NK Cells and MSCs: Possible Implications for MSC Therapy in Renal Transplantation

The immunogenic profile and immunomodulatory function of mesenchymal stromal / stem cells in the presence of Ptychotis verticillata

Mesenchymal stromal/stem cells (MSCs) are considered to be a promising immunotherapeutic tool due to their easy accessibility, culture expansion possibilities, safety profile, and immunomodulatory properties. Although several studies have demonstrated the therapeutic effects of MSCs, their efficacy needs to be improved while also preserving their safety. It has been suggested that cell homeostasis may be particularly sensitive to plant extracts. The impact of natural compounds on immunity is thus a fascinating and growing field. Ptychotis verticillata and its bioactive molecules, carvacrol and thymol, are potential candidates for improving MSC therapeutic effects. They can be used as immunotherapeutic agents to regulate MSC functions and behavior during immunomodulation. Depending on their concentrations and incubation time, these compounds strengthened the immunomodulatory functions of MSCs while maintaining their immune-evasive profile. Incubating MSCs with carvacrol and thymol does not alter their hypoimmunogenicity, as no induction of the allogeneic immune response was observed. MSCs also showed enhanced abilities to reduce the proliferation of activated T cells. Thus, MSCs are immunologically responsive to bioactive molecules derived from PV. The bioactivity may depend on the whole phyto-complex of the oil. These findings may contribute to the development of safe and efficient immunotherapeutic MSCs by using medicinal plant-derived active molecules.

A State-of-the-Art Review on the Recent Advances of Mesenchymal Stem Cell Therapeutic Application in Systematic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease with an unknown etiology that has widespread clinical and immunological manifestations. Despite the increase in knowledge about the pathogenesis process and the increase in treatment options, however, the treatments fail in half of the cases. Therefore, there is still a need for research on new therapies. Mesenchymal stem cells (MSCs) are powerful regulators of the immune system and can reduce the symptoms of systemic lupus erythematosus. This study aimed to review the mechanisms of immune system modulation by MSCs and the role of these cells in the treatment of SLE. MSCs suppress T lymphocytes through various mechanisms, including the production of transforming growth factor-beta (TGF-B), prostaglandin E2 (PGE2), nitric oxide (NO), and indolamine 2 and 3-oxygenase (IDO). In addition, MSCs inhibit the production of their autoantibodies by inhibiting the differentiation of lymphocytes. The production of autoantibodies against nuclear antigens is an important feature of SLE. On the other hand, MSCs inhibit antigen delivery by antigen-presenting cells (APCs) to T lymphocytes. Studies in animal models have shown the effectiveness of these cells in treating SLE. However, few studies have been performed on the effectiveness of this treatment in humans. It can be expected that new treatment strategies for SLE will be introduced in the future, given the promising results of MSCs application.

Cellular activation pathways and interaction networks in vascularized composite allotransplantation

Vascularized composite allotransplantation (VCA) is an evolving field of reconstructive surgery that has revolutionized the treatment of patients with devastating injuries, including those with limb losses or facial disfigurement. The transplanted units are typically comprised of different tissue types, including skin, mucosa, blood and lymphatic vasculature, muscle, and bone. It is widely accepted that the antigenicity of some VCA components, such as skin, is particularly potent in eliciting a strong recipient rejection response following transplantation. The fine line between tolerance and rejection of the graft is orchestrated by different cell types, including both donor and recipient-derived lymphocytes, macrophages, and other immune and donor-derived tissue cells (e.g., endothelium). Here, we delineate the role of different cell and tissue types during VCA rejection. Rejection of VCA grafts and the necessity of life-long multidrug immunosuppression remains one of the major challenges in this field. This review sheds light on recent developments in decoding the cellular signature of graft rejection in VCA and how these may, ultimately, influence the clinical management of VCA patients by way of novel therapies that target specific cellular processes.

MSCs cell fates in murine acute liver injury and chronic liver fibrosis induced by carbon tetrachloride

Mesenchymal stem cells (MSCs) therapy has shown potential benefits in multiple diseases. However, their clinic performance is not as satisfactory as expected. This study aimed to provide an alternative explanation by comparing MSCs' fates in different liver diseases. The distribution and therapeutic effects of hMSCs were investigated in acute liver injury (ALI) and chronic liver fibrosis (CLF) mice models, respectively. The two models were induced by single or repeated injection of carbon tetrachloride (CCl4) separately. The increase of hMSCs exposure in the liver (AUCliver 0-72 h) were more significant in ALI than in CLF (177.1% vs. 96.2%). In the ALI model, the hMSCs exposures in the lung (AUClung 0-72 h) increased by nearly 50% while decreased by 60.7% in CLF. The efficacy satellite study indicated that hMSCs could significantly ameliorate liver injury in ALI, but its effects in CLF were limited. In the ALI, suppressed Natural Killer (NK) cell activities were observed, while NK cell activities were increased in CLF. The depletion of NK cells could increase hMSCs exposure in mice. For mice MSC (mMSCs), their cell fates in ALI were very similar to hMSCs in ALI: mMSCs' exposure in the liver and lung increased in ALI. In conclusion, our study revealed the distinct cell pharmacokinetic patterns of MSCs in ALI and CLF mice, which might be at least partially attributed to the different NK cell activities in the two liver diseases. This finding provided a novel insight into the varied MSCs' therapeutic efficacy in the clinic. Significance Statement Currently, there is little knowledge about the PK behavior of cell products like MSCs. This study was the first time investigating the influence of liver diseases on cell fates and efficacies of MSCs and the underneath rationale. The exposure was distinct between two representative liver disease models, which directly linked with the therapeutic performance that MSCs achieved. The difference could be attributed to the NK cells-mediated MSCs clearance.

Precursor structure-determined fluorescence labeling for mesenchymal stem cells among four polyethylenimine-based carbon quantum dots

A series of polyethylenimine (PEI)-based CQDs have been synthesized via a hydrothermal method by mixing linear PEI with linear citric acid (CA with COOH groups, PEICA), linear glucose (G with OH groups, PEIG), cyclic hyaluronic acid (HA with COOH groups, PEIHA) and cyclic boron nitride (BN with OH groups, PEIBN). PEICA had the best labeling effect (100.00 ± 0.26%) and the lowest cytotoxicity (100.89 ± 18.00%) for mesenchymal stem cells (MSCs), followed by PEIG (91.83 ± 7.60%; 92.84 ± 5.56%), PEIHA (84.34 ± 7.87%; 61.27 ± 11.34%) and PEIBN (1.33 ± 0.84%; 22.72 ± 11.47%). The labeling effect of PEIHA for MSCs is lower than that of PEIG because the surface potential of PEIHA (6.58 mV) is higher than that of PEIG (0.50 mV). For PEIBN, it is likely that the precursor (BN) is less biocompatible than CA, HA and glucose. Thus, the linear acid (CA) is more appropriate to react with PEI for synthesizing CQDs with high labeling performance for MSCs. The control experimental results show that factors (such as surface potential, aromatic component, etc.) may all contribute to MSC labeling by PEICA. This work is helpful to design CQDs with high MSC labeling efficiency.

Mesenchymal stem cells and natural killer cells interaction mechanisms and potential clinical applications

Natural killer cells (NK cells) are innate immune cells that are activated to fight tumor cells and virus-infected cells. NK cells also play an important role in the graft versus leukemia response. However, they can over-develop inflammatory reactions by secreting inflammatory cytokines and increasing Th1 differentiation, eventually leading to tissue damage. Today, researchers have attributed some autoimmune diseases and GVHD to NK cells. On the other hand, it has been shown that mesenchymal stem cells (MSCs) can modulate the activity of NK cells, while some researchers have shown that NK cells can cause MSCs to lysis. Therefore, we considered it is necessary to investigate the effect of these two cells and their signaling pathway in contact with each other, also their clinical applications.

Current Progress in Vascular Engineering and Its Clinical Applications

Coronary heart disease (CHD) is caused by narrowing or blockage of coronary arteries due to atherosclerosis. Coronary artery bypass grafting (CABG) is widely used for the treatment of severe CHD cases. Although autologous vessels are a preferred choice, healthy autologous vessels are not always available; hence there is a demand for tissue engineered vascular grafts (TEVGs) to be used as alternatives. However, producing clinical grade implantable TEVGs that could healthily survive in the host with long-term patency is still a great challenge. There are additional difficulties in producing small diameter (<6 mm) vascular conduits. As a result, there have not been TEVGs that are commercially available. Properties of vascular scaffolds such as tensile strength, thrombogenicity and immunogenicity are key factors that determine the biocompatibility of TEVGs. The source of vascular cells employed to produce TEVGs is a limiting factor for large-scale productions. Advanced technologies including the combined use of natural and biodegradable synthetic materials for scaffolds in conjunction with the use of mesenchyme stem cells or induced pluripotent stem cells (iPSCs) provide promising solutions for vascular tissue engineering. The aim of this review is to provide an update on various aspects in this field and the current status of TEVG clinical applications.

Developing electropositive citric acid–polyethylenimine carbon quantum dots with high biocompatibility and labeling performance for mesenchymal stem cells in vitro and in vivo

The positive CQD has good biocompatibility (≤800 μg mL−1) and labelling performance for mesenchymal stem cell in vitro and in vivo.

Mesenchymal stem cells transfected with anti-miRNA-204-3p inhibit acute rejection after heart transplantation by targeting C-X-C motif chemokine receptor 4 (CXCR4) in vitro

Background

Mesenchymal stem cells (MSCs) are a promising treatment for acute rejection (AR) after heart transplantation (HTx) owing to their immunomodulatory functions by promoting the transformation of macrophages from the M0 to M2 phenotype. However, it is undetermined whether surface expression of C-X-C motif chemokine receptor 4 (CXCR4) by MSCs influences macrophage polarization. In this study, we investigated the effects of MSCs on macrophages caused by CXCR4, and detected the underlying mechanism, which may contribute to improving HTx outcomes.

Methods

The MSCs were extracted from rat bone marrow and identified using flow cytometry. We subsequently observed the effects of CXCR4 and anti-miRNA-204-3p on cell proliferation and migration, and the effects on macrophage polarization. Dual luciferase reporter assay was used to explore whether miRNA-204-3p was an upstream microRNA (miRNA) of CXCR4. A series of rescue experiments were performed to further confirm the inhibitory effect of miRNA-204-3p on CXCR4.

Results

The results showed that CXCR4 could promote the proliferation and migration of MSCs. Furthermore, it facilitated MSC-mediated macrophage transformation from the M0 to M2 phenotype. In addition, miRNA-204-3p inhibited the function of CXCR4 of MSCs.

Conclusions

Regulated by miRNA-204-3p, CXCR4 could inhibit the progression of AR after HTx. This study provides a new insight of the treatment of AR after HTx.

Mesenchymal stromal cell therapy for coronavirus disease 2019: which? when? and how much?

Mesenchymal stromal cells (MSCs) are under active consideration as a treatment strategy for controlling the hyper-inflammation and slow disease progression associated with coronavirus disease 2019 (COVID-19). The possible mechanism of protection through their immunoregulatory and paracrine action has been reviewed extensively. However, the importance of process control in achieving consistent cell quality, maximum safety and efficacy—for which the three key questions are which, when and how much—remains unaddressed. Any commonality, if it exists, in ongoing clinical trials has yet to be analyzed and reviewed. In this review, the authors have therefore compiled study design data from ongoing clinical trials to address the key questions of “which” with regard to tissue source, donor profile, isolation technique, culture conditions, long-term culture and cryopreservation of MSCs; “when” with regard to defining the transplantation window by identifying and staging patients based on their pro-inflammatory profile; and “how much” with regard to the number of cells in a single administration, number of doses and route of transplantation. To homogenize MSC therapy for COVID-19 on a global scale and to make it readily available in large numbers, a shared understanding and uniform agreement with respect to these fundamental issues are essential.

Phosphodiesterase 4A confers resistance to PGE2-mediated suppression in CD25+ /CD54+ NK cells

Inadequate persistence of tumor‐infiltrating natural killer (NK) cells is associated with poor prognosis in cancer patients. The solid tumor microenvironment is characterized by the presence of immunosuppressive factors, including prostaglandin E2 (PGE2), that limit NK cell persistence. Here, we investigate if the modulation of the cytokine environment in lung cancer with IL‐2 or IL‐15 renders NK cells resistant to suppression by PGE2. Analyzing Cancer Genome Atlas (TCGA) data, we found that high NK cell gene signatures correlate with significantly improved overall survival in patients with high levels of the prostaglandin E synthase (PTGES). In vitro, IL‐15, in contrast to IL‐2, enriches for CD25⁺/CD54⁺ NK cells with superior mTOR activity and increased expression of the cAMP hydrolyzing enzyme phosphodiesterase 4A (PDE4A). Consequently, this distinct population of NK cells maintains their function in the presence of PGE2 and shows an increased ability to infiltrate lung adenocarcinoma tumors in vitro and in vivo. Thus, strategies to enrich CD25⁺/CD54⁺ NK cells for adoptive cell therapy should be considered.

Mesenchymal Stromal Cells in Solid Organ Transplantation

Over the past decade, the clinical application of mesenchymal stromal cells (MSCs) has generated growing enthusiasm as an innovative cell-based approach in solid organ transplantation (SOT). These expectations arise from a significant number of both transplant- and non-transplant-related experimental studies investigating the complex anti-inflammatory, immunomodulatory, and tissue-repair properties of MSCs. Promising preclinical results have prompted clinical trials using MSC-based therapy in SOT. In the present review, the general properties of MSCs are summarized, with a particular emphasis on MSC-mediated impact on the immune system and in the ischemic conditioning strategy. Next, we chronologically detail all clinical trials using MSCs in the field of SOT. Finally, we envision the challenges and perspectives of MSC-based cell therapy in SOT.

The immunomodulatory effects of mesenchymal stromal cell-based therapy in human and animal models of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic systemic autoimmune inflammatory disease with no absolute cure. Although the exact etiopathogenesis of SLE is still enigmatic, it has been well demonstrated that a combination of genetic predisposition and environmental factors trigger a disturbance in immune responses and thereby participate in the development of this condition. Almost all available therapeutic strategies in SLE are primarily based on the administration of immunosuppressive drugs and are not curative. Mesenchymal stromal cells (MSCs) are a subset of non-hematopoietic adult stem cells that can be isolated from many adult tissues and are increasingly recognized as immune response modulating agents. MSC-mediated inhibition of immune responses is a complex mechanism that involves almost every aspect of the immune response. MSCs suppress the maturation of antigen-presenting cells (DC and MQ), proliferation of T cells (Th1, T17, and Th2), proliferation and immunoglobulin production of B cells, the cytotoxic activity of CTL and NK cells in addition to increasing regulatory cytokines (TGF-β and IL10), and decreasing inflammatory cytokines (IL17, INF-ϒ, TNF-α, and IL12) levels. MSCs have shown encouraging results in the treatment of several autoimmune diseases, in particular SLE. This report aims to review the beneficial and therapeutic properties of MSCs; it also focuses on the results of animal model studies, preclinical studies, and clinical trials of MSC therapy in SLE from the immunoregulatory aspect.

The Achievements and Challenges of Mesenchymal Stem Cell-Based Therapy in Inflammatory Bowel Disease and Its Associated Colorectal Cancer

Approximately 18.1 × 10⁶ new cases of cancer were recorded globally in 2018, out of which 9.6 million died. It is known that people who have Inflammatory Bowel Disease (IBD) turn to be prone to increased risks of developing colorectal cancer (CRC), which has global incident and mortality rates of 10.2% and 9.2%, respectively. Over the years, conventional treatments of IBD and its associated CRC have been noted to provide scarce desired results and often with severe complications. The introduction of biological agents as a better therapeutic approach has witnessed a great deal of success in both experimental and clinical models. With regard to mesenchymal stem cell (MSC) therapy, the ability of these cells to actively proliferate, undergo plastic differentiation, trigger strong immune regulation, exhibit low immunogenicity, and express abundant trophic factors has ensured their success in regenerative medicine and immune intervention therapies. Notwithstanding, MSC-based therapy is still confronted with some challenges including the likelihood of promoting tumor growth and metastasis, and possible overestimated therapeutic potentials. We review the success story of MSC-based therapy in IBD and its associated CRC as documented in experimental models and clinical trials, examining some of the challenges encountered and possible ways forward to producing an optimum MSC therapeutic imparts.

Human Fetal Liver Mesenchymal Stem Cell-Derived Exosomes Impair Natural Killer Cell Function

Mesenchymal stem cells (MSCs) are powerful immunomodulators that regulate the diverse functions of immune cells involved in allogeneic reactions, such as T cells and natural killer (NK) cells, through cell-cell contact or secreted factors. Exosomes secreted by MSCs may be involved in their regulatory functions, providing new therapeutic tools. Here, we showed that fetal liver (FL) MSC-derived exosomes inhibit proliferation, activation, and cytotoxicity of NK cells. Exosomes bearing latency associated peptide (LAP), TGFβ, and thrombospondin 1 (TSP1), a regulatory molecule for TGFβ, induced downstream TGFβ/Smad2/3 signaling in NK cells. The inhibition of TGFβ, using a neutralizing anti-TGFβ antibody, restored NK proliferation, differentiation, and cytotoxicity, demonstrating that FL-MSC-derived exosomes exert their inhibition on NK cell function via TGFβ. These results suggest that FL-MSC-derived exosomes regulate NK cell functions through exosome-associated TGFβ.

The immunoregulation of mesenchymal stem cells plays a critical role in improving the prognosis of liver transplantation

The liver is supplied by a dual blood supply, including the portal venous system and the hepatic arterial system; thus, the liver organ is exposed to multiple gut microbial products, metabolic products, and toxins; is sensitive to extraneous pathogens; and can develop liver failure, liver cirrhosis and hepatocellular carcinoma (HCC) after short-term or long-term injury. Although liver transplantation (LT) serves as the only effective treatment for patients with end-stage liver diseases, it is not very popular because of the complications and low survival rates. Although the liver is generally termed an immune and tolerogenic organ with adaptive systems consisting of humoral immunity and cell-mediated immunity, a high rejection rate is still the main complication in patients with LT. Growing evidence has shown that mesenchymal stromal cell (MSC) transplantation could serve as an effective immunomodulatory strategy to induce tolerance in various immune-related disorders. MSCs are reported to inhibit the immune response from innate immune cells, including macrophages, dendritic cells (DCs), natural killer cells (NK cells), and natural killer T (NKT) cells, and that from adaptive immune cells, including T cells, B cells and other liver-specific immune cells, for the generation of a tolerogenic microenvironment. In this review, we summarized the relationship between LT and immunoregulation, and we focused on how to improve the effects of MSC transplantation to improve the prognosis of LT. Only after exhaustive clarification of the potential immunoregulatory mechanisms of MSCs in vitro and in vivo can we implement MSC protocols in routine clinical practice to improve LT outcome.

Ex vivo perfusion-based engraftment of genetically engineered cell sensors into transplantable organs

Cellular rejection of liver transplant allografts remains a concern despite immunosuppressant use. Existing transplant biomarkers are often not sensitive enough to detect acute or chronic rejection at an early enough stage to allow successful clinical intervention. We herein developed a cell-based sensor that can potentially be used for monitoring local events following liver transplantation. Utilizing a machine perfusion system as a platform to engraft the cells into a donor liver, we effectively established the biocompatibility of the biosensor cells and confirmed efficient delivery of cells distributed throughout the organ. This work proves an innovative concept of integrating synthetic reporter cells ex vivo into organs as a transplant-within-a-transplant during functional organ preservation with a vision to use cell biosensors as a broad way to monitor and treat tissue transplants.

Immune responses towards bioengineered tissues and strategies to control them

PURPOSE OF REVIEW

Research into development of artificial tissues and bioengineered organs to replace physiological functions of injured counterparts has highlighted a previously underestimated challenge for its clinical translatability: the immune response against biomaterials. Herein, we will provide an update and review current knowledge regarding this important barrier to regenerative medicine.

RECENT FINDINGS

Although a clear understanding of the immune reactivity against biomaterials remains elusive, accumulating evidence indicates that innate immune cells, primarily neutrophils and macrophages, play a key role in the initial phases of the immune response. More recently, data have shown that in later phases, T and B cells are also involved. The use of physicochemical modifications of biomaterials and cell-based strategies to modulate the host inflammatory response is being actively investigated for effective biomaterial integration.

SUMMARY

The immune response towards biomaterials and bioengineered organs plays a crucial role in determining their utility as transplantable grafts. Expanding our understanding of these responses is necessary for developing protolerogenic strategies and delivering on the ultimate promise of regenerative medicine.

The Anti-Inflammatory, Anti-Oxidative, and Anti-Apoptotic Benefits of Stem Cells in Acute Ischemic Kidney Injury

Ischemia-reperfusion injury (IRI) plays a significant role in the pathogenesis of acute kidney injury (AKI). The complicated interaction between injured tubular cells, activated endothelial cells, and the immune system leads to oxidative stress and systemic inflammation, thereby exacerbating the apoptosis of renal tubular cells and impeding the process of tissue repair. Stem cell therapy is an innovative approach to ameliorate IRI due to its antioxidative, immunomodulatory, and anti-apoptotic properties. Therefore, it is crucial to understand the biological effects and mechanisms of action of stem cell therapy in the context of acute ischemic AKI to improve its therapeutic benefits. The recent finding that treatment with conditioned medium (CM) derived from stem cells is likely an effective alternative to conventional stem cell transplantation increases the potential for future therapeutic uses of stem cell therapy. In this review, we discuss the recent findings regarding stem cell-mediated cytoprotection, with a focus on the anti-inflammatory effects via suppression of oxidative stress and uncompromised immune responses following AKI. Stem cell-derived CM represents a favorable approach to stem cell-based therapy and may serve as a potential therapeutic strategy against acute ischemic AKI.

Induction of CD4+CD25+Foxp3+ regulatory T cells by mesenchymal stem cells is associated with RUNX complex factors

Among the particular immunomodulation properties of mesenchymal stem cells (MSCs), one relies on their capacity to regulatory T cell (Treg) induction from effector T cells. Stable expression of Foxp3 has a dominant role in suppressive phenotype and stability of induced regulatory T cells (iTregs). How MSCs induce stable Foxp3 expression in iTregs remains unknown. We previously showed MSCs could enhance demethylation of Treg-specific demethylated region (TSDR) in iTregs in cell-cell contact manner (unpublished data). Here, we evaluated the possible effect of MSCs on the mRNA expression of Runx complex genes (Runx1, Runx3, and CBFB) that perch on TSDR in iTregs and play the main role in suppressive properties of Tregs, a regulatory pathway that has not yet been explored by MSCs. Also, we investigated the mRNA expression of MBD2 that promotes TSDR demethylation in Tregs. We first showed that in vitro MSC-iTreg induction was associated with strong mRNA modifications of genes involved in Runx complex. We next injected high doses of MSCs in a murine model of C57BL/6 into Balb/C allogeneic skin transplantation to prolong allograft survival. When splenocytes of grafted mice were analyzed, we realized that the Foxp3 expression was increased at day 5 and 10 post-graft merely in MSC-treated mice. Furthermore, Foxp3 mRNA expression was associated with modified Runx complex mRNA expression comparable to what was shown in in vitro studies. Hence, our data identify a possible mechanism in which MSCs convert conventional T cells to iTreg through strong modifications of mRNA of genes that are involved in Runx complex of Foxp3.

Induction of CD4+CD25+FOXP3+ regulatory T cells by mesenchymal stem cells is associated with modulation of ubiquitination factors and TSDR demethylation

Background

Mesenchymal stem cells (MSCs) are known for their ability to induce the conversion of conventional T cells (Tconvs) into induced regulatory T cells (iTregs) in specific inflammatory contexts. Stable Foxp3 expression plays a major role in the phenotypic and functional stability of iTregs. However, how MSCs induce stable Foxp3 expression remains unknown.

Methods

We first investigated the role of cell–cell contact and cytokine secretion by bone marrow-derived MSCs (BM-MSCs) on the induction, stability, and suppressive functions of Tregs under various experimental conditions that lead to Foxp3 generation by flow cytometry and ELISA respectively. Second, we studied the effect of MSCs on TRAF6, GRAIL, USP7, STUB1, and UBC13 mRNA expression in CD4⁺ T cells in correlation with the suppressive function of iTregs by real-time PCR; also, we investigated Foxp3 Treg-specific demethylated region (TSDR) methylation in correlation with Foxp3 stability by the high-resolution melting technique. Third, we studied the effect of ex-vivo-expanded BM-MSCs on the induction of transplant tolerance in a model of fully allogeneic skin transplantation. We further analyzed the cytokine secretion patterns in grafted mice as well as the mRNA expression of ubiquitination genes in CD4⁺ T cells collected from the spleens of protected mice.

Results

We found that in-vitro MSC-induced Tregs express high mRNA levels of ubiquitination genes such as TRAF6, GRAIL, and USP7 and low levels of STUB1. Moreover, they have enhanced TSDR demethylation. Infusion of MSCs in a murine model of allogeneic skin transplantation prolonged allograft survival. When CD4⁺ T cells were harvested from the spleens of grafted mice, we observed that mRNA expression of the Foxp3 gene was elevated. Furthermore, Foxp3 mRNA expression was associated with increased TRAF6, GRAIL, UBC13, and USP7 and decreased STUB1 mRNA levels compared with the levels observed in vitro.

Conclusions

Our data suggest a possible ubiquitination mechanism by which MSCs convert Tconvs to suppressive and stable iTregs.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0991-1) contains supplementary material, which is available to authorized users.

How to Hit Mesenchymal Stromal Cells and Make the Tumor Microenvironment Immunostimulant Rather Than Immunosuppressive

Experimental evidence indicates that mesenchymal stromal cells (MSCs) may regulate tumor microenvironment (TME). It is conceivable that the interaction with MSC can influence neoplastic cell functional behavior, remodeling TME and generating a tumor cell niche that supports tissue neovascularization, tumor invasion and metastasization. In addition, MSC can release transforming growth factor-beta that is involved in the epithelial-mesenchymal transition of carcinoma cells; this transition is essential to give rise to aggressive tumor cells and favor cancer progression. Also, MSC can both affect the anti-tumor immune response and limit drug availability surrounding tumor cells, thus creating a sort of barrier. This mechanism, in principle, should limit tumor expansion but, on the contrary, often leads to the impairment of the immune system-mediated recognition of tumor cells. Furthermore, the cross-talk between MSC and anti-tumor lymphocytes of the innate and adaptive arms of the immune system strongly drives TME to become immunosuppressive. Indeed, MSC can trigger the generation of several types of regulatory cells which block immune response and eventually impair the elimination of tumor cells. Based on these considerations, it should be possible to favor the anti-tumor immune response acting on TME. First, we will review the molecular mechanisms involved in MSC-mediated regulation of immune response. Second, we will focus on the experimental data supporting that it is possible to convert TME from immunosuppressive to immunostimulant, specifically targeting MSC.

Tyrosine kinase inhibitors and mesenchymal stromal cells: effects on self-renewal, commitment and functions

The hope of selectively targeting cancer cells by therapy and eradicating definitively malignancies is based on the identification of pathways or metabolisms that clearly distinguish “normal” from “transformed” phenotypes. Some tyrosine kinase activities, specifically unregulated and potently activated in malignant cells, might represent important targets of therapy. Consequently, tyrosine kinase inhibitors (TKIs) might be thought as the “vanguard” of molecularly targeted therapy for human neoplasias. Imatinib and the successive generations of inhibitors of Bcr-Abl1 kinase, represent the major successful examples of TKI use in cancer treatment. Other tyrosine kinases have been selected as targets of therapy, but the efficacy of their inhibition, although evident, is less definite. Two major negative effects exist in this therapeutic strategy and are linked to the specificity of the drugs and to the role of the targeted kinase in non-malignant cells. In this review, we will discuss the data available on the TKIs effects on the metabolism and functions of mesenchymal stromal cells (MSCs). MSCs are widely distributed in human tissues and play key physiological roles; nevertheless, they might be responsible for important pathologies. At present, bone marrow (BM) MSCs have been studied in greater detail, for both embryological origins and functions. The available data are evocative of an unexpected degree of complexity and heterogeneity of BM-MSCs. It is conceivable that this grade of intricacy occurs also in MSCs of other organs. Therefore, in perspective, the negative effects of TKIs on MSCs might represent a critical problem in long-term cancer therapies based on such inhibitors.

An engineered biomarker system to monitor and modulate immune clearance of cell therapies

BACKGROUND AIMS

Cell transplants offer a new opportunity to deliver therapies with novel and complex mechanisms of action. Understanding the pharmacology of cell transplants is important to deliver this new therapy effectively. Currently, however, there are limited techniques to easily track cells after intravenous administration due to the dispersion of the graft throughout the entire body.

METHODS

We herein developed an engineered cell system that secretes a luciferase enzyme to sensitively detect cell transplants independent of their locale by a simple blood test. We specifically studied a unique feature of cell transplant pharmacology-namely, immune clearance-using mesenchymal stromal cells (MSCs) as a proof-of-concept cell therapy. MSCs are a clinically relevant cell therapy that has been explored in several disease indications due to their innate properties of altering an immune response.

RESULTS

Using this engineered reporter, we observed specific sensitivity of cell therapy exposure to the preparation of cells, cytolysis of MSCs in an allogeneic setting and a NK cell-mediated destruction of MSCs in an autologous setting.

CONCLUSIONS

Our cellular tracking method has broader implications at large for assessing in vivo kinetics of various other cell therapies.

Mesenchymal stem cells can induce regulatory T cells via modulating miR-126a but not miR-10a

Among the different immunosuppressive properties attributed to mesenchymal stem cells (MSCs), one relies on their ability to induce regulatory T cells (iTregs) from conventional T cells under particular inflammatory context. Stable Foxp3 expression plays a major role in the phenotypic and functional stability of iTregs. However, the mechanism behind Foxp3 induction in iTregs by MSCs remains unknown. Here, we assessed the possible effect of MSCs on miR-126a and miR-10a expression in iTregs and, consequently on Foxp3 stability, a regulatory pathway that has not yet been explored. We first demonstrated that in vitro MSC-iTreg generation was directly associated with strong modifications of miR-126a. We next infused high doses of MSCs in a murine model of allogeneic skin transplantation (C57BL/6 into Balb/c). This treatment significantly prolonged skin allograft survival compared to PBS treated mice. When splenocytes from grafted mice were collected, we observed that the expression of Foxp3 gene was elevated at day 5 and 10 post-graft merely in MSCs treated mice. Moreover, Foxp3 expression was not associated with modified miR-10a expression comparable to in vitro experiments. Thus, our data identify a solid mechanism where MSCs induce conversion of conventional T cells to iTregs through strong modifications of miR-126a. Although miR-10a expression level remains unchanged in vitro and in vivo, we observed expression of this miR in MSC-DC condition.

Immunomodulation by Mesenchymal Stromal Cells and Their Clinical Applications

Mesenchymal stromal cells (MSCs) are multipotent progenitor cells that can be isolated and expanded from various sources. MSCs modulate the function of immune cells, including T and B lymphocytes, dendritic cells, and natural killer cells. An understanding of the interaction between MSCs and the inflammatory microenvironment will provide critical information in revealing the precise in vivo mechanisms involved in MSCs-mediated therapeutic effects, and for designing more practical protocols for the clinical use of these cells. In this review we describe the current knowledge of the unique biological properties of MSCs, the immunosuppressive effects on immune-competent cells and the paracrine role of soluble factors. A summary of the participation of MSCs in preclinical and clinical studies in treating autoimmune diseases and other diseases is described. We also discuss the current challenges of their use and their potential roles in cell therapies.

The roles of immune cells in bone healing; what we know, do not know and future perspectives

Key events occurring during the bone healing include well-orchestrated and complex interactions between immune cells, multipotential stromal cells (MSCs), osteoblasts and osteoclasts. Through three overlapping phases of this physiological process, innate and adaptive immune cells, cytokines and chemokines have a significant role to play. The aim of the escalating immune response is to achieve an osseous healing in the shortest time and with the least complications facilitating the restoration of function. The uninterrupted progression of these biological events in conjunction with a favourable mechanical environment (stable fracture fixation) remains the hallmark of successful fracture healing. When failure occurs, either the biological environment or the mechanical one could have been disrupted. Not infrequently both may be compromised. Consequently, regenerative treatments involving the use of bone autograft, allograft or synthetic matrices supplemented with MSCs are increasingly used. A better understanding of the bone biology and osteoimmunology can help to improve these evolving cell-therapy based strategies. Herein, an up to date status of the role of immune cells during the different phases of bone healing is presented. Additionally, the known and yet to know events about immune cell interactions with MSCs and osteoblasts and osteoclasts and the therapeutic implications are being discussed.

Mesenchymal stromal cells and immunomodulation: A gathering of regulatory immune cells

Because of their well-recognized immunomodulatory properties, mesenchymal stromal cells (MSCs) represent an attractive cell population for therapeutic purposes. In particular, there is growing interest in the use of MSCs as cellular immunotherapeutics for tolerance induction in allogeneic transplantations and the treatment of autoimmune diseases. However, multiple mechanisms have been identified to mediate the immunomodulatory effects of MSCs, sometimes with several ambiguities and inconsistencies. Although published studies have mainly reported the role of soluble factors, we believe that a sizeable cellular component plays a critical role in MSC immunomodulation. We refer to these cells as regulatory immune cells, which are generated from both the innate and adaptive responses after co-culture with MSCs. In this review, we discuss the nature and role of these immune regulatory cells as well as the role of different mediators, and, in particular, regulatory immune cell induction by MSCs through interleukin-10. Once induced, immune regulatory cells accumulate and converge their regulatory pathways to create a tolerogenic environment conducive for immunomodulation. Thus, a better understanding of these regulatory immune cells, in terms of how they can be optimally manipulated and induced, would be suitable for improving MSC-based immunomodulatory therapeutic strategies.

Biodistribution, migration and homing of systemically applied mesenchymal stem/stromal cells

Mesenchymal stem/stromal cells (MSCs) are increasingly used as an intravenously applied cellular therapeutic. They were found to be potent in situations such as tissue repair or severe inflammation. Still, data are lacking with regard to the biodistribution of MSCs, their cellular or molecular target structures, and the mechanisms by which MSCs reach these targets. This review discusses current hypotheses for how MSCs can reach tissue sites. Both preclinical and clinical studies using MSCs applied intravenously or intra-arterially are discussed in the context of our current understanding of how MSCs might work in physiological and pathological situations.

Bone marrow stromal cells as immunomodulators. A primer for dermatologists

Bone marrow stromal cells (BMSCs, also known as mesenchymal stem cells or MSCs) represent a unique cell population in the bone marrow with a long-known function to support hematopoiesis and replace skeletal tissues. The recent discovery that BMSCs also possess potent immunoregulatory features attracted a great deal of attention from stem cell biologists, immunologists and clinicians of different specialties worldwide. Initial clinical experience along with several animal models suggested that intravenously delivered BMSCs are able to regulate a wide variety of host immune cells and act in a way that is beneficial for the recipient in a variety of diseases. The role of the present review is to give a short introduction to the biology of BMSCs and to summarize our current understanding of how BMSCs modulate the immune system with special emphasis on available clinical data. Considering the audience of this journal we will also attempt to guide dermatologists in choosing the right skin conditions where BMSCs might be considered as a therapeutic alternative.