Effect of Storage Conditions on the Integrity of Human Umbilical Cord Mesenchymal Stromal Cell-Derived Microvesicles

Lyoprotectant Constituents Suited for Lyophilization and Reconstitution of Stem-Cell-Derived Extracellular Vesicles

Stem-cell-derived extracellular vesicles (EVs) are emerging as an alternative approach to stem cell therapy. Successful lyophilization of EVs could enable convenient storage and distribution of EV medicinal products at room temperature for long periods, thus considerably increasing the accessibility of EV therapeutics to patients. In this study, we aimed to identify an appropriate lyoprotectant composition for the lyophilization and reconstitution of stem-cell-derived EVs. MSC-derived EVs were lyophilized using different lyoprotectants, such as dimethyl sulfoxide, mannitol, trehalose, and sucrose, at varying concentrations. Our results revealed that a mixture of trehalose and sucrose at high concentrations could support the formation of amorphous ice by enriching the amorphous phase of the solution, which successfully inhibited the acceleration of buffer component crystallization during lyophilization. Lyophilized and reconstituted EVs were thoroughly evaluated for concentration and size, morphology, and protein and RNA content. The therapeutic effects of the reconstituted EVs were examined using a tube formation assay with human umbilical vein endothelial cells. After rehydration of the lyophilized EVs, most of their generic characteristics were well-maintained, and their therapeutic capacity recovered to levels similar to those of freshly collected EVs. The concentrations and morphologies of the lyophilized EVs were similar to the initial features of the fresh EV group until day 30 at room temperature, although their therapeutic capacity appeared to decrease after 7 days. Our study suggests an appropriate composition of lyoprotectants, particularly for EV lyophilization, which could encourage the applications of stem-cell-derived EV therapeutics in the health industry.

Extracellular Vesicles as Therapeutic Resources in the Clinical Environment

The native role of extracellular vesicles (EVs) in mediating the transfer of biomolecules between cells has raised the possibility to use them as therapeutic vehicles. The development of therapies based on EVs is now expanding rapidly; here we will describe the current knowledge on different key points regarding the use of EVs in a clinical setting. These points are related to cell sources of EVs, isolation, storage, and delivery methods, as well as modifications to the releasing cells for improved production of EVs. Finally, we will depict the application of EVs therapies in clinical trials, considering the impact of the COVID-19 pandemic on the development of these therapies, pointing out that although it is a promising therapy for human diseases, we are still in the initial phase of its application to patients.

Effect of Pre-Processing Storage Condition of Cell Culture-Conditioned Medium on Extracellular Vesicles Derived from Human Umbilical Cord-Derived Mesenchymal Stromal Cells

EVs can be isolated from a conditioned medium derived from mesenchymal stromal cells (MSCs), yet the effect of the pre-processing storage condition of the cell culture-conditioned medium prior to EV isolation is not well-understood. Since MSCs are already in clinical trials, the GMP-grade of the medium which is derived from their manufacturing might have the utility for preclinical testing, and perhaps, for clinical translation, so the impact of pre-processing storage condition on EV isolation is a barrier for utilization of this MSC manufacturing by-product. To address this problem, the effects of the pre-processing storage conditions on EV isolation, characterization, and function were assessed using a conditioned medium (CM) derived from human umbilical cord-derived MSCs (HUC-MSCs). Hypothesis: The comparison of three different pre-processing storage conditions of CM immediately processed for EV isolation would reveal differences in EVs, and thus, suggest an optimal pre-processing storage condition. The results showed that EVs derived from a CM stored at room temperature, 4 °C, −20 °C, and −80 °C for at least one week were not grossly different from EVs isolated from the CM immediately after collection. EVs derived from an in pre-processing −80 °C storage condition had a significantly reduced polydispersity index, and significantly enhanced dot blot staining, but their zeta potential, hydrodynamic size, morphology and size in transmission electron microscopy were not significantly different from EVs derived from the CM immediately processed for isolation. There was no impact of pre-processing storage condition on the proliferation of sarcoma cell lines exposed to EVs. These data suggest that the CM produced during GMP-manufacturing of MSCs for clinical applications might be stored at −80 °C prior to EV isolation, and this may enable production scale-up, and thus, and enable preclinical and clinical testing, and EV lot qualification.

Cryopreservation of mesenchymal stromal cell-derived extracellular vesicles using trehalose maintains their ability to expand hematopoietic stem cells in vitro

The multitude of clinical trials using mesenchymal stromal cells (MSCs) has underscored their significance as a promising cell source for regenerative therapies. Most studies have however shown that MSCs get entrapped into the microvasculature of lungs, liver and spleen. In addition to intercellular communication, MSCs exert their effects in a paracrine manner by secretion of extracellular vesicles (EVs). The therapeutic effects of MSC-derived EVs have been examined in several diseases such as hepatic failure, liver injury, hematopoiesis etc. Therefore, optimization of cryopreservation strategies for the long-term storage of functional EVs could help in the development of off-the-shelf biologics. The aim of this study was to develop an optimal cryopreservation strategy for the efficient storage of both types of EVs - Microvesicles (MVs) and exosomes, independently, and to further examine the effect of the cryopreserved EVs on the ex vivo expansion of HSCs. MVs and exosomes were separately cryopreserved at different temperatures using PBS or PBS supplemented with trehalose (pTRE), and these cryopreserved EVs were then assessed for their functionality after revival. We found that addition of trehalose during cryopreservation helped in maintaining the morphology and functionality of the EVs, as assessed by their HSC-supportive potential, ability to expand phenotypically defined HSCs and ability to maintain the chemotactic migration potential of the HSCs co-cultured with them. This strategy could prove to be beneficial for facilitating the use of EVs as cell-free ready-to-use biologics for the ex vivo expansion of HSCs and in regenerative medicine.

Mesenchymal Stem Cell-Derived Extracellular Vesicles: Opportunities and Challenges for Clinical Translation

Extracellular vesicles (EVs), including exosomes and microvesicles, derived from mesenchymal stem/stromal cells (MSCs) exert similar effects as their parental cells, and are of interest for various therapeutic applications. EVs can act through uptake by the target cells followed by release of their cargo inside the cytoplasm, or through interaction of membrane-bound ligands with receptors expressed on target cells to stimulate downstream intracellular pathways. EV-based therapeutics may be directly used as substitutes of intact cells or after modification for targeted drug delivery. However, for the development of EV-based therapeutics, several production, isolation, and characterization requirements have to be met and the quality of the final product has to be tested before its clinical implementation. In this review, we discuss the challenges associated with the development of EV-based therapeutics and the regulatory specifications for their successful clinical translation.

Conditioned Medium of Mesenchymal Stromal Cells: A New Class of Therapeutics

Mesenchymal stromal cell (MSCs) represent a class of biologics with the prospects for employment as immunomodulatory, tissue-protective, and regenerative therapeutics. In parallel with cellular therapy, cell-free therapy based on MSC-secreted bioactive factors is being actively developed. MSCs secrete a variety of protein, peptide, RNA, and lipid mediators which can be concentrated, frozen, or even lyophilized without loss of activity, which gives them a certain advantage over cellular products requiring liquid nitrogen storage and infrastructure to revive frozen cells. This review (i) describes currently conducted clinical trials of cell-free products containing MSC secretome; (ii) summarizes main approaches to the generation and characterization of conditioned media concentrates and extracellular vesicle isolates; (iii) analyzes a variety of preclinical studies where effectiveness of secretome products has been shown; and (iv) summarizes current knowledge about secretome bioactive components obtained by analysis of in vivo models testing the therapeutic potential of the MSC secretome.