Good afternoon, and welcome to the Xilio Therapeutics Virtual Program Spotlight on XTX301, a tumor-activated IL-12. At this time, all participants are in a listen-only mode. A question-and-answer session will follow the formal presentations. If you want to ask a question, you may do so at any time throughout the program by using the Q&A function below the webcast player. As a reminder, this program will be recorded and a replay will be made available on the Xilio Therapeutics website following the conclusion of the event. At this time, I would now like to turn the call over to your host, Stacey Davis, Chief Business Officer at Xilio Therapeutics. Please go ahead, Stacey. Thank you. Next slide. Hello, welcome to Xilio Therapeutics virtual program spotlighting XTX301, a tumor-activated engineered IL-12. I'm Stacey Davis, our Chief Business Officer, and I'll be moderating this live presentation. Before we get started, I would like to remind everyone that statements we make on this webcast will include forward-looking statements. These statements are based upon management's current expectations and beliefs as of December 1st, 2022, and they are subject to risks, uncertainties and other factors, including those set forth in the Risk Factors section of our SEC filings. In addition, any forward-looking statements made on this webcast represent our views only as of today and should not be relied upon as representing our views of any subsequent days. Except as required by law, we specifically disclaim any obligation to update or revise any forward-looking statements. Next slide. The three main focus areas of today's discussion are the unmet needs in cancer, focusing on the differences between cold and hot tumors, XTX301, a tumor-activated engineered IL-12, and Xilio's development plans for XTX301. Next slide. Joining me on today's call are René Russo, our Chief Executive Officer, who will provide introductory remarks, Dr. Diwakar Davar, a key opinion leader and Assistant Professor of Medicine and a Medical Oncologist/Hematologist from UPMC Hillman Cancer Center, Uli Bialucha, our Chief Scientific Officer, who will review preclinical data for XTX301, our tumor-activated engineered IL-12, and Marty Huber, our President and Head of R&D, who will review the clinical trial design for our planned phase I trial for XTX301. I would now like to turn the call over to René Russo, our Chief Executive Officer, for brief introductory remarks. Thank you, Stacey. Good afternoon, everyone. If we can turn to the next slide, please. Thank you. Over the last decade, the field of immuno-oncology has given many people living with cancer new hope for long-term cures, right? That is really the hope and the meaning of the field of immuno-oncology. Unfortunately, we see that true potential of IO continues to benefit really a small subset of patients. The problem holding us back, we believe, is that the way we're delivering these therapies today exposes the entire body to these powerful immune stimulating effects, which leads to serious adverse events that ultimately limit us in terms of the effective doses we can administer. It limits us in terms of the combinations of IO therapies we can give, and in some cases has completely eliminated very promising therapies like IL-12 for patients. We believe at Xilio there is a way to solve this problem and to be much more sophisticated and precise in how we give these potent cancer therapies. Our approach is to utilize a tumor's own biology against itself. Specifically, we're leveraging the high activity of matrix metalloproteases in the solid tumor microenvironment to essentially trick the tumor into activating these highly potent treatments once they're inside the TME. By doing this, we can localize those high concentrations of potent antitumor medicine exactly where we want it, while protecting the rest of the body, including healthy cells and tissues, from unintended toxicity. If we're successful in doing this, we envision a new paradigm of cancer medicine, where future cancer therapies can be given at unprecedented high doses and in powerful novel combinations that are delivered directly to the tumor with that geographic precision and attacking the cancer really at its source, while protecting patients from that collateral damage and severe side effects. That is our goal. Can you turn to the next slide, please? Thank you. Before we jump in and begin the discussion of IL-12, I'd first like to share some very recent emerging clinical data from our first cytokine program in the clinic, XTX202. This is a tumor-selective IL-2 molecule, and I want to share some of these data to really demonstrate how the platform technology works. What you see here are data from a 51-year-old male patient with stage four melanoma. This patient was heavily pretreated, including multiple types of IO therapies, and was treated at dose level two in our phase I-A dose escalation trial. The dose received was 0.38 milligrams per kilogram. Just as an aside, we're currently dosing at one milligram per kilogram in that trial. This patient underwent biopsies at pretreatment and then on treatment cycle two. Actually, it was right before cycle three was administered, so day 20 of cycle two. Importantly, at this dose of 0.38 milligrams per kilogram, which is a substantial dose for an IL-2 agent, we saw no signs of systemic vascular leak syndrome, which is the hallmark toxicity of IL-2. What we were looking at to understand the platform technology in this patient were two things. The first was to look for evidence of immune activation in peripheral blood, and that's in the center panel here. What we saw was what we had hoped to see, was evidence that our masking technology was shutting down the activity of this IL-2 agent in the periphery. You'll see here pre-treatment in black, on treatment in the orange bar, we saw no increase in CD8 positive T-cells in the periphery and no change in Tregs. As a reminder, if this was a systemic wild type IL-2 molecule, you would expect to see increases in both of these, the CD8 and Tregs. This was evidence that we're seeing the masking technology working in the periphery. The next question we've asked ourselves about this technology platform is whether the molecule then is unmasking and activating in the tumor. To answer this, we looked at tumor samples from baseline, again, here in the black. Now we're on the right-hand panel, baseline in black and the orange post cycle two. What we saw here was an increase in tumor-infiltrating lymphocytes from about 5%-10%, and simultaneously an increase in the percent of those that were CD8+ T-cells. Overall, we saw about a threefold increase in CD8 T-cells from baseline to the on treatment biopsy. Importantly, we saw no evidence of increasing Tregs, which we believe is due to the beta-gamma common chain design of our molecule. We wanted to begin sharing these data because they represent the first clinical evidence of our tumor-selective platform technology in a patient, and are important in informing how we think about the potential of this technology, which is now being applied to our IL-12 molecule, XTX301, and how that may impact the tumor biopsies in patients. If you'll turn to the next slide, please. We'll now spend the remaining time today taking a closer look at our latest and third molecule to enter the clinic, XTX301. This is our tumor-selective IL-12, and we look forward to discussing the potential for this agent as an IO therapy. You can turn to the next slide. I'll now turn it over to Dr. Davar, who we're very pleased is joining us today as an expert in this field who will begin the discussion of the potential of IL-12. Hi, my name is Diwakar and thank you to the Xilio team for inviting me to give you this overview of this area, very important area. I'm a cancer immunologist, right? What that means is I've been trying to give patients with advanced cancers immunotherapy. The problem that I face is that we have very effective drugs, but these drugs only work in literally half the people we give it to. Our major problem with cancer immunotherapy is that we have hot tumors. These are tumors which are essentially hallmarked by the presence of interferon gamma or CD8 T-cells within the tumor microenvironment. In these tumors, checkpoint inhibitor therapy works reasonably well. There's a complete separate class of tumors, cold tumors. Unfortunately, cold tumors actually outnumber hot tumors. In these cold tumors, which represent some of the most common cancers that we have right now, patients with colorectal cancer that's microsatellite stable, patients with breast cancer, patients with prostate cancer, ovarian cancer, endometrial cancer. These are tumors wherein checkpoint inhibitor therapy does not work at all. Really, in the context of cancer immunotherapy, despite the tremendous advances we have made in using both checkpoint inhibitor immunotherapy as well as T-cell-based therapeutics, the major advances that have been made have been in primarily hot tumors with no advances in cold tumors. Next slide, please. Now we know why tumors are cold. Tumors are cold because they lack T-cells. They lack NK cells. They are oftentimes cold also because they're the presence of certain immunosuppressive cells such as T regulatory cells or myeloid-derived suppressor cells. The combination of these cellular types from the T-cell, the NK cell, and these innate suppressive immune cells result in a poor response to not just checkpoint inhibitors, primarily checkpoint inhibitors, but also T-cell therapies. Hot tumors are found to have tremendous amounts of CD8 T-cells and NK cells. They have a pro-inflammatory tumor microenvironment, and the presence of these factors results in improved response and killing of the tumor cells upon receipt of immunotherapy. An IL-12 is a key immunocytokine that can remodel the cold tumor microenvironment towards an inflammatory state. Next slide, please. IL-12 is a tremendous cytokine. Right? IL-12 was actually first purified and discovered in 1989. That's kind of like when I was eight years old. All right? In the years since then, right? In the 30 years since then, we have made zero progress in moving this into the clinic, and the reason for that is several. In the very early stages of IL-12 development, it was found that unlike any other cytokine identified at the time, this was a heterodimeric cytokine. All the cytokines found up until then were homodimeric. They were essentially identical parts. IL-12 is a heterodimeric cytokine with a p35 chain and a p40 chain. The p35 sequence, you know, is basically homologous to the IL-6 and the GCSF sequence with, you know, so sort of four alpha helixes. Then the p40 portion of the chain has got a different structure. The point is that the combination of the heterodimeric structure of the IL-12 chain results in some tremendous unusual activities that are not seen with other homodimeric cytokines. The first is, it is a key bridge, a key cytokine that bridges both the innate and the adaptive compartment. Firstly, it activates NK cells and NKT cells. It also activates key components of the adaptive immune compartment, such as CD4 cells and CD8 cells. It therefore results in immune increasing amounts of antigen presentation, immune infiltration, very importantly, macrophage polarization, and also has got anti-angiogenic effects. In fact, pre-clinically, it is one of the most potent stimulators NK cell and T-cell function and cytotoxicity and interferon gamma production ever observed. It is clearly capable of polarizing naive cells towards the Th1 phenotype. The robust interferon production, both activates T cells as well as remodels the tumor microenvironment towards a more immune permissive phenotype. As a result of all of these, IL-12 was fast-tracked into the clinic. Unfortunately, that's kind of where we started running into problems. One of the very first dose escalation trials of IL-12 that was done, and again, this was done in the late 1990s. Again, for context, that's when, you know, kind of when I was in medical school. Again, 20 years ago and long before we had checkpoint inhibitor therapies, we had single agent responses to this, but there were some serious toxicities. We had responses in melanoma. We also had responses in colorectal cancer. We wanna highlight at this point in time, even with the early, you know, single agent dose escalation trials, there were disease stabilizations at relatively low levels of drug exposure in traditionally cold tumors such as ovarian cancer. The problem with this agent at the time is that the agent that we were using was recombinant human IL-12, so rhIL-12. This agent, which is actually still in the NCI portfolio, had tremendous side effects. In fact, there were patients that died in the original dose escalation trial. The MTD was declared at 500 nanograms per kilogram. The profound toxicities included in the patients that, you know, did get some evidence of benefit, profound amounts of fatigue and systemic symptoms that are clearly a result of the exposure of interferon gamma. When you have tremendous amounts of interferon gamma, you have these horrible side effects. The key thing was that we were giving cytokines that were causing a release of this because the cytokine was causing a circulating effective interferon gamma. It wasn't in any way tumor microenvironment specific. More recently, we have got some very interesting data speaking to the synergy of IL-12 with cellular therapy. Even before we have a agent that is gonna be active in the clinic, we do know that even with the old, you know, recombinant versions, we do have a clear synergy with existing checkpoint inhibitor therapies and T-cell therapeutics. Clearly speaking to not only the potential for IL-12 transformative development in the if it were to be found to be active, but also showing that it can synergize with existing therapies, clearly therefore telling you that you can not only make cold tumors hot and thereby start causing responses in these tumors, but you can actually make hot tumors even hotter, suggesting that we can therefore transform both cold and hot tumors for more therapeutic effect. Next slide, please. What is exciting about, you know, where we can go with IL-12? The first thing is, you know, why bother, right? We already have got existing IL-12 approaches in the clinic. For example, the Tavo agent, essentially Tavokinogene telseplasmid, which is this agent that has been developed, which is a electroporated IL-12, that requires essentially the drug to be injected. This is the OncoSec agent. You need to inject it within the tumor, and then you need to electroporate it. Essentially you need to apply like this giant Tesla field to allow the drug to move into the tumor. Not exactly easy to administer. One, it requires intratumoral administration, and two, it requires this electroporation technology. There's clear activity, right? There's activity, both single agent and in combination with checkpoint inhibitor immunotherapy. There's some very nice pre-clinical and clinical data that the response is associated with antigen-specific immune responses. What is the problem? This agent is administered intratumorally, right? One, so that's like 25% of melanoma. It is something like 20% of Merkel cell carcinoma, but it's like all of 0% of colorectal cancer. Sure, you know, you can, you can use these agents in certain hot tumors, but you're never really gonna affect even the majority of the patients that need it, nor are you gonna be able to go too far beyond the intratumoral, given the limitations of the intratumoral approach. There have been attempts to try to move this into other settings. For example, there's a lipid nanoparticle mRNA encoding IL-12, and there's an MDV approach from AZ and a gene therapy approaches as well that have been recently been described, but none of these approaches are anywhere near the clinic. The major limitation that we have at this time is we clearly know that this is important. We've got some great evidence that clinically that local administration is effective in injected lesions, but local administration is always gonna be a problem because there's a ceiling to how much and how effective these drugs are going to be. There's really no way to move it beyond that in an intratumoral patient population. Even within the intratumoral patient population, effects distantly, meaning effects in uninjected site are rare. Therefore, what we have is a, is a situation in which the greatest unmet need for IL-12 is actually the tumors with inaccessible lesions. Having an agent that can potentially do that will truly be transformative. Thank you. Then I'll transition to the Xilio people for the next part of this. Thank you, Dr. Davar. My name is Uli Bialucha. I'm the CSO at Xilio. For us, really one key question, if we can go to the next slide, is how to harness the potential of IL-12 that Diwakar Davar just talked about in a systemically delivered drug while addressing the toxicity concerns. At Xilio, our approach to molecule design is not a one-size-fits-all. We believe that actually building the best molecules is important, and to us, this involves developing custom, highly optimized masking solutions for each of the targets that we go after. I'd like to walk you through the components of XTX301 and how we built this molecule. For XTX301 specifically, we understood that masking a heterodimeric cytokine like IL-12 might be particularly challenging and require a slightly different masking approach compared to what we've done for XTX202, our IL-2 product candidate. We spent some significant time and effort to identify a custom mask that could effectively inhibit IL-12 signaling while also appropriately being tuned to effectively release the molecule upon proteolytic activation in the tumor microenvironment. Now, to enable anybody like half-life of the intact masked molecule, we again utilized the heterodimeric Fc architecture, a highly validated approach for half-life extension used for many Fc fusion proteins as well as bispecific antibodies. We then made a data-driven decision to incorporate a protease cleavage site between the half-life extension domain, and this is a single protease recognition sequence, and the cytokine. The molecule here is therefore designed to release a non-half-life extended IL-12 in the tumor microenvironment and elicit the potent biology that we just heard about. I'd like to next show you some preclinical data with a focus on antitumor activity as well as tolerability. If we could go to the next slide. I'll also make a note here up front that for preclinical work in mouse models, we've had to use a murine surrogate molecule since human IL-12 does not bind to the mouse IL-12 receptor. Importantly, however, the architecture of our surrogate molecule, including the cleavage element, is the same as in our clinical development candidate, so we believe that this is a faithful surrogate molecule. Focusing on the left-hand side of the graph here, we are looking at tumor growth inhibition, so tumor growth on the Y-axis, time on the X-axis. On this mouse model, which actually in our hands is anti-PD-1 insensitive, what we observe is XTX301 surrogate treatment resulting in significant dose-dependent antitumor activity. In fact, XTX301 demonstrated antitumor activity in response to a single one-time dose given at 0.039 milligrams per kilogram. We also observed complete tumor regressions in a subset of the animals, which were particularly encouraging considering that this happened in response again to a single one-time dose of XTX301. Importantly, if we focus on the right-hand side of this slide, the antitumor activity that we observed occurred in the absence of overt toxicity as measured by body weight loss. You can see here that the animals treated with XTX301 maintained their body weight. That's in stark contrast to what we observe when we use a non-masked control molecule in black. You can see that this molecule is active even at low doses. However, focusing again on the right hand, dosing with this non-masked version of IL-12 results in rapid body weight loss, this molecule is not well-tolerated. It was important for us to confirm that the antitumor activity that we're observing here in the absence of that toxicity was actually linked to the mechanism that we have designed into the molecule. We ran a series of experiments, and I'd like to show you some data. If we could go to the next slide. In one experiment shown here on the left-hand side, we dosed animals, tumor-bearing animals, and we followed the production of active molecule over time. When we measured the full difference in the relative amounts of active drug in the tumor compared to plasma, we observed that over time, there is a relative increase in active XTX301 in tumor over plasma, indicating to us that we are observing tumor-specific activation. We went one step further and ran another experiment that is shown here on the right-hand side. In this experiment, we designed a control molecule that is architecturally again the same as XTX301, except that it does not contain a protease recognition sequence in the linker. It's therefore non-activatable. When we dose this molecule at 0.039 milligrams per kilogram, you can see it has no activity. The activity overlaps with that of the vehicle control. That's again in contrast to when we use now XTX301 that is activatable, that does have that protein recognition sequence. Together, these data to us indicate that XTX is preferentially activated in the tumor and that the antitumor activity is dependent on protease-mediated activation. If we can go to the next slide. Given the potency of IL-12 as well as the clinical experience with recombinant IL-12 in the early 2000s, we felt it was important to robustly assess the potential for toxicity of our clinical lead molecule. We ran a set of experiments, quite comprehensive non GLP as well as GLP toxicology in non-human primate. These studies affirmed that our masking design can limit peripheral activity as well as toxicity, and we were able to show that XTX301, our development candidate, was tolerated at up to two milligrams per kilogram given weekly four times. I'll point out once again that the MTD for recombinant IL-12 in the clinic is sub-microgram per kilogram. This is a clear difference in the amount of IL-12 we were able to deliver here without severe toxicity in the primate. When we look at the exposures achieved over a week using this dosing regimen and compare that to tolerable exposures required for activity in the mirroring model, we can see that there is a clear gap between the two. The tolerable exposures far exceed the exposures needed for activity, suggesting to us that there is a clear potential for a broad therapeutic index with XTX301. We can go to the next slide. Just to summarize this section briefly, what I've covered in this section is that XTX301's unique design enabled exquisite potency with favorable tolerability in the preclinical setting. The molecule uses an innovative custom masking approach and single optimized protease recognition sequence while leveraging validated components where we feel that makes sense, like for half-life extension. XTX301 has now achieved clearance of our IND application. At this point, I would like to hand over to Dr. Marty Huber to talk us through the clinical development plans for XTX301. Thank you, Uli. If I could have the next slide, please. One more. Just as a quick to show you how old I am, I actually did the clinical lead for the Roche IL-12 that one of the two that was being referred to by Dr. Davar back in the 1990s. As he said, we have this fundamental challenge of we actually saw efficacy. We had renal cell cancer patients, for example, with responses. You know, back then, the fundamental problem was we could not separate that response, the dose necessary for response from the toxicity. That's why that slide about the therapeutic index is so important. What are we gonna do now that we have a molecule that gives us the potential to limit IL-12 into the tumor? First is we're gonna initiate this with monotherapy. Consistent with our philosophy, we need to look in patients with dose escalation to see can we get up to a dose that has activity in the tumor with limited peripheral activity. Once we have those doses, we wanna look at where is that activity. One of the differences, whereas with other IO, people tend to focus development as monotherapy only in hot tumors. We see an opportunity to actually look in cold tumors to see if there's evidence of activity. Finally, as was alluded to, while we think it's important to understand our molecule in these monotherapy settings, the ultimate utility of an IL-12 agent is gonna be in combinations with a PD-1, or for that matter, an IL-2, such as XTX202. Because I mean, in fact, IL-2 plus IL-12 was something that the IO community was excited 20 years ago about. Because of the limitations of peripheral toxicity, never was able to achieve a meaningful dose of either agent when given in combination. If we go to the next slide, the way we're going to do this is we will start off with a monotherapy dose escalation study in advanced solid tumors. We do not wanna restrict it only to hot tumors 'cause we're also doing signal seeking. Importantly, on the basis of our preclinical data set, the agency has agreed with a starting dose of five micrograms per kilogram. Think about that. That's an order of magnitude higher than the maximum tolerated dose for recombinant human IL-12. We're very excited about what we got for our starting dose, and based on that, we will continue the escalation with the goal of delivering safety data, you know, in that green target exposure range. As Uli showed you, by the end of the year of 23, our goal will be show you that we can get safety, showing that the mask is blocking the peripheral activity while starting to get to target dose exposure. Once we've achieved that, we are gonna be looking at pharmacodynamic cohorts in monotherapy in both hot and cold tumors. As René showed you earlier, what's important for us is not looking just only at PD activation in the periphery, but actually getting tumor biopsies on these patients to show that we're seeing pharmacodynamic effects in the tumor. Once we've started to those two, we will move into combinations with either PD-1 and/or in combination with our IL-2, XTX202, transition into phase II studies. We think what's important to remind you is, because of this potential to make cold tumors hot, we're looking at once we've established proof of mechanism, proof of concept, these combinations can then be done in a range of tumor types as you see listed across the bottom of the slide. In conclusion, if I could go to the next slide, please. We believe that IL-12 has a significant potential for activity of both hot and cold. There is no approved IL-12 agent today, this has been due to these fatal toxicities that have been observed. We think the data that Uli showed you is compelling. We see complete regressions. We see a wide therapeutic index in our preclinical setting. Finally, we believe we should be able to demonstrate monotherapy proof of mechanism and proof of concept in patients with both cold and hot tumors. If we go to the final slide, please. We step back and put this in the context of the overall Xilio platform, we're very excited that our IND has now been cleared. What we look forward is in the first half of 2023 is initiating the dose escalation study. Over the second half of 2023, we have some very important readouts for the company, not only for our 101 data and 202 data, but that preliminary safety data showing that our masking technology is getting us into target dose ranges that are acceptable for patients. On that note, I'd like to wrap it up and turn it over to the moderator for any questions. Thank you, Marty. Just a reminder, any participants that would like to submit a question, you can do so in the chat on your screen. We have received a series of questions throughout the presentation, we'll begin with those now. First question, which we'll direct to Dr. Davar and then to Marty. Assuming a favorable safety profile, what are your thoughts on IL-12 combinations? Which other modalities do you see having synergy? Sure. I think both Marty and I can answer this from different perspectives. I personally am extraordinarily excited about IL-12, just from the sheer virtue of being able to combine it with so many different things. The preclinical data suggests that IL-12 can clearly synergize with checkpoint inhibitor therapy, right? You take every checkpoint inhibitor therapy indication, and you look at the Kaplan-Meier plot in that. The key thing to keep in mind is that it flatlines, but it doesn't flatline at 75%, it doesn't flatline at 50%. In the hottest tumor we have, which is melanoma, it flatlines at 37% for combination immunotherapy, meaning PD-1/CTLA-4, and 27% for PD-1 monotherapy. That's the ceiling that we can do. It's not 27, it's 100 minus 27. 73% of melanoma patients do not have durable PFS. That is the hottest tumor we have. In hot tumors, you can easily add to checkpoint by adding a cytokine, right? Clear evidence that it's gonna potentially have magnitude benefit. What about the 95% of patients with colorectal cancer that do not have microsatellite stable disease, who have microsatellite stable disease, do not have access to a checkpoint inhibitor where the efficacy of checkpoint is like a grand total of 0%. In those patients, if you can transform, for example, a third of them or a quarter of them to checkpoint inhibitor responders, that would be tremendous. And that could have potential monotherapy effects and potential even more with PD-1. I think that's just if you look at those two scenarios, right? Cold tumors where you can have single agent activity, potentially additive effects with checkpoint. Even in hot tumors where you can certainly improve upon the small fraction of patients with who have response to checkpoint inhibitor therapy, that would be tremendous if you could just do that alone. Just to keep in mind, right, these are not rare patient populations. The PFS curves, the four-year, five-year PFS curves in melanoma, 27%. That's 100,000 cases a year. Lung cancer, something like 30%. That's 250,000 cases a year. These, these markets are tremendous. That's, that's not considered, I mean, that's not even taking into account the fact that this could certainly add to cell therapy, right? If I'm potentially giving somebody a cellular therapy agent in the solid tumor space, where right now we're restricted by T-cell based therapies that have, are almost all classified, pigeonholed into agents that have high index of response but short-term duration of activity, one can start imagining that, you know, that could potentially add to that as well. I think, you know, as a scientist and as a person giving people these drugs, I will certainly, if this program is hitting the RP2D, I'll be petitioning Dr. Huber and Dr. Russo to give me hundreds of thousands of dollars to investigate initiated trials in combinations of novel sorts. Just to build on that a little bit is, Dr. Davar talked about the PD-1s, which is I think everybody wants to look at checkpoint inhibitors. To us, the IL-2 combination is something that, you know, our scientific advisory board, that was one of the first things they threw out there. For us, having two masking agent, and if you think about the patient that were shown to you at the beginning, that patient started out with 5% TIL in the tumor. That's, even though it's a hot tumor, quote-unquote, from a histology point of view, that's not a lot of immune cells in the tumor. If you could drive that up, you. In that patient, you had a three times increase in the CD8 cells from that low baseline. Think about if you could get more immune cells in there and then add the multiplier effect of IL-2 on top of that. That's that potential to make, you know, what is a histologically, quote-unquote, you know, hot tumor, but has low. Realistically, when you look at it's not that hot, into something that gives you the opportunity for more immune response. We look at our, the idea of applying a mask approach for both an IL-2 and IL-12, and for that matter, even a mass CTLA-4 as a tremendous upside. Thank you. Next question is from Michael Oliphant at Morgan Stanley. You mentioned a starting dose of five mics per kilogram in phase I dose escalation study. At what dose do you anticipate seeing monotherapy activity, and do you anticipate needing to use a higher dose for cold tumors compared to hot tumors? Marty, we'll direct that one to you. I don't have a good answer on the cold versus hot, but if we think about based on our data, our goal is to get around 50 micrograms per kilogram by the end of the year, assuming the human PK exposure matches what we've been observing in the preclinical models. That should be in the green bar that Uli was showing you above the minimal efficacious dose. There's always a little bit of variability in that. We don't wanna get too precise. We'll continue to escalate beyond that. If we're at 50 mics per kg at the end of the year, we would be comfortable if that's the dose we take forward into looking for efficacy. You know, obviously we'll continue to explore above that, but that's our goal. Thank you. Next question is coming from Michael Schmidt at Guggenheim. When evaluating early clinical data for recombinant IL-12, which key PD biomarkers related to IL-12 receptor signaling and/or pro-inflammatory response should be in focus? I'll direct that to Marty, to you and to Dr. Davar. I'll actually let Dr. Davar start, because I'd like to hear his thoughts on this one again as a first glance. Sure. I think that, you know, I think Marty brought up a very important point earlier, which I just wanna echo, and that is everybody lives in a very T-cell-centric world. We oftentimes divide these tumors into tumors that, you know, even the very definition of hot versus cold is based on checkpoint inhibitor response, right? You know, there are all these other cells that are important in mediating immune activity that we don't do anything about. We don't talk about them. We don't, apparently don't care about them, but like NK cells, right? I think that what you are really going to be doing with, interested in looking at with a program like this is if you're designing kinda like the PD assay, the optimal set of PD assays to try to look at IL-12 engagement, you're gonna be looking at essentially upregulation, not just of CD8 T cells. Whether, you know, whether that's a proximal readout by IHC-IF or a readout by RNA-Seq, you know, using some kind of deconvoluted approach or inflammatory gene expression, such as the inflammatory gene expression signatures. You also... I would be very interested in looking at the effect of IL-12 on NK cells, clearly to make the link between the ability to re-engage not just the kind of T cell compartment but also the innate compartment. The other thing that I'd be very interested in looking at is the certain key aspects of certain immune cell subsets that have been shown to be very important in sustaining and mediating immune effect. That would be, for example, there's some very good data looking, showing that IL-12 is very key to generate certain immune cell subsets, so the stemness phenotype of T cells, also certain key B cell subsets. It would be very interesting to look at whether or not these data hold up in human cancer patients. I'd be looking very broadly both at the innate and the adaptive, but basically NK cells and T cells in those compartments. Uli, why don't you... If you'd mind sharing, because we will, we certainly will be looking at those as part of the biopsies. I mean, we've already shown you, we look at CD8 effector. We are looking at, you know, immunohistochemistry for NK in our agents going forward. Uli, any additional thoughts? Yeah. No. Thank you. I think the key here is we understand IL-12 biology, right, based on the years of experience, both clinically and pre-clinically. What we're doing is to really develop a biomarker plan that taps into that biology, whether that is to be very deliberate in measuring interferon-driven responses, as well as combining histology with genomic readouts that then also can interpret and give us insight into the broader tumor microenvironmental remodeling capability of IL-12, including the cell types that Dr. Davar mentioned, from Th1 polarization to macrophage polarization. It, it has to be comprehensive, and that's how we are progressing. Thank you. We have one additional question from Michael Schmidt, also from Guggenheim. I'll direct this one to René, since you included some discussion of two-oh-two clinical observations in your opening. How should the audience be thinking about read-through from the clinical experience on XTX202 to what we might expect from XTX301 over the course of the next year? Thank you. Yep, this is something we think about pretty often internally in the company, I think there are two parts to this. The basic premise of MMP activation of cytokines in the tumor, we think is important to validate clinically with all of our programs and to continue to build that evidence for the platform and this approach generally. We're seeing evidence of MMP activation beyond the work at Xilio that other companies are doing as well. We believe this is evidence that we're seeing early in our IL-2 program that carries forward generally for our platform, for our molecules and the field overall, using MMPs to activate preferentially in the tumor. That said, our platform is not, quote-unquote, "plug-and-play parts." Each molecule has specific components designed to mask and to activate in the tumor, trying to ideally optimize the structure and the behavior of each molecule. While there is some read-through on the basic premise, we do think each molecule will need to be evaluated individually, given our spec-specificity and approach for each specific design. I'd ask Uli to please feel free to comment as well. No, I think you've absolutely covered it, right? Our approach, as I mentioned, is not one size fits all. You've seen that, for instance, in XTX301. We made a data-driven decision to have the molecule release only IL-12. For IL-2, the molecule retains the half-life extension domain. Those were clear choices based on data. I think overall, our approach has been understand the biology, design the best possible molecule for that biology. While there are some similarities in our activation mechanism, we're all leveraging across the molecules proteolytic dysregulation in the tumor, there are also some clear differences. Thank you. The next question is coming from Marc Frahm at Cowen, relating to differences between hot and cold tumors. The question is centered around how quickly would we expect that the activated IL-12 might be utilized in a cold tumor that largely lacks immune cells? I'll direct that to you, Uli. Yeah, sure. I'm happy to take that. I think here one of the key benefits is in the ability of IL-12 to initiate an immune response where there essentially isn't one already going. Now, there will be cells in most tumor microenvironments that can respond to IL-12, even if that is in the peripheral stroma, and the idea is that you get a bit of a feed-forward loop going, and there's certainly evidence for that in preclinical settings. The idea is to stimulate that initial response and then propagate it as the tumor warms up. When we look at that in our clinical program, we're still looking at the biopsy probably after about six weeks, so before that third cycle, to give sufficient time for the molecule to become unmasked and to have some biology. I think we've already seen with XTX202 that, you know, a six-week timeframe is sufficient to see initiation of the activity. From a clinical testing point of view, though, just to remind you, we will be including cold tumors in the dose escalation. We will be looking for signals early on as we go through the program. Thank you. Next question is coming from Mark Engelhart of Bloomberg. Could your tumor-specific cytokines be engineered into adoptive cell therapy constructs? I'll direct that one to you, Uli, as a starting point. Yeah, sure. I would love to hear from Marty as well. I think as Dr. Davar mentioned, cytokine, it's sort of your signal three, which in many ways is expected to synergize well with other immune agents. Ultimately, for any immunotherapy, the business end that actually affects antitumor activity are cells. We think that there's a natural place for masked cytokines in the context of cellular therapy. I would say that is the case for IL-2, our XTX202 molecule, but also for XTX301. Whether there are opportunities to design more custom molecules to fit a certain cell product, I think that might be determined. I think the potential is really much more broad, especially now with allogeneic cell products becoming a bit more, getting more attention and seeing more validation. We think that the ability of a cell product with a tumor-targeted cytokine now to perhaps see activity in those hard-to-treat solid tumor settings for cell therapy is a huge potential. The reason Uli included me in this is we spend a lot of time talking about this internally. In fact, the future of the platform is not so much directly that we would engineer to the cell directly, but that we would engineer T-cell binding or other active agents. Uli recently gave a talk at PEGS where we talked about how do we do, you know, take advantage of cis engineering, where you have a multifunctional and that you mask one. The problem with multifunctionals is you don't wanna bring The antigens still tend to be everywhere or in multiple normal places. In the absence of masking, You don't wanna bring the T cells to the normal tissue. The way we're looking at this is this kind of dual approach where you use multifunctionals to activate in the tumor only, but then use the binding to not only target the tumor, but also looking at what are the other ends of it sticking to. It's a how do you kinda. We see that kind of multifunctional approach, you know, bringing T-cell engagers or other approaches in as a tool to add into our kit, but still using our core approach of tumor selectivity using MMP activation as a foundation. Thank you. Next question goes back to IL-12 monotherapy and lacking an approved predicate to compare against in terms of efficacy. We'll direct this question first to you, Dr. Davar, and then to you, Marty. How should we be thinking about what might be possible in terms of ORR in hot tumors and what might also be possible in terms of cold tumors? Sure. I think the key thing to keep in mind, I guess, is the setting that this is being assessed in, right? Presumably, we're talking about relapsed refractory patients, and these patients are all in the current context checkpoint inhibitor experience. Again, I wanna caution that at least in melanoma, in depending on when we are talking about readouts, a certain portion of these patients are likely to be T-cell therapy experienced as well because there's a near-term readout for a TIL product in this disease that with an expected PDUFA date of a couple of months from now. In that context, I think the first thing to keep in mind is that actually benchmarks are personally, in my opinion, not that helpful. Because what happens is people have this mental idea of a 15% number or a 25% number, and you cannot keep in mind that, take the number outside of the context. People remember the number, and they don't remember the context. One was, you know, Marty, Marty talked a little bit about this, you know, in that Genentech program that he was involved in. When I'm, for example, doing an IL-12 trial right now, and what we are really struck by in these completely refractory patients, right? Like subcutaneous administration of recombinant IL-12 at, you know, vanishingly small doses produces stable disease, right? You know, it's almost homeopathic, the doses that we're giving recombinant IL-12 at in this NCI trial that I'm leading. Even at that, you know, quasi-homeopathic dose, we're seeing some disease stabilization. Right. I think the key thing to keep in mind is it's not just the number, but it's actually the patient population. What I think would be important to see is durable responses. It's the nature and the durability of the response. The key thing are durable responses. We have to see some proportion of people on a spider plot that are going out past six to 12 months. It has to meet the kind of innate sense that our oncologist has that this is not, you know, some random chance experiment. I think we need to see durable responses in a subset of patients that includes both hot tumors and cold tumors, to get a sense that this is not just, you know, random chance alone. The second thing we need to see is PD effect. Like, it's impossible to develop a drug these days without seeing clear, compelling evidence that what you're doing is related to what you think the drug is supposed to do. The reason that's important is CTLA-4 has got a delayed mechanism of action of about 12 months. Which means that if you see a patient at month 12 after dosing that person on IL-12, if that person's immediate prior therapy was CTLA-4, you know, there's like a 6%-12% chance that that month-12 response is actually IP-related. However, if you have got on-treatment biopsies showing that there's macrophage polarization in addition to T-cell influx, well, then that cannot be IP-related, right? It must be due to the agent that was most recently administered. I think the key thing is it's not the number, it's the context, and within the context, it's also the PD effect. Meaning you have to see responses, and the responses have to kinda have a biology after talking about that with our translational colleagues, that speaks to the MOA of the agent. I think what we've learned from interleukin twelve is, one, we can get objective responses. I do think, 'cause this is with all our programs, 100% agree. We want to see some evidence that you can shrink a tumor. Really it's gonna be these spiders, is if you see multiple patients showing long-term disease stabilization and the right biology, given that this is foundational, that you can then... Especially if we see that in cold, you know, this is where back to the context. If you have cold tumors where you're showing disease stabilization you just don't see with other IO and the right PD, the combos are then where you're gonna really answer the question in phase II, is if you give a combination in cold tumors, then I think it's fair to ask the question in a IO-naive cold tumor, can we generate a 15% or 20% response rate? I think we probably wanna be a little cautious about asking that question too early, but a 100% agree, if we're not seeing evidence of anti-tumor activity and PD, then this drug won't make it to combo. We gotta see that before we proceed further. Thank you. Our final question, is directed to you, René. Assuming that XTX301 is safe and effective in the clinic, could you discuss the potential that you see for this molecule long term? Yeah. Thanks, Stacey. I think given what we've heard today, particularly from Dr. Davar, I think we all agree that the potential for a tumor-selective IL-12 agent that can be administered systemically like XTX301 can be really meaningful. You know, what we hope to do is develop this molecule to really expand the universe of tumor types and patients that are able to respond to IO, ultimately, improving the benefit of IO for more patients. We see there are multiple opportunities to study this agent, as Marty said, both as a monotherapy, but importantly, I think in combination with multiple agents, like checkpoints, potentially cell therapies, and perhaps most exciting in our mind, is with other cytokines, like an IL-2. With that tumor-selective technology, you can imagine doing this, which would never be feasible without this type of approach. That's how we're thinking about it, and we see, you know, tumor types being quite broad as Marty had alluded to, both, hot and cold tumors. That's where we really hope to expand the universe of patients that can benefit from IO with an agent like XTX301. Thank you. This concludes the Q&A portion of our presentation today. We'd like to thank Dr. Davar for joining us, as well as the Xilio leadership team for participating in the call. I'd like to thank all of the participants that joined us live today and also remind everyone that a replay of this call will be available on the Xilio website. Thank you.