Stem Cell Research & Therapy | Full text | Mesenchymal stem …

Abstract Introduction

Mesenchymal stem cells (MSCs) are adult, multipotent, stem cells with immunomodulatory properties. The mechanisms involved in the capacity of MSCs to inhibit the proliferation of proinflammatory T lymphocytes, which appear responsible for causing autoimmune disease, have yet to be fully elucidated. One of the underlying mechanisms studied recently is the ability of MSCs to generate T regulatory (Treg) cells in vitro and in vivo from activated peripheral blood mononuclear cells (PBMC), T-CD4+ and also T-CD8+ cells. In the present work we investigated the capacity of MSCs to generate Treg cells using T-CD4+ cells induced to differentiate toward the proinflammatory Th1 and Th17 lineages.

MSCs were obtained from mouse bone marrow and characterized according to their surface antigen expression and their multilineage differentiation potential. CD4+ T cells isolated from mouse spleens were induced to differentiate into Th1 or Th17 cells and co-cultured with MSCs added at day 0, 2 or 4 of the differentiation processes. After six days, CD25, Foxp3, IL-17 and IFN- expression was assessed by flow cytometry and helios and neuropilin 1 mRNA levels were assessed by RT-qPCR. For the functional assays, the conditioned subpopulation generated in the presence of MSCs was cultured with concanavalin A-activated CD4+ T cells labeled with carboxyfluorescein succinimidyl ester. Finally, we used the encephalomyelitis autoimmune diseases (EAE) mouse model, in which mice were injected with MSCs at day 18 and 30 after immunization. At day 50, the mice were euthanized and draining lymph nodes were extracted for Th1, Th17 and Treg detection by flow cytometry.

MSCs were able to suppress the proliferation, activation and differentiation of CD4+ T cells induced to differentiate into Th1 and Th17 cells. This substantial suppressive effect was associated with an increase of the percentage of functional induced CD4+CD25+Foxp3+ regulatory T cells and IL-10 secretion. However, using mature Th1 or Th17 cells our results demonstrated that while MSCs suppress the proliferation and phenotype of mature Th1 and Th17 cells they did not generate Treg cells. Finally, we showed that the beneficial effect observed following MSC injection in an EAE mouse model was associated with the suppression of Th17 cells and an increase in the percentage of CD4+CD25+Foxp3+ T lymphocytes when administrated at early stages of the disease.

This study demonstrated that MSCs contribute to the generation of an immunosuppressive environment via the inhibition of proinflammatory T cells and the induction of T cells with a regulatory phenotype. Together, these results might have important clinical implications for inflammatory and autoimmune diseases.

Mesenchymal stem cells (MSCs) are multipotent stromal cells characterized by their ability to differentiate into cells from mesodermal tissue making them an interesting cell source for application in regenerative medicine [1,2]. Another attractive potential of MSCs is their capacity to inhibit the proliferation of T and B lymphocytes, natural killer and dendritic cells both in vitro and in vivo[3-6]. These immunosuppressive abilities are mediated by different mechanisms specific for human or mouse MSCs, such as indoleamine 2,3-dioxygenase (IDO) or nitric oxide (NO), respectively, or overlapping suppressive factors, such as transforming growth factor 1 (TGF-1), prostaglandin E2 (PGE2) and IL-10 among others [7-9]. Moreover, it has been shown that MSCs are able to generate CD4+CD25+high Foxp3+ T regulatory (Treg) cells in vitro, from activated human peripheral blood mononuclear cells (PBMC), mouse splenocytes or isolated T-CD4 cells. Indeed, MSCs promote the induction of CD4+CD25+high regulatory cells from human PBMC cells activated with IL-2 [10]. In the same line, Maccario et al. demonstrated that MSCs favor the differentiation of CD4+ T-cell subsets co-expressing CD25 and/or CTLA4, two markers of Treg cells [11]. These observations were supported and extended by a study showing that direct MSC-T cell contact is required for Foxp3 and CD25High expression by CD4+ T cells; however, soluble factors produced by MSCs, such as TGF-1 and PGE2, also played a non-redundant contribution in the generation of CD4+CD25+Foxp3+[8]. A role for other molecules including the human leukocyte antigen-G5 (HLA-G5) and the stress inducible enzyme heme-oxygenase-1 (HO-1) has also been described in the generation of regulatory T cell phenotype mediated by human MSCs [12,13]. The ability of MSCs to induce such a regulatory phenotype in T cells was described both in vitro and in vivo. As an example, in a mouse animal model of inflammatory bowel disease (IBD), the beneficial effect of injected human adipose derived MSCs (hASCs) on the clinical and histological scores of mice was associated with an increased number of CD4+CD25+Foxp3+ and CD4+IL10+ cells in the lymph nodes [14]. The induction of a regulatory T cell phenotype population has also been shown in clinical applications. Indeed, a significant induction of CD4+CD25+Foxp3+ cells was observed in two systemic lupus erythematous (SLE) patients [15]. Moreover, after autologous MSC administration in patients with kidney transplantation, Perico et al. reported not only an increase in the number of CD4+CD25+Foxp3+ cells but also a substantial decrease of the activity of CD4+ and CD8+ effectors as well as a subsequent improvement in their renal function [16].

In the context of inflammatory diseases, T helper 1 (Th1) and Th17 T cell subsets are well known to mediate inflammation [17,18]. Interestingly, we showed that MSCs inhibit human Th17 cell differentiation and function and induce a regulatory T cell phenotype [19]. This result revealed that, even under inflammatory conditions, MSCs exert in vitro anti-inflammatory effects through the induction of a regulatory T cell phenotype. However, the capacity of MSCs to generate functional Treg cells in vitro during the differentiation process or on fully differentiated Th1 and Th17 cells still remains to be elucidated. Therefore, in this study, we explored the capacity of MSCs to generate, in vitro, functional CD4+CD25+Foxp3+ Treg cells under Th1 and Th17 inflammatory culture conditions. In parallel, in the experimental autoimmune encephalomyelitis (EAE) model, we assessed the percentage of regulatory T cells after MSC administration at two different time points post-immunization. The aim of this study was to determine whether MSCs are able to increase the percentage of regulatory T cells in vitro when co-cultured with either CD4+ cells induced to differentiate into Th1 and Th1 or with fully differentiated Th1 and Th17 cells and in vivo in the EAE model.

MSCs were isolated from eight- to ten-week-old C57BL/6 mice. Bone marrow cells were collected by flushing femurs and tibias and the cell suspension (1 106cells/cm2) was plated in a modified minimum essential Eagle's medium (MEM) (-MEM, Gibco, Auckland, NZ) supplemented with 20% fetal bovine serum (FBS) (Hyclone, Thermo Fisher Scientific, Brebires, France), 2 mM glutamine and 100 U/mL penicillin with 100 mg/mL streptomycin (Gibco, Auckland, NZ) (-20). At sub-confluence, cells were replated at a density of 20,000 cells/cm2 and, after the second passage, MSCs were isolated by
negative selection using a CD45+ microbeads kit (Miltenyi Biotec, Bergisch-Gladbach, Germany). MSCs were characterized for expression of hematopoietic and mesenchymal cell antigens by fluorescence-activated cell sorting (FACS) analysis and by their capacity to differentiate into adipogenic, chondrogenic and osteogenic lineages as previously described [20].

CD4+ T cells from spleen of C57BL/6 mice were purified by negative selection using the CD4+ T cell Isolation Kit MicroBeads (Miltenyi Biotec) according to the manufacturers instructions. Purified CD4+ T cells were cultured in complete medium containing RPMI 1640 supplemented with 10% heat-inactivated FBS, 2 mM l-glutamine, 100 U/mL penicillin/100 g/mL streptomycin. In a 24-well plate, 2 106 CD4+ T cells were cultured in the presence of 2.5 g/ml coated antibodies against CD3 and 1.5 g/ml CD28 (BD Biosciences, San Jose, CA, USA) under Th1 or Th17 differentiation conditions. Th1 cells were differentiated with 20 ng/ml of IL-12 (R&D Systems, Minneapolis, MN, USA) and 2.5 g/ml anti-IL-4 antibodies (BD Biosciences). Th17 cells were differentiated with 50 ng/ml IL-6 (R&D Systems, Minneapolis, MN, USA), 5 ng/ml of TGF-1 (BioVision, Milpitas, CA USA) and 2.5 g/ml of anti-IFN- and -IL-4 antibodies (BD Biosciences). MSCs were added at a MSC:Th ratio of 1:10 or 1:100 at day 0, 2 or 4 of the Th1 and Th17 differentiation process. After six days of culture, relative cell quantification was measured using the CellTiter-Glo luminescent cell viability assay (Promega, Charbonnires-les-Bains, France) and intracellular cytokine detection was measured by flow cytometry.

After six days of culture, T cells were stimulated for four hours with 50 ng/ml phorbolmyristate acetate (PMA) (Sigma-Aldrich, St Louis, MO, USA) and 1g/ml ionomycin (Sigma-Aldrich), prior to the addition of 10 g/ml brefeldin A (eBiosciences, San Diego, CA, USA). For the detection of surface markers, cells were stained with CD4-PEcy5 (eBiosciences) and CD25-PE-texas red (Invitrogen, Grand Island, NY, USA) and incubated for 20 minutes at 4C in the dark. After two washing steps, we performed intracellular staining for IFN--FITC, IL-17-PE or FoxP3-Alexa488 detection. For that purpose, cells were fixed and permeabilized using the Cytofix/Cytoperm (BD Biosciences) kit according to the manufacturers instructions. Acquisition was performed with a Coulter Epics-XL flow cytometer using the System II software (Coulter Corporation, Brea, CA, USA). Analysis was performed using the FCS express software (De novo softwares, Los Angeles, CA, USA).

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Stem Cell Research & Therapy | Full text | Mesenchymal stem ...