Mesenchymal stem cells in the treatment of inflammatory and autoimmune diseases in experimental animal models

Multipotent mesenchymal stromal cells [also known as mesenchymal stem cells(MSCs)] are currently being studied as a cell-based treatment for inflammatory disorders. Experimental animal models of human immune-mediated diseases have been instrumental in establishing their immunosuppressive properties. In this review, we summarize recent studies examining the effectiveness of MSCs as immunotherapy in several widely-studied animal models, including type 1 diabetes, experimental autoimmune arthritis, experimental autoimmune encephalomyelitis, inflammatory bowel disease, graft-vs-host disease, and systemic lupus erythematosus. In addition, we discuss mechanisms identified by which MSCs mediate immune suppression in specific disease models, and potential sources of functional variability of MSCs between studies.     

Mesenchymal stem cells as a therapeutic tool to treat sepsis

Sepsis is a clinical syndrome caused by a deregulated host response to an infection. Sepsis is the most frequent cause of death in hospitalized patients. Although knowledge of the pathogenesis of sepsis has increased substantially during the last decades, attempts to design effective and specific therapiestargeting components of the derailed host response have failed. Therefore, there is a dramatic need for new and mechanistically alternative therapies to treat this syndrome. Based on their immunomodulatory properties, adult mesenchymal stem or stromal cells(MSCs) can be a novel therapeutic tool to treat sepsis. Indeed, MSCs reduce mortality in experimental models of sepsis by modulating the deregulated inflammatory response against bacteria through the regulation of multiple inflammatory networks, the reprogramming of macrophages and neutrophils towards a more antiinflammatory phenotype and the release of antimicrobial peptides. This report will review the current knowledge on the effects of MSC treatment in preclinical experimental small animal models of sepsis.     

Mesenchymal stem cells in arthritic diseases

Mesenchymal stem cells (MSCs), the nonhematopoietic progenitor cells found in various adult tissues, are characterized by their ease of isolation and their rapid growth in vitro while maintaining their differentiation potential, allowing for extensive culture expansion to obtain large quantities suitable for therapeutic use. These properties make MSCs an ideal candidate cell type as building blocks for tissue engineering efforts to regenerate replacement tissues and repair damaged structures as encountered in various arthritic conditions. Osteoarthritis (OA) is the most common arthritic condition and, like rheumatoid arthritis (RA), presents an inflammatory environment with immunological involvement and this has been an enduring obstacle that can potentially limit the use of cartilage tissue engineering. Recent advances in our understanding of the functions of MSCs have shown that MSCs also possess potent immunosuppression and anti-inflammation effects. In addition, through secretion of various soluble factors, MSCs can influence the local tissue environment and exert protective effects with an end result of effectively stimulating regeneration in situ. This function of MSCs can be exploited for their therapeutic application in degenerative joint diseases such as RA and OA. This review surveys the advances made in the past decade which have led to our current understanding of stem cell biology as relevant to diseases of the joint. The potential involvement of MSCs in the pathophysiology of degenerative joint diseases will also be discussed. Specifically, we will explore the potential of MSC-based cell therapy of OA and RA by means of functional replacement of damaged cartilage via tissue engineering as well as their anti-inflammatory and immunosuppressive activities.     

Mesenchymal stem cells: A therapeutic update

Mesenchymal stem cells/multipotent marrow stromal cells (MSC) have the ability to participate in there construction of tissues both directly by providing repair cells (essentially those originating from mesoderm)and indirectly by modulating inflammatory and immune responses. This wide range of properties makes these cells very appealing to treat various pathological conditions. They have been first used in 1995 as supportive cells to facilitate hematopoietic stem cells engraftment, and then to minimize the deleterious consequences of graft versus host disease by their immunosuppressive function. Their robust osteogenic differentiation capacity has also been evaluated in numerous preclinical settings of healing/repair but more rarely in human clinical trials. During the past 10-15 years, the potential benefit of their paracrine actions has been tested in various situations such as to facilitate repair after cutaneous defects after burns or lower consequences of ischemic strokes. The purpose of this series of short texts is not to give an exhaustive panorama, but to discuss some well-identified indications in four different fields : auto-immune diseases,bone repair, vascular regeneration and eye lesions such as corneal and retinal defects.     

Mesenchymal stem cell-derived extracellular vesicles as a new therapeutic strategy for ocular diseases

Mesenchymal stem cells (MSCs) have attracted considerable attention for their activity in the treatment of refractory visual disorders. Since MSCs were found to possess the beneficial effects by secreting paracrine factors rather than direct differentiation, MSC-derived extracellular vesicles (EVs) were widely studied in various disease models. MSCs generate abundant EVs, which act as important mediators by exchanging protein and genetic information between MSCs and target cells. It has been confirmed that MSC-derived EVs possess unique anti-inflammatory, anti-apoptotic, tissue repairing, neuroprotective, and immunomodulatory properties, similar to their parent cells. Upon intravitreal injection, MSC-derived EVs rapidly diffuse through the retina to alleviate retinal injury or inflammation. Due to possible risks associated with MSC transplantation, such as vitreous opacity and pathological proliferation, EVs appear to be a better choice for intravitreal injection. Small size EVs can pass through biological barriers easily and their contents can be modified genetically for optimal therapeutic effect. Hence, currently, they are also explored for the possibility of serving as drug delivery vehicles. In the current review, we describe the characteristics of MSC-derived EVs briefly, comprehensively summarize their biological functions in ocular diseases, and discuss their potential applications in clinical settings.     

Neural stem cells as therapeutic agents for age-related brain repair

Neurogenesis occurs in two germinal centres of the adult brain and persists with increasing age, although at a reduced level. This observation, that the mature brain can support neurogenesis, has given rise to the hope that neural stem cells could be used to repair the brain by repopulating regions suffering from neuronal loss as a result of injury or disease. The aging brain is vulnerable to mild cognitive impairment, increasing incidence of stroke, and a variety of neurodegenerative diseases. However, most studies to date have focused on the young adult brain, and relatively little information is available about the regulation of neurogenesis in the aged brain or the potential of using neural stem cells to repair the aged brain. This review summarizes the current state of knowledge on neurogenesis in the young adult brain and discusses the information available on age-related changes in neurogenesis. Possible therapeutic strategies using neural stem cells for repair of the aging brain are considered.     

Mesenchymal stem cells: therapeutic outlook for stroke

Adult bone marrow-derived mesenchymal stem cells (MSCs) display a spectrum of functional properties. Transplantation of these cells improves clinical outcome in models of cerebral ischemia and spinal cord injury via mechanisms that may include replacement of damaged cells, neuroprotective effects, induction of axonal sprouting, and neovascularization. Therapeutic effects have been reported in animal models of stroke after intravenous delivery of MSCs, including those derived from adult human bone marrow. Initial clinical studies on intravenously delivered MSCs have now been completed in human subjects with stroke. Here, we review the reparative and protective properties of transplanted MSCs in stroke models, describe initial human studies on intravenous MSC delivery in stroke, and provide a perspective on prospects for future progress with MSCs.     

Mesenchymal stem cells as trophic mediators

Adult marrow-derived Mesenchymal Stem Cells (MSCs) are capable of dividing and their progeny are further capable of differentiating into one of several mesenchymal phenotypes such as osteoblasts, chondrocytes, myocytes, marrow stromal cells, tendon-ligament fibroblasts, and adipocytes. In addition, these MSCs secrete a variety of cytokines and growth factors that have both paracrine and autocrine activities. These secreted bioactive factors suppress the local immune system, inhibit fibrosis (scar formation) and apoptosis, enhance angiogenesis, and stimulate mitosis and differentiation of tissue-intrinsic reparative or stem cells. These effects, which are referred to as trophic effects, are distinct from the direct differentiation of MSCs into repair tissue. Several studies which tested the use of MSCs in models of infarct (injured heart), stroke (brain), or meniscus regeneration models are reviewed within the context of MSC-mediated trophic effects in tissue repair.     

Dendritic cells,chemokine receptors and autoimmune inflammatory diseases

Dendritic cells (DC) have been implicated in the induction of autoimmune diseases and have been identified in lesions associated with several autoimmune inflammatory diseases. Since DC are regarded as the professional antigen-presenting cell (APC) of the immune system and the only APC capable of activating na?ve T cells, they are likely to play a significant role in breaking tolerance of self-reactive lymphocytes and in supporting autoimmune responses in these diseases. A number of studies have revealed that small molecular weight chemotactic proteins known as chemokines are present within the autoimmune lesions and may contribute to the recruitment not only of DC populations, but also of immune cells such as T cells, B cells, neutrophils and monocytes into the site, and to the formation of organized lymphoid tissue structures within the target organ. The focus of this review will be a discussion of the role of chemokines in the recruitment of DC in human autoimmune inflammatory disorders, specifically the trafficking of DC into the inflammatory sites and the subsequent migration of differentiated DC from the inflammatory sites into the draining lymph nodes. Once DC are properly positioned within the lymph nodes, circulating antigen specific na?ve T cells can interact with DC and become activated, clonally expanded and stimulated to undergo differentiation into antigen-experienced memory T cells. Subsequent reactivation of memory T cells that enter the autoimmune lesions by DC present in the inflammatory lesion is thought to play a central role in tissue inflammation.     

Dendritic cells and cytokines in human inflammatory and autoimmune diseases

Dendritic cells (DCs) produce cytokines and are susceptible to cytokine-mediated activation. Thus, interaction of resting immature DCs with TLR ligands, for example nucleic acids, or with microbes leads to a cascade of pro-inflammatory cytokines and skewing of T cell responses. Conversely, several cytokines are able to trigger DC activation (maturation) via autocrine, for example TNF and plasmacytoid DCs, and paracrine, for example type I IFN and myeloid DCs, pathways. By controlling DC activation, cytokines regulate immune homeostasis and the balance between tolerance and immunity. The increased production and/or bioavailability of cytokines and associated alterations in DC homeostasis have been implicated in various human inflammatory and autoimmune diseases. Targeting these cytokines with biological agents as already is the case with TNF and IL-1 represents a success of immunology and the coming years will expand the range of cytokines as therapeutic targets in autoinflammatory and autoimmune pathology.     

Mesenchymal stem cells as mediators of neural differentiation

Mesenchymal stem cells (MSCs) represent a promising source of material for autologous cell transplantation therapies, in particular, their potential use for the treatment of damaged nervous tissue. Much of the work in this area has focused on the transplantation of MSCs into animal models of neurological disorders, including stroke and spinal cord injury. Although numerous studies have reported significant functional improvements in these systems, the exact mechanism(s) by which MSCs elicit recovery remains largely undefined. While it has been proposed that 'trans'-differentiation and/or cell fusion events underly MSC-mediated neural repair, there is considerable doubt that the low frequency of these phenomena is sufficient to account for the observed levels of recovery. Furthermore, in vitro studies call into question the ability of MSCs to produce authentic neural derivatives. In this review we focus on recent evidence indicating that transplanted MSCs promote endogenous repair of neurologically damaged areas via the release of soluble trophic factors and cytokines. Through the modern analysis of MSC-conditioned media it is becoming possible to gain new insight into the release and interplay of these soluble factors and their neurogenic effects. Ultimately this understanding may lead to the rational design of new therapies for the treatment of neurological and neurodegenerative disorders.     

Mesenchymal stem cells

Within the bone marrow stroma there exists a subset of nonhematopoietic cells referred to as mesenchymal stem or mesenchymal progenitor cells. These cells can be ex vivo expanded and induced, either in vitro or in vivo, to terminally differentiate into osteoblasts, chondrocytes, adipocytes, tenocytes, myotubes, neural cells, and hematopoietic-supporting stroma. The multipotential of these cells, their easy isolation and culture, as well as their high ex vivo expansive potential make these cells an attractive therapeutic tool. In this work we will review the information dealing with the biology of mesenchymal progenitors as it has been revealed mainly by ex vivo studies performed with bone marrow-derived cells. The discussed topics include, among others, characteristics of mesenchymal progenitors, evidence for the existence of a vast repertoire of uncommitted and committed progenitors both in the bone marrow and in mesenchymal tissues, a diagram for their proliferative hierarchy, and comments on mobilization, microenvironment, and clinical use of mesenchymal progenitors. Despite the enormous data available at molecular and cellular levels, it is evident that a number of fundamental questions still need to be resolved before mesenchymal progenitors can be used for safe and effective clinical applications in the context of both cell and gene therapies.     

Mesenchymal stem cells as a potential therapeutic tool to cure cognitive impairment caused by neuroinflammation

An established contribution of neuroinflammation to multiple brain pathologies has raised the requirement for therapeutic strategies to overcome it in order to prevent age- and disease-dependent cognitive decline. Mesenchymal stem cells (MSCs) produce multiple growth and neurotrophic factors and seem to evade immune rejection due to low expression of major histocompatibility complex class I molecules. Therefore, MSCs are widely used in experiments and clinical trials of regenerative medicine. This review summarizes recent data concerning the optimization of MSC use for therapeutic purposes with the emphasis on the achievements of the last 2 years. Specific attention is paid to extracellular vesicles secreted by MSCs and to the role of α7 nicotinic acetylcholine receptors. The reviewed data demonstrate that MSCs have a significant therapeutic potential in treating neuroinflammation-related cognitive disfunctions including age-related neurodegenerative diseases. The novel data demonstrate that maximal therapeutic effect is being achieved when MSCs penetrate the brain and produce their stimulating factors in situ. Consequently, therapeutic application using MSCs should include measures to facilitate their homing to the brain, support the survival in the brain microenvironment, and stimulate the production of neurotrophic and anti-inflammatory factors. These measures include but are not limited to genetic modification of MSCs and pre-conditioning before transplantation.     

Identification and characterization of potential new therapeutic targets in inflammatory and autoimmune diseases.

The isoxazole derivative Leflunomide (HWA 486) is a novel immunoregulatory and anti-inflammatory drug. Affinity chromatography was used to purify and identify Leflunomide binding proteins, which might play a role as potential cellular targets in the molecular mode of action. The Leflunomide derivative A 0273 was covalently coupled to a Fractogel(R) matrix. This column was used to separate a cytosolic protein extract of the macrophage cell line RAW 264.7 by several selected and specific gradient elution steps. Proteins that were specifically eluted through the active metabolite of Leflunomide, A 1726, were identified by subsequent protein sequence analysis. This allowed us to specify 10 cytosolic proteins, which bind with high affinity to this matrix. Three of them, glyceraldehyde 3-phosphate dehydrogenase, pyruvate kinase and phosphoglycerate mutase belong to the second part of the glycolytic pathway. The binding specificity of these protein/drug interactions was further evaluated using BIAcore(R) analysis. Kd values of glyceraldehyde 3-phosphate dehydrogenase, pyruvate kinase and lactic dehydrogenase were similar to the Kd value of a known Leflunomide target protein, dihydroorotate dehydrogenase. In order to elucidate the features as well as the overall relevance of these results, cytosolic fractions of three additional cell lines MOLT-4, A20.2J, HeLa were compared using the same chromatographic protocol. The elution profiles as well as subsequent Western blot analyses confirmed the data obtained previously for the macrophage cell line RAW 264.7.     

Mesenchymal stem cells - The challenge of a good therapeutic product

Mesenchymal stem cells (or stromal cells) have been initially characterized in bone marrow, but since, they have been identified in almost every tissue. Their multiple properties, namely differentiative capacity, production of cytokines and trophic molecules, and their immunosuppressive potential undoubtedly offer many therapeutic advantages, both for regenerative medecine or to relieve immune or inflammatory diseases. This is illustrated by the high number (>?100) of ongoing clinical trials with these cells. However, a prerequsite for their safe use in clinics is to guarantee that their production meet the good manufacturing practices, and that the final product is validated by adequate controls. It is thus quite a challenge to move from procedures defined for a research use to large scale production that fits with the national and international rules in terms of standardisation and controls. This underlines the importance of developping interacting networks between research teams, physicians and the industrial R&D departments. This fruitful collaboration will ensure the definition of appropriate and safe procedures for a successful therapeutic application.     

Gold compounds as therapeutic agents for human diseases

The application of gold in medicine is traceable for several thousand years and Au(i) compounds have been used clinically to treat rheumatoid arthritis since the last century. Recently research into gold-based drugs for a range of human diseases has seen a renaissance. Old as well as new Au(i) and Au(iii) compounds have been used and designed with an aim of targeting cellular components that are implicated in the onset or progression of cancers, rheumatoid arthiritis, viral and parasitic diseases. In addition, new disease targets have been found for gold compounds that have given insight into the mechanism of action of these compounds, as well as in the molecular pathophysiology of human diseases. Here we discuss the rationale for the design and use of gold compounds that have specific and selective targets in cells to alleviate the symptoms of a range of human diseases. We summarise the most recent findings in this research and our own discoveries to show that gold compounds can be developed to become versatile and powerful drugs for diseases caused by dysfunction of selenol and thiol containing proteins.     

Mesenchymal stem cells as tool for antitumor therapy

The development of antitumor preparations with low toxicity and high selectivity of action is one of the top priorities of cancer gene therapy. Mesenchymal stem cells possess natural tropism towards tumors, a property that makes it possible to use them as vehicles for the targeted delivery of therapeutic genes to tumors of various etiologies. At present, genes that encode enzymes (cytosine deaminase, thymidine kinase, carboxyl esterase), cytokines (IL-2, IL-4, IL-12, and IFN-β), and apoptosis inducing factors (TRAIL) are used as therapeutic genes. Mesenchymal stem cells, as demonstrated using experimental models of tumors of various etiologies, as well as animals with metastases in brain and lungs, are able to successfully deliver therapeutic genes into tumors and produce a significant antitumor effect. However, to effectively use this therapeutic strategy in a clinical setting, a number of technical problems must be solved.     

Mesenchymal stem cells originating from ES cells show high telomerase activity and therapeutic benefits

We establish a novel method for the induction and collection of mesenchymal stem cells using a typical cell surface marker, CD105, through adipogenesis from mouse ES cells. ES cells were cultured in a medium for adipogenesis. Mesenchymal stem cells from mouse ES cells were easily identified by the expression of CD105, and were isolated and differentiated into multiple mesenchymal cell types. Mesenchymal stem cells showed remarkable telomerase activity and sustained their growth for a long time with a high potential for differentiation involving skeletal myogenesis in vitro. When mesenchymal stem cells were transplanted into the injured tibialis anterior muscles, they differentiated into skeletal muscle cells in vivo. In addition, they improved the vascular formation, but never formed teratoma for longer than 6 months. Gene expression profiles revealed that mesenchymal stem cells lost pluripotency, while they acquired high potential to differentiate into mesenchymal cell lines. They thus indicate a promising new source of cell-based therapy without teratoma formation.     

The use of patient-specific stem cells in different autoimmune diseases

Autoimmune diseases are developed when the immune system mistakenly attacks the body’s cells. These inflammatory disorders can be inherited or triggered by external forces, such as type 1 diabetes, which is caused by the immune system's destruction of pancreatic beta cells. So far, stem cells such as hESC and iPSC have been used to treat autoimmune disorders such as type 1 diabetes, rheumatoid arthritis (RA), multiple sclerosis (MS), and systemic lupus erythematosus (SLE), although these procedures have certain ethical concerns. On the other hand, bone marrow-derived mesenchymal stem cells (BM-MSC) are thought to be the best source of stem cells. Later, it was shown that mesenchymal stem cells produced from autologous adipose tissues have a great potential for producing huge volumes of stem cells. In-vitro and in-vivo investigations using autologous hematopoietic stem cells and autologous mesenchymal stem cells have been carried out on various rodent and human models, while clinical trials for inflammatory diseases such as multiple sclerosis and diabetes mellitus have yielded promising results. We attempted to summarise the usage of diverse stem cells in the therapy of various autoimmune disorders in this review. Shortly, we expect that the use of autologous stem cells will provide a new perspective on the treatment of autoimmune disorders.