Culturing Human Cells: Optimizing Growth Conditions for ... · Optimizing Growth Conditions for...
Transcript of Culturing Human Cells: Optimizing Growth Conditions for ... · Optimizing Growth Conditions for...
1
Culturing Human Cells: Optimizing Growth Conditions for Immunotherapy
Webinar October 1, 2014
[0:00:00] Slide 1 Sean Sanders: Hello, everyone, and a very warm welcome to this Science/AAAS webinar.
My name is Sean Sanders and I'm editor for custom publishing at Science and I will be the moderator for today's webinar presentation, "Culturing Human Cells: Optimizing Growth Conditions for Immunotherapy".
In our webinar today, we will broadly discuss the process of
immunotherapy, as well as examine in more detail some of the most critical steps necessary to generate a therapeutic dose of modified cells. It is one thing to grow human cells in culture for research, but the isolation and culture of high quality cells that will eventually be re‐injected back into a donor is quite another.
Growth and survival needs to be optimized and quality control is
paramount. There is often only a single opportunity for successful treatment, so the chances of success need to be maximized, including high yield isolation of good quality cells from patients, cell culture conditions, cell characterization, and reperfusion back into the patients.
Our speakers today will describe how immunotherapy is currently being
applied in the clinic, as well as discuss some of the factors necessary to optimize the culture conditions to produce cells suitable for clinical use. It is my great pleasure to introduce those speakers to you now.
To my left is Dr. Laurence Cooper from MD Anderson Cancer Center in
Houston, Texas. Next to him is Dr. Michelle Janas from GE Healthcare in Cardiff, Wales. A warm welcome to both of you! Thanks for being here.
Dr. Laurence Cooper: Hello! Dr. Michelle Janas: Thank you.
2
Sean Sanders: Before we get started, some important information for our audience. Note that you can resize or hide any of the windows in your viewing console. The widgets at the bottom of the console control what you see. Click on these to see the speaker bios or download a PDF of the slides.
Each of our guests will give a short presentation followed by a Q&A
session, during which we will address questions submitted by our live online viewers. So if you're joining us live, start thinking about some questions now and submit them at any time by typing them into the box on the bottom left of the viewing console and clicking the "Submit" button. If you don't see this box, just click the red Q&A widget at the bottom of the screen.
Please do remember to keep your questions short and concise as that will
give them the best chance of being put to our panel. You can also log in to your Facebook, Twitter or LinkedIn accounts during the webinar to post updates or send tweets about the event. Just click the relevant widgets at the bottom of the screen. For tweets, you can add the hashtag #sciencewebinar.
Finally, thank you to GE Healthcare for sponsoring today's webinar. Now,
I'd like to introduce our first speaker, Dr. Laurence Cooper. Slide 2 Dr. Cooper is a tenured professor at The University of Texas MD
Anderson Cancer Center in Houston with joint appointments in the Division of Pediatrics and Department of Immunology. He is section chief of Cell Therapy at the Children's Cancer Hospital at MD Anderson and associate director of the Center for Cancer Immunology Research.
He was recruited to join the Children's Cancer Hospital in 2006 where he
cares for children undergoing bone marrow transplantation and leads scientific efforts to develop new treatment approaches which pair gene engineering with immunotherapy.
Dr. Cooper is also undertaking the first protocols using a new approach to
gene therapy based on the Sleeping Beauty transposon/transposase system and has helped develop clinical‐grade activating and propagating cells for numerically expanding lymphocytes for human applications.
A warm welcome, Dr. Cooper! Slide 3
3
Dr. Laurence Cooper: Thank you very much, Sean, and thank you for inviting me and a good day
to everybody. I'm going to talk to you for about the next 20 minutes about how bioprocessing can be used for advanced T cell therapy.
Slide 4 This is based on two core principles really, the premise as well as the
promise of adoptive cell therapy. In other words, the administration of T cells to patients, and I'm going to focus most of my remarks for the application for oncology.
First off, the premise is that T cells could be manufactured or modified ex
vivo to improve their therapeutic potential in vivo, and this has really driven a new field. And increasingly, a field is being commercialized in which T cells are administered to patients in distress.
There have been some outstanding examples where T cells, for instance,
have been genetically modified to target a molecule called CD19, and there've been Lazarus moments where those CD19 specific T cells have been introduced into patients and have resulted in dramatic anti‐tumor effects.
This sets the stage now really for understanding how bioprocessing can
be used to generate T cells that have specificity and potency, and using essentially the tricks of the trade, how we can do cell culture, how we can do genetic modification to generate a biologic product.
Slide 5 First off, to give some sense of the history and really before 2013 when
Science Magazine had named T cell therapy among its signature events of the last year is that T cells were being produced at medical centers really across the planet.
[0:05:03] I'll comment really more on the North American experience here where
individual investigators and teams were producing those T cells and they were being infused there at points‐of‐care.
In other words, a patient would come to a medical center. He or she will
get their T cells manufactured at that medical center and then the biology would be uncovered at a particular site. That has driven the field
4
to date and it's allowed for both advances, but increasingly it's becoming under question as we think about commercializing or industrializing the T cell therapy space.
For instance, if T cells are infused at multiple points of care, then it has
essentially limited the number of patients that can be infused. What's the size, for instance, of the manufacturing suite that's available at any particular medical center and how many patients could be processed through that manufacturing site?
It also has limited the numbers of T cells that are manufactured and in
some ways, our trials are powered to the maximally‐manufactured dose, not necessarily the maximally‐tolerated dose. How many flasks, for instance, can you grow to generate the therapeutic product?
The distribution of T cell manufacturing across multiple campuses has
fueled a lot of innovation, but has uncovered real heterogeneity in the manufacturing processes. How I, for instance, grow T cells at the MD Anderson Cancer Center may be a lot different, for instance, than how T cells are grown, for instance, at the University of Pennsylvania, Sloan Kettering, NCI, et cetera.
As a result of this, and I think this is where I will spend a lot of time today,
the bioprocessing of these T cells, the art and the science of growing T cells is asynchronous essentially with the manufacturing process. In other words, we are generating ideas in the good laboratory practice area that are out of step with what's actually being applied in the good manufacturing practice facilities.
Slide 6 Many medical centers, ourselves included, have developed a code of
conduct where we've assembled a team approach. For instance, we have a research group that does fundamental biology uncovering new ideas, for instance, around the T cell and its ability to target tumor cell.
That's passed to a development group, typically speaking, growing the T
cells in an organized way under good laboratory practices that they're going to hand off to the manufacturing team who makes the biological product. It's handed off again to the trials team so that those T cells can indeed be infused into patients, and then we have to make a statement about authenticity. Did something actually happen for that patient?
5
Here, we're joined by our colleagues who understand correlative studies. A simple question, do the T cells persist in that patient? Do they home in that patient?
All of this is wrapped up under a complex web of regulatory affairs both
at the institutional level as well as the federal level. The reason to set the stage here for you is that all of this has to be taken into account with the idea that you're manufacturing a cell, that you're undergoing bioprocessing.
Slide 7 This may not be immediately visible to our audience, and I'll drill in just a
second, but I want to spend a few moments with you just exploring the regulatory landscape because anything that we do is the manufacturing suites has to essentially be approved. What is that approval process?
Slide 8 So I've taken the last slide and divided it really into two for the purposes
of just blowing up the text so you can see it. You can see now that there are a variety of boxes that have to essentially be passed, and these are stage gates.
For instance, if one is going to source out the viral vector, if you're going
to have a third party contractor generate your lentivirus, your retrovirus, or for instance in our world, in our DNA plasmids, who's doing that? What is the authenticity of that product? What are the checkpoints essentially that allow the regulatory agencies to approve that?
What are the processes that you would take to migrate your idea, your
platform technology, through essentially the burdens of institutional and federal review? Well, if it's in the federal review, you have to pass through the NIH‐OBA, in other words, the RAC. Your responses to the so‐called Appendix M documents are critical in their ability to look at your technology and ask questions about your technology.
And then in parallel, you are working with your institution to go through
the various regulatory bodies, for instance, your CRC, your IBC, et cetera, to achieve regulatory compliance.
Slide 9
6
Again, the slide is sort of a two‐step slide here and I'm giving you the second half of this. You can see that as the regulatory approvals come into focus, you still continue to have to meet the needs of the federal and the institutional regulatory bodies.
Putting all this together allows you to open your trial and the reason to
emphasize this is that when teams are developing the bioprocessing steps, it's critically important to keep in mind that at the end of the day, you're going to need federal regulatory approval.
[0:10:04] There are many outstanding ideas and advances that are being practiced
in many major centers, as well as in our colleagues in industry. Some of those, for instance, will never see the light of day because they're not essentially ready for regulatory approval and therefore, compliance.
Slide 10 I give the audience just a few bullet points here of some links that you
can turn to if you wish to learn a little bit more about the regulatory affairs, particularly the federal landscape.
Slide 11 Now, I'd like to really tunnel into what it is to do bioprocessing, what it is
to make a T cell, and I have divided my comments here about the product actually touching the patient, as well as the idea of what it is as a biologist touching the product.
Slide 12 We're going to just spend the first slide looking at what it is when a T cell
flows into a human being, and this isn't necessarily the topic of today's webinar, but I'll just introduce the concepts to the audience because these are the types of things that have to be thought about to generate a product that has therapeutic optimism, and we'll just highlight some of them here.
For instance, what is the recipient and the environment that he or she
has when those T cells are infused? Are you going to, for instance, infuse patients that have a very high tumor burden? We've seen examples of where that actually can result in dramatic anti‐tumor effects, but those T cells can be synchronously activated by essentially seeing the bioburden
7
of antigen, for instance, T cells that are targeting CD19 or activated and could produce a lot of cytokines that can actually injure the patient during essentially that patient's journey to complete response.
Are you going to infuse your T cells with cytokines? Are you going to give
them IL‐2? Are you going to give them IL‐7, IL‐15, these types of cytokines that activate T cells through the common gamma chain? Are you going to infuse one dose of T cells or multiple doses of T cells? How are you going to power your trial in terms of intra‐patient dose escalation versus inter‐patient dose escalation?
Again, a lot of biology here, a lot of variables, and I want to make the
audience essentially aware that as T cells enter into the human system, as they're applied, essentially one would have to uncover and think about each one of these variables that I've noted on the slide.
Slide 13 Let's just now roll back the processing, if you would, and go to the good
manufacturing practice facility. Let's think about it now in terms of what it is to set up a bioprocessing event to generate T cells that have a code of conduct that would come, for instance, in the autologous setting from the patient, go through the manufacturing process, and then be returned to that patient.
This slide now is in large format print so that the audience can see. I'm
just going to pick out a few of these boxes really as vignettes to go through and start to understand the variables that would touch on each of these steps. I would add that I think a successful manufacturing team has to have the entire constellation in mind if you're going to achieve the types of products that are going to meet essentially your patient's needs.
Let's begin really in the box at the top where we're now tunneling in on
the idea of how do you source the T cells? Where are they coming from? Slide 14 For instance, many practitioners are obtaining T cells from steady‐state
apheresis, and steady‐state apheresis really is the word that's used to say that we're collecting T cells by apheresis in the absence of a growth hormone, for instance, GCSF.
Well, that steady‐state apheresis can be accomplished under standard
operating procedures. There's nothing particularly special about this
8
particular moment except when you start to think about what it is to apherese a patient who has, for instance, received a lot of chemotherapy, who may be lymphopenic.
Those numbers of T cells that are circulating in that patient, once those T
cells are being collected in the drum, in the spinning drum of the apheresis apparatus, it can be very few and it can be quite difficult for the technician in the apheresis center, for he or she to introduce the probe to just suck out the river of white blood cells when that band of white blood cells is few and far between.
It's one thing to mobilize patients with GCSF and suck out the
immobilized white blood cell product when there are large numbers of circulating white blood cells. It's another thing when you consider how you harvest T cells from patients that are lymphopenic using the same type of apparatus.
For instance, in our program and I think for others in the community that
are online today, we think about alternatives to apheresis. Apheresis is expensive. It's actually invasive. It hurts. I don't know how many of the audience that have been out there who've been platelet donors, but it's obviously a life‐benefitting thing and you should become platelet donors, but essentially you have to have catheters in your arms to become a donor.
[0:15:12] Contrast that with a simple venipuncture for the purposes of blood
banking, giving up a unit of blood, for instance, if you were donating to the Red Cross. Well, that same code of conduct could be the type of way that you harvest T cells for the purposes of then going on and making your T cell product.
So why is it that we couldn't get T cells from using common blood
banking processes? Again, these are the types of things and questions that are on our minds as we develop our code of conduct to make a biologic product.
I also add another bullet point that circulating T cells in adult blood are
not the only source of T cells. Those, for instance, are generating T cells now from neonatal blood or in other words, umbilical cord blood.
Slide 15
9
Let's return to our diagram and just tunnel in on another point of discussion, and that is, what type of environment are you going to use when you propagate the T cell? What are those elements that are essentially going to be used to activate the T cell?
Slide 16 The first question is do you want to activate the T cell at all? We have a
general understanding that those T cells that are activated certainly through non‐physiologic mechanisms undergo a program event in which they're differentiated and can actually turn to a terminally differentiated state in that they could not recycle their effective functions. They're in some ways one‐hit or one‐kill wonders.
It seems suboptimal to be making T cells that would participate in that
type of biology, so a thought is, can you harvest T cells from the blood and minimally manipulate them in short periods of culture time, or if you are indeed culturing them, culture them under physiologic conditions?
There's a variety of shots on goal here, the ways to tickle a T cell, if you
would, to activate it can be done using artificial means and there are two main areas there. For instance, there are beads. These beads come in a variety of sizes, microbe scale to nanoscale.
These beads are decorated with molecules typically derived from
antibody that would crosslink, for instance, CD3 or crosslink CD28, and they would be used to try and provide a physiologic growth signal to those T cells to activate those T cells, to propagate them to numbers, to swell the number of T cells that are actually in the tissue culture to meet some type of therapeutic dose.
Again, I return the audience to those initial comments with if you're
dosing that patient to have multiple infusions or if you're dosing that patient to have a dose escalation, it's going to be critically important to make sure that your manufacturing approach, your ability essentially to grow those cells can be met.
You don't have to use beads. You can use cells as essentially the ability to
activate a T cell to proliferate. Here I'm referring to, for instance, these so‐called artificial antigen presenting cells or I like to refer to them as activating and propagating cells.
These cells are typically derived from tumor cells. We use K562 cells as
our source material. Many in the community use the same type of
10
cellular template and these are decorated with molecules that allow the T cell to have some type of co‐stimulation event, for instance, through 4‐1‐BB ligand or CD28 along with an activation molecule, pick one, for instance, anti‐CD3.
Into that constellation then of the propagating technology flows ancillary
material that also has to be sourced under the appropriate control systems for good manufacturing practice. Here, I'm referring to, for instance, the soluble cytokines. What other growth factors are you going to add? There's terrific literature now commenting on the idea that you would add IL‐7, 1521, that would allow "younger" T cells to be propagated through the bioprocessing steps.
Slide 17 Let's return again to the diagram and now tunnel into another particular
piece of the puzzle, and that is the type of gene transfer event. Slide 18 Here, I've listed the common approaches to introduce a transgene into a
T cell. For the most part, we should just direct our comments for this particular moment to the idea that we're introducing a targeting molecule; for instance, we're introducing a T cell receptor complex or introducing a single chain chimeric antigen receptor or CAR.
There are a variety of ways to put these immunoreceptors into a T cell.
You can use virus. There are two major flavors of virus. There's the retrovirus and the lentivirus, and the audience will have its particular reasons for choosing one over the other.
At the Anderson campus, we have brought to practice a new approach
based on non‐viral gene transfer. It has its merits, as well as it has its detractors. The way we're doing it is using supercoil DNA plasmids derived from the so‐called Sleeping Beauty system that is a transposon/transposase system that can be used to stably introduce a chimeric antigen receptor or a T cell receptor.
[0:20:11] There's also an emerging literature on introducing immunoreceptors into
T cells that are not stably integrated. Here, I'm referring to the electrotransfer of in vitro transcribed RNA, the codes for a chimeric antigen receptor, and then the physiologic decay of that mRNA means
11
that the introduced immunoreceptor decays over time. This is something that is expected and enjoyed to try and increase the therapeutic window of this particular way of gene transfer.
Here, the audience is presented with a list of gene transfer modalities
and it will be up to the individual team to pick which modality meets the need for their particular design of experiments and their particular patient, but again, I'm introducing the idea that there are many different types of variables that are needed to be understood.
Slide 19 We return to the diagram and we're going to tunnel into another piece of
the puzzle. Slide 20 That is the types of propagation technology where you're looking at
different modalities, as I've talked about, beads, artificial antigen presenting cells, et cetera, and then how much time are you going to allow those T cells to exist in culture.
We alluded to the fact that T cells that are propagated for very long
periods of time might undergo replication senescence. The telomere length might be shortened and they essentially would have very curtailed in vivo persistence.
How can one, for instance, overcome that? Do you use IL‐21 for instance
to activate through the STAT pathway to essentially up‐regulate the telomerase activities, to keep your telomere lengths lengthened in that propagation time period? Again, these types of biology, these fundamental discoveries can inform on the types of bioprocessing that one would use to advance your therapeutic product to the clinic.
Slide 21 The last time we'll return to this diagram and again, we're just pulling out
some ideas here, and that is the final product formulation. Slide 22 I think many of us in the community share the idea that for T cell therapy
to advance, you have to be cryopreserving your product and then infusing it at the time essentially of need. This makes a lot of sense
12
because many of our patients are medically fragile and they don't necessarily meet eligibility criteria at a particular time that's convenient for the manufacturing facility, whereas if you had those products that were essentially cryopreserved, they can be infused when the patient is "ready".
What does that look like in terms of manufacturing? What are the
cryoprotectants that we're using? Is this idea that DMSO is going to be the way of preserving T cell going forward or is there a new biology? Are there new ways of freezing and thawing cells to maintain viability? Again, these are variables that are critically important for us to make a product that would essentially have therapeutic potential.
Slide 23 Let's now assume that that product has been made and that you've
digested that large table and those variables. The bioprocessing team also has to have authenticity. We have to have a sense that those T cells that are being made meet a set of release criteria.
Those release criteria come in two major flavors. One is actually not
release criteria at all. It's in process testing, but this is critical for us to not only understand the types of products that are being made today, but in order to prepare us to make next generation products tomorrow.
One of the types of correlative studies that can be undertaken, I share
with the audience a paper that is an immunology review and this table essentially shows some of those in process and in testing that I take on with my team back at the MD Anderson campus, and you can read that with me or offline.
Slide 24 I also reveal the type of release testing that makes up the certificate of
analysis. These are the go/no go decisions that would essentially say whether or not that T cell product could be infused and you can read them along with me. Again, these are published material.
Slide 25 As we get to the closing comments, I want to leave the audience with this
idea that the ability to manufacture T cells is in really two broad campuses. One is that the manufacture product being essentially generated at multiple points of care. In other words, we're making the
13
products where the patients reside at different campuses really across the globe now.
That is to be contrasted with an idea that actually is being populated
increasingly by industry in which there's a centralized manufacturing that T cells will flow to, to be made, and then will be released and then distributed out to multiple points of care.
The comments I've shared with you around how bioprocessing will be
used to optimize the T cell product will essentially influence how you generate products using both of those types of schema, distributed or centralized manufacturing, again, important variables to consider.
[0:25:14] Slide 26 Looking towards the future, there are a number of challenges that I share
with you and that we're also thinking about in our manufacturing teams in that at the current time, the resources that are available to undertake clinical trials are currently limiting the amount of bandwidth we have to take innovative ideas from the development team to the manufacturing team.
We're also in a frame of mind that one technician is producing one
product. This is not necessarily the case, but it gives the audience a sense of the amount of personnel and sweat equity that's needed by these terrific technicians that we employ in our GMP facilities to manufacture those products. Essentially, the manufacturing of T cells is an art as much as it is a science of the present time.
The reason for that is that there are simply too many variables that I've
alluded to and there's essentially two little infrastructure in place to adequately inform on what products, on what ideas to take forward from the GLP to the GMP process. We really need better correlative studies that allow us to say which idea is a go and which is not a go.
Slide 27 As we go forward and conclude now for my comments, I'll just share this
slide here and I want to accelerate just a little bit so we have time for questions. You can read these along with me, in this idea that there are really some important milestones to be made, for instance, automation being a critical one to reduce the demands on our technical colleagues.
14
Slide 28 This is how I think about cell therapy. It's a fun slide. This is how, for
instance, I talk about T cell therapy, how Cooper explains it, and you can read the rest of the slide. These essentially circles that are popping up on your screen show you that what we think about today, the ideas we have for a particular patient may not meet what the needs of the patient really are.
Again, this idea that we can close the loop here, we can have bench‐to‐
bedside and actually iterative science, going back from the bedside to the bench, is critically important in the bioprocessing world as we make better products.
Slide 29 In conclusion, the distribution of T cells, getting essentially our ideas from
the GMP facilities to the patient is actually a limiting step. We have many different variables that need to be addressed and we have an imperfect knowledge base. This is what makes it both exciting as well as a challenge to be on this field.
I would submit to the audience that the human experience is the only
valid experience. We have to do a better job in our community, accelerating the pipeline and the translation time to go from essentially the manufacturing suite to the bedside, and there really is an ongoing need to refine our processes.
Slide 30 Thank you very much for listening to me. I appreciate you bearing with
me and working through those slides, and I'm available offline if you should wish to contact me.
Sean Sanders: Great! Thank you so much, Dr. Cooper. We're going to move right on to
our second speaker today, and that is Dr. Michelle Janas. Slide 31 Dr. Janas is trained as an immunologist, primarily in the development of
the adaptive immune system. Dr. Janas pursued postdoctoral training at the Queensland Institute of Medical Research in Brisbane and the
15
Babraham Institute in Cambridge in the United Kingdom before becoming a senior scientist for cell therapy technologies at GE's Cardiff, Wales site.
In her current role at GE Healthcare, she is focused on developing
solutions that allow cell therapies to become a mainstream treatment option.
Welcome, Dr. Janas. Slide 32 Dr. Michelle Janas: Thank you, Sean, and thank you to everybody for logging in today. Slide 33 T cell therapies offer the latest in new cancer treatments. However, for
every T cell dose that's generated, there's a very complex workflow behind it.
Broadly speaking, cells are taken from the patient either through a blood
draw or from a TRIM or biopsy. T cells are then separated and selected for. The T cells are activated and expanded in culture, and in some cases, the T cells are genetically modified, so they express a unique tumor‐recognizing a receptor. The T cells are then harvested, concentrated, and infused back into the patient. It's this workflow that causes many problems for scientists, clinicians, and regulatory bodies alike.
Slide 34 To illustrate that, for example, if a typical cell dose for an adult is 10⁸ cells
per kilogram, for an adult male, that may equate to 10 billion cells, and using traditional tissue culture techniques, that would equate to 50 tissue culture flasks. This is neither safe nor practical and alternative methods need to be found and developed.
[0:30:10] Slide 35 When considering those alternative methods, there are several key
points to consider. First is that any solution must be scalable. The cells should be able to be cultured within a single vessel and that vessel needs to be able to accommodate the increasing volumes as this culture progresses.
16
The system should be automatable and this is to reduce the chance of
human error through the manufacturing process. The cells should be contained within a single use container to eliminate any potential cross‐contamination with other patient cells. The system should be closed and that's to eliminate the chance of contamination with adventitious agents through the handling of the product.
Finally, the process should be robust and compliant, and as Laurence was
talking about, it needs to meet the approval of regulatory agents such as the FDA.
In terms of the expansion phase of this process, growing cells in a
bioreactor has been adopted across the field. Slide 36 The Xuri Cell Expansion Systems have been used to generate T cells for
therapy. Xuri is the name that some of you might have previously known as the wave bioreactor.
In the Xuri bioreactors, cells are grown within a single plastic bag that sits
on top of a heated rocking platform. The rocking platform keeps cells in suspension and it allows for sufficient oxygen transfer through a large volume of media so that the cells can grow in normoxic conditions.
Finally, the bioreactor allows for media perfusion, which enables cells to
grown at much higher cell concentrations than what they would be under normal traditional tissue culture techniques.
Slide 37 Let's concentrate on perfusion. What is perfusion? Well, it's a very simple
process of removing media from a culture and adding fresh media to the culture while keeping the entire volume of the culture the same. This is a way to remove waste and feed cells simultaneously.
Slide 38 Now, I want to demonstrate today the effect the perfusion has on T cells
grown in bioreactors. The experiment or protocol we use is to take peripheral blood mononuclear cells, activate them with beads in a static culture, and after five days when the T cells are in exponential growth phase, they're transferred on to the Xuri bioreactor.
17
The cells are grown for an additional nine days and during that time,
perfusion is enabled. In terms of the amount of perfusion, we use cell concentration as a guide. For example, when cells reach two million cells per mille, 50% of the culture is perfused. That's equivalent to 500 milles from a one‐liter culture in a 24‐hour period.
When the cells are between 10 million and 15 million cells per mille, we
increase the perfusion rate to 75% of the culture volume. Once the cells reach about 15 million cells per mille, we perfuse 100% of the culture media every 24 hours. This method is scalable for both one‐liter and five‐liter culture volumes.
Slide 39 When we follow that experimental protocol, we generate a growth
kinetic curve that looks like the one you can see on the screen now. So from a starting population of 15 million cells of PBMCs, we finish typically with 20 billion T cells, and that's a 400‐fold expansion. The cells reach much higher cell densities than they would using traditional tissue culture techniques and in this example here, the cells have reached 20 million cells per mille.
Slide 40 If we set up another bioreactor treated in the exactly the same way but
without perfusion, we find that at about day ten of culture, which is three days after perfusion would've normally been initiated, the cells go into a growth arrest. We find that the cells in this case don't reach densities above eight million cells per mille.
Slide 41 We also find that the cells that are growing in conditions without
perfusion begin to die and they have loss of viability. And by the end of culture, Day 14, we're typically looking at a population of 80% viability compared to the T cells that are grown in the presence of perfusion where their viability is typically above 95%.
[0:35:13] Slide 42
18
I wanted to have a look at the reasons why this growth arrest occurs and this loss of viability occurs. The first thing we looked at was the concentrations of two key metabolites that we see in culture, lactate and ammonia. Lactate is the product of glycolysis and ammonia is a product of glutamine metabolism.
We found that in the absence of perfusion, both lactate and ammonia
accumulated in the culture and remained at high concentrations, whereas where perfusion is enabled, these metabolites are removed from the culture and held at much lower concentrations.
Now, both lactate and ammonia have been shown to inhibit cell growth
and cause loss of viability in immortalized cell lines, but we wanted to demonstrate what happens when lactate is cultured in the presence of primary T cells.
Slide 43 To do this, we took T cells that were in the exponential growth phase.
The cells were washed and re‐plated in the presence of increasing concentrations of lactic acid. The cells were left for 24 hours and then the fold expansion and the viability of the cells were measured.
We found that at above 20 millimole of lactic acid or 20 millimole of lactic
acid and above, we found that there was growth inhibition of the T cells, and that 30 millimole of lactic acid and above, we saw a loss of viability.
This then demonstrates the real importance of making sure that these
metabolites are removed from culture in order to maintain a healthy bioreactor culture and in order to maintain the health of the T cells.
Slide 44 Perfusion not only removes metabolites, but it also ensures that there
are sufficient growth factors around. We've also measured the concentration of glucose in the media and IL‐2.
In the presence of perfusion, both of these growth factors are held at
constant concentrations, whereas in the absence of perfusion, the concentrations of both of these growth factors drops, and in the case of IL‐2, have become negligible by the end of culture.
Slide 45
19
We know that glucose is an important energy source for T cells when they're expanding, but what about IL‐2? We wanted to look at this more closely. In this case, again, we set up parallel bioreactor cultures except one of the bioreactors was cultured with perfusion and the other without. Except in this case, in the culture without perfusion, daily injections of IL‐2 were given and the concentration of IL‐2 that was given to the bioreactor was the equivalent to that being delivered through perfusion in the parallel bioreactor.
We found that these additions of IL‐2 did not really abrogate the growth
arrest that we see in the absence of perfusion. However, the viability of these T cells was equivalent to that of T cells grown in the presence of perfusion. This data shows that IL‐2 is really critical for maintaining the viability of T cells throughout the culture.
Slide 46 Perfusion is important for growing T cells of high cell densities in
bioreactor conditions. Now, I want to just switch to talk to you and introduce to you about another method for determining cell concentration in bioreactor cultures.
Slide 47 And by extension, I will also introduce to you a way to automate
perfusion. Going back to our previous slide, one of the key components of a manufacturing process for T cell therapies is that the system should be a closed one, and that is to eliminate the chance of any contamination that might happen.
However, in order to determine the concentration of cells in the Cellbag
and therefore in order to determine the perfusion rate that should be set, samples need to be taken. And when samples are taken, the sampling port is opened and the closed nature of the bioreactor is compromised, although very briefly.
Slide 48 The latest model of the Xuri Cell Expansion System, the W25, allows for
the continuous monitoring of both the pH in the media and in the dissolved oxygen concentration. An optical sensor is embedded in the bottom of the Cellbag and is connected externally by an optical fiber cable.
20
[0:40:09] Slide 49 Dissolved oxygen is a relative measure of the amount of oxygen that is
dissolved in the culture media. Saturation is considered to be 100% and that is what freshly prepared media has. However, media are incubated in the presence of 5% CO2 and have a dissolved oxygen concentration of 95%, which is what we typically have when we culture T cells and we use 5% CO2.
Slide 50 We took continual measurements of dissolved oxygen throughout seven
independent bioreactor cultures, so seven independent donors were used, and we found that as we the concentration of the cells increase in the bioreactor, the concentration of dissolved oxygen decreases, and this is not a surprise. It makes perfect sense that the more cells that are in the culture, the more respiration that will occur, the more oxygen is used up, and the lower the dissolved oxygen concentration will be.
What we found that was surprising is this relationship is linear and it's a
very tight relationship with an R² value of 94%. We can exploit this relationship and use it to extrapolate the T cell concentration in the Cellbag without having to take a sample.
Slide 51 For example, when the dissolved oxygen concentration is at 60%, that
correlates to a cell concentration in the bag of 20 million cells per mille. Slide 52 By extension, because we use cell concentration to set what our
perfusion rate should be, we can use this relationship between dissolved oxygen and cell concentration to set perfusion rates.
For example, using the rates that I've described in our experimental
protocol, if the dissolved oxygen concentrations are between 75% and 87%, we should set the perfusion rate to be 50%. Also, if the dissolved oxygen concentration drops below 66%, we should use a perfusion rate of 100%.
Slide 53
21
Just to summarize then, throughout this talk, I've shown you that media
perfusion enables cells to be grown at high cell densities. Perfusion is important for both the addition of critical growth factors and the removal of unwanted metabolites. I've shown you that dissolved oxygen is a predictor of T cell density and I've shown you that dissolved oxygen readings can be used to set perfusion rates and monitor the growth kinetics of T cell cultures without having to take a sample.
Slide 54 This work was completed by the GE Healthcare team in Cardiff, UK, and
the GE Global Research Center in Niskayuna in the USA. I'd like to thank you for your attention.
Slide 55 Sean Sanders: Great! Thank you so much, Dr. Janas, and many thanks to both Dr. Janas
and Dr. Cooper for the very engaging presentations. We've got a lot of questions come in, so we're going to get right to those now, the ones submitted by our live online audience.
Just a quick reminder. If you're watching live, you can still submit
questions by typing them into the text box and clicking the "submit" button.
Slide 56 If you don't see the box on your screen, click the red Q&A icon and it
should appear. We've got a broad range of questions from the beginning to the end, so
I'm going to throw one at you, Dr. Cooper, to start off with looking at the end of the process.
What is the success rate of T cell therapy that you've seen more broadly,
and then more specifically, what is your success rate of the reprogramming process in the T cell therapy? And also, this viewer asks what the time period is for the whole process.
Dr. Laurence Cooper: Thank you. This is really getting at the excitement that T cell therapy is
with us in terms of the types of anti‐tumor responses you can see in patients.
22
I'm going to take the opportunity for this question actually and just parse it a little bit more broadly, and that is that T cell therapy, as it's being practiced, I think has to be understood in the context of a patient. Here, let's just take one particular example.
There is a chimeric antigen receptor or CAR targeting CD19 and they
come in two major flavors right now. What I mean by that is that the activation molecules can be divided into T cell receptors or CARs that are activated through CD28 married to CD3 zeta versus 4‐1‐BB or CD137 married to CD3 zeta.
Those two molecules essentially can have activity against a B cell
malignancy and they're probably as equipoised in the literature about those two types of immunoreceptors targeting, for instance, ALL, a B cell leukemia that has CD19 on the surface.
[0:45:12] Those same molecules that are used to target ALL have a different set of
biology when they use to target another B cell leukemia that's chronic in nature called chronic lymphocytic leukemia or CLL. There, instead of seeing the major advances in terms of the anti‐tumor effect, the patients who are enjoying in the ALL area, the patients with CLL are seeing less essentially complete responses, less durable responses.
Look, we've got the same immunoreceptor going into two different types
of patients. I think what this audience member is prompting me is around the idea that even though we have the same design, the context that that design has put into the place, the types of T cells that they're being put into, the source material from a patient with ALL versus CLL, the types of CD19 that are on the target cell, is that CD19 presented or is it presented along with inhibitory molecules, for instance, inhibiting the T cells through the PD1 pathway? All of that then is context‐dependent.
So what I would say to sort of summarize this little piece is that for the
biologic processing, I think the successful team has to keep their eye on the idea that the cells you're making have to meet the needs of the patient and to be able to essentially build receptors that are not necessarily one size fits all, but you may actually have to get quite specific and you may have to personalize for the disease, ALL versus CLL, or even personalize for the patient, and that really is to be determined.
Sean Sanders: That actually brings me nicely to a second question for you, and that is,
are there ways to determine whether certain patients are better
23
candidates for immunotherapy than others and are certain T cell population simply not going to grow?
Dr. Laurence Cooper: Yeah, that's a great question and this is something that keeps me up at
night. We don't, to be honest, have a great idea about which patient is going to do better in terms of antitumor response versus another. Let's now move away from the B cell malignancy sphere and talk about now solid tumors.
Here, I think, there's really going to be some heavy lifting that has to be
uncovered not only to understand which antigens we're going to go after. There isn't a B cell antigen or a lineage antigen that's the equivalent on the solid tumor space, so we may have to make T cells with a variety of targeting molecules to represent the heterogeneity of antigen expression for a given patient. Not only that, but what patient might be better or more favorable? What's the tumor microenviroment for that particular patient?
Look, hope is not lost here. The reason there, I think, is a lot of
excitement in the field is that what we've seen in the area of B cell malignancies, as well as actually some other antitumor effects, gives you a sense that it can work.
I think where the field will be advanced, for instance, with our colleagues
at GE Health, is to recycle and tighten up that translational arc so that if we want to go after, for instance, a patient with pancreas cancer, he or she is brought into the hospital, we biopsy the tumor microenvironment, we do our very best to understand those types of T cells that will be infused, and then we do the heavy lifting.
We say, "Did it work?" If it didn't work, what are the biologic correlates
that allow us to say why it failed and how do we then get back into the bioprocessing steps to make a better product?
Sean Sanders: Any comments from you, Dr. Janas? Dr. Michelle Janas: No. I think Dr. Cooper did a great job there. I think certainly in terms of
solid tumors, one of the most promising is in the melanoma world. We've talked about leukemia, but also we should acknowledge the success in the melanoma treatment as well.
Sean Sanders: Excellent! Well, let me give you a question, Dr. Janas. Do problems with
the quantity of ex vivo manufactured T cells reflect the inability to select
24
the correct T cell specificity i.e. the highest efficiency against the target because highly effective T cell should survive and proliferate in vivo?
Dr. Michelle Janas: That's a really good question, this question of numbers, and I think the
field at the moment is still really unsure of itself in terms of what is the correct dose to give to patients.
Certainly, from a starting block, more is better seem to be the
philosophy, but there is a shift away from that now to looking at what are the best sub‐populations of T cells that are going to go and do the job once they get infused back into the patient.
Yeah, there is a thought that for example, central memory T cells might
be those unique cells that are going to, when they're transferred back into the patient, proliferate the best, survive the longest.
[0:50:10] However, if you take a patient with massive tumor burden, we also have
to think of the huge job that we're asking those T cells to do, and we're asking one T cell to go and essentially kill potentially thousands of other cells. Here, numbers are important especially I think for solid tumors where even ten billion cells is hardly a match for a solid tumor that's spread right throughout the body.
Dr. Laurence Cooper: And I join you that in this idea of treating kilograms of tumor is one in
which the investigative teams have to measure quality versus quantity. This is a real tension and again, it's context‐dependent. If you're putting T cells into a patient in extremis with a large bioburden of tumor, that is one shot on goal.
If you're for instance treating a patient let's say with a brain tumor, that
tumor is anatomically isolated, yet you may be delivering the T cells to the venous system, so you have to have the T cell survive, get to the tumor, and potentially then proliferate in that tumor, so you may need a different product.
Again, I think what I leave the audience with this is this idea that the
human experience is the only real valid experience and we have to get into that area to understand if it's really going to work.
Sean Sanders: Excellent! That actually brings me nicely to a second question I think for
both of you, but I'll come to you, Dr. Janas, first. Do you do any type of
25
characterization on the T cells that you're working with and when would you perform this characterization?
Dr. Michelle Janas: Through our experimental protocol, something that I didn't present
today, we actually follow the cells right from the start of the culture to ‐‐ we take samples of Day 0, Day 5, Day 10, and Day 14, and we follow the maturation of those T cells.
I think it's important particularly in terms of process development here to
make sure that your process that you're setting up isn't resulting in the outgrowth of a senescent population of T cells. That is what Dr. Cooper was referring to before in terms of you can push your cells so hard or T cells so hard that you might get fantastic cell growth, but in the end, they're just exhausted, so when they get transferred back into the patient, they're not going to do the job, so you really need to monitor what you're actually looking for.
In terms of what we're looking for, we follow the maturation markers. I
talked about central memory T cells before, that you can divide your T cell population into effective memory T cells, effector cells in your naïve population, so we have a look at that. We also have a look at the types of cytokines that are being produced, and a great killer will produce a lot of interferon gamma, for example.
Dr. Laurence Cooper: Yes, I think this is exactly right, is that ability to have two types of inquiry.
One is obviously to meet the release testing. You have to have a product that essentially has validity and authenticity based on your relationship with your regulatory team, but importantly, the development team has to understand the types of biology that are ongoing in the tissue culture vessel or in the new Xuri system.
There, flow cytometry, multiparameter flow cytometry helps. Gene
signature is a very useful tool to look at panels of gene expression, and new biologies all the time being exposed to us.
For instance, the immunologists' comment as they think about translating
into immunotherapy, whether or not a so‐called T cell or stem cell type subset of T cells actually might be the favorite type of T cell to carry forward. Again, new biology is being revealed all the time, and how the bioprocessing team incorporates that biology and can do it in a way that meets regulatory compliance obviously is the key to the story.
26
Sean Sanders: That's a perfect lead in to the question I had pulled up next, which is, can you talk a little bit about the use of induced pluripotent stem cells and allogeneic T cells as well?
Dr. Laurence Cooper: Right. Again, this is a far‐reaching question, although maybe not so far
because we've just heard from our Japanese colleagues that they're now for the first time using IPS, not for T cell work, but for restorative therapy.
IPS cell is a cellulous substrate for doing high‐end genetic engineering and
then essentially those manipulated stem cells are then essentially differentiated into T cells. This is in some ways the promise land. We join with the questioner about this area and have our own biology. Others, for instance, the Sloan Kettering Group, have terrific biology in this space.
[0:55:06] The reason that there's optimism around the IPS cell is that the types of
genetic engineering that can be done, putting genes in maybe with a transposon/transposase system, taking genes out with your favorite nuclease, your ZFN, your TALEN, your Cas9, your meganuclease, whatever, that genetic manipulation can be then understood at the clonal level.
You can essentially identify safe harbor and the types of genetic
engineering that would allow then you to have a sense of confidence, that taking that clone and propagating from then all the daughter cells that would essentially be genetically engineered to exacting standard, and then those would be generated into a biologic product such as, for instance, an off‐the‐shelf T cell for instance, something that I'm actually working very hard on.
The trick of course is that the genetic engineering and the genetic
manipulation of the IPS cell stage is going very well. The differentiation into the T cell and getting enough T cells from those IPS cells, that's really still exploratory, so I see this coming and to be honest, inevitable, but still work to be done.
Sean Sanders: Dr. Janas, have you done any work with IPS? Dr. Michelle Janas: No, we haven't done any work with IPS, but I'll just add to your
comments as well. I think some of the promise also lies in the thought that IPS cells that are differentiated into T cells will also be of a younger phenotype just as you mentioned before and therefore, you'll overcome some of these problems about T cell senescence and the theory is that
27
they'll be better able to survive for much longer periods in the body once they're transferred.
Dr. Laurence Cooper: A very good point, thank you. Sean Sanders: Dr. Janas, let me stay with you. This viewer asks whether the T cells
require optimization with serum‐free media, so maybe you can talk about the media that you use.
Dr. Michelle Janas: Yeah. At the moment, we use ex vivo media from Lonza. We supplement
it with human serum and I should add that we also supplement it with IL‐2, 300 international units per mille is what we use, if anybody is interested.
I think that serum‐free is really where everybody wants to head. I think at
the moment, it's a play‐off between serum‐free medias that are on offer that don't perform as well to generating a fantastic cell culture within the presence of sera. We're all trying to move towards serum‐free and I think that's where we should be heading.
Dr. Laurence Cooper: Yeah, and that's the same for us. Our manufacturing group is led by Helen
Huls and she really in almost real time as we're speaking now is generating those types of data where we're taking vendors and understanding essentially the ability of their serum‐free media to support T cell growth.
We're actually finding some success there and just as you're saying, I
think the field, to be honest, is almost a done deal now. I think the transition of getting away from serum really needs to be taken into account by the audience members.
Sean Sanders: Dr. Cooper, a question for you. What might be the criteria that you would
look at when choosing your gene transfer solution? Dr. Laurence Cooper: Again, a critical question. Some of this actually is the experience of you
and your team. People have grown up in the lentiviral world or retroviral world and that's worked very well for them.
We actually took a step backwards when we were thinking about gene
transfer and said, "What is it that we can do to accelerate the arc of translation from bench to bedside?" and realized that for many people, viral‐based systems are very expensive and quite difficult to make in a clinically compliant manner.
28
That's the reason that we have advanced the Sleeping Beauty system, this DNA transposon/transposase technology to really reduce essentially the time to take an idea and to get it from the bench to the bedside because DNA plasmid is cheap to make and there are many, many players out there either in your own facility or for instance, from contract manufacturing groups that can make that DNA.
For us, we have seen the DNA approach as a democratizing approach that
really will enable you to accelerate and reduce the cost to go from the bench to the bedside.
Sean Sanders: Great! I'm going to come back to you, Dr. Janas, with a quick question
that I actually want to ask when we were talking about media. This viewer says, "If you perfuse a bag with fresh medium, doesn't that change the relationship of dissolved oxygen to cell density and can you continue to monitor the cell density over time in this way?"
Dr. Michelle Janas: Yeah. It's a very good question and we were concerned about that
ourselves, but the data that I showed was in the presence of perfusion. The perfusion happened so slowly, so 500 milles over 24 hours or even a liter over 24 hours. It's literally drip, drip, drip in, and the same out, but actually, it doesn't affect that relationship and you can still use it in the presence of perfusion.
[1:00:09] Sean Sanders: Great! I'm going to come back to Dr. Cooper with the final question for
today, and that is maybe quite a broad one, so hopefully we can do this in a short time.
With the goal of overcoming the "art of manufacturing" and variabilities
in patients and processing strategies, what parameters do you consider critical for control?
Dr. Laurence Cooper: Okay. Do you want a short answer? Sean Sanders: If possible. Dr. Laurence Cooper: Again, we can join offline if the audience member wants to contact me
directly. Look, the critical parameters are that the immunoreceptor has to be
stably expressed. It has to be in a cell that is not a one‐hit wonder. You
29
can't have a terminally differentiated state. You have to have a catalog of differentiated states coming out of that culture.
That T cell has to exhibit an ability to kill and importantly to recycle its
killing. You cannot just kill one and undergo activation‐induced cell death, and it has to make some type of cytokine. Gamma interferon is an excellent cytokine because it can call in or recruit in other cells.
Essentially, it's the ability to express the receptor. It's the ability to have
that T cell, not be a highly differentiated cell to kill and to make cytokine. I think these are the four tenants at least that are the minimal threshold to generate a biologic product.
Sean Sanders: Excellent! Well, we are unfortunately out of time for this webinar, so on
behalf of myself and our viewing audience, I wanted to thank our speakers very much for being with us today, Dr. Laurence Cooper from MD Anderson Cancer Center and Dr. Michelle Janas from GE Healthcare.
Slide 57 Please go to the URL now at the bottom of your slide viewer to learn
more about products and technologies related to today's webinar and look out for more webinars from Science available at webinar.sciencemag.org.
This webinar will be made available to you again as an on‐demand
presentation within about 48 hours from now. We're interested to know what you thought of the webinar. Send us an email at the address now up in your slide viewer, [email protected].
Again, thank you so much to our panel for being with us and to GE
Healthcare for their kind sponsorship of today's educational seminar. Goodbye.
[1:02:16] End of Audio