Mesenchymal stem cells fail to trigger effector functions of cytotoxic T lymphocytes

Fate and long-lasting therapeutic effects of mesenchymal stromal/stem-like cells: mechanistic insights

A large body of evidence suggests that mesenchymal stromal cells (MSCs) are able to respond rapidly to the cytokine milieu following systemic infusion. This encounter has the potential to dictate their therapeutic efficacy (also referred to as licensing). MSCs are able to rapidly react to cellular damage by migrating to the inflamed tissue and ultimately modifying the inflammatory microenvironment. However, the limited use of MSCs in clinical practice can be attributed to a lack of understanding of the fate of MSCs in patients after administration and long term MSC-derived therapeutic activity. While the known physiological effectors of viable MSCs make a relative contribution, an innate property of MSCs as a therapeutic agent is their caspase-dependent cell death. These mechanisms may be involving the functional reprogramming of myeloid phagocytes via efferocytosis, the process by which apoptotic bodies (ABs) are identified for engulfment by both specialized and non-specialized phagocytic cells. Recent studies have provided evidence that the uptake of ABs with a distinct genetic component can induce changes in gene expression through the process of epigenetic remodeling. This phenomenon, known as 'trained immunity', has a significant impact on immunometabolism processes. It is hypothesized that the diversity of recipient cells within the inflammatory stroma adjacent to MSCs may potentially serve as a biomarker for predicting the clinical outcome of MSC treatment, while also contributing to the variable outcomes observed with MSC-based therapies. Therefore, the long-term reconstructive process of MSCs may potentially be mediated by MSC apoptosis and subsequent phagocyte-mediated efferocytosis.

New therapeutic approaches for type 1 diabetes: Disease-modifying therapies

It has been 100 years since the first successful clinical use of insulin, yet it remains the only treatment option for type 1 diabetes mellitus (T1DM) patients. Advances in diabetes care, such as insulin analogue therapies and new devices, including continuous glucose monitoring with continuous subcutaneous insulin infusion have improved the quality of life of patients but have no impact on the pathogenesis of the disease. They do not eliminate long-term complications and require several lifestyle sacrifices. A more ideal future therapy for T1DM, instead of supplementing the insufficient hormone production (a consequence of β-cell destruction), would also aim to stop or slow down the destructive autoimmune process. The discovery of the autoimmune nature of type 1 diabetes mellitus has presented several targets by which disease progression may be altered. The goal of disease-modifying therapies is to target autoimmune mechanisms and prevent β-cell destruction. T1DM patients with better β-cell function have better glycemic control, reduced incidence of long-term complications and hypoglycemic episodes. Unfortunately, at the time symptomatic T1DM is diagnosed, most of the insulin secreting β cells are usually lost. Therefore, to maximize the salvageable β-cell mass by disease-modifying therapies, detecting autoimmune markers in an early, optimally presymptomatic phase of T1DM is of great importance. Disease-modifying therapies, such as immuno- and regenerative therapies are expected to take a relevant place in diabetology. The aim of this article was to provide a brief insight into the pathogenesis and course of T1DM and present the current state of disease-modifying therapeutic interventions that may impact future diabetes treatment.

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.

Multipotent Mesenchymal Stromal Cells Interact and Support Islet of Langerhans Viability and Function

Type 1 diabetes (T1D) is a widespread disease, affecting approximately 41.5 million people worldwide. It is generally treated with exogenous insulin, maintaining physiological blood glucose levels but also leading to long-term therapeutic complications. Pancreatic islet cell transplantation offers a potential alternative treatment to insulin injections. Shortage of human organ donors has raised the interest for porcine islet xenotransplantation. Neonatal porcine islets are highly available, can proliferate and mature in vitro as well as after transplantation in vivo. Despite promising preclinical results, delayed insulin secretion caused by immaturity and immunogenicity of the neonatal porcine islets remains a challenge for their clinical application. Multipotent mesenchymal stromal cells (MSCs) are known to have pro-angiogenic, anti-inflammatory and immunomodulatory effects. The current state of research emphasizes the great potential of co-culture and co-transplantation of islet cells with MSCs. Studies have shown enhanced islet proliferation and maturation, insulin secretion and graft survival, resulting in an improved graft outcome. This review summarizes the immunomodulatory and anti-inflammatory properties of MSC in the context of islet transplantation.

The Emerging Role of Stem Cells in Regenerative Dentistry

Progress of modern dentistry is accelerating at a spectacular speed in the scientific, technological and clinical areas. Practical examples are the advancement in the digital field, which has guaranteed an average level of prosthetic practices for all patients, as well as other scientific developments, including research on stem cell biology. Given their plasticity, defined as the ability to differentiate into specific cell lineages with a capacity of almost unlimited self-renewal and release of trophic/immunomodulatory factors, stem cells have gained significant scientific and commercial interest in the last 15 years. Stem cells that can be isolated from various tissues of the oral cavity have emerged as attractive sources for bone and dental regeneration, mainly due to their ease of accessibility. This review will present the current understanding of emerging conceptual and technological issues of the use of stem cells to treat bone and dental loss defects. In particular, we will focus on the clinical application of stem cells, either directly isolated from oral sources or in vitro reprogrammed from somatic cells (induced pluripotent stem cells). Research aimed at further unraveling stem cell plasticity will allow to identify optimal stem cell sources and characteristics, to develop novel regenerative tools in dentistry.

Made to Measure: Patient-Tailored Treatment of Multiple Sclerosis Using Cell-Based Therapies

Currently, there is still no cure for multiple sclerosis (MS), which is an autoimmune and neurodegenerative disease of the central nervous system. Treatment options predominantly consist of drugs that affect adaptive immunity and lead to a reduction of the inflammatory disease activity. A broad range of possible cell-based therapeutic options are being explored in the treatment of autoimmune diseases, including MS. This review aims to provide an overview of recent and future advances in the development of cell-based treatment options for the induction of tolerance in MS. Here, we will focus on haematopoietic stem cells, mesenchymal stromal cells, regulatory T cells and dendritic cells. We will also focus on less familiar cell types that are used in cell therapy, including B cells, natural killer cells and peripheral blood mononuclear cells. We will address key issues regarding the depicted therapies and highlight the major challenges that lie ahead to successfully reverse autoimmune diseases, such as MS, while minimising the side effects. Although cell-based therapies are well known and used in the treatment of several cancers, cell-based treatment options hold promise for the future treatment of autoimmune diseases in general, and MS in particular.

From Mesenchymal Stromal/Stem Cells to Insulin-Producing Cells: Immunological Considerations

Mesenchymal stem cell (MSC)-based therapy for type 1 diabetes mellitus (T1DM) has been the subject matter of many studies over the past few decades. The wide availability, negligible teratogenic risks and differentiation potential of MSCs promise a therapeutic alternative to traditional exogenous insulin injections or pancreatic transplantation. However, conflicting arguments have been reported regarding the immunological profile of MSCs. While some studies support their immune-privileged, immunomodulatory status and successful use in the treatment of several immune-mediated diseases, others maintain that allogeneic MSCs trigger immune responses, especially following differentiation or in vivo transplantation. In this review, the intricate mechanisms by which MSCs exert their immunomodulatory functions and the influencing variables are critically addressed. Furthermore, proposed avenues to enhance these effects, including cytokine pretreatment, coadministration of mTOR inhibitors, the use of Tregs and gene manipulation, are presented. As an alternative, the selection of high-benefit, low-risk donors based on HLA matching, PD-L₁ expression and the absence of donor-specific antibodies (DSAs) are also discussed. Finally, the necessity for the transplantation of human MSC (hMSC)-derived insulin-producing cells (IPCs) into humanized mice is highlighted since this strategy may provide further insights into future clinical applications.

The 15-Months Clinical Experience of SARS-CoV-2: A Literature Review of Therapies and Adjuvants

BACKGROUND

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the virus responsible for the coronavirus disease of 2019 (COVID-19) that emerged in December 2019 in Wuhan, China, and rapidly spread worldwide, with a daily increase in confirmed cases and infection-related deaths. The World Health Organization declared a pandemic on the 11th of March 2020. COVID-19 presents flu-like symptoms that become severe in high-risk medically compromised subjects. The aim of this study was to perform an updated overview of the treatments and adjuvant protocols for COVID-19.

METHODS

A systematic literature search of databases was performed (MEDLINE PubMed, Google Scholar, UpToDate, Embase, and Web of Science) using the keywords: "COVID-19", "2019-nCoV", "coronavirus" and "SARS-CoV-2" (date range: 1 January 2019 to 31st October 2020), focused on clinical features and treatments.

RESULTS

The main treatments retrieved were antivirals, antimalarials, convalescent plasma, immunomodulators, corticosteroids, anticoagulants, and mesenchymal stem cells. Most of the described treatments may provide benefits to COVID-19 subjects, but no one protocol has definitively proven its efficacy.

CONCLUSIONS

While many efforts are being spent worldwide in research aimed at identifying early diagnostic methods and evidence-based effective treatments, mass vaccination is thought to be the best option against this disease in the near future.

The Usefulness of Mesenchymal Stem Cells beyond the Musculoskeletal System in Horses

Simple Summary

The main target of mesenchymal stem cell therapy in horses has long been the locomotor system, because these athletic animals commonly suffer from tendon and joint lesions. Originally, mesenchymal stem cells were thought to act by just differentiating into the cells of the injured tissue. However, these cells are also able to regulate and stimulate the body’s own repair mechanisms, opening the door to many applications in inflammatory and immune-mediated disorders in both animals and humans. In horses, beyond their traditional application in the musculoskeletal system, these cells have been studied for ophthalmologic pathologies such as corneal ulcers or immune-mediated processes, and for reproductive disorders such as endometritis/endometrosis. Their potential has been explored for equine pathologies very similar to those affecting people, such as asthma, metabolic syndrome, aberrant wound healing, or endotoxemia, as well as for equine-specific pathologies such as laminitis. Current evidence is still preliminary, and further research is needed to clarify different aspects, although research performed so far shows the promising potential of mesenchymal stem cells to treat a wide variety of equine pathologies, some of which are analogous to human disorders. Therefore, advancements in this path will be beneficial for both animals and people.

Abstract

The differentiation ability of mesenchymal stem cells (MSCs) initially raised interest for treating musculoskeletal injuries in horses, but MSC paracrine activity has widened their scope for inflammatory and immune-mediated pathologies in both equine and human medicine. Furthermore, the similar etiopathogenesis of some diseases in both species has advanced the concept of “One Medicine, One Health”. This article reviews the current knowledge on the use of MSCs for equine pathologies beyond the locomotor system, highlighting the value of the horse as translational model. Ophthalmologic and reproductive disorders are among the most studied for MSC application. Equine asthma, equine metabolic syndrome, and endotoxemia have been less explored but offer an interesting scenario for human translation. The use of MSCs in wounds also provides a potential model for humans because of the healing particularities in both species. High-burden equine-specific pathologies such as laminitis have been suggested to benefit from MSC-therapy, and MSC application in challenging disorders such as neurologic conditions has been proposed. The available data are preliminary, however, and require further development to translate results into the clinic. Nevertheless, current evidence indicates a significant potential of equine MSCs to enlarge their range of application, with particular interest in pathologies analogous to human conditions.

TGF-β2 Reduces the Cell-Mediated Immunogenicity of Equine MHC-Mismatched Bone Marrow-Derived Mesenchymal Stem Cells Without Altering Immunomodulatory Properties

Allogeneic mesenchymal stem cells (MSCs) are a promising cell therapy for treating numerous diseases, but major histocompatibility complex (MHC)-mismatched MSCs can be rejected by the recipient’s immune system. Pre-treating MSCs with transforming growth factor-β2 (TGF-β2) to downregulate surface expression of MHC molecules may enhance the ability of allogeneic MSCs to evade immune responses. We used lymphocyte proliferation assays and ELISAs to analyze the immunomodulatory potential of TGF-β2-treated equine bone marrow-derived MSCs. T cell activation and cytotoxicity assays were then used to measure the in vitro cell-mediated immunogenicity. Similar to untreated MSCs, TGF-β2-treated MSCs inhibited T cell proliferation and did not stimulate MHC-mismatched T cells to proliferate. Additionally, similar quantities of prostaglandin E2 and TGF-β1 were detected in assays with untreated and TGF-β2-treated MSCs supporting that TGF-β2-treated MSCs retain their strong immunomodulatory properties in vitro. Compared to untreated MSCs, TGF-β2-treated MSCs induced less T cell activation and had reduced cell-mediated cytotoxicity in vitro. These results indicate that treating MSCs with TGF-β2 is a promising strategy to reduce the cell-mediated immunogenicity of MHC-mismatched MSCs and facilitate allogeneic MSC therapy.

Stem cell therapy for COVID-19: Possibilities and challenges

Since its eruption in China, novel coronavirus disease (COVID-19) has been reported in most of the countries and territories (>200) of the world with ∼18 million confirmed cases (as of August 3, 2020). In most of the countries, COVID-19 upsurge is uncontrolled with a significant mortality rate. Currently, no treatment effective for COVID-19 is available in the form of vaccines or antiviral drugs and patients are currently treated symptomatically. Although the majority of the patients develop mild symptoms and recover without mechanical ventilation for respiratory management, severe respiratory illness develops in a significant portion of affected patients and may result in death. While the scientific community is working to develop vaccines and drugs against the COVID-19 pandemic, novel alternative therapies may reduce the mortality rate. Recent use of stem cells for critically ill COVID-19 patients in a small group of patients in China and subsequent Emergency Use Authorization of stem cells by Food and Drug Administration to Global Institute of Stem Cell Therapy and Research and Athersys has created excitement among the medical community. As a result, several clinical trials have been registered using stem cells for COVID-19 treatment that aim to use different cell sources, dosage, and importantly diverse targeted patient groups. In this brief review, the possibilities of stem cell use in COVID-19 patients and relevant challenges in their use have been discussed.

Novel Stem Cells and Nucleic Acid-Based Vaccine Trials Against Viral Outbreak: A Systematic Evaluation During COVID-2019 Pandemic

The current Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) outbreak, the cause of coronavirus disease (COVID-19), has influenced health globally. So far, there are no established management options and prophylaxis for those who have been exposed to SARS-CoV-2, and those who develop COVID-19. Documented scientific evidences in similar viral outbreaks in past suggested few therapy regimens. These rather have not shown promising results in management of current pandemic. So, in the current review, we are exploring novel treatment strategies and therapies that are being explored and are in clinical and preclinical stages of research. To explore more about the same, we directed our search towards stem cell based, DNA based, or RNA based vaccines against COVID-19 under development by various universities, institutes or pharmaceutical companies. The current scientific literature and database search were performed by exploring various Trials registry (NIH: https://clinicaltrials.gov/ and https://www.coronavirus.gov) and Chinese clinical trial registry http://www.chictr.org.cn/) and for preclinical trials various University, Institutions, Pharmaceutical companies websites and news bulletins along with google search were checked routinely from 3rd March 2020 to 16 May 2020. The term "Stem Cell therapy and COVID-19", "Mesenchymal stem cell and corona 2019 virus", "DNA Vaccines and COVID-19, RNA Vaccines and COVID-19" and "Cell-based therapy with SARS-CoV-2, University/Institutions and COVID-19 research" were used. The vaccine trials (Stem Cells/DNA/RNA) which were cancelled were not included in this review. Similarly, few others like repurposing of drugs, Nano Vaccines, other miscellaneous trials of Herbs, Music therapy etc., were also excluded. In the present review, we have included the various novel therapies like stem cell therapy, DNA or RNA vaccines which are under development and if proven successful may have a lasting impact on the health industry.

Characterization and Immunomodulation of Canine Amniotic Membrane Stem Cells

PURPOSE

Amniotic membrane stem cells have a high capacity of proliferation, cell expansion, and plasticity, as well as immunomodulatory properties that contribute to maternal-fetal tolerance. Owing to the lack of research on human amniotic membrane at different gestational stages, the canine model is considered ideal because of its genetic and physiological similarities. We aimed to characterize the canine amniotic membrane (CAM) cell lineage in different gestational stages and evaluate the expression of immunomodulatory genes.

MATERIALS AND METHODS

Twenty CAMs from early (20-30 days) (n=7), mid- (31-45 days) (n=7), and late gestation (46-63 days) (n=6) stages were studied. The cell features were assessed by cell viability tests, growth curve, colony-forming units, in vitro differentiation, cell labeling for different immunophenotypes, and pluripotent potential markers. The cells were subjected to RT-PCR and qPCR analysis to determine the expression of IDO, HGF, EGF, PGE2, and IL-10 genes.

RESULTS

CAM cells exhibited a fibroblastoid morphology and adherence to plastic with an average cell viability of 78.5%. The growth curve indicated a growth peak in the second passage and we obtained an average of 138.2 colonies. Osteogenic, chondrogenic, and adipogenic lineages were confirmed by in vitro differentiation assays. Cellular immunophenotyping experiments confirmed the presence of positive mesenchymal markers (CD90 and CD105) and the low or negative expression of hematopoietic markers (CD45 and CD34). Qualitative analysis of the immunomodulatory functions indicated the expression of the IDO, HGF, EGF5, and PGE2 genes. When stimulated by interferon-gamma, CAM cells exhibited higher IDO levels throughout gestation.

CONCLUSION

The CAMs from different gestational stages presented features consistent with mesenchymal stem cell lineage; better results were observed during the late gestation stage. Therefore, the gestational stage is a key factor that may influence the functionality of therapies when using fetal membrane tissues from different periods of pregnancy.

The Use of Mesenchymal Stem Cells and their Derived Extracellular Vesicles in Cardiovascular Disease Treatment

BACKGROUND

Cardiovascular disease (CVD), including disorders of cardiac muscle and vascular, is the major cause of death globally. Many unsuccessful attempts have been made to intervene in the disease's pathogenesis and treatment. Stem cell-based therapies, as a regeneration strategy, cast a new hope for CVD treatment. One of the most well-known stem cells is mesenchymal stem cells (MSCs), classified as one of the adult stem cells and can be obtained from different tissues. These cells have superior properties, such as proliferation and highly specialized differentiation. On the other hand, they have the potential to modulate the immune system and anti-inflammatory activity. One of their most important features is the secreting the extracellular vesicles (EVs) like exosomes (EXOs) as an intercellular communication system mediating the different physiological and pathophysiological affairs.

METHODS

In this review study, the importance of MSC and its secretory exosomes for the treatment of heart disease has been together and specifically addressed and the use of these promising natural and accessible agents is predicted to replace the current treatment modalities even faster than we imagine.

RESULTS

MSC derived EXOs by providing a pro-regenerative condition allowing innate stem cells to repair damaged tissues successfully. As a result, MSCs are considered as the appropriate cellular source in regenerative medicine. In the plethora of experiments, MSCs and MSC-EXOs have been used for the treatment and regeneration of heart diseases and myocardial lesions.

CONCLUSION

Administration of MSCs has been provided a replacement therapeutic option for heart regeneration, obtaining great attention among the basic researcher and the medical doctors.

Human placenta-derived mesenchymal stem cells ameliorate orbital adipogenesis in female mice models of Graves' ophthalmopathy

Background

Graves’ ophthalmopathy (GO) is a complication of Graves’ disease (GD), in which orbital connective tissues become inflamed and increase in volume and orbital fibroblasts within the orbital fat and extraocular muscles differentiate into adipocytes in vitro when stimulated by hormones, several cytokines, and growth factors including TSH, IGF-1, IL-1, interferon γ, and platelet-derived growth factor. Human placental mesenchymal stem cells (hPMSCs) have immunomodulatory effects in disease pathogenesis. Although a number of studies have reported that hPMSCs can elicit therapeutic effects, these are not sufficient. Therefore, we constructed a GO animal model in order to find out the hPMSCs recovery effect.

Methods

We investigated their anti-adipogenic effects in in vitro cultures of orbital fibroblasts established from GO patients. Primary orbital fibroblasts were exposed to differentiation medium for 10 days. After being co-cultured with hPMSCs, the characteristics of orbital fibroblast were determined by Oil Red O stain and real-time PCR. Then, we explored the in vivo regulatory effects of hPMSCs in an experimental mouse model of GO. We developed the GO mouse model using immunization by leg muscle electroporation of pTriEx1.1Neo-hTSHR A-subunit plasmid. Human PMSC injection was performed into the left orbit. We also analyzed the effects of hPMSCs in the GO animal model.

Result

We found that hPMSCs inhibited a lipid accumulation and activated factors, such as ADIPONECTIN, PPARγ, C/EBPα, and TGFβ2 genes in adipogenesis-induced primary orbital fibroblasts from GO patients. Moreover, hPMSCs were highly effective at ameliorating adipogenesis in the orbital tissue of the model.

Conclusion

These data indicate that hPMSCs recover pathogenic activation of orbital fibroblasts in animals undergoing experimental GO and confirm the feasibility of applying hPMSCs as a novel treatment for GO patients.

A novel direct co-culture assay analyzed by multicolor flow cytometry reveals context- and cell type-specific immunomodulatory effects of equine mesenchymal stromal cells

The immunomodulatory potential of multipotent mesenchymal stromal cells (MSC) provides a basis for current and future regenerative therapies. In this study, we established an approach that allows to address the effects of pro-inflammatory stimulation and co-culture with MSC on different specific leukocyte subpopulations. Equine peripheral blood leukocyte recovery was optimized to preserve all leukocyte subpopulations and leukocyte activation regimes were evaluated. Allogeneic labeled equine adipose-derived MSC were then subjected to direct co-culture with either non-stimulated, concanavalin A (ConA)-activated or phosphate 12-myristate 13-acetate and ionomycin (PMA/I)-activated leukocytes. Subsequently, production of the cytokines interferon-γ (IFN- γ), interleukin-1 (IL-1) and tumor necrosis factor-α (TNF-α) and presence of FoxP3 were determined in specific cell populations using multicolor flow cytometry. Prostaglandin E2 (PGE2) was measured in the supernatants. ConA-stimulation induced mild activation of leukocytes, whereas PMA/I-stimulation led to strong activation. In T cells, PMA/I promoted production of all cytokines, with no distinct suppressive effects of MSC. However, increased numbers of CD25/FoxP3-positive cells indicated that MSC supported regulatory T cell differentiation in PMA/I-activated leukocyte cultures. MSC also reduced numbers of cytokine-producing B cells and granulocytes, mostly irrespective of preceding leukocyte activation, and reversed the stimulatory effect of ConA on IFN-γ production in monocytes. Illustrating the possible suppressive mechanisms, higher numbers of MSC produced IL-10 when co-cultured with non-stimulated or ConA-activated leukocytes. This was not observed in co-culture with PMA/I-activated leukocytes. However, PGE2 concentration in the supernatant was highest in the co-culture with PMA/I-activated leukocytes, suggesting that PGE2 could still mediate modulatory effects in strongly inflammatory environment. These context- and cell type-specific modulatory effects observed give insight into the interactions between MSC and different types of immune cells and highlight the roles of IL-10 and PGE2 in MSC-mediated immunomodulation. The approach presented could provide a basis for further functional MSC characterization and the development of potency assays.

Stem Cells in Dentistry: Types of Intra- and Extraoral Tissue-Derived Stem Cells and Clinical Applications

Stem cells are undifferentiated cells, capable of renewing themselves, with the capacity to produce different cell types to regenerate missing tissues and treat diseases. Oral facial tissues have been identified as a source and therapeutic target for stem cells with clinical interest in dentistry. This narrative review report targets on the several extraoral- and intraoral-derived stem cells that can be applied in dentistry. In addition, stem cell origins are suggested in what concerns their ability to differentiate as well as their particular distinguishing quality of convenience and immunomodulatory for regenerative dentistry. The development of bioengineered teeth to replace the patient's missing teeth was also possible because of stem cell technologies. This review will also focus our attention on the clinical application of stem cells in dentistry. In recent years, a variety of articles reported the advantages of stem cell-based procedures in regenerative treatments. The regeneration of lost oral tissue is the target of stem cell research. Owing to the fact that bone imperfections that ensue after tooth loss can result in further bone loss which limit the success of dental implants and prosthodontic therapies, the rehabilitation of alveolar ridge height is prosthodontists' principal interest. The development of bioengineered teeth to replace the patient's missing teeth was also possible because of stem cell technologies. In addition, a “dental stem cell banking” is available for regenerative treatments in the future. The main features of stem cells in the future of dentistry should be understood by clinicians.

Pilot trial of intravenous autologous culture-expanded mesenchymal stem cell transplantation in multiple sclerosis

BACKGROUND

Mesenchymal stem cells (MSCs) exhibit immunomodulatory, tissue-protective, and repair-promoting properties in vitro and in animals. Clinical trials in several human conditions support the safety and efficacy of MSC transplantation. Published experience in multiple sclerosis (MS) is modest.

OBJECTIVE

To assess feasibility, safety, and tolerability and explore efficacy of autologous MSC transplantation in MS.

METHODS

Participants with relapsing-remitting multiple sclerosis (RRMS) or secondary progressive multiple sclerosis (SPMS), Expanded Disability Status Scale score 3.0-6.5, disease activity or progression in the prior 2 years, and optic nerve involvement were enrolled. Bone-marrow-derived MSCs were culture-expanded and then cryopreserved. After confirming fulfillment of release criteria, 1-2 × 106 MSCs/kg were thawed and administered IV.

RESULTS

In all, 24 of 26 screened patients were infused: 16 women and 8 men, 10 RRMS and 14 SPMS, mean age 46.5, mean Expanded Disability Status Scale score 5.2, 25% with gadolinium-enhancing magnetic resonance imaging (MRI) lesions. Mean cell dosage (requiring 1-3 passages) was 1.9 × 106 MSCs/kg (range, 1.5-2.0) with post-thaw viability uniformly ⩾95%. Cell infusion was tolerated well without treatment-related severe or serious adverse events, or evidence of disease activation.

CONCLUSION

Autologous MSC transplantation in MS appears feasible, safe, and well tolerated. Future trials to assess efficacy more definitively are warranted.

Characterisation and immunosuppressive activity of human cartilage-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) exert potent immuno-regulatory activities on various immune cells and also differentiate into various mesodermal lineages besides retaining a distinct self-renewal ability. Such exclusive characteristics had enabled MSCs to be recognised as an ideal source for cell-based treatment in regenerative medicine and immunotherapy. Thus, considering MSCs for treating degenerative disease of organs with limited regenerative potential such as cartilage would serve as an ideal therapy. This study explored the feasibility of generating human cartilage-derived MSCs (hC-MSCs) from sports injured patients and characterised based on multipotent differentiation and immunosuppressive activities. Cartilage tissues harvested from a non-weight bearing region during an arthroscopy procedure were used to generate MSCs. Despite the classic morphology of fibroblast-like cells and a defined immunophenotyping, MSCs expressed early embryonic transcriptional markers (SOX2, REX1, OCT4 and NANOG) and differentiated into chondrocytes, adipocytes and osteocytes when induced accordingly. Upon co-culture with PHA-L activated T-cells, hC-MSCs suppressed the proliferation of the T-cells in a dose-dependent manner. Although, hC-MSCs did not alter the activation profile of T cells significantly, yet prevented the entering of activated T cells into S phase of the cell cycle by cell cycle arrest. The present study has strengthened the evidence of tissue-resident mesenchymal stem cells in human cartilage tissue. The endogenous MSCs could be an excellent tool in treating dysregulated immune response that associated with cartilage since hC-MSCs exerted both immunosuppressive and regenerative capabilities.

Current status of stem cells in cardiac repair

One out of every two men and one out of every three women greater than the age of 40 will experience an acute myocardial infarction (AMI) at some time during their lifetime. As more patients survive their AMIs, the incidence of congestive heart failure (CHF) is increasing. 6 million people in the USA have ischemic cardiomyopathies and CHF. The search for new and innovative treatments for patients with AMI and CHF has led to investigations and use of human embryonic stem cells, cardiac stem/progenitor cells, bone marrow-derived mononuclear cells and mesenchymal stem cells for treatment of these heart conditions. This paper reviews current investigations with human embryonic, cardiac, bone marrow and mesenchymal stem cells, and also stem cell paracrine factors and exosomes.

Molecular Mechanisms Responsible for Anti-inflammatory and Immunosuppressive Effects of Mesenchymal Stem Cell-Derived Factors

Mesenchymal stem cells (MSCs) are self-renewable cells capable for multilineage differentiation and immunomodulation. MSCs are able to differentiate into all cell types of mesodermal origin and, due to their plasticity, may generate cells of neuroectodermal or endodermal origin in vitro. In addition to the enormous differentiation potential, MSCs efficiently modulate innate and adaptive immune response and, accordingly, were used in large number of experimental and clinical trials as new therapeutic agents in regenerative medicine. Although MSC-based therapy was efficient in the treatment of many inflammatory and degenerative diseases, unwanted differentiation of engrafted MSCs represents important safety concern. MSC-based beneficial effects are mostly relied on the effects of MSC-derived immunomodulatory, pro-angiogenic, and trophic factors which attenuate detrimental immune response and inflammation, reduce ischemic injuries, and promote tissue repair and regeneration. Accordingly, MSC-conditioned medium (MSC-CM), which contains MSC-derived factors, has the potential to serve as a cell-free, safe therapeutic agent for the treatment of inflammatory diseases. Herein, we summarized current knowledge regarding identification, isolation, ontogeny, and functional characteristics of MSCs and described molecular mechanisms responsible for MSC-CM-mediated anti-inflammatory and immunosuppressive effects in the therapy of inflammatory lung, liver, and kidney diseases and ischemic brain injury.

Mesenchymal stem cell-derived factors: Immuno-modulatory effects and therapeutic potential

Stem cell-based therapy is considered to be a new hope in transplantation medicine. Among stem cells, mesenchymal stem cells (MSCs) are, due to their differentiation and immuno-modulatory characteristics, the most commonly used as therapeutic agents in the treatment of immune-mediated diseases. MSCs migrate to the site of inflammation and modulate immune response. The capacity of MSC to alter phenotype and function of immune cells are largely due to the production of soluble factors which expression varies depending on the pathologic condition to which MSCs are exposed. Under inflammatory conditions, MSCs-derived factors suppress both innate and adaptive immunity by attenuating maturation and capacity for antigen presentation of dendritic cells, by inducing polarization of macrophages towards alternative phenotype, by inhibiting activation and proliferation of T and B lymphocytes and by reducing cytotoxicity of NK and NKT cells. In this review, we emphasized current findings regarding immuno-modulatory effects of MSC-derived factors and emphasize their potential in the therapy of immune-mediated diseases. © 2017 BioFactors, 43(5):633-644, 2017.

Mesenchymal stem cells protect from acute liver injury by attenuating hepatotoxicity of liver natural killer T cells in an inducible nitric oxide synthase- and indoleamine 2,3-dioxygenase-dependent manner

The effects of mesenchymal stem cells (MSCs) on the phenotype and function of natural killer T (NKT) cells is not understood. We used concanavalin A (Con A) and α-galactosylceramide (α-GalCer)-induced liver injury to evaluate the effects of MSCs on NKT-dependent hepatotoxicity. Mouse MSCs (mMSCs) significantly reduced Con A- and α-GalCer-mediated hepatitis in C57Bl/6 mice, as demonstrated by histopathological and biochemical analysis, attenuated the influx of inflammatory [T-bet⁺ , tumour necrosis factor-α (TNF-α), interferon-γ (IFN-γ)-producing and GATA3⁺ , interleukin-4 (IL-4)-producing] liver NKT cells and downregulated TNF-α, IFN-γ and IL-4 levels in the sera. The liver NKT cells cultured in vitro with mMSCs produced lower amounts of inflammatory cytokines (TNF-α, IFN-γ, IL-4) and higher amounts of immunosuppressive IL-10 upon α-GalCer stimulation. mMSC treatment attenuated expression of apoptosis-inducing ligands on liver NKT cells and suppressed the expression of pro-apoptotic genes in the livers of α-GalCer-treated mice. mMSCs reduced the cytotoxicity of liver NKT cells against hepatocytes in vitro. The presence of 1-methyl-dl-tryptophan, a specific inhibitor of indoleamine 2,3-dioxygenase (IDO), or l-N^G -monomethyl arginine citrate, a specific inhibitor of inducible nitric oxide synthase (iNOS), in mMSC-conditioned medium injected into α-GalCer-treated mice, counteracted the hepatoprotective effect of mMSCs in vivo and restored pro-inflammatory cytokine production and cytotoxicity of NKT cells in vitro. Human MSCs attenuated the production of inflammatory cytokines in α-GalCer-stimulated human peripheral blood mononuclear cells in an iNOS- and IDO-dependent manner and reduced their cytotoxicity against HepG2 cells. In conclusion, MSCs protect from acute liver injury by attenuating the cytotoxicity and capacity of liver NKT cells to produce inflammatory cytokines in an iNOS- and IDO-dependent manner.

Mesenchymal Stem Cells Promote Metastasis of Lung Cancer Cells by Downregulating Systemic Antitumor Immune Response

Since majority of systemically administered mesenchymal stem cells (MSCs) become entrapped within the lungs, we used metastatic model of lung cancer, induced by intravenous injection of Lewis lung cancer 1 (LLC1) cells, to investigate the molecular mechanisms involved in MSC-mediated modulation of metastasis. MSCs significantly augmented lung cancer metastasis, attenuate concentrations of proinflammatory cytokines (TNF-α, IL-17), and increase levels of immunosuppressive IL-10, nitric oxide, and kynurenine in sera of LLC1-treated mice. MSCs profoundly reduced infiltration of macrophages, TNF-α-producing dendritic cells (DCs), TNF-α-, and IL-17-producing CD4+ T cells but increased IL-10-producing CD4+ T lymphocytes in the lungs of tumor-bearing animals. The total number of lung-infiltrated, cytotoxic FasL, perforin-expressing, TNF-α-, and IL-17-producing CD8+ T lymphocytes, and NKG2D-expressing natural killer (NK) cells was significantly reduced in LLC1 + MSC-treated mice. Cytotoxicity of NK cells was suppressed by MSC-conditioned medium. This phenomenon was abrogated by the inhibitors of inducible nitric oxide synthase (iNOS) and indoleamine 2,3-dioxygenase (IDO), suggesting the importance of iNOS and IDO for MSC-mediated suppression of antitumor cytotoxicity of NK cells. This study provides the evidence that MSCs promote lung cancer metastasis by suppressing antitumor immune response raising concerns regarding safety of MSC-based therapy in patients who have genetic susceptibility for malignant diseases.

Effect of Fibroblast-Like Cells of Mesenchymal Origin of Cytotoxic Activity of Lymphocytes against NK-Sensitive Target Cells

We studied immunosuppressive properties of skin fibroblasts and mesenchymal stromal cells against NK cells. In vitro experiments showed that mesenchymal stromal cells isolated from human umbilical cord and human skin fibroblasts can considerably attenuate cytotoxic activity of NK cells against Jurkat cells sensitive to NK-mediated lysis. NK cells cultured in lymphocyte population exhibited higher cytotoxic activity than isolated NK cells. Mesenchymal stromal cells or fibroblasts added 1:1 to lymphocyte culture almost completely suppressed NK cell cytotoxicity. This suggests that fibroblast-like cells can suppress not only isolated NK cells, but also NK cells in natural cell microenvironment.

Mesenchymal Stromal Cells Protect Endothelial Cells from Cytotoxic T Lymphocyte-Induced Lysis

The integrity of the vasculature plays an important role in the success of allogeneic organ and haematopoietic stem cell transplantation. Endothelial cells (EC) have previously been shown to be the target of activated cytotoxic T lymphocytes (CTL) resulting in extensive cell lysis. Mesenchymal stromal cells (MSC) are multipotent cells which can be isolated from multiple sites, each demonstrating immunomodulatory capabilities. They are explored herein for their potential to protect EC from CTL-targeted lysis. CD8(+) T cells isolated from human PBMC were stimulated with mitotically inactive cells of a human microvascular endothelial cell line (CDC/EU.HMEC-1, further referred to as HMEC) for 7 days. Target HMEC were cultured in the presence or absence of MSC for 24 h before exposure to activated allogeneic CTL for 4 h. EC were then analysed for cytotoxic lysis by flow cytometry. Culture of HMEC with MSC in the efferent immune phase (24 h before the assay) led to a decrease in HMEC lysis. This lysis was determined to be MHC Class I restricted linked and further analysis suggested that MSC contact is important in abrogation of lysis, as protection is reduced where MSC are separated in transwell experiments. The efficacy of multiple sources of MSC was also confirmed, and the collaborative effect of MSC and the endothelium protective drug defibrotide were determined, with defibrotide enhancing the protection provided by MSC. These results support the use of MSC as an adjuvant cellular therapeutic in transplant medicine, alone or in conjunction with EC protective agents such as defibrotide.

Mesenchymal Stem Cell Treatment of Inflammation-Induced Cancer

Cancer development is often associated with chronic inflammation. To date, research into inflammation-induced cancer has largely focused on chemokines, cytokines, and their downstream targets. These inflammatory mediators may promote tumor growth, invasion, metastasis, and facilitate angiogenesis. However, the exact mechanisms by which inflammation promotes neoplasia remain unclear. Inflammatory bowel disease (IBD) is characterized by recurrent, idiopathic intestinal inflammation, the complications of which are potentially fatal. IBD incidence in Australia is 24.2 per 100,000 and its peak onset is in people aged 15 to 24 years. Symptoms include abdominal pain, cramps, bloody stool, and persistent diarrhoea or constipation and so seriously compromise quality of life. However, due to its unknown etiology, current treatment strategies combat the symptoms rather than the disease and are limited by inefficacy, toxicity, and adverse side-effects. IBD is also associated with an increased risk of colorectal cancer, for which treatment options are similarly limited. In recent years, there has been much interest in the therapeutic potential of mesenchymal stem cells (MSCs). However, whether MSCs suppress or promote tumor development is still contentious within the literature. Many studies indicate that MSCs exert anti-tumor effects and suppress tumor growth, whereas other studies report pro-tumor effects. Studies using MSCs as treatment for IBD have shown promising results in both animal models and human trials. However, as MSC treatment is still novel, the long-term risks remain unknown. This review aims to summarize the current literature on MSC treatment of inflammation-induced cancer, with a focus on colorectal cancer resulting from IBD.

CD271+ Mesenchymal Stem Cells as a Possible Infectious Niche for Leishmania infantum

Visceral leishmaniasis (VL) is a serious and fatal disease. Therapeutic drugs are toxic and non-sterilizing. The etiological agents Leishmania infantum and Leishmania donovani cause active and asymptomatic diseases. Effective drugs to treat VL exist but unfortunately, post-treatment relapses are common. Little is known why drugs are non-sterilizing or how these intracellular pathogens can escape treatment. Here, using a murine model of VL we found that CD271+/Sca1+ bone marrow mesenchymal stem cells (BM-MSCs) are readily infected in vitro and in vivo by L. infantum. Because BM-MSCs express potent drug efflux pumps, e.g., ABCG2 it is possible that this unique intracellular infectious niche could allow L. infantum to escape anti-parasite drugs.

Clinical-Grade Human Multipotent Adult Progenitor Cells Block CD8+ Cytotoxic T Lymphocytes

: MultiStem cells are clinical-grade multipotent adult bone marrow-derived progenitor cells (MAPCs), with extensive replication potential and broader differentiation capacity compared with mesenchymal stem cells. Human MAPCs suppress T-cell proliferation induced by alloantigens and mutually interact with allogeneic natural killer cells. In this study, the interaction between MultiStem and CD8⁺ cytotoxic T lymphocytes (CTLs) was addressed for the first time. In an in vitro setting, the immunogenicity of MultiStem, the susceptibility of MultiStem toward CTL-mediated lysis, and its effects on CTL function were investigated. MultiStem was nonimmunogenic for alloreactive CTL induction and was-even after major histocompatibility complex class I upregulation-insensitive to alloantigen-specific CTL-mediated lysis. Furthermore, MultiStem reduced CTL proliferation and significantly decreased perforin expression during the T-cell activation phase. As a consequence, MultiStem dose-dependently impaired the induction of CTL function. These effects of MultiStem were mediated predominantly through contact-dependent mechanisms. Moreover, MultiStem cells considerably influenced the expression of T-cell activation markers CD25, CD69, and human leukocyte antigen-DR. The MultiStem-induced CD8^-CD69⁺ T-cell population displayed a suppressive effect on the induction of CTL function during a subsequent mixed-lymphocyte culture. Finally, the killer activity of activated antigen-specific CTLs during their cytolytic effector phase was also diminished in the presence of MultiStem. This study confirms that these clinical-grade MAPCs are an immune-modulating population that inhibits CTL activation and effector responses and are, consequently, a highly valuable cell population for adoptive immunosuppressive therapy in diseases where damage is induced by CTLs.

SIGNIFICANCE

Because multipotent adult progenitor cells (MAPCs) are among the noteworthy adult mesenchymal stem cell populations for immune therapy and have the advantage over mesenchymal stem cells (MSCs) of large-scale manufacturing and banking potential and thus prompt availability, it is important to understand how MAPCs interact with immune cells to validate their widespread therapeutic applicability. Cytotoxic immune effector cells play a crucial role in immune homeostasis and in the pathogenesis of some autoimmune diseases. This study assessed for the first time the in vitro influence of a clinical-grade human MAPC product (MultiStem) on the cytotoxic function of CD8⁺ T cells (CTLs) by evaluating the immunogenicity of MAPCs and the susceptibility of MAPCs toward CTL-mediated lysis and by analyzing the mechanism of MAPC-mediated modulation of CTL functionality. These results may represent a highly relevant contribution to the current knowledge and, in combination with the results of future phase II/III trials using MultiStem, could lead to an intriguing continuation of stem cell-based research for immunotherapy.

Rebuilding the Damaged Heart: Mesenchymal Stem Cells, Cell-Based Therapy, and Engineered Heart Tissue

Mesenchymal stem cells (MSCs) are broadly distributed cells that retain postnatal capacity for self-renewal and multilineage differentiation. MSCs evade immune detection, secrete an array of anti-inflammatory and anti-fibrotic mediators, and very importantly activate resident precursors. These properties form the basis for the strategy of clinical application of cell-based therapeutics for inflammatory and fibrotic conditions. In cardiovascular medicine, administration of autologous or allogeneic MSCs in patients with ischemic and nonischemic cardiomyopathy holds significant promise. Numerous preclinical studies of ischemic and nonischemic cardiomyopathy employing MSC-based therapy have demonstrated that the properties of reducing fibrosis, stimulating angiogenesis, and cardiomyogenesis have led to improvements in the structure and function of remodeled ventricles. Further attempts have been made to augment MSCs' effects through genetic modification and cell preconditioning. Progression of MSC therapy to early clinical trials has supported their role in improving cardiac structure and function, functional capacity, and patient quality of life. Emerging data have supported larger clinical trials that have been either completed or are currently underway. Mechanistically, MSC therapy is thought to benefit the heart by stimulating innate anti-fibrotic and regenerative responses. The mechanisms of action involve paracrine signaling, cell-cell interactions, and fusion with resident cells. Trans-differentiation of MSCs to bona fide cardiomyocytes and coronary vessels is also thought to occur, although at a nonphysiological level. Recently, MSC-based tissue engineering for cardiovascular disease has been examined with quite encouraging results. This review discusses MSCs from their basic biological characteristics to their role as a promising therapeutic strategy for clinical cardiovascular disease.

Mesenchymal stem cells (MSCs) as skeletal therapeutics - an update

Mesenchymal stem cells hold the promise to treat not only several congenital and acquired bone degenerative diseases but also to repair and regenerate morbid bone tissues. Utilizing MSCs, several lines of evidences advocate promising clinical outcomes in skeletal diseases and skeletal tissue repair/regeneration. In this context, both, autologous and allogeneic cell transfer options have been utilized. Studies suggest that MSCs are transplanted either alone by mixing with autogenous plasma/serum or by loading onto repair/induction supportive resorb-able scaffolds. Thus, this review is aimed at highlighting a wide range of pertinent clinical therapeutic options of MSCs in the treatment of skeletal diseases and skeletal tissue regeneration. Additionally, in skeletal disease and regenerative sections, only the early and more recent preclinical evidences are discussed followed by all the pertinent clinical studies. Moreover, germane post transplant therapeutic mechanisms afforded by MSCs have also been conversed. Nonetheless, assertive use of MSCs in the clinic for skeletal disorders and repair is far from a mature therapeutic option, therefore, posed challenges and future directions are also discussed. Importantly, for uniformity at all instances, term MSCs is used throughout the review.

Surgical meshes coated with mesenchymal stem cells provide an anti-inflammatory environment by a M2 macrophage polarization

Surgical meshes are widely used in clinics to reinforce soft tissue's defects, and to give support to prolapsed organs. However, the implantation of surgical meshes is commonly related with an inflammatory response being difficult to eradicate without removing the mesh. Here we hypothesize that the combined use of surgical meshes and mesenchymal stem cells (MSCs) could be a useful tool to reduce the inflammatory reaction secondary to mesh implantation. In vitro determinations of viability, metabolic activity and immunomodulation assays were performed on MSCs-coated meshes. Magnetic resonance imaging, evaluation by laparoscopic optical system and histology were performed for safety assessment. Finally, flow cytometry and qRT-PCR were used to elucidate the mechanism of action of MSCs-coated meshes. Our results demonstrate the feasibility to obtain MSCs-coated surgical meshes and their cryopreservability to be used as an 'off the shelf' product. These biological meshes fulfill the safety aspects as non-adverse effects were observed when compared to controls. Moreover, both in vitro and in vivo studies demonstrated that, local immunomodulation of implanted meshes is mediated by a macrophage polarization towards an anti-inflammatory phenotype. In conclusion, the combined usage of surgical meshes with MSCs fulfills the safety requirements for a future clinical application, providing an anti-inflammatory environment that could reduce the inflammatory processes commonly observed after surgical mesh implantation.

STATEMENT OF SIGNIFICANCE

Surgical meshes are medical devices widely used in clinics to resolve hernias and organs' prolapses, among other disorders. However, the implantation of surgical meshes is commonly related with an inflammatory response being difficult to eradicate without removing the mesh, causing pain and discomfort in the patient. Previously, the anti-inflammatory, immunomodulatory and pro-regenerative ability of mesenchymal stem cells (MSCs) have been described. To our knowledge, this is the first report where the anti-inflammatory and pro-regenerative ability of MSCs have been successfully applied in combination with surgical meshes, reducing the inflammatory processes commonly observed after mesh implantation. Moreover, our in vitro and in vivo results highlight the safety and efficacy of these bioactive meshes as a 'ready to use' medical product.

Mesenchymal stem cells: a friend or foe in immune-mediated diseases

Mesenchymal stem cells (MSCs) are adult, self-renewable, multipotent cells that can be found in almost all postnatal tissues. Because of their capacity for self-renewal and differentiation into tissues of mesodermal origin and due to their immunomodulatory ability, MSCs are used in many preclinical and clinical studies as possible new therapeutic agents for the autoimmune or degenerative diseases treatment. In dependence of inflammatory environment to which they are exposed to, MSCs adopt immunosuppressive or pro-inflammatory phenotype. In the presence of high levels of pro-inflammatory cytokines or through activation of Toll-like receptor (TLR)-3, MSCs adopt an immune-suppressive phenotype and suppress the proliferation, activation and effector function of professional antigen presenting cells (dendritic cells, macrophages, B lymphocytes), T lymphocytes, NK cells, NKT cells, and neutrophils. During the early phase of inflammation, through TLR4 activation and in the presence of low levels of inflammatory cytokines, MSCs adopt a pro-inflammatory phenotype, promote neutrophil and T cell activation and enhance immune response. Here we review the current findings on the immunoregulatory plasticity of MSCs involved in regulation of immune response.

Immunomodulatory properties of stem cells and bioactive molecules for tissue engineering

The immune system plays a crucial role in the success of tissue engineering strategies. Failure to consider the interactions between implantable scaffolds, usually containing cells and/or bioactive molecules, and the immune system can result in rejection of the implant and devastating clinical consequences. However, recent research into mesenchymal stem cells, which are commonly used in many tissue engineering applications, indicates that they may play a beneficial role modulating the immune system. Likewise, direct delivery of bioactive molecules involved in the inflammatory process can promote the success of tissue engineering constructs. In this article, we will review the various mechanisms in which modulation of the immune system is achieved through delivered bioactive molecules and cells and contextualize this information for future strategies in tissue engineering.

Mesenchymal Stromal Cells and Viral Infection

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

Influence of Immunogenicity of Allogeneic Bone Marrow Mesenchymal Stem Cells on Bone Tissue Engineering

Allogeneic bone marrow mesenchymal stem cell (allo-BMSC)-based tissue-engineered bone (TEB) has great potential for bone defect repair. However, the immunogenicities and biological roles of allo-BMSCs are still controversial. In this study, we established an animal model of critical-sized mandibular defect in beagle dogs and compared the repairing effects of allo-BMSC-based TEB with autogenic BMSC (auto-BMSC)-based TEB without the administration of immunosuppressants. During the first 2 weeks postimplantation, a transient immune response in the allo-BMSC group was detected with an increase in proinflammation cytokines TNF-α, IFN-γ, and IL-2, a declination of anti-inflammation cytokine IL-10, and an increase in percentages of CD4(+) and CD8(+) T-cell subsets in peripheral blood. Nevertheless, there was no significant difference in bone union achievement, bone mineral density, and biomechanical properties between the two groups at 12 and 24 weeks postimplantation. Further subcutaneous implantation of allo-BMSCs/scaffold also exhibited the similar transient immune responses in the first 2 weeks postimplantation but followed by a decreased bone formation at 4 and 8 weeks postimplantation. These findings indicate that allo-BMSCs can induce a transient immunoreaction, which may temporally delay the osteogenesis of allo-BMSC/scaffold complex in early stage of in vivo implantation, whereas the long-term engineered bone formation was not affected.

Interferon-gamma modification of mesenchymal stem cells: implications of autologous and allogeneic mesenchymal stem cell therapy in allotransplantation

Bone marrow-derived mesenchymal stem cells (MSC) have unique immunomodulatory and reparative properties beneficial for allotransplantation cellular therapy. The clinical administration of autologous or allogeneic MSC with immunosuppressive drugs is able to prevent and treat allograft rejection in kidney transplant recipients, thus supporting the immunomodulatory role of MSC. Interferon-gamma (IFN-γ) is known to enhance the immunosuppressive properties of MSC. IFN-γ preactivated MSC (MSC-γ) directly or indirectly modulates T cell responses by enhancing or inducing MSC inhibitory factors. These factors are known to downregulate T cell activation, enhance T cell negative signalling, alter T cells from a proinflammatory to an anti-inflammatory phenotype, interact with antigen-presenting cells and increase or induce regulatory cells. Highly immunosuppressive MSC-γ with increased migratory and reparative capacities may aid tissue repair, prolong allograft survival and induce allotransplant tolerance in experimental models. Nevertheless, there are contradictory in vivo observations related to allogeneic MSC-γ therapy. Many studies report that allogeneic MSC are immunogenic due to their inherent expression of major histocompatibility (MHC) molecules. Enhanced expression of MHC in allogeneic MSC-γ may increase their immunogenicity and this can negatively impact allograft survival. Therefore, strategies to reduce MSC-γ immunogenicity would facilitate "off-the-shelf" MSC therapy to efficiently inhibit alloimmune rejection and promote tissue repair in allotransplantation. In this review, we examine the potential benefits of MSC therapy in the context of allotransplantation. We also discuss the use of autologous and allogeneic MSC and the issues associated with their immunogenicity in vivo, with particular focus on the use of enhanced MSC-γ cellular therapy.

Mesenchymal stem cells suppress CD8+ T cell-mediated activation by suppressing natural killer group 2, member D protein receptor expression and secretion of prostaglandin E2, indoleamine 2, 3-dioxygenase and transforming growth factor-β

Bone marrow mesenchymal stem cells (BMSCs) inhibit immune cell responsiveness, and especially of T lymphocytes. We showed that BMSCs markedly inhibited the proliferation and cytokine production by CD8(+) T cells by a cell-to-cell contact phenomenon and secretion of soluble factors. BMSCs down-regulate the expression of natural killer group 2, member D protein (NKG2D) receptors on CD8(+) T cells when co-cultured with them. Moreover, CD8(+) T cells that express low levels of NKG2D had impaired proliferation after triggering by a mitogen. The major histocompatibility complex (MHC) class I chain-related (MIC) A/B molecule, which is a typical ligand for NKG2D, was expressed on BMSCs, and caused dampening of cell proliferation. Monoclonal antibody blocking experiments targeted to MIC A/B impaired CD8(+) T cell function, as evaluated by proliferation and cytokine production. In addition, the production of prostaglandin E2 (PGE2 ), indoleamine 2, 3-dioxygenase (IDO) and transforming growth factor (TGF)-β1 were increased when BMSCs were co-cultured with CD8(+) T cells. The addition of specific inhibitors against PGE2 , IDO and TGF-β partially restored the proliferation of CD8(+) T cells. Our results suggest that BMSCs suppress CD8(+) T cell-mediated activation by suppressing NKG2D expression and secretion of PGE2, IDO and TGF-β. Our observations further confirm the feasibility of BMSCs as a potential adoptive cellular therapy in immune-mediated diseases such as graft-versus-host disease (GVHD).

Mesenchymal stem cells: Emerging mechanisms of immunomodulation and therapy

Mesenchymal stem cells (MSCs) are a pleiotropic population of cells that are self-renewing and capable of differentiating into canonical cells of the mesenchyme, including adipocytes, chondrocytes, and osteocytes. They employ multi-faceted approaches to maintain bone marrow niche homeostasis and promote wound healing during injury. Biomedical research has long sought to exploit their pleiotropic properties as a basis for cell therapy for a variety of diseases and to facilitate hematopoietic stem cell establishment and stromal reconstruction in bone marrow transplantation. Early results demonstrated their usage as safe, and there was little host response to these cells. The discovery of their immunosuppressive functions ushered in a new interest in MSCs as a promising therapeutic tool to suppress inflammation and down-regulate pathogenic immune responses in graft-versus-host and autoimmune diseases such as multiple sclerosis, autoimmune diabetes, and rheumatoid arthritis. MSCs produce a large number of soluble and membrane-bound factors, some of which inhibit immune responses. However, the full range of MSC-mediated immune-modulation remains incompletely understood, as emerging reports also reveal that MSCs can adopt an immunogenic phenotype, stimulate immune cells, and yield seemingly contradictory results in experimental animal models of inflammatory disease. The present review describes the large body of literature that has been accumulated on the fascinating biology of MSCs and their complex effects on immune responses.

Adipose tissue-derived mesenchymal stem cells differentiated into hepatocyte-like cells in vivo and in vitro

Cell-based therapy is a potential alternative to liver transplantation. The goal of the present study was to examine the in vivo and in vitro hepatic differentiation potential of adipose tissue-derived mesenchymal stem cells (AT-MSCs) and to explore its therapeutic use. AT-MSCs were isolated and cultured with hepatic differentiation medium. Bioactivity assays were used to study the properties of AT-MSCs. The morphology of differentiated AT-MSCs in serum-free hepatic differentiation medium changed into polygonal epithelial cells, while the morphology of AT-MSCs in a similar medium containing 2% fetal bovine serum remained unchanged. The differentiated cells cultured without serum showed hepatocyte-like cell morphology and hepatocyte-specific markers, including albumin (ALB) and α-fetoprotein. The bioactivity assays revealed that hepatocyte-like cells could take up low-density lipoprotein (LDL) and store glycogen. Furthermore, trichostatin A (TSA) enhanced ALB production and LDL uptake by the hepatocyte-like cells, analogous to the functions of human liver cells. ALB was detected in the livers of the CCl₄-injured mice one month post-transplantation. This suggested that transplantation of the human AT-MSCs could relieve the impairment of acute CCl₄-injured livers in nude mice. This therefore implied that adipose tissue was a source of multipotent stem cells which had the potential to differentiate into mature, transplantable hepatocyte-like cells in vivo and in vitro. In addition, the present study determined that TSA was essential to promoting differentiation of human MSC towards functional hepatocyte-like cells. The relief of liver injury following treatment with AT-MSCs suggested their potential as a novel therapeutic method for liver disorders or injury.

Immunomodulatory Potential of Human Adipose Mesenchymal Stem Cells Derived Exosomes on in vitro Stimulated T Cells

In the recent years, it has been demonstrated that the biological activity of mesenchymal stem cells (MSCs) is mediated through the release of paracrine factors. Many of these factors are released into exosomes, which are small membranous vesicles that participate in cell–cell communication. Exosomes from MSCs are thought to have similar functions to MSCs such as repairing and regeneration of damaged tissue, but little is known about the immunomodulatory effect of these vesicles. Based on an extensive bibliography where the immunomodulatory capacity of MSCs has been demonstrated, here we hypothesized that released exosomes from MSCs may have an immunomodulatory role on the differentiation, activation and function of different lymphocyte subsets. According to this hypothesis, in vitro experiments were performed to characterize the immunomodulatory effect of human adipose MSCs derived exosomes (exo-hASCs) on in vitro stimulated T cells. The phenotypic characterization of cytotoxic and helper T cells (activation and differentiation markers) together with functional assays (proliferation and IFN-γ production) demonstrated that exo-hASCs exerted an inhibitory effect in the differentiation and activation of T cells as well as a reduced T cell proliferation and IFN-γ release on in vitro stimulated cells. In summary, here we demonstrate that MSCs-derived exosomes are a cell-derived product that could be considered as a therapeutic agent for the treatment of inflammation-related diseases.

Human adipose tissue-derived mesenchymal stromal cells promote B-cell motility and chemoattraction

BACKGROUND AIMS

Mesenchymal stromal cells hold special interest for cell-based therapy because of their tissue-regenerative and immunosuppressive abilities. B-cell involvement in chronic inflammatory and autoimmune pathologies makes them a desirable target for cell-based therapy. Mesenchymal stromal cells are able to regulate B-cell function; although the mechanisms are little known, they imply cell-to-cell contact.

METHODS

We studied the ability of human adipose tissue-derived mesenchymal stromal cells (ASCs) to attract B cells.

RESULTS

We show that ASCs promote B-cell migration through the secretion of chemotactic factors. Inflammatory/innate signals do not modify ASC capacity to mediate B-cell motility and chemotaxis. Analysis of a panel of B cell-related chemokines showed that none of them appeared to be responsible for B-cell motility. Other ASC-secreted factors able to promote cell motility and chemotaxis, such as the cytokine interleukin-8 and prostaglandin E2, did not appear to be implicated.

CONCLUSIONS

We propose that ASC promotion of B-cell migration by undefined secreted factors is crucial for ASC regulation of B-cell responses.

Mesenchymal stromal cells inhibit proliferation of virus-specific CD8(+) T cells

Mesenchymal stromal cells (MSCs) possess broad immunomodulatory capacities that are currently investigated for potential clinical application in treating autoimmune disorders. Third-party MSCs suppress alloantigen-induced proliferation of peripheral blood mononuclear cells providing the rationale for clinical use in graft-versus-host disease (GvHD). We confirmed that MSCs strongly inhibited proliferation of CD8(+) T cells in a mixed lymphocyte reaction. However, MSCs also suppressed proliferation of T cells specifically recognizing cytomegalovirus (CMV) and influenza virus. Inhibition was dose dependent, but independent of the culture medium. MSCs inhibited proliferation of specific CD8(+) T cells and the release of IFN-γ by specific CD8(+) T cells for immunodominant HLA-A2- and HLA-B7- restricted antigen epitopes derived from CMV phosphoprotein 65 and influenza matrix protein. This is in contrast to a recently reported scenario where MSCs exert differential effects on alloantigen and virus-specific T cells potentially having an impact on surveillance and prophylaxis of patients treated by MSCs.

CD4(+)CD25 (+) regulatory T cells are not required for mesenchymal stem cell function in fully MHC-mismatched mouse cardiac transplantation

Although the immunomodulative properties of mesenchymal stem cells (MSCs) open up attractive possibilities in solid-organ transplantation, information concerning the optimal dose, route, timing of administration, major histocompatibility complex (MHC)-restriction and relevant mechanisms is currently lacking. Therefore, better characterization of MSC immunoregulatory activity and elucidation of its mechanisms are crucial. In this study, we confirmed that MSCs did not elicit proliferation by allogeneic CD4(+) T cells, suggesting that MSCs were not immunogenic. By using C57BL/6 mouse MSCs as donor-derived or recipient-derived or as third-party MSCs, we discovered that MSCs suppressed CD4(+) T cell proliferation and prolonged mouse cardiac allograft survival in a dose-dependent and non-MHC-restricted manner. We also found that intraperitoneal administration favored survival prolongation, although this prolongation was weaker than that via the intravenous route. Only infusion at earlier time points favored survival prolongation. Depletion of CD4(+)CD25(+) T cells did not affect the immunosuppression of MSCs on CD4(+) T cells. Moreover, MSCs did not induce regulatory T cells. The in vivo data revealed that MSCs did not increase the percentage of CD4(+)CD25(+) T cells and FoxP3 expression. More importantly, we demonstrated for the first time that depletion of CD4(+)CD25(+) T cells did not hinder MSC-induced survival prolongation, indicating that CD4(+)CD25(+) regulatory T cells were not essential for the prolongation of MSC-mediated allograft survival.

Combined 4-1BB and CD28 costimulation could unleash lymphocytes from immunosuppression induced by adipose derived stem cell soluble products

Adipose derived stem cells (ASCs) have the potential to differentiate into multiple cell lineages with the capacity to suppress immune cells. However, the exact mechanism of this suppression is not fully understood. We hypothesized that supplying additional lymphocyte costimulation through CD28 and 4-1BB could overturn the inhibitory effect of ASCs. To that end, PHA-activated human PBMCs were cocultured with ASCs or with conditioned media (CM) prepared from cultured ASCs. Growth was analyzed in the presence or absence of anti-CD28 and anti-4-1BB antibodies. Results from CFSE dilution analysis with flow cytometry showed that significant and dose-dependent suppression of PHA-activated lymphocytes occurred in the presence of ASC-like cells or ASC's CM. However, additional costimulation of T cells through CD28 and 4-1BB was able to fully recover lymphocyte proliferative capacity in the presence of ASC's CM. Neither of the costimulatory antibodies could fully recover lymphocyte proliferation following coculture with ASCs. Reversal of ASC's immunosuppression through costimulation suggests that further investigation of ASC suppression mechanisms is warranted, since many clinical applications of ASCs are based on this feature. Moreover, such findings have the potential to boost the usefulness of ASCs in the treatment of autoimmune disease.