Interactive explainer · Exosome science

Inside a mesenchymal stem cell exosome.

Explore a human MSC-derived small extracellular vesicle molecule by molecule — then compare it with vesicles from other cells, blood, milk, plants and bacteria. Scientists increasingly say “small extracellular vesicle” rather than “exosome” — both appear here, and claims are referenced to peer-reviewed sources.

typical small EV diameter
~100 nm
lipid bilayer thickness
~5 nm
registered MSC-EV trials
109
FDA-approved exosome products
0
Membrane
Core EV markers
MSC identity markers
Adhesion & immune
Inside machinery
Cargo
Surface coat

Keyboard: arrow keys rotate · + / − zoom · C cutaway · Esc clears

Interactive 3D model
Human MSC small EV · ~30–150 nm

Scale

How small is an exosome?

Slide from cells down to molecules. Everything in the lineup is drawn at true relative size for the current zoom.

Microvesicle (~0.1–1 µm)Microvesicle~0.1–1 µmInfluenza virus (~80–120 nm)Influenza virus~80–120 nmSmall EV / exosome (~30–150 nm)Small EV / exosome~30–150 nmExomere (non-membranous) (~25–50 nm)Exomere (non-membranous)~25–50 nmRibosome (~25 nm)Ribosome~25 nmAntibody (IgG) (~10–15 nm)Lipid bilayer thickness (~5 nm)DNA double helix (width) (~2 nm)

A typical small EV (~100 nm) is roughly 700× narrower than a human hair and about 200× smaller than the stem cell that made it. Sizes are approximate.

Biogenesis → delivery

How an MSC makes an exosome — and how the message is received.

Scroll through the eight steps. The diagram follows along.

  1. 01

    Endocytosis / membrane invagination

    The cell surface folds inward, engulfing surface receptors and surrounding fluid to form an early endosome.

    Sources [3, 4]

  2. 02

    Early endosome maturation

    The endosome matures and begins sorting which proteins and lipids will be kept, recycled, or packaged for disposal.

    Sources [4]

  3. 03

    Intraluminal vesicle (ILV) formation inside the multivesicular body (MVB)

    The endosome’s own membrane buds inward, into its own interior, creating many tiny vesicles inside one larger compartment — this larger compartment is now called a multivesicular body.

    Sources [1, 3, 4, 21, 22]

  4. 04

    MVB fate decision: lysosome vs. plasma membrane

    The cell decides whether to destroy the multivesicular body’s contents or ship it to the cell surface for release.

    Sources [3, 4, 26]

  5. 05

    Docking and fusion at the plasma membrane / direct budding

    The MVB fuses with the outer cell membrane and releases its internal vesicles as exosomes; separately, some vesicles (microvesicles) form by budding directly outward from the plasma membrane without ever passing through an endosome.

    Sources [1, 4]

  6. 06

    Extracellular travel

    Released EVs move through interstitial fluid or a biofluid (blood, etc.), protected by their lipid bilayer and surface glycocalyx/corona, toward nearby or distant target cells.

    Sources [1, 3]

  7. 07

    Uptake and effect in the recipient cell

    A target cell binds the EV at its surface and internalizes it, and the delivered cargo can then influence the recipient cell’s behavior.

    Sources [3, 4, 31]

  8. 08

    Effects in the recipient tissue

    In lab and animal studies, MSC-EVs calm inflammation, support new blood vessels, protect stressed cells and help skin cells migrate and rebuild — the basis for regenerative interest.

    Sources [16, 17, 25, 28]

The EV family

Not every vesicle is an exosome.

Particles released by cells span a ~500-fold size range and several routes of origin — and some that co-isolate with vesicles have no membrane at all. [1, 9, 10]

Shaded: the operational “small EV” range (< 200 nm). Size alone can’t tell an exosome from a small microvesicle, or from a particle with no membrane at all. [1]

  • Supermereno membrane

    Unclear; a third co-secreted nanoparticle class distinguished from both exosomes and exomeres

    Emerging / debated

    Not yet defined; identified as a morphologically and compositionally distinct fraction that separates from exomeres and small EVs during high-resolution fractionation.

    Sources [10]

  • Exomereno membrane

    Unclear; co-secreted alongside exosomes but is not itself a classical membrane-bound vesicle

    Emerging / debated

    Not yet fully defined; separated from true (membrane-bound) small and large exosome subpopulations by asymmetric flow field-flow fractionation (AF4) rather than by a known budding pathway.

    Sources [9]

  • Exosome (small EV)

    Endosomal system

    Consensus

    Buds inward as an intraluminal vesicle (ILV) inside a multivesicular body (MVB); released when the MVB fuses with the plasma membrane instead of a lysosome.

    Sources [1, 3, 4]

  • Microvesicle / ectosome

    Plasma membrane

    Consensus

    Buds directly outward from the cell surface and pinches off (fission), without passing through an endosome.

    Sources [1, 4, 23]

  • Apoptotic body

    Dying (apoptotic) cell surface

    Consensus

    Formed by membrane blebbing during programmed cell death as the dying cell fragments.

    Sources [1, 3]

  • Migrasome

    Retraction fibers left behind by a migrating cell

    Emerging / debated

    As a cell crawls, it leaves thin tubular “retraction fibers” behind; large pomegranate-like vesicles (each packed with smaller internal vesicles) grow at the fibers’ tips/junctions, then break free (“migracytosis”) once the fiber snaps.

    Sources [11]

Quality & standards

How to tell real EV science from marketing.

The field's reporting standards, turned into a checklist you can use on any product or paper.

Evaluate a product

What does the data sheet actually show?

Tick what a product or paper reports. This mirrors MISEV2023 and ISCT/ISEV guidance — it's an educational aid, not a certification. [1, 5, 27]

0/8 · Insufficient evidence to call it an EV product

MISEV2023 essentials

  1. Use operational names — “small EV” (under ~200 nm) or “large EV” — unless an endosomal origin has actually been shown; “exosome” is a claim, not a default.
  2. Report positive protein markers from more than one category: at least one membrane-bound or GPI-anchored protein (e.g. a tetraspanin) and at least one cytosolic protein (e.g. TSG101, ALIX, syntenin-1).
  3. Test and report at least one negative marker to show the preparation isn’t dominated by non-EV material.
  4. Quantify with at least two independent measures (e.g. particle number and total protein) and describe the separation method in enough detail to reproduce it.
  5. Confirm intact, membrane-bound vesicles with single-vesicle imaging such as (cryo-)electron microscopy.

Source [1]

Common purity (negative) markers

  • Calnexin (endoplasmic reticulum)
  • GM130 (Golgi apparatus)
  • Cytochrome c / other mitochondrial proteins
  • Albumin and lipoproteins (main co-isolate contaminants for blood/serum/plasma-derived preparations)

How EVs are separated — and what each method trades off

MethodPrincipleStrengthsLimitations
Ultracentrifugation (UC)Sequential high-speed spins pellet vesicles by size and density, often followed by a sucrose or iodixanol density-gradient step.Long-standing reference-standard method; requires no added reagents; scalable to larger sample volumes.Co-pellets protein aggregates and lipoproteins; can damage or aggregate vesicles; time- and equipment-intensive; modest batch-to-batch reproducibility without an added gradient step.
Size-exclusion chromatography (SEC)Vesicles and free soluble proteins separate as they pass through a porous resin, with larger particles eluting first.Gentle, low-shear method with good preservation of vesicle structure/function; better separation from free protein than plain ultracentrifugation.Lower throughput and scalability; still co-elutes similarly sized lipoproteins; typically needs a concentration step before or after.
Polymer-based precipitationA hydrophilic polymer (e.g., polyethylene glycol) reduces vesicle solubility, causing EVs to precipitate out of solution.Simple, fast, minimal equipment, easy to package as a commercial kit.Co-precipitates substantial non-EV protein and polymer material; the lowest specificity of the common methods; residual polymer can interfere with downstream assays.
Immunoaffinity captureAntibody-coated beads or surfaces selectively bind EVs displaying a chosen surface marker (e.g., a tetraspanin).High specificity for a defined EV subpopulation; enables subpopulation-specific analysis.Captures only the vesicles expressing the targeted marker (a biased subset, not total EVs); reagent cost; elution conditions can be harsh on vesicle integrity.
Tangential flow filtration (TFF)Fluid is pumped parallel to a membrane filter, concentrating and buffer-exchanging vesicles while smaller solutes pass through.Scalable to clinical/manufacturing volumes; gentler than ultracentrifugation; well suited to GMP-style production.Requires dedicated equipment; membrane fouling and vesicle loss must be optimized per product; usually still needs a polishing step for high purity.

Sources [1, 23]

Clinical landscape

Where MSC-EV medicine actually stands.

Registered trials

109

interventional studies of MSC exosomes / MSC-EVs on ClinicalTrials.gov (all statuses), counted September 25, 2026. [19]

A 2014 report described treating a patient with therapy-refractory graft-versus-host disease with MSC-derived exosomes — an early human use. [30]

Regulatory status (U.S.)

As of September 2026, the FDA states that there are no FDA-approved exosome products. Exosome products intended to treat, prevent or diagnose disease — or to affect the structure or function of the body — are regulated as drugs/biologics and require premarket approval. The FDA has issued public safety notifications, including reports of serious adverse events, and continues to send warning letters to marketers of unapproved stem-cell and exosome products. [18]

Myths vs evidence

Seven claims, checked.

References

31 peer-reviewed and primary sources.

Verified against PubMed and publisher records. Numbers in brackets throughout the page link here.

  1. Welsh et al. 2024, J Extracell Vesicles. Minimal information for studies of extracellular vesicles (MISEV2023): From basic to advanced approaches. Journal of Extracellular Vesicles 2024. PMID 38326288. doi:10.1002/jev2.12404
  2. Théry et al. 2018, J Extracell Vesicles. Minimal information for studies of extracellular vesicles 2018 (MISEV2018): a position statement of the International Society for Extracellular Vesicles and update of the MISEV2014 guidelines. Journal of Extracellular Vesicles 2018. PMID 30637094. doi:10.1080/20013078.2018.1535750
  3. Kalluri & LeBleu 2020, Science. The biology, function, and biomedical applications of exosomes. Science 2020. PMID 32029601. doi:10.1126/science.aau6977
  4. van Niel et al. 2018, Nat Rev Mol Cell Biol. Shedding light on the cell biology of extracellular vesicles. Nature Reviews Molecular Cell Biology 2018. PMID 29339798. doi:10.1038/nrm.2017.125
  5. Witwer et al. 2019, J Extracell Vesicles. Defining mesenchymal stromal cell (MSC)-derived small extracellular vesicles for therapeutic applications. Journal of Extracellular Vesicles 2019. PMID 31069028. doi:10.1080/20013078.2019.1609206
  6. Chevillet et al. 2014, PNAS. Quantitative and stoichiometric analysis of the microRNA content of exosomes. Proceedings of the National Academy of Sciences 2014. PMID 25267620. doi:10.1073/pnas.1408301111
  7. Combe, Isaac, Plews & Sokolenko 2025, Stem Cell Res Ther (review). Quantifying extracellular vesicle heterogeneity: the effect of process conditions on protein cargo for skin therapy. Stem Cell Research & Therapy 2025. PMID 40320543. doi:10.1186/s13287-025-04279-5
  8. Baglio et al. 2015, Stem Cell Res Ther. Human bone marrow- and adipose-mesenchymal stem cells secrete exosomes enriched in distinctive miRNA and tRNA species. Stem Cell Research & Therapy 2015. PMID 26129847. doi:10.1186/s13287-015-0116-z
  9. Zhang et al. 2018, Nat Cell Biol. Identification of distinct nanoparticles and subsets of extracellular vesicles by asymmetric flow field-flow fractionation. Nature Cell Biology 2018. PMID 29459780. doi:10.1038/s41556-018-0040-4
  10. Zhang et al. 2021, Nat Cell Biol. Supermeres are functional extracellular nanoparticles replete with disease biomarkers and therapeutic targets. Nature Cell Biology 2021. PMID 34887515. doi:10.1038/s41556-021-00805-8
  11. Ma et al. 2015, Cell Res. Discovery of the migrasome, an organelle mediating release of cytoplasmic contents during cell migration. Cell Research 2015. PMID 25342562. doi:10.1038/cr.2014.135
  12. Teng et al. 2018, Cell Host Microbe. Plant-Derived Exosomal MicroRNAs Shape the Gut Microbiota. Cell Host & Microbe 2018. PMID 30449315. doi:10.1016/j.chom.2018.10.001
  13. Toyofuku et al. 2023, Nat Rev Microbiol. Composition and functions of bacterial membrane vesicles. Nature Reviews Microbiology 2023. PMID 36932221. doi:10.1038/s41579-023-00875-5
  14. Albert & Brown 2026, Transfus Med Hemother. Platelet Products and Artificial Platelets for Regenerative Medicine. Transfusion Medicine and Hemotherapy 2026. PMID 42578151. doi:10.1159/000553404
  15. Arif et al. 2026, J Control Release. Exosomes as next-generation drug carriers: Transforming cancer therapy. Journal of Controlled Release 2026. PMID 42603664. doi:10.1016/j.jconrel.2026.115265
  16. Li et al. 2026, Front Immunol. Application of stem cell-derived exosomes in skin wound healing: mechanisms, prospects, and challenges. Frontiers in Immunology 2026. PMID 42713281. doi:10.3389/fimmu.2026.1846916
  17. Raza et al. 2026, Front Pharmacol. Stem cell-derived extracellular vesicles as immunomodulators: a novel paradigm for post-myocardial infarction repair and regeneration. Frontiers in Pharmacology 2026. PMID 42344804. doi:10.3389/fphar.2026.1860228
  18. FDA 2026, Public Safety Notification on Exosome Products. Public Safety Notification on Exosome Products / Consumer Alert on Regenerative Medicine Products Including Stem Cells and Exosomes. U.S. Food and Drug Administration (fda.gov) 2026. Source
  19. ClinicalTrials.gov search, accessed 2026-09-25. Trials matching intervention: mesenchymal stem cell exosome OR MSC-derived extracellular vesicles. ClinicalTrials.gov (NIH/NLM registry) 2026. Source
  20. Valadi et al. 2007, Nat Cell Biol. Exosome-mediated transfer of mRNAs and microRNAs is a novel mechanism of genetic exchange between cells. Nature Cell Biology 2007. PMID 17486113. doi:10.1038/ncb1596
  21. Trajkovic et al. 2008, Science. Ceramide triggers budding of exosome vesicles into multivesicular endosomes. Science 2008. PMID 18309083. doi:10.1126/science.1153124
  22. Baietti et al. 2012, Nat Cell Biol. Syndecan-syntenin-ALIX regulates the biogenesis of exosomes. Nature Cell Biology 2012. PMID 22660413. doi:10.1038/ncb2502
  23. Jeppesen et al. 2019, Cell. Reassessment of exosome composition. Cell 2019. PMID 30951670. doi:10.1016/j.cell.2019.02.029
  24. Kowal et al. 2016, PNAS. Proteomic comparison defines novel markers to characterize heterogeneous populations of extracellular vesicle subtypes. Proceedings of the National Academy of Sciences 2016. PMID 26858453. doi:10.1073/pnas.1521230113
  25. Lai et al. 2010, Stem Cell Res. Exosome secreted by MSC reduces myocardial ischemia/reperfusion injury. Stem Cell Research 2010. PMID 20138817. doi:10.1016/j.scr.2009.12.003
  26. Ostrowski et al. 2010, Nat Cell Biol. Rab27a and Rab27b control different steps of the exosome secretion pathway. Nature Cell Biology 2010. PMID 19966785. doi:10.1038/ncb2000
  27. Dominici et al. 2006, Cytotherapy (ISCT). Minimal criteria for defining multipotent mesenchymal stromal cells. The International Society for Cellular Therapy position statement. Cytotherapy 2006. PMID 16923606. doi:10.1080/14653240600855905
  28. Zhang et al. 2015, Stem Cells. HucMSC-exosome mediated-Wnt4 signaling is required for cutaneous wound healing. Stem Cells 2015. PMID 24964196. doi:10.1002/stem.1771
  29. Hu et al. 2019, ACS Nano. Needle-free injection of exosomes derived from human dermal fibroblast spheroids ameliorates skin photoaging. ACS Nano 2019. PMID 31449388. doi:10.1021/acsnano.9b04384
  30. Kordelas et al. 2014, Leukemia. MSC-derived exosomes: a novel tool to treat therapy-refractory graft-versus-host disease. Leukemia 2014. PMID 24445866. doi:10.1038/leu.2014.41
  31. Mulcahy et al. 2014, J Extracell Vesicles. Routes and mechanisms of extracellular vesicle uptake. Journal of Extracellular Vesicles 2014. PMID 25143819. doi:10.3402/jev.v3.24641

Educational content, not medical advice. The 3D model is schematic: shapes are simplified, and copy numbers and positions are illustrative rather than measured for any specific preparation.

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