This article in 30 seconds
- An exosome preparation is an isolated part. It contains only the membrane sacs separated out of conditioned medium (the secretome); the components dissolved in the liquid (the soluble factors) are not carried over.
- The part did not behave like the whole. In both peer-reviewed studies that compared the three fractions under identical conditions, the vesicle-only fraction (the part separated out of the whole) did not produce the same cellular changes as the whole it was taken from.
- Both studies are in vitro, however. They demonstrate neither superiority in humans nor the efficacy of our products; the article spells out how far the results may reasonably be read.
1. An exosome preparation: the “solids” scooped out of the soup
In short, what is being compared is the whole and two parts separated out of it. Hold on to that relationship, and the design of both studies becomes much easier to read.
The secretome (the totality of components cells secrete during culture) contains both soluble factors secreted by the cells — cytokines, growth factors, and the like — and membrane vesicles (extracellular vesicles, including exosomes). In cooking terms, the secretome is a soup with both the solid ingredients and the broth. An exosome preparation corresponds to the solids (the membrane vesicles) lifted out with a strainer — and the broth dissolved in the soup does not come up with them.
The studies frame this relationship as three fractions to be compared.
The key point
“Exosome” and “secretome (conditioned medium)” are not interchangeable names for the same liquid — they stand in a part-to-whole relationship. Choosing between the two product formats is therefore also a choice about whether to keep the soluble factors dissolved in the liquid. For the definition and structure of exosomes themselves, see our complete guide to exosomes (in Japanese).
2. Study 1: in inflamed tendon cells, the whole worked most strongly
The first study’s conclusion is clear-cut. Of the three fractions, the one that shifted the cells’ gene expression the most was the whole.
The study was published in 2023 by a group at the University of Veterinary Medicine Vienna[1]. Equine bone-marrow-derived mesenchymal stem cells were cultured under serum-free conditions for 48 hours, and the collected conditioned medium was separated by size-exclusion chromatography (a method that sorts components by size). This yielded three preparations: the complete conditioned medium (CM), the extracellular vesicle fraction (EVs), and the soluble protein fraction (PF).
Each was applied to equine tenocytes in which inflammation had been induced with TNF-α and IL-1β, and the resulting changes in gene expression were compared. The result: the whole medium produced the largest shift in gene expression away from the inflamed controls. Neither the exosome fraction alone nor the soluble protein fraction alone matched it.
This conclusion is written into the paper’s very title.
“Mesenchymal Stem Cell Conditioned Medium Modulates Inflammation in Tenocytes: Complete Conditioned Medium Has Superior Therapeutic Efficacy than Its Extracellular Vesicle Fraction”
In plain terms: the unfractionated medium outperformed the vesicle-only fraction taken from it.
From the title of Soukup R, et al. Int J Mol Sci. 2023;24(13):10857 (a title based on in vitro experiments)3. Study 2: in immune cells, the remaining liquid outworked the isolated sacs
In the second study the ranking flips. What performed roughly on par with the whole was the remaining liquid — the fraction with the exosomes removed.
The second study was published in 2022[2] — this time using human cells. From human amniotic mesenchymal stromal cells (largely synonymous with mesenchymal stem cells), the researchers prepared the whole preparation, the exosome fraction, and the exosome-depleted fraction, applied each to human peripheral blood mononuclear cells, and compared their immunomodulatory activity.
The result: the exosome-depleted fraction showed immunomodulatory activity roughly equivalent to the whole. The exosome fraction, by contrast, showed almost no activity on the measured endpoints — even though it was confirmed to have been taken up by the cells. The point worth noting is that the vesicles did not fail to arrive; they arrived, and the measured endpoints still did not move.
| Item | Study 1 (2023) | Study 2 (2022) |
|---|---|---|
| Cell source | Equine bone-marrow-derived mesenchymal stem cells | Human amniotic mesenchymal stromal cells |
| Target cells | Equine tenocytes (inflammation induced) | Human peripheral blood mononuclear cells |
| Endpoint measured | Changes in gene expression | Immunomodulatory activity |
| Most active fraction | Whole preparation | Exosome-depleted fraction (roughly equal to the whole) |
| Exosome fraction alone | Fell short of the whole | Almost no measurable change |
| Study format | In vitro | In vitro |
4. What the two studies share — the part was no substitute for the whole
The bottom line is this. Two systems that differ in species, target cells, and endpoints produced results pointing the same way: the vesicle-only fraction did not cause the same changes as the whole.
A fraction containing only membrane vesicles (the tiny membrane-bound sacs cells release) did not reproduce the changes the whole produced — that is the finding common to both papers. One study alone could be chance; what gives the result weight is that two different systems point in the same direction.
At the same time, the two studies are not saying the same thing. In Study 1 the whole was the most active, and the soluble fraction alone also fell short of it. In Study 2 the soluble fraction alone was roughly equal to the whole. The reasonable reading is that the relative contributions of soluble factors (components that act in dissolved form) and membrane vesicles vary from system to system.
The key point
Back to the soup: Study 1 found that the full soup — solids and broth together — worked the hardest, while Study 2 found that the broth alone was roughly as good as the soup. The rankings differ, but the direction is shared: the solids alone were no substitute for the soup.
What the studies share is the finding that the exosome fraction alone did not match the whole — not that the soluble factors account for everything. In Study 1, the soluble fraction alone also fell short of the whole preparation.
5. How to weigh these results — four limits to keep in mind
A caution up front: these two papers are not grounds for declaring that the secretome is superior. Check how far the results may be read against the following four points.
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Both are in vitro studies
The fractions were applied directly to cultured cells; the results do not describe administration to humans. Neither paper contains data on superiority in humans.
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Study 1 used equine cells
Its findings cannot be carried over to humans as they stand. The defensible reading stops at “a common trend appeared across different species.”
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Neither study tested our products
Both used fractions the research groups prepared themselves. Differences in production method and concentration between individual products are not reflected in these results.
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They do not show that exosomes are inactive
Study 2 confirmed that the exosome fraction was taken up by the cells. The accurate statement is that the measured endpoints changed little. Different endpoints or different target cells could yield different results.
With that said, one point stands for anyone selecting a raw material. A process that isolates only the membrane vesicles is also a process that discards the soluble factors. Decide first what you want to keep; the choice of product format follows from that.
How the three terms relate — and the conditions we require before calling a product a secretome — is covered in What Is a Secretome?; how residual components differ by production method is covered in Stem Cell Conditioned Medium vs. Secretome. For how to read the particle counts on exosome products, see How to Read Exosome “Counts”.
Frequently Asked Questions
Which is superior — an exosome preparation or the secretome?
At present, no conclusion can be drawn about which is superior. The two studies introduced here applied the fractions to cells in vitro; neither compared the two by administration to humans. What the research shows goes no further than this: the fraction containing only the membrane vesicles did not produce the same changes as the whole or the soluble fraction.
Does this mean exosomes have no effect?
No. In Study 2, the exosome fraction was confirmed to have been taken up by the cells. The finding is that, after uptake, the measured immunomodulatory endpoints showed no large change. Different endpoints or different target cells could yield different results.
Can a study in equine cells be read as applying to humans?
Not directly. Study 1 is an in vitro experiment using equine mesenchymal stem cells (stem cells that can differentiate into bone, fat, and other tissues) and equine tenocytes. Study 2 used human amnion-derived cells and human peripheral blood mononuclear cells, but it too is an in vitro experiment. The sound reading is that what matters is the common trend seen across different species and different cell types.
References
- [1] Soukup R, Gerner I, Mohr T, Gueltekin S, Grillari J, Jenner F. Mesenchymal Stem Cell Conditioned Medium Modulates Inflammation in Tenocytes: Complete Conditioned Medium Has Superior Therapeutic Efficacy than Its Extracellular Vesicle Fraction. Int J Mol Sci. 2023;24(13):10857. doi:10.3390/ijms241310857
- [2] Papait A, Ragni E, Cargnoni A, et al. Comparison of EV-free fraction, EVs, and total secretome of amniotic mesenchymal stromal cells for their immunomodulatory potential: a translational perspective. Front Immunol. 2022;13:960909. doi:10.3389/fimmu.2022.960909
The quotation is excerpted from the paper’s title; the plain-language restatement is ours.
This article summarizes published research. Our stem cell secretome is supplied for research use only and is not intended to demonstrate efficacy against any specific disease. The studies discussed here did not test our products.
View Stem Cell Secretome specifications What Is a Secretome?