Experimental artefacts can lead to misattribution of bioactivity from soluble mesenchymal stem cell paracrine factors to extracellular vesicles

Lung fibroblast-derived extracellular vesicles and soluble factors alleviate elastase-induced lung injury

One of the main pathological features of chronic obstructive pulmonary disease (COPD) is the loss of functional alveolar tissue as a consequence of impaired regenerative capacities (emphysema). Recent research suggests that the secretome from mesenchymal cells, particularly extracellular vesicles (EVs), may possess regenerative properties beneficial for lung repair. However, the regenerative potential of the soluble factors (SFs) within the secretome remains largely unexplored in COPD. To this extent, we purified EVs and SFs secreted by lung fibroblasts to generate EV-enriched and SF-enriched fractions, and evaluated their effects on elastase-induced lung injury in both precision-cut lung slices (PCLS) and a mouse model. EV- and SF-enriched fractions were concentrated and purified from the conditioned medium of cultured MRC-5 lung fibroblasts using a combination of ultrafiltration and size exclusion chromatography, and were subsequently characterized according to the MISEV guidelines. Treatment with EV- or SF-enriched concentrates prevented and improved elastase-induced emphysema in PCLS, leading to reduced lung injury and upregulated markers of alveolar epithelial cells (aquaporin 5 and surfactant protein C), indicating potential parenchymal regeneration. Accordingly, prophylactic intratracheal treatment with lung fibroblast-derived EV- and SF-enriched concentrates in vivo attenuated elastase-induced lung tissue destruction, improved lung function, and enhanced gene expression of alveolar epithelial cell markers. Here, alveolar repair not only serves the purpose of facilitating gas exchange, but also by reinstating the essential parenchymal tethering required for optimal airway mechanics. In conclusion, this study highlights the therapeutic potential of both lung fibroblast-derived EV- and SF-enriched concentrates for the treatment of lung injury and emphysema.

Influence of a pro-inflammatory stimulus on the miRNA and lipid content of human dental stem cell-derived extracellular vesicles and their impact on microglial activation

Neuro-inflammation occurs in numerous disorders such as multiple sclerosis, Alzheimer's disease and Parkinson's disease. However, anti-inflammatory drugs for the central nervous system have failed to show significant improvement when compared to a placebo in clinical trials. Our previous work demonstrated that stem cells from the apical papilla (SCAP) can decrease neuro-inflammation and stimulate oligodendrocyte progenitor cell differentiation. One hypothesis is that the therapeutic effect of SCAP could be mediated by their secretome, including extracellular vesicles (EV). Here, our objectives were to characterize SCAP-EV and to study their effect on microglial cells. We isolated EV from non-activated SCAP and from SCAP activated with TNFα and IFN-γ and characterized them according to their size, EV markers, miRNA and lipid content. Their ability to decrease pro-inflammatory cytokine expression in vitro and ex vivo was also assessed. We showed that the miRNA content was impacted by a pro-inflammatory environment but not their lipid composition. SCAP-EV reduced the expression of pro-inflammatory markers in LPS-activated microglial cells while their effect was limited on mouse spinal cord sections. In conclusion, we were able to isolate EV from SCAP, to show that their miRNA content was impacted by a pro-inflammatory stimulus, and to describe that SCAP-EV and not the protein fraction of conditioned medium could reduce pro-inflammatory marker expression in LPS-activated BV2 cells.

Scalable purification of extracellular vesicles with high yield and purity using multimodal flowthrough chromatography

Extracellular vesicles (EVs) are cell derived membranous nanoparticles. EVs are important mediators of cell-cell communication via the transfer of bioactive content and as such they are being investigated for disease diagnostics as biomarkers and for potential therapeutic cargo delivery to recipient cells. However, existing methods for isolating EVs from biological samples suffer from challenges related to co-isolation of unwanted materials such as proteins, nucleic acids, and lipoproteins. In the pursuit of improved EV isolation techniques, we introduce multimodal flowthrough chromatography (MFC) as a scalable alternative to size exclusion chromatography (SEC). The use of MFC offers significant advantages for purifying EVs, resulting in enhanced yields and increased purity with respect to protein and nucleic acid co-isolates from conditioned 3D cell culture media. Compared to SEC, significantly higher EV yields with similar purity and preserved functionality were also obtained with MFC in 2D cell cultures. Additionally, MFC yielded EVs from serum with comparable purity to SEC and similar apolipoprotein B content. Overall, MFC presents an advancement in EV purification yielding EVs with high recovery, purity, and functionality, and offers an accessible improvement to researchers currently employing SEC.

Adipose Stromal Cell-Derived Secretome Attenuates Cisplatin-Induced Injury In Vitro Surpassing the Intricate Interplay between Proximal Tubular Epithelial Cells and Macrophages

(1) Background: The chemotherapeutic drug cisplatin exerts toxic side effects causing acute kidney injury. Mesenchymal stromal cells can ameliorate cisplatin-induced kidney injury. We hypothesize that the MSC secretome orchestrates the vicious cycle of injury and inflammation by acting on proximal tubule epithelial cells (PTECs) and macrophages individually, but further by counteracting their cellular crosstalk. (2) Methods: Conditioned medium (CM) from adipose stromal cells was used, first assessing its effect on cisplatin injury in PTECs. Second, the effects of cisplatin and the CM on macrophages were measured. Lastly, in an indirect co-culture system, the interplay between the two cell types was assessed. (3) Results: First, the CM rescued PTECs from cisplatin-induced apoptosis by reducing oxidative stress and expression of nephrotoxicity genes. Second, while cisplatin exerted only minor effects on macrophages, the CM skewed macrophage phenotypes to the anti-inflammatory M2-like phenotype and increased phagocytosis. Finally, in the co-culture system, the CM suppressed PTEC death by inhibiting apoptosis and nuclei fragmentation. The CM lowered TNF-α release, while cisplatin inhibited macrophage phagocytosis, PTECs, and the CM to a greater extent, thus enhancing it. The CM strongly dampened the inflammatory macrophage cytokine secretion triggered by PTECs. (4) Conclusions: ASC-CM surpasses the PTEC-macrophage crosstalk in cisplatin injury. The positive effects on reducing cisplatin cytotoxicity, on polarizing macrophages, and on fine-tuning cytokine secretion underscore MSCs' CM benefit to prevent kidney injury progression.

Size matters: Functional differences of small extracellular vesicle subpopulations in cardiac repair responses

Cardiac progenitor cell (CPC)-derived small extracellular vesicles (sEVs) exhibit great potential to stimulate cardiac repair. However, the multifaceted nature of sEV heterogeneity presents a challenge in understanding the distinct mechanisms underlying their regenerative abilities. Here, a dual-step multimodal flowthrough and size-exclusion chromatography method was applied to isolate and separate CPC-derived sEV subpopulations to study the functional differences related to cardiac repair responses. Three distinct sEV subpopulations were identified with unique protein profiles. Functional cell assays for cardiac repair-related processes demonstrated that the middle-sized and smallest-sized sEV subpopulations exhibited the highest pro-angiogenic and anti-fibrotic activities. Proteasome activity was uniquely seen in the smallest-sized subpopulation. The largest-sized subpopulation showed no effect in any of the functional assays. This research uncovers the existence of sEV subpopulations, each characterized by a distinct composition and biological function. Enhancing our understanding of sEV heterogeneity will provide valuable insights into sEV mechanisms of action, ultimately accelerating the translation of sEV therapeutics.

Extracellular vesicles modulate key signalling pathways in refractory wound healing

Chronic wounds are wounds that cannot heal properly due to various factors, such as underlying diseases, infection or reinjury, and improper healing of skin wounds and ulcers can cause a serious economic burden. Numerous studies have shown that extracellular vesicles (EVs) derived from stem/progenitor cells promote wound healing, reduce scar formation and have significant advantages over traditional treatment methods. EVs are membranous particles that carry various bioactive molecules from their cellular origins, such as cytokines, nucleic acids, enzymes, lipids and proteins. EVs can mediate cell-to-cell communication and modulate various physiological processes, such as cell differentiation, angiogenesis, immune response and tissue remodelling. In this review, we summarize the recent advances in EV-based wound healing, focusing on the signalling pathways that are regulated by EVs and their cargos. We discuss how EVs derived from different types of stem/progenitor cells can promote wound healing and reduce scar formation by modulating the Wnt/β-catenin, phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin, vascular endothelial growth factor, transforming growth factor β and JAK-STAT pathways. Moreover, we also highlight the challenges and opportunities for engineering or modifying EVs to enhance their efficacy and specificity for wound healing.

Adipose stromal cells bioproducts as cell-free therapies: manufacturing and therapeutic dose determine in vitro functionality

BACKGROUND

Extracellular vesicles (EV) are considered a cell-free alternative to mesenchymal stromal cell (MSC) therapy. Numerous reports describe the efficacy of EV in conferring immunomodulation and promoting angiogenesis, yet others report these activities to be conveyed in EV-free bioproducts. We hypothesized that this discrepancy may depend either on the method of isolation or rather the relative impact of the individual bioactive components within the MSC secretome.

METHODS

To answer this question, we performed an inter-laboratory study evaluating EV generated from adipose stromal cells (ASC) by either sequential ultracentrifugation (UC) or size-exclusion chromatography (SEC). The effect of both EV preparations on immunomodulation and angiogenesis in vitro was compared to that of the whole secretome and of the EV-free protein fraction after SEC isolation.

RESULTS

In the current study, neither the EV preparations, the secretome or the protein fraction were efficacious in inhibiting mitogen-driven T cell proliferation. However, EV generated by SEC stimulated macrophage phagocytic activity to a similar extent as the secretome. In turn, tube formation and wound healing were strongly promoted by the ASC secretome and protein fraction, but not by EV. Within the secretome/protein fraction, VEGF was identified as a potential driver of angiogenesis, and was absent in both EV preparations.

CONCLUSIONS

Our data indicate that the effects of ASC on immunomodulation and angiogenesis are EV-independent. Specific ASC-EV effects need to be dissected for their use as cell-free therapeutics.

Taste papilla cell differentiation requires the regulation of secretory protein production by ALK3-BMP signaling in the tongue mesenchyme

Taste papillae are specialized organs, each of which comprises an epithelial wall hosting taste buds and a core of mesenchymal tissue. In the present study, we report that during early taste papilla development in mouse embryos, bone morphogenetic protein (BMP) signaling mediated by type 1 receptor ALK3 in the tongue mesenchyme is required for epithelial Wnt/β-catenin activity and taste papilla differentiation. Mesenchyme-specific knockout (cKO) of Alk3 using Wnt1-Cre and Sox10-Cre resulted in an absence of taste papillae at E12.0. Biochemical and cell differentiation analyses demonstrated that mesenchymal ALK3-BMP signaling governed the production of previously unappreciated secretory proteins, i.e. it suppressed those that inhibit and facilitated those that promote taste papilla differentiation. Bulk RNA-sequencing analysis revealed many more differentially expressed genes (DEGs) in the tongue epithelium than in the mesenchyme in Alk3 cKO versus control. Moreover, we detected downregulated epithelial Wnt/β-catenin signaling and found that taste papilla development in the Alk3 cKO was rescued by the GSK3β inhibitor LiCl, but not by Wnt3a. Our findings demonstrate for the first time the requirement of tongue mesenchyme in taste papilla cell differentiation.

EV-mediated promotion of myogenic differentiation is dependent on dose, collection medium, and isolation method

Extracellular vesicles (EVs) have been implicated in the regulation of myogenic differentiation. C2C12 murine myoblast differentiation was reduced following treatment with GW4869 or heparin (to inhibit exosome biogenesis and EV uptake, respectively). Conversely, treatment with C2C12 myotube-conditioned medium enhanced myogenic differentiation. Ultrafiltration-size exclusion liquid chromatography (UF-SEC) was used to isolate EVs and non-EV extracellular protein in parallel from C2C12 myoblast- and myotube-conditioned medium. UF-SEC-purified EVs promoted myogenic differentiation at low doses (≤2 × 108 particles/mL) and were inhibitory at the highest dose tested (2 × 1011 particles/mL). Conversely, extracellular protein fractions had no effect on myogenic differentiation. While the transfer of muscle-enriched miRNAs (myomiRs) has been proposed to mediate the pro-myogenic effects of EVs, we observed that they are scarce in EVs (e.g., 1 copy of miR-133a-3p per 195 EVs). Furthermore, we observed pro-myogenic effects with undifferentiated myoblast-derived EVs, in which myomiR concentrations are even lower, suggestive of a myomiR-independent mechanism underlying the observed pro-myogenic effects. During these investigations we identified technical factors with profound confounding effects on myogenic differentiation. Specifically, co-purification of insulin (a component of Opti-MEM) in non-EV LC fractions and polymer precipitated EV preparations. These findings provide further evidence that polymer-based precipitation techniques should be avoided in EV research.

Extracellular Vesicle Heterogeneity and Its Impact for Regenerative Medicine Applications

Extracellular vesicles (EVs) are cell-derived membrane-enclosed particles that are involved in physiologic and pathologic processes. EVs are increasingly being studied for therapeutic applications in the field of regenerative medicine. Therapeutic application of stem cell-derived EVs has shown great potential to stimulate tissue repair. However, the exact mechanisms through which they induce this effect have not been fully clarified. This may to a large extent be attributed to a lack of knowledge on EV heterogeneity. Recent studies suggest that EVs represent a heterogeneous population of vesicles with distinct functions. The heterogeneity of EVs can be attributed to differences in their biogenesis, and as such, they can be classified into distinct populations that can then be further subcategorized into various subpopulations. A better understanding of EV heterogeneity is crucial for elucidating their mechanisms of action in tissue regeneration. This review provides an overview of the latest insights on EV heterogeneity related to tissue repair, including the different characteristics that contribute to such heterogeneity and the functional differences among EV subtypes. It also sheds light on the challenges that hinder clinical translation of EVs. Additionally, innovative EV isolation techniques for studying EV heterogeneity are discussed. Improved knowledge of active EV subtypes would promote the development of tailored EV therapies and aid researchers in the translation of EV-based therapeutics to the clinic. SIGNIFICANCE STATEMENT: Within this review we discuss the differences in regenerative properties of extracellular vesicle (EV) subpopulations and implications of EV heterogeneity for development of EV-based therapeutics. We aim to provide new insights into which aspects are leading to heterogeneity in EV preparations and stress the importance of EV heterogeneity studies for clinical applications.

The developing role of extracellular vesicles in autoimmune diseases: special attention to mesenchymal stem cell-derived extracellular vesicles

Autoimmune diseases are complex, chronic inflammatory conditions initiated by the loss of immunological tolerance to self-antigens. Nowadays, there is no effective and useful therapy for autoimmune diseases, and the existing medications have some limitations due to their nonspecific targets and side effects. During the last few decades, it has been established that mesenchymal stem cells (MSCs) have immunomodulatory functions. It is proposed that MSCs can exert an important therapeutic effect on autoimmune disorders. In parallel with these findings, several investigations have shown that MSCs alleviate autoimmune diseases. Intriguingly, the results of studies have demonstrated that the effective roles of MSCs in autoimmune diseases do not depend on direct intercellular communication but on their ability to release a wide spectrum of paracrine mediators such as growth factors, cytokines and extracellular vehicles (EVs). EVs that range from 50 to 5,000 nm were produced by almost any cell type, and these nanoparticles participate in homeostasis and intercellular communication via the transfer of a broad range of biomolecules such as modulatory proteins, nucleic acids (DNA and RNA), lipids, cytokines, and metabolites. EVs derived from MSCs display the exact properties of MSCs and can be safer and more beneficial than their parent cells. In this review, we will discuss the features of MSCs and their EVs, EVs biogenesis, and their cargos, and then we will highlight the existing discoveries on the impacts of EVs from MSCs on autoimmune diseases such as multiple sclerosis, arthritis rheumatic, inflammatory bowel disease, Type 1 diabetes mellitus, systemic lupus erythematosus, autoimmune liver diseases, Sjögren syndrome, and osteoarthritis, suggesting a potential alternative for autoimmune conditions therapy.

Cardiac progenitor cell-derived extracellular vesicles promote angiogenesis through both associated- and co-isolated proteins

Extracellular vesicles (EVs) are cell-derived lipid bilayer-enclosed particles that play a role in intercellular communication. Cardiac progenitor cell (CPC)-derived EVs have been shown to protect the myocardium against ischemia-reperfusion injury via pro-angiogenic effects. However, the mechanisms underlying CPC-EV-induced angiogenesis remain elusive. Here, we discovered that the ability of CPC-EVs to induce in vitro angiogenesis and to stimulate pro-survival pathways was lost upon EV donor cell exposure to calcium ionophore. Proteomic comparison of active and non-active EV preparations together with phosphoproteomic analysis of activated endothelial cells identified the contribution of candidate protein PAPP-A and the IGF-R signaling pathway in EV-mediated cell activation, which was further validated using in vitro angiogenesis assays. Upon further purification using iodixanol gradient ultracentrifugation, EVs partly lost their activity, suggesting a co-stimulatory role of co-isolated proteins in recipient cell activation. Our increased understanding of the mechanisms of CPC-EV-mediated cell activation will pave the way to more efficient EV-based therapeutics.

Depletion of soluble cytokines unlocks the immunomodulatory bioactivity of extracellular vesicles

Despite an enormous interest in understanding the bioactivity of extracellular vesicles (EV) in physiology and disease for the development of therapeutic applications, the impact of EV preparation methods remains minimally explored. In this study, we implemented density gradient ultracentrifugation combined with size-exclusion chromatography (DG-SEC), differential ultracentrifugation (dUC) and/or stand-alone SEC (sSEC) to fractionate media conditioned by different cancer cells and/or cancer-associated fibroblasts (CAF). EV-enriched but protein-depleted versus EV-depleted but protein-enriched DG-SEC fractions, and EV-containing dUC and sSEC preparations were quality controlled for particle number, protein concentration, selected protein composition and ultrastructure, characterized for their cytokine content, and dose-dependently evaluated for monocyte-derived dendritic cell (MoDC) maturation by measuring surface marker expression and/or cytokine secretion. EV preparations obtained by DG-SEC from media conditioned by different cancer cell lines or CAF, were depleted from soluble immune suppressive cytokines such as VEGF-A and MCP-1 and potently stimulated MoDC maturation. In contrast, EV-containing dUC or sSEC preparations were not depleted from these soluble cytokines and were unable to mature MoDC. Subsequent processing of dUC EV preparations by SEC dose-dependently restored the immunomodulatory bioactivity. Overall, our results demonstrate that method-dependent off-target enrichment of soluble cytokines has implications for the study of EV immunomodulatory bioactivity and warrants careful consideration.

Manufacture of extracellular vesicles derived from mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) are a promising therapy for various diseases ranging from ischemic stroke to wound healing and cancer. Their therapeutic effects are mainly mediated by secretome-derived paracrine factors, with extracellular vesicles (EVs) proven to play a key role. This has led to promising research on the potential of MSC-EVs as regenerative, off-the-shelf therapeutic agents. However, the translation of MSC-EVs into the clinic is hampered by the poor scalability of their production. Recently, new advanced methods have been developed to upscale MSC cultivation and EV production yields, ranging from new cell culture devices to priming procedures. This review gives an overview of these innovative strategies for manufacturing MSC-EVs.

Exosomal miR-125b-5p derived from adipose-derived mesenchymal stem cells enhance diabetic hindlimb ischemia repair via targeting alkaline ceramidase 2

INTRODUCTION

Ischemic diseases caused by diabetes continue to pose a major health challenge and effective treatments are in high demand. Mesenchymal stem cells (MSCs) derived exosomes have aroused broad attention as a cell-free treatment for ischemic diseases. However, the efficacy of exosomes from adipose-derived mesenchymal stem cells (ADSC-Exos) in treating diabetic lower limb ischemic injury remains unclear.

METHODS

Exosomes were isolated from ADSCs culture supernatants by differential ultracentrifugation and their effect on C2C12 cells and HUVECs was assessed by EdU, Transwell, and in vitro tube formation assays separately. The recovery of limb function after ADSC-Exos treatment was evaluated by Laser-Doppler perfusion imaging, limb function score, and histological analysis. Subsequently, miRNA sequencing and rescue experiments were performed to figure out the responsible miRNA for the protective role of ADSC-Exos on diabetic hindlimb ischemic injury. Finally, the direct target of miRNA in C2C12 cells was confirmed by bioinformatic analysis and dual-luciferase report gene assay.

RESULTS

ADSC-Exos have the potential to promote proliferation and migration of C2C12 cells and to promote HUVECs angiogenesis. In vivo experiments have shown that ADSC-Exos can protect ischemic skeletal muscle, promote the repair of muscle injury, and accelerate vascular regeneration. Combined with bioinformatics analysis, miR-125b-5p may be a key molecule in this process. Transfer of miR-125b-5p into C2C12 cells was able to promote cell proliferation and migration by suppressing ACER2 overexpression.

CONCLUSION

The findings revealed that miR-125b-5p derived from ADSC-Exos may play a critical role in ischemic muscle reparation by targeting ACER2. In conclusion, our study may provide new insights into the potential of ADSC-Exos as a treatment option for diabetic lower limb ischemia.

Extracellular vesicles as personalized medicine

Extracellular vesicles (EVs) are released from all cells in the body, forming an important intercellular communication network that contributes to health and disease. The contents of EVs are cell source-specific, inducing distinct signaling responses in recipient cells. The specificity of EVs and their accumulation in fluid spaces that are accessible for liquid biopsies make them highly attractive as potential biomarkers and therapies for disease. The duality of EVs as favorable (therapeutic) or unfavorable (pathological) messengers is context dependent and remains to be fully determined in homeostasis and various disease states. This review describes the use of EVs as biomarkers, drug delivery vehicles, and regenerative therapeutics, highlighting examples involving viral infections, cancer, and neurological diseases. There is growing interest to provide personalized therapy based on individual patient and disease characteristics. Increasing evidence suggests that EV biomarkers and therapeutic approaches are ideal for personalized medicine due to the diversity and multifunctionality of EVs.

A new isolation method for bacterial extracellular vesicles providing greater purity and improved proteomic detection of vesicle proteins

Contaminants within cell culture media often co-isolate with eukaryotic extracellular vesicles (EVs) thus affecting their biological properties. It has yet to be investigated if this is also true for bacterial EVs (BEVs), especially for organisms grown in complex culture media containing animal-derived products. To address this question, we isolated BEVs from the fastidious bacterium Helicobacter pylori grown in either standard Brain Heart Infusion (BHI) medium or BHI depleted of animal-derived products (D-BHI). We show that BEVs prepared from bacteria grown in D-BHI medium have similar morphologies, size ranges and yields to those prepared from standard medium. Similarly, no differences were found in the ability of H. pylori BEVs to induce IL-8 responses in epithelial cells. However, H. pylori BEVs prepared from D-BHI medium were of higher purity than those prepared from standard medium. Importantly, proteomic analyses detected 3.4-fold more H. pylori proteins and 10-fold fewer bovine-derived proteins in BEV samples prepared from D-BHI rather than the standard method. Fifty-seven H. pylori proteins were uniquely detected in BEV samples prepared from D-BHI. In conclusion, we have described an improved method for BEV isolation. Furthermore, we demonstrate how animal-derived products in bacteriological culture media may adversely affect proteomic analyses of BEVs.

Taste papilla cell differentiation requires tongue mesenchyme via ALK3-BMP signaling to regulate the production of secretory proteins

Taste papillae are specialized organs each of which is comprised of an epithelial wall hosting taste buds and a core of mesenchymal tissue. In the present study, we report that during the early stages of embryonic development, bone morphogenetic protein (BMP) signaling mediated by type 1 receptor ALK3 in the tongue mesenchyme is required for the epithelial Wnt/β-catenin activity and taste papilla cell differentiation. Mesenchyme-specific knockout ( cKO ) of Alk3 using Wnt1-Cre and Sox10-Cre resulted in an absence of taste papillae at E12.0. Biochemical and cell differentiation analyses demonstrated that mesenchymal ALK3-BMP signaling governs the production of previously unappreciated secretory proteins, i.e., suppresses those that inhibiting and facilitates those promoting taste cell differentiation. Bulk RNA-Sequencing analysis revealed many more differentially expressed genes (DEGs) in the tongue epithelium than in the mesenchyme in Alk3 cKO vs control. Moreover, we detected a down-regulated epithelial Wnt/β-catenin signaling, and taste papilla development in the Alk3 cKO was rescued by GSK3β inhibitor LiCl, but not Wnt3a. Our findings demonstrate for the first time the requirement of tongue mesenchyme in taste papilla cell differentiation.

Summary statement

This is the first set of data to implicate the requirement of tongue mesenchyme in taste papilla cell differentiation.

Assessment of anti-inflammatory bioactivity of extracellular vesicles is susceptible to error via media component contamination

Extracellular vesicles (EVs) are widely implicated as novel diagnostic and therapeutic modalities for a wide range of diseases. Thus, optimization of EV biomanufacturing is of high interest. In the course of developing parameters for a human embryonic kidney cells (HEK293T) EV production platform, we examined the combinatorial effects of cell culture conditions (i.e., static versus dynamic) and isolation techniques (i.e., ultracentrifugation versus tangential flow filtration versus size-exclusion chromatography) on functional characteristics of HEK293T EVs, including anti-inflammatory bioactivity using a well-established lipopolysaccharide-stimulated mouse macrophage model. We unexpectedly found that, depending on culture condition and isolation strategy, HEK293T EVs appeared to significantly suppress the secretion of pro-inflammatory cytokines (i.e., interleukin-6, RANTES [regulated upon activation, normal T cell expressed and secreted]) in the stimulated mouse macrophages. Further examination revealed that these results were most likely due to non-EV fetal bovine serum components in HEK293T EV preparations. Thus, future research assessing the anti-inflammatory effects of EVs should be designed to account for this phenomenon.

A survey to evaluate parameters governing the selection and application of extracellular vesicle isolation methods

Extracellular vesicles (EVs) continue to gain interest across the scientific community for diagnostic and therapeutic applications. As EV applications diversify, it is essential that researchers are aware of challenges, in particular the compatibility of EV isolation methods with downstream applications and their clinical translation. We report outcomes of the first cross-comparison study looking to determine parameters (EV source, starting volume, operator experience, application and implementation parameters such as cost and scalability) governing the selection of popular EV isolation methods across disciplines. Our findings highlighted an increased clinical focus, with 36% of respondents applying EVs in therapeutics and diagnostics. Data indicated preferential selection of ultracentrifugation for therapeutic applications, precipitation reagents in clinical settings and size exclusion chromatography for diagnostic applications utilising biofluids. Method selection was influenced by operator experience, with increased method diversity when EV research was not the respondents primary focus. Application and implementation criteria were indicated to be major influencers in method selection, with UC and SEC chosen for their abilities to process large and small volumes, respectively. Overall, we identified parameters influencing method selection across the breadth of EV science, providing a valuable overview of practical considerations for the effective translation of research outcomes.

Density-Based Fractionation of Cell-Conditioned Medium to Prepare Proteomics Grade Extracellular Vesicles

The identification of the molecular composition of extracellular vesicles (EV) by omics approaches, including proteomics, requires the separation of EV from non-EV confounding factors present in the source biofluid. In this protocol, we present the sequential implementation of density gradient ultracentrifugation and size-exclusion chromatography to prepare EV from cell-conditioned medium with high specificity and repeatability. This approach enables the recovery of intact purified EV suited for downstream functional assays and biomarker discovery by omics approaches.

Transcript Engineered Extracellular Vesicles Alleviate Alloreactive Dynamics in Renal Transplantation

Direct contact of membrane molecules and cytokine interactions orchestrate immune homeostasis. However, overcoming the threshold of distance and velocity barriers, and achieving adhesion mediated immune interaction remain difficult. Here, inspired by the natural chemotaxis of regulatory T cells, multifunctionalized FOXP3 genetic engineered extracellular vesicles, termed Foe-TEVs, are designed, which display with adhesive molecules, regulatory cytokines, and coinhibitory contact molecules involving CTLA-4 and PD-1, by limited exogenous gene transduction. Foe-TEVs effectively adhere to the tubular, endothelial, and glomerular regions of allogeneic injury in the renal allograft, mitigating cell death in situ and chronic fibrosis transition. Remarkably, transcript engineering reverses the tracking velocity of vesicles to a retained phenotype and enhanced arrest coefficient by a factor of 2.16, directly interacting and attenuating excessive allosensitization kinetics in adaptive lymphoid organs. In murine allogeneic transplantation, immune adhesive Foe-TEVs alleviate pathological responses, restore renal function with well ordered ultrastructure and improved glomerular filtration rate, and prolong the survival period of the recipient from 30.16 to 92.81 days, demonstrating that the delivery of extracellular vesicles, genetically engineered for immune adhesive, is a promising strategy for the treatment of graft rejection.

Transfection reagent artefact likely accounts for some reports of extracellular vesicle function

Extracellular vesicles (EV) are important mediators of cell communication and physiology. EVs are frequently investigated by transiently transfecting cells with plasmid DNA to produce EVs modified with protein(s) or nucleic acid(s) of interest. DNA-transfection reagent complexes (DTC) are approximately the same size as EVs, raising the possibility that some purification procedures may fail to separate these two species and activity arising from carryover DTC may be improperly attributed to EVs. We find that differential ultracentrifugation, a commonly employed EV isolation procedure, does not separate EVs from DTC present in the cell culture supernatant of transiently transfected cells. We demonstrate that the biological activity of an EV-directed Cre recombinase is due to contaminating plasmid DNA and not EV-mediated delivery of Cre protein. Moreover, steps commonly taken to remove plasmid DNA from EV samples, such as media exchanges and treatment with nucleases, are ineffective at avoiding this artefact. Due to the pernicious nature of plasmid DNA in these cellular assays, some reports of EV function are likely artefacts produced by contaminating DTC. EVs and DTC can be separated by density gradient ultracentrifugation, highlighting the importance of validating elimination of DTC when using transient transfection of EV-producing cells to interrogate EV function.

Small Extracellular Vesicles Secreted by Nigrostriatal Astrocytes Rescue Cell Death and Preserve Mitochondrial Function in Parkinson's Disease

Extracellular vesicles (EVs) are emerging as powerful players in cell-to-cell communication both in healthy and diseased brain. In Parkinson's disease (PD)-characterized by selective dopaminergic neuron death in ventral midbrain (VMB) and degeneration of their terminals in striatum (STR)-astrocytes exert dual harmful/protective functions, with mechanisms not fully elucidated. Here, this study shows that astrocytes from the VMB-, STR-, and VMB/STR-depleted brains release a population of small EVs  in a region-specific manner. Interestingly, VMB-astrocytes secreted the highest rate of EVs, which is further exclusively increased in response to CCL3, a chemokine that promotes robust dopaminergic neuroprotection in different PD models. The neuroprotective potential of nigrostriatal astrocyte-EVs is investigated in differentiated versus undifferentiated SH-SY5Y cells exposed to oxidative stress and mitochondrial toxicity. EVs from both VMB- and STR-astrocytes counteract H₂ O₂ -induced caspase-3 activation specifically in differentiated cells, with EVs from CCL3-treated astrocytes showing a higher protective effect. High resolution respirometry further reveals that nigrostriatal astrocyte-EVs rescue neuronal mitochondrial complex I function impaired by the neurotoxin MPP⁺ . Notably, only EVs from VMB-astrocyte fully restore ATP production, again specifically in differentiated SH-SY5Y. These results highlight a regional diversity in the nigrostriatal system for the secretion and activities of astrocyte-EVs, with neuroprotective implications for PD.

Comparison of EV-free fraction, EVs, and total secretome of amniotic mesenchymal stromal cells for their immunomodulatory potential: a translational perspective

Amniotic mesenchymal stromal cells (hAMSCs) have unique immunomodulatory properties demonstrated in vitro and in vivo in various diseases in which the dysregulated immune system plays a major role. The immunomodulatory and pro-regenerative effects of MSCs, among which hAMSCs lie in the bioactive factors they secrete and in their paracrine activity, is well known. The mix of these factors (i.e., secretome) can be either freely secreted or conveyed by extracellular vesicles (EV), thus identifying two components in the cell secretome: EV-free and EV fractions. This study aimed to discern the relative impact of the individual components on the immunomodulatory action of the hAMSC secretome in order to obtain useful information for implementing future therapeutic approaches using immunomodulatory therapies based on the MSC secretome. To this aim, we isolated EVs from the hAMSC secretome (hAMSC-CM) by ultracentrifugation and validated the vesicular product according to the International Society for Extracellular Vesicles (ISEV) criteria. EVs were re-diluted in serum-free medium to maintain the EV concentration initially present in the original CM. We compared the effects of the EV-free and EV fractions with those exerted by hAMSC-CM in toto on the activation and differentiation of immune cell subpopulations belonging to both the innate and adaptive immune systems.

We observed that the EV-free fraction, similar to hAMSC-CM in toto, a) decreases the proliferation of activated peripheral blood mononuclear cells (PBMC), b) reduces the polarization of T cells toward inflammatory Th subsets, and induces the induction of regulatory T cells; c) affects monocyte polarization to antigen-presenting cells fostering the acquisition of anti-inflammatory macrophage (M2) markers; and d) reduces the activation of B lymphocytes and their maturation to plasma cells. We observed instead that all investigated EV fractions, when used in the original concentrations, failed to exert any immunomodulatory effect, even though we show that EVs are internalized by various immune cells within PBMC. These findings suggest that the active component able to induce immune regulation, tested at original concentrations, of the hAMSC secretome resides in factors not conveyed in EVs. However, EVs isolated from hAMSC could exert actions on other cell types, as reported by others.

Practical Considerations for Translating Mesenchymal Stromal Cell-Derived Extracellular Vesicles from Bench to Bed

Extracellular vesicles (EVs) derived from mesenchymal stromal cells (MSCs) have shown potential for the treatment of tendon and ligament injuries. This approach can eliminate the need to transplant live cells to the human body, thereby reducing issues related to the maintenance of cell viability and stability and potential erroneous differentiation of transplanted cells to bone or tumor. Despite these advantages, there are practical issues that need to be considered for successful clinical application of MSC-EV-based products in the treatment of tendon and ligament injuries. This review aims to discuss the general and tissue-specific considerations for manufacturing MSC-EVs for clinical translation. Specifically, we will discuss Good Manufacturing Practice (GMP)-compliant manufacturing and quality control (parent cell source, culture conditions, concentration method, quantity, identity, purity and impurities, sterility, potency, reproducibility, storage and formulation), as well as safety and efficacy issues. Special considerations for applying MSC-EVs, such as their compatibility with arthroscopy for the treatment of tendon and ligament injuries, are also highlighted.

Comparing extracellular vesicles and cell membranes as biocompatible coatings for gold nanorods: Implications for targeted theranostics

Extracellular vesicles (EVs) and cell membrane nanoghosts are excellent coatings for nanomaterials, providing enhanced delivery in the target sites and evasion of the immune system. These cell-derived coatings allow the exploration of the delivery properties of the nanoparticles without stimulation of the immune system. Despite the advances reported on the use of EVs and cell-membrane coatings for nanomedicine applications, there are no standards to compare the benefits and main differences between these technologies. Here we investigated macrophage-derived EVs and cell membranes-coated gold nanorods and compared both systems in terms of target delivery in cancer and stromal cells. Our results reveal a higher tendency of EV-coated nanorods to interact with macrophages yet both EV and cell membrane-coated nanorods were internalized in the metastatic breast cancer cells. The main differences between these nanoparticles are related to the presence or absence of CD47 in the coating material, not usually addressed in EVs characterization. Our findings highlight important delivery differences exhibited by EVs- or cell membranes- coated nanorods which understanding may be important to the design and development of theragnostic nanomaterials using these coatings for target delivery.

Secretion of the disulfide bond generating catalyst QSOX1 from pancreatic tumor cells into the extracellular matrix: association with extracellular vesicles and matrix proteins

Quiescin sulfhydryl oxidase 1 (QSOX1) is a disulfide bond generating catalyst that is overexpressed in solid tumors. Expression of QSOX1 is linked to cancer cell invasion, tumor grade, and extracellular matrix (ECM) protein deposition. While the secreted version of QSOX1 is known to be present in various fluids and secretory tissues, its presence in the ECM of cancer is less understood. To characterize secreted QSOX1, we separated conditioned media based on size and density. We discovered that the majority of secreted QSOX1 resides in the EV-depleted fraction and in the soluble protein fraction. Very little QSOX1 could be detected in the EVP fraction. We used immunofluorescence to image subpopulations of EVs and found QSOX1 in Golgi-derived vesicles and medium/large vesicles, but in general, most extracellular QSOX1 was not attributed to these vesicles. Next, we quantified QSOX1 co-localization with the EV marker Alix. For the medium/large EVs, ~98% contained QSOX1 when fibronectin was used as a coating. However, on collagen coatings, only ~60% of these vesicles contained QSOX1, suggesting differences in EV cargo based on ECM coated surfaces. About 10% of small EVs co-localized with QSOX1 on every ECM protein surface except for collagen (0.64%). We next investigated adhesion of QSOX1 to ECM proteins in vitro and in situ and found that QSOX1 preferentially adheres to fibronectin, laminins, and Matrigel compared to gelatin and collagen. This mechanism was found to be, in part, mediated by the formation of mixed disulfides between QSOX1 and cysteine-rich ECM proteins. In summary, we found that QSOX1 (1) is in subpopulations of medium/large EVs, (2) seems to interact with small Alix+ EVs, and (3) adheres to cysteine-rich ECM proteins, potentially through the formation of intermediate disulfides. These observations offer significant insight into how enzymes, such as QSOX1, can facilitate matrix remodeling events in solid tumor progression.

Pattern Analysis of Organellar Maps for Interpretation of Proteomic Data

Localization of organelle proteins by isotope tagging (LOPIT) maps are a coordinate-directed representation of proteome data that can aid in biological interpretation. Analysis of organellar association for proteins as displayed using LOPIT is evaluated and interpreted for two types of proteomic data sets. First, test and control group protein abundances and fold change data obtained in a proximity labeling experiment are plotted on a LOPIT map to evaluate the likelihood of true protein interactions. Selection of true positives based on co-localization of proteins in the organellar space is shown to be consistent with carboxylase enrichment which serves as a positive control for biotinylation in streptavidin affinity selected proteome data sets. The mapping in organellar space facilitates discrimination between the test and control groups and aids in identification of proteins of interest. The same representation of proteins in organellar space is used in the analysis of extracellular vesicle proteomes for which protein abundance and fold change data are evaluated. Vesicular protein organellar localization patterns provide information about the subcellular origin of the proteins in the samples which are isolates from the extracellular milieu. The organellar localization patterns are indicative of the provenance of the vesicular proteome origin and allow discrimination between proteomes prepared using different enrichment methods. The patterns in LOPIT displays are easy to understand and compare which aids in the biological interpretation of proteome data.

Harnessing the Therapeutic Potential of Extracellular Vesicles for Biomedical Applications Using Multifunctional Magnetic Nanomaterials

Extracellular vesicles (e.g., exosomes) carrying various biomolecules (e.g., proteins, lipids, and nucleic acids) have rapidly emerged as promising platforms for many biomedical applications. Despite their enormous potential, their heterogeneity in surfaces and sizes, the high complexity of cargo biomolecules, and the inefficient uptake by recipient cells remain critical barriers for their theranostic applications. To address these critical issues, multifunctional nanomaterials, such as magnetic nanomaterials, with their tunable physical, chemical, and biological properties, may play crucial roles in next-generation extracellular vesicles (EV)-based disease diagnosis, drug delivery, tissue engineering, and regenerative medicine. As such, one aims to provide cutting-edge knowledge pertaining to magnetic nanomaterials-facilitated isolation, detection, and delivery of extracellular vesicles and their associated biomolecules. By engaging the fields of extracellular vesicles and magnetic nanomaterials, it is envisioned that their properties can be effectively combined for optimal outcomes in biomedical applications.

HOTAIR-Loaded Mesenchymal Stem/Stromal Cell Extracellular Vesicles Enhance Angiogenesis and Wound Healing

Chronic wounds remain a substantial source of morbidity worldwide. An emergent approach that may be well-suited to induce the complex, multicellular processes such as angiogenesis that are required for wound repair is the use of extracellular vesicles (EVs). EVs contain a wide variety of proteins and nucleic acids that enable multifactorial signaling. Here, the capability of EVs is leveraged to be engineered via producer cell modification to investigate the therapeutic potential of EVs from mesenchymal stem/stromal cells (MSCs) transfected to overexpress long non-coding RNA HOX transcript antisense RNA (HOTAIR). HOTAIR is previously shown by the authors' group to be critical in mediating angiogenic effects of endothelial cell EVs, and MSCs are chosen as EV producer cells for this study due to their widely reported intrinsic angiogenic properties. The results indicate that MSCs overexpressing HOTAIR (HOTAIR-MSCs) produce EVs with increased HOTAIR content that promote angiogenesis and wound healing in diabetic (db/db) mice. Further, endothelial cells exposed to HOTAIR-MSC EVs exhibit increased HOTAIR content correlated with upregulation of the angiogenic protein vascular endothelial growth factor. Thus, this study supports EV-mediated HOTAIR delivery as a strategy for further exploration toward healing of chronic wounds.

Extracellular vesicle research in reproductive science- Paving the way for clinical achievements

Mammalian conception involves a multitude of reciprocal interactions via a molecular dialogue between mother and conceptus. Extracellular vesicles (EVs) are secreted membrane-encapsulated particles that mediate cell-to-cell communication in various contexts. EVs, which are present in seminal, follicular, oviductal, and endometrial fluids, as well as in embryo secretions, carry molecular constituents that impact gamete maturation, fertilization, early embryo development, and embryo-maternal communication. The distribution, concentration, and molecular cargo of EVs are regulated by steroid hormones and the health status of the tissue of origin, and thus are influenced by menstrual phase, stage of conception, and the presence of infertility-associated diseases. EVs have been recognized as a novel source of biomarkers and potential reproductive medicine therapeutics, particularly for assisted reproductive technology (ART). There are still many technological and scientific hindrances to be overcome before EVs can be used in clinical diagnostic and therapeutic ART applications. Issues to be resolved include the lack of standardized measurement protocols and an absence of absolute EV quantification technologies. Additionally, clinically suitable and robust EV isolation methods have yet to be developed. In this review, we provide an overview of EV-mediated interactions during the early stages of reproduction from gamete maturation to embryo implantation and then outline the technological progress that must be made for EV applications to be translated to clinical settings.

Development of extracellular vesicle-based medicinal products: A position paper of the group "Extracellular Vesicle translatiOn to clinicaL perspectiVEs - EVOLVE France"

Extracellular vesicles (EV) are emergent therapeutic effectors that have reached clinical trial investigation. To translate EV-based therapeutic to clinic, the challenge is to demonstrate quality, safety, and efficacy, as required for any medicinal product. EV research translation into medicinal products is an exciting and challenging perspective. Recent papers, provide important guidance on regulatory aspects of pharmaceutical development, defining EVs for therapeutic applications and critical considerations for the development of potency tests. In addition, the ISEV Task Force on Regulatory Affairs and Clinical Use of EV-based Therapeutics as well as the Exosomes Committee from the ISCT are expected to contribute in an active way to the development of EV-based medicinal products by providing update on the scientific progress in EVs field, information to patients and expert resource network for regulatory bodies. The contribution of our work group "Extracellular Vesicle translatiOn to clinicaL perspectiVEs - EVOLVE France", created in 2020, can be positioned in complement to all these important initiatives. Based on complementary scientific, technical, and medical expertise, we provide EV-specific recommendations for manufacturing, quality control, analytics, non-clinical development, and clinical trials, according to current European legislation. We especially focus on early phase clinical trials concerning immediate needs in the field. The main contents of the investigational medicinal product dossier, marketing authorization applications, and critical guideline information are outlined for the transition from research to clinical development and ultimate market authorization.

Single Particle Automated Raman Trapping Analysis of Breast Cancer Cell-Derived Extracellular Vesicles as Cancer Biomarkers

Extracellular vesicles (EVs) secreted by cancer cells provide an important insight into cancer biology and could be leveraged to enhance diagnostics and disease monitoring. This paper details a high-throughput label-free extracellular vesicle analysis approach to study fundamental EV biology, toward diagnosis and monitoring of cancer in a minimally invasive manner and with the elimination of interpreter bias. We present the next generation of our single particle automated Raman trapping analysis─SPARTA─system through the development of a dedicated standalone device optimized for single particle analysis of EVs. Our visualization approach, dubbed dimensional reduction analysis (DRA), presents a convenient and comprehensive method of comparing multiple EV spectra. We demonstrate that the dedicated SPARTA system can differentiate between cancer and noncancer EVs with a high degree of sensitivity and specificity (>95% for both). We further show that the predictive ability of our approach is consistent across multiple EV isolations from the same cell types. Detailed modeling reveals accurate classification between EVs derived from various closely related breast cancer subtypes, further supporting the utility of our SPARTA-based approach for detailed EV profiling.

Thinking Quantitatively of RNA-Based Information Transfer via Extracellular Vesicles: Lessons to Learn for the Design of RNA-Loaded EVs

Extracellular vesicles (EVs) are 50–1000 nm vesicles secreted by virtually any cell type in the body. They are expected to transfer information from one cell or tissue to another in a short- or long-distance way. RNA-based transfer of information via EVs at long distances is an interesting well-worn hypothesis which is ~15 years old. We review from a quantitative point of view the different facets of this hypothesis, ranging from natural RNA loading in EVs, EV pharmacokinetic modeling, EV targeting, endosomal escape and RNA delivery efficiency. Despite the unique intracellular delivery properties endowed by EVs, we show that the transfer of RNA naturally present in EVs might be limited in a physiological context and discuss the lessons we can learn from this example to design efficient RNA-loaded engineered EVs for biotherapies. We also discuss other potential EV mediated information transfer mechanisms, among which are ligand–receptor mechanisms.

Reporter gene assay for membrane fusion of extracellular vesicles

Extracellular vesicles (EVs) secreted by living cells are expected to deliver biological cargo molecules, including RNA and proteins, to the cytoplasm of recipient cells. There is an increasing need to understand the mechanism of intercellular cargo delivery by EVs. However, the lack of a feasible bioassay has hampered our understanding of the biological processes of EV uptake, membrane fusion, and cargo delivery to recipient cells. Here, we describe a reporter gene assay that can measure the membrane fusion efficiency of EVs during cargo delivery to recipient cells. When EVs containing tetracycline transactivator (tTA)-fused tetraspanins are internalized by recipient cells and fuse with cell membranes, the tTA domain is exposed to the cytoplasm and cleaved by tobacco etch virus protease to induce tetracycline responsive element (TRE)-mediated reporter gene expression in recipient cells. This assay (designated as EV-mediated tetraspanin-tTA delivery assay, ETTD assay), enabled us to assess the cytoplasmic cargo delivery efficiency of EVs in recipient cells. With the help of a vesicular stomatitis virus-derived membrane fusion protein, the ETTD assay could detect significant enhancement of cargo delivery efficiency of EVs. Furthermore, the ETTD assay could evaluate the effect of potential cargo delivery enhancers/inhibitors. Thus, the ETTD assay may contribute to a better understanding of the underlying mechanism of the cytoplasmic cargo delivery by EVs.

When Origin Matters: Properties of Mesenchymal Stromal Cells From Different Sources for Clinical Translation in Kidney Disease

Advanced therapy medicinal products (ATMPs) offer new prospects to improve the treatment of conditions with unmet medical needs. Kidney diseases are a current major health concern with an increasing global prevalence. Chronic renal failure appears after many years of impairment, which opens a temporary window to apply novel therapeutic approaches to delay or halt disease progression. The immunomodulatory, anti-inflammatory, and pro-regenerative properties of mesenchymal stromal cells (MSCs) have sparked interest for their use in cell-based regenerative therapies. Currently, several early-phase clinical trials have been completed and many are ongoing to explore MSC safety and efficacy in a wide range of nephropathies. However, one of the current roadblocks to the clinical translation of MSC therapies relates to the lack of standardization and harmonization of MSC manufacturing protocols, which currently hinders inter-study comparability. Studies have shown that cell culture processing variables can have significant effects on MSC phenotype and functionality, and these are highly variable across laboratories. In addition, heterogeneity within MSC populations is another obstacle. Furthermore, MSCs may be isolated from several sources which adds another variable to the comparative assessment of outcomes. There is now a growing body of literature highlighting unique and distinctive properties of MSCs according to the tissue origin, and that characteristics such as donor, age, sex and underlying medical conditions may alter the therapeutic effect of MSCs. These variables must be taken into consideration when developing a cell therapy product. Having an optimal scale-up strategy for MSC manufacturing is critical for ensuring product quality while minimizing costs and time of production, as well as avoiding potential risks. Ideally, optimal scale-up strategies must be carefully considered and identified during the early stages of development, as making changes later in the bioprocess workflow will require re-optimization and validation, which may have a significant long-term impact on the cost of the therapy. This article provides a summary of important cell culture processing variables to consider in the scale-up of MSC manufacturing as well as giving a comprehensive review of tissue of origin-specific biological characteristics of MSCs and their use in current clinical trials in a range of renal pathologies.

Adherence to minimal experimental requirements for defining extracellular vesicles and their functions

Rigorous measures are required to cope with the advance of extracellular vesicle (EV) research, from 183 studies published in 2012 to 2,309 studies published in 2020. The International Society for Extracellular Vesicles (ISEV) proposed Minimal Information for Studies of Extracellular Vesicles (MISEV) guidelines in 2014, updated in 2018, for assuring and improving EV research quality. We performed a systematic review using a text mining approach to assess adherence to MISEV criteria. A keyword search was conducted in 5,093 accessible publications over the period 2012-2020 and analyzed the methodology used for EV isolation and characterization. We found a significant improvement over the years particularly regarding EV characterization where recent papers used a higher number of methods and EV markers to check for quantity and purity. Interestingly, we also found that EV papers using more methods and EV markers were cited more frequently. Papers citing MISEV criteria were more prone to use a higher number of characterization methods. We therefore established a concise checklist summarizing MISEV criteria to support EV researchers towards reaching the highest standards in the field.

Technological advances towards extracellular vesicles mass production

Extracellular vesicles (EVs) are becoming essential actors in bio-therapeutics, as much for their regenerative or immunomodulatory properties as for their potential as cargo delivery vehicles. To enable the democratization of these EV-based therapies, many challenges remain such as large-scale production which is necessary to reduce costs of treatment. Herein, we review some advanced works on high-yield EV manufacturing. One approach consists in developing large-scale cell culture platforms, while others focus on cell stimulation to increase particle yield per cell. This can be done by moderate physico-chemical stresses or by disrupting cell membrane towards autoassembled vesicle-like particles. We critically compare these different techniques, keeping in mind that the field still lacks shared characterization standards, underline the importance of therapeutic potency assessment and discuss mass production strategies that have been identified in current clinical trials.

Extracellular vesicles for tissue repair and regeneration: Evidence, challenges and opportunities

Extracellular vesicles (EVs) are biological nanoparticles naturally secreted by cells, acting as delivery vehicles for molecular messages. During the last decade, EVs have been assigned multiple functions that have established their potential as therapeutic mediators for a variety of diseases and conditions. In this review paper, we report on the potential of EVs in tissue repair and regeneration. The regenerative properties that have been associated with EVs are explored, detailing the molecular cargo they carry that is capable of mediating such effects, the signaling cascades triggered in target cells and the functional outcome achieved. EV interactions and biodistribution in vivo that influence their regenerative effects are also described, particularly upon administration in combination with biomaterials. Finally, we review the progress that has been made for the successful implementation of EV regenerative therapies in a clinical setting.

Therapeutic Potential of Extracellular Vesicles for Sepsis Treatment

Sepsis is a deadly condition lacking a specific treatment despite decades of research. This has prompted the exploration of new approaches, with extracellular vesicles (EVs) emerging as a focal area. EVs are nanosized, cell-derived particles that transport bioactive components (i.e., proteins, DNA, and RNA) between cells, enabling both normal physiological functions and disease progression depending on context. In particular, EVs have been identified as critical mediators of sepsis pathophysiology. However, EVs are also thought to constitute the biologically active component of cell-based therapies and have demonstrated anti-inflammatory, anti-apoptotic, and immunomodulatory effects in sepsis models. The dual nature of EVs in sepsis is explored here, discussing their endogenous roles and highlighting their therapeutic properties and potential. Related to the latter component, prior studies involving EVs from mesenchymal stem/stromal cells (MSCs) and other sources are discussed and emerging producer cells that could play important roles in future EV-based sepsis therapies are identified. Further, how methodologies could impact therapeutic development toward sepsis treatment to enhance and control EV potency is described.

Separation, characterization, and standardization of extracellular vesicles for drug delivery applications

Extracellular vesicles (EVs) are membranous nanovesicles secreted from living cells, shuttling macromolecules in intercellular communication and potentially possessing intrinsic therapeutic activity. Due to their stability, low immunogenicity, and inherent interaction with recipient cells, EVs also hold great promise as drug delivery vehicles. Indeed, they have been used to deliver nucleic acids, proteins, and small molecules in preclinical investigations. Furthermore, EV-based drugs have entered early clinical trials for cancer or neurodegenerative diseases. Despite their appeal as delivery vectors, however, EV-based drug delivery progress has been hampered by heterogeneity of sample types and methods as well as a persistent lack of standardization, validation, and comprehensive reporting. This review highlights specific requirements for EVs in drug delivery and describes the most pertinent approaches for separation and characterization. Despite residual uncertainties related to pharmacodynamics, pharmacokinetics, and potential off-target effects, clinical-grade, high-potency EV drugs might be achievable through GMP-compliant workflows in a highly standardized environment.

EV Cargo Sorting in Therapeutic Development for Cardiovascular Disease

Cardiovascular disease remains the leading cause of morbidity and mortality in the world. Thus, therapeutic interventions to circumvent this growing burden are of utmost importance. Extracellular vesicles (EVs) actively secreted by most living cells, play a key role in paracrine and endocrine intercellular communication via exchange of biological molecules. As the content of secreted EVs reflect the physiology and pathology of the cell of their origin, EVs play a significant role in cellular homeostasis, disease pathogenesis and diagnostics. Moreover, EVs are gaining popularity in clinics as therapeutic and drug delivery vehicles, transferring bioactive molecules such as proteins, genes, miRNAs and other therapeutic agents to target cells to treat diseases and deter disease progression. Despite our limited but growing knowledge of EV biology, it is imperative to understand the complex mechanisms of EV cargo sorting in pursuit of designing next generation EV-based therapeutic delivery systems. In this review, we highlight the mechanisms of EV cargo sorting and methods of EV bioengineering and discuss engineered EVs as a potential therapeutic delivery system to treat cardiovascular disease.

Small extracellular vesicles obtained from hypoxic mesenchymal stromal cells have unique characteristics that promote cerebral angiogenesis, brain remodeling and neurological recovery after focal cerebral ischemia in mice

Obtained from the right cell-type, mesenchymal stromal cell (MSC)-derived small extracellular vesicles (sEVs) promote stroke recovery. Within this process, microvascular remodeling plays a central role. Herein, we evaluated the effects of MSC-sEVs on the proliferation, migration, and tube formation of human cerebral microvascular endothelial cells (hCMEC/D3) in vitro and on post-ischemic angiogenesis, brain remodeling and neurological recovery after middle cerebral artery occlusion (MCAO) in mice. In vitro, sEVs obtained from hypoxic (1% O2), but not 'normoxic' (21% O2) MSCs dose-dependently promoted endothelial proliferation, migration, and tube formation and increased post-ischemic endothelial survival. sEVs from hypoxic MSCs regulated a distinct set of miRNAs in hCMEC/D3 cells previously linked to angiogenesis, three being upregulated (miR-126-3p, miR-140-5p, let-7c-5p) and three downregulated (miR-186-5p, miR-370-3p, miR-409-3p). LC/MS-MS revealed 52 proteins differentially abundant in sEVs from hypoxic and 'normoxic' MSCs. 19 proteins were enriched (among them proteins involved in extracellular matrix-receptor interaction, focal adhesion, leukocyte transendothelial migration, protein digestion, and absorption), and 33 proteins reduced (among them proteins associated with metabolic pathways, extracellular matrix-receptor interaction, focal adhesion, and actin cytoskeleton) in hypoxic MSC-sEVs. Post-MCAO, sEVs from hypoxic MSCs increased microvascular length and branching point density in previously ischemic tissue assessed by 3D light sheet microscopy over up to 56 days, reduced delayed neuronal degeneration and brain atrophy, and enhanced neurological recovery. sEV-induced angiogenesis in vivo depended on the presence of polymorphonuclear neutrophils. In neutrophil-depleted mice, MSC-sEVs did not influence microvascular remodeling. sEVs from hypoxic MSCs have distinct angiogenic properties. Hypoxic preconditioning enhances the restorative effects of MSC-sEVs.

Immunomodulatory extracellular vesicles: an alternative to cell therapy for COVID-19

Introduction: SARS-CoV-2 induces a cytokine storm and can cause inflammation, fibrosis and apoptosis in the lungs, leading to acute respiratory distress syndrome (ARDS). ARDS is the leading cause of mortality and morbidity the associated to COVID-19, and the cytokine storm is a prominent etiological factor. Mesenchymal stem cell-derived extracellular vesicles are an alternative therapy for the management of inflammatory and autoimmune conditions due to their immunosuppressive properties. The immunomodulatory and tissue regeneration capabilities of extracellular vesicles may support their application as a prospective therapy for COVID-19.Areas Covered: We explored the clinical evidence on extracellular vesicles as antiviral agents and in mitigating ARDS, and their therapeutic potential in COVID-19.Expert Opinion: Clinical trials using extracellular vesicles are registered against COVID-19 associated complications, with some evidence of safety and efficacy. Extracellular vesicles present an alternative potential for cell therapy for COVID-19 management, but further preclinical and clinical investigations are needed.

Angiogenic Properties of Placenta-Derived Extracellular Vesicles in Normal Pregnancy and in Preeclampsia

Angiogenesis is one of the main processes that coordinate the biological events leading to a successful pregnancy, and its imbalance characterizes several pregnancy-related diseases, including preeclampsia. Intracellular interactions via extracellular vesicles (EVs) contribute to pregnancy's physiology and pathophysiology, and to the fetal-maternal interaction. The present review outlines the implications of EV-mediated crosstalk in the angiogenic process in healthy pregnancy and its dysregulation in preeclampsia. In particular, the effect of EVs derived from gestational tissues in pro and anti-angiogenic processes in the physiological and pathological setting is described. Moreover, the application of EVs from placental stem cells in the clinical setting is reported.

Endothelial Extracellular Vesicles: From Keepers of Health to Messengers of Disease

Endothelium has a rich vesicular network that allows the exchange of macromolecules between blood and parenchymal cells. This feature of endothelial cells, along with their polarized secretory machinery, makes them the second major contributor, after platelets, to the particulate secretome in circulation. Extracellular vesicles (EVs) produced by the endothelial cells mirror the remarkable molecular heterogeneity of their parent cells. Cargo molecules carried by EVs were shown to contribute to the physiological functions of endothelium and may support the plasticity and adaptation of endothelial cells in a paracrine manner. Endothelium-derived vesicles can also contribute to the pathogenesis of cardiovascular disease or can serve as prognostic or diagnostic biomarkers. Finally, endothelium-derived EVs can be used as therapeutic tools to target endothelium for drug delivery or target stromal cells via the endothelial cells. In this review we revisit the recent evidence on the heterogeneity and plasticity of endothelial cells and their EVs. We discuss the role of endothelial EVs in the maintenance of vascular homeostasis along with their contributions to endothelial adaptation and dysfunction. Finally, we evaluate the potential of endothelial EVs as disease biomarkers and their leverage as therapeutic tools.

Embryonic Stem Cell Derived Small Extracellular Vesicles Modulate Regulatory T Cells to Protect against Ischemic Stroke

Stem cell derived small extracellular vesicles (sEVs) have been proved to promote neurological recovery after stroke. Recent studies demonstrate a phenomenal tissue repair ability in embryonic stem cell derived sEVs (ESC-sEVs). However, whether ESC-sEVs could protect against ischemic stroke remains unknown. Immune responses play an essential role in the pathogenesis of ischemic stroke, and modulating post-stroke immune responses ameliorates ischemia-induced brain damage. In this study, we aim to determine the therapeutic function of ESC-sEVs, specifically focusing on their role in immunomodulation after ischemic stroke. ESC-sEVs are intravenously administered after transient middle cerebral artery occlusion. ESC-sEVs significantly decrease leukocyte infiltration, inflammatory cytokine expression, neuronal death, and infarct volume and alleviate long-term neurological deficits and tissue loss after ischemic stroke. Interestingly, ESC-sEVs induce a marked increase in regulatory T cells (Tregs) after stroke. Further, ESC-sEV-afforded immunomodulatory function and neuroprotection against stroke are dependent on Tregs, as the depletion of Tregs almost completely abrogates the protective effects. Mechanistically, proteomic analysis reveals the enrichment of TGF-β, Smad2, and Smad4 proteins in ESC-sEVs, which could be delivered to activate the TGF-β/Smad pathway in CD4⁺ T cells and therefore induce Treg expansion. ESC-sEVs modulate neuroinflammation and protect against ischemic stroke through the expansion of Tregs, a process that is partially dependent on the activation of the TGF-β/Smad signaling pathway by the transfer of TGF-β, Smad2, and Smad4. The results suggest ESC-sEVs might be a candidate for immune modulation.

Real-Time Luminescence Assay for Cytoplasmic Cargo Delivery of Extracellular Vesicles

Extracellular vesicles (EVs) have been considered to deliver biological cargos between cells and mediate intercellular communication and potential drug delivery carriers. However, the mechanisms that underlie the biological process of EV uptake and cytoplasmic cargo release in recipient cells are largely unknown. Quantitative and real-time assays for the assessment of cargo delivery efficiency inside recipient cells have not been feasible. In this study, we developed an EV cargo delivery (EVCD) assay using a split luciferase called a NanoBiT system. Recipient cells expressing LgBiT, a large subunit of luciferase, emit luminescence when EV cargo proteins fused with a small luminescence tag (HiBiT tag) that can complement LgBiT are delivered to the cytoplasm of recipient cells. Using the EVCD assay, the cargo delivery efficiency of EVs could be quantitatively measured in real time. This assay was highly sensitive in detecting a single event of cargo delivery per cell. We found that modification of EVs with a virus-derived fusogenic protein significantly enhanced the cytoplasmic cargo delivery; however, in the absence of a fusogenic protein, the cargo delivery efficiency of EVs was below the threshold of the assay. The EVCD assay could assess the effect of entry inhibitors on EV cargo delivery. Furthermore, using a luminescence microscope, the cytoplasmic cargo delivery of EVs was directly visualized in living cells. This assay could reveal the biological mechanism of the cargo delivery processes of EVs.

Ultrafiltration and Injection of Islet Regenerative Stimuli Secreted by Pancreatic Mesenchymal Stromal Cells

The secretome of mesenchymal stromal cells (MSCs) is enriched for biotherapeutic effectors contained within and independent of extracellular vesicles (EVs) that may support tissue regeneration as an injectable agent. We have demonstrated that the intrapancreatic injection of concentrated conditioned media (CM) produced by bone marrow MSC supports islet regeneration and restored glycemic control in hyperglycemic mice, ultimately providing a platform to elucidate components of the MSC secretome. Herein, we extend these findings using human pancreas-derived MSC (Panc-MSC) as "biofactories" to enrich for tissue regenerative stimuli housed within distinct compartments of the secretome. Specifically, we utilized 100 kDa ultrafiltration as a simple method to debulk protein mass and to enrich for EVs while concentrating the MSC secretome into an injectable volume for preclinical assessments in murine models of blood vessel and islet regeneration. EV enrichment (EV+) was validated using nanoscale flow cytometry and atomic force microscopy, in addition to the detection of classical EV markers CD9, CD81, and CD63 using label-free mass spectrometry. EV+ CM was predominately enriched with mediators of wound healing and epithelial-to-mesenchymal transition that supported functional regeneration in mesenchymal and nonmesenchymal tissues. For example, EV+ CM supported human microvascular endothelial cell tubule formation in vitro and enhanced the recovery of blood perfusion following intramuscular injection in nonobese diabetic/severe combined immunodeficiency mice with unilateral hind limb ischemia. Furthermore, EV+ CM increased islet number and β cell mass, elevated circulating insulin, and improved glycemic control following intrapancreatic injection in streptozotocin-treated mice. Collectively, this study provides foundational evidence that Panc-MSC, readily propagated from the subculture of human islets, may be utilized for regenerative medicine applications.