Christian Jorgensen

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.

Mesenchymal Stem Cells Inhibit Human Th17 Cell Differentiation and Function and Induce a T Regulatory Cell Phenotype

Mesenchymal stem cells (MSCs) exert immunomodulatory properties via the inhibition of T cell activation and proliferation. Because of the deleterious role of Th17 cells in the pathogenesis of inflammatory disease, we investigated whether proinflammatory cytokines could modify the expression of adhesion molecules on human MSCs, thereby contributing to increased Th17 cell adhesion to MSCs and, as a consequence, modulating the function of the latter cells. IFN-γ and TNF-α synergistically enhanced the expression of CD54 by MSCs, enabling the CCR6 chemokine ligand CCL20 to induce in vitro adhesion of Th17 cells to MSCs. MSCs prevented the in vitro differentiation of naive CD4+ T cells into Th17 cells and inhibited the production of IL-17, IL-22, IFN-γ, and TNF-α by fully differentiated Th17 cells; this was mediated, in part, via PGE2, the production of which was enhanced in cocultures with Th17 cells. Moreover, MSCs induced the production of IL-10 and trimethylation of histone H3K4me3 at the promoter of the FOXP3 gene locus, whereas it suppressed trimethylation of the corresponding region in the RORC gene in Th17 cells. These epigenetic changes were associated with the induction of fork head box p3 and the acquisition by Th17 cells of the capacity to inhibit in vitro proliferative responses of activated CD4+ T cells, which was enhanced when MSCs were preincubated with IFN-γ and TNF-α. These results showed that, under inflammatory conditions, MSCs mediate the adhesion of Th17 cells via CCR6 and exert anti-inflammatory effects through the induction of a T cell regulatory phenotype in these cells.

Cartilage engineering: a crucial combination of cells, biomaterials and biofactors

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. The lack of efficient modalities of treatment has prompted research into 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 potential of biomaterial-assisted cell therapy for cartilage engineering. We discuss the requirements for identifying additional specific growth factors and evaluating the optimal combination of cells, growth factors and scaffolds that is able to respond to the functional demand placed upon cartilage tissue replacement in clinics. Finally, some of the major obstacles encountered in cartilage engineering are discussed, as well as future trends in clinical applications.

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

Cell specific differences between human adipose-derived and mesenchymal–stromal cells despite similar differentiation potentials

Stromal cells from bone marrow and adipose tissue are attractive sources of adult progenitors for cell-based therapy. However, whether those cell populations represent intrinsically different cell types is still largely under debate. The aim of this study was to systematically and quantitatively compare adipose-derived stromal cells (ADSC) and bone marrow-derived multipotent mesenchymal-stromal cells (BM-MSC). The quantitative comparison was realized using Taqman Low Density Array, 2D electrophoresis and differentiation functional assays in vitro. Furthermore, cells engineered to express TGFbeta1 were injected into the intra-articular space of mouse knee joints in order to determine whether they were able to form new differentiated tissues in vivo. Our data revealed cell specific differences at transcriptional and proteomic levels between both cell types according to their tissue origin as well as functional differences in their differentiation processes towards adipogenic, osteogenic and chondrogenic programs. Nevertheless, in vitro as well as in vivo ADSC displayed the same ability than MSC to differentiate towards chondrocytes/osteoblasts, comforting the status of both cell sources as promising regenerative cells. In summary, our observations indicate that ADSC and MSC are fundamentally different cell types and differently committed cells.

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.

Short-Term BMP-2 Expression Is Sufficient for In Vivo Osteochondral Differentiation of Mesenchymal Stem Cells

Currently available murine models to evaluate mesenchymal stem cell (MSC) differentiation are based on cell injection at ectopic sites such as muscle or skin. Due to the importance of environmental factors on the differentiation capacities of stem cells in vivo, we investigated whether the peculiar synovial/cartilaginous environment may influence the lineage specificity of bone morphogenetic protein (BMP)‐2‐engineered MSCs. To this aim, we used the C3H10T1/2‐derived C9 MSCs that express BMP‐2 under control of the doxycycline (Dox)‐repressible promoter, Tet‐Off, and showed in vitro, using the micropellet culture system that C9 MSCs kept their potential to differentiate toward chondrocytes. Implantation of C9 cells, either into the tibialis anterior muscles or into the joints of CB17‐severe combined immunodeficient bg mice led to the formation of cartilage and bone filled with bone marrow as soon as day 10. However, no differentiation was observed after injection of naïve MSCs or C9 cells that were repressed to secrete BMP‐2 by Dox addition. The BMP‐2‐induced differentiation of adult MSCs is thus independent of soluble factors present in the local environment of the synovial/cartilaginous tissues. Importantly, we demonstrated that a short‐term expression of the BMP‐2 growth factor is necessary and sufficient to irreversibly induce bone formation, suggesting that a stable genetic modification of MSCs is not required for stem cell‐based bone/cartilage engineering.

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.

Concise review: adult multipotent stromal cells and cancer: risk or benefit?

This review focuses on the interaction between multipotent stromal cells (MSCs) and carcinoma and the possible use of MSCs in cell‐based anticancer therapies. MSCs are present in multiple tissues and are defined as cells displaying the ability to differentiate in multiple lineages, including chondrocytes, osteoblasts, and adipocytes. Recent evidence also suggests that they could play a role in the progression of carcinogenesis and that MSCs could migrate toward primary tumors and metastatic sites. It is possible that MSCs could also be involved in the early stages of carcinogenesis through spontaneous transformation. In addition, it is thought that MSCs can modulate tumor growth and metastasis, although this issue remains controversial and not well understood. The immunosuppressive properties and proangiogenic properties of MSCs account, at least in part, for their effects on cancer development. On the other hand, cancer cells also have the ability to enhance MSC migration. This complex dialog between MSCs and cancer cells is certainly critical for the outcome of tumor development. Interestingly, several studies have shown that MSCs engineered to express antitumor factors could be an innovative choice as a cell‐mediated gene therapy to counteract tumor growth. More evidence will be needed to understand how MSCs positively or negatively modulate carcinogenesis and to evaluate the safety of MSC use in cell‐mediated gene strategies.

Transcriptional profiles discriminate bone marrow-derived and synovium-derived mesenchymal stem cells

Previous studies have reported that mesenchymal stem cells (MSC) may be isolated from the synovial membrane by the same protocol as that used for synovial fibroblast cultivation, suggesting that MSC correspond to a subset of the adherent cell population, as MSC from the stromal compartment of the bone marrow (BM). The aims of the present study were, first, to better characterize the MSC derived from the synovial membrane and, second, to compare systematically, in parallel, the MSC-containing cell populations isolated from BM and those derived from the synovium, using quantitative assays. Fluorescent-activated cell sorting analysis revealed that both populations were negative for CD14, CD34 and CD45 expression and that both displayed equal levels of CD44, CD73, CD90 and CD105, a phenotype currently known to be characteristic of BM-MSC. Comparable with BM-MSC, such MSC-like cells isolated from the synovial membrane were shown for the first time to suppress the T-cell response in a mixed lymphocyte reaction, and to express the enzyme indoleamine 2,3-dioxygenase activity to the same extent as BM-MSC, which is a possible mediator of this suppressive activity. Using quantitative RT-PCR these data show that MSC-like cells from the synovium and BM may be induced to chondrogenic differentiation and, to a lesser extent, to osteogenic differentiation, but the osteogenic capacities of the synovium-derived MSC were significantly reduced based on the expression of the markers tested (collagen type II and aggrecan or alkaline phosphatase and osteocalcin, respectively). Transcription profiles, determined with the Atlas Human Cytokine/Receptor Array, revealed discrimination between the MSC-like cells from the synovial membrane and the BM-MSC by 46 of 268 genes. In particular, activin A was shown to be one major upregulated factor, highly secreted by BM-MSC. Whether this reflects a different cellular phenotype, a different amount of MSC in the synovium-derived population compared with BM-MSC adherent cell populations or the impact of a different microenvironment remains to be determined. In conclusion, although the BM-derived and synovium-derived MSC shared similar phenotypic and functional properties, both their differentiation capacities and transcriptional profiles permit one to discriminate the cell populations according to their tissue origin.