Considerations in the Quality Control towards Translation of Extracellular Vesicles Derived from Eukaryotic Prokaryotic Cells

According to concept of ISEV (The international Society for Extracellular Vesicles), “extracellular vesicles (EVs) are defined as the particles naturally released from cells that are comprised of a lipid bilayer membrane [1]. Acting as important mediators between cells that regulate both physiological and pathological conditions in the living bodies, EVs are nanosized spherical compartments and contain lipids, proteins and various nucleic acids of their source cells [2,3]. Based on their biogenesis and sizes, EVs are generally categorized into three types, including exosomes, microvesicles and apoptotic bodies. In general, sizes of EVs vary within the range 305000 nm [4,5]. Besides EVs derived from eukaryotes, prokaryotes also secrete EVs. It has been reported that Gram-positive and Gramnegative bacteria can both generate EVs [6-8]. The size of the outer membrane-derived vesicles (OMVs) from both Gram-positive and Gram-negative bacteria was reported to be around 20–100 nm in diameter [8,9]. Inspired by the generation of naturally secreted EVs, scientists are also seeking to prepare biomimetic EVs by physical [10,11], and chemical [12] methods in recent years. In general, the artificial EVs exhibit similar properties to the natural ones. As a supplementary to the natural EVs, biomimetic EVs possess some advantages in some aspects, such as purity, yield, targeting ability, etc. Either EVs or OMVs can perform as vaccines without loading. They also can be loaded by bioactive ingredients as drug delivery carriers. In the past decades, a lot of efforts had been made to translate EVs for clinical use. However, there are many challenges existing at each stage of commercialization of EVs. One of them is quality control. Generally, to control the quality of EVs as drug carriers or vaccines, the following aspects should be taken into consideration. • Impurities. Safety is always the priority when quality is taken into consideration. Deriving from parent cells, EVs will unavoidably inherit some ingredients of their source cells. Obviously, some impurities, such as DNA [13] and RNA [14], are bioactive and may impair the functions of cargoes. Other potential impairments also need keeping an eye on include enzymes, kinases and some potential carcinoma-inducing agents especially when prepared from cancer source cells. Except endogenous impurities, the exogenous pathogens also need to be monitored when prepared from prokaryotic cells.