Challenges of manufacturing mesenchymal stromal cell-derived extracellular vesicles in regenerative medicine

The field of regenerative medicine has expanded greatly in the past decade, with more than 1000 current clinical trials involving mesenchymal stromal cell (MSC) treatment. Multiple recent publications have demonstrated that the beneficial effects from MSCs are not simply due to engraftment into the target organ as classically thought but rather are largely attributable to the release of paracrine factors including cytokines, growth factors and extracellular vesicles (EVs). These EVs contain miRNAs, free fatty acids and proteins that promote regeneration, proliferation and cell function and improve inflammation. Although EVs have shown promising results in animal studies, there are many obstacles to the manufacturing of EVs for clinical applications. This review discusses challenges associated with the manufacturing of clinical-grade EVs in regard to identity, purity, reproducibility, sterility, storage, potency and safety. We discuss currently employed methods and approaches for developing clinical Good Manufacturing Practices (GMP)-grade EVs and the limitations for each. We further discuss the best approaches to overcome the current hurdles in developing clinical GMP-grade EVs.