EXTRACELLULAR VESICLES DERIVED FROM MESENCHYMAL STEM CELLS INHIBIT TUBULAR INJURY, T CELL PROLIFERATION AND PROMOTE REGULATORY T CELL DIFFERENTIATION THROUGH TRANSFER OF SPECIFIC RNAs: PROTECTIVE ROLE IN T-CELL-MEDIATED KIDNEY GRAFT REJECTION

Introduction and Aims:Mesenchymal stem cells (MSCs) are known to exert regenerative and immunomodulatory effects by releasing paracrine mediators including extracellular vesicles (EVs), small particles involved in cell-to-cell communication through transfer of proteins and genetic information. The aim of this study was to evaluate the protective role of MSC-derived EVs in the mechanisms of T-cell mediated rejection (TCMR) in kidney transplantation. Methods:MSCs were isolated from bone marrow and EVs were characterized for size, protein and RNA content. The biological effects of EVs were studied on T cells isolated from peripheral blood of kidney transplant recipients co-cultured with B cells purified by the spleen of matched deceased donors or on human kidney-derived tubular epithelial cells cultured in an inflammatory microenvironment typical of TCMR. Results:MSC-derived EVs sized 60-150 nm and expressed on their surface molecules of the integrin family essential for their internalization within target cells. EVs carried different microRNAs and mRNAs including the immunoregulatory Foxp3, Tim-1 and thrombospondin-1 similarly to cells from which they originated. EVs were internalized in activated T cells isolated from kidney transplant recipients inhibiting their proliferation induced by phytohemagglutinin + ionomycine or by co-culture with matched-donor B cells used as antigen presenting cells. Of interest, EVs horizontally transferred to T cells Foxp3 mRNA, inducing a Treg phenotype. In addition, EVs can be internalized in human tubular epithelial cells inhibiting functional alterations and apoptosis induced by inflammatory cytokines, Fas-Ligand, perforin and granzymes. In particular, EVs preserved the expression of different solute carriers down-regulated by the inflammatory microenvironment typical of TCMR. All the biological effects exerted by EVs were decreased after their treatment with RNase, suggesting a key role for RNAs carried by EVs. Conclusions:MSC-derived EVs may have a protective role in TCMR by inhibition of T cell proliferation, by differentiation toward a T regulatory phenotype and by reduction of apoptosis and preservation of functional integrity of tubular cells. These protective effects are mediated by the horizontal transfer of specific RNAs from EVs to target cells.