Minimum information to report about a flow cytometry experiment on extracellular vesicles: Communication from the ISTH SSC subcommittee on vascular biology

Monitoring and reporting the composition of plasma and serum to improve biobanks and comparability of extracellular vesicle research: communication from the ISTH SSC Subcommittee on Vascular Biology

Transparent reporting is key to improving the reproducibility of scientific research. In 2023, the International Society for Extracellular Vesicles updated the "Minimal information for studies of extracellular vesicles" (MISEV) reporting guidelines and published new recommendations for blood extracellular vesicle (EV) research entitled "MIBlood-EV: Minimal information to enhance the quality and reproducibility of blood extracellular vesicle research." The MIBlood-EV recommendations are part of MISEV 2023 and promote reporting not only the protocols used for blood collection and handling but also the composition of the prepared samples that are used to measure EVs. Plasma and serum are commonly used starting materials for EV research; reporting their composition can help to improve reproducibility, comparison of measurement results, and support evidence-based guideline development. We conducted an online survey among the International Society on Thrombosis and Haemostasis (ISTH) EV researchers. Of the 20 respondents, 95% were familiar with MISEV, but 35% were unaware of the 2023 update, and only 65% applied these guidelines to their reports. With regard to MIBlood-EV, 40% were unaware of this reporting tool, and 20% did not follow its recommendations. This is surprising because most respondents agree that preanalytical variables of blood EV research are not satisfactorily described (75%), confirm that having a standardized reporting tool is beneficial for blood EV research (90%), and consider MIBlood-EV applicable to other fields of ISTH research (80%). In this Scientific and Standardization Committee communication, we summarize the survey results, as well as the background and goals of MISEV and how MIBlood-EV can be useful to improve the reproducibility of blood research within the ISTH community.

Plasma Microvesicles May Contribute to Muscle Damage in the mdx Mouse Model of Duchenne Muscular Dystrophy

Extracellular vesicles (EVs) are cell-derived lipid-bound vesicles divided into apoptotic bodies, microvesicles (MVs), and exosomes based on their biogenesis, release pathway, size, content, and functions. EVs are intercellular mediators that significantly affect muscle diseases such as Duchenne muscular dystrophy (DMD). DMD is a fatal X-linked disorder caused by mutations in the dystrophin gene, leading to muscle degeneration. Mdx mice are the most commonly used model to study the disease, and in this study, we phenotypically characterized plasma MVs from mdx mice by flow cytometry. Furthermore, we assessed the ability of plasma MVs to modulate muscle inflammation, damage, and/or regeneration by intramuscular injection of MVs from mdx mice into mdx or DBA/2 mice as a control. In both mouse lineages, platelets and erythrocytes were the primary sources of MVs, and CD3+ CD4+ MVs were observed only in mdx mice. We also observed that plasma MVs from mdx mice induced muscle damage in mdx mice but not in DBA/2 mice, while plasma MVs from DBA/2 mice did not induce muscle damage in either mouse lineage. These results indicate that plasma MVs from mdx are potentially pathogenic. However, this condition also depends on the muscular tissue status, which must be responsive due to active inflammatory or regenerative responses.

Flow cytometric procedures for deep characterization of nanoparticles

In recent years, there has been a notable increasing interest surrounding the identification and quantification of nano-sized particles, including extracellular vesicles (EVs) and viruses. The challenge posed by the nano-sized dimension of these particles makes precise examination a significant undertaking. Among the different techniques for the accurate study of EVs, flow cytometry stands out as the ideal method. It is characterized by high sensitivity, low time consumption, non-destructive sampling, and high throughput. In this article, we propose the optimization of flow cytometry procedures to identify, quantify, and purify EVs and virus-like particles. The protocol aims to reduce artefacts and errors in nano-sized particles counting, overall caused by the swarming effect. Different threshold strategies were compared to ensure result specificity. Additionally, the critical parameters to consider when using conventional flow cytometry outside of the common experimental context of use have also been identified. Finally, fluorescent-EVs sorting protocol was also developed with highly reliable results using a conventional cell sorter.

Flow virometry: recent advancements, best practices, and future frontiers

The imperative for developing robust tools to detect, analyze, and characterize viruses has become increasingly evident as they continue to threaten human health. In this review, we focus on recent advancements in studying human viruses with flow virometry (FV), an emerging technique that has gained considerable momentum over the past 5 years. These advancements include the application of FV in viral surface phenotyping, viral protein functionality, virus sorting, vaccine development, and diagnostics. With examples illustrated using primary data from our recent studies, we demonstrate that FV is a powerful yet underutilized methodology that, when employed with best practices and experimental rigor, can be highly valuable for studying individual virion heterogeneity, virus phenotypes, and virus-antibody interactions. In this review, we also address the current challenges when performing FV studies, propose strategies to overcome these obstacles, and outline best practices for both new and experienced researchers. Finally, we discuss the promising future prospects of FV within the broader context of virology research.

Resistive-Pulse Sensing Coupled with Fluorescence Lifetime Imaging Microscopy for Differentiation of Individual Liposomes

Characterization of individual biological nanoparticles can be significantly improved by coupling complementary analytical methods. Here, we combine resistive-pulse sensing (RPS) with fluorescence lifetime imaging microscopy (FLIM) to differentiate liposomes at the single-particle level. RPS measures the particle volume, shape, and surface-charge density, and FLIM determines the fluorescence lifetime of the fluorophore associated with the lipid membrane. The RPS devices are fabricated in-plane on a glass substrate to facilitate coupling of RPS with FLIM measurements. For proof-of-concept, we studied liposomes containing various cholesterol concentrations with membrane-intercalated Di-8-ANEPPS, whose fluorescence lifetime is known to be sensitive to cholesterol concentrations in the membrane. RPS-FLIM revealed that increasing cholesterol concentrations in the liposome from 0% to 50% increased the fluorescence lifetimes from 2.1 ± 0.2 to 3.4 ± 0.5 ns, respectively. Moreover, RPS-FLIM discerned liposome populations with the same cholesterol concentration but labeled with dyes that have different fluorescence lifetimes (Di-8-ANEPPS and COE-S6), parsing two particle populations with statistically identical volumes, cholesterol concentration, and lipid composition. Interrogation with RPS-FLIM occurred with individual particles making a single pass through the detection region and overcomes issues with fluorescence spectral overlap that limits traditional methods. We envision RPS-FLIM as a versatile and scalable technique with the potential to differentiate biological particles at the single-particle level to simultaneously inform on particle size, surface-charge density, membrane composition, and identity.

Harnessing extracellular vesicle heterogeneity for diagnostic and therapeutic applications

Extracellular vesicles (EVs) are diverse nanoparticles with large heterogeneity in size and molecular composition. Although this heterogeneity provides high diagnostic value for liquid biopsy and confers many exploitable functions for therapeutic applications in cancer detection, wound healing and neurodegenerative and cardiovascular diseases, it has also impeded their clinical translation-hence heterogeneity acts as a double-edged sword. Here we review the impact of subpopulation heterogeneity on EV function and identify key cornerstones for addressing heterogeneity in the context of modern analytical platforms with single-particle resolution. We outline concrete steps towards the identification of key active biomolecules that determine EV mechanisms of action across different EV subtypes. We describe how such knowledge could accelerate EV-based therapies and engineering approaches for mimetic artificial nanovesicle formulations. This approach blunts one edge of the sword, leaving only a single razor-sharp edge on which EV heterogeneity can be exploited for therapeutic applications across many diseases.

A critical systematic review of extracellular vesicle clinical trials

This systematic review examines the landscape of extracellular vesicle (EV)-related clinical trials to elucidate the field's trends in clinical applications and EV-related methodologies, with an additional focus on the acknowledgement of EV subpopulations. By analysing data from public reporting repositories, we catalogued 471 EV-related clinical trials to date, with indications for over 200 diseases. Diagnostics and companion diagnostics represented the bulk of EV-related clinical trials with cancer being the most frequent application. EV-related therapeutics trials mainly utilized mesenchymal stromal cell (MSC) EVs and were most frequently used for treatment of respiratory illnesses. Ultracentrifugation and RNA-sequencing were the most common isolation and characterization techniques; however, methodology for each was not frequently reported in study records. Most of the reported characterization relied on bulk characterization of EV isolates, with only 11% utilizing EV subpopulations in their experimental design. While this may be connected to a lack of available techniques suitable for clinical implementation, it also highlights the opportunity for use of EV subpopulations to improve translational efforts. As academic research identifies more chemically distinct subpopulations and technologies for their enrichment, we forecast to more refined EV trials in the near future. This review emphasizes the need for meticulous methodological reporting and consideration of EV subpopulations to enhance the translational success of EV-based interventions, pointing towards a paradigm shift in personalized medicine.

Factors to consider before choosing EV labeling method for fluorescence-based techniques

A well-designed fluorescence-based analysis of extracellular vesicles (EV) can provide insights into the size, morphology, and biological function of EVs, which can be used in medical applications. Fluorescent nanoparticle tracking analysis with appropriate controls can provide reliable data for size and concentration measurements, while nanoscale flow cytometry is the most appropriate tool for characterizing molecular cargoes. Label selection is a crucial element in all fluorescence methods. The most comprehensive data can be obtained if several labeling approaches for a given marker are used, as they would provide complementary information about EV populations and interactions with the cells. In all EV-related experiments, the influence of lipoproteins and protein corona on the results should be considered. By reviewing and considering all the factors affecting EV labeling methods used in fluorescence-based techniques, we can assert that the data will provide as accurate as possible information about true EV biology and offer precise, clinically applicable information for future EV-based diagnostic or therapeutic applications.

HaloTag display enables quantitative single-particle characterisation and functionalisation of engineered extracellular vesicles

Extracellular vesicles (EVs) play key roles in diverse biological processes, transport biomolecules between cells and have been engineered for therapeutic applications. A useful EV bioengineering strategy is to express engineered proteins on the EV surface to confer targeting, bioactivity and other properties. Measuring how incorporation varies across a population of EVs is important for characterising such materials and understanding their function, yet it remains challenging to quantitatively characterise the absolute number of engineered proteins incorporated at single-EV resolution. To address these needs, we developed a HaloTag-based characterisation platform in which dyes or other synthetic species can be covalently and stoichiometrically attached to engineered proteins on the EV surface. To evaluate this system, we employed several orthogonal quantification methods, including flow cytometry and fluorescence microscopy, and found that HaloTag-mediated quantification is generally robust across EV analysis methods. We compared HaloTag-labelling to antibody-labelling of EVs using single vesicle flow cytometry, enabling us to measure the substantial degree to which antibody labelling can underestimate proteins present on an EV. Finally, we demonstrate the use of HaloTag to compare between protein designs for EV bioengineering. Overall, the HaloTag system is a useful EV characterisation tool which complements and expands existing methods.

Higher EpCAM-Positive Extracellular Vesicle Concentration in Ascites Is Associated with Shorter Progression-Free Survival of Patients with Advanced High-Grade Serous Carcinoma

Platinum-resistant high-grade serous carcinoma (HGSC) is an incurable disease, so biomarkers that could help with timely treatment adjustments and personalized approach are extensively being sought. Tumor-derived extracellular vesicles (EVs) that can be isolated from ascites and blood of HGSC patients are such promising biomarkers. Epithelial cell adhesion molecule (EpCAM) expression is upregulated in most epithelium-derived tumors; however, studies on prognostic value of EpCAM overexpression in ovarian carcinoma have shown contradictory results. The aim of our study was to evaluate the potential of total and EpCAM-positive EVs as prognostic and predictive biomarkers for advanced HGSC. Flow cytometry was used to determine the concentration of total and EpCAM-positive EVs in paired pretreatment ascites and plasma samples of 37 patients with advanced HGSC who underwent different first-line therapy. We found that higher EpCAM-positive EVs concentration in ascites is associated with shorter progression-free survival (PFS) regardless of treatment strategy. We also found a strong correlation of EpCAM-positive EVs concentration between ascites and plasma. Our findings indicate that EpCAM-positive EVs in ascites of patients with advanced HGSC have the potential to serve as prognostic biomarkers for predicting early recurrence and thereby likelihood of more aggressive tumor biology and development of chemoresistance.

HaloTag display enables quantitative single-particle characterization and functionalization of engineered extracellular vesicles

Extracellular vesicles (EVs) play key roles in diverse biological processes, transport biomolecules between cells, and have been engineered for therapeutic applications. A useful EV bioengineering strategy is to express engineered proteins on the EV surface to confer targeting, bioactivity, and other properties. Measuring how incorporation varies across a population of EVs is important for characterizing such materials and understanding their function, yet it remains challenging to quantitatively characterize the absolute number of engineered proteins incorporated at single-EV resolution. To address these needs, we developed a HaloTag-based characterization platform in which dyes or other synthetic species can be covalently and stoichiometrically attached to engineered proteins on the EV surface. To evaluate this system, we employed several orthogonal quantification methods, including flow cytometry and fluorescence microscopy, and found that HaloTag-mediated quantification is generally robust across EV analysis methods. We compared HaloTag-labeling to antibody-labeling of EVs using single vesicle flow cytometry, enabling us to measure the substantial degree to which antibody labeling can underestimate proteins present on an EV. Finally, we demonstrate the use of HaloTag to compare between protein designs for EV bioengineering. Overall, the HaloTag system is a useful EV characterization tool which complements and expands existing methods.

Density-based lipoprotein depletion improves extracellular vesicle isolation and functional analysis

BACKGROUND

Blood plasma is the main source of extracellular vesicles (EVs) in clinical studies aiming to identify biomarkers and to investigate pathophysiological processes, especially regarding EV roles in inflammation and thrombosis. However, EV isolation from plasma has faced the fundamental issue of lipoprotein contamination, representing an important bias since lipoproteins are highly abundant and modulate cell signaling, metabolism, and thromboinflammation.

OBJECTIVES

Here, we aimed to isolate plasma EVs after depleting lipoproteins, thereby improving sample purity and EV thromboinflammatory analysis.

METHODS

Density-based gradient ultracentrifugation (G-UC) was used for lipoprotein depletion before EV isolation from plasma through size-exclusion chromatography (SEC) or serial centrifugation (SC). Recovered EVs were analyzed by size, concentration, cellular source, ultrastructure, and bottom-up proteomics.

RESULTS

G-UC efficiently separated lipoproteins from the plasma, allowing subsequent EV isolation through SEC or SC. Combined analysis from EV proteomics, cholesterol quantification, and apoB-100 detection confirmed the significant reduction in lipoproteins from isolated EVs. Proteomic analysis identified similar gene ontology and cellular components in EVs, regardless of lipoprotein depletion, which was consistent with similar EV cellular sources, size, and ultrastructure by flow cytometry and transmission electron microscopy. Importantly, lipoprotein depletion increased the detection of less abundant proteins in EV proteome and enhanced thromboinflammatory responses of platelets and monocytes stimulated in vitro with EV isolates.

CONCLUSION

Combination of G-UC+SEC significantly reduced EV lipoprotein contamination without interfering in EV cellular source, gene ontology, and ultrastructure, allowing the recovery of highly pure EVs with potential implications for functional assays and proteomic and lipidomic analyses.

Current Methods for Analysing Mesenchymal Stem Cell-Derived Extracellular Vesicles

The use of extracellular vesicles (EVs) generated by mesenchymal stem cells (MSCs) holds great promise as a novel therapeutic approach. Although their immunomodulatory and regeneration potential has been reported to be similar to that of MSCs, the use of MSC-derived EVs in clinical settings will require several problems to be resolved. It is necessary to develop a standardised and widely accepted isolation technology and to improve methods such as the quantification and characterisation of MSC-derived EVs. In this way, EV studies can be compared, the acquired knowledge can be safely transferred to clinical platforms and the clinical results can be evaluated appropriately. There are many procedures for the collection and analysis of vesicles derived from different cells; however, this review provides an overview of methods for the determination of the total protein amount, specific proteins, particle number, non-protein markers like lipids and RNA, microscopy and other methods focusing on MSC-derived EVs.

The fluorochrome-to-protein ratio is crucial for the flow cytometric detection of tissue factor on extracellular vesicles

Extracellular vesicles (EVs) have crucial roles in hemostasis and coagulation. They sustain coagulation by exposing phosphatidylserine and initiate clotting by surface expression of tissue factor (TF) under inflammatory conditions. As their relevance as biomarkers of coagulopathy is increasingly recognized, there is a need for the sensitive and reliable detection of TF+ EVs, but their flow cytometric analysis is challenging and has yielded controversial findings for TF expression on EVs in the vascular system. We investigated the effect of different fluorochrome-to-protein (F/P) ratios of anti-TF-fluorochrome conjugates on the flow cytometric detection of TF+ EVs from activated monocytes, mesenchymal stem cells (MSCs), and in COVID-19 plasma. Using a FITC-labeled anti-TF antibody (clone VD8), we show that the percentage of TF+ EVs declined with decreasing F/P ratios. TF was detected on 7.6%, 5.4%, and 1.1% of all EVs derived from activated monocytes at F/P ratios of 7.7:1, 6.6:1, and 5.2:1. A similar decline was observed for EVs from MSCs and for EVs in plasma, whereas the detection of TF on cells remained unaffected by different F/P ratios. We provide clear evidence that next to the antibody clone, the F/P ratio affects the flow cytometric detection of TF+ EVs and should be carefully controlled.

Minimal information for studies of extracellular vesicles (MISEV2023): From basic to advanced approaches

Extracellular vesicles (EVs), through their complex cargo, can reflect the state of their cell of origin and change the functions and phenotypes of other cells. These features indicate strong biomarker and therapeutic potential and have generated broad interest, as evidenced by the steady year-on-year increase in the numbers of scientific publications about EVs. Important advances have been made in EV metrology and in understanding and applying EV biology. However, hurdles remain to realising the potential of EVs in domains ranging from basic biology to clinical applications due to challenges in EV nomenclature, separation from non-vesicular extracellular particles, characterisation and functional studies. To address the challenges and opportunities in this rapidly evolving field, the International Society for Extracellular Vesicles (ISEV) updates its 'Minimal Information for Studies of Extracellular Vesicles', which was first published in 2014 and then in 2018 as MISEV2014 and MISEV2018, respectively. The goal of the current document, MISEV2023, is to provide researchers with an updated snapshot of available approaches and their advantages and limitations for production, separation and characterisation of EVs from multiple sources, including cell culture, body fluids and solid tissues. In addition to presenting the latest state of the art in basic principles of EV research, this document also covers advanced techniques and approaches that are currently expanding the boundaries of the field. MISEV2023 also includes new sections on EV release and uptake and a brief discussion of in vivo approaches to study EVs. Compiling feedback from ISEV expert task forces and more than 1000 researchers, this document conveys the current state of EV research to facilitate robust scientific discoveries and move the field forward even more rapidly.

Red blood cell transfusion-related dynamics of extracellular vesicles in intensive care patients: a prospective subanalysis

Extracellular vesicles (EVs) accumulate during packed red blood cell (PRBC) storage. To date, the involvement of EVs in transfusion-related immunomodulation (TRIM) has not been prospectively evaluated in intensive care unit (ICU) patients. This was a prospective subanalysis of a recent observational feasibility study in postoperative ICU patients after: (1) open aortic surgery (Aorta), (2) bilateral lung transplantation (LuTx), and (3) other types of surgery (Comparison). Patient plasma was collected three times each before and after leukoreduced PRBC transfusion at 30-min intervals. The total number of EVs and EVs derived from erythrocytes (EryEVs), total platelets (total PEVs), activated platelets, granulocytes (GEVs), monocytes, and myeloid cells in PRBC samples and patient plasma were analyzed by flow cytometry. Statistical analysis was performed by Spearman's correlation test, linear mixed models and pairwise comparisons by Wilcoxon matched-pairs test. Twenty-three patients (Aorta n = 5, LuTx n = 9, Comparison n = 9) were included in the final analysis. All EV subgroups analyzed were detectable in all PRBCs samples (n = 23), but concentrations did not correlate with storage time. Moreover, all EVs analyzed were detectable in all plasma samples (n = 138), and EV counts were consistent before transfusion. Concentrations of total EVs, EryEVs, total PEVs, and GEVs increased after transfusion compared with baseline in the entire cohort but not in specific study groups. Furthermore, the change in plasma EV counts (total EVs and EryEVs) after transfusion correlated with PRBC storage time in the entire cohort. Extracellular vesicles were detectable in all PRBC and plasma samples. Individual EV subtypes increased after transfusion in the entire cohort, and in part correlated with storage duration. Future clinical studies to investigate the role of EVs in TRIM are warranted and should anticipate a larger sample size.Trial registration: Clinicaltrials.gov: NCT03782623.

Identification of CD38, CD97, and CD278 on the HIV surface using a novel flow virometry screening assay

While numerous cellular proteins in the HIV envelope are known to alter virus infection, methodology to rapidly phenotype the virion surface in a high throughput, single virion manner is lacking. Thus, many human proteins may exist on the virion surface that remain undescribed. Herein, we developed a novel flow virometry screening assay to discover new proteins on the surface of HIV particles. By screening a CD4+ T cell line and its progeny virions, along with four HIV isolates produced in primary cells, we discovered 59 new candidate proteins in the HIV envelope that were consistently detected across diverse HIV isolates. Among these discoveries, CD38, CD97, and CD278 were consistently present at high levels on virions when using orthogonal techniques to corroborate flow virometry results. This study yields new discoveries about virus biology and demonstrates the utility and feasibility of a novel flow virometry assay to phenotype individual virions.

The role of Extracellular Genomic Materials (EGMs) in psychiatric disorders

Extracellular Genomic Materials (EGMs) are the nucleic acids secreted or released from all types of cells by endogenous or exogenous stimuli through varying mechanisms into the extracellular region and inevitably to all biological fluids. EGMs could be found as free, protein-bound, and/ or with vesicles. EGMs can potentially have immunophenotypic and/or genotypic characteristics of a cell of origin, travel to distant organs, and interact with the new microenvironment. To achieve all, EGMs might bi-directionally transit through varying membranes, including the blood-brain barrier. Such ability provides the transfer of any information related to the pathophysiological changes in psychiatric disorders in the brain to the other distant organ systems or vice versa. In this article, many aspects of EGMs have been elegantly reviewed, including their potential in diagnosis as biomarkers, application in treatment modalities, and functional effects in the pathophysiology of psychiatric disorders. The psychiatric disorders were studied under subgroups of Schizophrenia spectrum disorders, bipolar disorder, depressive disorders, and an autism spectrum disorders. EGMs provide a robust and promising tool in clinics for prognosis and diagnosis. The successful application of EGMs into treatment modalities might further provide encouraging outcomes for researchers and clinicians in psychiatric disorders.

OxLDL sensitizes platelets for increased formation of extracellular vesicles capable of finetuning macrophage gene expression

Platelet extracellular vesicles (PEVs) generated upon platelet activation may play a role in inflammatory pathologies such as atherosclerosis. Oxidized low-density lipoprotein (oxLDL), a well-known contributor to atherogenesis, activates platelets and presensitizes them for activation by other agonists. We studied the effect of oxLDL on the secretion, composition, and inflammatory functions of PEVs using contemporary EV analytics. Platelets were activated by co-stimulation with thrombin (T) and collagen (C) ± oxLDL and characterized by high-resolution flow cytometry, nanoparticle tracking analysis, proximity extension assay, western blot, and electron microscopy. The effect of PEVs on macrophage differentiation and functionality was examined by analyzing macrophage surface markers, cytokine secretion, and transcriptome. OxLDL upregulated TC-induced formation of CD61⁺, P-selectin⁺ and phosphatidylserine⁺ PEVs. Blocking the scavenger receptor CD36 significantly suppressed the oxLDL+TC-induced PEV formation, and HDL caused a slight but detectable suppression. The inflammatory protein cargo differed between the PEVs from stimulated and unstimulated platelets. Both oxLDL+TC- and TC-induced PEVs enhanced macrophage HLA-DR and CD86 expression and decreased CD11c expression as well as secretion of several cytokines. Pathways related to cell cycle and regulation of gene expression, and immune system signaling were overrepresented in the differentially expressed genes between TC PEV -treated vs. control macrophages and oxLDL+TC PEV -treated vs. control macrophages, respectively. In conclusion, we speculate that oxLDL and activated platelets contribute to proatherogenic processes by increasing the number of PEVs that provide an adhesive and procoagulant surface, contain inflammatory mediators, and subtly finetune the macrophage gene expression.

A compendium of single extracellular vesicle flow cytometry

Flow cytometry (FCM) offers a multiparametric technology capable of characterizing single extracellular vesicles (EVs). However, most flow cytometers are designed to detect cells, which are larger than EVs. Whereas cells exceed the background noise, signals originating from EVs partly overlap with the background noise, thereby making EVs more difficult to detect than cells. This technical mismatch together with complexity of EV-containing fluids causes limitations and challenges with conducting, interpreting and reproducing EV FCM experiments. To address and overcome these challenges, researchers from the International Society for Extracellular Vesicles (ISEV), International Society for Advancement of Cytometry (ISAC), and the International Society on Thrombosis and Haemostasis (ISTH) joined forces and initiated the EV FCM working group. To improve the interpretation, reporting, and reproducibility of future EV FCM data, the EV FCM working group published an ISEV position manuscript outlining a framework of minimum information that should be reported about an FCM experiment on single EVs (MIFlowCyt-EV). However, the framework contains limited background information. Therefore, the goal of this compendium is to provide the background information necessary to design and conduct reproducible EV FCM experiments. This compendium contains background information on EVs, the interaction between light and EVs, FCM hardware, experimental design and preanalytical procedures, sample preparation, assay controls, instrument data acquisition and calibration, EV characterization, and data reporting. Although this compendium focuses on EVs, many concepts and explanations could also be applied to FCM detection of other particles within the EV size range, such as bacteria, lipoprotein particles, milk fat globules, and viruses.

Extracellular vesicles in atherothrombosis: From biomarkers and precision medicine to therapeutic targets

Atherosclerotic cardiovascular disease (ASCVD) remains the leading cause of global mortality. Extracellular vesicles (EVs) are small phospholipid vesicles that convey molecular bioactive cargoes and play essential roles in intercellular communication and, hence, a multifaceted role in health and disease. The present review offers a glimpse into the current state and up-to-date concepts on EV field. It also covers their association with several cardiovascular risk factors and ischemic conditions, being subclinical atherosclerosis of utmost relevance for prevention. Interestingly, we show that EVs hold promise as prognostic and diagnostic as well as predictive markers of ASCVD in the precision medicine era. We then report on the role of EVs in atherothrombosis, disentangling the mechanisms involved in the initiation, progression, and complication of atherosclerosis and showing their direct effect in the context of arterial thrombosis. Finally, their potential use for therapeutic intervention is highlighted.

Reproducibility of extracellular vesicle research

Cells release membrane-delimited particles into the environment. These particles are called "extracellular vesicles" (EVs), and EVs are present in fluids contacting cells, including body fluids and conditioned culture media. Because EVs change and contribute to health and disease, EVs have become a hot topic. From the thousands of papers now published on EVs annually, one easily gets the impression that EVs provide biomarkers for all diseases, and that EVs are carriers of all relevant biomolecules and are omnipotent therapeutics. At the same time, EVs are heterogeneous, elusive and difficult to study due to their physical properties and the complex composition of their environment. This overview addresses the current challenges encountered when working with EVs, and how we envision that most of these challenges will be overcome in the near future. Right now, an infrastructure is being developed to improve the reproducibility of EV measurement results. This infrastructure comprises expert task forces of the International Society of Extracellular Vesicles (ISEV) developing guidelines and recommendations, instrument calibration, standardized and transparent reporting, and education. Altogether, these developments will support the credibility of EV research by introducing robust reproducibility, which is a prerequisite for understanding their biological significance and biomarker potential.