a16z Podcast - Journal Club: Slaying the Sleeper Cells of Aging with CAR T

Episode Date: August 9, 2020

CAR T therapy is a groundbreaking medicine that uses engineered T cells to attack cancer. But CAR T cells (that is, chimeric antigen receptor T cells) can be programmed to recognize a huge range of target proteins and cell types. So what other types of cells should we train CAR Ts to recognize and destroy to improve human health?On this episode of the a16z Journal Club, a16z General Partner Jorge Conde, bio deal team partner Andy Tran, and Lauren Richardson discuss new research published in Nature in which the authors engineer CAR T cells to recognize and kill senescent cells. Cellular senescence is a process where cells stop dividing (sort of go to sleep), and in many cases this can be protective, like its role in tumor suppression, but if too many cells become senescent of if they are not removed, they can trigger inflammation and cause disease, like in atherosclerosis and type 2 diabetes. Critically, senescent cells build up as we age and contribute to a whole host of age-related conditions. In this episode we cover how the authors created these senescence killing (aka senolytic) CAR T cells, the diseases that could be treated with senolytic CAR Ts, the hurdles to getting them into the clinic, and how they could potentially be used to treat aging and possibly improve longevity.“Senolytic CAR T cells reverse senescence-associated pathologies” in Nature (June 2020) by Corina Amor, Judith Feucht, Josef Leibold, Yu-Jui Ho, Changyu Zhu, Direna Alonso-Curbelo, Jorge Mansilla-Soto, Jacob A. Boyer, Xiang Li, Theodoros Giavridis, Amanda Kulick, Shauna Houlihan, Ellinor Peerschke, Scott L. Friedman, Vladimir Ponomarev, Alessandra Piersigilli, Michel Sadelain & Scott W. Lowea16z bio Journal Club (part of the a16z Podcast), curates and covers recent advances from the scientific literature -- what papers we’re reading, and why they matter from our perspective at the intersection of biology & technology. You can find all these episodes at a16z.com/journalclub.

Hello and welcome to the A16Z Journal Club. I'm Lauren Richardson. This is our podcast where we cover recent scientific advances, why they matter, and how to take them from proof of principle to practice. CAR-T therapy is a groundbreaking medicine that uses engineered T cells to attack cancer. It has revolutionized oncology, and today we're digging into new research using CAR-T to treat a wide range of conditions, including those related to aging. Car-T stands for chimeric antigen receptor T-cells. and the basic idea is to create an immune cell that is programmed to target and destroy specific cells. But until recently, CAR-T have primarily been trained to go after cancer. But given the incredible tractability of these engineered T cells, new specificity can be encoded.

So what other cells should we target with CAR-T? I'm joined by A16Z general partner Jorge Condé and BioDeal team partner Andy Tran to discuss a recent article in nature in which the author's engineered CAR-T cells to recognize and kill senescent cells. Cellular senescence is a process where cells stop dividing or sort of go to sleep. And in many cases, it can be protective. But if too many cells become senescent or are not removed from an area, they can trigger inflammation and cause disease. Critically, senescent cells build up as we age and contribute to a whole host of aging-related conditions. In our discussion today, we cover how the authors created and validated these senescent

killing or senolytic carti cells, the various diseases that could be treated with these sinalytic cartis, the hurdles to getting them into the clinic, and how they could potentially be used to treat aging and possibly improve longevity. We kick off with Jorge laying out the three key questions this work sets out to address. First of all, can we identify biomarkers that are uniquely associated with the synestine cells so that we can identify these cells and target them? The second question is, can Carty cells be used to clear them out? And then I think the last question is, is the removal of senescent cells have a beneficial clinical impact? Yeah, I think the big picture question is, how do we use this new and amazing therapeutic tool that we have in

carty cells and apply it to difficult to treat diseases beyond blood cancers? There's a lot of really cool things happening in this paper. The opportunity to remove detrimental cells from the body is really important, and the technology that they're using is really important. So let's start with the biology and dig in a little bit more to what senescent cells are and some of their roles in health and disease. The biological process of senescence is where the cells essentially stop dividing. In effect, they kind of go to sleep. In many ways, that's protective against the development of disease, because the cells get older, you start to accumulate mutations that can be propagated if those cells were to continue to divide.

So having these cells stop dividing can actually help prevent things like new cancers emerging. The challenge becomes, as these cells accumulate, they can also kick off inflammatory processes, and that can lead to several disease states that result from chronic inflammation. And so there really is a fine balance between when senestine cells are helpful in avoiding diseases like cancer and when they can be harmful for things like atherosclerosis and many other diseases associated with chronic inflammation. I think you bring up two really important points about senescence. It has this critical function that is really necessary. But the accumulation of too many senescent cells or the lack of removal of senescent cells is really where the problem comes from.

And then the second point is you mentioned that they can generate this inflammatory response. And that's because the cells are not dividing, but they're still metabolically active, and they actually secrete a set of cytokines known as the senescence-associated secretary program. And if you have a lot of sedescent cells, and they're all secreting these proteins, that creates this inflammation, which we know can lead to a lot of different conditions. And in sort of healthy, normal, biological function, senescent cells do get cleared out by the immune system. And it's really when you get to the point of dysregulation that causes a disease state, where things accumulate above and beyond for whatever reason, body's ability to clear those cells.

Yeah, one example of senescence that was really helpful for me when thinking about this is that senescence is something that's induced in atherosclerosis initially to help stop that plaque formation. But when you're older, you have a less strong immune risk. response and the senescent cells aren't cleared out. And now you've got this big bulk of senescent cells, which are not only occluding your artery, but they're also promoting inflammation. And so it is a very fine balance where the same process can both benefit from senescence, and it can be detrimental. So let's dive in a little bit more into the therapeutic benefit of targeting and destroying these cells. Eliminating these senescent cells with

senolytic agents has amelioring a range of different pathologies like liver fibrosis, arthritis, diabetes, in mice very clearly. There's a number of companies that are working on small molecules that exhibit these senolytic properties, but a lot of them lack the precision and also the potency. And because of that, there's pretty substantial side effects. So the hope here is that carty cells can have a much more precise targeting and a stronger effect when we use these as agents to target these senescent cells. Let's talk about car T cells more specifically. The article describes targeting and killing senescent cells

with these engineered immune cells as opposed to small molecules. So can you give me just a brief description of what car T cells are and what their other applications have been in the past? So CAR T cells stand for chimeric antigen receptor T cells. T cell is a type of immune cell that exists in the body. you can take these T cells and genetically engineer them with an artificial chimeric T-cell receptor. A chimeric T-cell receptor allows you to create a targeting ability for these cells where they can now identify a specific protein. And the chimeric refers to the fact that these

receptors have essentially two functions. One is to identify the novel protein, and the other is to activate the killing potential of the T-cell. And so in the case of CAR-T cell therapy for cancer, most of the work to date has been targeting CD-19, primarily in liquid cancers, like leukemias and lymphomas. And with this paper addresses, is this tantalizing concept that should we be using cart-tee cell therapy for a broader range of diseases, not just cancers. So now we have the background on what senescent cells are, why we want to target them and remove them, how the authors do this with engineered T cells. So the very first thing that they did was to identify a specific protein that is expressed on senescent cells, not expressed on other cells,

so that they can engineer these T cells to directly target that protein and kill the cells. So how did they identify this protein? What they did here was essentially they took three robust models of senescence. And then they did RNA-SEC, and their criteria, of course, was highly expressed on the target cells, but not in the vital tissues. And then after doing that comparison, they found this PL-A-U-R gene, which encodes for U-PAR or Eurokinase-type plasminogen activator receptor. They confirmed that U-PAR is really highly expressed in a number of cell models as well, and tissues from patients with senescence-associated disorders. So they've identified this marker, this U-PAR.

which also has a bonus feature is that this protein UPAR is cleaved and then has this soluble fragment, which is called SUPAR, and that's part of this senescence associated secretary program, which then makes it a really convenient biomarker for the validation inpatient samples of these senescence associated pathologies. The other thing is that this paper really shows the evolution of CAR-T therapy and that their description of how they constructed this CAR-T-Sysic. system was just like, and then we constructed it. Like, this has become so due rigor. People just know how to make these cells now.

And I'm sure they did a lot of validation and troubleshooting and things like that. But it was really neat that it was just like, we found the target and then we made the cells and then we tested it. Well, it's one of the things that we find particularly fascinating about these kinds of modalities, right? These therapies like Cartith therapy, they're engineered systems more than they are anything else. And the benefit of that is you can essentially dial in different and enhanced and more sophisticated functionality over time. So the meat of this paper was the validation of these

Carty cells and their ability to target senescent cells in a bunch of different contexts. The first validation is looking at cell culture toxicity with lines either forced to express upar or senescent cell lines that endogenously express upar. And for both, of those, they see that, of course, these cells can target and kill senescent cells. So, as we mentioned earlier, one of the natural roles for senescence is to shut down pre-malignant cancer cells. The next validation is this model called an oncogene-induced senescence. To get this model to work, those mice had to be immune compromise, triggered by the overexpression of this one particular oncogene. So what's the importance of this particular validation? They're essentially

trying to confirm that these U-PAR-C-T cells are the bona fide synolytic agents when they did this validation study. They also showed the U-PAR-K-T compared it with your standard CD-19 CAR-T cells. And then together they confirm the target-level precision of these CAR-T cells. So in validation number three, now they're looking in an immune-competent model. And this validation, they're looking at senescence that's induced by a cancer therapy. So there are actually drugs which induce senescence as part of their therapeutic effect. And so they had this cancer model, which they then gave these senescence promoting drugs to, and they're looking to see if these T cells can now target the senescent cells that have been

induced as part of the cancer therapy. So talk to me about the importance of this validation. What's really exciting here is seeing the therapeutic efficacy that you really want, There's prolonged survival, and you could clearly see senescent cells really decreasing. This also leads to thinking about different combination therapies for these types of diseases, combining synolytic carty therapy with these MAC and CDK, 4 and 6 inhibitors, to have an even more enhanced and robust effect. So the fourth and fifth validations were both addressing chronic tissue pathologies.

So liver fibrosis, which was induced either through a chemical or liver fibrosis that was diet-induced, that mimics this condition known as non-alcoholic, steato hepatitis, or Nash. They induced liver damage and then looked at their ability of the cells to target this. So what is the message from this validation? So it actually showed that they could reduce liver damage for these chronic diseases. So that's actually potentially very interesting because, again, this extends the horizon of the kinds of conditions that you might potentially be able to address with something like a CART, based therapy.

Yeah, for the fifth validation study on Nash, I think one of the interesting things was the contribution to solar senescence to the Nash pathology is actually not that well understood. And what they were able to find was indeed, senesence cells were actually prevalent around those fibrodite areas, and it also, using the same type of treatment, had a therapeutic benefit for Nash. Yeah, that experiment actually is kind of a twofer because whether senescent cells were actually part of the pathology of Nash is not entirely clear. So they showed that senescent cells are contributing to the pathology and that removing them causes a benefit from Nash.

So now that we've talked about the studies, all the different ways that they were able to show that these cells could indeed target senescent cells and lead to really important impacts such as prolonging survival and cancer models, increasing the efficacy of anti-cancer drugs, let's talk about the bigger picture. As we covered this article looked at a number of different pathologies associated with senescence, but what other indications

do you think that these senolytic car T cells might be applied to? Sinescence is a key integrative hallmark of aging. So since senescence influence an integrative range of aging biomarkers, potentially these type of U-PAR car T cells can one day be efficacious for not only a broad range of age-related indications,

but to longevity more broadly. Carty is the fountain of youth. Yeah, it's the buildup of senescent cells with aging and the fact that the immune system is less able to remove senescent cells as people get older and that they underline so many conditions that are associated with aging really speaks to a possible therapy that might be broadly health promoting as we age. Yeah, I think that is very interesting. here because we have historically thought about Carty, it's about killing cells that shouldn't

exist in the first place, right? And here what we're talking about is removing cells that have appropriately gone senescent, just haven't been removed as they needed to. So in many ways, the vision here is, can you use Carty to essentially re-engineer and reboot the immune system to act as a younger, healthier individual's immune system would likely act? And that's a very different framework for thinking about how we develop these, because in the case of cancer, we're using it as a very targeted weapon. In this particular case, you'd almost be using it as a sort of broad surveillance system for keeping people healthy. Yeah, almost restoring a youthful phenotype to your immune system's ability to target these cells. We've talked a lot about how

effective this was, but let's talk about what the limitations of actually using these therapies and getting them into people are. First of all, studying anything in the field of age, and finding clinical benefit of removing the senescent cells poses its own challenges in terms of how you study this in the human population. As is well understood, you can't really have clinical trials for aging per se because they would literally take a lifetime to conduct. And so then the question becomes like, all right, what are the right endpoints? What are the right markers that you should be looking for to demonstrate and determine whether there's clinical benefit for removing in senescent cells in some of these complex chronic conditions. So that wouldn't be without its

challenges. And then the second one, from a very practical standpoint, if you're looking at using complex modalities like CAR-T therapy to treat a broad range of diseases, it presupposes that we're going to be able to address a lot of the challenges that are inherent to developing CAR-T therapies, like the cost of manufacturing, like whether or not these need to be autologous. In other words, the T cells are engineered from the patient themselves, or can they be allergenic where you can have a universal donor that would reduce the cost of developing these therapies and increase their ability to scale from a manufacturing standpoint? There are a lot of challenges associated with these kinds of new modalities that would have to be

addressed if we do eventually want to see this more broadly applied across a range of diseases. Right. You know, perhaps if we're able to show that CAR-T cells can be transformative in so many different diseases that will drive innovation in this area. If they were just for blood cancers, which is such a small portion of cancers, then you can see it staying really expensive and niche, but whereas if it's for a lot of different things, you know, then perhaps there'll be enough of a drive to really make this feasible from a cost standpoint and from a scientific standpoint. I think another thing is, of course, in this paper, we saw a lot of promising in vivo results. But we also saw that mice

treated at the super therapeutic dose did see rise in serum cytokines. This is really typical for carty therapies in having this cytokine release syndrome response. And so for carty therapy to be really translated from the lab to the clinic, getting the dosing right for humans is non-trivial. A key next step is actually spend time to refine the cell engineering component and then also incorporate different things like safety switches, use combinatorial strategies, other types of synthetic promoters that might drive safer expression. All of these things are going to be key

for the Gen 2 version of the synodalytic carti cell before it actually makes its way all the way to human testing. So what is the key take-home message from this article? I think take-home message is CAR-T therapy is really this powerful,

potent, and really versatile new modalities on a cuspid, a lot of the breakthroughs. If we look at the crystal ball and project into the future, this might be the standard modalities for years to come for a while, variety of diseases. I think that for me, the big broad takeaway is that CAR-T therapy has the potential for restoring health, not just for combating acute diseases like cancer. And that for me

is a remarkable thing.