To Protect and to Preserve: Novel Preservation Strategies for Extracellular Vesicles

Abstract

Extracellular vesicles (EVs)-based therapeutics are based on the premise that EVs shed by stem cells exert similar therapeutic effects and these have been proposed as an alternative to cell therapies. EV-mediated delivery is an effective and efficient system of cell-to-cell communication which can confer therapeutic benefits to their target cells. EVs have been shown to promote tissue repair and regeneration in various animal models such as, wound healing, cardiac ischemia, diabetes, lung fibrosis, kidney injury, and many others. Given the unique attributes of EVs, considerable thought must be given to the preservation, formulation and cold chain strategies in order to effectively translate exciting preclinical observations to clinical and commercial success. This review summarizes current understanding around EV preservation, challenges in maintaining EV quality, and also bioengineering advances aimed at enhancing the long-term stability of EVs.

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“…It should be noted that different laboratories use diverse methods to isolate and purify MSC-EVs and, accordingly, it is critical to define and standardize highly effective method for MSC-EV yields [31]. Additionally, clinical applications of MSC-EVs require their long-term use and considerable thought must be given to the preservation of their immunosuppressive potential [21]. A large number of studies demonstrated that the most convenient mode of storage for MSC-EVs remains −80 • C [109].…”

“…A large number of studies demonstrated that the most convenient mode of storage for MSC-EVs remains −80 • C [109]. Nevertheless, due to the complex cold chain logistics, alternatives such as lyophilization and the incorporation of additives might be necessary to improve MSC-EV storage stability during transportation [21,109].…”

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“…A recent review summarized the recommended preservation and storage methods for EVs, 69 and some consensus is emerging towards using −80°C for EV transportation and storage. 70,71 However, temperatures of around −80°C, may alter the functional activities, while storage at 4°C causes EV damage and aggregation.…”

“…The addition of cryoprotectants (eg sugars, amino acid, etc. ), may help preserve EVs and their cargo 69 with good effects found in particular using trehalose. 65,74 Freeze-drying with a cryoprotectant does not seem to significantly affect EVs, and enzymes within the lyophilized EVs were found to exhibit activity comparable to that of EVs stored at −80°C.…”

“…75 However, defining the optimal concentration of cryoprotectants is critical as excessively low concentrations may result in damage during the freezing process, whereas an excess can be toxic. 69 Consideration should also be given to the type of vials, as some materials may affect the integrity of stored EVs through irreversible binding and detrimental impacts on quality and concentration. 8 Use of siliconized vessels and containers throughout purification and storage can help prevent EV adherence and loss onto surfaces.…”