This article in 30 seconds
- Conditioned medium is not “a liquid made of exosomes.” It is the whole liquid that remains after the cells are removed; exosomes are only one part of what it contains.
- No pharmaceutical product has regulatory approval — in Japan or in any other country. What a supplier can show is not efficacy, but measured quality.
- Origin alone (adipose, deciduous tooth pulp, umbilical cord) does not determine quality. Nine factors are known to drive quality variability, and origin is only one of them.
1. What is conditioned medium? — Not “a liquid made of exosomes”
To state the conclusion first: stem cell conditioned medium is the whole liquid that remains after stem cells have been cultured and the cells themselves have been removed. It is known as conditioned medium (CM); when derived from mesenchymal stem cells (stem cells that can differentiate into bone, fat, and other tissues), it is written MSC-CM.
A cooking analogy: it is much like the broth left after the kombu kelp has been lifted out of the pot. The kelp — the cells — is no longer in the liquid, but the components it released are dissolved throughout it.
Its contents fall into two broad categories.
- Soluble factors — proteins, nucleic acids, lipids, and other components that act in dissolved form.
- Extracellular vesicles — tiny membrane-enclosed sacs released by cells (a collective term that includes exosomes). Think of them as small capsules that wrap components in a membrane.
The key point
“Conditioned medium” and “exosomes” are not synonymous. The medium is the whole liquid, which may contain vesicles; it is not the vesicles themselves. This distinction is the starting point for reading any product literature.
How conditioned medium, secretome, and exosomes nest inside one another is mapped out in the figure in What Is a Secretome.
2. How is it positioned in Japan? — No approved pharmaceutical product exists
There are two points here. No pharmaceutical product has regulatory approval, and most of the settings in which these preparations are used sit outside the review process of the Act on the Safety of Regenerative Medicine. Misunderstand this, and the meaning of the specifications gets misread with it.
No pharmaceutical product has regulatory approval
In an administrative notice dated July 31, 2024, the Ministry of Health, Labour and Welfare (MHLW) states the following[1].
At present, there are no pharmaceutical products — in Japan or in any other country — in which the exosomes or related materials used have been shown to be effective and safe, and which are manufactured and marketed under regulatory approval.
From the administrative notice of the Research and Development Policy Division, Health Policy Bureau, MHLW (July 31, 2024)Note the wording: not merely “none in Japan,” but none “in any other country” either. Any product literature that claims efficacy is therefore, by itself, a reason to question its content. What a supplier can show is not efficacy, but measured quality.
It falls outside the Act on the Safety of Regenerative Medicine
Medical procedures using extracellular vesicles or conditioned medium prepared under the direction of a physician or dentist and administered to that clinic’s own patients fall outside the scope of the current Act on the Safety of Regenerative Medicine[2]. They are not reviewed by a certified committee for regenerative medicine.
This is not a matter of regulation being lax — it means there is no third party doing the review. It is like a delivery with no inspector at the receiving dock: the job of opening the box and checking falls to whoever receives it. The guidance from the Japanese Society for Regenerative Medicine states explicitly that the physician or dentist providing the treatment bears the responsibility for understanding its quality and risks.
The key point
No approved pharmaceutical product, and no third-party review. In other words, the responsibility for verifying quality rests with whoever reads the literature. The checks made at the stage of selecting raw materials are, in effect, the last line of defense.
Supplementary provisions to the amended Act promulgated in June 2024 call for medical technologies using cell secretions and similar materials to be reviewed within roughly two years of the Act’s entry into force. The regulatory framework is still in motion.
3. How to read the specifications — the domestic guidance as your yardstick
A specification sheet is not read by hunting for the biggest numbers; it is read by checking what was measured against the guidance. In April 2024, the Japanese Society for Regenerative Medicine, in cooperation with the Japanese Society for Extracellular Vesicles, published the Guidance on the Clinical Application of Extracellular Vesicles and Related Products, 1st Edition[2]. It sets out what the specification of a preparation should demonstrate.
The guidance asks for two proofs
The conclusion is simple: both “particles are present” and “markers are present.” The items listed as generally set as specifications are these two:
- That particles with the shape and size of extracellular vesicles are present
- That marker molecules of extracellular vesicles are present
The marker molecules cited include the tetraspanins (CD9, CD63, CD81, and others) and late-endosome-associated factors (Tsg101, Alix, and others). The international position paper calls for semi-quantitative analysis of at least three such proteins.
In other words, “we saw particles” is not enough on its own, and neither is “markers were present.” Both are required.
Read particle counts and protein content against each other
The guidance notes that particle count and protein content are the measures most often used for dosing, and adds that “a correlation between the two is desirable.”
It is possible to make either number look large on its own. When the two diverge, that is a cue to suspect one of two things: something other than particles is being counted, or much of the protein is not from vesicles.
The key point
The first thing to look for in a specification sheet is whether particle count and protein content are shown together, and whether the two are consistent with each other. Literature that prints only one of the numbers in large type has no more information to offer.
Protein concentration is not “the amount of active ingredient”
Total protein is, so to speak, a weight taken with the pot included. It includes components derived from the culture medium, so it is not a measure of what the cells actually secreted. In concentrated samples, moreover, interfering substances have been reported to inflate the measured values.
The reading “higher protein concentration = more active ingredient” does not hold.
Endotoxin can only be judged together with the dose
The acceptable level of endotoxin (a fever-inducing substance derived from bacteria) is not a fixed absolute value. As with a drug dose, it is calculated back from the amount administered. For parenteral preparations, 5.0 EU per kilogram of body weight per hour is taken as the pyrogenic threshold, and the limit is obtained by dividing that figure by the maximum amount that could be administered in one hour.
A label reading “0.1 EU/mL or less” is therefore not, by itself, a basis for judging safety. It only becomes meaningful together with how much will be used, and on what assumptions.
What sterility testing, mycoplasma testing, and endotoxin testing each detect — and fail to detect — is covered in Safety Testing of Conditioned Medium.
What the guidance says about raw materials — is serum being used?
The guidance states that xeno-free culture media, free of animal-derived components, should be used. When fetal bovine serum is used, it warns, extracellular vesicles derived from the bovine serum can contaminate the product and express unexpected biological activity.
The substances of concern are listed specifically: albumin, fibrinogen, fibronectin, apolipoprotein B, macroglobulin, hemoglobin, coagulation factors, and others.
4. How to think about differences between origins (adipose, deciduous tooth pulp, umbilical cord)
The conclusion first: cell-biological differences have been reported, but no study has compared their effects in humans. Because this question comes up often, the reported facts are listed as they stand.
| Aspect | Reported findings |
|---|---|
| Composition of secreted factors | A study comparing umbilical cord- and dental pulp-derived conditioned media under identical conditions reported HGF higher in the umbilical cord-derived medium and VEGF-A higher in the dental pulp-derived medium[3] |
| Gene expression trends | Dental pulp-derived cells have been reported to show relatively higher expression of neurotrophic factor genes, and adipose-derived cells of angiogenesis-related genes. These, however, are differences at the level of gene expression, not differences in clinical effect[4] |
| Donor-to-donor variability | In an analysis of umbilical cord tissue from 71 donors, cells were obtained from every donor, with consistent growth rates and surface antigen criteria. Being neonatal in origin, the tissue is unaffected by donor age, which is a concern with adult tissues[5] |
| Donor age | A systematic review holds that aging advances cellular senescence, while another report found no difference in proliferative capacity or osteochondral differentiation capacity across donors aged 30–60 in serum-free medium. Culture conditions confound the picture, so it cannot be simplified |
This article does not assign uses to particular origins. The evidence consists mainly of in vitro gene expression and cytokine quantification; no study has compared their effects in humans. Article 68 of the Pharmaceuticals and Medical Devices Act prohibits anyone from suggesting the efficacy or effects of an unapproved product.
5. Nine factors determine quality — origin is one of them
A review article identifies nine factors that introduce variability into secretome quality[6]. Origin is only one of the nine.
- Source tissue
- Donor characteristics (age, sex, metabolic state, disease)
- Passage number (how many times the cells have been subcultured)
- Medium composition and use of serum
- Cell density and the collection period for secreted components
- Culture environment (3D culture, hypoxia, mechanical stimulation)
- Purification method
- Manufacturing scale and equipment
- Storage and transport conditions
If coffee is the analogy, origin is the growing region of the beans. Just as beans from the same region make a different cup depending on the roast and the brew, the same origin yields a different product when the medium and the process differ. Before comparing origins, looking at production methods and specifications is the more substantive move.
How production methods affect residual components is covered in Conditioned Medium vs. Secretome, and the questions to put to a supplier in Six Points to Confirm with Your Supplier.
Frequently Asked Questions
Are conditioned medium and exosomes the same thing?
No. Conditioned medium is the whole liquid that remains after cells have been cultured and then removed. Its contents fall into two broad categories: soluble factors dissolved in the liquid, and extracellular vesicles (membrane-bound sacs that include exosomes). Exosomes are one component contained in conditioned medium, not the medium itself.
Is conditioned medium subject to the Act on the Safety of Regenerative Medicine?
When prepared under the direction of a physician or dentist and used for that clinic’s own patients, it falls outside the scope of the current Act. No review by a certified committee for regenerative medicine takes place. For that reason, the guidance from the Japanese Society for Regenerative Medicine states explicitly that the physician or dentist providing the treatment bears the responsibility for understanding its quality and risks. Supplementary provisions to the amended Act promulgated in June 2024 call for this area to be reviewed within roughly two years of its entry into force.
Which origin should I choose?
At present there is no evidence that would support assigning different origins to different uses. What has been reported are differences in secreted factor composition and gene expression trends in vitro; no study has compared their effects in humans. Nine factors are known to introduce quality variability, and origin is only one of them. Checking the medium design, manufacturing process, and test items first makes for a more substantive comparison.
References
- [1] Research and Development Policy Division, Health Policy Bureau, Ministry of Health, Labour and Welfare. Administrative notice “On Medical Care Using Stem Cell Conditioned Medium, Exosomes, and Related Products (Notification)”, July 31, 2024
- [2] Japanese Society for Regenerative Medicine (in cooperation with the Japanese Society for Extracellular Vesicles). “Guidance on the Clinical Application of Extracellular Vesicles and Related Products, 1st Edition”, April 30, 2024
- [3] Caseiro AR, et al. Mesenchymal Stem/Stromal Cells metabolomic and bioactive factors profiles: A comparative analysis on the umbilical cord and dental pulp derived Stem/Stromal Cells secretome. PLoS One. 2019;14(11):e0221378.
- [4] Terunuma A, et al. Comparative transcriptomic analysis of human mesenchymal stem cells derived from dental pulp and adipose tissue. J Stem Cells Regen Med.
- [5] Raileanu VN, et al. Banking Mesenchymal Stromal Cells from Umbilical Cord Tissue: Large Sample Size Analysis Reveals Consistency Between Donors.
- [6] Trigo CM, et al. Towards the Standardization of Mesenchymal Stem Cell Secretome-Derived Product Manufacturing for Tissue Regeneration. Int J Mol Sci. 2023.
This article explains terminology, regulatory positioning, and how to read quality specifications. Our stem cell secretome is supplied as a research-use reagent (a classification restricted to research purposes; not a pharmaceutical product) and is not intended to demonstrate efficacy against any specific disease.
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