1 cells differentiation, and enhances Treg cells proportion.

CONCLUSION

Over-expression of CD73 on MSC-sEVs enhances their immunosuppressive effects in EAU, indicating that sEVs-CD73 has the potential as an efficient immunotherapeutic agent for autoimmune uveitis.

Compounding engineered mesenchymal stem cell-derived exosomes: A potential rescue strategy for retinal degeneration

The prevalence of retinal degenerative diseases, including age-related macular degeneration and retinitis pigmentosa, has been increasing globally and is linked to the aging population and improved life expectancy. These diseases are characterized by chronic, progressive neuronal damage or depletion of the photoreceptor cells in the retina, and limited effective treatment options are currently available. Mesenchymal stem cell-derived exosomes (MSC-EXOs) containing cytokines, growth factors, lipids, mRNA, and miRNA, which act as mediators of intercellular communication transferring bioactive molecules to recipient cells, offer an appealing, non-cellular nanotherapeutic approach for retinal degenerative diseases. However, treatment specificity is compromised due to their high heterogeneity in size, content, functional effects, and parental cellular source. To improve this, engineered MSC-EXOs with increased drug-loading capacity, targeting ability, and resistance to bodily degradation and elimination have been developed. This review summarizes the recent advances in miRNAs of MSC-EXOs as a treatment for retinal degeneration, discussing the strategies and methods for engineering therapeutic MSC-EXOs. Notably, to address the single functional role of engineered MSC-EXOs, we propose a novel concept called "Compound Engineered MSC-EXOs (Co-E-MSC-EXOs)" along with its derived potential therapeutic approaches. The advantages and challenges of employing Co-E-MSC-EXOs for retinal degeneration in clinical applications, as well as the strategies and issues related to them, are also highlighted.

Adenosine metabolism by mesenchymal stromal cells isolated from different human tissues

Mesenchymal stromal cells (MSCs) have unique biological properties and play important functions, which make them attractive tools for cell-based therapies. The basic mechanisms of these cells are not fully understood. However, the adenosinergic pathway contributes to the main effects attributed to MSCs. Adenosine is a highly immunosuppressive molecule and exerts a central role in inflammation by neutralizing the proinflammatory ATP influence. This nucleoside is produced by purinergic signaling, an important physiological pathway for MSCs, which involves proliferation, migration, differentiation, and apoptosis. Therefore, in this study, we analyzed the extracellular AMP hydrolysis and consequent adenosine production, as well as the expression of CD73 and adenosine receptors on the cell surface of MSCs isolated from different human tissues: dermis (D-MSCs), adipose tissue (AD-MSCs), and umbilical cord (UC-MSCs). All cells confirmed their multipotent capacity by adipogenic, osteogenic, and chondrogenic differentiation, as well as the expression of cell surface markers including CD44 + , CD105 + , and CD90 + . All MSCs expressed similar levels of CD73 and CD26 without a statistical difference among the different tissues, whereas ADA expression was lower in AD-MSCs. In addition, A1R and A3R mRNA levels were higher in D-MSCs and AD-MSCs, respectively. Enzymatic assay showed that AD-MSCs have the highest hydrolysis rate of AMP, leading to increased amount of adenosine production. Moreover, despite all MSCs completely hydrolyze extracellular AMP generating adenosine, the pattern of nucleosides metabolism was different. Therefore, although MSCs share certain characteristics as the multilineage potential and immunophenotype, they show different adenosinergic profiles according to tissue origin.

ENPP1 Immunobiology as a Therapeutic Target

ENPP1 (ecto-nucleotide pyrophosphatase/phosphodiesterase) participates in the hydrolysis of different purine nucleotides in an array of physiologic processes. However, ENPP1 is frequently overexpressed in local relapses and tumor metastases, which are associated with poor prognosis and survival in a range of solid tumors. ENPP1 promotes an immunosuppressive tumor microenvironment (TME) by tilting the balance of ATP/adenosine (Ado) in conjunction with other components (CD38, CD39/ENTPD1, and CD73/NT5E). Moreover, ENPP1 intersects with the stimulator of interferon genes (STING), impairing its robust immune response through the hydrolysis of the effector 2´,3´-cyclic GMP-AMP. Thus, ENPP1 blockade emerges as a unique target eliciting immune remodeling and leveraging the STING pathway. Several ENPP1 inhibitors have shown an immunostimulatory effect, and their combination with other therapeutic modalities, such as immune-checkpoint blockade, STING activation, DNA damage response (DDR) inhibitors, and radiotherapy (RT), represents a promising avenue to boost antitumor-immune responses and to improve current clinical outcomes in several tumors. This comprehensive review summarizes the current state of the art and opens new perspectives for novel treatment strategies.

Pertussis toxin-induced inhibition of Wnt/β-catenin signaling in dendritic cells promotes an autoimmune response in experimental autoimmune uveitis

BACKGROUND

Previous reports have indicated that disrupting the Wnt/β-catenin pathway in dendritic cells (DCs) may affect the progression of autoimmune inflammation; however, the factors and timing that regulate Wnt/β-catenin signaling have not been clearly understood.

METHODS

Experimental autoimmune uveitis (EAU) mice and Vogt-Koyanagi-Harada disease (VKH) patient samples were used to detect the expression of Wnt/β-catenin pathway genes. Western blot, real-time PCR, flow cytometry, and ELISA were performed to examine the expression of components of the Wnt/β-catenin pathway and inflammatory factors. DC-specific β-catenin knockout mice and 6-bromoindirubin-3'-oxime (BIO) administered mice were used to observe the effect of disrupting the Wnt pathway on EAU pathogenesis.

RESULTS

Wnt/β-catenin signaling was inhibited in DCs during the induction phase of EAU. The inhibition was mediated by pertussis toxin (PTX), which promoted DC maturation, in turn promoting pathogenic T cell proliferation and differentiation. In vivo experiments confirmed that deleting β-catenin in DCs enhanced EAU severity, and pre-injection of PTX advanced EAU onset. Administration of a Wnt activator (BIO) limited the effects of PTX, in turn ameliorating EAU.

CONCLUSIONS

Our results demonstrate that PTX plays a key role as a virulence factor in initiating autoimmune inflammation via DCs by inhibiting Wnt/β-catenin signaling in EAU, and highlight the potential mechanism by which infection can trigger apparent autoimmunity.

Microglia: The breakthrough to treat neovascularization and repair blood-retinal barrier in retinopathy

Microglia are the primary resident retinal macrophages that monitor neuronal activity in real-time and facilitate angiogenesis during retinal development. In certain retinal diseases, the activated microglia promote retinal angiogenesis in hypoxia stress through neurovascular coupling and guide neovascularization to avascular areas (e.g., the outer nuclear layer and macula lutea). Furthermore, continuously activated microglia secrete inflammatory factors and expedite the loss of the blood-retinal barrier which causes irreversible damage to the secondary death of neurons. In this review, we support microglia can be a potential cellular therapeutic target in retinopathy. We briefly describe the relevance of microglia to the retinal vasculature and blood-retinal barrier. Then we discuss the signaling pathway related to how microglia move to their destinations and regulate vascular regeneration. We summarize the properties of microglia in different retinal disease models and propose that reducing the number of pro-inflammatory microglial death and conversing microglial phenotypes from pro-inflammatory to anti-inflammatory are feasible for treating retinal neovascularization and the damaged blood-retinal barrier (BRB). Finally, we suppose that the unique properties of microglia may aid in the vascularization of retinal organoids.

Mesenchymal-Stem-Cell-Based Strategies for Retinal Diseases

Retinal diseases are major causes of irreversible vision loss and blindness. Despite extensive research into their pathophysiology and etiology, pharmacotherapy effectiveness and surgical outcomes remain poor. Based largely on numerous preclinical studies, administration of mesenchymal stem cells (MSCs) as a therapeutic strategy for retinal diseases holds great promise, and various approaches have been applied to the therapies. However, hindered by the retinal barriers, the initial vision for the stem cell replacement strategy fails to achieve the anticipated effect and has now been questioned. Accumulating evidence now suggests that the paracrine effect may play a dominant role in MSC-based treatment, and MSC-derived extracellular vesicles emerge as a novel compelling alternative for cell-free therapy. This review summarizes the therapeutic potential and current strategies of this fascinating class of cells in retinal degeneration and other retinal dysfunctions.

Variability in CD39 and CD73 protein levels in uveal melanoma patients

Extracellular adenosine is produced from ATP by CD39 and CD73, and can modulate tumor development by acting on cancer cells or immune cells. Adenosine metabolism has been poorly studied in uveal melanoma. We studied the protein levels of CD39 and CD73 in a small, well described cohort of patients with uveal melanoma. Our results show a high variability in the levels of the two proteins, both in positivity and in intensity. Our results suggest that similar studies on larger cohorts could determine the clinical value and the druggability of these enzymes in the given clinical setting.Supplemental data for this article is available online at http://dx.doi.org/10.1080/15257770.2022.2032738.

Stem cells from exfoliated deciduous teeth transplantation ameliorates Sjögren's syndrome by secreting soluble PD-L1

Mesenchymal stem cell transplantation (MSCT) regulates immune cells, and is a promising therapeutic approach for treating autoimmune diseases. Stem cells from human exfoliated deciduous teeth (SHED) are a unique postnatal stem cell population from the cranial neural crest with high self-renewal, multipotent differentiation, and superior immunomodulatory properties. However, the mechanisms by which SHED can treat autoimmune diseases remain unclear. Sjögren's syndrome (SS) is an autoimmune disease histologically characterized by high lymphocytic infiltration in the salivary and lacrimal glands that results in dryness symptoms. This study explores the potential of systemic transplantation of SHED to ameliorate SS-induced dryness symptoms in mice. Overall, SHED could rescue the balance of regulatory T cell (Treg)/T helper cell 17 (Th17) in the recipient SS mice. Mechanistically, SHED promoted Treg conversion and inhibited Th17 function via paracrine effects, which were related to the secretion of soluble programmed cell death ligand 1 (sPD-L1). Moreover, it directly induced Th17 apoptosis via cell-cell contact, leading to the up-regulation of Treg and down-regulation of Th17 cells. In summary, SHED-mediated rescue of Treg/Th17 balance via the sPD-L1/PD-1 pathway ameliorates the gland inflammation and dryness symptoms in SS mice. These findings suggest that SHED are a promising stem cell source for the treatment of autoimmune diseases in the clinical setting.

Immortalization of Mesenchymal Stromal Cells by TERT Affects Adenosine Metabolism and Impairs their Immunosuppressive Capacity

Mesenchymal stromal cells (MSCs) are promising candidates for cell-based therapies, mainly due to their unique biological properties such as multipotency, self-renewal and trophic/immunomodulatory effects. However, clinical use has proven complex due to limitations such as high variability of MSCs preparations and high number of cells required for therapies. These challenges could be circumvented with cell immortalization through genetic manipulation, and although many studies show that such approaches are safe, little is known about changes in other biological properties and functions of MSCs. In this study, we evaluated the impact of MSCs immortalization with the TERT gene on the purinergic system, which has emerged as a key modulator in a wide variety of pathophysiological conditions. After cell immortalization, MSCs-TERT displayed similar immunophenotypic profile and differentiation potential to primary MSCs. However, analysis of gene and protein expression exposed important alterations in the purinergic signaling of in vitro cultured MSCs-TERT. Immortalized cells upregulated the CD39/NTPDase1 enzyme and downregulated CD73/NT5E and adenosine deaminase (ADA), which had a direct impact on their nucleotide/nucleoside metabolism profile. Despite these alterations, adenosine did not accumulate in the extracellular space, due to increased uptake. MSCs-TERT cells presented an impaired in vitro immunosuppressive potential, as observed in an assay of co-culture with lymphocytes. Therefore, our data suggest that MSCs-TERT have altered expression of key enzymes of the extracellular nucleotides/nucleoside control, which altered key characteristics of these cells and can potentially change their therapeutic effects in tissue engineering in regenerative medicine.

Analysis of Key Distinct Biological Characteristics of Human Placenta-Derived Mesenchymal Stromal Cells and Individual Heterogeneity Attributing to Donors

For potential clinical applications in the future, we investigated the distinct biological features of mesenchymal stromal cells (MSCs) derived from different origin areas of human placenta and individual heterogeneity among different donors. Chorionic plate MSCs (CP-MSCs), amniotic membrane MSCs (AM-MSCs), and decidual plate MSCs (DP-MSCs) were isolated from 5 human placentae and were analyzed in terms of main features of MSCs including surface marker profile, growth, differentiation potential, immune regulation capability, and tubulin acetylation (Ac-tubulin). The expression profile of surface markers in the 3 types of MSCs derived from the 5 donors was relatively stable. Heterogeneity was found in growth, differentiation potential, and immune regulation among MSCs according to the different areas of isolation and different donors. CP-MSCs and AM-MSCs derived from the placentae of donors 1-3 had a higher osteogenic differentiation potential than the corresponding DP-MSCs, but those derived from the placentae of donors 4 and 5 had a markedly lower osteogenic differentiation potential than DP-MSCs. All CP-MSCs derived from donors 1-3 had the highest adipogenic differentiation potential, but CP-MSCs derived from donors 4 and 5 did not show strong capability of adipogenic differentiation. CP-MSCs markedly inhibited the proliferation of peripheral blood mononuclear cells (PBMCs) induced by phytohemagglutinin, whereas AM- and DP-MSCs did not. All MSCs decreased the proportion of CD3+/CD8-/IFN-γ+ Th1 and CD3+/CD8-/IL17+ Th17 cells, but increased the proportion of Treg cells in PBMCs, with individual differences among the 5 donors. DP-MSCs from donors 1 and 2 had higher levels of Ac-tubulin compared with CP- and AM-MSCs. However, the levels of Ac-tubulin in AM-MSCs from donors 3 and 5 were higher than those of the other 2 types of MSCs. Our results revealed that there was tissue-specific heterogeneity among the 3 types of MSCs from different origin tissues of placenta and individual heterogeneity among donors. In future, the pre-selected placenta-derived MSCs with specific biological advantages may improve the curative effect of cell therapy in different situations.

Mesenchymal stromal cells for the treatment of ocular autoimmune diseases

Mesenchymal stromal cells, commonly referred to as MSCs, have emerged as a promising cell-based therapy for a range of autoimmune diseases thanks to several therapeutic advantages. Key among these are: 1) the ability to modulate innate and adaptive immune responses and to promote tissue regeneration, 2) the ease of their isolation from readily accessible tissues and expansion at scale in culture, 3) their low immunogenicity enabling use as an allogeneic "off-the-shelf" product, and 4) MSC therapy's safety and feasibility in humans, as demonstrated in more than one thousand clinical trials. Evidence from preclinical studies and early clinical trials indicate the therapeutic potential of MSCs and their derivatives for efficacy in ocular autoimmune diseases such as autoimmune uveoretinitis and Sjögren's syndrome-related dry eye disease. In this review, we provide an overview of the current understanding of the therapeutic mechanisms of MSCs, and summarize the results from preclinical and clinical studies that have used MSCs or their derivatives for the treatment of ocular autoimmune diseases. We also discuss the challenges to the successful clinical application of MSC therapy, and suggest strategies for overcoming them.

The adenosinergic pathway in mesenchymal stem cell fate and functions

Mesenchymal stem cells (MSCs) play an important role in tissue homeostasis and damage repair through their ability to differentiate into cells of different tissues, trophic support, and immunomodulation. These properties made them attractive for clinical applications in regenerative medicine, immune disorders, and cell transplantation. However, despite multiple preclinical and clinical studies demonstrating beneficial effects of MSCs, their native identity and mechanisms of action remain inconclusive. Since its discovery, the CD73/ecto-5'-nucleotidase is known as a classic marker for MSCs, but its role goes far beyond a phenotypic characterization antigen. CD73 contributes to adenosine production, therefore, is an essential component of purinergic signaling, a pathway composed of different nucleotides and nucleosides, which concentrations are finely regulated by the ectoenzymes and receptors. Thus, purinergic signaling controls pathophysiological functions such as proliferation, migration, cell fate, and immune responses. Despite the remarkable progress already achieved in considering adenosinergic pathway as a therapeutic target in different pathologies, its role is not fully explored in the context of the therapeutic functions of MSCs. Therefore, in this review, we provide an overview of the role of CD73 and adenosine-mediated signaling in the functions ascribed to MSCs, such as homing and proliferation, cell differentiation, and immunomodulation. Additionally, we will discuss the pathophysiological role of MSCs, via CD73 and adenosine, in different diseases, as well as in tumor development and progression. A better understanding of the adenosinergic pathway in the regulation of MSCs functions will help to provide improved therapeutic strategies applicable in regenerative medicine.

Tumor-resident adenosine-producing mesenchymal stem cells as a potential target for cancer treatment

The development of new therapies based on tumor biology is one of the main topics in cancer treatment. In this regard, investigating the microenvironment and cellular composition of the tumor is of particular interest. Mesenchymal stem cells (MSCs) are a major group of cells in the tumor tissue and play a critical role in tumor growth and development. Investigating the mechanisms by which MSCs influence tumor growth and progression is very useful in establishing new therapeutic approaches. MSCs have some immunological capacities, including anti-inflammatory, immune-regulatory, and immune-suppressive abilities, which help the tumor growth in the inflammatory condition. They can suppress the proliferation and activation of CD4 + T cells and direct them toward the regulatory phenotype through the release of some factors such as indoleamine 2,3-dioxygenase, prostaglandin E2, and HO-1, PD-1 ligands (PD-L1 and PD-L2) and promote tolerance and apoptosis. Besides, these cells are able to produce adenosine. Adenosine has a key role in controlling the immune system by signaling through receptors located on the surface of immune cells. It plays a very essential role in tumor growth and progression. In the present review, we investigate and introduce adenosine-producing mesenchymal stem cells as a potential target for cancer treatment.

CD73 Overexpression Promotes Progression and Recurrence of Papillary Thyroid Carcinoma

Simple Summary

This study aimed to evaluate the clinicopathologic significance of CD73 expression in patients with papillary thyroid carcinoma (PTC) and the potential for CD73 to serve as a therapeutic target of PTC. CD73 was highly expressed in PTC, but not in the normal thyroid tissue. Overexpression of CD73 was associated with unfavorable clinicopathologic characteristics and a shorter recurrence-free survival. The expression level of CD73 mRNA was associated with the abundance of Tregs and dendritic cells, depletion of natural killer (NK) cells, and high expression of immune checkpoint genes and epithelial-to-mesenchymal transition-related genes. CD73 inhibitor attenuated PTC cell proliferation, migration, and invasion in vitro, and suppressed PTC xenograft tumor growth in nude mice. These results suggest that CD73 expression is an unfavorable prognostic marker for patients with PTC. CD73 blockade would be an attractive candidate for therapeutic strategies in patients with advanced PTC.

Abstract

CD73 is involved in tumor immune escape and promotes the growth and progression of cancer cells. The functional role of CD73 expression in papillary thyroid carcinoma (PTC) has not yet been established. In 511 patients with PTC, immunohistochemistry for CD73 on tissue microarrays showed that the high expression of CD73 was associated with an aggressive histologic variant (p = 0.002), extrathyroidal extension (p < 0.001), lymph node metastasis (p < 0.001), and BRAF^V600E mutation (p = 0.015). Survival analysis results showed that patients with high CD73 expression had worse recurrence-free survival (p = 0.023). CD73 inhibitors induced G1 cell cycle arrest and apoptosis, inhibited the migration and invasion of PTC cells, and suppressed tumor growth in PTC xenograft nude mice. High expression of CD73 (NT5E) mRNA was associated with unfavorable clinicopathologic characteristics, the abundance of Tregs and dendritic cells, depletion of natural killer (NK) cells, and high expression of immune checkpoint genes and epithelial-to-mesenchymal transition-related genes in The Cancer Genome Atlas (TCGA) dataset. Taken together, CD73 expression promotes tumor progression and predicts low recurrence-free survival. Targeting the CD73–adenosine axis in the tumor microenvironment offers an attractive pathway for therapeutic strategies aimed at advanced PTC.

Effect of Mesenchymal Stem Cell-Derived Exosomes on Retinal Injury: A Review of Current Findings

In recent years, various studies have followed in the literature on the therapeutic effects of mesenchymal stem cells (MSC) on damage in retinal cells. The evidence that MSCs exert their regenerative and damage reduction effect in a paracrine way, through the release of soluble factors and exosomes, is now consolidated. Exosomes are microvesicles formed by a double layer of phospholipid membrane and carry proteins and RNA, through which they play a therapeutic role on target cells. Scientific research has recently focused on the use of exosomes derived from MSC in various models of retinal damage in vitro and in vivo as they, compared to MSCs, have similar functions and at the same time have different advantages such as greater stability and handling, a lower chance of immunological rejection and no risk of malignant transformation. The purpose of this review is to summarize current knowledge on the therapeutic use of exosomes derived from MSCs in retinal damage and to stimulate new clinical perspectives regarding their use.

Mesenchymal Stromal Cell Immunology for Efficient and Safe Treatment of Osteoarthritis

Mesenchymal stem cell (MSC) therapy represents a promising approach for the treatment of osteoarthritis (OA). MSCs can be readily isolated from multiple sources and expanded ex vivo for possible clinical application. They possess a unique immunological profile and regulatory machinery that underline their therapeutic effects. They also have the capacity to sense the changes within the tissue environment to display the adequate response. Indeed, there is a close interaction between MSCs and the host cells. Accordingly, MSCs demonstrate encouraging results for a variety of diseases including OA. However, their effectiveness needs to be improved. In this review, we selected to discuss the importance of the immunological features of MSCs, including the type of transplantation and the immune and blood compatibility. It is important to consider MSC immune evasive rather than immune privileged. We also highlighted some of the actions/mechanisms that are displayed during tissue healing including the response of MSCs to injury signals, their interaction with the immune system, and the impact of their lifespan. Finally, we briefly summarized the results of clinical studies reporting on the application of MSCs for the treatment of OA. The research field of MSCs is inspiring and innovative but requires more knowledge about the immunobiological properties of these cells. A better understanding of these features will be key for developing a safe and efficient medicinal product for clinical use in OA.

Immune modulation by mesenchymal stem cells

Mesenchymal stem cells (MSCs) can be derived from various adult tissues with multipotent and self-renewal abilities. The characteristics of presenting no major ethical concerns, having low immunogenicity and possessing immune modulation functions make MSCs promising candidates for stem cell therapies. MSCs could promote inflammation when the immune system is underactivated and restrain inflammation when the immune system is overactivated to avoid self-overattack. These cells express many immune suppressors to switch them from a pro-inflammatory phenotype to an anti-inflammatory phenotype, resulting in immune effector cell suppression and immune suppressor cell activation. We would discuss the mechanisms governing the immune modulation function of these cells in this review, especially the immune-suppressive effects of MSCs.

The CD73/Ado System-A New Player in RT Induced Adverse Late Effects

Radiotherapy (RT) is a central component of standard treatment for many cancer patients. RT alone or in multimodal treatment strategies has a documented contribution to enhanced local control and overall survival of cancer patients, and cancer cure. Clinical RT aims at maximizing tumor control, while minimizing the risk for RT-induced adverse late effects. However, acute and late toxicities of IR in normal tissues are still important biological barriers to successful RT: While curative RT may not be tolerable, sub-optimal tolerable RT doses will lead to fatal outcomes by local recurrence or metastatic disease, even when accepting adverse normal tissue effects that decrease the quality of life of irradiated cancer patients. Technical improvements in treatment planning and the increasing use of particle therapy have allowed for a more accurate delivery of IR to the tumor volume and have thereby helped to improve the safety profile of RT for many solid tumors. With these technical and physical strategies reaching their natural limits, current research for improving the therapeutic gain of RT focuses on innovative biological concepts that either selectively limit the adverse effects of RT in normal tissues without protecting the tumor or specifically increase the radiosensitivity of the tumor tissue without enhancing the risk of normal tissue complications. The biology-based optimization of RT requires the identification of biological factors that are linked to differential radiosensitivity of normal or tumor tissues, and are amenable to therapeutic targeting. Extracellular adenosine is an endogenous mediator critical to the maintenance of homeostasis in various tissues. Adenosine is either released from stressed or injured cells or generated from extracellular adenine nucleotides by the concerted action of the ectoenzymes ectoapyrase (CD39) and 5′ ectonucleotidase (NT5E, CD73) that catabolize ATP to adenosine. Recent work revealed a role of the immunoregulatory CD73/adenosine system in radiation-induced fibrotic disease in normal tissues suggesting a potential use as novel therapeutic target for normal tissue protection. The present review summarizes relevant findings on the pathologic roles of CD73 and adenosine in radiation-induced fibrosis in different organs (lung, skin, gut, and kidney) that have been obtained in preclinical models and proposes a refined model of radiation-induced normal tissue toxicity including the disease-promoting effects of radiation-induced activation of CD73/adenosine signaling in the irradiated tissue environment. However, expression and activity of the CD73/adenosine system in the tumor environment has also been linked to increased tumor growth and tumor immune escape, at least in preclinical models. Therefore, we will discuss the use of pharmacologic inhibition of CD73/adenosine-signaling as a promising strategy for improving the therapeutic gain of RT by targeting both, malignant tumor growth and adverse late effects of RT with a focus on fibrotic disease. The consideration of the therapeutic window is particularly important in view of the increasing use of RT in combination with various molecularly targeted agents and immunotherapy to enhance the tumor radiation response, as such combinations may result in increased or novel toxicities, as well as the increasing number of cancer survivors.

Cell membrane and bioactive factors derived from mesenchymal stromal cells: Cell-free based therapy for inflammatory bowel diseases

Inflammatory bowel diseases (IBD) are chronic inflammatory disorders of the gastrointestinal tract associated with multifactorial conditions such as ulcerative colitis and Crohn's disease. Although the underlying mechanisms of IBD remain unclear, growing evidence has shown that dysregulated immune system reactions in genetically susceptible individuals contribute to mucosal inflammation. However, conventional treatments have been effective in inducing remission of IBD but not in preventing the relapse of them. In this way, mesenchymal stromal cells (MSC) therapy has been recognized as a promising treatment for IBD due to their immunomodulatory properties, ability to differentiate into several tissues, and homing to inflammatory sites. Even so, literature is conflicted regarding the location and persistence of MSC in the body after transplantation. For this reason, recent studies have focused on the paracrine effect of the biofactors secreted by MSC, especially in relation to the immunomodulatory potential of soluble factors (cytokines, chemokines, and growth factors) and extracellular vehicles that are involved in cell communication and in the transfer of cellular material, such as proteins, lipids, and nucleic acids. Moreover, treatment with interferon-γ, tumor necrosis factor-α, and interleukin-1β causes MSC to express immunomodulatory molecules that mediate the suppression via cell-contact dependent mechanisms. Taken together, we present an overview of the role of bioactive factors and cell membrane proteins derived from MSC as a cell-free therapy that can improve IBD treatment.

Ionizing radiation effects on the tumor microenvironment

The broad use of radiotherapy (RT) in the management of solid human tumors is based on its ability to damage cellular macromolecules, particularly the DNA, effectively inducing growth arrest and cell death locally in irradiated tumor cells. However, bystander effects, such as the transmission of lethal signals between cells via gap junctions or the production of diffusible cytotoxic mediators, can also contribute to the local antineoplastic action of RT. Traditionally, RT has been considered to exert immunosuppressive effects on the host. This idea largely stems from the radiosensitivity of quiescent lymphocytes and on the use of total body irradiation as part of myeloablative conditioning regimens preceding hematopoietic stem cell transplantation. Additionally, the occurrence of the so-called "abscopal effect," where nonirradiated distant lesions display effects of RT response, suggests that RT may also induce tumor immunization. Several RT-induced effects on cancer, immune and stromal cells, contribute to the abscopal effect: (1) induction of "immunogenic cell death", with release of tumor-associated antigens, (2) alterations of cancer cell immunophenotype, and (3) modulation of the tumor microenvironment. Damage and death of cancer cells leads to the surface exposure of immunogenic molecules as well as the release of damage associated molecular patterns such as adenosine triphosphate or High-Mobility-Group-Protein B1, and potentially tumor antigens that activate the innate and adaptive immune systems. Moreover, nuclear release and cytoplasmic sensing of altered nucleic acids via cyclic GMP-AMP Synthase/Stimulator of Interferon Genes is connected to the secretion of cytokines that support innate and adaptive antitumor immunity. As a result of the above, irradiated tumor cells may potentially act as an "in situ vaccine."

Human Platelet Lysate Improves Bone Forming Potential of Human Progenitor Cells Expanded in Microcarrier-Based Dynamic Culture

Xenogeneic‐free media are required for translating advanced therapeutic medicinal products to the clinics. In addition, process efficiency is crucial for ensuring cost efficiency, especially when considering large‐scale production of mesenchymal stem cells (MSCs). Human platelet lysate (HPL) has been increasingly adopted as an alternative for fetal bovine serum (FBS) for MSCs. However, its therapeutic and regenerative potential in vivo is largely unexplored. Herein, we compare the effects of FBS and HPL supplementation for a scalable, microcarrier‐based dynamic expansion of human periosteum‐derived cells (hPDCs) while assessing their bone forming capacity by subcutaneous implantation in small animal model. We observed that HPL resulted in faster cell proliferation with a total fold increase of 5.2 ± 0.61 in comparison to 2.7 ± 02.22‐fold in FBS. Cell viability and trilineage differentiation capability were maintained by HPL, although a suppression of adipogenic differentiation potential was observed. Differences in mRNA expression profiles were also observed between the two on several markers. When implanted, we observed a significant difference between the bone forming capacity of cells expanded in FBS and HPL, with HPL supplementation resulting in almost three times more mineralized tissue within calcium phosphate scaffolds. FBS‐expanded cells resulted in a fibrous tissue structure, whereas HPL resulted in mineralized tissue formation, which can be classified as newly formed bone, verified by μCT and histological analysis. We also observed the presence of blood vessels in our explants. In conclusion, we suggest that replacing FBS with HPL in bioreactor‐based expansion of hPDCs is an optimal solution that increases expansion efficiency along with promoting bone forming capacity of these cells. stem cells translational medicine2019;8:810&821

Targeting the Immunomodulatory CD73/Adenosine System to Improve the Therapeutic Gain of Radiotherapy

Extracellular adenosine is a potent endogenous immunosuppressive mediator critical to the maintenance of homeostasis in various normal tissues including the lung. Adenosine is either released from stressed or injured cells or generated from extracellular adenine nucleotides by the concerted action of the ectoenzymes ectoapyrase (CD39) and 5′ ectonucleotidase (CD73) that catabolize ATP to adenosine. An acute CD73-dependent increase of adenosine in normal tissues mostly exerts tissue protective functions whereas chronically increased adenosine-levels in tissues exposed to DNA damaging chemotherapy or radiotherapy promote pathologic remodeling processes and fibrosis for example in the skin and the lung. Importantly, cancer cells also express CD73 and high CD73 expression in the tumor tissue has been linked to poor overall survival and recurrence free survival in patients suffering from breast and ovarian cancer. CD73 and adenosine support growth-promoting neovascularization, metastasis, and survival in cancer cells. In addition, adenosine can promote tumor intrinsic or therapy-induced immune escape by various mechanisms that dampen the immune system. Consequently, modulating CD73 or cancer-derived adenosine in the tumor microenvironment emerges as an attractive novel therapeutic strategy to limit tumor progression, improve antitumor immune responses, avoid therapy-induced immune deviation, and potentially limit normal tissue toxicity. However, the role of CD73/adenosine signaling in the tumor and normal tissue responses to radiotherapy and its use as therapeutic target to improve the outcome of radiotherapy approaches is less understood. The present review will highlight the dual role of CD73 and adenosine in tumor and tissue responses to radiotherapy with a special focus to the lung. It will also discuss the potential benefits and risks of pharmacologic modulation of the CD73/adenosine system to increase the therapeutic gain of radiotherapy or combined radioimmunotherapy in cancer treatment.

Adenosine from a biologic source regulates neutrophil extracellular traps (NETs)

Neutrophil extracellular traps (NETs) are implicated in autoimmune, thrombotic, malignant, and inflammatory diseases; however, little is known of their endogenous regulation under basal conditions. Inflammatory effects of neutrophils are modulated by extracellular purines such as adenosine (ADO) that is inhibitory or ATP that generally up-regulates effector functions. In order to evaluate the effects of ADO on NETs, human neutrophils were isolated from peripheral venous blood from healthy donors and stimulated to make NETs. Treatment with ADO inhibited NET production as quantified by 2 methods: SYTOX green fluorescence and human neutrophil elastase (HNE)-DNA ELISA assay. Specific ADO receptor agonist and antagonist were tested for their effects on NET production. The ADO _2A receptor (A_2A R) agonist CSG21680 inhibited NETs to a similar degree as ADO, whereas the A_2A R antagonist ZM241385 prevented ADO's NET-inhibitory effects. Additionally, CD73 is a membrane bound ectonucleotidase expressed on mesenchymal stromal cells (MSCs) that allows manipulation of extracellular purines in tissues such as bone marrow. The effects of MSCs on NET formation were evaluated in coculture. MSCs reduced NET formation in a CD73-dependent manner. These results imply that extracellular purine balance may locally regulate NETosis and may be actively modulated by stromal cells to maintain tissue homeostasis.

Perspectives of Autologous Mesenchymal Stem-Cell Transplantation in Macular Hole Surgery: A Review of Current Findings

The main treatment available for idiopathic macular holes is represented by pars plana vitrectomy with internal limiting membrane peeling. However, late-stage macular holes are affected by a higher risk of surgical failure. Although adjuvant techniques can be employed, a satisfactory functional recovery is difficult to achieve in refractory macular holes. Given their neuroprotective and antiapoptotic properties, mesenchymal stem cells (MSCs) may represent an appealing approach to treat these extreme cases. The purpose of this review is to highlight the findings regarding healing mechanisms exerted by mesenchymal stem cells and preliminary application in cases of refractory macular holes. When compared with MSCs, MSC-derived exosomes may represent a feasible alternative, given their reduced risk of undesired proliferation and easiness of use.

Improvement of Mesenchymal Stem Cell Immunomodulatory Properties by Heat-Killed Propionibacterium acnes via TLR2

Mesenchymal stem cells (MSCs) are an essential tool for regenerative medicine, which aims to develop new technologies to improve their effects to obtain useful transplantation results. MSC immunomodulatory role has been just demonstrated; however, how they react when they are stimulated by an adjuvant is poorly understood. Our group showed the adjuvant effect of killed Propionibacterium acnes (P. acnes) on hematopoietic stem cells. As these cells share the same MSCs bone marrow (BM) site and interact with each other, here we evaluated the P. acnes and its soluble polysaccharide (PS) effect on MSCs and their immunomodulatory role in a murine model of traumatic brain injury (TBI). The bacteria increased the absolute number of MSCs, including MSC subpopulations, and maintained MSC plasticity. P. acnes and PS enhanced MSC proliferation and improved their immunomodulatory effect. P. acnes-MSC and PS-MSC transplantation increased anti-inflammatory cytokine expression and diminished pro-inflammatory cytokine expression after injury. This effect seemed to be mediated via TLR2 since P. acnes-KOTLR2-MSC transplantation decreased TGF-β and IL-10 expression. Increasing in neural stem cells and neuroblasts after PS-MSC transplantation was also observed. The adjuvant effect of P. acnes is an alternative means of expanding MSCs and important to identify their subpopulations to know better their role under exogenous stimuli including inflammation resolution in an experimental model.

Rescuing mesenchymal stem cell regenerative properties on hydrogel substrates post serial expansion

The use of human mesenchymal stem/stromal cells (hMSCs) in most clinical trials requires millions of cells/kg, necessitating ex vivo expansion typically on stiff substrates (tissue culture polystyrene [TCPS]), which induces osteogenesis and replicative senescence. Here, we quantified how serial expansion on TCPS influences proliferation, expression of hMSC-specific surface markers, mechanosensing, and secretome. Results show decreased proliferation and surface marker expression after five passages (P5) and decreased mechanosensing ability and cytokine production at later passages (P11-P12). Next, we investigated the capacity of poly(ethylene glycol) hydrogel matrices (E ~ 1 kPa) to rescue hMSC regenerative properties. Hydrogels reversed the reduction in cell surface marker expression observed at P5 on TCPS and increased secretion of cytokines for P11 hMSCs. Collectively, these results show that TCPS expansion significantly changes functional properties of hMSCs. However, some changes can be rescued by using hydrogels, suggesting that tailoring material properties could improve in vitro expansion methods.

Effects of mesenchymal stem cells and their exosomes on the healing of large and refractory macular holes

PURPOSE

To assess the efficacy of mesenchymal stem cells (MSCs) and MSC-derived exosomes (MSC-Exos) to promote the healing of large and refractory macular holes (MHs).

METHODS

Seven patients (age 51-75 years old) with large and long-standing idiopathic MHs underwent vitrectomy, internal limiting membrane peeling, MSC (two patients) or MSC-Exo (five patients) intravitreal injection, and heavy silicon oil, air, 20% SF6, or 14% C3F8 tamponade. The MSCs were isolated from human umbilical cord tissue, and MSC-Exos were isolated from the supernatants of cultured MSCs using sequential ultracentrifugation.

RESULTS

Five eyes underwent pars plana vitrectomy (PPV) only, while two underwent PPV combined with cataract surgery. Six MHs were closed, while one remained in a flat-open state. The best-corrected visual acuity (BCVA) was improved in five patients with MH closure and remained unchanged in one patient with MH closure who had a 4-year history of MH. A fibrotic membrane was observed on the surface of the retina in one patient who underwent MSC therapy. One patient who received a higher dose of MSC-Exos exhibited an inflammatory reaction.

CONCLUSIONS

MSC and MSC-Exo therapy may promote functional and anatomic recovery from MH. MSC-Exo therapy may be a useful and safe method for improving the visual outcomes after surgery for refractory MHs.

Immune Privilege and Eye-Derived T-Regulatory Cells

Certain cellular components of the eye, such as neural retina, are unable to regenerate and replicate after destructive inflammation. Ocular immune privilege provides the eye with immune protection against intraocular inflammation in order to minimize the risk to vision integrity. The eye and immune system use strategies to maintain the ocular immune privilege by regulating the innate and adaptive immune response, which includes immunological ignorance, peripheral tolerance to eye-derived antigens, and intraocular immunosuppressive microenvironment. In this review, we summarize current knowledge regarding the molecular mechanism responsible for the development and maintenance of ocular immune privilege via regulatory T cells (Tregs), which are generated by the anterior chamber-associated immune deviation (ACAID), and ocular resident cells including corneal endothelial (CE) cells, ocular pigment epithelial (PE) cells, and aqueous humor. Furthermore, we examined the therapeutic potential of Tregs generated by RPE cells that express transforming growth factor beta (TGF-β), cytotoxic T lymphocyte-associated antigen-2 alpha (CTLA-2α), and retinoic acid for autoimmune uveoretinitis and evaluated a new strategy using human RPE-induced Tregs for clinical application in inflammatory ocular disease. We believe that a better understanding of the ocular immune privilege associated with Tregs might offer a new approach with regard to therapeutic interventions for ocular autoimmunity.

The Role of Extracellular Adenosine Generation in the Development of Autoimmune Diseases

Adenosine (ADO) is an immunosuppressive molecule, which suppresses the immune responses by interacting with specific receptors expressed by immune effector cells. ADO is produced from ATP through the enzymatic activities of CD39 and CD73. Alternatively, ADO can be generated starting from NAD⁺, which is metabolized by the concerted action of CD38, CD203a/PC-1, and CD73. The role of ADO in immunity has been characterized in the last years in physiology and in pathological settings. This review examines a panel of reports focused on the functions of ADO in the context of human autoimmune/inflammatory diseases and the selected animal models. The final aim is to consider the role of adenosinergic ectoenzymes and ADO receptors as novel therapeutic targets for selected diseases.

Canonical and non-canonical adenosinergic pathways

Adenosine (ADO) is an immunosuppressive molecule with multiple functions in different human organs. ADO is released through the concerted action of surface molecules endowed with enzymatic functions, that belong to two different adenosinergic pathways. The canonical pathway is started by CD39, that converts ATP to AMP. On the other hand, the non-canonical pathway metabolizes NAD⁺ to ADPR, through the action of CD38. The latter byproduct is then converted to AMP by CD203a/PC-1. Both pathways converge to CD73, that fully degrades AMP to the final product ADO. In this Review we take into account the most relevant finding regarding the expression of ectoenzymes belonging to both adenosinergic pathways in different cell types, including regulatory cell subsets and neoplastic cells. Moreover, we summarize the role of these molecules in different physiological and pathological settings. Finally, we discuss potential therapeutic application of specific inhibitors of ectoenzymes and/or ADO receptors.

Adenosine Production by Biomaterial-Supported Mesenchymal Stromal Cells Reduces the Innate Inflammatory Response in Myocardial Ischemia/Reperfusion Injury

BACKGROUND

During myocardial ischemia/reperfusion (MI/R) injury, there is extensive release of immunogenic metabolites that activate cells of the innate immune system. These include ATP and AMP, which upregulate chemotaxis, migration, and effector function of early infiltrating inflammatory cells. These cells subsequently drive further tissue devitalization. Mesenchymal stromal cells (MSCs) are a potential treatment modality for MI/R because of their powerful anti-inflammatory capabilities; however, the manner in which they regulate the acute inflammatory milieu requires further elucidation. CD73, an ecto-5'-nucleotidase, may be critical in regulating inflammation by converting pro-inflammatory AMP to anti-inflammatory adenosine. We hypothesized that MSC-mediated conversion of AMP into adenosine reduces inflammation in early MI/R, favoring a micro-environment that attenuates excessive innate immune cell activation and facilitates earlier cardiac recovery.

METHODS AND RESULTS

Adult rats were subjected to 30 minutes of MI/R injury. MSCs were encapsulated within a hydrogel vehicle and implanted onto the myocardium. A subset of MSCs were pretreated with the CD73 inhibitor, α,β-methylene adenosine diphosphate, before implantation. Using liquid chromatography/mass spectrometry, we found that MSCs increase myocardial adenosine availability following injury via CD73 activity. MSCs also reduce innate immune cell infiltration as measured by flow cytometry, and hydrogen peroxide formation as measured by Amplex Red assay. These effects were dependent on MSC-mediated CD73 activity. Finally, through echocardiography we found that CD73 activity on MSCs was critical to optimal protection of cardiac function following MI/R injury.

CONCLUSIONS

MSC-mediated conversion of AMP to adenosine by CD73 exerts a powerful anti-inflammatory effect critical for cardiac recovery following MI/R injury.

Membrane particles generated from mesenchymal stromal cells modulate immune responses by selective targeting of pro-inflammatory monocytes

Mesenchymal stromal cells (MSC) are a promising therapy for immunological disorders. However, culture expanded MSC are large and get trapped in the capillary networks of the lungs after intravenous infusion, where they have a short survival time. Hypothetically, living cells are a risk for tumor formation. To reduce risks associated with MSC infusion and improve the distribution in the body, we generated membrane particles (MP) of MSC and MSC stimulated with IFN-γ (MPγ). Tracking analysis and electron microscopy indicated that the average size of MP was 120 nm, and they showed a round shape. MP exhibited ATPase, nucleotidase and esterase activity, indicating they are enzymatically active. MP and MPγ did not physically interact with T cells and had no effect on CD4+ and CD8+ T cells proliferation. However, MP and MPγ selectively bound to monocytes and decreased the frequency of pro-inflammatory CD14+CD16+ monocytes by induction of selective apoptosis. MP and MPγ increased the percentage of CD90 positive monocytes, and MPγ but not MP increased the percentage of anti-inflammatory PD-L1 monocytes. MPγ increased mRNA expression of PD-L1 in monocytes. These data demonstrate that MP have immunomodulatory properties and have potential as a novel cell-free therapy for treatment of immunological disorders.

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.

Effects of Mesenchymal Stem Cell-Derived Exosomes on Experimental Autoimmune Uveitis

We previously demonstrated that mesenchymal stem cells (MSCs) ameliorated experimental autoimmune uveoretinitis (EAU) in rats. Recently, MSC-derived exosomes (MSC-Exo) were thought to carry functions of MSCs. In this study, we tested the effect of local administration of human MSC-Exo on established EAU in the same species. Rats with EAU induced by immunization with interphotoreceptor retinol-binding protein 1177-1191 peptide were treated by periocular injections of increasing doses of MSC-Exo starting at the disease onset for 7 consecutive days. The in vitro effects of MSC-Exo on immune cell migration and responder T cell proliferation were examined by chemotactic assays and lymphocyte proliferation assays, respectively. We found that MSC-Exo greatly reduced the intensity of ongoing EAU as their parent cells by reducing the infiltration of T cell subsets, and other inflammatory cells, in the eyes. Furthermore, the chemoattractive effects of CCL2 and CCL21 on inflammatory cells were inhibited by MSC-Exo. However, no inhibitory effect of MSC-Exo on IRBP-specific T cell proliferation was observed. These results suggest that MSC-Exo effectively ameliorate EAU by inhibiting the migration of inflammatory cells, indicating a potential novel therapy of MSC-Exo for uveitis.

Extracellular Nucleotide Hydrolysis in Dermal and Limbal Mesenchymal Stem Cells: A Source of Adenosine Production

Human Limbal (L-MSCs) and Dermal Mesenchymal Stem Cell (D-MSCs) possess many properties that increase their therapeutic potential in ophthalmology and dermatology. It is known that purinergic signaling plays a role in many aspects of mesenchymal stem cells physiology. They release and respond to purinergic ligands, altering proliferation, migration, differentiation, and apoptosis. Therefore, more information on these processes would be crucial for establishing future clinical applications using their differentiation potential, but without undesirable side effects. This study evaluated and compared the expression of ecto-nucleotidases, the enzymatic activity of degradation of extracellular nucleotides and the metabolism of extracellular ATP in D-MSCs and L-MSCs, isolated from discard tissues of human skin and sclerocorneal rims. The D-MSCs and L-MSCs showed a differentiation potential into osteogenic, adipogenic, and chondrogenic lineages and the expression of markers CD105⁺ , CD44⁺ , CD14^- , CD34^- , CD45^- , as expected. Both cells hydrolyzed low levels of extracellular ATP and high levels of AMP, leading to adenosine accumulation that can regulate inflammation and tissue repair. These cells expressed mRNA for ENTPD1, 2, 3, 5 and 6, and CD73 that corresponded to the observed enzymatic activities. Thus, considering the degradation of ATP and adenosine production, limbal MSCs are very similar to dermal MSCs, indicating that from the aspect of extracellular nucleotide metabolism L-MSCs are very similar to the characterized D-MSCs. J. Cell. Biochem. 118: 2430-2442, 2017. © 2017 Wiley Periodicals, Inc.

Mouse Mesenchymal Progenitor Cells Expressing Adipogenic and Osteogenic Transcription Factors Suppress the Macrophage Inflammatory Response

Mesenchymal progenitor cell characteristics that can identify progenitor populations with specific functions in immunity are actively being investigated. Progenitors from bone marrow and adipose tissue regulate the macrophage (MΦ) inflammatory response by promoting the switch from an inflammatory to an anti-inflammatory phenotype. Conversely, mesenchymal progenitors from the mouse aorta (mAo) support and contribute to the MΦ response under inflammatory conditions. We used cell lines with purported opposing immune-regulatory function, a bone marrow derived mesenchymal progenitor cell line (D1) and a mouse aorta derived mesenchymal progenitor cell line (mAo). Their interaction and regulation of the MΦ cell response to the inflammatory mediator, lipopolysaccharide (LPS), was examined by coculture. As expected, D1 cells suppressed NO, TNF-α, and IL-12p70 production but MΦ phagocytic activity remained unchanged. The mAo cells enhanced NO and TNF-α production in coculture and enhanced MΦ phagocytic activity. Using flow cytometry and PCR array, we then sought to identify sets of MSC-associated genes and markers that are expressed by these progenitor populations. We have determined that immune-supportive mesenchymal progenitors highly express chondrogenic and tenogenic transcription factors while immunosuppressive mesenchymal progenitors highly express adipogenic and osteogenic transcription factors. These data will be useful for the isolation, purification, and modification of mesenchymal progenitors to be used in the treatment of inflammatory diseases.

Adenosine Producing Mesenchymal Stem Cells

Recent findings support the importance of the adenosine pathway in human immunology. Tissue specific differences exist with respect to the capacity of mesenchymal stem cells (MSC) to produce immune regulatory ATP metabolites. While some MSC may produce adenosine in a cell-autonomous fashion, other types of MSC require the cooperative activity of T-cells. Stem Cells 2017;35:1647-1648.

Mesenchymal stromal cells derived from cervical cancer produce high amounts of adenosine to suppress cytotoxic T lymphocyte functions

BACKGROUND

In recent years, immunomodulatory mechanisms of mesenchymal stem/stromal cells (MSCs) from bone marrow and other "classic" sources have been described. However, the phenotypic and functional properties of tumor MSCs are poorly understood. The aim of this study was to analyze the immunosuppressive capacity of cervical cancer-derived MSCs (CeCa-MSCs) on effector T lymphocytes through the purinergic pathway.

METHODS

We determined the expression and functional activity of the membrane-associated ectonucleotidases CD39 and CD73 on CeCa-MSCs and normal cervical tissue-derived MSCs (NCx-MSCs). We also analyzed their immunosuppressive capacity to decrease proliferation, activation and effector cytotoxic T (CD8+) lymphocyte function through the generation of adenosine (Ado).

RESULTS

We detected that CeCa-MSCs express higher levels of CD39 and CD73 ectonucleotidases in cell membranes compared to NCx-MSCs, and that this feature was associated with the ability to strongly suppress the proliferation, activation and effector functions of cytotoxic T-cells through the generation of large amounts of Ado from the hydrolysis of ATP, ADP and AMP nucleotides.

CONCLUSIONS

This study suggests that CeCa-MSCs play an important role in the suppression of the anti-tumor immune response in CeCa through the purinergic pathway.

Adenosine production: a common path for mesenchymal stem-cell and regulatory T-cell-mediated immunosuppression

Adenosine is an important molecule that exerts control on the immune system, by signaling through receptors lying on the surface of immune cells. This nucleotide is produced, in part, by the action of the ectoenzymes CD39 and CD73. Interestingly, these proteins are expressed on the cell surface of regulatory T-cells (Tregs) and mesenchymal stromal cells (MSCs)-two cell populations that have emerged as potential therapeutic tools in the field of cell therapy. In fact, the production of adenosine constitutes a mechanism used by both cell types to control the immune response. Recently, great scientific progress was obtained regarding the role of adenosine in the inflammatory environment. In this context, the present review focuses on the advances related to the impact of adenosine production over the immune modulatory activity of Tregs and MSCs, and how this nucleotide controls the biological functions of these cells. Finally, we mention the main challenges and hurdles to bring such molecule to clinical settings.