This article in 30 seconds
- “Secretome” has no official definition. Its meaning varies from supplier to supplier, so buyers need to verify products against a yardstick of their own.
- The three terms nest like matryoshka dolls. The outermost layer is stem cell conditioned medium; inside it sits the secretome — only what the cells secreted — and exosomes are one component nested further inside.
- A definition is verified in a test report, not declared. We impose six conditions — secreted components only, no bovine serum, and more — and disclose the results in a test report for each production lot.
1. The conclusion first — the three terms are “nested”
“Stem cell conditioned medium.” “Secretome.” “Exosome.” These three are not parallel alternatives: they nest inside one another like matryoshka dolls. Start by fixing this arrangement in mind with a single diagram.
The outermost layer, stem cell conditioned medium, refers to everything contained in the liquid after stem cells have been cultured. Alongside the components the cells secreted, it may also contain medium-derived components, animal-derived components such as bovine serum, factors added to support the culture, and cell debris or ammonia generated during culture.
Inside it sits the secretome: the fraction composed only of the components the cells secreted. “Conditioned medium or secretome” is therefore not a comparison of two different things but a question of where the line is drawn — how much of the outer frame goes into the product.
Innermost of all, exosomes are one type of membrane vesicle (extracellular vesicle) contained in the secretome (covered in What Is an Exosome). They are not something that stands alongside the secretome. An exosome preparation is made by isolating only the membrane vesicles from the secretome, and the isolation process loses the soluble factors such as cytokines (proteins that mediate signaling between cells) and growth factors (see What Is Lost When Only the Exosomes Are Isolated).
The key point
The either–or question “exosomes or secretome?” is like asking “the smallest doll, or the whole matryoshka set?” — it does not work as a comparison. What is worth asking is not which is superior, but a difference in design: isolate only the membrane vesicles, or keep the full body of secreted components.
2. “Secretome” has no official definition
This is the starting point. The word “secretome” has no official definition and no industry standard. It is not a category under the Pharmaceuticals and Medical Devices Act, nor a standard set by any academic society.
That is why suppliers’ explanations diverge. Some use the word almost interchangeably with conditioned medium; others use it to indicate a degree of concentration; and none of them can be called wrong. It is like arguing over lengths without a shared ruler — set the words side by side and the discussion still never meshes.
Buyers, therefore, have no choice but to bring their own yardstick. What follows is the definition we impose on our own products. It is not an industry-wide standard, but it does indicate what is worth confirming.
3. The six conditions we require before calling it a “secretome”
Here is the conclusion up front: we use the word “secretome” only for products that meet all six of the following conditions. The numbers are identifiers only; they do not indicate order or priority.
- 1
Composed only of components secreted by cells or tissue
- 2
No cytokines or growth factors remain in the collection medium
- 3
Contains proteins, peptides, nucleic acids, and membrane vesicles such as exosomes
- 4
Free of impurities such as ammonia, harmful substances including heavy metals, and dead cells
- 5
No bovine serum is used
- 6
The composition is verified (protein quantification, measurement of major cytokines, exosome analysis, and more)
The key point
In practice, conditions 2 and 5 do the most work. If the water already contained seasoning before the stock was made, tasting the finished soup cannot tell you which flavors came from the ingredients and which were added afterward. In the same way, if growth factors remain in the collection medium, the numbers on the compositional data sheet can no longer distinguish “the amount the cells secreted” from “the amount that was in the medium to begin with.”
Why these six? Three groups of different character
The six conditions sort into three groups of different character: what to keep out, what to keep in, and whether it can be verified.
Conditions 1, 2, and 5 define what must be kept out. They restrict the origin of every component in the product to what the cells secreted. This cannot be ensured by post-collection processing; it is decided by the design of the medium and the culture process.
Condition 3 defines what must be kept in. Pursue impurity reduction alone and the target components are lost as well. What is required is both at once: retain the full range of secreted components, membrane vesicles included, while excluding what does not belong.
Conditions 4 and 6 define what must be verifiable. However carefully conditions 1 through 3 are engineered, buyers cannot confirm them unless they are measured and shown. Our conditions therefore extend to being able to present the results in writing, as a test report.
For how to confirm each of the six with your supplier, see Six Items to Confirm with Your Supplier.
4. How it is made — not “remove it later” but “never let it in”
The short answer: whether the six conditions can be met is decided not by post-collection purification technology but by designing the medium and the culture process so that unwanted components are never introduced in the first place. Rather than filtering murky water until it runs clear, it is more reliable to start with clean water — that is the thinking.
Manufacturing approaches fall broadly into three: conditioned medium with no processing at all, conditioned medium with post-collection removal of unwanted components, and designs that never introduce them. The middle approach — removal afterward — runs into the limitation that complete removal is difficult.
For how residual components differ across the three approaches, see the diagrams in Stem Cell Conditioned Medium vs. Secretome.
Medium design
We develop our media from scratch to be free of animal-derived raw materials, serum-free, and protein-free (no proteins added to the medium). The collection medium contains no medium-derived proteins. Conditions 2 and 5 are met by this medium design itself.
Manufacturing environment
Production takes place in a Class 100 biosafety cabinet housed inside a Class 10,000 clean booth, operated in line with the environmental standards recommended for the manufacture of regenerative medicine products.
Personnel
Every member of the manufacturing staff holds a doctorate in medicine or pharmaceutical sciences. Development and production are handled by people with more than ten years of research experience at national universities and other research institutions.
5. How it is verified — quality standards you can check in a test report
However thoroughly a definition and a process are explained, explanation alone is not verification. What settles the matter is condition 6 — verified composition: whether measured results can be presented in writing. The tests we perform are as follows.
| Category | Test items |
|---|---|
| Product testing | Sterility testing / mycoplasma testing / endotoxin testing |
| Raw material (donor) screening | Human immunodeficiency virus (types 1 and 2) / hepatitis B virus / hepatitis C virus / syphilis / human T-lymphotropic virus (types 1 and 2) / human transmissible spongiform encephalopathy |
| Compositional analysis | Protein quantification / measurement of major cytokines (EGF, VEGF, TGF-α/β, IGF, etc.) / analysis of miRNA contained in exosomes |
| Other | Issuance of material safety data sheets (MSDS) / patch testing |
Performed in accordance with the manufacturing regulations for biological raw materials. Test results can be confirmed in the Certificate of Analysis (COA) issued for each lot.
The key point
In compositional analysis we do more than measure the target components: we also confirm that the pro-inflammatory cytokines IL-6 and TNF-α, which can trigger inflammation, are below the limit of quantification. What is absent matters as much as what is present.
6. Dosage forms and storage — owning a freezer changes the choice
Two dosage forms are available — freeze-dried and liquid-frozen — and they require different storage equipment. The freeze-dried form stores at room temperature, protected from light (up to 40°C), so facilities without a freezer can adopt it. The liquid-frozen form requires frozen storage at −20°C or below.
Storage conditions and inventory management are covered in detail in Room-Temperature Handling with Freeze-Drying.
What is not yet known — measured and understood are different things
Everything above concerns definitions, manufacturing, and measurable items. What can be measured and what is understood are two different things. When comparing products, please also keep the following three points in mind.
- A list of components is not an explanation of effects. Cytokine quantification shows what is present and in what amount — not how it acts.
- Lot-to-lot variation never reaches zero. Because the raw material is of biological origin, a perfectly identical composition cannot be reproduced. That is precisely why we measure every lot and attach a report.
- The word “secretome” itself has not yet settled. The six conditions in this article are our own definition, not an industry consensus. A different framework may well be the standard a few years from now.
When choosing a supplier, the most reliable signal is not confident assertion but whether they can say clearly where measured fact ends and inference begins.
Frequently Asked Questions
Are “secretome” and “stem cell conditioned medium” just two names for the same thing?
No. Stem cell conditioned medium refers to everything contained in the liquid after culture. Alongside the components the cells secreted, it may contain medium-derived components, animal-derived components, factors added for culture, and cell debris. A secretome consists only of the components the cells secreted. That said, because the term has no official definition, some use it in a broader sense.
Should I choose an exosome preparation or a secretome?
The two are not parallel alternatives. Exosomes are one component contained in the secretome, and an exosome preparation is what remains after isolating only the membrane vesicles from the secretome. The isolation process loses soluble factors (components that act while dissolved in the liquid) such as cytokines and growth factors. The choice depends on what you want to keep.
Is there an industry-wide standard for “secretome”?
No. There is neither an official definition nor an industry standard, which is why explanations differ from supplier to supplier. The six conditions presented in this article are the definition we apply to our own products. Use them as a yardstick for comparison.
This article explains terminology, manufacturing methods, and quality control. Our Stem Cell Secretome is supplied for research use only and is not intended to demonstrate efficacy against any specific disease.
View Stem Cell Secretome specifications Request Certificates of Analysis and compositional data