Extracellular vesicles from mesenchymal stem cells prevent contact hypersensitivity through the suppression of Tc1 and Th1 cells and expansion of regulatory T cells.

Extracellular vesicles (EVs) secreted by mesenchymal stem cells (MSC-EVs) are taken more seriously as immunomodulatory and anti-inflammatory agents. We studied the therapeutic effects of MSC-EVs on allergic contact dermatitis (ACD), a typical T cell-mediated disorder. A contact hypersensitivity (CHS) mouse model for ACD was established and treated by intravenous MSC-EVs injection. We found that human umbilical cord MSC-EVs could significantly prevent the pathology of CHS, including reduced ear swelling and leukocyte infiltration. Injection of MSC-EVs significantly inhibited CD8+IFN-γ+ cytotoxic T (Tc1) cells and CD4+IFN-γ+ type 1 helper T (Th1) cells, and reduced the level of pro-inflammatory Tumor Necrosis Factor-alpha (TNF-α) and interferon gamma (IFN-γ), and induced CD4+CD25+Foxp3+ regulatory T cells (Tregs) and the level of anti-inflammatory IL-10. In vitro, MSC-EVs also suppressed Tc1 and Th1 cells and induced Tregs and the related cytokines, further indicating the immune regulatory role of MSC-EVs. Interestingly, PKH26-labeled MSC-EVs were found to be directly internalized by CD3+ T cells, resulting in reduced signal transducer and activator of transcription 1 (STAT1) protein levels in vitro. In summary, MSC-EVs can prevent the onset of CHS by inhibiting Tc1 and Th1 immune responses and inducing the Tregs phenotype in vivo and in vitro. The mechanism by which MSC-EVs influence CD3+ T cells might partially involve targeting STAT1 in vitro. Therefore, MSC-EVs are ideal candidates for cell-free immunomodulatory therapy for T cell-mediated diseases such as ACD.