Susan Hoffman: Good afternoon, everyone! Welcome to Freight and Salvage, and I also want to welcome our listening audience who will be taking part in the next hour as a podcast on Berkeley Talks. I’m Susan Hoffman and this is the Spring Speakers Series, the first of four Wednesdays where we’ll gather here, and I’m really delighted that today we have Dr. David Raulet, who will be talking about immunotherapy, and I want to say a few words about him.
As you can tell, he’s from the Department of Molecular and Cell Biology, and he is a recognized expert in NK cells. Do people know what NK cells are? Okay, the natural killer cells? He’ll tell you more about that, and he’ll talk more about tumor immunology. He’s collaborated on stories to differentiate mouse natural killer cells from embryonic stem cells, and to look at the adaptation in the human culture system that promotes the differentiation of human NK cells, and gamma delta cells, as well.
He’s going to explain all of this so you will understand it. He also has success in developing the culture system that will enable detailed dissections of cellular interactions, genetic regulatory events, and DNA rearrangements that underlie T- and NK cell development.
So, for all of us who are not from the scientific field, put on your seat belts; you are going to be in for a great hour of enlightenment, and I’m really delighted to recognize Dr. David Raulet.
David Raulet: Thanks, it’s really a great opportunity to come here. I was especially excited to be up on this stage where I’ve seen so many musicians. I got to go into the green room before; that was exciting! But, let me introduce myself a little bit; as you’ve heard, I’m a professor at Berkeley. I’ve been there since 1991. I’m in the Cancer Research Lab, and the Department of Molecular and Cell Biology, and I currently direct the Immunotherapeutics and Vaccine Research Initiative.
My research more recently … and well, for years, in fact … has addressed mechanisms of immune recognition; how immune cells and antibodies recognize pathogens in cancer, and how they interact to destroy cancer cells. That’s been a major focus in recent years; increasingly, we’re focused on immunotherapy itself, devising new ways to get the immune system to attack cancer.
Like many of you, I’m sure, I’ve also been touched by cancer personally. My father died of bladder cancer; this was frustrating and, of course, sad; but he was being treated with chemotherapy, it was ineffective, there was a lot of suffering, and that’s been a motivation for me to develop better therapies for cancer.
I’m also a cancer survivor myself; I’ve had prostate cancer and then a recurrence of it, and one of the things you experience is … in the mostly common current treatments now, which we nickname Slash, Burn, and Poison … referring, of course, to surgery, radiotherapy, and chemotherapy … that we hope we can do better. I mean, those therapies have been helpful and I don’t want to minimize their importance, but we were hoping we can do better, and that’s really what the revolution in immunotherapy is all about … is developing therapies that are more effective and less toxic, less debilitating to patients.
Now, I should tell you what I’m not. I’m not an MD, I’m not a clinician, I don’t treat patients, and I’m probably not going to be able to answer a lot of your questions about specific clinical questions, and I apologize for that in advance. While I’m not a clinician, I do want to emphasize what will be one of the main messages of this talk, which is that tomorrow’s cures are going to come really from fundamental research, basic research that is as likely to be carried out by Ph.Ds as MDs, and as likely to be carried out as Berkeley as at a medical school like UCSF; and I’ll provide a Berkeley-specific example for you that really illustrates this.
And finally, before I proceed, I should mention that I do consult with bio-tech companies, and I, in fact, co-founded a bio-tech company. I’ll mention some of that in this talk; I wanted to say that up front. In our system of therapeutics, industry is a necessary participant because they underwrite the costs of clinical development and testing that no university researcher could carry out.
I’m going to try and do this at a fairly basic level; I’m not going to try and get too complicated here, and I’ll show some data, but simple data, I think, and I know there’s probably a great range of experience and knowledge about these matters here. I’ll just do what I can to try and reach as many of you as possible.
I’m going to start with just a little lesson about immune recognition and immune cells; I mean, everyone’s heard of antibodies. I want to point out that antibodies are not cells, they’re molecules, this little Y-shaped molecule in this cartoon. They are made by cells, but they’re not themselves cells, and they work by binding to things, principally; so they, for example, can bind to a virus or bind to a bacterium, and in so doing can neutralize them and prevent their infectivity, so that’s one mechanism by which antibodies work. They can also work together with cells to mediate other kinds of immunity that I’ll mention at the end of the talk.
On the other side, we have what we call cellular immunity, and it’s mediated in part by killer cells; and so, these are cells that kill. And there’s two kinds: killer T-cells and natural killer cells, and as you’ll see, they have different modes of recognition and different roles in the immunoresponse, and they both are relevant for cancer.
I want to show you this: These are tumor cells here, and what you’ll see is a T-cell, in this case, coming in and it’s going to recognize this cancer cell; now, it’s going to kill it, and when it kills it, it flashes red, as you’ll see. So, there are these phases where the T-cell recognizes the tumor cell, and then boom, it kills it; you see the cell kind of shrivel up, and then another T-cell below is killing the tumor cell below it, which takes a little bit longer to die … there you go.
These are very extraordinarily good killers of cells, and therefore they’re a major component of our efforts to target cancer, because of course, we want to kill cancer cells. Let me show you one more image or video: this is how the killer cells kill, they have in their … inside of them, in their cytoplasm … granules that contain toxic substances, which are shown in red in this green T-cell here; and as you’ll see in the image, when it confronts the blue tumor cell, the granules re-focus on one part of the cell towards the target cell … the tumor cell, in this case … and then they deliver it on to the membrane of the cell, killing it. In fact, in this image, it’s kind of cool because you become the target cell the way the image resolves, so you’ll see that here.
First you see the recognition; you see the red granules moving towards the tumor cell, and boom … now we focus in right on that plane, and you see those … you’re getting killed now by the granules.
Okay, so that’s what T-cells and NK cells do, and that’s why they’re obviously useful in killing cancer cells. What I want to do in the first part of the talk is tell you about anatomy, if you will, of a great discovery in cancer research that occurred at Berkeley, and that’s really changed how we do cancer therapy in the world. It was led by Jim Allison, a former Berkeley colleague of ours, who was in our department and led the Cancer Research Laboratory from 1984-2004. This image is actually from a new documentary film that’s been made about him that was just premiered at the South by Southwest Film Festival, and will be making its way to the Bay sometime relatively soon.
Let’s talk about how that happened, and what I want to do is take you through it, and the precursor discovery that was actually a collaboration between my lab and Jim’s lab, to illustrate how curiosity-driven research, which is really designed just to understand mechanisms, can lead to breakthroughs in therapy. As an aside, this type of research is sometimes called basic research, meaning it focuses on basic mechanisms, but we learn that sometimes people understand that to mean basic in the sense of simple or easy, and of course, it’s anything but that. It’s hard. I like to call it mechanism-focused research, and it’s usually driven by curiosity, but with an eye
What mechanism are we focused on in these early studies? The question was: how does a T-cell recognize a tumor cell or other cell, and how does it recognize it, and how is it triggered to kill it? What are the molecular participants in that event? So by the early 1980s, it was clear that T-cells have on their surface a protein called a receptor that can recognize antigens. Now, by way of vocabulary here, antigens in immunology are just things that are recognized by the immune system, so it’s a fairly general term.
So, tumor cells, as we’ll see, can present antigens and T-cells have a receptor that can bind to them, and when that interaction happens, it conveys a signal into the T-cell which we’ve come to call Signal One, and it’s a key signal that can trigger the T-cell now to kill the tumor cell. So, Signal One triggers killing, but to understand this second part, you need to know that when T-cells are just in your bloodstream, for example, they’re actually not yet activated. They’re not yet good killer cells. They need to be pre-activated, and that was really the event that we were studying in these experiments around 1990 or ’92, and the question is: how do you pre-activate the T-cell? Is this signal enough? And it became clear that Signal One is not enough.
Signal One can trigger a cell once it’s active, but you need another signal to pre-activate it. And so that came to be called Signal Two, but we didn’t know what it was; the question is what is this missing second signal? So, that came to be called co-stimulation, and the idea was, the hypothesis was, that there’s a co-stimulatory receptor of some kind; it recognizes something on a cell that presents antigens; and that Signal One and Signal Two work together to activate the T-cell. You really need this in order to make a T-cell respond, and that turns out to be true.
What is Signal Two? That was what we set out to understand, and this was a major issue around just in the late 1980s. And so Jim and I … I was interested in this question before I came to Berkeley, when I was a professor at MIT, and Jim was interested in this question at Berkeley; when I came to Berkeley, we worked on this together … that’s Jim and I with my son Michael, who’s now 26 … a while ago!
And what we showed is we identified the co-stimulatory receptor, and it turned out to be a molecule called CD-28, and this molecule was known, but it wasn’t known what it did; and what we showed, clearly, was that it has a partner that it interacts with on another cell, and that provides a second signal, and Signal One and Signal Two work together to activate the T-cell.
I’m going to use this analogy here throughout the talk, that’s commonly used in the field, and say that CD-28 is the accelerator of the T-cell response, and as you’ll see, there are brakes, as well. So this was a landmark discovery; it kind of changed how we viewed how T-cells are activated. But it also had potential applications, and those have been borne out in many studies. At this juncture, however, I began to focus more actively on another kind of killer cell, the natural killer cell, which I’ll tell you about shortly.
But I do want to say what happened subsequently here, which is that Jim became interested in following up on this, and proteins come in families; that’s something you may know … proteins with related sequences, so you can discern that they’re recent relatives of each other … and CD-28 had a relative, and it was a protein called CTLA-4, and really no one knew what it did, but it was known that it bound to this same molecules that CD28 binds to, and so it was assumed that it probably does the same thing; it probably also is another form of accelerator or co-stimulator for T-cells; so, that was the assumption.
But Jim and his graduate student Max Krummel showed that, in fact, CTLA-4 has an opposite activity; it actually curtails the response. It inhibits the response; so, when it engages the receptor, it turns the T-cell down, or off. So now, CTLA-4 can be considered the brakes of the response.
Now, a few years later, a Japanese scientist named Tasuku Honjo showed that another relative of CD28 that’s called PD-1 is also an inhibitor of T-cells; so now, we have two kinds of brakes that can curtail or inhibit T-cell activation. These two receptors, and actually others now, have come to be called collectively “checkpoint receptors,” and that really refers to the fact that their main role in the immune response is to prevent or inhibit auto-immunity. They’re failsafe mechanism checkpoints that make sure the immune system doesn’t overdo it by inhibiting the response when it begins over-exuberant, and if you don’t have those interactions, you can get auto-immunity.
But the concern that, of course, became obvious was that maybe sometimes they do too much inhibition and prevent responses that we want, and that’s what Jim immediately thought of when this discovery was made. He had the very important insight that maybe CTLA-4 inhibits the response of T-cells to cancer; so the idea is that T-cells are responding to cancer, they’re attacking cancer … or, at least, they have the capacity to do that … but they’re being inhibited by CTLA-4, and how then can you release the brakes to enable T-cells to attack cancer cells?
And the way you can imagine doing that is to block the receptor, and in immunology, we like to use antibodies, and so you can make an antibody that binds to CTLA-4; and if it binds to CTLA-4, it blocks that interaction. You don’t get that inhibitory signal, and therefore you unleash the T-cells potentially to kill cancer. So, that was the hypothesis, but of course, it had to be tested.
I do want to mention that this is … well, I think, approach-wise … this is a revealing progression of findings because really, you’re revealing basic mechanisms here; you don’t know what to expect; you make these findings, but then you have an eye towards treating disease when you make findings like this, and this is really, I think, the way that important new discoveries will happen in the future.
Okay. So, Jim did go about testing it, and he used a cancer model in mice. Now, I’m going to have several studies I’ll show you of cancer in mice, and I just want to predicate this by pointing out that these experiments are done humanely. The mice are sacrificed if the tumors grow to a point; they don’t undergo great suffering. And if nothing else, I hope I convince you today that this type of research leads to curative treatments in humans, so it’s critically important research.
So, what Jim found … he basically used a model where tumor cancer cells are transplanted into mice, and without any antibodies injected, the tumors grow progressively and the mice have to be euthanized; but if you inject CTLA-4 antibody, the tumors just melted away … so that was really a remarkable finding, and it really changed everything; although, I have to say, it wasn’t entirely clear at the time. It turned out this was a Nobel Prize-winning experiment, and one that had a huge impact in the client, but there was just a lot of skepticism about it initially. People sneered that mice and people are different; that’s something you hear all the time, but this is a beautifully illustrated case of how this kind of discovery in mice turned out to be very well translated into humans, and I think that’s more common than not, frankly.
This shows the time course for developing this cancer drug. This is nothing that happened quickly. The discoveries at Berkeley were in ’95, ’96 … shown here at the very beginning. And then, as I mentioned, industry had to become involved, ’cause they had to develop the human drug and do all the testing, which we can’t readily do in small numbers of patients; even in a med school, they couldn’t readily do that.
So this took years, you know, a total of about 15 years, and the drug name that was developed for use in humans was called Ipilimumab, and I think it’s called Yervoy on the bottle, if you will. So, this drug underwent extensive testing and finally what’s so-called Phase Three clinical trials, where it was tested for efficacy in double blind control trials, and in 2011 it showed clear efficacy and it achieved FDA approval, and this is now an approved drug used to treat patients.
I do want to point out here … I think this is really, in many ways, the limiting part; good ideas coming up, you know, figuring out how to manipulate the response. This is expensive and time-consuming, but fairly standardized.
Their findings were that tumors shrank; so, it was first tested in metastatic melanoma. Now, I think most of you know that metastases are when pieces of a tumor, or cells from a primary tumor, break off of the tumor and migrate to distant sites where they form secondary tumors, and this is the stage of cancer which is the hardest to treat. This patient had a metastasis in the lung, and melanoma can metastasize to the brain, lung, liver and elsewhere.
After treatment, that lung mass disappeared; so, that was great news. It was clearly having a major effect, but it’s sometimes the case that therapies cause tumors to shrink, but then they grow back. So, I want to … this is our sort of Holy Grail slide, what we try and do nowadays and what immunotherapy has proven that it can do, is to do better. So, many therapies will basically delay cancer; many chemotherapies, for example, will delay cancer. It gives you time. Time is good. I have no problem with time; that’s a great thing. But, clearly what you want to do is to cure more patients, and so we always say we want to raise the tail on the survival curves of people with cancer, and ultimately, raise it all the way to the top.
And so that’s what immunotherapy has proven that it can do, and this shows the data now 10 years out on patients with previously incurable metastatic melanoma treated with this drug called Ipilimumab. And it doesn’t work for everyone; so, it works for about 20 percent of these patients. But what you see is they have … the tail is raised. These people seem to be cured effectively of their disease; and so, this was really a major breakthrough that has kind of changed everything, ’cause this is I think one of the first cases where this type of metastatic disease could be cured in double blind controlled clinical trials.
So, it works, but more importantly, you can build on it; and when you see a good think like this, you copycat it. You try and make it better by combining it with other therapies, and that is going on very extensively now and has occurred already.
The first major breakthrough following the CTLA-4 findings occurred for this receptor called PD-1. So, PD-1, as I mentioned, is another inhibitory receptor, and if blocking CTLA-4 works, why not block PD-1? So this, of course, was done, and the results were really quite remarkable; PD-1 actually works better than CTLA-4. This is now four-year data, also in melanoma, where in this case, anti-CTLA-4 works in something like 34 percent of patients; but now, more than 50 percent of patients respond to anti-PD-1, and the combination of anti-PD-1 and anti-CTLA-4 is approaching 60 percent efficacy in these patients … so this was really quite remarkable improvement over what was previously available, and has had a huge impact now on clinical medicine and oncology.
There is a caveat, of course, as many of you will be aware; these therapies can cause side effects, sometimes substantial: fevers, nausea, diarrhea; sometimes auto-immunity, but rarely. Usually the side effects occur during treatment, and then they resolve after treatment. Okay, so that just summarizes what I told you.
One really interesting part of immunotherapy is it doesn’t treat the tumor; it doesn’t treat the cancer. It treats the immune system. So, this suggests it might work with other kinds of cancer, not just with melanoma. So that proved to be the case; immunotherapy is effective in other kinds of cancer. This is showing a stage four recurrent non-small cell lung cancer, and you see a clear improvement in patients treated with PD-1 and anti-CTLA-4; the tail has been raised, and these survival curves compared to what chemotherapy does; and in fact, it works in several kinds of cancers … not all cancers, but several kinds of cancer, including melanoma, non-small cell lung cancer, renal cancer, Hodgkin’s Lymphoma, bladder cancer, head and neck cancer and certain colorectal cancers.
What are the lessons learned? That understanding basic molecular mechanisms leads to curative therapies, and that immunotherapy where you target the immune system and not the tumor is the most effective curative mode of cancer therapy developed in many decades. So, these studies were obviously important, and Jim Allison and Tasuku Honjo were awarded the 2018 Nobel Prize for this work in medicine, and I was fortunate to go to the ceremony … which was great, to celebrate with Jim and other colleagues. This is Jim showing, in fact, that same slide I showed … you know, raising the tail in the survival curves during his Nobel lecture, receiving the award.
And this young woman came, Sharon Belvin … she was a 22-year-old with metastatic melanoma diagnosed a couple of weeks before her wedding, and treated subsequently with chemotherapy and basically, of course, didn’t respond and ultimately, her … when she had run out of all options, her oncologist, Jedd Wolchok, shown here on the right … suggested she join the Ipilimumab clinical trial, which she did … and her cancer went away, so she’s 10 years out now and has a family, and seems to be perfectly healthy. So that’s a great success story, and she likes to come to all these kinds of ceremonies to lend her support to all these efforts.
Another famous recipient, of course, is Jimmy Carter, who had brain metastases and was in … you know, basically told he had a few weeks, and he went on a trial with anti-PD-1 therapy, and remarkably he responded very well, and he now seems to be fine; this was in 2015. I think this was actually quite remarkable; he’s a 90-year-old man, and so even with a very aging immune system, this type of therapy can work.
One of my messages here is that this type of breakthrough is often not made by doctors or in medical schools, but by people just trying to understand basic mechanisms, and Jim and his … these are all members of Jim’s Berkeley lab, who came to join him in Stockholm, along with myself and my colleague, Ellen Robey; and this is Dana Leach, who was first author on the classic paper. You know, Jim really sang the praises of Berkeley, and the fact that he thought this was a place where he could really do the kind of work he did, that really made these incredible changes in how we treat cancer now.
Now I want to transition and I want to actually emphasize the limitations of this kind of therapy, and this gets … again, mechanistic questions: what do the T-cells recognize on tumor cells? And this is what’s been worked out: it turns out when normal cells become cancer cells, there’s dysregulation, and poorly regulated DNA replication which occurs in cancer cells can lead to mutations in DNA. At the same time, many kinds of cancer arise because of carcinogens: cigarette smoke, ultraviolet light on your skin, et cetera; and so, cells are accumulating mutations anyhow.
And it turns out, it’s the mutations that generate the variations or antigens that T-cells see; so you have altered sequences of normal cellular proteins that are carrying mutations, and those are foreign to us, because they’re not part of our normal proteins. They’re mutated proteins. They’re aberrant proteins with different sequences, and T-cells recognize them as foreign. Those are really the major antigens that T-cells recognize. So, T-cells can rise, they can recognize these mutated peptides on cancer cells, and they can destroy them.
What do we know about mutations in cancer cells? So, this is a complicated plot, but it shows on the top a list of many different kinds of cancer, and on the vertical axis is the rate of mutation in these tumors; so, actually, each dot here is a separate … is a different human tumor, cancer from a patient, that’s been sequenced and compared to their normal DNA, and it shows the number of mutations in that kind of cancer; so the higher they are up here, the more mutations they have.
And so what you see is the tumors on the right have a lot of mutations, and the tumors on the left have relatively few mutations; what that means is that these tumors on the right have lots of antigens, and these tumors on the left don’t have very many antigens, if any. And in fact, the red font here shows the kinds of cancer in which checkpoint therapy is effective, and you can see that cluster on the right side of this curve. And the bottom line is that this type of therapy is just not very effective against tumors on the left here that don’t have very many mutations, and we think it’s because these kinds of cancers are relatively invisible to T-cells; I mean, there may be exceptions, but in general, they don’t present many antigens that T-cells can see.
So what are we going to do about those kinds of cancers? We have to find another approach for immunotherapy, and that’s where my more recent work comes in. We are trying to target these other kinds of immune cells called natural killer cells to immobilize them against those kinds of cancers, so let me tell you a little bit now about NK cells, or natural killer cells.
These are related to T-cells; they kill tumor cells just like T-cells do, same mechanisms; but they have a distinct type of recognition that’s broader than that of T-cells, and I’ll tell you about that in a sec. And so we think that due to this broader kind of recognition, that we can mobilize them against many additional kinds of cancer.
How do you figure out what they recognize? Well, I just put this slide up to help you appreciate that, you know, we’ve been working on it for almost 30 years, and it’s not something you do overnight, but you begin to understand how they work; and what you come to understand is that there’s several types of recognition receptors on NK cells, but there’s a couple, actually, of common themes, and I want to emphasize one of them now.
So that common theme is that natural killer cells recognize stress; they recognize stress that occurs in cells, because it turns out that tumor cells are very stressed out. They have various forms of stress that can be called oncogenic stress, and other types of stress pathways that are activated in those cells; so let me just illustrate this with a cartoon. Normal cells are generally unstressed, but when cells become tumor cells, and they’re replicating very rapidly and inappropriately, there can be damage to the genome. There can be overproduction of proteins, which … there can be overly rapid cell proliferation; all these things activate stress pathways and cells, and it turns out these stress pathways are wired to turn on in cells some proteins on the membrane that you can call “kill me flags.” And there’s a bunch of them, and basically what they do is they invite natural killer cells to kill these cells; so, highly stressed cells basically invite themselves to be killed. That’s one of our protective mechanisms that we have. So, NK cells have receptors, they can recognize those “kill me flags,” and then they can kill them.
In terms of broad recognition, what’s exciting is that these flags I’m mentioning are displayed on the surface of almost all cancer cells, including those that don’t have very many mutations, and including the ones that are on the left side of that graph that I showed earlier.
You might ask, “Well, why don’t they just kill all the tumors then? They should just kill them, and there shouldn’t be any problems.” But, you know, NK cells, like T-cells, have accelerators and brakes, and in cancer, we now know there’s too little acceleration and too much braking, and therefore they are often inactivated in cancer cells. So what we need to do is identify accelerators and brakes, we need to intervene to provide the tumor the former and block the latter.
I’ll take you through this quickly: colleagues of mine at Berkeley, Russell Vance and Dan Portnoy, were studying bacteria and they showed that a bacterial product causes general activation of the immune system. So, this was work that came from studying bacteria; they weren’t studying cancer, and this, I think, illustrates the importance of basic research; and how if you’re thinking about it, and when these findings are revealed, if you consider how to apply them, you can come up with new therapeutics.
The product that the bacteria make has a name: it’s called a cyclic dinucleotide. It’s a small molecule, I’ll abbreviate it CDN, and basically, the CDN enter cells. They bind inside the cells to a protein called STING, and that activates the cell to secrete interferons, these hormone-like proteins that, it turns out, activate NK cells and T-cells … so here’s a cartoon: the CDNs enter the cells, they interact with STING, STING turns on gene expression such that cells make interferons, they secrete interferons, and the interferons can then activate NK cells and T-cells, in fact. So, clearly CDNs might have potential as therapeutic agents against cancer because of that activity.
A post-doctoral fellow in the lab, Assaf Marcus, investigated this not too long ago, and you know, the question was do CDNs activate NK cells? This was really one of the studies that showed this, and so he showed that if you inject CDNs into mice, you activate NK cells. You don’t have to worry about what we’re actually measuring here; they activate NK cells very effectively, and they only do it if the mice have a functional gene for that protein called STING. If we have a mutant STING, they don’t respond, so it depends on that pathway I mentioned.
On the basis of these kinds of findings, that CDNs activate T-cells and NK cells, they’re now being tested in clinical trials for various forms of cancer. So we wanted to test them in the context of NK cells, to see whether we can mobilize NK cells against cancer. So, this is work by Chris Nicolai, a grad student in the lab, and these, again, will be looking at transplanted tumor models in mice, and showing you some results here. Chris investigated a whole series of cancer models that NK cells can recognize but killer T-cells can’t, so we really wanted to see what NK cells can do here.
And this is leukemia line, and you can see the tumors are growing, and if you treat them with saline, they continue to grow; but if you treat them with the CDNs, the tumors melt away; and this isn’t temporary, these mice are cured! They survived indefinitely. So, this was a hundred percent cure rate in this model, and that was very exciting.
Now, that’s not always the case; at the other extreme, this is a melanoma line that we work with. This line is known to be very hard to cure in general; it’s not even easily cured by T-cells. And you treat it with the CDNs … it delays the tumors, but eventually they grow, and the mice all have to be euthanized … less than 10 percent cure rate. And in between, there was four other models that gave intermediate results: 30 percent, 50 percent, 70 percent cure rates; so this is the range of results you may get. Chris showed that tumor rejection in these models is mediated by NK cells, not by T-cells, so this is NK-dependent tumor rejection, induced by CDNs.
Okay, so here we have, we think, an accelerator for NK cells … these CDNs … that they can help activate the NK cells … but then, what about the brakes? And we’d shown that NK cells, when they enter tumors, are often de-sensitized or inhibited, and therefore ineffective. And what we really wanted to do then, of course, if amp up the acceleration and take off the brakes, have more activated NK cells and therefore more tumor cell activity. This principle of combining approaches is really the principle of combination therapy, the ideas that drugs that act by different mechanisms or different stages of a process in the same disease may work better together than separately, and that combining agents that accelerate with agents that take off the brakes is a good principle for combination therapy, and that’s something that we then tested.
The question was can we improve therapy that mobilizes NK cells by taking off their brakes? So, some years ago we discovered that NK cells are often inactivated with tumors, as I mentioned; but we also showed that proteins called cytokines, and in particular in the IL-2, IL-15 family, can reactivate the NK cells. They can take off the brakes, so this was exciting; we could show they have therapeutic effects in certain tumor models. So, we used one particular cytokine that’s called super-2, and it’s a designer cytokine, in fact, made by our collaborator at Stanford, Chris Garcia … and it’s a very effective cytokine at stimulating this in NK cells.
And basically, it kinds of reactivates NK cells from this desensitized state, and has this effect we want of reversing or taking off the brakes. And so, we tested that in combination, and we used this model that I mentioned before … this very hard to cure model … where with CDNs alone we get a delay, but not a high cure rate.
And so, this is work by Natalie Wolf, a graduate student in the lab, and Natalie treated with CDNs alone … or with super-2 alone … and you can see in both cases, tumor growth is delayed, but continues to grow in many of the mice; but the combination of the CDN and the super-2 show these much more substantial effects. And when we look at survival, it’s even more remarkable; so, first, CDNs alone? None of the mice survive, as I already indicated; but with super-2, you get some survivors; and with the combination, now we’re up to 70 percent survival in this difficult model. So, this was exciting and encouraging, and we hope to develop this for therapeutic applications in
Let me introduce what we call the Immunotherapeutics and Vaccine Research Initiative at Berkeley. You know, the story I just told you about the CDNs … worked on in bacteria, translates into cancer therapies, illustrates the theme behind the Immunotherapeutics and Vaccine Research Initiative. At Berkeley, we have very strong cancer immunology. We have very strong infectious disease immunology, and we realize that our work … although in seemingly different subjects … was informing, synergistically, progress in cancer … so that was sort of principle one: research done to understand the immuno-response to bacteria or viruses lead to development of drugs for cancer.
But then we also think the converse is true, and there’s increasing evidence for this, that research in cancer immunology can lead to advances in vaccines and new treatments for infectious disease. So what we do in the IVRI is we combine our efforts to generate synergy between these groups to develop new generations of drugs for both infections disease and cancer immunology.
I also want to mention a sub-group of the IVRI that’s focused on pediatric immunotherapy, and this is a group of us, including myself and my colleagues Lin He and Michel DuPage and Dirk Hockemeyer, who work on cancer immunology, but also basic principles in cancer biology … but focused on pediatric immunotherapy. And I’ll tell you why pediatric immunotherapy is interesting, with respect to the work we do … and we do this work in collaboration with the local hospital, Children’s Hospital Oakland, and collaboration with oncologists Anu Agrawal and Jennifer Michlitsch, and in collaboration with physician scientists at UCSF Department of Pediatrics, Bill Weiss and Clay Gustafson. So these people are all experts in children’s cancers, and why children’s cancers?
Well, here’s that plot again of cancers, and what’s quite remarkable is that children’s cancers cluster on the left side of this plots; they have very few mutations generally, and in fact, don’t work well for checkpoint therapy subjects; so, checkpoint therapy has not worked well at all in pediatric cancer; and that’s really a shortcoming, and obviously we want to do something about that. Turns out NK cells are known to kill many of these types of cancer cells, these are … by the way, it’s leukemia, AML and ALL, and then neuroblastoma, and then brain cancers like medulloblastoma and glioblastoma.
So, NK cells are known to kill many of those cancer cells effectively, and we think they represent an exciting alternative target for immunotherapy of pediatric cancers. So we’re investigating that; I’ll just show you a little data. This is work from a post-doc in the lab, Christina Blaj, and we tested it in a neuroblastoma model that our colleagues, Bill Weiss at UCSF, developed. This is a very hard model to cure, very aggressive cancer, in a mouse model, and we find … and we’re very encouraged by this … that this combination of CDNs and super-2 has an important effect. It causes a strong delay in tumor growth and really delays the survival curve out quite a large number of days. You know, they’ve tried a lot of therapies in this model and basically, they tell us this is the best effect they’ve ever seen in this type of model.
But so far, it doesn’t lead to many long-term survivors, so what are we going to do about that? And we think improvements are coming, and I’ll tell you about one of the things we’re planning to do. And this involves a different kind of therapy that I haven’t told you about yet, and that’s mediated by antibodies.
Antibodies are another approach to cancer therapy that … there are cases where you can develop antibodies that target cancer, that interact with cancer cells, and with the help of natural killer cells, kill cancer cells … and I’ll show you how that kind of works. So, first of all, it turns out that tumor cells often express, on their surface, proteins that are selectively expressed by the tumor cells. These are not mutated proteins; they’re self proteins, but they’re just not expressed by most normal cells. They may have been expressed in the embryo, but they’re no longer expressed in adult cells … but they can be re-expressed on cancer cells … that would be one example.
These are attractive targets for therapy, if you can target them; and … so antibodies can be prepared that bind to the tumor antigen, like that, and it turns out that antibodies have in their rear end, [inaudible 00:43:53] that bind to NK cell receptors. So, NK cells have a receptor on their membrane that binds to antibodies; they binds to the rear end of antibodies; it’s called an FC receptor.
And when it binds, that can activate the NK cell, and then the NK cell can kill the tumor cell; so this is a cooperation now between an antibody and a NK cell. So, several of these drugs have been developed; actually, you may have heard of some of them: Rituximab, Trastuzumab, Siltuximab, Dinutuximab … these are for different kinds of cancer. They generally delay the tumors; there’s relatively few cures; the question, of course, is why? And I’d like to just tell you about one of them, this Dinutuximab, because it’s relevant to our neuroblastoma work.
It turns out that neuroblastoma cells express, on their membrane, this antigen called GD-2, and antibodies can be prepared against GD-2, and they can bind to them, and then with NK cells you can try and kill the neuroblastoma cells. This is not approved therapy in neuroblastoma patients. The problem is it has only modest efficacy and we think it’s because NK cells are less than fully active. And so, we think that combining anti-GD-2 with NK activators like CDNs and super-2s, as we’ve done, is the right way to go here … to really ramp up the activity of NK cells, prevent desensitization, and combine it with this increased improved targeting of the neuroblastoma cells of an antibody … will give us improved therapeutic outcomes in these models. So, that’s where we’re going with this, and we’re very optimistic about it. And of course, we want to do that to help children, ’cause it’s often fatal disease.
I haven’t told you about every kind of immunotherapy; there are others for want of time, these are ones related, at least, to what we work on; but there’s a lot going on. It’s really an exploding field now, and I think there are going to be many advances in the fields coming … so, we’re very optimistic.
Let me summarize what I’ve told you today: that immunotherapy has revolutionized cancer therapy; that checkpoint therapy is now standard therapy for several different kinds of cancer; that many variations of this approach are in development, and different kinds of immunotherapies are in development. Most of those focus on T-cells, mobilizing T-cell responses, but many tumors we think may be invisible to T-cells, and therefore NK cells are an attractive target for additional immunotherapy implementation, and we think they offer great potential for treating many of the types of cancers that are not responsive to existing therapies.
And then, finally, this general message that the big breakthroughs come from basic research to uncover mechanisms, not so much from saying, “Okay, this is a bad disease. Let’s try and cure it.” ‘Cause if you don’t understand the disease, if you don’t understand the mechanisms … you’re really kind of wandering around in the dark. You really have to understand how the cells work, and how you can target them better to make this all work.
I will stop there. These are the members of my laboratory; I’ve been privileged to work with wonderful post-docs and grad students in my Berkeley lab over many years, and undergraduates. It’s been really a pleasure to work there, and we’re very excited about all the different work we’re doing. Thanks, I’d be happy to take questions.
David Raulet: There’s a question on the front here, yeah.
Audience 1: Could you describe in the context of what you’ve been speaking about … exactly what a cancer cell is? And how it develops?
David Raulet: Wow! That’s a … I mean, you know, cancer cells interestingly change, so it’s hard to pin them down on what they are. I mean, we know how they’re initiated, by mutations and in genes that control normal cell proliferation and homeostasis. Normal cells have various mechanisms to prevent them from growing inappropriately, et cetera, et cetera; but when the proteins that control that become mutated, you lose those controls and the cells begin to proliferate.
So, an early cancer is really just a normal cell that’s sort of lost the ability to control itself with respect to proliferation, and it may start growing. But it turns out there’s many mechanisms to try and suppress that cancer; some of them are intrinsic in the cell itself … it tries to commit suicide with so-called tumor suppressors … and others are extrinsically involved in the immune system, which attacks the tumor … and there’s other mechanisms, as well.
And what happens is as the tumor is growing, you can make variant tumor cells that escape these different controls, and then they evolve; and so, by the time … you know, many solid cancers only get diagnosed when you’ve had them for five years, and there’s a lot of evolution that occurs by that time. And as a result, they really change a lot; so this is why it’s so hard to answer the question. They become very capable of evading many of these mechanisms, which is why we have to find ways to re-invigorate them, to kill the cancer cell.
Audience 2: Yeah, the question I have is: infantile paralysis, the crippling disease that Roosevelt had? I understand that the drug used for infantile paralysis has been used at Duke University to shrink cancer cells in the brain. Are you familiar with that?
David Raulet: No, I’m not. Told you I wouldn’t be able to answer all of these questions!
Audience 3: I wanted to talk about the same thing … about the development, you know, the birth of the cancer cell. With the blood cancer, it’s right at the very beginning in the plasma, and … I don’t know, they call it the stem cell, but … maybe there’s something before that even. And it is true that the initial makeup of when you had your first diagnosis was one combination, and it changes over the years.
David Raulet: Yes.
Audience 3: And so, that’s why … the question is this immunology would address whatever state that the cancer cell is at at that time.
David Raulet: I mean, of course, you mean … would it work better with … at a stem cell stage as opposed to a later stage, or something like that?
Well, I mean, usually the problem is that cancer is usually … you know, by the time it’s diagnosed, it’s already progressed to these later stages; and so we have to treat the cancer you have, not the cancer you had. That’s one of the problems. So, by the time it presents itself, we know its features, and certainly the immune system can target it … so we do think that immune approaches can be effective against leukemias, for sure.
Leukemias, by the way … certain leukemias have shown to be susceptible to another kind of therapy I didn’t have time to tell you about, which is called CAR T-cells … which is a complicated process where you take T-cells out, you engineer them, and then you put them back in so that they attack your leukemic cells. And that’s proven to be effective in some blood cancers; not so far effective against solid cancers.