Extracellular Vesicles of Mesenchymal Stromal Cells Can be Taken Up by Microglial Cells and Partially Prevent the Stimulation Induced by ß-amyloid.

Mesenchymal stromal/stem cells (MSCs) have great capacity for immune regulation. MSCs provide protective paracrine effects, which are partially exerted by extracellular vesicles (EVs). It has been reported that MSCs-derived EVs (MSC-EVs) contain soluble factors, such as cytokines, chemokines, growth factors and even microRNAs, which confer them similar anti-inflammatory and regenerative effects to MSCs. Moreover, MSCs modulate microglia activation through a dual mechanism of action that relies both on cell contact and secreted factors. Microglia cells are the central nervous system immune cells and the main mediators of the inflammation leading to neurodegenerative disorders. Here, we investigated whether MSC-EVs affect the activation of microglia cells by ß-amyloid aggregates. We show that the presence of MSC-EVs can prevent the upregulation of pro-inflammatory mediators such as tumor necrosis factor (TNF)-α and nitric oxide (NO). Both are up-regulated in neurodegenerative diseases representing chronic inflammation, as in Alzheimer's disease. We demonstrate that MSC-EVs are internalized by the microglia cells. Further, our study supports the use of MSC-EVs as a promising therapeutic tool to treat neuroinflammatory diseases.Significance StatementIt has been reported that mesenchymal stromal/stem cells and MSC-derived small extracellular vesicles have therapeutic effects in the treatment of various degenerative and inflammatory diseases. Extracellular vesicles are loaded with proteins, lipids and RNA and act as intercellular communication mediators. Here we show that extracellular vesicles can be taken up by murine microglial cells. In addition, they partially reduce the activation of microglial cells against ß-amyloid aggregates. This inhibition of microglia activation may present an effective strategy for the control/therapy of neurodegenerative diseases such as Alzheimer's disease.

Mesenchymal Stem Cell-Derived Microvesicles Modulate Lipopolysaccharides-Induced Inflammatory Responses to Microglia Cells.

Microglia cells are the central nervous system immune cells and have been pointed out as the main mediators of the inflammation leading to neurodegenerative disorders. Mesenchymal stromal cells (MSCs) are a heterogeneous population of cells with very high self-renewal properties and uncomplicated in vitro culture. Research has shown that MSCs have the capacity to induce tissue regeneration and reduce inflammation. Studies demonstrated that MSCs have complex paracrine machineries involving shedding of cell-derived microvesicles (MVs), which entail part of the regulatory and regenerative activity of MSCs, as observed in animal models. We proposed MSC-derived MVs as potent regulators of microglia activation and used an in vitro model of stimulation for BV-2 cells, a microglia cell line, with lipopolysaccharides (LPS). Here we demonstrated that presence of MSCs-derived MVs (MSC-MVs) prevents Tumor necrosis factor-α, Interleukin (IL)-1ß and IL-6 upregulation by BV-2 cells and primary microglia cells toward LPS. Also, inducible isoform of nitric oxide synthases and Prostaglandin-endoperoxide synthase 2 upregulation were hampered in presence of MSC-MVs. Higher levels of the M2 microglia marker chemokine ligand-22 were detectable in BV-2 cells after coculture with MSC-MVs in presence and absence of LPS. Moreover, upregulation of the activation markers CD45 and CD11b by BV-2 cells was prevented when cocultured with MSC-MVs. Furthermore, MSC-MVs suppressed the phosphorylation of the extracellular signal kinases 1/2, c-Jun N-terminal kinases and the p38 MAP kinase (p38) molecules. Consequently, MSC-MVs might represent a modulator of microglia activation with future therapeutic impact. Stem Cells 2017;35:812-823.

Anti-human CD4 induces peripheral tolerance in a human CD4+, murine CD4-, HLA-DR+ advanced transgenic mouse model.

Selection in vivo of potent mAbs to human CD4 useful for immunotherapy, e.g., for the induction of immunological tolerance, is restricted for ethical reasons. We therefore used multiple transgenic mice that lack murine CD4, but express human CD4 specifically on Th cells, and HLA-DR3 as its natural counterligand (CD4/DR3 mice). The injection of CD4/DR3 mice with anti-human CD4 (mAb Max.16H5) before immunization with tetanus toxoid (TT, day 0) totally blocked the formation of specific Abs. This state of unresponsiveness persisted a subsequent boost again performed in the presence of anti-human CD4. When these mice were left untreated for at least 40 days, and were then re-exposed with TT, but in the absence of anti-human CD4, they consistently failed to induce specific Abs (long-term unresponsiveness). Exposure to second party Ags (hen egg lysozyme, human acetylcholine receptor) induced specific Abs comparable with control mice, demonstrating that the anti-CD4-induced unresponsiveness was Ag specific (immunological tolerance). Importantly, the concurrent injection of TT and anti-human CD4 at day 0, followed by another two anti-CD4 treatments, also led to tolerant animals, indicating that tolerance was inducible at the same day as the Ag exposure is provided. We finally demonstrate a limited ability of spleen cells to respond to TT in vitro, indicating that T cells are essentially involved in the maintenance of TT-specific tolerance. These data show for the first time that the human CD4 coreceptor mediates tolerance-inducing signals when triggered by an appropriate ligand in vivo.