Human mesenchymal stem cells inhibit antibody production induced in vitro by allostimulation

Background. Antibodies directed against alloantigens are implicated in the pathogenesis of several immune reactions complicating transplantation, including humoral rejection after solid organ transplantation. Mesenchymal stem cells (MSCs) have immunomodulatory capacity, since in vivo they may prolong skin graft survival in the animal model and can rescue patients with life-threatening graft-versus-host disease. Methods. To investigate whether MSCs exert an inhibitory effect on antibody production during allostimulation, we stimulated peripheral blood mononuclear cells, obtained from healthy controls or sensitized patients undergoing dialysis for end-stage renal failure, in mixed lymphocyte culture (MLC), and evaluated immunoglobulin production either in the absence or in the presence of third-party allogeneic MSCs. We also evaluated the effect of MSCs on B-cell allostimulation performed adding to MLC a polyclonal stimulus delivered by an agonist anti-CD40 monoclonal antibody. Results. We found that the addition of MSCs at the beginning of MLC considerably inhibited immunoglobulin production in standard MLC, irrespective of the MSC dose employed. Conversely, immunoglobulin secretion induced by direct CD40-CD40L binding was not significantly inhibited. Furthermore, we demonstrated, in one sensitized patient, that secretion of donor-specific anti-HLA class I antibodies detected both in baseline serum and in the supernatant of control MLC was inhibited by the addition of MSCs. Mechanistically, the addition of MSCs induced a striking decrease of IL-5 production in the cultures. Conclusions. Our findings suggest that third-party MSC are able to suppress allo-specific antibody production in vitro, and may therefore help overcome a positive cross-match in sensitized transplant recipients.