Microvescicles Derived from Mesenchymal Stromal Cells Are Not as Effective as Their Cellular Counterpart in the Ability to Modulate Immune Responses In Vitro

Mesenchymal stromal cells (MSCs) are multipotent cells that possess broad immunomodulatory properties; the mechanisms underlying these properties have not been completely clarified. Aim of this study was to compare in vitro immunomodulatory effects of MSCs with those of microvesicles (MVs) released in supernatants from the same MSCs. MSCs were generated from bone marrow of 12 healthy donors (HDs) and MVs were isolated from their supernatant by serial ultracentrifugation according to two different procedures. Both MSCs and MVs were characterized by flow cytometry and incubated in vitro with peripheral blood mononuclear cells (PBMCs) of 12 HDs after stimulation with PHA and CpG. Growth factors and cytokines were quantified by ELISA. MVs were identified as 0.1-1 mu m particles positive for CMFDA, CD107, and CD13. MSCs were significantly more capable to inhibit in vitro PHA-induced T-cell proliferation as compared with the corresponding MVs (PP<0.05 for MSC:PBMC ratio 1:2 and 1:10, respectively). While MVs displayed similar inhibitory activity on B-cell proliferation (P=0.43 as compared with PBMCs/CpG/MSCs; MSC:PBMC ratio 1:10) they induced lower inhibitory effect on plasmacell differentiation and antibody secretion (P<0.05 as compared with PBMCs/CpG/MSCs). For both T and B cells, MSC co-colture induced a statistically significant increase in IL-10 and TGF beta and decrease of GM-CSF and IFN gamma, as compared with MV incubation. Our data indicate a lower in vitro immunomodulatory effect of MVs on T-cell proliferation and antibody formation, as compared with their cellular counterpart. The relative clinical benefit of either MSCs or MVs needs to be compared in proper prospective studies.