One question I am often asked about cell therapy is whether fresh cells are better than frozen cells.
At first glance, the answer may seem obvious. A freshly prepared living cell has not been frozen, exposed to cryoprotectants, stored, shipped, and then thawed before use. It is therefore easy to assume that “fresh” must mean better.
But cell biology is rarely that simple.
When discussing mesenchymal stromal/stem cells, or MSCs, and the specialized, stress-resistant population known as Muse cells, the more important question is not simply whether the cells are fresh or cryopreserved. The real question is whether the product delivers a safe, viable, well-characterized, and functionally active cell population when administered to the patient.
That distinction is important because a cell can be alive without necessarily functioning at its best.
What Does “Fresh” vs. “Cryopreserved” Actually Mean?
A fresh MSC product generally refers to cells that have been cultured, expanded, or otherwise prepared and then administered without being frozen first.
Cryopreserved cells, by contrast, are frozen under carefully controlled conditions, usually with a cryoprotectant such as dimethyl sulfoxide, or DMSO. They are then stored at extremely low temperatures and thawed before administration.
Cryopreservation is not simply a matter of convenience. It allows a manufacturer to produce a large, well-characterized cell lot, perform extensive safety and quality testing, divide that lot into standardized doses, and store those doses for future use.
This can be particularly valuable with donor-derived, or allogeneic, products because patients receiving repeat treatments may be able to receive cells from the same qualified donor lot rather than a biologically different preparation each time.
Fresh cells therefore avoid freeze-thaw stress, while cryopreserved cells offer important advantages in quality control, consistency, storage, transportation, and reproducibility.
What Happens to Cells During Freezing and Thawing?
Freezing a living cell is not biologically neutral.
During cryopreservation and thawing, cells experience changes in temperature, water movement, osmotic pressure, and cryoprotectant concentration. Cell membranes can be stressed, mitochondria may temporarily function less efficiently, and the cytoskeleton, the internal framework that helps a cell maintain its shape, attach to tissue, and migrate, can become temporarily disrupted.
Some cells may appear viable immediately after thawing but undergo delayed cell death over the next several hours. Others may remain alive but temporarily lose some of their normal biological responsiveness.
Importantly, these post-thaw changes are not always permanent.
In some studies, MSCs were allowed to recover after thawing and regained aspects of their metabolic activity, cytoskeletal organization, and immunomodulatory function. This suggests that cryopreservation may temporarily stress cells rather than necessarily causing an irreversible loss of function.
How the cells are thawed, handled, and prepared for administration can therefore be just as important as the freezing process itself.
Viability Is Not the Same as Potency
This is why simply stating that a vial contains “90% viable cells” does not tell us everything we need to know.
Viability and potency are not the same thing.
A cell may be counted as alive in a laboratory test while still having temporarily impaired migration, signaling, immune modulation, or tissue interaction.
In regenerative medicine, what ultimately matters is not simply whether a cell survived freezing. It is whether that cell can still perform the biological functions we expect from it.
What the Research Shows With MSCs
MSCs have been extensively studied for their anti-inflammatory, immunomodulatory, angiogenic, and tissue-supportive properties.
They can be obtained from several tissues, including bone marrow, adipose tissue, umbilical cord tissue, Wharton’s jelly, and the placenta. Perinatal tissues such as the umbilical cord and placenta are particularly interesting because they provide relatively young cell populations with substantial proliferative and signaling capabilities.
Laboratory studies have shown that freshly cultured MSCs can sometimes outperform cells tested immediately after thawing.
Post-thaw cells may temporarily show reduced adhesion, altered migration, mitochondrial stress, or diminished responsiveness to inflammatory signals. Some studies have also reported temporary reductions in immunomodulatory function.
Importantly, however, some of these changes appear to be reversible. When thawed MSCs are allowed time to recover, parts of their metabolic activity, cytoskeletal organization, and immunomodulatory function can return.
This suggests that the biology is more complicated than simply comparing “fresh” with “frozen.”
A more accurate comparison may be among freshly cultured cells, cells immediately after thawing, and thawed cells given time to recover. These populations may not behave identically.
Laboratory Differences Do Not Always Equal Clinical Differences
Just as importantly, differences detected in a laboratory dish do not necessarily translate into meaningful differences in a living organism.
Reviews comparing fresh and cryopreserved MSCs across preclinical studies have generally found that most in vivo outcomes were not significantly different between the two groups.
In other words, cryopreservation can measurably stress MSCs without necessarily producing a major loss of their therapeutic biological activity.
What Placenta-Derived MSC Studies Tell Us
Placenta-derived MSCs provide a particularly useful example.
Published studies have shown that these cells maintain substantial viability after cryopreservation and thawing.
In a recent Phase I human study of patients with knee osteoarthritis, placenta-derived MSCs were expanded, cryopreserved, thawed, washed, and evaluated immediately before injection. Average post-thaw viability was approximately 85%. Patients received 20 million cells per injection, demonstrating that cryopreserved placental MSCs can be thawed, prepared, and administered clinically while maintaining a substantial viable-cell population.
Laboratory studies using optimized cryopreservation techniques have reported even higher post-thaw viability.
In one study, placenta-derived stromal cells cryopreserved with 10% DMSO showed post-thaw viability of about 94%, compared with about 95% in unfrozen controls. Importantly, nearly 90% of thawed cells also retained the ability to adhere, suggesting that the cells were not merely alive but had preserved at least some important functional characteristics.
These numbers should not be taken to mean that every cryopreserved placental MSC product will achieve the same results.
The freezing solution, freezing rate, storage conditions, thawing procedure, washing technique, cell concentration, and time before administration can all influence the final product.
Nevertheless, these studies demonstrate an important point: properly cryopreserved placenta-derived MSCs can remain highly viable after thawing.
The Potential Advantages of Fresh Cells
Fresh cells still have potential advantages.
Because they have not undergone freeze-thaw stress, they may have greater immediate metabolic readiness and may perform somewhat better in functions such as adhesion, migration, or early signaling.
In certain applications, particularly those that depend on rapid local tissue interaction, that could be important.
But “fresh” does not automatically mean “better.”
A fresh product can still have poor viability, inadequate potency, excessive culture expansion, inconsistent cell identity, contamination, or substantial donor-to-donor variability.
Fresh products also have a relatively narrow window between preparation and administration, making complete quality-control testing and transportation more challenging.
Therefore, the word “fresh” should not be viewed as a guarantee of quality.
The Advantages of Cryopreserved Cell Products
Cryopreserved products offer a distinct set of advantages.
A well-manufactured cell lot can undergo extensive testing before release for clinical use. You can evaluate identity, viability, purity, sterility, endotoxin, mycoplasma, genomic stability, and functional potency.
Once a qualified lot is established, it can be divided into multiple standardized doses and stored.
This provides something particularly valuable in medicine: consistency.
Where Muse Cells Fit Into the Discussion
Muse cells add another interesting dimension to the discussion.
Muse stands for multilineage-differentiating stress-enduring cells. These cells are a specialized population found within mesenchymal tissues and MSC populations and are commonly characterized in part by SSEA-3 expression.
They have attracted considerable attention because of their unusual ability to survive severe cellular stress, migrate toward sites of tissue injury, and participate in tissue repair.
Their stress-resistant biology naturally raises the question of whether Muse cells might tolerate cryopreservation particularly well.
That is biologically plausible, but it should not be overstated.
Resistance to metabolic or oxidative stress does not automatically mean complete resistance to the unique stresses created by freezing and thawing. Cryopreservation involves changes in osmotic pressure, membrane integrity, mitochondria, and cellular structure.
For that reason, direct studies comparing fresh and cryopreserved Muse cells are still needed.
Cryopreserved Muse Cells Are Already Being Studied Clinically
Importantly, cryopreservation of Muse cells is not merely theoretical.
The investigational allogeneic Muse-cell product CL2020 was developed as a frozen cellular preparation for storage, thawing, and intravenous administration.
Cryopreserved Muse-cell products have been studied in humans for conditions including ischemic stroke, amyotrophic lateral sclerosis, myocardial infarction, and neonatal hypoxic-ischemic encephalopathy.
That experience demonstrates that Muse cells can be manufactured, banked, thawed, and administered clinically. It supports the practicality of an off-the-shelf Muse-cell model.
However, those studies do not prove that cryopreserved Muse cells are biologically identical to freshly cultured Muse cells, nor do they demonstrate that one approach is superior to the other.
Those questions will require direct head-to-head comparisons.
What Happens After Thawing May Matter Just as Much
One of the most overlooked aspects of cryopreserved cell therapy is what happens between the freezer and the patient.
In many ways, this may be as important as the freezing process itself.
Two clinics could start with the same cryopreserved cell product and still deliver biologically different treatments depending on how they handle the cells after thawing.
The thawing procedure matters.
The carrier solution matters.
Cell concentration matters.
Residual DMSO matters.
Temperature, mechanical handling, and cell aggregation all matter.
Perhaps most importantly, time matters.
A cellular product may have excellent viability immediately after thawing but gradually lose viable cells or functional activity while sitting in a syringe, IV bag, or transport container.
This means the clinically relevant number is not simply how many viable cells were originally placed into a vial.
The more meaningful question is how many viable and functionally competent cells actually reach the patient.
Why Cell Count Alone Can Be Misleading
Cell number alone can also be misleading.
A vial labeled as containing 20 million cells is not necessarily biologically equivalent to another vial containing 20 million cells.
We also need to know how many cells survive preparation, whether they remain properly dispersed rather than forming aggregates, and whether they retain the characteristics that define the intended therapeutic population.
For that reason, when evaluating a cellular product, I believe four concepts are more important than simply asking whether the cells are fresh or frozen:
Identity. Viability. Purity. Potency.
We need to know what cells are present, how many remain alive when administered, whether the intended cell population is truly represented, and, perhaps most importantly, whether those surviving cells can still perform the biological functions for which they are being used.
For MSCs, that may include the ability to modulate inflammation, influence immune cells, support blood-vessel formation, and release tissue-supportive signaling molecules.
For Muse cells, additional considerations may include preservation of the Muse phenotype, stress resistance, migration toward injury signals, and other functions involved in tissue repair.
Put simply, a cell can be alive without necessarily being therapeutically competent.
So, Is There Really a Major Difference?
From a biological standpoint, fresh and cryopreserved cells are not completely identical.
Fresh cells avoid freeze-thaw stress and may have an advantage in immediate metabolic activity, membrane integrity, adhesion, migration, and certain signaling functions.
Those differences are real.
The more important question, however, is whether those differences are large enough to produce a meaningful difference in clinical performance.
For MSCs, the evidence available today does not suggest that there is a major or consistent difference in therapeutic effect simply because a properly manufactured cell product has been cryopreserved.
Laboratory studies can detect changes immediately after thawing, but most preclinical comparisons have not demonstrated a major difference in overall in vivo outcomes.
The placenta-derived MSC literature adds additional support to this conclusion by demonstrating that properly cryopreserved placental MSCs can retain high levels of viability after thawing and can be used in human clinical studies.
For Muse cells, direct fresh-versus-frozen evidence is less available, so we need to be more cautious.
However, the fact that cryopreserved Muse-cell products have already been manufactured under controlled conditions and administered in multiple human clinical studies strongly supports the idea that these cells can remain clinically usable after appropriate cryopreservation and thawing.
So when a patient asks me, “Is there a major difference between fresh and frozen cells?”, my answer based on the evidence we have today is:
Probably not, provided the cryopreserved product has been properly manufactured, stored, thawed, and handled before administration.
Fresh cells may have a modest advantage in immediate biological readiness because they have never undergone freeze-thaw stress.
But no convincing evidence currently shows that a high-quality cryopreserved MSC product is substantially inferior simply because it was frozen.
With Muse cells, the direct comparative evidence is less complete, but the clinical experience with cryopreserved preparations is encouraging.
The Bottom Line
Fresh and cryopreserved cells are not biologically identical, and freezing stresses living cells.
But a measurable biological difference does not necessarily translate into a major clinical difference.
Properly cryopreserved MSCs, including placenta-derived MSCs, can maintain high levels of post-thaw viability, and current evidence does not show that they are broadly or meaningfully inferior to fresh cells simply because they have been frozen.
Cryopreserved Muse-cell products have also been manufactured and administered in human clinical studies, although direct fresh-versus-frozen comparisons remain limited.
For that reason, I do not believe the current evidence supports telling patients that fresh cells are categorically better than cryopreserved cells.
The better question is not simply:
“Are these cells fresh or frozen?”
It is:
“What is the quality and functional potency of this exact cell product when it reaches the patient?”
That is where the real difference is likely to be found.
Dr. P
