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When comparing stem cell clinics, patients often see enormous numbers advertised:
50 million cells.
100 million cells.
Sometimes hundreds of millions.
It is natural to assume that more cells must mean a better treatment.
But where did all of those cells come from?
To produce very large numbers of mesenchymal stromal cells, or MSCs, cells may be grown and repeatedly expanded in a laboratory. Each time a population is transferred and divided into new culture vessels, it goes through what researchers call a passage.
Expansion is a normal and important part of cell manufacturing.
But cells are biological systems, not photocopies.
Research has shown that repeated culture expansion can change characteristics such as cell growth, gene expression, differentiation potential, telomere length, and cellular senescence. Exactly when those changes occur depends on the cell source and how the cells are cultured.
That is one reason The Re/ Clinic focuses on what we describe as first-generation, low-passage umbilical cord-derived cells rather than simply choosing a product because it advertises the largest possible cell count.
Here is what passage number actually means and why it matters.
Table of Contents
Quick Answer: Why Does The Re/ Clinic Prefer Low-Passage Cells?
The Re/ Clinic prioritizes early or low-passage umbilical cord-derived MSC products because repeated laboratory expansion can alter cellular characteristics.
Human MSC research has documented passage-associated changes involving:
- Proliferation
- Cell morphology
- Gene expression
- Differentiation potential
- Senescence
- Telomere length
- Functional characteristics
For example, researchers studying human Wharton’s jelly MSCs through multiple passages found slower proliferation after extended culture, progressive changes in cellular appearance, increased DNA-damage measurements, and shortening telomeres later in expansion.
Another study examining human Wharton’s jelly cells over 10 passages found that viability itself did not simply decline in a straight line. Viability peaked around passages 5 and 6 before declining later, illustrating that passage biology is more complicated than “lower is always better.”
That is why we do not believe passage number should be used as a stand-alone marketing claim.
Instead, low passage is one part of a broader quality discussion involving:
- Cell identity
- Viability
- Potency
- Tissue source
- Culture conditions
- Population doublings
- Storage and thawing
- Sterility
- Product testing
Watch: Dr. John Dame and Dr. Rob Kellar Explain Stem Cell Generations
Video Transcript
Dr. John Dame:
One of the things I find in my research and in talking with patients is some clinics talk about tens of millions and large, really large numbers, in the millions of mesenchymal stem cells.
And often when I dig into that, it’s because they’re tissue-culture expanded multiple, multiple, multiple generations.
Can you speak to what that does?
Dr. Rob Kellar:
Sure.
So, expansion of stem cells. Let’s say you have Wharton’s jelly, you pull out the stem cells, and you put them in a little dish and you have ten stem cells. Let’s just make up a number.
You add some media and you let them grow, and two days later you have a hundred. A week later you have ten thousand in the dish.
You can subdivide.
So you can take one dish and say, “I’m going to take one tenth of everything in that dish and separate it amongst ten more dishes.”
When you do that, that’s called a passage, a generation.
It’s kind of like now they just had babies.
So, in order to get hundreds of millions of cells out of one cord, you would want to passage it maybe twenty, thirty times, right?
The longer you go generationally, the more passages, the less stem-cell-like they stay.
There’s really, in the literature, definitely an encouragement or a push to stay very low passage or no passage.
Important Context About the Video
Dr. Kellar’s explanation is an accessible introduction to cell expansion, but there are a few important scientific nuances.
“Passage” and “generation” are not exactly the same measurement.
A passage happens when cultured cells are transferred into a new vessel so they can continue growing.
But the number of times cells have actually divided is better described using measurements such as population doubling level.
Two cell populations labeled “passage 4” may have experienced different numbers of actual cell divisions depending on:
- Starting cell density
- Culture vessel
- Media
- Growth rate
- Time between passages
So passage number is useful, but it does not completely describe the biological age or manufacturing history of a cell population.
Later passage does not automatically mean a cell is useless.
Studies have found passage-related cellular aging and functional changes, but the exact pattern depends on:
- Cell source
- Donor
- Culture conditions
- Oxygen exposure
- Media
- Seeding density
- Other manufacturing variables
One human umbilical-cord MSC study even found stronger immunomodulatory activity in later-passage cells, despite the cells also developing a more senescent appearance and different gene-expression profile.
That demonstrates why “early passage = good, late passage = bad” is too simplistic.
The better takeaway is:
Repeated expansion changes cells, so passage history should be understood rather than ignored.
1. What Does “First-Generation Stem Cells” Mean?
This term deserves clarification.
“First-generation stem cells” is not a standardized scientific classification.
Scientific papers are much more likely to describe MSCs by:
- Passage number
- Population doubling
- Cell source
- Culture method
- Viability
- Phenotype
- Potency
At The Re/ Clinic, we use “first generation” to communicate our preference for early, low-passage umbilical cord-derived cells rather than extensively expanded cell populations.
Patients should still ask for the actual product-specific information.
For example:
What passage are these cells?
is more meaningful scientifically than simply asking:
Are these first generation?
The exact passage number and manufacturing history of the product being administered should be verified through current supplier documentation.
2. What Is a Stem Cell Passage?
Imagine a small group of cells growing across the bottom of a laboratory culture dish.
As those cells multiply, they eventually begin to fill the available space.
To continue expanding them, technicians can:
- Remove the cells from the original culture surface
- Divide the population
- Transfer portions into new culture vessels
- Allow the cells to continue growing
That transfer is called a passage.
Depending on the laboratory’s labeling system, the first isolated culture may be called P0, followed by:
- P1
- P2
- P3
- P4
and so on.
Each passage creates an opportunity to generate more cells.
But each passage also means the cells have spent additional time outside their original tissue environment and undergone additional replication.
3. Why Are Stem Cells Expanded in the First Place?
Because there are not unlimited MSCs sitting inside one piece of tissue.
Researchers and manufacturers may begin with a relatively small population and expand those cells to produce enough material for research or clinical development.
Expansion itself is therefore not inherently a bad thing.
It is often necessary.
The challenge is finding a balance between:
producing enough cells
and
preserving the biological characteristics researchers care about.
This is one of the central challenges of MSC manufacturing.
4. What Happens as MSCs Are Repeatedly Passaged?
Several human studies have examined this question.
Gene Expression Changes
Researchers comparing human MSCs across passages 4 through 28 found progressive differences in gene expression.
They also found reduced osteogenic differentiation capacity during later-stage culture, with evidence that adipogenic differentiation changed as well.
This means the cells at passage 20 were not necessarily biologically identical to the same donor’s cells at passage 4.
Cell Appearance Can Change
Another human MSC study compared passage 4 with passage 8.
As cells aged in culture, researchers observed:
- Changes in morphology
- Reduced population-doubling rate
- Changes in surface-marker expression
- Evidence of genetic instability
- Reduced osteogenic differentiation potential
Wharton’s Jelly MSCs Also Change Over Time
In research specifically involving human Wharton’s jelly-derived MSCs, cells began as relatively small, spindle-shaped cells and became flatter and broader at later passages.
Researchers observed:
- Reduced proliferation after approximately passage 10
- Shortening telomeres at later passages
- Increasing DNA-damage measurements
- Continued expression of several MSC-associated markers during the period studied
That last point is important.
Cells can still express common MSC markers while other biological properties are changing.
5. What Is Cellular Senescence?
One reason researchers care about prolonged cell culture is senescence.
Cellular senescence is essentially a state in which a cell remains alive but has lost its normal ability to continue dividing.
Senescent cells may also behave differently.
They can develop changes involving:
- Shape
- Metabolism
- Gene expression
- Protein secretion
- Replication
- Differentiation
Research has demonstrated that human MSCs accumulate passage-associated changes as they approach replicative senescence.
Think of it less like:
“At passage 10 the cell suddenly becomes old.”
and more like:
“Repeated division and time in culture can gradually alter the cell population.”
6. Do Later-Passage Cells Stop Being Stem Cells?
Not necessarily.
This is another area where marketing can oversimplify the research.
The International Society for Cell & Gene Therapy established commonly used minimum criteria for identifying mesenchymal stromal cells.
Among other characteristics, MSC populations should express markers including:
- CD73
- CD90
- CD105
while lacking several hematopoietic markers, and should demonstrate specific differentiation capabilities in laboratory testing.
Later-passage cells may continue meeting some or all of those criteria.
For example, studies of Wharton’s jelly MSCs have demonstrated retention of important markers during multiple passages even as proliferation, morphology, telomere length, and other characteristics changed.
So Dr. Kellar’s phrase:
“less stem-cell-like”
is best understood as shorthand for the possibility that prolonged culture may alter some of the functional characteristics associated with an earlier cell population.
It does not mean a cell necessarily crosses a precise passage and instantly becomes a completely different cell type.
7. Why Wharton’s Jelly Matters
The source of the MSC population matters too.
Wharton’s jelly is the connective tissue within the human umbilical cord.
Researchers study Wharton’s jelly MSCs partly because these cells can demonstrate substantial proliferative capacity.
That means they may tolerate culture expansion differently from MSC populations obtained from adult tissues.
Human Wharton’s jelly research has shown that some characteristics can remain intact through numerous passages.
One study of 10 consecutive passages found the highest viability around passages 5 and 6, rather than at the earliest passage tested.
Another study followed human Wharton’s jelly MSCs through passage 14 and reported no chromosomal abnormality during that study period, although DNA-damage measurements increased and telomere length decreased at later passages.
This matters because it prevents us from making a claim like:
“Every cell gets dramatically worse every single time it is passaged.”
The actual biology is more complicated.
8. Is Lower Passage Always Better?
Not automatically.
Low passage is attractive because it generally means less time in artificial culture and fewer rounds of expansion.
But passage number alone cannot prove cell quality or potency.
Imagine two P4 products.
Product A might have:
- Excellent viable-cell recovery
- Well-characterized identity
- Controlled manufacturing
- Strong functional testing
- Good sterility testing
Product B might also be labeled P4 but have:
- Poor post-thaw viability
- Inadequate characterization
- Different culture conditions
- Poor storage
- Little functional documentation
They share the same passage number.
That does not make them equivalent.
One study investigating clinical MSC products found that freezing and post-thaw handling affected functional characteristics, with growth after thawing differing by sample and passage.
So low passage should be considered one quality variable among many.
9. Does a Higher Cell Count Mean Better Treatment?
Not automatically.
This is the main question Dr. Dame raises in the video.
A very high cell count may tell you that there are many cells in the preparation.
It does not automatically tell you:
- How many are viable
- What those cells are
- How many passages they underwent
- Their population doubling history
- Their functional potency
- Whether they were properly stored
- Whether the product was sterile
- Whether that dose improves clinical outcomes
There is no universal rule that:
100 million cells must produce twice the clinical benefit of 50 million cells.
Dose-response relationships need to be established for a particular cell product, condition, route, and clinical protocol.
That is why comparing clinics solely by their advertised cell count can be misleading.
10. Passage Number vs Population Doubling
This distinction is worth understanding if you really want to compare cell products.
Passage Number
How many times the culture has been transferred into a new culture vessel.
Population Doubling
How many times the cell population has effectively doubled.
For example:
10 cells becoming 20 = one population doubling.
20 becoming 40 = another.
40 becoming 80 = another.
Two laboratories can passage cells differently.
One laboratory may allow much more growth between each passage than another.
Therefore, two P4 products may have undergone different amounts of actual replication.
This is why asking only:
“What passage is it?”
does not tell the entire manufacturing story.
11. What Else Determines Stem Cell Quality?
At The Re/ Clinic, we believe the conversation should go beyond one impressive number.
Important questions include:
Tissue Source
Where did the cells originate?
The biological characteristics of umbilical-cord-derived MSCs can differ from adult bone-marrow or adipose-derived MSC populations.
Passage Number
How extensively were the cells cultured?
Cell Identity
Were the cells appropriately characterized?
Common MSC characterization includes markers such as CD73, CD90, and CD105.
Viability
How many cells are alive in the final preparation?
Post-Thaw Recovery
Cryopreservation and thawing can affect cell behavior, so pre-freeze numbers do not necessarily tell the whole story.
Potency
What can the cells actually do in a relevant laboratory assay?
Being alive is not the same thing as demonstrating biological function.
Sterility and Safety Testing
The product should have appropriate quality-control testing for contamination and other safety concerns.
Culture Conditions
Factors such as media, oxygen conditions, time in culture, and growth environment can change cellular behavior.
12. Why The Re/ Clinic Chooses Low-Passage Cells
Our philosophy is relatively simple:
We do not want to choose a regenerative product solely because it can advertise the biggest number.
The purpose of cell expansion is to produce enough cells while maintaining the biological characteristics that matter.
Research gives us good reason to pay attention to how much expansion a population has undergone.
Long-term culture has been associated with:
- Replicative senescence
- Changes in gene expression
- Altered differentiation
- Slower proliferation
- Telomere shortening
- Changes in cellular morphology
That is why The Re/ Clinic favors an early, low-passage approach when selecting umbilical cord-derived MSC products.
It does not mean:
“Low passage guarantees a better clinical result.”
It means:
“We consider manufacturing history and cellular quality more important than chasing the biggest advertised cell count.”
13. Questions to Ask When a Clinic Advertises Millions of Stem Cells
If a clinic tells you it uses 50 million, 100 million, or 200 million stem cells, consider asking:
What tissue are the cells derived from?
Umbilical cord?
Bone marrow?
Adipose tissue?
Something else?
What passage number are they?
Ask for the actual number rather than only a label such as “first generation.”
How many population doublings occurred?
This provides additional information about how much replication occurred during manufacturing.
When was the cell count measured?
Before freezing?
After thawing?
Immediately before administration?
What is the viable cell count?
Total cells and viable cells are not necessarily the same number.
How was cell identity confirmed?
Ask what markers or testing were used to demonstrate the cell population is what the clinic claims.
Is there potency testing?
Viability measures whether cells are alive.
Potency testing attempts to characterize relevant biological activity.
Can I see product documentation?
Ask what lot-specific information is available.
Is more actually proven to be better for my condition?
The provider should be able to explain why a particular dose was chosen.
Frequently Asked Questions
What are first-generation stem cells?
“First generation” is not a standardized scientific term.
At The Re/ Clinic, we use the term to describe our preference for an early, low-passage umbilical cord-derived MSC product rather than a heavily culture-expanded population.
The actual passage and manufacturing specifications should be verified using current product documentation.
What does P1, P2, P3, or P4 mean in stem cells?
The “P” generally refers to passage.
Each passage represents another round of transferring cultured cells so they can continue expanding.
Exact labeling conventions can vary between laboratories.
Are P1 stem cells better than P4 stem cells?
Not necessarily.
Passage number is only one variable.
Human Wharton’s jelly research has found strong viability at middle passages as well as changes that occur later in culture.
Quality also depends on cell identity, viability, potency, culture conditions, manufacturing, and final preparation.
Are P20 stem cells bad?
“Bad” is too simplistic.
Extended culture can produce changes in proliferation, gene expression, senescence, and differentiation potential.
But cell source and culture methods matter, and some biological functions may remain preserved or even change in different directions during later passage.
The better question is what testing demonstrates about that specific cell product.
Do stem cells become weaker every time they divide?
Not in a simple stepwise way.
Repeated expansion can gradually alter MSC populations, but the changes are not identical across every passage, cell source, donor, or manufacturing system.
Why do some clinics advertise hundreds of millions of cells?
Large cell numbers can be produced through laboratory expansion.
However, the advertised number alone does not tell you the passage number, population doubling history, post-thaw viability, or potency of those cells.
Is a higher stem cell dose better?
Not necessarily.
A clinical dose has to be evaluated in relation to a particular product, condition, route of administration, and treatment protocol.
More cells should not automatically be assumed to produce a better clinical result.
What is stem cell senescence?
Cellular senescence is a biological state in which cells remain alive but have undergone changes that limit normal replication and alter other cellular functions.
Long-term culture can contribute to replicative senescence in MSC populations.
Can umbilical cord stem cells be expanded?
Yes.
Umbilical-cord-derived MSCs can be expanded in laboratory culture.
Human Wharton’s jelly MSCs demonstrate substantial proliferative capacity, although their characteristics can change during extended culture.
Is “first generation” the same as “no passage”?
Not necessarily.
Because “first generation” is not a universally standardized scientific term, clinics and manufacturers may use it differently.
That is why we recommend asking for the actual passage number and manufacturing documentation.
Are low-passage stem cells FDA-approved?
Low passage does not determine FDA approval status.
The FDA regulates human cell and tissue products based on their specific characteristics, processing, intended use, and applicable regulatory pathway.
The FDA currently states that regenerative medicine products have not been approved for orthopedic conditions such as osteoarthritis, tendonitis, disc disease, back pain, knee pain, hip pain, neck pain, or shoulder pain.
Don’t Choose Stem Cells Based on the Biggest Number
When someone advertises:
“200 million stem cells!”
it sounds impressive.
But there are better questions.
Where did those cells come from?
How were they expanded?
What passage are they?
How many are viable?
What happened during freezing and thawing?
How were they characterized?
What testing was performed?
And most importantly:
Is there evidence that this particular product and dose are appropriate for what you are trying to treat?
At The Re/ Clinic in Sandy, Utah, our preference for first-generation, low-passage umbilical cord-derived MSCs reflects a broader philosophy:
Quality should be evaluated before quantity.
We believe patients deserve to understand what is actually being used in their treatment rather than simply being shown the largest possible cell count.
Schedule a consultation with The Re/ Clinic to discuss our regenerative medicine products, sourcing, treatment protocols, and whether regenerative treatment may be appropriate for you.
Call: 385-240-1000
Location: 9035 S 700 E, Sandy, UT 84070
References
- Dominici M, Le Blanc K, Mueller I, et al. Minimal criteria for defining multipotent mesenchymal stromal cells. The International Society for Cellular Therapy position statement. Cytotherapy. 2006. Defines widely used criteria for MSC identification, including surface markers and differentiation characteristics.
- Tanabe S, Sato Y, Suzuki T, et al. Gene expression profiling of human mesenchymal stem cells for identification of novel markers in early- and late-stage cell culture. Journal of Biochemistry. 2008. Researchers evaluated MSCs across passages 4 through 28 and documented passage-associated gene-expression and differentiation changes.
- Wagner W, Horn P, Castoldi M, et al. Replicative senescence of mesenchymal stem cells: a continuous and organized process. PLoS One. 2008. Researchers documented progressive gene-expression and morphological changes during prolonged MSC culture.
- Changes in phenotype and differentiation potential of human mesenchymal stem cells aging in vitro. Human MSC study comparing early and later passage and evaluating morphology, proliferation, genetic characteristics, and differentiation.
- Assessment of Long-Term in vitro Multiplied Human Wharton’s Jelly-Derived Mesenchymal Stem Cells prior to Their Use in Clinical Administration. 2021. Human Wharton’s jelly MSC study evaluating cell morphology, proliferation, markers, chromosome stability, telomere length, and DNA damage through extended passage.
- Evaluation of the Cell Viability of Human Wharton’s Jelly Stem Cells for Use in Cell Therapy. Human Wharton’s jelly study evaluating viability over 10 consecutive passages. Viability varied rather than declining linearly and was highest around passages 5 and 6.
- Comparison of Biological Properties of Umbilical Cord-Derived Mesenchymal Stem Cells From Early and Late Passages. Human UC-MSC research demonstrating senescence-related changes while also observing increased immunomodulatory activity in later-passage cells, illustrating that passage effects are not uniformly negative across every function.
- Clinical Mesenchymal Stromal Cell Products Undergo Functional Changes in Response to Freezing. Research demonstrating that cryopreservation, thawing, sample characteristics, and passage can influence functional behavior in MSC preparations.
- U.S. Food and Drug Administration. Important Patient and Consumer Information About Regenerative Medicine Therapies. Current FDA information regarding regenerative medicine products and unapproved orthopedic uses.
- Utah Code § 58-1-512. Stem Cell Disclosure. Effective May 6, 2026. Requires the specified disclosure for applicable non-FDA-approved stem cell therapy and related advertising.
Utah Stem Cell Therapy Notice
THIS NOTICE MUST BE PROVIDED TO YOU UNDER UTAH LAW.
This health care practitioner performs one or more stem cell therapies that have not yet been approved by the United States Food and Drug Administration.
You are encouraged to consult with your primary care provider before undergoing a stem cell therapy.