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Exosomes and Extracellular Vesicles Explained | iPS Cells & Regenerative Medicine

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TECHNOLOGY EXPLAINER

Exosomes (Extracellular Vesicles)
— what they contain matters less than the fact that no one has yet agreed what to measure as quality

Exosomes are tiny bags made of a lipid membrane and released by cells. They are attracting hope as a way to deliver what cells do without using the cells themselves, and the Japanese Society for Regenerative Medicine has warned that self-pay clinics offer treatments using "exosomes" for purposes such as anti-aging. Yet in July 2024 Japan's Ministry of Health, Labour and Welfare (MHLW) notified medical institutions that no drug containing exosomes has been approved and marketed, and the US FDA likewise states that it has approved no exosome product. This article sets out isolation and purification, quantification and specifications, drug delivery and the regulatory position, seen through the eyes of materials and analytical science.

Built from primary sources: the PMDA Science Board report, MHLW notices and advisory-council materials, FDA publications, guidance from the Japanese Society for Regenerative Medicine, statements from the International Society for Extracellular Vesicles (ISEV), and peer-reviewed papers / Last updated October 2026

Small vesicles form inside a multivesicular body and are released from a cell
AI-generated conceptual image reused from the Japanese edition. Conceptual view of vesicle formation and release from a multivesicular body. It cannot establish that any particular observed particle is an exosome.
What this article covers
  1. What exosomes are (the short version)
  2. Sorting out the names — exosomes are one kind of extracellular vesicle
  3. How they are made — from cell culture to formulation
  4. Why isolation and purification are hard — ultracentrifugation, size exclusion, affinity, membrane filtration
  5. A materials engineer's view (1): purification is a materials problem of carriers, membranes, containers and reagents
  6. What to measure as quality — the challenge of quantification and specifications
  7. Our calculation: the "weight" of 1010 particles, and the protein that travels with them
  8. As carriers for drug delivery — natural and engineered types
  9. A materials engineer's view (2): how they differ from lipid nanoparticles
  10. Regulatory position — the United States and Japan
  11. Open issues, and what this article could not confirm
  12. Glossary / References / Claim-to-source audit
How claims are labelled in this article

Sourced = content stated in published material or a paper (link given)
Our calculation = a figure this article derived from stated assumptions
Not yet confirmed = research-stage, under discussion, or an outlook, with no confirmed track record
Structural readings and interpretations from the materials and process side are marked separately as Commentary.

A note on medical matters

This article explains materials technology, analytical technology and regulation. It does not assess the efficacy or safety of treatments or procedures that use exosomes, does not recommend any product, facility or treatment, and is not medical advice. It quotes only what regulators and academic societies have published, and does not intend to evaluate any particular provider.

1. What exosomes are (the short version)

An exosome is a vesicle made of a lipid bilayer and secreted by many kinds of cells. The PMDA Science Board report describes exosomes as present in body fluids such as blood, saliva, urine and cerebrospinal fluid and in cell culture medium, and as "a kind of extracellular vesicle (EV)"Sourced.

  • What they carry: besides proteins, EVs enclose nucleic acids such as microRNA and mRNA, and are thought to hand functional molecules over to other cellsSourced
  • Why they draw attention: reports that part of the effect of mesenchymal stem cells (MSCs) comes from what they secrete (EVs included) rather than from the cells themselves have raised hopes for a next-generation, cell-free therapeutic toolSourced. For example, Lai et al. reported in 2010 that vesicles purified from the culture supernatant of human embryonic stem cell-derived MSCs reduced infarct size in a mouse model of myocardial ischemia and reperfusion injury [Source 15]Sourced. Phinney et al. pointed out that the contents of MSC-derived exosomes change with the tissue the MSCs came from and with the surrounding cells [Source 16]Sourced. This background was covered in our explainer on mesenchymal stem cells
  • What makes them hard: EVs are not one defined substance but a heterogeneous population of particles whose contents differ with the cell and its state. There is no agreed best method of isolation and purification, and agreement on "what to measure as quality" is still under waySourced
The single most important line in this article

Products calling themselves "exosome" are spreading, but that is a separate matter from there being an approved drug. In a notice dated 31 July 2024, the MHLW told medical institutions, regarding medical care that uses stem-cell culture supernatant or exosomes, that no drug containing the exosomes in question has been shown to be effective and safe, including outside Japan, and approved by regulators for manufacture and saleSourced. In December 2019 the FDA likewise stated that it has not approved any exosome productSourced.

2. Sorting out the names — exosomes are one kind of extracellular vesicle

The PMDA report divides extracellular vesicles by their route of production and size into three groups: endosome-derived vesicles of about 100 nm (exosomes), plasma membrane-derived vesicles of micrometre size (microvesicles), and apoptotic bodies derived from the membranes of dying cellsSourced. These definitions are loose, however, and the report adds that unless the moment of release is captured by live imaging, it is hard to tell which route a vesicle took, which is why the naming has stayed confusedSourced.

Approximate EV size ranges, and what tends to mix in at similar sizes Note: the horizontal axis is logarithmic. The EV range follows the PMDA report; the 200 nm split follows MISEV2018. All extracellular vesicles (EVs): tens of nm to several µm Umbrella term: cell-derived lipid-membrane complexes of diverse molecules (PMDA report) Small EVs (sEV) 200 nm or smaller Exosomes (about 100 nm) Medium / large EVs (m/lEV) Above 200 nm Microvesicles, apoptotic bodies, etc. Similar size to EVs, hard to separate Virus particles (similar in size to EVs) Protein aggregates, lipoproteins 10 nm 100 nm 1 µm 10 µm Note: EV size range from the PMDA report [Source 3]; the sEV and m/lEV split follows MISEV2018 [Source 1], as cited there. Note: band edges are approximate, for layout, and are not exact size ranges for each vesicle type.
Fig. 1 Conceptual diagram (vector drawing). The EV range and the split into small EVs (200 nm or smaller) and medium / large EVs follow the PMDA report [Source 3] and MISEV2018 [Source 1]. The band edges are approximate and do not give the size range of any vesicle type. That viruses and protein aggregates readily mix in is this article's depiction of a point made in the PMDA report.

The International Society for Extracellular Vesicles (ISEV) recommends calling all of these "extracellular vesicles (EVs)"Sourced. Its 2018 guidelines (MISEV2018) say that attributing a particular function to "exosomes" takes more than describing the function of a preparation that may be crude or heterogeneous, and that claims of special exosome activity are hard to support experimentally because the molecular machinery of their biogenesis and release is still not well understoodSourced. MISEV2023 says that naming, separation from extracellular particles other than EVs, and characterization remain challengesSourced.

In line with this, unless stated otherwise this article uses "exosome" and "EV" almost interchangeably, on the premise that the types of particle cannot be told apart (a note from this article).

3. How they are made — from cell culture to formulation

The PMDA report divides therapeutic preparations in which cell-derived EVs are administered into the body into two broad groupsSourced.

  • Natural EVs: used unmodified, relying on the therapeutic effect of the EVs themselves and recovered from, for example, cell culture supernatant
  • Engineered EVs: given a particular function by genetically modifying the source cells, or by attaching peptides or antibodies or loading a drug after purification (for example, carriers for drug delivery)
Manufacturing flow of an EV therapeutic, and the challenge noted at each stage (our summary) Note: the challenges at each stage come from the PMDA Science Board report and individual research reports. Source cells Cell bank Culture Medium, cell density Harvest, concentrate Bulk harvest Purification Column, membrane, spin Formulate, store Freezing, aliquoting Using cells free of virus is the top priority (virus is hard to remove) Each bank renewal needs virus testing Fetal bovine serum can bring in serum EVs and cause unexpected activity Animal-derived components best avoided Ultracentrifugation is common in labs but hard at commercial scale; concentrating first is Tangential-flow (TFF) comparisons exist No single best method Scalable column methods are preferred A method to confirm residual impurities is essential At -80 °C, particle count falls and size rises Repeated freeze-thaw changes it further; some observations hint at vesicle fusion Note: stages follow the PMDA report [Source 3]; membrane filtration, Visan et al. [Source 6]; storage, Gelibter et al. [Source 8]. Note: the five stages are this article's grouping and do not give the number or order of steps in any real plant. Note: storage changes were seen in EVs from plasma and mouse cells and may not apply to every preparation.
Fig. 2 Conceptual diagram (vector drawing). The challenge at each stage follows the PMDA report [Source 3], Visan et al. [Source 6] and Gelibter et al. [Source 8]. The division into five stages is this article's own and does not show the actual process at any manufacturing site. The effects of storage are laboratory-scale observations.

The PMDA report notes that EV manufacture has several steps "from selecting source cells to dispensing and storage", and recommends setting several checkpoints between culture and purification. Examples are checking the state of cells after seeding (morphology, dead-cell rate, viability) and checking how many EVs are in the culture fluid before purification and how much of the active ingredient they containSourced. Because cell density affects the amount of EVs secreted and their molecular makeup, it also says that comparability and homogeneity must be assessed before and after scale-upSourced.

Viruses are treated with particular weight. The report states that EVs and viruses are similar in size and are likely to behave alike during purification, so it is difficult to apply a virus-clearance step to manufacture, and that using cells free of virus contamination as the EV-producing substrate is the most important measureSourced.

4. Why isolation and purification are hard — ultracentrifugation, size exclusion, affinity, membrane filtration

There is no single definitive way to isolate and purify EVs. The PMDA report says that there is currently no best method, and that the existence of so many methods is itself the problem, and that although ultracentrifugation is widely used in papers, it cannot process large volumes and is therefore hard to carry over unchanged into practical useSourced.

In a worldwide survey by Gardiner et al. in 2016, the most common source material for EVs was cell culture supernatant (83%), the most common separation method was ultracentrifugation (81%), and 59% of respondents combined several methodsSourced.

MethodPrinciple of separationWhat the literature and regulators sayCautions noted
UltracentrifugationSedimentation by differences in density and sizeMost widely used at the research stage [Source 4]. In a comparison on rat plasma, yield was lower than with size-exclusion chromatography but purity was higher [Source 5]Hard to process at commercial scale, and concentration by bulk harvest is essential beforehand [Source 3]. One comparison found it inferior to membrane filtration in yield, reproducibility, time, cost and scale [Source 6]
Size-exclusion chromatography (SEC)Sieving by sizeReported to have been used to purify and separate EVs as a column method that can be scaled up [Source 3]Protein aggregates of the same size can remain as impurities [Source 3]. In plasma, lipoproteins (APOB-positive) and non-EV protein were also abundant [Source 5]
Anion-exchange chromatographyDifferences in surface chargeReported to have been used to purify and separate EVs [Source 3]A way to confirm residual impurities, as a purification indicator, is needed [Source 3]
Affinity purificationBinding by antibodies and the likeUseful if the active component is known to be a protein on the EV membrane or similar [Source 3]CD63 and CD9 are not on every EV, so whether positive EVs carry the intended activity must be examined. Carry-over of the buffer used to release EVs must also be checked [Source 3]
Polymer precipitation (PEG, etc.)EVs are precipitated with a polymer and recovered by low-speed centrifugationUsed at the research stage as commercial EV-purification reagents [Source 3]Reagent carry-over is a concern, and establishing a way to confirm residual impurities after purification is essential [Source 3]
Membrane filtration (tangential-flow filtration, TFF)Sieving by membrane pore sizeA report that TFF combined with SEC gave higher yield than ultracentrifugation combined with SEC, and was better in reproducibility, time, cost and scale [Source 6]Results from several cancer cell lines the authors cultured in serum-containing medium; may not apply to every material or purpose [Source 6]

All Sourced (PMDA report [Source 3], Gardiner et al. [Source 4], Takov et al. [Source 5], Visan et al. [Source 6]). The table is this article's arrangement by method and does not rank the methods.

Takov et al. separated EVs from the same rat plasma by ultracentrifugation and by SEC and compared them. They reported that SEC gave more particles and more protein but also more lipoproteins and non-EV protein, while ultracentrifugation gave a lower yield but higher purity. They also found that the activity that moves cells (migration of vascular endothelial cells) varied with the separation method and did not simply track the amount of EVs, and pointed out that co-purified material other than EVs may contribute to the activitySourced.

5. A materials engineer's view (1): purification is a materials problem of carriers, membranes, containers and reagents

What a materials engineer should read here: the materials used to separate become the source of impurities and of quality

Reading the table in chapter 4 from the materials side shows the following points of contact (commentary from this article).

  • Column carriers, membranes and ligands: the PMDA report says that, whichever purification method is used, indicators must be set for removing process-related impurities (ligands and column carriers used in the culture or purification steps)Sourced. What leaches or sheds from carriers and membranes can itself become a subject of specification
  • Foreign matter of the same size: the report says that particles the same size as EVs, whether biological or man-made, are hard to separate once they have got in, and that airborne particles in the work environment and artificial microparticles from labware such as tubes can quite plausibly be mixed inSourced. The cleanliness of single-use parts, low-particle containers and filters, and the material of tubing bear directly on EV purity
  • Residual polymer reagents: for methods that precipitate with a polymer such as PEG, a way to confirm reagent residue is stated to be essentialSourced. The molecular-weight distribution and removability of polymers are a strength of materials makers
  • Storage containers and freezing: Gelibter et al. reported that on storage at -80 °C the concentration and purity of EVs fell over time, particle size and its spread increased, and zeta potential changed, and that repeated freeze-thaw cut the particle count further and enlarged the particles. They state that none of the storage conditions they examined prevented thisSourced. Whether cryoprotectants or container materials can improve matters is an open questionNot yet confirmed

Just as vials and culture medium are part of quality in a cell product (see the MSC explainer), for EV products "the cleanliness and leachables of the materials used for separation" are themselves the quality.

6. What to measure as quality — the challenge of quantification and specifications

The hardest part of EV quality control is deciding what unit to measure in and what to set as the specification. The PMDA report asks whether the amount administered to the body should be EV protein mass, EV particle number, or the amount of the active ingredient, and says that the reagents, instruments and conditions used for measurement must be stated and fixedSourced.

Four "yardsticks" for measuring EVs, and the cautions stated for each (our summary) Note: none is said to suffice alone; the premise is that they are used in combination. Particle count Protein mass Active amount Potency (activity) Single-particle counting Colorimetric assays, etc. Assay a specific component Biological response assay Size distribution varies with principle and model Particles must be dispersed, not clumped together A heterogeneous population: see the spread, not just mean Also counts protein that lies outside the EVs Its ratio to particle count has been proposed as a purity indicator Ideally correlates with particle count Clearest when the active component is known EVs are complexes; not all molecules are effective Hard to define if the mechanism is unknown Ideally a test that reflects the mechanism If that is hard, evaluate with several tests together Divide by particle count or protein: specific activity Critical quality attributes (CQAs) are unclear, and are said to stay open until analytics leads the way Note: particle count, active amount and potency follow the PMDA report [Source 3]; protein mass, Webber et al. [Source 7] Note: and the JSRM guidance [Source 22]; CQAs follow the MHLW advisory-council materials [Source 24].
Fig. 3 Conceptual diagram (vector drawing). The cautions for each yardstick follow the PMDA report [Source 3], Webber et al. [Source 7], the guidance of the Japanese Society for Regenerative Medicine (JSRM) [Source 22] and the materials of the MHLW Regenerative Medicine Evaluation Subcommittee [Source 24]. The grouping into four is this article's own and is not an officially fixed classification.

A guide to purity — the ratio of particle count to protein mass

In 2013, Webber et al. proposed estimating the purity of an EV preparation by the ratio of particle count to protein concentration. In their own measurements (nanoparticle tracking analysis and the BCA assay), they sorted preparations as high purity above 3×10¹⁰ particles per µg, low purity at 2×10⁹ to 2×10¹⁰, and impure below 1.5×10⁹Sourced. They state that simple precipitation and washing left the ratio at about a third of that (1×10¹⁰), with plenty of contaminating proteinSourced. These figures are a proposal based on the authors' own instruments and conditions and are not a standard that can be applied unchanged to other instruments or samples (a note from this article).

The unit of dose is still not unified

Some early clinical trials of EVs set the dose not by protein mass or particle count but by the number of MHC class II molecules on the EVs. In 2005, Escudier et al. set the dose in a phase I trial giving dendritic cell-derived exosomes to 15 melanoma patients by the number of MHC class II molecules (0.13 or 0.40×10¹⁴)Sourced. The guidance from the Japanese Society for Regenerative Medicine says that particle count and protein mass are the indicators most often used to show EV quantity, and that it is desirable for the two to correlateSourced. For small EVs derived from MSCs, members of several societies have proposed defining them by quantifiable indicators such as identification of the originating cells, the presence of lipid-membrane vesicles, and physical and biochemical integrity, and comparing them with a well-characterised biological reference materialSourced.

On marker molecules for EVs, the PMDA report notes that there is no consensus EV marker and that several markers should be analysed together, and introduces the ISEV guideline that at least three proteins and the like regarded as specific to the EV fraction should be analysed semi-quantitativelySourced.

7. Our calculation: the "weight" of 1010 particles, and the protein that travels with them

When the dose is set by particle count, the amount of the particles themselves is surprisingly small, and the accompanying impurities can be relatively large. This calculation is meant to give a sense of the orders of magnitude. It does not indicate any particular dose.

Our calculation

We make the following assumptionsOur calculation.

  • An EV is a sphere 100 nm in diameter (the PMDA report describes exosomes as vesicles of about 100 nm)
  • Particle density is 1.1 g/cm³ (this article's assumption)
  • The particle count is 10¹⁰ (a number chosen for illustration, not a proposed dose)
  • Volume of one particle: π/6 × (100 nm)³ = 5.24×10⁻²² m³ = 5.24×10⁻¹⁶ cm³
  • Volume of 10¹⁰ particles: 5.24×10⁻¹⁶ × 10¹⁰ = 5.24×10⁻⁶ cm³ = about 5.2 nL
  • Mass of 10¹⁰ particles: 5.24×10⁻⁶ cm³ × 1.1 g/cm³ = about 5.8 µg
  • Accompanying protein (worked back from Webber's ratios): for 10¹⁰ particles, 0.33 µg at 3×10¹⁰ particles/µg, 5.0 µg at 2×10⁹ particles/µg, and 6.7 µg at 1.5×10⁹ particles/µg (in each case the total protein measured together with the particles)
  • Comparison: for the same 10¹⁰ particles, the accompanying protein differs between purity classes by 6.7 ÷ 0.33 = about 20-fold

Premises and limits: particle size and density are assumptions, and real EVs vary in size. Webber's ratios came from one particular method, nanoparticle tracking analysis, and the values change with instrument and conditions. This calculation is for grasping orders of magnitude; it does not claim that particle count, mass and protein mass can be simply converted into one another.

Protein with 10¹⁰ particles varies ~20-fold with purity class (our calculation) Bar length = accompanying protein (µg). Dotted line = mass of 10¹⁰ particles (100 nm, 1.1 g/cm³; about 5.8 µg) Benchmark: high purity 3×10¹⁰ particles/µg Low purity, lower limit 2×10⁹ particles/µg Benchmark: impure 1.5×10⁹ particles/µg 0.33 µg 5.0 µg 6.7 µg Particle mass about 5.8 µg (assumed) 0 µg Note: ratios are the values proposed by Webber et al. [Source 7].
Fig. 4 Drawing that includes our calculation (vector drawing). The particle-count-to-protein ratios are the values proposed by Webber et al. [Source 7]. The figures 0.33 µg, 5.0 µg, 6.7 µg, about 5.8 µg and about 20-fold are values this article derived, not published values. The 100 nm diameter, 1.1 g/cm³ density and 10¹⁰ particles are this article's assumptions.

8. As carriers for drug delivery — natural and engineered types

Because EVs enclose nucleic acids and proteins, travel through the body and hand them to cells, they are also being studied as carriers that transport drugs (containers for drug delivery). The PMDA report explains that engineered EVs are used mainly for drug delivery systems (DDS), because EVs can deliver functional molecules to distant organs and to specific cellsSourced. It also cites reports that nano-sized EVs are less immunogenic and mutagenic than viral carriers, and that the nucleic acids they enclose resist degrading enzymes in the bloodSourced.

Natural EVs, and three routes to engineered EVs (our summary) Note: the routes are sometimes used in combination. Natural EVs: used unmodified, recovered from cell culture supernatant, etc. The EVs themselves are assumed to carry the therapeutic effect (e.g. MSC-derived EVs, dendritic cell-derived EVs) Route 1: modify source cells Route 2: modify the surface Route 3: load a drug Introduce a gene into the cells that make the EVs, so the secreted EVs carry the molecule After purification, attach a peptide or antibody to the EV membrane to set the destination After purification, force a drug into the EVs by physical means (electroporation, etc.) e.g. a neuron-targeting peptide (RVG) fused to Lamp2b, in dendritic cells e.g. the EGFR-targeting GE11 peptide on the membrane (cited in PMDA report) e.g. siRNA loaded into EVs by electroporation (mouse study) Note: the split and examples follow the PMDA report [Source 3]; RVG, Lamp2b and electroporation, Alvarez-Erviti et al. (2011) [Source 11]. Note: the PMDA report states that no engineered EV (DDS preparation) has yet reached practical use (January 2023). Note: the three routes are this article's grouping and do not show the process for any real product.
Fig. 5 Conceptual diagram (vector drawing). The split into natural and engineered EVs and the examples follow the PMDA report [Source 3]; the RVG peptide and siRNA-loading example follows Alvarez-Erviti et al. (2011) [Source 11]. The grouping into three routes is this article's own, and the routes are sometimes combined. No engineered-EV drug that has reached practical use is within what this article confirmed.

Research-stage examples — delivery in mice

In 2011, Alvarez-Erviti et al. made EVs from the animals' own dendritic cells (aiming to lower immunogenicity), expressed a nerve-binding peptide (RVG) fused to the EV membrane protein Lamp2b, and loaded siRNA into the purified EVs by electroporation. After intravenous injection, they reported gene silencing specific to neurons, microglia and oligodendrocytes in the brain, with no nonspecific uptake in other tissues. For BACE1, a target in Alzheimer's disease, mRNA was reduced by 60% and protein by 62% in wild-type miceSourced.

In 2017, Kamerkar et al. made "iExosomes" by loading EVs from fibroblast-like mesenchymal cells with siRNA or shRNA aimed at the cancer-driving KRAS mutation (KrasG12D). They suggested that EVs stay in the circulation of mice longer than liposomes apparently because CD47 protects them from phagocytosis, and reported that iExosomes suppressed cancer and prolonged overall survival in several mouse models of pancreatic cancerSourced.

Both are results from animal experiments and do not show efficacy or safety in humans (a note from this article).

Natural EVs in human trials — dendritic cell-derived exosomes

An early example of EVs given to humans is the use of dendritic cell-derived exosomes in cancer immunotherapy. In 2005, Escudier et al. reported a phase I trial in which 15 melanoma patients received exosomes derived from their own dendritic cells, concluding that large-scale exosome production is feasible and administration was safe. There was no toxicity of grade II or above, and the maximum tolerated dose was not reachedSourced. In 2016, Besse et al. reported a phase II trial of second-generation dendritic cell-derived exosomes, with interferon-gamma added, given to 22 patients as maintenance therapy for non-small cell lung cancer. The primary endpoint (at least 50% of patients progression-free 4 months after chemotherapy) was not met. Enhanced NK cell function was reported in some patientsSourced.

Registration of a phase 3 trial of MSC-derived EVs

ClinicalTrials.gov lists a phase 3 trial (NCT05354141, sponsor: Direct Biologics) in which bone-marrow MSC-derived EVs (trial name ExoFlo) are given intravenously to hospitalised patients with moderate-to-severe acute respiratory distress syndrome (ARDS). It began in July 2022 and is randomised, double-blind and placebo-controlled, with planned enrollment of 970; at the record's last update (23 February 2026) its status was "recruiting"Sourced. We could not confirm any results at the time of writingNot yet confirmed.

9. A materials engineer's view (2): how they differ from lipid nanoparticles

What a materials engineer should read here: LNPs are "made", EVs are "harvested"

As containers for carrying nucleic acids, the LNPs covered in our explainer on lipid nanoparticles are already approved products. EVs and LNPs are close in size (LNPs are about 60 to 100 nm), but quite different in character as materials (commentary from this article).

AspectLipid nanoparticles (LNPs)Extracellular vesicles (EVs)
CompositionFour components (ionizable lipid, phospholipid, cholesterol, PEG lipid), with the mixing ratio designedA complex that holds proteins, nucleic acids, glycans and more besides lipids. The contents differ with the cell and its state, so it is hard to define by a particular molecule [Source 3]
How madeAssembled from components, for example by rapid mixing of a lipid solution and a nucleic acid solution (bottom-up)What cells have made is recovered and purified from culture supernatant and the like (top-down)
Basis of qualityComponents and physical properties (particle size, encapsulation rate and so on) are easy to turn into specificationsThe source cells, the medium and the purification method all affect quality, and critical quality attributes are unclear [Sources 3 and 24]
Reaching the targetComposition tends to determine distribution, for example to the liver (see the LNP explainer)There is research that uses molecules native to EVs (for example CD47) and research on modifying the membrane [Sources 12 and 3]
Approval statusApproved products exist among nucleic acid drugs and mRNA vaccines (see the LNP explainer)No approved drug in either Japan or the United States [Sources 20 and 21]

The LNP column draws on our explainer on lipid nanoparticles; the EV column draws on the sources in brackets. The table is this article's arrangement and does not rank the two.

In short, LNPs are a material whose composition is designed and turned into a specification, whereas EVs are a material in which a complex made by cells must be taken out as intact and as pure as possible. The freedom of design is lower, but there may be a chance to use the properties of a natural membrane. The point to start from, in materials and analytical terms, is not which is better but that the way the specification is built is fundamentally different.

10. Regulatory position — the United States and Japan

Main statements, notices and reports on EVs (exosomes) confirmed for this article Note: not an exhaustive timeline; these are the items this article could confirm in primary sources. When Source Content 2015 ISEV (international) Classify by whether EVs are the active ingredient or a delivery carrier 2018 ISEV (international) MISEV2018: claims of exosome-specific function need extra information Dec 2019 FDA (US) States no exosome product is approved; regulated as drugs / biologics Jan 2023 PMDA (Japan) Science Board report: sets out quality and safety issues for EV therapeutics Apr 2024 JSRM (Japan) Guidance on clinical use of extracellular vesicles (1st edition) Jul 2024 MHLW (Japan) Notice: no approved drug; the physician is responsible for safety Dec 2024 JSRM / FDA Alert on iPS cell-derived exosomes / FDA warning letter to a firm Jan 2026 MHLW council Interim report: EVs and culture supernatant should fall under the Safety Act Note: sources are Sources 9, 1, 17, 18, 3, 22, 21, 23, 19 and 24. The January 2026 item is an interim report, not a legal amendment. Note: official documents from the European regulator (EMA) are not shown, because this article did not confirm them.
Fig. 6 Conceptual diagram (vector drawing). Each item follows Sources 9, 1, 17, 18, 3, 22, 21, 23, 19 and 24. The January 2026 entry is a study group's interim report and does not decide any amendment of the law. Documents from EMA and other European regulators were not checked for this article.

United States — the FDA

On 6 December 2019 the FDA stated that it has not approved any exosome product. The background was that several serious adverse events were reported in patients in Nebraska after they received unapproved products marketed as containing exosomes. The same document says that exosomes used to treat human diseases or conditions are, under the Public Health Service Act and the Federal Food, Drug, and Cosmetic Act, regulated as drugs and biological products and require premarket review and approval. It advises patients to confirm, before treatment, the investigational new drug application number (IND number) reviewed by the FDASourced.

A warning letter dated 30 December 2024 to a firm marketing an exosome product describes that product as an unapproved new drug and also an unlicensed biological product, and says the product is not eligible for the light regulation of human cell and tissue products under section 361 of the Public Health Service ActSourced. The FDA's list of approved cellular and gene therapy products (updated 17 September 2026) does not name any exosome or EV product eitherSourced.

Japan — the MHLW, PMDA and the Japanese Society for Regenerative Medicine

  • PMDA Science Board (17 January 2023): summarising discussions from August 2021 to September 2022, it set out as issues safety evaluation against viruses and other infectious agents, quality attributes of the active component, consistency of manufacture, evaluation in nonclinical studies, and points to note in clinical trialsSourced
  • Japanese Society for Regenerative Medicine (30 April 2024): Guidance on the Clinical Application of Extracellular Vesicles, etc. (1st edition). As general safety risks of EV preparations it lists transmission of infection, unwanted immune reactions, contamination with impurities, unintended changes in EV properties, unwanted biodistribution, toxicity to vital organs, the germ line and development, tumours or unwanted tissue arising from the patient's cells, and failure to achieve the expected efficacySourced
  • MHLW (31 July 2024): in an administrative notice addressed to the administrators of institutions that provide regenerative medicine, it said that, for medical care using stem-cell culture supernatant or exosomes, no approved drug is manufactured and marketed, so particular attention to safety is needed under the responsibility of the physician or dentist carrying it out, and asked institutions to refer to the society's guidanceSourced
  • Japanese Society for Regenerative Medicine (27 December 2024): it warned patients and the public that self-pay clinics increasingly offer expensive exosome treatments made from iPS cell culture supernatant, promoted for anti-aging and similar purposes, while clinical evidence has not been adequately established. It said that at the society's annual meeting that year it saw no specific research presentation or sharing of clinical trial results on iPS cell-derived exosomesSourced
  • MHLW advisory-council materials (15 January 2026): an interim report from a research group, noting that EVs and culture supernatant can currently be administered directly to people, set out the view that they should be covered by the Act on the Safety of Regenerative Medicine. The material says that for EVs the critical quality attributes, the mechanism of action and disease-specific potency assays are not yet established, so setting quality specifications and a control strategy is difficult at this stage. It also records an expert view that EVs are currently outside that ActSourced. We have not confirmed what amendment, or when, followed from thisNot yet confirmed

International position

In a 2015 position paper, ISEV and a network of EU researchers said that to fit EV-based treatments into existing regulatory frameworks it is important to define whether the EVs are the active ingredient or mainly a delivery carrier. This is because the classification determines the requirements for manufacture, quality control and clinical trialsSourced.

11. Open issues, and what this article could not confirm

(1) Standardising isolation, purification and measurement

No best method of isolation and purification has been settled (chapter 4), and both particle count and protein mass change with the measurement method and instrument (chapter 6). Several societies have proposed defining MSC-derived small EVs by quantifiable indicators and a reference material [Source 10], but we could not confirm whether a widely agreed reference material existsNot yet confirmed.

(2) Mechanism of action and potency

To make EVs a drug, a potency assay based on what actually works is needed, yet the MHLW advisory-council material states that critical quality attributes, the mechanism of action and disease-specific potency assays have not been established [Source 24]Sourced.

(3) Viral safety

Because EVs and viruses are close in size, a virus-clearance step is hard to apply in purification, so using cells free of virus contamination is regarded as the most important measure [Source 3]Sourced.

(4) Clinical evidence

The phase II trial of dendritic cell-derived exosomes did not meet its primary endpoint (chapter 8) [Source 14]. The phase 3 trial of MSC-derived EVs is listed as ongoing, but no results could be confirmed [Source 25]Not yet confirmed.

(5) What this article could not confirm

  • The official position of the EU (EMA). We confirmed the 2015 ISEV position paper but not any EMA document
  • Regulation in countries and regions other than the United States and Japan
  • The content and timing of any amendment to Japan's Act on the Safety of Regenerative Medicine (developments after the January 2026 interim report)
  • The composition and quality of individual EV products and treatments (not covered, because little published primary information is available)
  • Market-size estimates (cited in the advisory-council material, but not covered because we do not use market-research estimates)
  • A tally of ClinicalTrials.gov registrations (keyword searches also return non-EV trials, so we give no count)
Summary of this article
  • Exosomes are one kind of EV, and the definition is loose. They are described as endosome-derived vesicles of about 100 nm, but identifying the route of production is said to be difficultSourced
  • There is no best method of isolation and purification. Ultracentrifugation is hard at commercial scale, and SEC, membrane filtration, affinity and polymer precipitation each carry cautions about impurities or residuesSourced
  • Whether to use particle count, protein mass, active amount or potency as the unit is still not unified. The ratio of particle count to protein mass has been proposed as a purity guideSourced
  • The mass of 1010 particles is about 5.8 µg (assumed), and the accompanying protein differs about 20-fold between purity classesOur calculation
  • As drug-delivery carriers, work is centred on mice. The PMDA states that no engineered EV has been put to practical useSourced
  • There is no approved drug in Japan or in the United States. The FDA states that exosomes are regulated as drugs and biological products, and in Japan the January 2026 council material set out a view that EVs and culture supernatant should come under the Safety ActSourced

12. Glossary

Extracellular vesicle (EV)
Umbrella term for lipid-membrane vesicles released by cells. Includes exosomes, microvesicles and apoptotic bodies.
Exosome
An EV of about 100 nm thought to derive from endosomes. Identifying the route of production is difficult.
sEV / m/lEV
Small EVs (200 nm or smaller) and medium / large EVs (above 200 nm). The split used in MISEV2018.
MISEV
Minimal information guidelines for EV studies issued by the International Society for Extracellular Vesicles (ISEV). Editions exist for 2014, 2018 and 2023.
Culture supernatant
The liquid part left after culturing cells. It contains secretions such as EVs and proteins.
Bulk harvest
The large volume of fluid collected at the end of culture, before purification.
Ultracentrifugation
Sedimenting particles with very high centrifugal force. The most used method in laboratories.
SEC (size-exclusion chromatography)
A column method that sieves particles by size.
TFF (tangential-flow filtration)
Filtration in which the fluid flows along the membrane surface, which limits clogging.
NTA
Nanoparticle tracking analysis. Finds size and number from the motion of particles.
Potency assay
A test of the biological activity of a product. One that reflects the mechanism of action is ideal.
CQA (critical quality attribute)
A property that must be controlled to assure product quality.
Natural EV / engineered EV
EVs used unmodified, and EVs given a function by genetic modification, drug loading and the like.
Act on the Safety of Regenerative Medicine
The Japanese law that sets the procedures and safety requirements for institutions providing regenerative medicine.

13. References

  1. Théry C et al. (ISEV) "Minimal information for studies of extracellular vesicles 2018 (MISEV2018)", J Extracell Vesicles 7:1535750 (2018) — doi.org
  2. Welsh JA et al. (ISEV) "Minimal information for studies of extracellular vesicles (MISEV2023): From basic to advanced approaches", J Extracell Vesicles 13:e12404 (2024) — doi.org
  3. Pharmaceuticals and Medical Devices Agency (PMDA) Science Board Report on therapeutic preparations using extracellular vesicles (EVs) including exosomes (in Japanese), 17 January 2023 (PDF) — pmda.go.jp
  4. Gardiner C et al. "Techniques used for the isolation and characterization of extracellular vesicles: results of a worldwide survey", J Extracell Vesicles 5:32945 (2016) — doi.org
  5. Takov K, Yellon DM, Davidson SM "Comparison of small extracellular vesicles isolated from plasma by ultracentrifugation or size-exclusion chromatography: yield, purity and functional potency", J Extracell Vesicles 8:1560809 (2019) — doi.org
  6. Visan KS et al. "Comparative analysis of tangential flow filtration and ultracentrifugation, both combined with subsequent size exclusion chromatography, for the isolation of small extracellular vesicles", J Extracell Vesicles 11:e12266 (2022) — doi.org
  7. Webber J, Clayton A "How pure are your vesicles?", J Extracell Vesicles 2:19861 (2013) — doi.org
  8. Gelibter S et al. "The impact of storage on extracellular vesicles: A systematic study", J Extracell Vesicles 11:e12162 (2022) — doi.org
  9. Lener T et al. (ISEV) "Applying extracellular vesicles based therapeutics in clinical trials - an ISEV position paper", J Extracell Vesicles 4:30087 (2015) — doi.org
  10. Witwer KW et al. "Defining mesenchymal stromal cell (MSC)-derived small extracellular vesicles for therapeutic applications", J Extracell Vesicles 8:1609206 (2019) — doi.org
  11. Alvarez-Erviti L et al. "Delivery of siRNA to the mouse brain by systemic injection of targeted exosomes", Nat Biotechnol 29:341 (2011) — doi.org
  12. Kamerkar S et al. "Exosomes facilitate therapeutic targeting of oncogenic KRAS in pancreatic cancer", Nature 546:498 (2017) — doi.org
  13. Escudier B et al. "Vaccination of metastatic melanoma patients with autologous dendritic cell (DC) derived-exosomes: results of the first phase I clinical trial", J Transl Med 3:10 (2005) — doi.org
  14. Besse B et al. "Dendritic cell-derived exosomes as maintenance immunotherapy after first line chemotherapy in NSCLC", Oncoimmunology 5:e1071008 (2016) — doi.org
  15. Lai RC et al. "Exosome secreted by MSC reduces myocardial ischemia/reperfusion injury", Stem Cell Res 4:214 (2010) — doi.org
  16. Phinney DG, Pittenger MF "Concise Review: MSC-Derived Exosomes for Cell-Free Therapy", Stem Cells 35:851 (2017) — doi.org
  17. US FDA (CBER) "Public Safety Notification on Exosome Products", 6 December 2019 — fda.gov
  18. US FDA "Public Safety Alert Due to Marketing of Unapproved Stem Cell and Exosome Products", December 2019 — fda.gov
  19. US FDA Warning letter to a company marketing an exosome product, dated 30 December 2024 — fda.gov
  20. US FDA "Approved Cellular and Gene Therapy Products" (updated 17 September 2026) — fda.gov
  21. Ministry of Health, Labour and Welfare (MHLW), Research and Development Policy Division, Health Policy Bureau Administrative notice, "On medical care using stem-cell culture supernatant and exosomes (notification)" (in Japanese), 31 July 2024 (PDF) — mhlw.go.jp
  22. Japanese Society for Regenerative Medicine (JSRM) (with the Japanese Society for Extracellular Vesicles) "Guidance on the Clinical Application of Extracellular Vesicles, etc. (1st edition)" (in Japanese), 30 April 2024 (PDF) — jsrm.jp
  23. Japanese Society for Regenerative Medicine (JSRM) "On the clinical application of iPS cell-derived exosomes (public alert)" (in Japanese), 27 December 2024 (PDF) — jsrm.jp
  24. MHLW Regenerative Medicine Evaluation Subcommittee 113th meeting, Document 1, "Comprehensive research for risk assessment and validity assessment of new technology areas related to regenerative medicine (interim report)" (in Japanese), 15 January 2026 (PDF) — mhlw.go.jp
  25. ClinicalTrials.gov "NCT05354141: Extracellular Vesicle Treatment for Acute Respiratory Distress Syndrome (ARDS) (EXTINGUISH ARDS)" — clinicaltrials.gov

14. Claim-to-source audit

Claim in the textBasisLabel
That exosomes are vesicles with a lipid bilayer and a kind of EV found in blood, saliva, urine, cerebrospinal fluid and culture medium; that EVs are divided by route of production and size into endosome-derived exosomes of about 100 nm, plasma membrane-derived microvesicles and apoptotic bodies derived from membranes of dying cells; that the definitions are loose and the route is hard to identify unless the moment of release is captured by live imaging; that EVs are complexes from tens of nm to several µm; and that sEVs are 200 nm or smallerReference 3 https://www.pmda.go.jp/files/000249829.pdfSourced
The PMDA report's split into natural and engineered EVs, with examples; that engineered EVs are used mainly for DDS and nano-sized EVs are reported to be less immunogenic and mutagenic than viral carriers; that no engineered EV has so far been put to practical use; and the example of the EGFR-targeting GE11 peptide on the membraneReference 3 https://www.pmda.go.jp/files/000249829.pdfSourced
The PMDA report's statements on manufacture (cell banks and virus testing; serum-derived EV carry-over when FBS is used; checkpoints; cell density and comparability; the difficulty of ultracentrifugation at commercial scale; concentration as pretreatment; PEG reagent residue; the limits of CD63 and CD9 in affinity purification; aggregates of the same size remaining in SEC; process-related impurities; artificial microparticles from labware; the question of the unit of dose; the difficulty of virus clearance; fixing measurement conditions; combining several markers; ISEV's three or more proteins)Reference 3 https://www.pmda.go.jp/files/000249829.pdfSourced
The statement that there is no best method of isolation and purification and that ultracentrifugation is hard to carry over unchanged into practical useReference 3 https://www.pmda.go.jp/files/000249829.pdfSourced
That ISEV recommends calling extracellular vesicles collectively EVs; that MISEV2018 says attributing a function to exosomes needs more than describing the function of a crude preparation, and that specific exosome activity is hard to support experimentally because knowledge of the molecular mechanisms is limitedReference 1 https://doi.org/10.1080/20013078.2018.1535750Sourced
That MISEV2023 says challenges remain in naming, separation from extracellular particles other than EVs, and characterizationReference 2 https://doi.org/10.1002/jev2.12404Sourced
In a worldwide survey, culture supernatant was the source material for 83%, ultracentrifugation was the separation method for 81%, and 59% combined several methodsReference 4 https://doi.org/10.3402/jev.v5.32945Sourced
In rat plasma, SEC gave higher particle count, protein mass, particle-to-protein ratio and EV marker signal than ultracentrifugation but also more APOB-positive lipoproteins and non-EV protein; ultracentrifugation gave lower yield but higher purity; the migration activity of vascular endothelial cells varied with the separation method and was not explained by EV amount aloneReference 5 https://doi.org/10.1080/20013078.2018.1560809Sourced
A report that TFF combined with SEC gave higher yield than ultracentrifugation combined with SEC and was better in reproducibility, time, cost and scale (cancer cell lines, serum-containing medium); the authors' view that ultracentrifugation cannot combine high yield with separation free of non-EV materialReference 6 https://doi.org/10.1002/jev2.12266Sourced
The proposal to judge purity by the ratio of particle count to protein mass (above 3×10¹⁰ particles/µg is high purity, 2×10⁹ to 2×10¹⁰ low purity, below 1.5×10⁹ impure); that simple precipitation and washing gave about 1×10¹⁰; that NanoSight and the BCA assay were usedReference 7 https://doi.org/10.3402/jev.v2i0.19861Sourced
That on storage at -80 °C EV concentration and purity fell over time, particle size and its spread rose and zeta potential changed; that freeze-thaw reduced particle count from the first cycle and raised particle size with the number of cycles; the observation of double-positive particles suggesting vesicle fusion; and that no storage condition examined prevented thisReference 8 https://doi.org/10.1002/jev2.12162Sourced
That ISEV and an EU researcher network say classification as active ingredient or mainly delivery carrier is important because it determines requirements for manufacture, quality control and clinical useReference 9 https://doi.org/10.3402/jev.v4.30087Sourced
The proposal to define MSC-derived small EVs by quantifiable indicators such as identification of origin, the presence of lipid-membrane vesicles and physical and biochemical integrity, and to compare them with a well-characterised biological reference materialReference 10 https://doi.org/10.1080/20013078.2019.1609206Sourced
That siRNA was loaded by electroporation into EVs from the animals' own dendritic cells expressing the RVG peptide fused to Lamp2b; that after intravenous injection into mice, gene silencing occurred in neurons, microglia and oligodendrocytes in the brain with no nonspecific uptake in other tissues; and the 60% (mRNA) and 62% (protein) reductions of BACE1Reference 11 https://doi.org/10.1038/nbt.1807Sourced
That EVs from fibroblast-like mesenchymal cells (iExosomes) loaded with siRNA / shRNA against KrasG12D were retained in circulation longer than liposomes through protection from phagocytosis by CD47, and suppressed cancer and extended overall survival in several mouse models of pancreatic cancerReference 12 https://doi.org/10.1038/nature22341Sourced
In the phase I trial of dendritic cell-derived exosomes (15 melanoma patients), large-scale manufacture was shown feasible and safe, with no toxicity of grade II or above and the maximum tolerated dose not reached; that the dose was set by the number of MHC class II molecules (0.13 or 0.40×10¹⁴)Reference 13 https://doi.org/10.1186/1479-5876-3-10Sourced
In the phase II trial of interferon-gamma dendritic cell-derived exosomes (22 non-small cell lung cancer patients), the primary endpoint was not met and NK cell function rose in some patientsReference 14 https://doi.org/10.1080/2162402x.2015.1071008Sourced
That vesicles (exosomes) purified from the culture supernatant of human embryonic stem cell-derived MSCs reduced infarct size in mouse myocardial ischemia and reperfusion injuryReference 15 https://doi.org/10.1016/j.scr.2009.12.003Sourced
That the contents of MSC-derived exosomes change with the tissue of origin of the MSCs, their activity and the surrounding cells; that control of quality, reproducibility and potency is regarded as important for cell-free therapyReference 16 https://doi.org/10.1002/stem.2575Sourced
That on 6 December 2019 the FDA noted several serious adverse events in Nebraska patients from unapproved exosome products; that the FDA has approved no exosome product; that exosomes used to treat humans are regulated as drugs and biological products and need approval; and that it advises checking the IND numberReference 17 https://www.fda.gov/vaccines-blood-biologics/safety-availability-biologics/public-safety-notification-exosome-products Reference 18 https://www.fda.gov/safety/medical-product-safety-information/public-safety-alert-due-marketing-unapproved-stem-cell-and-exosome-productsSourced
That the FDA warning letter dated 30 December 2024 describes the exosome product as an unapproved new drug and an unlicensed biological product, and not eligible for regulation under section 361 aloneReference 19 https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/warning-letters/evolutionary-biologics-inc-681586-12302024Sourced
That the FDA's list of approved cellular and gene therapy products (updated 17 September 2026) does not name any exosome or EV productThe result of this article checking the product-name list; a check by name only, which did not look into the breakdown of active ingredients Reference 20 https://www.fda.gov/vaccines-blood-biologics/cellular-gene-therapy-products/approved-cellular-and-gene-therapy-productsSourced
That in an administrative notice dated 31 July 2024 the MHLW said that no approved drug using the exosomes in question has been shown effective and safe and marketed, that particular attention to safety is needed under the responsibility of the physician or dentist, and that it asked institutions to refer to the society's guidanceReference 21 https://www.mhlw.go.jp/content/10800000/001282062.pdfSourced
That the Japanese Society for Regenerative Medicine guidance lists as general safety risks of EV preparations transmission of infection, unwanted immune reactions, contamination with impurities, unintended changes in EV properties, unwanted biodistribution, toxicity to vital organs, the germ line and development, tumours or unwanted tissue, and failure to achieve the expected efficacy; and that particle count and protein mass are the indicators most often used for EV quantity and should ideally correlateReference 22 https://www.jsrm.jp/cms/uploads/2024/05/news14993-2.pdfSourced
That on 27 December 2024 the Japanese Society for Regenerative Medicine warned that self-pay clinics increasingly offer expensive exosome treatments from iPS cell culture supernatant while clinical evidence is not adequately established, and that no specific research presentation or sharing of clinical trial results was seen at that year's annual meetingReference 23 https://jsrm.jp/cms/uploads/2024/12/iPS_exosome_20241227.pdfSourced
That in the MHLW Regenerative Medicine Evaluation Subcommittee material (15 January 2026) the research group said EVs and culture supernatant should be covered by the Act on the Safety of Regenerative Medicine; that the critical quality attributes, mechanism of action and disease-specific potency assays of EVs are not established, making quality specifications and a control strategy difficult; that CQAs will not be fixed unless analytics leads; the expert view that EVs are currently outside that Act; and that the PMDA published its EV therapeutics report in 2023 and the Japanese Society for Regenerative Medicine published its thinking in 2021 and its guidance in April 2024Reference 24 https://www.mhlw.go.jp/content/11201250/001632480.pdfSourced
That the phase 3 trial NCT05354141 of bone-marrow MSC-derived EVs (ExoFlo) in hospitalised ARDS patients began in July 2022, is randomised, double-blind and placebo-controlled, plans to enrol 970, and was recruiting at the record's last update on 23 February 2026Reference 25 https://clinicaltrials.gov/study/NCT05354141Sourced
The volume of a 100 nm sphere (5.24×10⁻²² m³), the volume of 10¹⁰ particles (about 5.2 nL), mass (about 5.8 µg at 1.1 g/cm³), accompanying protein of 0.33 µg, 5.0 µg and 6.7 µg, and the roughly 20-fold differenceOur calculation. The 100 nm particle diameter, 1.1 g/cm³ density and 10¹⁰ particles are this article's assumptions. The ratio values are those proposed by Webber et al. (Reference 7). It is for grasping orders of magnitude and does not claim that particle count, mass and protein mass can be simply convertedOur calculation
The official documents of the EU regulator (EMA), regulation in countries other than the United States and Japan, the composition of individual EV products, whether any engineered EV has reached practical use as a drug, the content and timing of amendments to the Act on the Safety of Regenerative Medicine, and the results of the ExoFlo phase 3 trialNo primary source could be confirmed within the scope of this article, so these are not covered or are treated as not yet confirmedNot yet confirmed
The materials-side reading of purification methods (leachables and cleanliness of carriers, membranes, containers and reagents); the grouping of four yardsticks for measuring EVs; the contrast between LNPs and EVs (designed versus top-down); the grouping of natural and engineered EVs into three routes; the arrangement of manufacture into five stages; the selection of items in the regulatory timeline; the policy of using EV and exosome interchangeablyThis article's own arrangement and commentary based on published content; not views expressed by any author or institutionCommentary
That Figs. 1, 2, 3, 5 and 6 are drawings made for explanation (Fig. 4 includes our calculation), and that the hero image is AI-generatedA note from this articleCommentary

Last updated 1 October 2026. Sources are limited to primary material (documents from regulators and advisory councils, the PMDA report, academic-society guidance, peer-reviewed papers and clinical trial registrations). Market-size and share estimates are not used. Because the article includes structural readings and materials and analytical interpretations, those are marked as Commentary and kept separate from sourced fact. The official position of the EU (EMA), regulation outside the United States and Japan, the content and timing of amendments to Japanese law, the composition of individual EV products, whether any engineered EV has reached practical use as a drug, and the results of the ExoFlo phase 3 trial could not be confirmed in published primary sources, so they are not covered or are treated as not yet confirmed. All figures are for explanation. Figs. 1, 2, 3, 5 and 6 are conceptual diagrams (vector drawings), Fig. 4 is a drawing that includes our calculation (vector drawing), and the hero image is AI-generated; none of them shows a real vesicle, micrograph or physical product. This article explains technology and is neither medical advice nor a recommendation of any particular product or treatment.

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