Toward routine detection of extracellular vesicles in clinical samples

Optimizing Exosome Preparation Based on Size and Morphology: Insights From Electron Microscopy

Extracellular vesicles (EVs), including exosomes, are crucial in intercellular communication, but differentiating between exosomes and microvesicles is challenging due to their similar morphology and size. This study focuses on multivesicular bodies (MVBs), where exosomes mature, and optimizes exosome isolation using transmission electron microscopy (TEM) for size information. Considering that EVs are nanocolloidal particles, a salt-free Bis-Tris buffer is found to maintain EV integrity better than phosphate-buffered saline (PBS). Dynamic light scattering (DLS) and TEM analysis confirm that intact exosome fractions under the salt-free Bis-Tris buffer condition exhibit polydispersity, including a unique population of <50 nm vesicles resembling intraluminal membrane vesicles (ILVs) in MVBs, alongside larger populations. This <50 nm population disappears in PBS or Bis-Tris buffer with 140 mM NaCl, transforming into a monodisperse population >100 nm. Immunoelectron microscopy also validates the presence of CD63, an exosome biomarker, on approximately 50 nm EVs. These findings provide valuable insights into exosome characterization and isolation, essential for future biomedical applications in diagnostics and drug delivery.

Metal nanoprobe-decorated all-inorganic perovskite nanocrystal-based fluorescence-linked immunosorbent assay for the detection of tumor-derived exosomes

All-inorganic perovskite nanocrystals (CsPbX₃ NCs, X = Cl, Br, I) are promising fluorescence materials for biological detection due to their excellent optical properties. However, there is still a challenge to obtain stable CsPbX₃ NCs with more biofunctions. Here, we proposed a distinct strategy by absorbing the functionalized metal nanoprobes onto the phospholipid encapsulated CsPbX₃ NCs to achieve CsPbX₃-metal hybrids as probes for the detection of tumor-derived exosomes. Here, the metal nanoprobes have two functions: first, it endows phospholipid encapsulated CsPbX₃ NCs with recognition ability; second, it avoids the fluorescence quenching of CsPbX₃ NCs during the biological modification process by using metal nanoparticles as a bridge to connect with CsPbX₃ NCs and various biomolecules. The obtained CPXD-AD exhibited a bright fluorescence signal, narrow full width at half-maximum (FWHM), and high specificity. Under optimal conditions, the CPXD-AD-based fluorescence-linked immunosorbent assay (FLISA) was successfully established and used for both qualitative and quantitative detection of tumor-derived exosomes.

Utility of Exosomes in Ischemic and Hemorrhagic Stroke Diagnosis and Treatment

Stroke is the leading cause of death and neurological disorders worldwide. However, diagnostic techniques and treatments for stroke patients are still limited for certain types of stroke. Intensive research has been conducted so far to find suitable diagnostic techniques and treatments, but so far there has been no success. In recent years, various studies have drawn much attention to the clinical value of utilizing the mechanism of exosomes, low toxicity, biodegradability, and the ability to cross the blood–brain barrier. Recent studies have been reported on the use of biomarkers and protective and recovery effects of exosomes derived from stem cells or various cells in the diagnostic stage after stroke. This review focuses on publications describing changes in diagnostic biomarkers of exosomes following various strokes and processes for various potential applications as therapeutics.

Nanozyme-Based Lateral Flow Immunoassay (LFIA) for Extracellular Vesicle Detection

Extracellular vesicles (EVs) are biological nanoparticles of great interest as novel sources of biomarkers and as drug delivery systems for personalized therapies. The research in the field and clinical applications require rapid quantification. In this study, we have developed a novel lateral flow immunoassay (LFIA) system based on Fe₃O₄ nanozymes for extracellular vesicle (EV) detection. Iron oxide superparamagnetic nanoparticles (Fe₃O₄ MNPs) have been reported as peroxidase-like mimetic systems and competent colorimetric labels. The peroxidase-like capabilities of MNPs coated with fatty acids of different chain lengths (oleic acid, myristic acid, and lauric acid) were evaluated in solution with H₂O₂ and 3,3,5,5-tetramethylbenzidine (TMB) as well as on strips by biotin–neutravidin affinity assay. As a result, MNPs coated with oleic acid were applied as colorimetric labels and applied to detect plasma-derived EVs in LFIAs via their nanozyme effects. The visual signals of test lines were significantly enhanced, and the limit of detection (LOD) was reduced from 5.73 × 10⁷ EVs/μL to 2.49 × 10⁷ EVs/μL. Our work demonstrated the potential of these MNPs as reporter labels and as nanozyme probes for the development of a simple tool to detect EVs, which have proven to be useful biomarkers in a wide variety of diseases.

Microfluidic Platforms for the Isolation and Detection of Exosomes: A Brief Review

Extracellular vesicles (EVs) are a group of communication organelles enclosed by a phospholipid bilayer, secreted by all types of cells. The size of these vesicles ranges from 30 to 1000 nm, and they contain a myriad of compounds such as RNA, DNA, proteins, and lipids from their origin cells, offering a good source of biomarkers. Exosomes (30 to 100 nm) are a subset of EVs, and their importance in future medicine is beyond any doubt. However, the lack of efficient isolation and detection techniques hinders their practical applications as biomarkers. Versatile and cutting-edge platforms are required to detect and isolate exosomes selectively for further clinical analysis. This review paper focuses on lab-on-chip devices for capturing, detecting, and isolating extracellular vesicles. The first part of the paper discusses the main characteristics of different cell-derived vesicles, EV functions, and their clinical applications. In the second part, various microfluidic platforms suitable for the isolation and detection of exosomes are described, and their performance in terms of yield, sensitivity, and time of analysis is discussed.

Proteomic and Biochemical Analysis of Extracellular Vesicles Isolated from Blood Serum of Patients with Melanoma

Background: Malignant melanoma is the most serious type of skin cancer with the highest mortality rate. Extracellular vesicles (EVs) have potential as new tumor markers that could be used as diagnostic and prognostic markers for early detection of melanoma. Methods: EVs were purified from the blood serum of melanoma patients using two methods—ultracentrifugation and PEG precipitation—and analyzed by mass spectrometry and immunoblot. Results: We identified a total of 585 unique proteins; 334 proteins were detected in PEG-precipitated samples and 515 in UC-purified EVs. EVs purified from patients varied in their size and concentration in different individuals. EVs obtained from stage II and III patients were, on average, smaller and more abundant than others. Detailed analysis of three potential biomarkers—SERPINA3, LGALS3BP, and gelsolin—revealed that the expression of SERPINA3 and LGALS3BP was higher in melanoma patients than healthy controls, while gelsolin exhibited higher expression in healthy controls. Conclusion: We suggest that all three proteins might have potential to be used as biomarkers, but a number of issues, such as purification of EVs, standardization, and validation of methods suitable for everyday clinical settings, still need to be addressed.

Multiplexed Affinity Measurements of Extracellular Vesicles Binding Kinetics

Extracellular vesicles (EVs) have attracted significant attention as impactful diagnostic biomarkers, since their properties are closely related to specific clinical conditions. However, designing experiments that involve EVs phenotyping is usually highly challenging and time-consuming, due to laborious optimization steps that require very long or even overnight incubation durations. In this work, we demonstrate label-free, real-time detection, and phenotyping of extracellular vesicles binding to a multiplexed surface. With the ability for label-free kinetic binding measurements using the Interferometric Reflectance Imaging Sensor (IRIS) in a microfluidic chamber, we successfully optimize the capture reaction by tuning various assay conditions (incubation time, flow conditions, surface probe density, and specificity). A single (less than 1 h) experiment allows for characterization of binding affinities of the EVs to multiplexed probes. We demonstrate kinetic characterization of 18 different probe conditions, namely three different antibodies, each spotted at six different concentrations, simultaneously. The affinity characterization is then analyzed through a model that considers the complexity of multivalent binding of large structures to a carpet of probes and therefore introduces a combination of fast and slow association and dissociation parameters. Additionally, our results confirm higher affinity of EVs to aCD81 with respect to aCD9 and aCD63. Single-vesicle imaging measurements corroborate our findings, as well as confirming the EVs nature of the captured particles through fluorescence staining of the EVs membrane and cargo.

Extracellular Vesicles in Inflammatory Bowel Disease: Small Particles, Big Players

Extracellular vesicles are nanovesicles released by many cell types into the extracellular space. They are important mediators of intercellular communication, enabling the functional transfer of molecules from one cell to another. Moreover, their molecular composition reflects the physiological status of the producing cell and tissue. Consequently, these vesicles have been involved in many [patho]physiological processes such as immunomodulation and intestinal epithelial repair, both key processes involved in inflammatory bowel disease. Given that these vesicles are present in many body fluids, they also provide opportunities for diagnostic, prognostic, and therapeutic applications. In this review, we summarise functional roles of extracellular vesicles in health and disease, with a focus on immune regulation and intestinal barrier integrity, and review recent studies on extracellular vesicles and inflammatory bowel disease. We also elaborate on their clinical potential in inflammatory bowel disease.

Exosomes and Extracellular Vesicles as Emerging Theranostic Platforms in Cancer Research

Exosomes are endosome-derived nanovesicles produced by healthy as well as diseased cells. Their proteic, lipidic and nucleic acid composition is related to the cell of origin, and by vehiculating bioactive molecules they are involved in cell-to-cell signaling, both in healthy and pathologic conditions. Being nano-sized, non-toxic, biocompatible, scarcely immunogenic, and possessing targeting ability and organotropism, exosomes have been proposed as nanocarriers for their potential application in diagnosis and therapy. Among the different techniques exploited for exosome isolation, the sequential ultracentrifugation/ultrafiltration method seems to be the gold standard; alternatively, commercially available kits for exosome selective precipitation from cell culture media are frequently employed. To load a drug or a detectable agent into exosomes, endogenous or exogenous loading approaches have been developed, while surface engineering procedures, such as click chemistry, hydrophobic insertion and exosome display technology, allow for obtaining actively targeted exosomes. This review reports on diagnostic or theranostic platforms based on exosomes or exosome-mimetic vesicles, highlighting the diverse preparation, loading and surface modification methods applied, and the results achieved so far.

Liquid Biopsy of Bile based on Targeted Mass Spectrometry for the Diagnosis of Malignant Biliary Strictures

Bile holds biomarkers of malignant biliary strictures (MBS) but is unsuited for automated analyzers used in routine diagnostic laboratories. Selected reaction monitoring (SRM) is a flexible high‐throughput analytical approach based on targeted mass spectrometry (MS) already implemented in clinical settings. We tested the hypothesis that SRM could be used to quantify cancer biomarkers in human bile. An SRM‐based assay was developed to simultaneously quantify up to 37 peptides from 13 bile proteins in a developmental cohort of 15 patients (MBS, n = 8; benign biliary stricture or obstruction (BBS), n = 7). The most reliable biomarkers were then absolutely quantified by SRM in a verification cohort of 67 patients (MBS, n = 37; BBS, n = 30). The diagnostic performances of single and combined biomarkers were assessed. In the developmental cohort, SRM‐based analysis revealed six protein biomarkers with significantly higher peptide ratios (endogenous vs. standard) in bile from MBS vs. BBS. In the verification cohort, five of these biomarkers proved good diagnostic ability (individual receiver operating characteristic‐area under the receiver operating characteristic curve (ROC‐AUC) up to 0.889, accuracies from 67.8% to 83.1%). Combining bile biomarkers and serum CA19‐9 in 2 panels allowed differentiating MBS from BBS with up to 0.929 ROC‐AUC and 89.8% accuracy. In this study, a newly developed SRM‐based assay proved able to simultaneously quantify multiple biomarkers in bile samples. The combination of bile biomarkers with serum CA19‐9 was highly accurate for the diagnosis of MBS. Liquid biopsy of bile based on targeted MS is eligible to support MBS diagnosis in clinical practice.

Selected Tetraspanins Functionalized Niosomes as Potential Standards for Exosome Immunoassays

Quantitative detection of exosomes in bio-fluids is a challenging task in a dynamic research field. The absence of a well-established reference material (RM) for method development and inter-comparison studies could be potentially overcome with artificial exosomes: lab-produced biomimetic particles with morphological and functional properties close to natural exosomes. This work presents the design, development and functional characteristics of fully artificial exosomes based on tetraspanin extracellular loops-coated niosomes, produced by bio-nanotechnology methods based on supra-molecular chemistry and recombinant protein technology. Mono- and double-functionalized particles with CD9/CD63 tetraspanins have been developed and characterized from a morphological and functional point of view. Produced bio-particles showed close similarities with natural entities in terms of physical properties. Their utility for bioanalysis is demonstrated by their detection and molecular-type discrimination by enzyme-linked immunosorbent assays (ELISAs), one of the most frequent bio-analytical method found in routine and research labs. The basic material based on streptavidin-coated niosomes allows the surface functionalization with any biotinylated protein or peptide, introducing versatility. Although promising results have been reported, further optimizations and deeper characterization will help this innovative biomaterial become a robust RM for validation and development of diagnostic tools for exosomes determination.

Isolation and Detection Technologies of Extracellular Vesicles and Application on Cancer Diagnostic

The vast majority of cancers are treatable when diagnosed early. However, due to the elusive trace and the limitation of traditional biopsies, most cancers have already spread widely and are at advanced stages when they are first diagnosed, causing ever-increasing mortality in the past decades. Hence, developing reliable methods for early detection and diagnosis of cancer is indispensable. Recently, extracellular vesicles (EVs), as circulating phospholipid vesicles secreted by cells, are found to play significant roles in the intercellular communication as well as the setup of tumor microenvironments and have been identified as one of the key factors in the next-generation technique for cancer diagnosis. However, EVs present in complex biofluids that contain various contaminations such as nonvesicle proteins and nonspecific EVs, resulting in the interference of screening for desired biomarkers. Therefore, applicable isolation and enrichment methods that guarantee scale-up of sample volume, purity, speed, yield, and tumor specificity are necessary. In this review, we introduce current technologies for EV separation and summarize biomarkers toward EV-based cancer liquid biopsy. In conclusion, a novel systematic isolation method that guarantees high purity, recovery rate, and tumor specificity is still missing. Besides that, a dual-model EV-based clinical trial system includes isolation and detection is a hot trend in the future due to efficient point-of-care needs. In addition, cancer-related biomarkers discovery and biomarker database establishment are essential objectives in the research field for diagnostic settings.

Daily rhythms influence the ability of lung-derived extracellular vesicles to modulate bone marrow cell phenotype

Extracellular vesicles (EVs) are important mediators of intercellular communication and have been implicated in myriad physiologic and pathologic processes within the hematopoietic system. Numerous factors influence the ability of EVs to communicate with target marrow cells, but little is known about how circadian oscillations alter EV function. In order to explore the effects of daily rhythms on EV-mediated intercellular communication, we used a well-established model of lung-derived EV modulation of the marrow cell transcriptome. In this model, co-culture of whole bone marrow cells (WBM) with lung-derived EVs induces expression of pulmonary specific mRNAs in the target WBM. To determine if daily rhythms play a role in this phenotype modulation, C57BL/6 mice were entrained in 12-hour light/12-hour dark boxes. Lungs harvested at discrete time-points throughout the 24-hour cycle were co-cultured across a cell-impermeable membrane with murine WBM. Alternatively, WBM harvested at discrete time-points was co-cultured with lung-derived EVs. Target WBM was collected 24hrs after co-culture and analyzed for the presence of pulmonary specific mRNA levels by RT-PCR. In both cases, there were clear time-dependent variations in the patterns of pulmonary specific mRNA levels when either the daily time-point of the lung donor or the daily time-point of the recipient marrow cells was altered. In general, WBM had peak pulmonary-specific mRNA levels when exposed to lung harvested at Zeitgeber time (ZT) 4 and ZT 16 (ZT 0 defined as the time of lights on, ZT 12 defined as the time of lights off), and was most susceptible to lung-derived EV modulation when target marrow itself was harvested at ZT 8- ZT 12. We found increased uptake of EVs when the time-point of the receptor WBM was between ZT 20 -ZT 24, suggesting that the time of day-dependent changes in transcriptome modulation by the EVs were not due simply to differential EV uptake. Based on these data, we conclude that circadian rhythms can modulate EV-mediated intercellular communication.

Single molecule localization imaging of exosomes using blinking silicon quantum dots

Discovering new fluorophores, which are suitable for single molecule localization microscopy (SMLM) is important for promoting the applications of SMLM in biological or material sciences. Here, we found that silicon quantum dots (Si QDs) possess a fluorescence blinking behavior, making them an excellent candidate for SMLM. The Si QDs are fabricated using a facile microwave-assisted method. Blinking of Si QDs is confirmed by single particle fluorescence measurement and the spatial resolution achieved is about 30 nm. To explore the potential application of Si QDs as the nanoprobes for SMLM imaging, cell derived exosomes are chosen as the object owing to their small size (50-100 nm in diameter). Since CD63 is commonly presented on the membrane of exosomes, CD63 aptamers are attached to the surface of Si QDs to form nanoprobes which can specifically recognize exosomes. SMLM imaging shows that Si QDs based nanoprobes can indeed realize super resolved optical imaging of exosomes. More importantly, blinking of Si QDs is observed in water or PBS buffer with no need for special imaging buffers. Besides, considering that silicon is highly biocompatible, Si QDs should have minimal cytotoxicity. These features make Si QDs quite suitable for SMLM applications especially for live cell imaging.

New Technologies for Analysis of Extracellular Vesicles

Extracellular vesicles (EVs) are diverse, nanoscale membrane vesicles actively released by cells. Similar-sized vesicles can be further classified (e.g., exosomes, microvesicles) based on their biogenesis, size, and biophysical properties. Although initially thought to be cellular debris, and thus under-appreciated, EVs are now increasingly recognized as important vehicles of intercellular communication and circulating biomarkers for disease diagnoses and prognosis. Despite their clinical potential, the lack of sensitive preparatory and analytical technologies for EVs poses a barrier to clinical translation. New analytical platforms including molecular ones are thus actively being developed to address these challenges. Recent advances in the field are expected to have far-reaching impact in both basic and translational studies. This article aims to present a comprehensive and critical overview of emerging analytical technologies for EV detection and their clinical applications.

Interaction of Platelet-Derived Microparticles with a Human B-Lymphoblast Cell Line: A Clue for the Immunologic Function of the Microparticles

Background

Platelets are blood cells with extensive capabilities in hemostasis. They also play a central role in the development of innate and adaptive immune responses. Little information exists about the immunostimulatory role of platelet-derived microparticles (Plt-MPs). To further elucidate this issue, we conducted this study using the B-lymphoblast cell line 'Daudi' as an available surrogate cell line for peripheral blood B lymphocytes. This cell line does not produce immunoglobulins (Igs) and has low expression of activation markers.

Methods

Plt-MPs were isolated from platelet concentrate (PC) using a multi-step centrifugation method. Daudi cells were treated with Plt-MPs in the culture medium while no treatment was given to the control cells. During 5-day co-culture, Daudi cells were evaluated for the Ig production and the expression of the cell surface markers CD86, CD27, and IgD.

Results

An increase was observed for the production of IgG and the expression of CD27 and CD86 on Daudi cells in response to Plt-MPs, whereas the IgD level was decreased. The response of Daudi cells was dependent on the concentration of Plt-MPs and the time of their isolation from PCs during storage. The differences of the variables were significant between the treatment and control groups.

Conclusion

Plt-MPs could induce the activation and differentiation of immortalized cells of B-cell origin. Thus it is conceivable that Plt-MPs may play a significant role as immortalized cell activators in human monoclonal antibody technology in near future.

Concise Review: Developing Best-Practice Models for the Therapeutic Use of Extracellular Vesicles

Growing interest in extracellular vesicles (EVs, including exosomes and microvesicles) as therapeutic entities, particularly in stem cell-related approaches, has underlined the need for standardization and coordination of development efforts. Members of the International Society for Extracellular Vesicles and the Society for Clinical Research and Translation of Extracellular Vesicles Singapore convened a Workshop on this topic to discuss the opportunities and challenges associated with development of EV-based therapeutics at the preclinical and clinical levels. This review outlines topic-specific action items that, if addressed, will enhance the development of best-practice models for EV therapies. Stem Cells Translational Medicine 2017;6:1730-1739.

Analysis of extracellular RNA in cerebrospinal fluid

We examined the extracellular vesicle (EV) and RNA composition of pooled normal cerebrospinal fluid (CSF) samples and CSF from five major neurological disorders: Alzheimer’s disease (AD), Parkinson’s disease (PD), low-grade glioma (LGG), glioblastoma multiforme (GBM), and subarachnoid haemorrhage (SAH), representing neurodegenerative disease, cancer, and severe acute brain injury. We evaluated: (I) size and quantity of EVs by nanoparticle tracking analysis (NTA) and vesicle flow cytometry (VFC), (II) RNA yield and purity using four RNA isolation kits, (III) replication of RNA yields within and between laboratories, and (IV) composition of total and EV RNAs by reverse transcription–quantitative polymerase chain reaction (RT-qPCR) and RNA sequencing (RNASeq). The CSF contained ~106 EVs/μL by NTA and VFC. Brain tumour and SAH CSF contained more EVs and RNA relative to normal, AD, and PD. RT-qPCR and RNASeq identified disease-related populations of microRNAs and messenger RNAs (mRNAs) relative to normal CSF, in both total and EV fractions. This work presents relevant measures selected to inform the design of subsequent replicative CSF studies. The range of neurological diseases highlights variations in total and EV RNA content due to disease or collection site, revealing critical considerations guiding the selection of appropriate approaches and controls for CSF studies.

Association of ficolin-3 with abdominal aortic aneurysm presence and progression

Essentials Abdominal aortic aneurysm (AAA) is asymptomatic and its evolution unpredictable. To find novel potential biomarkers of AAA, microvesicles are an excellent source of biomarkers. Ficolin-3 is increased in microvesicles obtained from activated platelets and AAA tissue. Increased ficolin-3 plasma levels are associated with AAA presence and progression.

SUMMARY

Background Abdominal aortic aneurysm (AAA) patients are usually asymptomatic and AAA evolution is unpredictable. Ficolin-3, mainly synthesized by the liver, is a molecule of the lectin complement-activation pathway involved in AAA pathophysiology. Objectives To define extra-hepatic sources of ficolin-3 in AAA and investigate the role of ficolin-3 as a biomarker of the presence and progression of AAA. Methods Microvesicles (exosomes and microparticles) were isolated from culture-conditioned medium of ADP-activated platelets, as well as from AAA tissue-conditioned medium (thrombus and wall). Ficolin-3 levels were analyzed by western-blot, real-time PCR, immunohistochemistry and ELISA. Results Increased ficolin-3 levels were observed in microvesicles isolated from activated platelets. Similarly, microvesicles released from AAA tissue display increased ficolin-3 levels as compared with those from healthy tissue. Moreover, ficolin-3 mRNA levels in the AAA wall were greatly increased compared with healthy aortic walls. Immunohistochemistry of AAA tissue demonstrated increased ficolin-3, whereas little staining was present in healthy walls. Finally, increased ficolin-3 levels were observed in AAA patients' plasma (n = 478) compared with control plasma (n = 176), which persisted after adjustment for risk factors (adjusted odds ratio [OR], 5.29; 95% confidence interval [CI], 3.27, 8.57)]. Moreover, a positive association of ficolin-3 with aortic diameter (Rho, 0.25) and need for surgical repair was observed, also after adjustment for potential confounding factors (adjusted hazard ratio, 1.55; 95% CI, 1.11, 2.15). Conclusions In addition to its hepatic expression, ficolin-3 may be released into the extracellular medium via microvesicles, by both activated cells and pathological AAA tissue. Ficolin-3 plasma levels are associated with the presence and progression of AAA, suggesting its potential role as a biomarker of AAA.

Targeted si-RNA with liposomes and exosomes (extracellular vesicles): How to unlock the potential

The concept of RNA interference therapeutics has been initiated 18 years ago, and the main bottleneck for translation of the technology into therapeutic products remains the delivery of functional RNA molecules into the cell cytoplasm. In the present review article after an introduction about the theoretical basis of RNAi therapy and the main challenges encountered for its realization, an overview of the different types of delivery systems or carriers, used as potential systems to overcome RNAi delivery issues, will be provided. Characteristic examples or results obtained with the most promising systems will be discussed. Focus will be given mostly on the applications of liposomes or other types of lipid carriers, such as exosomes, towards improved delivery of RNAi to therapeutic targets. Finally the approach of integrating the advantages of these two vesicular systems, liposomes and exosomes, as a potential solution to realize RNAi therapy, will be proposed.

Extracellular vesicle mimetics: Novel alternatives to extracellular vesicle-based theranostics, drug delivery, and vaccines

Extracellular vesicles are nano-sized spherical bilayered proteolipids encasing various components. Cells of all domains of life actively release these vesicles to the surroundings including various biological fluids. These extracellular vesicles are known to play pivotal roles in numerous pathophysiological functions. Extracellular vesicles have distinct characteristics, like high biocompatibility, safety, and nano-sized diameters that allow efficient drug loading capacity and long blood circulation half-life. These characteristics of extracellular vesicles have engrossed many scientists to harness them as new tools for novel delivery systems. This review will highlight the current state of the arts and problems of such extracellular vesicle-based theranostics, drug delivery and vaccines, and introduce "extracellular vesicle mimetics" as the novel alternative of extracellular vesicles. We hope to provide insights into the potential of extracellular vesicle mimetics as superior substitute to the natural extracellular vesicles that can be applied to theranostics, drug delivery, and vaccines against various diseases.

Stem Cell Extracellular Vesicles: Extended Messages of Regeneration

Stem cells are critical to maintaining steady-state organ homeostasis and regenerating injured tissues. Recent intriguing reports implicate extracellular vesicles (EVs) as carriers for the distribution of morphogens and growth and differentiation factors from tissue parenchymal cells to stem cells, and conversely, stem cell-derived EVs carrying certain proteins and nucleic acids can support healing of injured tissues. We describe approaches to make use of engineered EVs as technology platforms in therapeutics and diagnostics in the context of stem cells. For some regenerative therapies, natural and engineered EVs from stem cells may be superior to single-molecule drugs, biologics, whole cells, and synthetic liposome or nanoparticle formulations because of the ease of bioengineering with multiple factors while retaining superior biocompatibility and biostability and posing fewer risks for abnormal differentiation or neoplastic transformation. Finally, we provide an overview of current challenges and future directions of EVs as potential therapeutic alternatives to cells for clinical applications.

Imaging flow cytometry for the characterization of extracellular vesicles

Extracellular Vesicles (EVs) are potent bio-activators and inter-cellular communicators that play an important role in both health and disease. It is for this reason there is a strong interest in understanding their composition and origin, with the hope of using them as important biomarkers or therapeutics. Due to their very small size, heterogeneity, and large numbers there has been a need for better tools to measure them in an accurate and high throughput manner. While traditional flow cytometry has been widely used for this purpose, there are inherent problems with this approach, as these instruments have traditionally been developed to measure whole cells, which are orders of magnitude larger and express many more molecules of identifying epitopes. Imaging flow cytometry, as performed with the ImagestreamX MKII, with its combination of increased fluorescence sensitivity, low background, image confirmation ability and powerful data analysis tools, provides a great tool to accurately evaluate EVs. We present here a comprehensive approach in applying this technology to the study of EVs.

Modulation of tissue tropism and biological activity of exosomes and other extracellular vesicles: New nanotools for cancer treatment

Exosomes are naturally secreted nanovesicles that have recently aroused a great interest in the scientific and clinical community for their roles in intercellular communication in almost all physiological and pathological processes. These 30-100nm sized vesicles are released from the cells into the extracellular space and ultimately into biofluids in a tightly regulated way. Their molecular composition reflects their cells of origin, may confer specific cell or tissue tropism and underlines their biological activity. Exosomes and other extracellular vesicles (EVs) carry specific sets of proteins, nucleic acids (DNA, mRNA and regulatory RNAs), lipids and metabolites that represent an appealing source of novel noninvasive markers through biofluid biopsies. Exosome-shuttled molecules maintain their biological activity and are capable of modulating and reprogramming recipient cells. This multi-faceted nature of exosomes hold great promise for improving cancer treatment featuring them as novel diagnostic sensors as well as therapeutic effectors and drug delivery vectors. Natural biological activity including the therapeutic payload and targeting behavior of EVs can be tuned via genetic and chemical engineering. In this review we describe the properties that EVs share with conventional synthetic nanoparticles, including size, liposome-like membrane bilayer with customizable surface, and multifunctional capacity. We also highlight unique characteristics of EVs, which possibly allow them to circumvent some limitations of synthetic nanoparticle systems and facilitate clinical translation. The latter are in particular correlated with their innate stability, ability to cross biological barriers, efficiently deliver bioactive cargos or evade immune recognition. Furthermore, we discuss the potential roles for EVs in diagnostics and theranostics, and highlight the challenges that still need to be overcome before EVs can be applied to routine clinical practice.

Microparticles as biomarkers of lung disease: enumeration in biological fluids using lipid bilayer microspheres

Extracellular vesicles, specifically microparticles (MPs), are rapidly gaining attention for their capacity to act as biomarkers for diagnosis, prognosis, or responsiveness to therapy in lung disease, in keeping with the concept of precision medicine. However, MP analysis by high-sensitivity flow cytometry (FCM) is complicated by a lack of accurate means for MP enumeration. To address this gap, we report here an enhanced FCM MP gating and enumeration technique based on the use of novel engineered lipid bilayer microspheres (LBMs). By comparison of LBM-based MP enumeration with conventional bead- or fluorescent-based FCM enumeration techniques and a gravimetric consumption gold standard, we found LBMs to be superior to commercial bead preparations, showing the smallest fixed bias and limits of agreement in Bland Altman analyses. LBMs had simultaneous capacity to aid FCM enumeration of MPs in plasma, BAL, and cell culture supernatants. LBM enumeration detected differences in MP counts in mice exposed to intraperitoneal lipopolysaccharide or saline. LBMs provided for 1) higher sensitivity for gating MPs populations, 2) reduced background within MP gates, 3) more appropriate size, and 4) an inexpensive alternative amenable to different fluorescent tags. LBM-based MP enumeration was useful for a series of different FCM systems assessed, whereas LBM gating benefited high- but not low-sensitivity FCM systems compared with fluorescence gating. By offering exclusive advantages over current means of gating and enumerating MPs, LBMs are uniquely suited to realizing the potential of MPs as biomarkers in biological lung fluids and facilitating precision medicine in lung disease.

Extracellular vesicle isolation and characterization: toward clinical application

Two broad categories of extracellular vesicles (EVs), exosomes and shed microvesicles (sMVs), which differ in size distribution as well as protein and RNA profiles, have been described. EVs are known to play key roles in cell-cell communication, acting proximally as well as systemically. This Review discusses the nature of EV subtypes, strategies for isolating EVs from both cell-culture media and body fluids, and procedures for quantifying EVs. We also discuss proteins selectively enriched in exosomes and sMVs that have the potential for use as markers to discriminate between EV subtypes, as well as various applications of EVs in clinical diagnosis.

Microvesicle phenotypes are associated with transfusion requirements and mortality in subjects with severe injuries

BACKGROUND

Severe injury often results in substantial bleeding and mortality. Injury provokes cellular activation and release of extracellular vesicles. Circulating microvesicles (MVs) are predominantly platelet-derived and highly procoagulant. They support hemostasis and vascular function. The roles of MVs in survival after severe injury are largely unknown. We hypothesized that altered MV phenotypes would be associated with transfusion requirements and poor outcomes.

METHODS

This single-centre study was approved by the Institutional Review Board. The study cohort consisted of patients with major trauma requiring blood product transfusion and 26 healthy controls. Plasma samples for MVs were collected upon admission to the emergency department (n=169) and post-resuscitation (n=42), and analysed by flow cytometry for MV counts and cellular origin: platelet (PMV), erythrocyte (RMV), leukocyte (LMV), endothelial (EMV), tissue factor (TFMV), and annexin V (AVMV). Twenty-four hour mortality is the outcome measurement used to classify survivors versus non-survivors. Data were compared over time and analysed with demographic and clinical data.

RESULTS

The median age was 34 (IQR 23, 51), 72% were male, Injury Severity Score was 29 (IQR 19, 36), and 24 h mortality was 13%. MV levels and phenotypes differed between patients and controls. Elevated admission EMVs were found both in survivors (409/µL) and non-survivors (393/µL) compared to controls (23/µL, p<0.001) and persisted over time. Admission levels of PMV, AVMV, RMV, and TFMV were significantly lower in patients who died compared to survivors, but were not independently associated with the 24 h mortality rate. Patients with low MV levels at admission received the most blood products within the first 24 h. AVMV and PMV levels either increased over time or stabilized in survivors but decreased in non-survivors, resulting in significantly lower levels at intensive care unit admission in non-survivors (1,048 vs. 1,880 AVMV/µL, p<0.00004 and 1,245 PMP/µL vs. 1,866 PMP/µL, p=0.003).

CONCLUSION

Severe injury results in endothelial activation and altered MV phenotypes. Significant differences in specific MV phenotypes or changes over time were associated with blood product requirements and the 24 h mortality rate.

Time-dependent release of extracellular vesicle subpopulations in tumor CABA I cells

Investigations into extracellular vesicles (EVs) have significantly increased since their role in physiological and pathological processes has become more clearly understood. Furthermore, it has become increasingly clear that several subpopulations of EVs exist, such as exosomes (EXOs) and microvesicles (MVs). Various methods and techniques used to identify and isolate the specific EVs subpopulations exist. However, these methods should be further elucidated. A deep understanding of the different factors that affect the EVs release may therefore be useful for the standardization of protocols and to establish guidelines for a more adequate analysis and correct inter‑laboratory comparison. In the present study, we investigated whether composition and molecular features of EVs altered over time following a trigger stimulus. Starved CABA I cells were stimulated with FBS and conditioned medium was collected after different time intervals (30 min and 4, 8 and 18 h). The dynamic of EVs release was time-dependent, as shown by the results of scanning electron microscopy. Additionally, the time elapsed from the stimulus affected the size distribution (as highlighted by transmission electron microscopy and NanoSight assay), amount (in terms of the number of particles and protein amount) and molecular composition (CD63, HLA, Ago-2, gelatinases, and plasminogen activators) suggesting that, different EVs subpopulations were released at different time intervals following cell stimulation. Collectively, the results suggested that, parameters useful to standardize procedures for EVs isolation, including stimulation time should be considered.

The potential of tumor-derived exosomes for noninvasive cancer monitoring

Tumor-derived exosomes (TEX) are emerging as a new type of cancer biomarker. TEX are membrane-bound, virus-size vesicles of endocytic origin present in all body fluids of cancer patients. Based on the expanding albeit incomplete knowledge of their biogenesis, secretion by tumor cells and cancer cell-specific molecular and genetic contents, TEX are viewed as promising, clinically-relevant surrogates of cancer progression and response to therapy. Preliminary proteomic, genetic and functional profiling of tumor cell-derived or cancer plasma-derived exosomes confirms their unique characteristics. Alterations in protein or nucleic acid profiles of exosomes in plasma of cancer patients responding to therapies appear to correlate with clinical endpoints. However, methods for TEX isolation and separation from the bulk of human plasma-derived exosomes are not yet established and their role as biomarkers remains to be confirmed. Further development and validation of TEX as noninvasive, liquid equivalents of tumor biopsies are necessary to move this effort forward.

Long-term high fat feeding of rats results in increased numbers of circulating microvesicles with pro-inflammatory effects on endothelial cells

Obesity and type 2 diabetes lead to dramatically increased risks of atherosclerosis and CHD. Multiple mechanisms converge to promote atherosclerosis by increasing endothelial oxidative stress and up-regulating expression of pro-inflammatory molecules. Microvesicles (MV) are small ( < 1 μm) circulating particles that transport proteins and genetic material, through which they are able to mediate cell-cell communication and influence gene expression. Since MV are increased in plasma of obese, insulin-resistant and diabetic individuals, who often exhibit chronic vascular inflammation, and long-term feeding of a high-fat diet (HFD) to rats is a well-described model of obesity and insulin resistance, we hypothesised that this may be a useful model to study the impact of MV on endothelial inflammation. The number and cellular origin of MV from HFD-fed obese rats were characterised by flow cytometry. Total MV were significantly increased after feeding HFD compared to feeding chow (P< 0·001), with significantly elevated numbers of MV derived from leucocyte, endothelial and platelet compartments (P< 0·01 for each cell type). MV were isolated from plasma and their ability to induce reactive oxygen species (ROS) formation and vascular cell adhesion molecule (VCAM)-1 expression was measured in primary rat cardiac endothelial cells in vitro. MV from HFD-fed rats induced significant ROS (P< 0·001) and VCAM-1 expression (P= 0·0275), indicative of a pro-inflammatory MV phenotype in this model of obesity. These findings confirm that this is a useful model to further study the mechanisms by which diet can influence MV release and subsequent effects on cardio-metabolic health.

Applications of microfluidics and microchip electrophoresis for potential clinical biomarker analysis

This article reviews advances over the last five years in microfluidics and microchip-electrophoresis techniques for detection of clinical biomarkers. The variety of advantages of miniaturization compared with conventional benchtop methods for detecting biomarkers has resulted in increased interest in developing cheap, fast, and sensitive techniques. We discuss the development of applications of microfluidics and microchip electrophoresis for analysis of different clinical samples for pathogen identification, personalized medicine, and biomarker detection. We emphasize the advantages of microfluidic techniques over conventional methods, which make them attractive future diagnostic tools. We also discuss the versatility and adaptability of this technology for analysis of a variety of biomarkers, including lipids, small molecules, carbohydrates, nucleic acids, proteins, and cells. Finally, we conclude with a discussion of aspects that need to be improved to move this technology towards routine clinical and point-of-care applications.

Immunoregulatory Effects of Mesenchymal Stem Cell-Derived Extracellular Vesicles on T Lymphocytes

The immunomodulatory activity of mesenchymal stem cells (MSCs) is largely mediated by paracrine factors. We have recently shown that the immunosuppressive effects of MSCs on B lymphocytes in peripheral blood mononuclear cell (PBMC) culture can be reproduced by extracellular vesicles (EVs) isolated from MSC culture supernatants. Here we investigated the effect of bone marrow-derived MSC-EVs on T cells on PBMC cultures stimulated with anti-CD3/CD28 beads. Stimulation increased the number of proliferating CD3(+) cells as well as of regulatory T cells (Tregs). Coculture with MSCs inhibited the proliferation of CD3(+) cells, with no significant changes in apoptosis. Addition of MSC-EVs to PBMCs did not affect proliferation of CD3(+) cells, but induced the apoptosis of CD3(+) cells and of the CD4(+) subpopulation and increased the proliferation and the apoptosis of Tregs. Moreover, MSC-EV treatment increased the Treg/Teff ratio and the immunosuppressive cytokine IL-10 concentration in culture medium. The activity of indoleamine 2,3-dioxygenase (IDO), an established mediator of MSC immunosuppressive effects, was increased in supernatants of PBMCs cocultured with MSCs, but was not affected by the presence of MSC-EVs. MSC-EVs demonstrate immunomodulatory effects on T cells in vitro. However, these effects and the underlying mechanisms appear to be different from those exhibited by their cells of origin.

Methods for extracellular vesicles isolation in a hospital setting

The research in extracellular vesicles (EVs) has been rising during the last decade. However, there is no clear consensus on the most accurate protocol to isolate and analyze them. Besides, most of the current protocols are difficult to implement in a hospital setting due to being very time-consuming or to requirements of specific infrastructure. Thus, our aim is to compare five different protocols (comprising two different medium-speed differential centrifugation protocols; commercially polymeric precipitation – exoquick – acid precipitation; and ultracentrifugation) for blood and urine samples to determine the most suitable one for the isolation of EVs. Nanoparticle tracking analysis, flow cytometry, western blot (WB), electronic microscopy, and spectrophotometry were used to characterize basic aspects of EVs such as concentration, size distribution, cell-origin and transmembrane markers, and RNA concentration. The highest EV concentrations were obtained using the exoquick protocol, followed by both differential centrifugation protocols, while the ultracentrifugation and acid-precipitation protocols yielded considerably lower EV concentrations. The five protocols isolated EVs of similar characteristics regarding markers and RNA concentration; however, standard protocol recovered only small EVs. EV isolated with exoquick presented difficult to be analyzed with WB. The RNA concentrations obtained from urine-derived EVs were similar to those obtained from blood-derived ones, despite the urine EV concentration being 10–20 times lower. We consider that a medium-speed differential centrifugation could be suitable to be applied in a hospital setting as it requires the simplest infrastructure and recovers higher concentration of EV than standard protocol. A workflow from sampling to characterization of EVs is proposed.

Applications of tunable resistive pulse sensing

This Review focusses on the recent surge in applied research using tunable resistive pulse sensing, a technique used to analyse submicron colloids in aqueous solutions on a particle-by-particle basis.

Extracellular vesicles as drug delivery systems: lessons from the liposome field

Extracellular vesicles (EVs) are membrane-derived particles surrounded by a (phospho)lipid bilayer that are released by cells in the human body. In addition to direct cell-to-cell contact and the secretion of soluble factors, EVs function as another mechanism of intercellular communication. These vesicles are able to efficiently deliver their parental cell-derived molecular cargo to recipient cells, which can result in structural changes at an RNA, protein, or even phenotypic level. For this reason, EVs have recently gained much interest for drug delivery purposes. In contrast to these 'natural delivery systems', synthetic (phospho)lipid vesicles, or liposomes, have been employed as drug carriers for decades, resulting in several approved liposomal nanomedicines used in the clinic. This review discusses the similarities and differences between EVs and liposomes with the focus on features that are relevant for drug delivery purposes such as circulation time, biodistribution, cellular interactions and cargo loading. By applying beneficial features of EVs to liposomes and vice versa, improved drug carriers can be developed which will advance the field of nanomedicines and ultimately improve patient outcomes. While the application of EVs for therapeutic drug delivery is still in its infancy, issues regarding the understanding of EV biogenesis, large-scale production and in vivo interactions need to be addressed in order to develop successful and cost-effective EV-based drug delivery systems.

Isolation of biologically-active exosomes from human plasma

Effects of exosomes present in human plasma on immune cells have not been examined in detail. Immunological studies with plasma-derived exosomes require their isolation by procedures involving ultracentrifugation. These procedures were largely developed using supernatants of cultured cells. To test biologic activities of plasma-derived exosomes, methods are necessary that ensure adequate recovery of exosome fractions free of contaminating larger vesicles, cell fragments and protein/nucleic acid aggregates. Here, an optimized method for exosome isolation from human plasma/serum specimens of normal controls (NC) or cancer patients and its advantages and pitfalls are described. To remove undesirable plasma-contaminating components, ultrafiltration of differentially-centrifuged plasma/serum followed by size-exclusion chromatography prior to ultracentrifugation facilitated the removal of contaminants. Plasma or serum was equally acceptable as a source of exosomes based on the recovered protein levels (in μg protein/mL plasma) and TEM image quality. Centrifugation on sucrose density gradients led to large exosome losses. Fresh plasma was the best source of morphologically-intact exosomes, while the use of frozen/thawed plasma decreased exosome purity but not their biologic activity. Treatments of frozen plasma with DNAse, RNAse or hyaluronidase did not improve exosome purity and are not recommended. Cancer patients' plasma consistently yielded more isolated exosomes than did NCs' plasma. Cancer patients' exosomes also mediated higher immune suppression as evidenced by decreased CD69 expression on responder CD4+ T effector cells. Thus, the described procedure yields biologically-active, morphologically-intact exosomes that have reasonably good purity without large protein losses and can be used for immunological, biomarker and other studies.