Carine Bouffi

Mesenchymal Stem Cells Inhibit the Differentiation of Dendritic Cells Through an Interleukin‐6‐Dependent Mechanism

Mesenchymal stem cells (MSC) are of particular interest for their potential clinical use in tissue engineering as well as for their capacity to reduce the incidence and severity of graft‐versus‐host disease in allogeneic transplantation. We have previously shown that MSC‐mediated immune suppression acts via the secretion of soluble factor(s) induced upon stimulation. The aim of this study was to identify the molecule(s) involved and the underlying mechanism(s). We show that murine MSC secrete high levels of interleukin (IL)‐6 and vascular endothelial growth factor, which are directly correlated to the inhibition of T‐cell proliferation. The T‐cell activation is partially restored upon addition of a neutralizing anti‐IL‐6 antibody or the prostaglandin E2 inhibitor indomethacin. Interestingly, no indoleamine 2,3‐dioxygenase activity was detected in our conditions. Instead, we show that MSC reduce the expression of major histocompatibility complex class II, CD40, and CD86 costimulatory molecules on mature dendritic cells (DC), which was responsible for a decrease in T‐cell proliferation. Moreover, we show that the differentiation of bone marrow progenitors into DC cultured with conditioned supernatants from MSC was partly inhibited through the secretion of IL‐6. Altogether, these data suggest that IL‐6 is involved in the immunoregulatory mechanism mediated by MSC through a partial inhibition of DC differentiation but is probably not the main mechanism.

Immunosuppression by mesenchymal stem cells: mechanisms and clinical applications

Mesenchymal stem cells (MSCs) are multipotential nonhematopoietic progenitor cells that are isolated from many adult tissues, in particular from the bone marrow and adipose tissue. Along with their capacity for differentiating into cells of mesodermal lineage, such as adipocytes, osteoblasts and chondrocytes, these cells have also generated great interest for their ability to display immunomodulatory capacities. Indeed, a major breakthrough came with the finding that they are able to induce peripheral tolerance, suggesting they may be used as therapeutic tools in immune-mediated disorders. The present review aims at discussing the current knowledge on the targets and mechanisms of MSC-mediated immunosuppression as well as the potential use of MSCs as modulators of immune responses in a variety of diseases related to alloreactive immunity or autoimmunity

IL-6-Dependent PGE2 Secretion by Mesenchymal Stem Cells Inhibits Local Inflammation in Experimental Arthritis

Background Based on their capacity to suppress immune responses, multipotent mesenchymal stromal cells (MSC) are intensively studied for various clinical applications. Although it has been shown in vitro that the immunomodulatory effect of MSCs mainly occurs through the secretion of soluble mediators, the mechanism is still not completely understood. The aim of the present study was to better understand the mechanisms underlying the suppressive effect of MSCs in vivo, using cells isolated from mice deficient in the production of inducible nitric oxide synthase (iNOS) or interleukin (IL)-6 in the murine model of collagen-induced arthritis. Principal Findings In the present study, we show that primary murine MSCs from various strains of mice or isolated from mice deficient for iNOS or IL-6 exhibit different immunosuppressive potential. The immunomodulatory function of MSCs was mainly attributed to IL-6-dependent secretion of prostaglandin E2 (PGE2) with a minor role for NO. To address the role of these molecules in vivo, we used the collagen-induced arthritis as an experimental model of immune-mediated disorder. MSCs effectively inhibited collagen-induced inflammation during a narrow therapeutic window. In contrast to wild type MSCs, IL-6-deficient MSCs and to a lesser extent iNOS-deficient MSCs were not able to reduce the clinical signs of arthritis. Finally, we show that, independently of NO or IL-6 secretion or Treg cell induction, MSCs modulate the host response by inducing a switch to a Th2 immune response. Significance Our data indicate that MSCs mediate their immunosuppressive effect via two modes of action: locally, they reduce inflammation through the secretion of anti-proliferative mediators, such as NO and mainly PGE2, and systemically they switch the host response from a Th1/Th17 towards a Th2 immune profile.

Mesenchymal stem cells: innovative therapeutic tools for rheumatic diseases

Mesenchymal stem cells (MSCs), or multipotent mesenchymal stromal cells as they are also known, have been identified in bone marrow as well as in other tissues of the joint, including adipose, synovium, periosteum, perichondrium, and cartilage. These cells are characterized by their phenotype and their ability to differentiate into three lineages: chondrocytes, osteoblasts and adipocytes. Importantly, MSCs also potently modulate immune responses, exhibit healing capacities, improve angiogenesis and prevent fibrosis. These properties might be explained at least in part by the trophic effects of MSCs through the secretion of a number of cytokines and growth factors. However, the mechanisms involved in the differentiation potential of MSCs, and their immunomodulatory and paracrine properties, are currently being extensively studied. These unique properties of MSCs confer on them the potential to be used for therapeutic applications in rheumatic diseases, including rheumatoid arthritis, osteoarthritis, genetic bone and cartilage disorders as well as bone metastasis.

Cartilage Tissue Engineering: Towards a Biomaterial-Assisted Mesenchymal Stem Cell Therapy

Injuries to articular cartilage are one of the most challenging issues of musculoskeletal medicine due to the poor intrinsic ability of this tissue for repair. Despite progress in orthopaedic surgery, the lack of efficient modalities of treatment for large chondral defects has prompted research on tissue engineering combining chondrogenic cells, scaffold materials and environmental factors. The aim of this review is to focus on the recent advances made in exploiting the potentials of cell therapy for cartilage engineering. These include: 1) defining the best cell candidates between chondrocytes or multipotent progenitor cells, such as multipotent mesenchymal stromal cells (MSC), in terms of readily available sources for isolation, expansion and repair potential; 2) engineering biocompatible and biodegradable natural or artificial matrix scaffolds as cell carriers, chondrogenic factors releasing factories and supports for defect filling, 3) identifying more specific growth factors and the appropriate scheme of application that will promote both chondrogenic differentiation and then maintain the differentiated phenotype overtime and 4) evaluating the optimal combinations that will answer to the functional demand placed upon cartilage tissue replacement in animal models and in clinics. Finally, some of the major obstacles generally encountered in cartilage engineering are discussed as well as future trends to overcome these limiting issues for clinical applications.

Multipotent mesenchymal stromal cells and immune tolerance

Multipotent mesenchymal stromal cells or mesenchymal stem cells (MSC) are isolated mainly from bone marrow and adipose tissue but are identified in other tissues such as synovium, periosteum or placenta. They are characterised by their property to adhere to plastic, their phenotype and their ability to differentiate into three lineages (chondrocytes, osteoblasts and adipocytes). More recently, these cells were shown to escape immune recognition and inhibit immune responses. MSC may modulate the function of the major immune cell populations, including antigen-presenting cells, T cells, B cells and natural killer cells. The aim of this review is to focus on the molecular mechanisms, still poorly understood, which are responsible of the immunosuppressive effects mediated by the MSC. Finally, the data obtained from in vivo experimentation in various animal models as well as potential therapeutic applications will be presented.

Multipotent mesenchymal stromal cells and rheumatoid arthritis: risk or benefit?

Multipotent mesenchymal stromal cells (MSCs) have raised interest mainly because of cartilage/bone differentiation potential which is now partly eclipsed by their capacity to counteract inflammation and suppress host immune responses as well as to prevent fibrosis. MSCs have been identified within joint tissues including synovium, cartilage, subchondral bone, periosteum or adipose tissue. They are characterized by their phenotype and their ability to differentiate into three lineages, chondrocytes, osteoblasts and adipocytes. MSCs have also paracrine effects through the secretion of a number of cytokines and growth factors. This may explain the trophic effects that may be of therapeutic value for rheumatic diseases including OA and RA. On the other hand, MSCs have been associated with tumour growth. MSCs migrate to the tumour stroma, express chemokines involved in the attraction of carcinoma cells in metastasis. Indeed, the aim of this review is not only to focus on new potential therapeutic applications in osteo-articular diseases, but also to assess the potential risk of MSC-based cell therapy.

Antitumoral Activity and Osteogenic Potential of Mesenchymal Stem Cells Expressing the Urokinase-Type Plasminogen Antagonist Amino-Terminal Fragment in a Murine Model of Osteolytic Tumor

Prostate cancer metastasis to bone results in mixed osteolytic and osteoblastic lesions associated with high morbidity, and there is mounting evidence that the urokinase‐type plasminogen system is causatively involved in the progression of prostate cancer. Adult mesenchymal stem cells (MSCs) are promising tools for cell‐mediated gene therapy with the advantage of osteogenic potential, a critical issue in the case of osteolytic metastases. In this study, we evaluated the therapeutic use of engineered murine MSCs for in vivo delivery of the urokinase‐type plasminogen antagonist amino‐terminal fragment (hATF) to impair osteolytic prostate cancer cell progression in bone and to repair bone lesions. Bioluminescence imaging revealed that both primary MSCs and the MSC line C3H10T1/2 (C3) expressing hATF (MSC‐hATF) significantly inhibited intratibial PC‐3 Luciferase (Luc) growth following coinjection in SCID mice. Furthermore, microcomputed tomography imaging of vascular network clearly demonstrated a significant decrease in tumor‐associated angiogenesis and a protection from tumor‐induced osteolysis in MSC‐hATF‐treated mice. Importantly, the osteogenic potential of MSC‐hATF cells was unaffected, and an area of new bone formation was evidenced in 60% of animals. Together, these data support the concept of MSC‐based therapy of tumor osteolysis disease, indicating that MSCs may combine properties of vehicle for angiostatic agent with osteogenic potential.

Multipotent mesenchymal stromal cells in articular diseases

Although cartilage defects are common features of osteoarthritis and rheumatoid arthritis, current treatments can rarely restore the full function of native cartilage. Recent studies have provided new perspectives for cartilage engineering using multipotent mesenchymal stromal cells (MSC). Moreover, MSC have been used as immunosuppressant agents in autoimmune diseases and have tested successfully in animal models of arthritis. However, the sequential events occurring during chondrogenesis must be fully understood before we can reproduce the complex molecular events that lead to MSC differentiation and long-term maintenance of cartilage characteristics in the context of chronic joint inflammation. This chapter focuses on the potential of MSC to repair cartilage, with an emphasis on the factors that are known to be required in inducing chondrogenesis and on their immunosuppressive potential.

Skin fibroblasts are potent suppressors of inflammation in experimental arthritis

Objectives Mesenchymal stromal cells (MSC) are characterised by their capacity to suppress immune reactions. This function was reported to be shared in vitro by fibroblasts but their role has been poorly investigated in vivo. This study explored whether fibroblasts isolated from skin may suppress the host immune response in a model of autoimmune disorder. Methods and Results It was first confirmed that skin fibroblasts lack the capacity to differentiate into osteoblasts or chondrocytes but possess the capacity to inhibit in vitro the proliferation of T lymphocytes. Fibroblasts also secrete modulatory molecules, in particular prostaglandin E2 and nitric oxide, similar to MSC. To assess their role in vivo, the collagen-induced arthritis model was used, and showed that similar to MSC the intravenous injection of fibroblasts efficiently suppress clinical signs of arthritis and delay disease onset. This effect was associated with reduced inflammation as reflected by biological parameters and increased levels of IL-5, IL-10 and IL-13 in the spleens of treated mice. To characterise the mechanism of immunosuppression further, phenotypic analyses were performed and could not detect any induction of CD4 CD25 Foxp3+ regulatory T (Treg) cells. A population of CD4 IL-10+ T cells was, however, detected that was slightly increased after fibroblast injection and significantly upregulated after MSC administration. Conclusions This study gives the first evidence for an immunosuppressive role of fibroblasts in vivo, and strongly suggests that fibroblasts induce a T-helper type 2 immune profile, although the possibility that IL-10-secreting Treg cells may be generated cannot be excluded.