The mesenchymal stromal cell contribution to homeostasis

Adult mesenchymal stromal cells (MSCs) are undifferentiated multi-potent cells predominantly residing in the bone marrow (BM), but also present with similar but not identical features in many other tissues such as blood, placenta, dental pulp, and adipose tissue. MSCs have the potential to differentiate into multiple skeletal phenotypes like osteoblasts, chondrocytes, adipocytes, stromal cells, fibroblasts, and possibly tendons. MSCs differentiation potential, ex vivo expansion capacity, nurturing and immunomodulatory proficiencies oriented these versatile cells in several areas of ongoing clinical applications. However, the absence of MSC-specific markers for isolation and characterization together with the lack of a comprehensive view of the molecular pathways governing their particular biological properties, remains a primary obstacle to their research and application. In this review we discuss some areas of growing interest in MSCs biology: their contribution to the hematopoietic stem cell (HSC) niche, to regenerative medicine, their role in cancer and in therapy as delivery tools and their micro-RNA (miRNA) signatures. Despite rapid progress in the MSC field, it is generally thought that only a fraction of their full potential has been realized thus far.     

Dental mesenchymal stromal/stem cells in different microenvironments— implications in regenerative therapy

Current research data reveal microenvironment as a significant modifier of physical functions, pathologic changes, as well as the therapeutic effects of stem cells. When comparing regeneration potential of various stem cell types used for cytotherapy and tissue engineering, mesenchymal stem cells (MSCs) are currently the most attractive cell source for bone and tooth regeneration due to their differentiation and immunomodulatory potential and lack of ethical issues associated with their use. The microenvironment of donors and recipients selected in cytotherapy plays a crucial role in regenerative potential of transplanted MSCs, indicating interactions of cells with their microenvironment indispensable in MSC-mediated bone and dental regeneration. Since a variety of MSC populations have been procured from different parts of the tooth and tooth-supporting tissues, MSCs of dental origin and their achievements in capacity to reconstitute various dental tissues have gained attention of many research groups over the years. This review discusses recent advances in comparative analyses of dental MSC regeneration potential with regards to their tissue origin and specific microenvironmental conditions, giving additional insight into the current clinical application of these cells.     

Could cancer and infection be adverse effects of mesenchymal stromal cell therapy?

Multipotent mesenchymal stromal cells [also referred to as mesenchymal stem cells(MSCs)] are a heterogeneous subset of stromal cells. They can be isolated from bone marrow and many other types of tissue. MSCs are currently being tested for therapeutic purposes(i.e., improving hematopoietic stem cell engraftment, managing inflammatory diseases and regenerating damaged organs). Their tropism for tumors and inflamed sites and their context-dependent potential for producing trophic and immunomodulatory factors raises the question as to whether MSCs promote cancer and/or infection. Thisarticle reviews the effect of MSCs on tumor establishment, growth and metastasis and also susceptibility to infection and its progression. Data published to date shows a paradoxical effect regarding MSCs, which seems to depend on isolation and expansion, cells source and dose and the route and timing of administration. Cancer and infection may thus be adverse or therapeutic effects arising form MSC administration.     

Mesenchymal stromal cells from human perinatal tissues: From biology to cell therapy

Cell-based regenerative medicine is of growing interest in biomedical research. The role of stem cells in this context is under intense scrutiny and may help to define principles of organ regeneration and develop innovative therapeutics for organ failure. Utilizing stem and progenitor cells for organ replacement has been conducted for many years when performing hematopoietic stem cell transplantation. Since the first successful transplantation of umbilical cord blood to treat hematological malignancies, non-hematopoietic stem and progenitor cell populations have recently been identified within umbilical cord blood and other perinatal and fetal tissues. A cell population entitled mesenchymal stromal cells (MSCs) emerged as one of the most intensely studied as it subsumes a variety of capacities: MSCs can differentiate into various subtypes of the mesodermal lineage, they secrete a large array of trophic factors suitable of recruiting endogenous repair processes and they are immunomodulatory.Focusing on perinatal tissues to isolate MSCs, we will discuss some of the challenges associated with these cell types concentrating on concepts of isolation and expansion, the comparison with cells derived from other tissue sources, regarding phenotype and differentiation capacity and finally their therapeutic potential.     

Functional differences in mesenchymal stromal cells from human dental pulp and periodontal ligament

Clinically reported reparative benefits of mesenchymal stromal cells (MSCs) are majorly attributed to strong immune‐modulatory abilities not exactly shared by fibroblasts. However, MSCs remain heterogeneous populations, with unique tissue‐specific subsets, and lack of clear‐cut assays defining therapeutic stromal subsets adds further ambiguity to the field. In this context, in‐depth evaluation of cellular characteristics of MSCs from proximal oro‐facial tissues: dental pulp (DPSCs) and periodontal ligament (PDLSCs) from identical donors provides an opportunity to evaluate exclusive niche‐specific influences on multipotency and immune‐modulation. Exhaustive cell surface profiling of DPSCs and PDLSCs indicated key differences in expression of mesenchymal (CD105) and pluripotent/multipotent stem cell–associated cell surface antigens: SSEA4, CD117, CD123 and CD29. DPSCs and PDLSCs exhibited strong chondrogenic potential, but only DPSCs exhibited adipogenic and osteogenic propensities. PDLSCs expressed immuno‐stimulatory/immune‐adhesive ligands like HLA‐DR and CD50, upon priming with IFNγ, unlike DPSCs, indicating differential response patterns to pro‐inflammatory cytokines. Both DPSCs and PDLSCs were hypo‐immunogenic and did not elicit robust allogeneic responses despite exposure to IFNγ or TNFα. Interestingly, only DPSCs attenuated mitogen‐induced lympho‐proliferative responses and priming with either IFNγ or TNFα enhanced immuno‐modulation capacity. In contrast, primed or unprimed PDLSCs lacked the ability to suppress polyclonal T cell blast responses. This study indicates that stromal cells from even topographically related tissues do not necessarily share identical MSC properties and emphasizes the need for a thorough functional testing of MSCs from diverse sources with respect to multipotency, immune parameters and response to pro‐inflammatory cytokines before translational usage.     

Early intervention with gene-modified mesenchymal stem cells overexpressing interleukin-4 enhances anti-inflammatory responses and functional recovery in experimental autoimmune demyelination

Mesenchymal stem/stromal cells (MSCs) can be isolated from most adult tissues and hold considerable promise for tissue regenerative therapies. Some of the potential advantages that MSCs have over other adult stem cell types include: (1) their relative ease of isolation, culture and expansion; (2) their immunomodulatory properties; (3) they can provide trophic support to injured tissues; (4) they can be transduced by retroviral vectors at a high efficiency; (5) they have an ability to home to sites of inflammation and injury. Collectively these characteristics suggest that MSCs are attractive vehicles for cell and gene therapy applications. In the current study, we investigated whether transplantation of human adipose-derived MSCs (Ad-MSCs) engineered to overexpress the anti-inflammatory cytokine interleukin (IL)-4 was efficacious in experimental autoimmune encephalomyelitis (EAE). Ad-MSCs transduced with a bicistronic lentiviral vector encoding mouse IL-4 and enhanced green fluorescent protein (Ad-IL4-MSCs) stably expressed, relatively high levels of both transgenes. Importantly the phenotypic and functional attributes of Ad-IL4-MSCs, such as the expression of homing molecules and differentiation capacity, was not altered by the transduction process. Notably, the early administration of Ad-IL4-MSCs in mice with EAE at the time of T-cell priming attenuated clinical disease. This protective effect was associated with a reduction in peripheral MOG-specific T-cell responses and a shift from a pro- to an anti-inflammatory cytokine response. These data suggest that the delivery of Ad-MSCs genetically engineered to express anti-inflammatory cytokines may provide a rational approach to promote immunomodulation and tissue protection in a number of inflammatory and degenerative diseases including multiple sclerosis.     

Early intervention with gene-modified mesenchymal stem cells overexpressing interleukin-4 enhances anti-inflammatory responses and functional recovery in experimental autoimmune demyelination

Mesenchymal stem/stromal cells (MSCs) can be isolated from most adult tissues and hold considerable promise for tissue regenerative therapies. Some of the potential advantages that MSCs have over other adult stem cell types include: (1) their relative ease of isolation, culture and expansion; (2) their immunomodulatory properties; (3) they can provide trophic support to injured tissues; (4) they can be transduced by retroviral vectors at a high efficiency; (5) they have an ability to home to sites of inflammation and injury. Collectively these characteristics suggest that MSCs are attractive vehicles for cell and gene therapy applications. In the current study, we investigated whether transplantation of human adipose-derived MSCs (Ad-MSCs) engineered to overexpress the anti-inflammatory cytokine interleukin (IL)-4 was efficacious in experimental autoimmune encephalomyelitis (EAE). Ad-MSCs transduced with a bicistronic lentiviral vector encoding mouse IL-4 and enhanced green fluorescent protein (Ad-IL4-MSCs) stably expressed, relatively high levels of both transgenes. Importantly the phenotypic and functional attributes of Ad-IL4-MSCs, such as the expression of homing molecules and differentiation capacity, was not altered by the transduction process. Notably, the early administration of Ad-IL4-MSCs in mice with EAE at the time of T-cell priming attenuated clinical disease. This protective effect was associated with a reduction in peripheral MOG-specific T-cell responses and a shift from a pro- to an anti-inflammatory cytokine response. These data suggest that the delivery of Ad-MSCs genetically engineered to express anti-inflammatory cytokines may provide a rational approach to promote immunomodulation and tissue protection in a number of inflammatory and degenerative diseases including multiple sclerosis.     

Trafficking and differentiation of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are a heterogeneous population of stem/progenitor cells with pluripotent capacity to differentiate into mesodermal and non‐mesodermal cell lineages, including osteocytes, adipocytes, chondrocytes, myocytes, cardiomyocytes, fibroblasts, myofibroblasts, epithelial cells, and neurons. MSCs reside primarily in the bone marrow, but also exist in other sites such as adipose tissue, peripheral blood, cord blood, liver, and fetal tissues. When stimulated by specific signals, these cells can be released from their niche in the bone marrow into circulation and recruited to the target tissues where they undergo in situ differentiation and contribute to tissue regeneration and homeostasis. Several characteristics of MSCs, such as the potential to differentiate into multiple lineages and the ability to be expanded ex vivo while retaining their original lineage differentiation commitment, make these cells very interesting targets for potential therapeutic use in regenerative medicine and tissue engineering. The feasibility for transplantation of primary or engineered MSCs as cell‐based therapy has been demonstrated. In this review, we summarize the current knowledge on the signals that control trafficking and differentiation of MSCs. J. Cell. Biochem. 106: 984–991, 2009. © 2009 Wiley‐Liss, Inc.     

Prospects for the therapeutic development of umbilical cord blood-derived mesenchymal stem cells

Umbilical cord blood (UCB) is a primitive and abundant source of mesenchymal stem cells (MSCs). UCB-derived MSCs have a broad and efficient therapeutic capacity to treat various diseases and disorders. Despite the high latent self-renewal and differentiation capacity of these cells, the safety, efficacy, and yield of MSCs expanded for ex vivo clinical applications remains a concern. However, immunomodulatory effects have emerged in various disease models, exhibiting specific mechanisms of action, such as cell migration and homing, angiogenesis, anti-apoptosis, proliferation, anti-cancer, anti-fibrosis, anti-inflammation and tissue regeneration. Herein, we review the current literature pertaining to the UCB-derived MSC application as potential treatment strategies, and discuss the concerns regarding the safety and mass production issues in future applications.     

Effects of living and metabolically inactive mesenchymal stromal cells and their derivatives on monocytes and macrophages

Mesenchymal stromal cells(MSCs) are multipotent and self-renewing stem cells that have great potential as cell therapy for autoimmune and inflammatory disorders, as well as for other clinical conditions, due to their immunoregulatory and regenerative properties. MSCs modulate the inflammatory milieu by releasing soluble factors and acting through cell-to-cell mechanisms. MSCs switch the classical inflammatory status of monocytes and macrophages towards a nonclassical and anti-inflammatory phenotype. This is characterized by an increased secretion of anti-inflammatory cytokines, a decreased release of pro-inflammatory cytokines, and changes in the expression of cell membrane molecules and in metabolic pathways. The MSC modulation of monocyte and macrophage phenotypes seems to be critical for therapy effectiveness in several disease models, since when these cells are depleted, no immunoregulatory effects are observed. Here, we review the effects of living MSCs(metabolically active cells) and metabolically inactive MSCs(dead cells that lost metabolic activity by induced inactivation) and their derivatives(extracellular vesicles, soluble factors, extracts, and microparticles) on the profile of macrophages and monocytes and the implications for immunoregulatory and reparative processes. This review includes mechanisms of action exhibited in these different therapeutic appro-aches, which induce the antiinflammatory properties of monocytes and macrophages. Finally, we overview several possibilities of therapeutic applications of these cells and their derivatives, with results regarding monocytes and macrophages in animal model studies and some clinical trials.     

Different priming strategies improve distinct therapeutic capabilities of mesenchymal stromal/stem cells: Potential implications for their clinical use

Mesenchymal stromal/stem cells (MSCs) have shown significant therapeutic potential, and have therefore been extensively investigated in preclinical studies of regenerative medicine. However, while MSCs have been shown to be safe as a cellular treatment, they have usually been therapeutically ineffective in human diseases. In fact, in many clinical trials it has been shown that MSCs have moderate or poor efficacy. This inefficacy appears to be ascribable primarily to the heterogeneity of MSCs. Recently, specific priming strategies have been used to improve the therapeutic properties of MSCs. In this review, we explore the literature on the principal priming approaches used to enhance the preclinical inefficacy of MSCs. We found that different priming strategies have been used to direct the therapeutic effects of MSCs toward specific pathological processes. Particularly, while hypoxic priming can be used primarily for the treatment of acute diseases, inflammatory cytokines can be used mainly to prime MSCs in order to treat chronic immune-related disorders. The shift in approach from regeneration to inflammation implies, in MSCs, a shift in the production of functional factors that stimulate regenerative or anti-inflammatory pathways. The opportunity to fine-tune the therapeutic properties of MSCs through different priming strategies could conceivably pave the way for optimizing their therapeutic potential.     

间充质干细胞与肿瘤形成的研究进展

间充质干细胞(Mesenchymal stem cells,MSCs)具有独特的免疫调节作用、自我更新和跨胚层多向分化的潜能,存在于许多组织中并活跃地向组织损伤部位迁移,参与伤口修复。在对肿瘤的信号发生反应后,MSCs不断被招募并成为肿瘤微环境的成分。肿瘤相关MSCs(Tumor-associated MSCs, TA-MSCs)在肿瘤发生、促进、进展和转移中有重要作用。本文对MSCs在调节肿瘤细胞的存活、增殖、迁移、药物抵抗中如何发挥作用,以及MSCs对肿瘤微环境免疫状态的影响作一综述。我们强调了MSCs和其他肿瘤基质细胞之间的复杂关系,特别是炎症细胞可以改变肿瘤微环境的免疫状态,以期通过对TA-MSCs进一步的研究来取得对不同肿瘤类型和肿瘤进展不同阶段中肿瘤相关MSCs功能的更好的理解,并优化MSCs来得到更有效和安全的MSCs为基础的肿瘤治疗。MSCs已被有效用于治疗慢性炎性疾病和慢性损伤,因此,其机制方面的研究还有利于在其他疾病中合理利用MSCs从而达到疾病治疗的目的。     

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.     

Phenotypic and functional heterogeneity of human bone marrow- and amnion-derived MSC subsets

Bone marrow-derived mesenchymal stromal/stem cells (MSCs) are nonhematopoietic cells that are able to differentiate into osteoblasts, adipocytes, and chondrocytes. In addition, they are known to participate in niche formation for hematopoietic stem cells and to display immunomodulatory properties. Conventionally, these cells are functionally isolated from tissue based on their capacity to adhere to the surface of culture flasks. This isolation procedure is hampered by the unpredictable influence of secreted molecules, the interactions between cocultured hematopoietic and other unrelated cells, and by the arbitrarily selected removal time of nonadherent cells before the expansion of MSCs. Finally, functionally isolated cells do not provide biological information about the starting population. To circumvent these limitations, several strategies have been developed to facilitate the prospective isolation of MSCs based on the selective expression, or absence, of surface markers. In this report, we summarize the most frequently used markers and introduce new targets for antibody-based isolation procedures of primary bone marrow- and amnion-derived MSCs.     

Mesenchymal stem cells and skin wound repair and regeneration: possibilities and questions

Adult mesenchymal stem cells (MSCs) have the capacity for self-renewal and for differentiating into a variety of cells and tissues. They may leave their niche to migrate to remote tissues and play a critical role in wound repair and tissue regeneration. Because of their multipotency, easy isolation and culture, highly expansive potential, and immunosuppression properties, these cells may be an attractive therapeutic tool for regenerative medicine and tissue engineering. Several studies have indicated a contribution of MSCs to reconstituting skin in cutaneous wounds, but problems still need resolution before MSCs can be widely used clinically. This review focuses mainly on the benefits of MSCs in skin wound healing and tissue regeneration and on the questions that remain to be answered before MSCs can be used in clinical practice. This study was supported in part by the National Natural Science Foundation of China (30730090, 30672176, 30500194) and by State Key Development Program of Basic Research of China (973 Program, 2005CB522603).     

Are mesenchymal stem cells in rheumatoid arthritis the good or bad guys?

The advancements in our understanding of the inflammatory and immune mechanisms in rheumatoid arthritis (RA) have fuelled the development of targeted therapies that block cytokine networks and pathogenic immune cells, leading to a considerable improvement in the management of RA patients. Nonetheless, no therapy is curative and clinical remission does not necessarily correspond to non-progression of joint damage. Hence, the biomedical community has redirected scientific efforts and resources towards the investigation of other biological aspects of the disease, including the mechanisms driving tissue remodelling and repair. In this regard, stem cell research has attracted extraordinary attention, with the ultimate goal to develop interventions for the biological repair of damaged tissues in joint disorders, including RA. The recent evidence that mesenchymal stem cells (MSCs) with the ability to differentiate into cartilage are present in joint tissues raises an opportunity for therapeutic interventions via targeting intrinsic repair mechanisms. Under physiological conditions, MSCs in the joint are believed to contribute to the maintenance and repair of joint tissues. In RA, however, the repair function of MSCs appears to be repressed by the inflammatory milieu. In addition to being passive targets, MSCs could interact with the immune system and play an active role in the perpetuation of arthritis and progression of joint damage. Like MSCs, fibroblast-like synoviocytes (FLSs) are part of the stroma of the synovial membrane. During RA, FLSs undergo proliferation and contribute to the formation of the deleterious pannus, which mediates damage to articular cartilage and bone. Both FLSs and MSCs are contained within the mononuclear cell fraction in vitro, from which they can be culture expanded as plastic-adherent fibroblast-like cells. An important question to address relates to the relationship between MSCs and FLSs. MSCs and FLSs could be the same cell type with functional specialisation or represent different functional stages of the same stromal lineage. This review will discuss the roles of MSCs in RA and will address current knowledge of the relative identity between MSCs and FLSs. It will also examine the immunomodulatory properties of the MSCs and the potential to harness such properties for the treatment of RA.     

Immunomodulatory properties of dental tissue-derived mesenchymal stem cells: Implication in disease and tissue regeneration

Mesenchymal stem cells (MSCs) are considered as an attractive tool for tissue regeneration and possess a strong immunomodulatory ability. Dental tissue-derived MSCs can be isolated from different sources, such as the dental pulp, periodontal ligament, deciduous teeth, apical papilla, dental follicles and gingiva. According to numerous in vitro studies, the effect of dental MSCs on immune cells might depend on several factors, such as the experimental setting, MSC tissue source and type of immune cell preparation. Most studies have shown that the immunomodulatory activity of dental MSCs is strongly upregulated by activated immune cells. MSCs exert mostly immunosuppressive effects, leading to the dampening of immune cell activation. Thus, the reciprocal interaction between dental MSCs and immune cells represents an elegant mechanism that potentially contributes to tissue homeostasis and inflammatory disease progression. Although the immunomodulatory potential of dental MSCs has been extensively investigated in vitro, its role in vivo remains obscure. A few studies have reported that the MSCs isolated from inflamed dental tissues have a compromised immunomodulatory ability. Moreover, the expression of some immunomodulatory proteins is enhanced in periodontal disease and even shows some correlation with disease severity. MSC-based immunomodulation may play an essential role in the regeneration of different dental tissues. Therefore, immunomodulation-based strategies may be a very promising tool in regenerative dentistry.     

Increased Proliferation and Analysis of Differential Gene Expression in Human Wharton's Jelly-derived Mesenchymal Stromal Cells under Hypoxia

Multipotent mesenchymal stromal cells (MSCs) from Wharton''s jelly (WJ) of umbilical cord bear higher proliferation rate and self-renewal capacity than adult tissue-derived MSCs and are a primitive stromal cell population. Stem cell niche or physiological microenvironment plays a crucial role in maintenance of stem cell properties and oxygen concentration is an important component of the stem cell niche. Low oxygen tension or hypoxia is prevalent in the microenvironment of embryonic stem cells and many adult stem cells at early stages of development. Again, in vivo, MSCs are known to home specifically to hypoxic events following tissue injuries. Here we examined the effect of hypoxia on proliferation and in vitro differentiation potential of WJ-MSCs. Under hypoxia, WJ-MSCs exhibited improved proliferative potential while maintaining multi-lineage differentiation potential and surface marker expression. Hypoxic WJ-MSCs expressed higher mRNA levels of hypoxia inducible factors, notch receptors and notch downstream gene HES1. Gene expression profile of WJ-MSCs exposed to hypoxia and normoxia was compared and we identified a differential gene expression pattern where several stem cells markers and early mesodermal/endothelial genes such as DESMIN, CD34, ACTC were upregulated under hypoxia, suggesting that in vitro culturing of WJ-MSCs under hypoxic conditions leads to adoption of a mesodermal/endothelial fate. Thus, we demonstrate for the first time the effect of hypoxia on gene expression and growth kinetics of WJ-MSCs. Finally, although WJ-MSCs do not induce teratomas, under stressful and long-term culture conditions, MSCs can occasionally undergo transformation. Though there were no chromosomal abnormalities, certain transformation markers were upregulated in a few of the samples of WJ-MSCs under hypoxia.     

WJSC 6th Anniversary Special Issues（2）:Mesenchymal stem cells Brain mesenchymal stem cells:The other stem cells of the brain?

Multipotent mesenchymal stromal cells(MSC),have the potential to differentiate into cells of the mesenchymal lineage and have non-progenitor functions including immunomodulation.The demonstration that MSCs are perivascular cells found in almost all adult tissues raises fascinating perspectives on their role in tissue maintenance and repair.However,some controversies about the physiological role of the perivascular MSCs residing outside the bone marrow and on their therapeutic potential in regenerative medicine exist.In brain,perivascular MSCs like pericytes and adventitial cells,could constitute another stem cell population distinct to the neural stem cell pool.The demonstration of the neuronal potential of MSCs requires stringent criteria including morphological changes,the demonstration of neural biomarkers expression,electrophysiological recordings,and the absence of cell fusion.The recent finding that brain cancer stem cells can transdifferentiate into pericytes is another facet of the plasticity of these cells.It suggests that the perversion of the stem cell potential of pericytes might play an even unsuspected role in cancer formation and tumor progression.