Increasing yield of msc-evs in scalable xeno-free manufacturing

Abstract

Background & Aim Extracellular vesicles (EVs) are increasingly being investigated as both drug delivery vehicles and as a cell-free therapy. EVs from mesenchymal stem/stromal cells (MSC-EVs), for example, have been shown to recapitulate many of the therapeutic effects of the cells themselves. A critical barrier in the development of MSC-EVs as a commercial therapy, however, is generating the large amount of EVs that will be required per dose. In a recent survey, the majority of those working with EVs were working with less than 100mL of sample (ISEV 2016). In this study, two strategies were investigated to maximize EV yield. First, timing parameters for culturing human bone-marrow derived MSCs and collecting MSC-EVs were evaluated to increase EV yield. Second, conditioning the cells was investigated by adding an EV activator during the EV collection period. Methods, Results & Conclusion MSCs were first cultured in an expansion media (RoosterNourishTM, RoosterBio) in a fed-batch system. The cultures were then switched to a collection media (RoosterCollectTM-EV, RoosterBio) with or without an EV activator (EV BoostTM, RoosterBio). After two days, the conditioned media was harvested. The EVs in the collected conditioned media were analyzed for particle concentration and particle size distributions by nanoparticle tracking analysis, protein expression, RNA expression, and wound healing capability. Particle concentration (particles per L of media) was used as a measure of EV yield. Particle concentration increased with increased culture time in expansion media, with confluent cultures generating the most EVs. The EV activator at a low concentration increased EV yield about 2-fold compared to without the activator after 24hrs. The EV yield from the low EV activator culture at 24hrs was still about 45% greater than the yield of the culture without the activator after 48hrs. After 6hrs of collection, the high EV activator concentration increased EV yield to about the same level as without the activator after 48hrs of collection. Optimizing protocols for EV yield will become increasingly important as MSC-EVs move towards the clinic and lot sizes of clinically-relevant doses are required. Pre-conditioning of cells or conditioning cells during EV collection offers one possibility to further increase EV yield and decrease process time.