AAAAI Podcast: Conversations from the World of Allergy
The American Academy of Allergy, Asthma & Immunology (AAAAI) podcast series will use different formats to interview thought leaders from the world of allergy and immunology. This podcast is not intended to provide any individual medical advice to our listeners. We do hope that our conversations provide evidence-based information. Any questions pertaining to one\'s own health should always be discussed with their personal physician. The AAAAI Find an Allergist is a useful tool to locate a listing of board-certified allergists in your area.
AAAAI Podcast: Conversations from the World of Allergy
Innate Lymphoid Cells: Early Responders Shaping Allergic Disease
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Innate lymphoid cells or ILCs respond rapidly to help defend mucosal barriers, maintain tissue homeostasis and shape the adaptive immune response that follows. In this episode, Taylor A. Doherty, MD, FAAAAI, will discuss the importance of ILCs and what we know about these uniquely positioned cells in allergic disease.
Hello and welcome to Conversations from the World of Allergy, the podcast of the American Academy of Allergy, Asthma & Immunology. I'm your host, Dr. Rebecca Saff. Allergy and Immunology is a field that's evolving at an incredible pace, and staying current isn't just important, it's essential. In this podcast, we'll talk with leading experts about the latest advances, challenge how we think about core topics, and explore how we can put what we learn into practice to provide the best care for our patients. Innate lymphoid cells, also known as ILCs, are relatively new kids on the block in immunology, but we now understand that they play a crucial role in early immune responses. Unlike their adaptive immune counterparts, ILCs respond rapidly without prior antigen exposure and are strategically found at mucosal surfaces where they help defend against infection, can maintain tissue homeostasis, and chase the immune response. And that is cell we think a lot about, and today I hope we can learn more about their role from one of the experts in the field. I'm excited to welcome Dr. Taylor Doherty. Dr. Doherty is a professor of medicine and the chief of the Division of Allergy and Immunology at the University of California, San Diego. He runs an active research group which studies innate two lung responses that contribute to asthma and allergic airway disease, including the key role of group two ILCs. Dr. Doherty, thank you so much for taking the time to join us today and welcome to the podcast.
Taylor A. Doherty, MD, FAAAAIThanks so much, Rebecca, for having me.
Rebecca Saff, MD, PhD, FAAAAII'd love to start by learning a little bit about you. Can you tell us a little bit more about yourself and maybe why you chose to study type two immune responses?
Taylor A. Doherty, MD, FAAAAIAbsolutely. So I trained in internal medicine at UC San Diego and did my fellowship at UCSD as well and have stayed on as faculty. And during fellowship, I was doing a consult for a severe asthmatic exacerbation at Raydy Children's Hospital. And I remember rounding with Dr. Sima Seves, who the world of our field knows for her EOE research. But she had mentioned something very interesting about potential triggers for this particular child in terms of what might have triggered the exacerbation. And I had never heard anything about different fungi as allergens, and she mentioned alternaria that could have been a predisposition in terms of the trigger for this particular patient. And we get Santa Ana's in Southern California where the winds change from going west to east, and that change makes the crop molds disperse in the air, and we get spores and high levels when the winds also blow from east to west. And so that was something in the differential for this patient. And then I clung on to this idea that why are allergens different? When you look at all these allergens and think about IgE responses, why do they behave differently? And so that was sometime circa 2006. And I went into the laboratory initially studying airway remodeling and mouse models at La Jolla Institute with Michael Croft and also jointly with David Bodie's lab at UCSD. And these models were several months long, and though remodeling is very important to asthma, as we know now for progressive lung function decline, I became very interested still in the back of my mind in this potential uh allergen ultranaria and what it might do. So at some point, I began playing with models where in unsensitized mice I would give one challenge of ultranaria extract, keeping in mind with the caveat that this is not the same as the spores that humans inhale. But very interestingly, you could get a type 2 response one day after one challenge in an unsensitized mouse. So this totally broke down paradigms of what we knew as mouse models of type 2 disease, where you have to have a sensitization, and then weeks later or a week later or so, you end up coming back with the antigen or allergen again, and you get a bunch of eosinophils in the lung. And so the this work was really spurred on by one of my heroes, Hirohita Kita, who in the late 2000s and somewhere around 2011 really did a lot of work in this field that really helped propel me, where he identified the fact that the alarm in IL-33 released from the airway epithelium in response to ultra naria could rapidly induce this type 2 response. And so it was with that that I really sort of launched what I felt was my own niche. And as a coincidence, at the same time, the three papers that were sentinel papers describing what we now know as ILC2s, these lineage negative innate lymphoid cells that produce high levels of type 2 cytokines, were basically being studied for their effects in Helminth models and type 2 disease that is independent of T cells and IgE. And so once that all sort of coalesced, my sort of passion with understanding alternareas response, along with the discovery of these cells that were called three different things at the time, now known as ILC2s, that then propelled my career to try to understand mechanisms of how they might be contributing to airway disease and type 2 immunity.
Rebecca Saff, MD, PhD, FAAAAIThat's great. I'm actually fascinated with the Santa Ana winds. Does that really change the allergen exposure to the population there, depending on which way the wind is blowing?
Taylor A. Doherty, MD, FAAAAIAbsolutely, but it's tough to say it's just allergen because so much happens within the air in terms of particulate matter and dust and other things that can contribute. There's a study done by Kaiser many decades ago looking at albuterol use during Santa Ana's, which significantly went up. But it, you know, it's hard like our very complex biological systems and ecosystems to really pinpoint that it's one particular allergen.
Rebecca Saff, MD, PhD, FAAAAIFair enough. And I think the you're what you were talking about with Osrenari is a great place to start about the fact that you see this kind of rapid activation. Um and it's not, you wouldn't expect from the adaptive immune response, which takes time to develop. So what activates ILCs? How are they how are they activated differently than the kind of adaptive immune response?
Taylor A. Doherty, MD, FAAAAIYeah, so the the activation, as you mentioned, is is rapid. And one of the reasons it's rapid is you don't have to have this interaction between a peptide MHC class 2 from a dendritic cell interacting with a T cell, sort of the lock-in-key mechanism. If you rapidly produce, say, IL-33, one of the sort of three alarmins that we talked about, in addition to TSLT, as well as IL-25, you then have potential responding cells that if they don't need that lock-in-key mechanism, can then be rapidly activated by these alarmins. And the way ILC2s at least were discovered, and I think we'll just maybe in a minute here mention the ILC1s and threes, because this ILC2s are part of a larger family of ILCs. The way they were discovered is giving IL-33 and even earlier studies giving IL-25 to mice and showing that you can get a type 2 response. You're not giving any allergen or antigen, there's no nothing besides the cytokine, and so you're getting this antigen-independent type 2 response. And so that really sort of spurred the field to discovery, but then also to better understand how the epithelial alarmins can activate ILC2s. And at that time when we were studying the effects of IL-33, and it really felt like everybody was studying the effects of IL-33 on these cells, we started to look at other mediators that could activate them to do something novel and hopefully add to the field. And we did an old school microarray on ILC2s after mice were given alternaria and found that cysteineoleucotriene 1 receptor was highly expressed on these cells. And then we did some studies to show that ILC2s can not only be activated by epithelial alarmins, but can also be activated by, in this case, cysteineoleucotriens, and then down the road, prostaglandin D2 can also activate these cells. And so one of the things that we have to talk about, though, is that as soon as we talk about activation, you have to talk about the suppression of these cells. Because it really is sort of the all the inputs coming into these cells, which ends up being the ultimate output and effect on their cytokine production. So just like we have the pro-inflammatory stimulatory lipid mediators, there's also lipid mediators like prostaglandin E2, prostacycline that can actually restrict ILC2 responses as well. And in the last 10 years, and this is very exciting work done by many, many impressive groups, we've learned that neuronal input and endocrine inputs really shape in different organs, different contexts, how ILC2s respond. It can be either activating or inhibitory or sometimes sort of modulating and do a little bit of both. And then sort of the fourth group, large group, that is also very exciting is this metabolic dietary stimulation, suppression, modulation as well. So it turns out that the microbiome, it always feels like we always go back to the microbiome, right, when we're talking about immune responses, but that there are certain caloric states and micronutrient status within an organism that could lead to ILC2 changes that could either be sort of protective, homeostatic, repair, but could also, in the wrong context, uh drive pro-inflammatory responses. So that's a long-winded answer to put into buckets. But we started with alarmins and we've gone through many other types of ways to modulate ILC2s. And I've left out some other things like co-stimulatory molecules just because of time, but there are great reviews on this particular topic.
Rebecca Saff, MD, PhD, FAAAAISo the ILCs primarily in the mucosal surfaces and other epithelial surfaces, how do they how do they interact with the environment like that?
Taylor A. Doherty, MD, FAAAAISo it mainly is thought to be to due to indirect alarm and recognition or say neuropeptide stimulation or inhibition, as well as from other immune cells that can provide signals, like I mentioned, say with the lipids. And so there are cases where ILC2s have been shown, especially in vitro, to directly respond to something, say like a TLR signal from a pathogen. But in general, sitting at these barriers as sentinels, they really do rely on the entire input from the milieu from other cell types, uh, whether it's cytokines, lipids, or other potential mediators that shape the entire response. And we should be a little careful here because the field's evolved enough to where when an ILC2 is quote unquote activated, there are many different fates of where that daughter population can end up. And so it actually really speaks in the human ILC2 single cell studies really support this, that there's so much heterogeneity even within these populations. So I think that it's good for us to have these basic paradigms, but there's so many ways that an ILC2 population can shape itself in different ways.
Rebecca Saff, MD, PhD, FAAAAIWell, I do want to think about kind of there's these ILC1, ILC2, and ILC3 kind of subclasses that we think about. Um and they they're comparable to kind of what we think of of TH1, TH2, and TH17. And how useful is that? How similar are they? And where does it break down and they're actually quite different?
Taylor A. Doherty, MD, FAAAAISo just for uh getting on the same page, ILC1's attended TH1 cells highly express the transcription factor TBET and produce interferon gamma along with other type 1 cytokines, and ILC2s, as we've been talking about, produce type 2 cytokines, including initially IL-5 and 13, but also IL-4, and sometimes people throw an IL-9 there, but that might be its own subset. ILC3s produce IL-17 as the quintessential cytokine from that population, and they're akin to TH17 cells. So no one, as far as I know, have called them ILC17s, but just to make everything more confusing, we have to have these different numbers. And ILC1s are also grouped with natural killer cells as well, because they are innate lymphoid cells that produce high levels of interferon gamma. So when we talk about ILCs in terms of the lineage negative population, we're kind of excluding NK cells, but just so everybody understands, they're often grouped because of the function and expression of T-BED. And so to get to your question, I think that the parallels are important, especially for people learning this. I think for incoming fellows in our field, as well as anybody starting to entertain what these cells do, it's good to start with this paradigm. But you mentioned the plasticity, which we'll talk about. That's where it really breaks down. And then the other place that it breaks down is that the T cell subsets are antigen-specific, and almost in all cases that I know of need to have that TCR signaling to really become activated, produce cytokines as well as proliferate, whereas the ILC subsets don't have that antigen recognition and can be activated as we've talked about with other types of inputs like cytokines. There's also a kinetics difference. So because ILCs are largely at the barriers, whether it's the airway or the skin or the GI tract, they can be rapidly activated. There's no having to go to a geranium lymph node by a dendritic cell and then find the right partner T cell and then undergo clonal expansion and then back into the tissues. The kinetics are very early within hours of whatever the stimulus may be that could activate one of these populations. And the plasticity, just to go back to that, can be similar in some ways to the T cell subsets, but also can differ significantly, or just too much is unknown. So I would say that's one area. And then also the numbers of ILCs. There's a reason we did not find these cells as a scientific community until the 2000s. There was hints of them in terms of ILC2s within the time period after 2000, somewhere up to 2010, when they were clearly reported and better defined. But the reason is because they are so rare, and yes, they expand in our models, but you have to exclude a bunch of cells. I always joke that in my lab we pay for a bunch of antibodies for cells we don't even look at because these cells are lineage negative, meaning we have to exclude T, B, and all other cell types that have lineages just to find the population of ILCs there. So that's one reason it took so long to discover them, and uh one reason that they are very different than the T cell subsets, which depending on the model, you can find lots of T cells. And there's some other differences too, just real quick to wrap up on this point, when it comes to the neuroendocrine modulation, that looks like so far it's more important for the ILC populations, specifically ILC2s, than it may be for, say, TH2 cells.
Rebecca Saff, MD, PhD, FAAAAIIt's funny, they're really looking for the absence of all those other markers in order to identify them. But but we knew there had to be something there that was making that early IL-5, IL-13 to get that response going.
Taylor A. Doherty, MD, FAAAAIRight. And the reporter mice, the IL13 reporter, IL-4 reporters, those really helped to figure that out because without lighting up these cells that were not T cells, it was it would have been a lot more difficult to characterize them.
Rebecca Saff, MD, PhD, FAAAAISo once they're activated, so the alarms are activating and kind of this neuroimmune communication, um, how are they forming the their effect on the adaptive immune response? Is it purely kind of what they're making, or are there other things that they're doing that's helping to shape that?
Taylor A. Doherty, MD, FAAAAIThat's a wonderful question, and so important when we think about chronic disease and whether it's sensitization in a type 2 system, or we're talking about our patients where we see this type 2 signature, and we're talking about what comes first, the chicken or the egg, and ILC, they're innate, were they only important in the beginning, or did they then they kind of go away in terms of function, and then the once the TH2 adaptive CD4 cells take over and IgE is there, they don't matter anymore. So a lot of these questions are still being addressed, but I will say that they're more like instructors and not just first responders. So when it comes to adaptive immunity, uh our lab and others had shown that ILC2s could make lots of IL-4. IL-4 is a critical cytokine for the differentiation of CD4-positive TH2 cells that can then support downstream IgE class switching and B cells as well. And so not only do you get activation of ILC2s producing these type 2 cytokines that can have effects on bringing in eosinophils and airway hyperresponsiveness and in remodeling mucus production, but you can also then really promote adaptive TH2 cell differentiation, which can then take over, but then also feedback to continually activate ILC2. So it's a sort of vicious cycle. And I think that especially in diseases where we don't think a lot about antigen specificity like AERD, you have these sort of effector adaptive cells that were brought in, and they can then produce mediators that activate ILC2s and get into this cycle. And since then, with the IL-4 story, we've also learned that ILC2s can express MHC class II and actually do some antigen presentation themselves. Now, this is most of what I'm talking about was initially and more fully shown in mice, so just with that caveat. And these are rare cell types, so how much ILC2 MHC class II really shapes a T cell response in a human, it's hard to say, but there is definitely the potential there along with co-stimulation from ILC2s to T cells and dendritic cell licensing by ILC2s. Most recently, KEDA's group had shown that GMCSF from ILC2s could then also in a mouse model system shape how the adaptive type 2 response is created. And so this is ongoing work, but it is clear that ILC2s aren't just early gatekeepers of the type 2 response and then hand a torch to the T cells, and that's that. There's a lot of reciprocal effects with both uh adaptive and innate type 2 responses.
Rebecca Saff, MD, PhD, FAAAAISo they're they're really chronically helping to drive that allergic response.
Taylor A. Doherty, MD, FAAAAIRight, right. So the initial shaping and they're highly active. We know in our patients, samples from patients with, you know, say severe asthmatics that you look in their sputum, and several groups have seen this, where even people on systemic steroids, there are still highly activated ILC2s in their induced sputum, suggesting that even though this is a chronic disease, these cells continue to pump out cytokine in some cases.
Rebecca Saff, MD, PhD, FAAAAIAre are ILCs less responsive to steroids than T cells?
Taylor A. Doherty, MD, FAAAAISo that is a wonderful question. Um, and that's something that I think is context dependent in in many ways. So we looked at the effects in Nasal polyp ILC2s cultured with varying concentrations of steroid and largely saw that the population could be reduced. And our mouse models, where we looked at steroid in an IL-33-driven alternaria model, also showed that high doses of systemic steroids could inhibit or basically induce apoptosis. So you could actually deplete a lot of the ILC2s. And Rafael Alam's group at National Jewish did outstanding work, both human and mouse, human asthma samples, showing that actually TSLP imparts the steroid resistance to ILC2s. So this makes it difficult to answer your question as sort of just a one brushstroke response, because in certain contexts, and mainly the literature suggests that TSLP can promote steroid resistance in ILC2s. And the CD4 story, I think, is different because you really would have to do a head-to-head comparison with TH2 cells that are activated and of course are have some antigen recognition going on. And I don't know if anybody's really compared that other than to say that patients treated with systemic steroids, asthma patients, where you find the ILC2s, they're not finding as much in terms of activated C D4 cells in some cases. So it's just hard to know, obviously, in vivo, if that's a direct effect on the CD4 cells or not.
Rebecca Saff, MD, PhD, FAAAAISo what do we know about ILC2s kind of in these more specific diseases? Is does the role in asthma or nasal polyps or atopic dermatitis, does it differ, or do we think it's just kind of overall part of that TH2 response?
Taylor A. Doherty, MD, FAAAAISo I think it does differ. I think that when we think about the diseases, and I mentioned AERD, uh aspirin exacerbated respiratory disease, or NSAID exacerbated respiratory disease, which I love being able to say nerd at times, anyway. So when you think about that as a sort of, it's possible they're self-antigens, but we don't think about that the same way we think about, say, food allergy or allergic rhinitis, where there's a more clearly defined antigen, an exogenous antigen that's driving this particular type 2 response. And so I think it is different because the ILC2 could play a more prominent or at least a different role in these sort of antigen-independent responses. And once you have a vicious cycle set up that I mentioned earlier, I think like with severe asthma, then the ILC2 could be, yes, contributing to the ongoing type 2 milieu, but independent of that could also be also shaping other immune responses in terms of adaptive immunity and reduction in antiviral immunity because we get this balance between sort of antiviral immunity and the type 2 response. And when I say antiviral immunity, I don't mean so much talking about TH1. I'm talking about your sort of early interferon response that you're getting to a viral infection, which we know plays a big role in many cases with different viruses in asthma pathogenesis. So you have a lot of yin and yang that it's playing a part of, where it's not just, okay, this is just another type 2 cytokine producing cell, and that's that. And I think it's so much more uh complex. But when we look at diseases that are more clearly IgE mediated, you kind of go back to two things. One would be did ILC2s promote the sensitization in the first place to create the milieu, the IL-4 production, let's say, to develop antigen-specific IgE. And then also in terms of amplification, um, we know that at least in some mouse models of, say, food allergy, that IL-33 can play a role even during the sort of effector phase. And so you're talking about alarmins and ILC activation later in these very antigen-specific processes. But I do think that there are some differences, and now, again, most of this in mice, but differences in that sort of type 2 disorder versus, say, something like AERD. And ILC2 is really nasal polyps because they're taken out, as we know, for the care of our patients, and so they're a lot easier to study in nasal polyposis versus other things. We were talking about GI disease, then EOE comes to mind, but it is still easier to find lots of ILC2s in nasal polyps, and they are likely playing a much bigger role in CRS with nasal polyps than in, say, food allergy. But a lot of that's speculation because just when we think we know something, um, something else comes out, and I wouldn't have even thought that they were big players in some of these other type 2 antigen-specific disorders.
Rebecca Saff, MD, PhD, FAAAAISo it sounds like even in these kind of IgE-mediated places where we know that allergen-specific IgE activates mast cells, and we think about that, you think ILCs are playing a role there just as much as in the place with where there isn't a specific antigen, like in nasal polyps.
Taylor A. Doherty, MD, FAAAAIMaybe not just as much, but still a significant role. So it's interesting you mentioned mast cells because not only could Ile-4 from ILC2s promote B cell IgE class switching, which then, if allergen-specific, can dock with its FC portion onto a mast cell, and sort of the loaded gun is ready to fire once the allergen is present, but ILC2s also make a significant amount, depending on context, of IL-9, which promotes mast cell accumulation in tissues as well. And because mast cells make lots of prostaglandin D2 and cystenole leucotrimes, that sort of back and forth stimulating each other could promote some of these antigen-specific diseases, but it is so hard to say when you're talking about, say, peanut-induced anaphylaxis during the event of what the patient's having, how much ILC2s are promoting that. Because we largely think that that is a mast cell-driven response in terms of severe reactions to uh food food allergens.
Rebecca Saff, MD, PhD, FAAAAISure. So probably playing a role in the feedback loop, but still the primary effector cell there is that mast cell and medium.
Taylor A. Doherty, MD, FAAAAIRight. That's that's uh to me at least what makes the most sense.
Rebecca Saff, MD, PhD, FAAAAIAnd then we have all these biologics now that target different pathways, which can some of which we've talked about with the TSLP and L13, L5. How much of the effect of those may come from the ILC2s versus kind of how we traditionally think of them working on more of that TH2 response?
Taylor A. Doherty, MD, FAAAAIThat is a wonderful question, especially as more and more biologics become available. And what I will say as a bottom line, just to start with, is that we need more ILC2 endpoints and all these amazing clinical trials that are being done. I know that there's always so many endpoints, and some of it comes down to cost and who can do what in these trials. But I think that if we had more ILC2 endpoints from tissue or at least from blood, we would be able to better understand because there is still a paucity of data despite all these clinical trials with these very targeted therapies that go after type 2 and alarm and pathways in terms of the ILC2 endpoints. So let me just start with tesopelamab. So I mentioned that TSLT, which tesopelamab blocks, can confer steroid resistance in some cases to ILC2s. But the one of the main trials, the Cascade study, really looked at subgeocostal eosinophils, and those were significantly reduced. And we know that the type 2 signature can be changed with tesopellamab, but we don't have really any current data that I'm aware of regarding an effect on ILC2s. And that would be most promising just because this is the first FDA-approved anti-alarmine therapy that we have for type 2 disease, mainly so far with nasal polyps and of course asthma. Interestingly, dupilumab, which blocks IL-4 receptor alpha, has had there have been some studies that have looked at peripheral blood ILC2s, and what we have to be careful about, just like with the eosinophil story in the blood with dupiliumab, is that are you really having an effect on these cells in terms of activity or trafficking or both? And so with the mechanisms whereby eosinophils get out of the bloodstream and into tissues, ILC2s use integrant pathways as well that could potentially be blocked by dupiliumab. And so some studies have shown an actual increase in ILC2 numbers. And even with, say, Mepalizomab, interestingly, there can be an effect on these numbers. But then at least one study that took out ILC2s after several months of treatment with Mepalizomab showed that there was a reduction in their activity. And so it's just hard to know what's happening where, and you are in those cases just capturing the blood ILC2s that could also just be coming from the bone marrow. And is there some indirect effect? Because we don't generally think of the IL-5 pathway being critical to activate ILC2s. We think of IL-5 coming from ILC2s. However, and this is a little bit controversial in the literature, there is at least one report showing that benralizomab could have an effect on ILC2s directly, and one group found that IL-5 receptor can be expressed on ILC2s. So maybe there's a direct depletion there, but I think there's more to come there. But the bottom line is that when you inhibit type 2 inflammation, especially if you're blocking, say, a stat 6 pathway through IL-4 receptor alpha, you you would expect that ILC2s could indirectly be affected as well. And so it's very hard to know without depleting ILC2s directly, which I'm actually against, even if you could do it, because they're so hard to detect in the first place and find a specific marker. But there's no way to tell where you are in the chain of events in terms of the effect on ILC2s. And nearly all of these studies haven't looked at tissue ILC2s, which I'd be most interested in, because those are the ones that are uh wreaking havoc basically in terms of organ disease in our patients.
Rebecca Saff, MD, PhD, FAAAAISo we talked, we're talking about that initially the activation of ILC2s is related to TSLP, IL-33. Do we know if that similarly maintains their activation, or are there other signals that are going on in these kind of more chronic inflammatory states?
Taylor A. Doherty, MD, FAAAAIYeah, that's a wonderful question. And that's something without blocking we don't really know in terms of, I guess we are in some ways. We are blocking with, say, Tesopelemad, blocking TSLP in a chronic disease. Alarming signatures are something that can be elevated throughout chronic disease. And I think we have to get away from this paradigm in my mind that this early thing happens because all of our cartoons have pollutants and allergens and viruses, other pathogens at the epithelial border, and then you get your alarmins and then ILC2, sort of this stepwise thing. And we think of innate immunity first, handing off to adaptive immunity. But the reality is persistent innate activation, and that includes alarmins. We have examples of that, both in mouse models and also identifying high levels of IL-33 and TSLP, less so IL-25, but in some cases IL-25, the sort of third stepchild alarmin. You can also see them in these chronic diseases. So therefore, we know that this is propagating. And you can see that, say, with a viral infection, and a type 2 asthmatic gets a viral infection, and this has been shown in humans that the ILC2s are activated and IL-33 goes up in these viral infections. And so it's also another way to explain against the antigen-specific system that didn't make sense to cover everything we see clinically. And so ILC2s activated in chronic diseases by alarmins, I think, is the current paradigm that you have parallel pathways as opposed to stepwise pathways in type 2 disease.
Rebecca Saff, MD, PhD, FAAAAII know there's not an anti-IL-33 approved yet, but it'll be there are at least, I think, phase two and phase three studies going on with that. And so it'll be interesting to see how it differs from the effect we see of anti-TSLP.
Taylor A. Doherty, MD, FAAAAIYeah, no, that's a good point. I think IL-33 is tricky. I think the TSLP story's been very successful in terms of the biologic and effects on patients. And interestingly, not surprisingly, these alarmins don't only have type 2 effects. And so this is in part why there is some efficacy for tesopellomab in non-type 2 asthma as well, because there can be sort of this pro-neutrophilic or ILC3 TH17 side that these alarmins can also promote. And so we know our patients are complex and there's a lot of mixed granulacytic, mixed endotype disease. And so the 33 story is tough because there can be homeostatic roles for 33, and in mice, 33 with alternaria especially, look like it was the dominant cytokine to activate ILC2s. In humans, and I think I'm surprised like a lot of other people that for COPD it may actually be more promising in terms of efficacy than in the space of where we already have these amazing anti-type two biologics in asthma, and so you know the jury is still out, people are still doing trials, and there will be a role, I think we just are in the process of defining it for IL-33.
Rebecca Saff, MD, PhD, FAAAAISure. No, I think it'll be a fascinating story. And then we were talking a little bit about the fact that ILCs don't have these antigen receptors. We don't think they really have a memory response. And yet there's my understanding is now we're starting to see some memory-like responses from ILCs. So how do I how does ILC exposure to a stimulus kind of change the response over time if you get a rechallenge or early exposure versus kind of later on in life? Um what do we know about the way ILC2s are shaped themselves?
Taylor A. Doherty, MD, FAAAAIYeah, this is a wonderful question as well in terms of the implications for re-exposures, right? When you're talking about innate immunity responding in a stronger fashion the next time you're exposed, and do you get this sort of staircase effect of more ILC2s, more active, ready-to-fire ILC2s with each subsequent exposure? And so the work really has been done in mice. Rafael Alam, who I mentioned before, has done amazing work looking at models where ILC2s take center stage, there's no T or B cells in these mice, and the ILC2s actually undergo epigenetic changes after alarm and initial activation, that then upon re-exposure, they're completely different. There's chromatin remodeling and the changes in terms of the expression that lead to enhanced activation on a per cell basis is really exciting because some people talk about is it trained immunity, is it actually memory? I think some of that personally is semantics. I think the important point is that we always think of adaptive immunity, especially, say, when it comes to vaccination, where you want to be protected and have a ready-to-go adaptive immune system upon re-exposure. In this case, and it's been shown, I think, initially with N-K cells that are also innate, but in this case we're now seeing other ILC subsets that show this memory-like response. Keeping in mind that when an ILC2 that's so so-called naive or non-experienced gets activated, not all of them go to this memory pool. You can get some activation-induced cell deaths, you can get actually some that turn into, with the plasticity, into say ILC1-like, you can get into sort of these IL10, which are more immunosuppressive or anti-inflammatory ILCs. And then with the plasticity as well as the memory, I think that all depends on context in the particular tissue. But the more we learn, the less we know, I think is the message here, and that this is particularly clinically important whether or not in humans we're seeing this increase over time longitudinally with ILC2 pools, and could there be a way to inhibit sort of that initial activation to where you can reduce the pool of memory ILC2s so that the subsequent exposure, you don't get the same level of activation. So these are all interesting questions. A lot of it does, as you can imagine, start with thinking about early intervention with some of these particular stimuli.
Rebecca Saff, MD, PhD, FAAAAII like the term experience style C2s rather than memory. That's a that's a good uh trait.
Taylor A. Doherty, MD, FAAAAIYes. It depends who you're talking to, right? You've got to be careful with uh you can get in long conversations about uh these particular words, right? Because I I actually don't still am getting used to the idea of them calling them memory just because of my initial programming.
Rebecca Saff, MD, PhD, FAAAAIAnd then let's talk a little bit about the plasticity. You initially thinking ILC2s or ILC one is kind of terminally differentiated, but now there's kind of more and more evidence that actually there's some plasticity, and an ILC2 can kind of revert back more like to an ILC one if it receives different stimulus. What do we know about the plasticity between the cell types?
Taylor A. Doherty, MD, FAAAAISo let me start with one that I think is more recent and more clinically relevant. So Rhomassamia McMaster, who's an outstanding ILC researcher and overall asthma researcher, has taken induced butum from patients with severe asthma and found these sort of hybrid-like cells and these that are ILCs that produce type 2 cytokines, but also have a type 3 signature as well. And these particular ILC2s, when you play with them in vitro with a cytokine mil U that includes IL-1 beta, IL18, so some of our sort of inflammation pro-inflammatory cytokines, can then start to morph into what you find out of the patient in these particular asthmatics as these hybrid ILC2, ILC3. So a lot of this is not esoteric. These are things that are relevant to what's going on in terms of the inflammation in patients. And then to backtrack from that recent story, and going back to what you mentioned, in 2016, several papers showed that if you add IL-12 and you block a few different things and create this cocktail with ILC2s from humans, that you can actually switch them to be interferon gamma producers and ILC1-like cells. And some people even call these X-ILC2s, and it it gets the nomenclature gets a little crazy, but a lot of them end up being more or less hybrids where they're sort of teetering, and just because they can produce this doesn't mean they can't produce this at the same time. It all depends on what they're stimulated with and when you measure these things. So I used to always say ILC2, but now I'm trying to be more careful and just say ILCs or IL-17 producing ILC2s, or to be very clear, because the plasticity is so prevalent across all of these populations. Yeah, and and you know, in the same population of cells, you call it one day after some stimuli, even in in in vivo. So you could then say, oh, I can't call them that anymore. And so that also goes to a point I'd like to make that kind of goes along parallels with the plasticity, and that's that early studies said this is how you identify ILC2s. And a lot of it was based on peripheral blood in humans and not so much in flame tissue and in mouse models, which could have completely different markers that are up and down. And Rafael Alarm's group showed that this is true in humans, our lab did in mice, that we're actually missing a lot. So we think that because we were told that these cells should express the IL-7 receptor, otherwise known as CD127. Well, it turns out when you really do the right omics and the sorting and really figure out what's going on in terms of what the cells are producing, that there's a lot of CD127 negative ILCs, I'll just say ILCs for now, that are producing type 2 cytokines. And so we're, as soon as we think we're advanced in the field, we're also a little bit in infancy because a lot of early studies said you identify ILC2s by CRTH2 and CD127, CRTH2 in humans is a receptor for prostaglandin D2, and is expressed certainly on a on a population of ILC2s, but not all ILC2s express that. So along with the plasticity story, you get the compounding issue of difficulties with identification of these cells. Which, of course, I can say, hey, all these clinical trials should look look for ILC2s. Now doing that is a bigger challenge than just saying that.
Rebecca Saff, MD, PhD, FAAAAIYeah, just identifying them as part of the issue.
Taylor A. Doherty, MD, FAAAAIRight. Right.
Rebecca Saff, MD, PhD, FAAAAIAnd then we've learned so much from different inborn errors of immunity about different parts of the immune system and kind of what losing something, you know, the effect it has. Are there any inborn errors of immunity that involve ILCs?
Taylor A. Doherty, MD, FAAAAISo it's not clear that ILCs are isolated enough in inborn errors of immunity to say, okay, this is their role or this isn't their role. But certainly there's a few interesting things. There's one study in nature immunology several years ago that showed that skid patients that were their IL-2 receptor mutations or JAC mutations, that when they were transplanted, that the T cell compartment, B cell compartment came back, but ILCs did not. And those patients, as healthy as a transplanted patient could be, did not appear to be particularly predisposed to certain infections. And so some people point at that study and say, well, that sort of isolates the role. And you know, I I could I would also argue that the care of these patients is different, and of course, exposure is also a factor, and transplanted patients are different, of course, than people with an immune system that's functioning from birth. And so, but there is something to be at least acknowledged from that as well. One particular disorder that I know is being studied is Omen syndrome that has rag mutations, and we often use rag mice that don't have T and B compartments or very limited T and B compartments, but do have ILCs. If people have looked at the very small population of unfortunate individuals that have Omen syndrome where there is a defect in RAG, and I know there was initial studies looking at ILCs being activated, actually. I don't know if it's a compartment issue. You don't have T and B cells, so you have ILC2s gone awry, and maybe that accounts for some of the awful dermatitis that these patients get. But there really isn't enough, just like the clinical trial statement that I made, enough ILC2 endpoint study for the IEIs. And also with how rare some of these can be, I think that what's going to have to happen is that techniques like single cell sequencing are going to have to get a lot cheaper. And hopefully in 10 to 20 years, we're so good at doing very rapid, multi-unbiased assays on these particular patients, so we really have a broader picture as opposed to I just am going to publish because I looked at T cells in these individuals. And so without that, it becomes very difficult to ask the investigators, oh, why don't you look at all populations in the immune system? And by the way, why don't you look at them with this stimulation, with that stimulation, and compare them to all these controls? So I think that that's an area that we should just add on all ILC subsets because the hope is that we can then learn at least, and it might be a developmental knowledge as opposed to a real-time activation knowledge with regards to ILCs and how they may or may not respond when a certain gene is mutated. So a lot to be done there.
Rebecca Saff, MD, PhD, FAAAAII think that's fascinating, this idea that in these patients where they don't have certain T cells or don't have T cells at all, that ILCs could expand to kind of fill some of that gap and be have this chronically activated phenotype in an attempt to kind of cover. I hadn't really thought about that, but what an interesting thing to look at.
Taylor A. Doherty, MD, FAAAAIRight. I think the fact that ILCs can shape so much, as we talked about, on their own, we need to also start to move the field forward as much as possible into humans because people say, well, what's the next step? Where do we need to go? And the mouse models have allowed us to learn so much. And I'm also in the same group that is like it's really pushed the mouse model, but not until we get better at looking at these populations in tissues will we really know the effects they may have. The good news is we have very targeted therapies, so we can ask real questions now. When you deplete this cytokine or get rid of this cell type, what happens to the ILC population? And so I think that there's great opportunities as opposed to the more broad-based therapies we gave 20 years ago, i.e., mostly corticosteroids, to really ask these interesting scientific questions about this population.
Rebecca Saff, MD, PhD, FAAAAII think that's a fantastic place to kind of uh finish up that we're really learning so much more as we have these targeted therapies. And um I would be really interested to kind of, as a final question, so for patient, for people who are primarily clinical who are listening, what are the kind of concepts about ILC biology that they they should remember or should be looking for as we kind of see new studies coming out?
Taylor A. Doherty, MD, FAAAAIYeah, so I think that one of the key things for those that take care of patients, because we are counseling patients that are educated, of course, by different means, which may be good or bad or misinformed, or some that are completely informed and really expect us to have the knowledge to say, this is what these therapies do, and to understand that we've gone from thinking about allergic inflammation and type 2 inflammation being the same thing, to you can have a non-allergic type 2 inflammation. Now, when I say allergic, of course, I'm meaning sort of the IgE antigen-specific pathway, and there's a Big Ben diagram there. But the fact is that ILC2s changed the paradigm because they were sort of the missing link when it came to how can you get the this type 2 inflammation. My patient has eosinophilic asthma, their FENO is super high, but when I do their IgE testing, there's barely anything there to really explain or to go along with this. And so that disconnect can be best currently explained by ILC2s. And I'm not totally, I think, crazy to say that at some point when we get better at using them as biomarkers, that likely use eosinophils, that there could be a potential role for looking at ILC changes. Some people have done this with before and after allergen immunotherapy and seen populations of ILCs change from more pro-inflammatory to less. And so we have to know about these cell types because we need to be able to educate our patients, understand how therapies work, but also the fact that someday they may be looked at in clinical practice, especially as biomarkers. So I would just say the message is clear that within our very evolving, amazing field, especially scientifically, including immunology, that to be able to be in this moment where we really can learn so much from targeting individual pathways, that not only within our field we should look at these cell types, but also if you look at oncology and say autoimmunity rheumatology, where they use different, whether it's checkpoint inhibitors or other biologics, to look at cells that matter to our field, like ILC2s a lot. So I think there's so much to be gained on the sort of clinical translational side as well.
Rebecca Saff, MD, PhD, FAAAAIAnd maybe we'll even discover yet another new cell type that's uh rarely present but has a plays a big role as we look.
Taylor A. Doherty, MD, FAAAAII might be retired by then, but uh well thank you so much.
Rebecca Saff, MD, PhD, FAAAAII think this was fantastic, and I know that um hopefully we're all better informed by ILCs and we'll be watching for these studies that are coming.
Taylor A. Doherty, MD, FAAAAIGreat. Well, thanks so much for having me on. Appreciate it.
Rebecca Saff, MD, PhD, FAAAAIWe hope you enjoyed listening to today's episode. Please visit aaaai.org for show notes and any pertinent links from today's conversation. If you like the show, please take a moment to rate and subscribe through wherever you download your podcast. As a reminder, this podcast is not intended to provide any individual medical advice to our listeners. We do hope that our conversations provide evidence-based information. Any questions pertaining to one's own health should always be discussed with our own personal physician. The Find an Allergist Search Engine on the Academy website is a useful tool to locate a listing of board certified allergists in your area. Use of this audio program is subject to the American Academy of Allergy, Asthma and Immunology Terms of Use Agreement, which you can find at aaaai.org. Thank you again for listening.