Independent human mesenchymal stromal cell-derived extracellular vesicle preparations differentially attenuate symptoms in an advanced murine graft-versus-host disease model

Background aims: Extracellular vesicles (EVs) harvested from conditioned media of human mesenchymal stromal cells (MSCs) suppress acute inflammation in various disease models and promote regeneration of damaged tissues. After successful treatment of a patient with acute steroid-refractory graft-versus-host disease (GVHD) using EVs prepared from conditioned media of human bone marrow-derived MSCs, this study focused on improving the MSC-EV production for clinical application.

Methods: Independent MSC-EV preparations all produced according to a standardized procedure revealed broad immunomodulatory differences. Only a proportion of the MSC-EV products applied effectively modulated immune responses in a multi-donor mixed lymphocyte reaction (mdMLR) assay. To explore the relevance of such differences in vivo, at first a mouse GVHD model was optimized.

Results: The functional testing of selected MSC-EV preparations demonstrated that MSC-EV preparations revealing immunomodulatory capabilities in the mdMLR assay also effectively suppress GVHD symptoms in this model. In contrast, MSC-EV preparations, lacking such in vitro activities, also failed to modulate GVHD symptoms in vivo. Searching for differences of the active and inactive MSC-EV preparations, no concrete proteins or miRNAs were identified that could serve as surrogate markers.

Conclusions: Standardized MSC-EV production strategies may not be sufficient to warrant manufacturing of MSC-EV products with reproducible qualities. Consequently, given this functional heterogeneity, every individual MSC-EV preparation considered for the clinical application should be evaluated for its therapeutic potency before administration to patients. Here, upon comparing immunomodulating capabilities of independent MSC-EV preparations in vivo and in vitro, we found that the mdMLR assay was qualified for such analyses.