Extracellular Vesicles
The general term for membrane-enclosed particles released by cells.
CELLMEX Scientific Library
Exosome Biology
Exosomes are nanoscale, membrane-enclosed extracellular vesicles associated with the endosomal pathway. They form part of a broader system of intercellular communication through which cells release proteins, lipids, nucleic acids and other biologically active molecules.
Scientific Definition
Exosomes within the extracellular-vesicle system
Extracellular vesicles, commonly abbreviated as EVs, are membrane-bound particles released by cells into the extracellular environment. They do not contain a functional nucleus and cannot reproduce independently.
Exosomes are generally understood as EVs formed within the endosomal system and released when multivesicular bodies fuse with the plasma membrane.
Because the precise cellular origin of an isolated particle is often difficult to demonstrate, scientific guidance recommends the broader terms extracellular vesicle or small extracellular vesicle when endosomal biogenesis has not been established.
Small Extracellular Vesicles
A size- or separation-based operational category commonly used when biological origin has not been directly demonstrated.
Exosomes
Extracellular vesicles associated specifically with formation inside endosomal multivesicular bodies.
Biogenesis
How exosomes are formed
Exosome formation is associated with the endosomal pathway. The process involves membrane remodelling, molecular cargo selection, intraluminal-vesicle formation and extracellular release.
Endocytosis
The plasma membrane folds inward and contributes to the formation of early endosomal compartments.
Endosomal Maturation
Early endosomes mature while receiving membrane proteins, lipids and selected cellular components.
Intraluminal Vesicle Formation
Sections of the endosomal membrane bud inward, creating small vesicles within multivesicular bodies.
Extracellular Release
Fusion of a multivesicular body with the plasma membrane releases its internal vesicles into the extracellular environment.
Molecular Composition
Cargo reflects the source cell and its environment
Extracellular-vesicle composition is influenced by the parent cell, physiological condition, passage number, culture medium, oxygen environment, collection method and downstream processing.
Potential Molecular Cargo
Extracellular-vesicle preparations may contain or display several classes of biological molecules.
- Membrane and cytosolic proteins
- Lipids and lipid-associated mediators
- Messenger RNA
- MicroRNA and other non-coding RNA
- DNA fragments in some preparations
- Metabolites and signalling molecules
Interaction with Recipient Cells
Extracellular vesicles may influence recipient cells through several non-exclusive mechanisms.
- Binding to cell-surface receptors
- Uptake through endocytic pathways
- Membrane fusion
- Transfer of proteins or nucleic acids
- Modification of intracellular signalling
- Alteration of immune responses
Physiological Roles
Extracellular-vesicle signalling has been studied in normal biological processes including:
- Immune communication
- Tissue homeostasis
- Angiogenic signalling
- Neural communication
- Coagulation-related processes
- Cellular stress responses
Disease-Associated Roles
Extracellular vesicles are also investigated in pathological processes involving:
- Cancer biology
- Chronic inflammation
- Infection
- Cardiovascular disease
- Neurodegeneration
- Metabolic disorders
Scientific Characterisation
A credible EV preparation requires multiple analytical methods
No single assay establishes that a preparation contains pure exosomes. Characterisation should combine complementary measurements of particle size, concentration, morphology, proteins, contaminants and biological function.
Particle Size and Concentration
Nanoparticle tracking analysis or related systems may estimate particle concentration and size distribution.
Morphology
Electron microscopy or other high-resolution imaging may demonstrate membrane-bound vesicular structures.
EV-Associated Proteins
Protein assessment may examine selected transmembrane, membrane-associated and cytosolic EV-related markers.
Non-Vesicular Components
Testing should consider soluble proteins, lipoproteins, protein aggregates and other co-isolated material.
Functional Assessment
Fit-for-purpose assays may evaluate the proposed biological activity or potency-related function of the preparation.
Process Documentation
Source cells, passage number, culture conditions, collection, separation, storage and handling should be clearly documented.
Separation and Enrichment
Isolation method affects the final preparation
Extracellular vesicles may be separated or enriched using differential centrifugation, ultracentrifugation, filtration, size-exclusion chromatography, density-gradient separation, affinity capture, precipitation or combinations of these methods.
These approaches differ in recovery, purity, scalability, processing time and suitability for downstream analytical or therapeutic development.
A high particle count does not by itself establish high purity, biological potency or clinical suitability.
Translational Research
Areas of current scientific investigation
Exosome and extracellular-vesicle research is active across mechanistic, diagnostic, drug-delivery and regenerative medicine applications. Evidence remains dependent on the specific biological source, manufacturing process and clinical indication.
Regenerative Signalling
Investigation of paracrine communication associated with tissue repair, angiogenesis, inflammation and cellular stress responses.
Immune Modulation
Study of how extracellular-vesicle-associated molecules may influence innate and adaptive immune responses.
Biomarker Development
Evaluation of circulating or tissue-derived extracellular vesicles as potential indicators of disease activity or treatment response.
Drug Delivery
Investigation of engineered or loaded vesicles for delivery of therapeutic molecules to selected tissues or cell populations.
Neurological Research
Study of extracellular-vesicle signalling, neural communication and potential transport across biological barriers.
Manufacturing Science
Development of reproducible culture, collection, purification, formulation, storage and potency-assessment methods.
Clinical and scientific qualification
Biological activity demonstrated in cell culture, laboratory models or animals does not by itself establish clinical safety or effectiveness in patients.
Extracellular-vesicle preparations produced by different laboratories cannot be assumed to be equivalent. Source cells, culture conditions, separation methods, formulation, dose, storage and route of administration may materially affect the final preparation.
Exosome or extracellular-vesicle preparations should not be described as established cures for neurological, autoimmune, metabolic, orthopaedic or other diseases without appropriate product-specific human evidence.
The CELLMEX Approach
From source cells to a characterised preparation
Source-Cell Control
Evaluation begins with the identity, passage number, condition and culture environment of the originating cells.
Controlled Collection
Culture-media composition, conditioning period, collection method and pre-processing variables should be defined.
Separation and Concentration
The selected process should reflect the intended purity, recovery, scale and downstream application.
Characterisation and Function
Particle, morphology, protein, contaminant and functional data should be interpreted together.
Selected Scientific References
Foundational guidance and biological literature
Welsh JA, et al. Minimal information for studies of extracellular vesicles: MISEV2023.
Journal of Extracellular Vesicles. 2024;13:e12404.
View publicationThéry C, et al. Minimal information for studies of extracellular vesicles 2018: MISEV2018.
Journal of Extracellular Vesicles. 2018;7(1):1535750.
View publicationYáñez-Mó M, et al. Biological properties of extracellular vesicles and their physiological functions.
Journal of Extracellular Vesicles. 2015;4:27066.
View publication
Scientific Information
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