Large-scale preparations of small extracellular vesicles from conditioned media of mesenchymal stromal cells modulate therapeutic impacts on a newly established Graft-versus-Host-Disease model in batch dependent manners

Background & Aim Extracellular vesicles (EVs) harvested from supernatants of humane adult bone marrow-derived mesenchymal stem/stromal cells (MSCs) can suppress acute inflammatory cues in a variety of different diseases, including Graft-versus-Host Disease (GvHD) and ischemic stroke. Furthermore, they can promote regeneration of affected tissues. Following a successful clinical treatment attempt of a steroid refractory GvHD patient, we intend to optimize MSC-EV production strategies for further clinical applications. As we observed functional differences of independent MSC-EV preparations in vitro, we aimed to adopt an in vivo GvHD model for the more advanced functional testing of different MSC-EV preparations. Methods, Results & Conclusion To this end we set up a bone marrow transplantation mouse model in which endogenous bone marrow was myeloablated by ionizing irradiation (IIR). GvHD was induced by the transplantation of major histocompatibility mismatched allogeneic spleen-derived murine T cells. If not treated otherwise, myeloablated mice developed severe GvHD symptoms. The GvHD symptoms were effectively suppressed, when MSC-EV preparations were applied at 3 consecutive days, which exerted immune modulatory effects in a mixed-lymphocyte reaction assay. MSC-EV preparations lacking in vitro immune modulating activities, however, hardly improved the symptoms of the GvHD mice. Thus, our results demonstrate that not all MSC-EV preparations harvested from adult bone marrow-derived MSCs contain the same therapeutic potential. Thus, successful transplantation of MSC-EVs into the clinics requires a platform allowing identification of MSC-EV preparations with sufficient therapeutic, most probably immune modulating activities.