Ep 40 What Does Stem Cell Passage Mean In Regenrative Therapy?

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Today we’re breaking down a term that comes up in regenerative medicine, but isn’t always clearly explained—stem cell passage.

If you’ve been researching treatments, you’ve probably seen numbers tied to cell counts. Millions of cells, sometimes more. But what’s often missing from that conversation is how those cells were grown before they were used.

That’s where passage comes in.

At its simplest, stem cell passage refers to how many times cells have been grown and re-cultured in a lab. It starts with an initial population—what’s often called passage zero. As those cells divide and multiply, they eventually need more space. So they’re split, transferred into new environments, and allowed to grow again.

Each time that cycle happens, the passage number increases.

So when someone refers to early passage or late passage cells, they’re talking about how many rounds of expansion those cells have gone through.

Now, this process—called in vitro expansion—is what allows labs to take a relatively small starting sample and grow it into a much larger number of cells. From a production standpoint, it’s efficient. It makes treatments more scalable.

But there’s another side to it.

As cells continue to divide, they don’t just increase in number—they also begin to change.

Early passage cells tend to behave more like they did in their original environment. They may be more responsive to signals, more adaptable, and more consistent in how they function.

As passage number increases, cells can gradually shift. Their signaling behavior may change. Their ability to adapt to new environments may become less predictable. Over time, they may begin to reflect the lab conditions they were grown in, rather than the tissue they came from.

This doesn’t happen all at once. And it doesn’t mean later passage cells don’t work. But it does introduce a variable.

So now you have a balance.

On one side, you have quantity. More passages mean more cells. On the other side, you have functional characteristics—how those cells behave once they’re used.

And that leads to a common question: is more always better?

The answer depends on what the treatment is trying to do.

If the goal is primarily signaling—helping influence inflammation or communicate with surrounding tissue—then higher passage cells may still play a meaningful role.

But if the goal involves more direct interaction with tissue—responding to damage, adapting to a specific environment, or participating in longer-term repair—then the characteristics of the cells may matter more than the total number.

This is especially relevant in targeted treatments, like joint or spine procedures, where cells are placed precisely into a specific area. In those cases, how the cells behave locally can be more important than how many are delivered overall.

Another important distinction is between viability and potency.

Viability refers to how many cells are alive. Potency refers to what those cells are capable of doing. You can have a high number of viable cells, but if their functional characteristics have shifted over time, their behavior may be different than earlier passage cells.

So again, it’s not just about the number—it’s about the profile.

One reason passage isn’t always discussed is because it’s more complex than a single metric. It doesn’t give you a simple comparison point like total cell count. Instead, it’s part of a bigger picture that includes how the cells were sourced, how they were processed, and how they’re being used.

But understanding it adds an important layer of context.

Because in regenerative medicine, how something is made can influence how it works.

So the takeaway here is simple: stem cell passage is a measure of how cells are expanded in the lab. As passage increases, so does quantity—but the cells may also undergo gradual changes that affect how they behave.

And when you’re evaluating treatment options, that balance between expansion and function is worth understanding.

Disclaimer

The information provided in this podcast episode is for educational and informational purposes only and is not intended as medical advice. Treatments and outcomes described may not be appropriate for every individual. Always consult a licensed healthcare provider to determine the best course of care for your specific needs.

Certain regenerative medicine procedures discussed – such as stem cell therapy, exosome therapy, or other biologic treatments – may be considered investigational or not FDA-approved for all conditions. Florida law requires that we disclose this status. While these procedures are offered in accordance with state and federal guidelines, their safety and efficacy have not been fully established by the U.S. Food and Drug Administration.

Results vary, and no guarantee of specific outcome or benefit is implied. All medical procedures involve potential risks, which should be discussed with your treating provider prior to treatment.

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