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“Understanding Cell & Gene Therapy Potency Assay Development” with Diana Colleluori

March 7, 2023  •  Podcast  •  Diana Colleluori and James Taylor
Posted In Other News & Insights, Biologics News & Insights – Biologics Consulting  •  Tagged CMC, Potency Assays

Insight at Biologics – Episode 6

In this episode of Insight at Biologics, industry expert, Diana Colleluori, explains everything that cell & gene therapy manufacturers need to know about potency assays. Learn about the definition, FDA guidances and regulations, best practices, and how to overcome the hurdles in potency assay development on this episode of Insight at Biologics.


James: How can you quantify and illustrate how well what you’re developing works? We talk with Diana Colleluori about potency assays. I’m James C. Taylor, and this is Insight at Biologics. 

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And joining me now is Diana. Diana, why don’t you tell us a little bit about yourself? 

Diana: I’m happy to. I have a PhD in biochemistry and an MBA in pharmaceutical and healthcare business. I have been in the industry for over 20 years now, mostly with varying small to large pharmaceutical companies, innovator companies. 

I would say the first half of my career was probably more focused in large molecules like monoclonal antibodies, but the latter half of my career has been primarily focused in the cell and gene therapy space. I joined Biologics Consulting just over a year ago and am happy to share my wisdom and knowledge in the potency assay space.

James: Awesome. So let’s start with that. What actually is a potency assay? 

Diana: So that is a bit of a loaded question. There are several FDA guidances. There is of course the US Code of Federal Regulations. I would say as far as regulations are concerned, the most important one that I have seen referenced and used is the potency test for cellular and gene therapy products and the potency assay.

I’ll give you the formal definition and we can talk a little bit about what that actually means. But potency is really defined as the specific ability or capacity of the product, drug product as, as indicated by lab tests is going to affect a given result. And that is the definition. So what, what that actually means is that the potency method is usually an in vitro assessment of the cellular level of the specific activity of your drug product. 

James: Mm-hmm. 

Diana: So that you are measuring the intended downstream biological effect of what you want your product to do in vivo and that that is essentially, what a potency assay is. Okay, and I would, I would add too, James, that unfortunately more often than not for cell and gene therapies, a single assay is not typically satisfactory. 

There are several reasons for this. I would say the two biggest reasons that a single potency assay is not satisfactory, is that cell and gene therapies are complex products and often have more than one mechanism of action and, sometimes even more than one active ingredient, which makes measurement of potency of your product very difficult.

James: Mm-hmm. 

Diana: The second reason is that, a lot of times the cell and gene therapy space. Those products have poorly characterized or poorly understood mechanisms of action. So there may be a cell therapy, for example, that isn’t gene modified, that is exerting a biological effect that is so complicated and not quite well understood.

So the measurement of potency of your drug product becomes very complicated. So using more than one potency assay tends to be the favored approach by the FDA, and this is considered a matrix approach.

James: Okay.

Diana: Where you’re using multiple complementary assays that measure different product attributes, but they each contribute to the quality, consistency, and stability of the drug product. So, when you ask what a potency assay is, it really is a loaded question unless you, unless you have a very well defined mechanism of action. 

James: Okay. All right. Fair enough.

Diana: Yep. 

James: So you were talking a little bit about the regulations for potency assays. What are the current regulations, especially where Gene and cell therapy are concerned?

Diana: Yeah. As I mentioned, the FDA guidance for industry on potency tests for cellular and gene therapy products is probably the most important one, aside from the Code of Federal regulations. And they sort of compliment each other, the regulations in the CFR, whether it’s 2 10 to 11 or 606 10, give more explanation and details around what potency is, but also what your potency assay has to do. So those are the regulations that I would look toward if I was trying to gain a better understanding of what’s being expected of a potency assay. 

James: Okay. Fair enough. So what is the most appropriate time during product development to begin developing your potency?

Diana: Yesterday. I’ll say it is never too early. And this goes all the way back to your preclinical development stages, that once the mechanism of action of your product is known or you have an idea of what it is or what your product is supposed to do, that’s when the development of a true potency assay or a matrix of assays should begin.

It’s important to understand, and I think a lot of, a lot of folks developing products get tripped up in this, in that they’re using maybe a pseudo potency assay in the beginning of the development of a potential product, and the expectations really have shifted to needing potency assessments earlier than phase two, phase three. The expectation is that these assays are at, at a minimum being developed in the preclinical stages. 

And I’ll say that there are lots of reasons to do this and I’ll go through a few, but what is really vital to understand is that the ability to measure potency is fundamental to understanding your drug product and therefore using the early product development time to fully characterize and understand your product is, is critical. And as I said, it is more of. An expectation today that –

James: Mm-hmm. 

Diana: – This is, that this is happening. And so, as I noted, there are lots of reasons to start measuring potency early. I’ll give you a few that I’ve seen: one is the ability to demonstrate your product’s activity, quality and consistency throughout product development.

So you’re starting in the preclinical stages, getting ready for filing an IND and making a clinical batch or two or more. And you want that consistency from pre IND all the way through the development of your product. The other important reason is that generating and collecting data for potency of product lots will support setting your specifications for your product with regard to potency.

So those are two big, big reasons in the beginning to get this started. Don’t wait. You really should begin to think about and develop, probably a battery of different potency measures that you have in your back pocket. You’re going to need potency for so many, so many things aside from lot release, changes in manufacturing process, the stability and setting your shelf life.

And I could go on and on, but the development has to start early. That is really critical and the data that you’re going to collect as early as possible will be extremely important for the future development of your product throughout its lifetime. 

James: Now we’ve kind of been discussing the beginning of the life cycle of an assay. So what is the progression of the life cycle of the assay? 

Diana: That is a great question. So the first thing is the appropriate potency assay design, right? So some examples are you need to understand the sources of method variability, and be able to work on reducing or eliminating those sources of variability that are just in your assay so that you can continue to develop and basically have continuous improvement around the development of your assay.

So appropriate assay design, understanding your method. I would say also, as you are beginning to design your assay and put it online for use, you have to consider a lot of other variables, critical assay reagents, for example. 

James: Mm-hmm. 

Diana: This should be thought about pretty early because you don’t wanna get locked into using a single source reagent or something that’s custom, that is expensive, or perhaps critical reagents that are not of the appropriate grade for use. Do you need to qualify a cell bank for the cells that you need in your potency assay? Do you have redundant equipment? What equipment are you going to use for the output of your assay? Or, even multiple lab sites, do they have the same equipment across multiple sites?

Those are some of the things that need to be thought about first and then of course, development, and that continuous improvement and optimization of the method can continue, right? 

James: Right. 

Diana: And, as you continue to understand your product and you continue learning about your method, you can continue to do improvements.

So I’m sure a lot of people are wondering, when should they start doing qualifications and validation activities? Once you have a solid method developed, even if there may be changes down the road for, usually for phase one, now you need to have, what everybody calls, a phase appropriate qualification.

This means you have a fairly solid method. It’s generally expected that this method is quantitative and that you do have acceptance criteria in place for that method. For example, for a lot release of batches. For phase one, the idea of a phase appropriate qualification generally is like a light version of a validation, maybe not as many runs.

Definitely not really looking at aspects of robustness at this point. It’s usually once you get to phase two that it gets a little bit closer to a validation state where you may not be doing robustness at that point either, but you’re definitely going to want to satisfy the ICH requirements for validation around the other parameters like precision and accuracy.

The full validation is now generally expected to be in place to test your pivotal drug product samples. And I don’t say phase three here because a lot of cell and gene therapy products are moving through clinical development at lightning speed and often, what would be a phase two may turn into your pivotal data.

So, not only do you need a validated method in place to be able to test your pivotal drug product samples, but the idea that the timeline of development of your product has shortened so much because so many of these products are fast tracked and just like I said, lightning speed through clinical development.

That it puts a lot more pressure on being able to develop your potency assay sooner and validating it sooner. So starting it yesterday and also, validating it sooner is sort of what is being expected, and then of course, commercial and beyond is the same idea.  , maintaining that validated state, trending the performance of your assay, re-validating the assay if significant changes occur, whether it’s to the method or to reagents or to your manufacturing process, et cetera.

But that’s generally what I have been seeing with the progression of a potency assay life cycle and when not only the development begins, but also the phase appropriate qualification and validation activities. 

James: Now, what are some of the pitfalls of an assay that should be avoided? 

I will give you three. The first one is probably obvious: waiting too long to develop your potency assay and, not only waiting too long, but also perhaps not realizing how long it takes to develop and qualify a potency assay. This can be a months-long process. I mean, some of these cell-based bioassays that are being used for potency take several days just to run one assay.

And if you are in the throes of trying to develop and understand the method and optimize the method, this could be weeks to months long before you can even have a method that is satisfactory enough to be able to do a qualification, would it even pass? See in precision, for example?

So waiting too long is probably the first pitfall. The second I would say is actually having an open and honest dialogue with the agency. I have seen in several instances where information about how the progression and development of the potency assay is going is not being shared openly and honestly with the agency, and it’s actually more beneficial to you to be upfront with them because ultimately the agency wants to see you succeed as well.

So every opportunity that you have to interact with the agency to share with them the progress of your potency assay is extremely important. I would actually say every meeting, every briefing, book or question should always have a potency related question answer in there. Because it’s happening so fast and you may have more information and data and you wanna get feedback from them on what are their thoughts.

Is this going to be a satisfactory enough potency method for, say, pivotal studies? And if you don’t communicate with them, you could get to that point in your product development with an assay without having any feedback from the agency and be told, at the 11th hour, that it’s not good enough.

So it is really important to be open and honest with them. I would also as a footnote to this pitfall, also note that when you do get feedback regarding potency methods, it’s important to read between the lines. I think we all know that the agency is not going to come out and tell you what to do, that that just doesn’t happen.

You are proposing to them what you want to do, what you think you should do, and they’re giving you feedback on how your approach is. If they ever recommend an approach or recommend a change to the method or recommend that you have a second potency assay, I recommend that you follow their recommendations. The recommendation is almost saying you really should do this. 

James: Right.

Diana: And so, I’ll stop there for that one. But the final pitfall that I have seen is not having enough product retains and I hope people that are listening will understand what I mean when I say that because the potency method often changes throughout the development, and the life cycle of not only the assay, but the product that – if you have from phase one to say phase three, made some pretty significant changes to your method, for example, you may need to go back and retest samples that have already been tested and released to gain the data of the, the potency of those batches using your newly qualified or newly validated method.

And, I’ve even seen this in phase three pivotal studies where, the method is still being optimized and trying to get it validated. So you may be in the throes of your pivotal study, but you still need retains from that study to be able to go back and, and test your product lots in that method.

And it’s really important because it’s not just for, well, of course, for specification setting of the product moving forward. But, all of the statistical analysis in relation to the clinical data, it’s all tied together. So product retains is another pitfall. I would say make sure you are putting aside enough retains for things that you can’t even fathom that you might need it for at that point in time. So be prepared for the unexpected. 

James: So we’re just about out of time here. So first of all, people can come to you for more information, correct? 

Diana: Absolutely. 

James: Yes, and I’m sure you’d welcome it, but what key takeaways would you like people to leave this conversation with? 

Diana: I would say the key takeaways will be, begin your potency assay development as early as possible. It is a dynamic and progressive process. Second, I would say, use all of your FDA interactions to communicate and discuss the progress of your potency assay, and finally, retains, retains, retains. There are so many reasons that you may need to go backwards to test lots. Potency, assays tend to be a big reason for having to do that. Those are the three main things that I think are important for the community to know.

James: Thank you, Diana. If you’d like to talk to her or any of us here at Biologics Consulting, just send us an email at That’s Insight, @ Biologics Consulting, all one word, .com. Also, we’d love it if you’d like, subscribe to, and rate and review our show. 

The executive producer of Insight at Biologics is Chris Kraihansel. This episode was produced and edited by James C. Taylor. The technical supervisor is Jeff Weiss. The Insight at Biologics theme is by Tom Rory Parsons. I’m James C. Taylor. Please come back for more insight at biologics.

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