Diverse impact of xeno-free conditions on biological and regenerative properties of hUC-MSCs and their extracellular vesicles

The therapeutic potential of mesenchymal stem cells (MSCs) not only has been widely studied in animal models [ 1 ] but was also validated for human patients, indicating efficacy in the treatment of a variety of diseases [ 2 , 3 ]. Among different populations of MSCs isolated from various sources, umbilical cord-derived MSC (UC-MSCs) are particularly promising, due to their high proliferative potential, longevity, immunomodulatory properties, and noninvasive isolation procedure [ 4 ]. Interestingly, although the beneficial effects of stem cell-based therapy have been widely appreciated, the level of engrafted cells was usually very low suggesting that the paracrine activity of stem cells rather than direct differentiation plays a key role in tissue repair [ 5 ]. Among paracrine factors, circular cell-membrane enclosed cytoplasmic structures termed extracellular vesicles (EVs) have been recognized as important mediators of cell-to-cell communication [ 6 ]. It was shown that EVs can interact with cell surface receptors or fuse with a cell membrane and transfer bioactive cargo in the form of messenger RNA (mRNA), microRNA (miRNA), proteins, and lipids to the recipient cells, triggering specific intracellular signaling pathways, thereby influencing cell fate [ 6 , 7 ]. Importantly, compelling evidence supports the significance of EV-mediated signaling in a variety of physiological and pathological processes, including embryonic development, the maintenance of tissue homeostasis [ 8 ], spread of pathogens or modulating disease onset, and progression [ 9 ]. Prominently, EVs derived from human mesenchymal stem cells (MCS-EVs) were shown to enhance regeneration of various tissues in animal models [ 10 – 16 ], thus creating a new treatment option for many disorders. In particular, such therapy could be used to improve regeneration of the infarcted or diseased heart, conditions which are the leading causes of morbidity and mortality worldwide [ 17 ], despite the available modalities. To prove this theory, there are reports showing that MSC-EVs infusion to the experimental animals ameliorated myocardial ischemia/reperfusion injury [ 14 ] and markedly enhanced blood flow recovery accompanied by reduction of the infarct size of the heart [ 15 ]. However, to fully translate the beneficial effects of MSC-EVs treatment into the clinic, there is a need to carefully define and standardize cell culture conditions for EVs collection, devoid of any substrates of animal origin.