Xencor Inc

NASDAQ:XNCR

Earnings Call Analysis

Xencor Focuses on T-cell Engagers, Solidifies Finances

In 2023, Xencor emphasized its T-cell engagers, particularly vudalimab for prostate and lung cancer, reducing investment in cytokine candidates. Its XmAb platform was validated by Amgen's data, and collaborative CD28 bispecific trials began with J&J, underscoring strong partnerships. A strategic royalty monetization significantly enhanced its balance sheet, resulting in a robust $697 million ending cash balance. Xencor now anticipates a financial runway extending into 2027.

Company Overview and Financial Update

During the earnings call, the company highlighted its refined focus on T-cell engagers for solid tumors and the decision to reduce investment in cytokine drug candidates. Key developments from the past year included promising data from a partnership with Amgen on prostate cancer therapies and the initiation of new clinical trials. A substantial financial milestone was the partial monetization of Ultomiris and Monjuvi royalties, which aided in closing 2023 with a robust $697 million in cash, ensuring financial stability through 2027.

Pipeline and Clinical Trials Progress

The company is advancing its pipeline with several T-cell engagers undergoing dose escalation studies in Phase I trials. XmAb819 and XmAb808 exemplify the company's focus on harnessing CD3 and CD28 pathways to combat solid tumors aggressively, with an expectation of significant advancements this year. Meanwhile, XmAb541, with its carefully engineered binding domains for solid tumor selectivity, is on the cusp of entering clinical trials within the first half of the year.

Vudalimab as a Prostate Cancer Monotherapy

There is substantial excitement around vudalimab's efficacy in heavily pre-treated metastatic castrate-resistant prostate cancer patients, with a RECIST response rate of 35% and a disease control rate of 50%. Efficacy data appears promising given the heavily pretreated nature of the patient population, encourages further patient enrollment, and provides a comparative advantage against other therapies in similar trials. The safety profile is also deemed consistent with other checkpoint inhibitors, despite a case of immune-mediated hepatitis.

Strategic Goals and Focus for the Upcoming Year

In 2024, the company intends to intensify its efforts on the solid tumor bispecifics pipeline, with ongoing discovery work to bolster its portfolio of CD3 and CD28 bispecifics further. The balance sheet's strength backs these ambitious plans, promising a year of potential innovation and therapy advancement. The subsequent IND candidate selection will mark another critical milestone for the company's strategic operations later in the year.

Clinical Data Outlook

While specific guidance on the timing of clinical data, particularly from the ENPP3 study, is not provided, the company is working on characterizing effective dose levels based on the outlined strategy for dosing regimens. It places importance on understanding the effective dose level with a reliable patient population and anticipates having more comprehensive data within the year.

Earnings Call Transcript 2023-Q4

[Operator]

Good afternoon, and thank you for standing by. Welcome to Xencor's Fourth Quarter and Year End 2023 Conference Call. [Operator Instructions] Please be advised that today's conference is being recorded at the Company's request.Now, I would like to turn the call over to your speaker today, Charles Liles, Head of Corporate Communications and Investor Relations. The floor is yours.

[Charles Liles, executive]

Thank you, and good afternoon. Earlier today, we issued a press release which outlines the topics we plan to discuss today. It's available at www.xencor.com.Providing comments on the call are Bassil Dahiyat, President and Chief Executive Officer; Nancy Valente, Chief Development Officer; and Dane Leone, Senior Vice President, Corporate Strategy. After the prepared remarks and presentation, we will then open up the call for your questions and we will then be joined by John Desjarlais, Chief Scientific Officer, and John Kuch, Chief Financial Officer.Slides that we are using today should be visible here on the webcast and [ were ] made available for download on the Events & Presentations page of our website.Before we begin, I would like to remind you that during the course of the conference call, Xencor management may make forward-looking statements, including statements regarding the company's future financial and operating results, future market conditions, plans and objectives of management, future operations, the company's partnering efforts, capital requirements, future product offerings, and research and development programs.These forward-looking statements are not historical facts, but rather are based on our current expectations and beliefs, and are based on information currently available to us. The outcome of the events described in these forward-looking statements are subject to known and unknown risks, uncertainties and other factors that could cause actual results to differ materially from the results anticipated by these forward-looking statements, including, but not limited to those factors contained in the Risk Factors section of our most recently filed annual report on Form 10-K.With that, I'll pass the call over to Bassil.

[Bassil Dahiyat, executive]

Thanks, Charles, and welcome, everyone. Today, we'll cover a few business highlights from 2023, briefly review our clinical pipeline, and provide a data update on vudalimab in prostate cancer. You can refer to our press release for more information about the last quarter and full year.We focused our pipeline and discovery work on our T-cell engagers because of growing validation for their potential in solid tumors. Supporting this is the continued advance of vudalimab in prostate cancer, where we'll provide an update today, and the start of a trial in frontline lung cancer for vudalimab. And we've decided to reduce our investment in our cytokine drug candidates as part of this focusing.Our partnerships and license has played a significant role for us last year, first with validating data for our XmAb [ 2+1 ] CD3 platform from our partner Amgen with their xaluritamig data in prostate cancer. And 2 Phase I programs started in our CD28 bispecific collaboration with J&J.And we significantly strengthened our balance sheet with a partial monetization of our Ultomiris and Monjuvi royalties. As a result of that and robust milestone in royalty revenues, we ended 2023 with $697 million and expect runway into 2027.Now, onto our pipeline. The focus of our clinical pipeline is bispecific T-cell engagers for solid tumors, an area with rapidly growing promise. Solid tumors have been challenging for antibody and cell therapies. But recent data, some of which we'll review momentarily, suggests that CD3 and CD28 bispecifics could play a role as therapies in a range of solid tumors.Key programs for us addressing this opportunity are XmAb819, an ENPP3 x CD3 XmAb bispecific for renal cell carcinoma, an XmAb808, a B7-H3 x CD28 XmAb bispecific in prostate and other cancers. Both are advancing in dose escalation in Phase I and right behind them is XmAb541, a CLDN6 x CD3 bispecific that we expect to start Phase I the first half of this year.For vudalimab, we initiated a new study, its first frontline study, in non-small cell lung cancer, based both on our Phase I data in lung cancer and external data suggesting potential advantages against standard checkpoint therapy in this setting. And we've made progress with our metastatic castration-resistant prostate cancer studies, both in combination with chemo and monotherapy, and with encouraging monotherapy data we're going to present in a moment.Finally, we're wrapping up our Phase I work next quarter for both XmAbs 564 and 662, taking the [ PK/PD ] and safety data in hand to establish initial product profiles and monitoring the field for further validation of these cytokines before we do any additional development [ work ].Underpinning our T-cell engagers is our XmAb bispecific technology. It lets us address the solid tumor opportunity by engineering our antibodies with a format and affinities designed to give tumor selectivity in the context of each tumor target's particular expression levels and tissue distributions. Solid tumor targets, in particular, need a customized approach because they're distributed more broadly than heme tumor targets, which have already been successfully addressed by CD3 bispecifics in lymphoma and myeloma.Our plug-and-play antibody modules let us do this work rapidly, and as a result, we've got a growing pipeline of molecules with our [ 2+1 ] design, which is particularly helpful with selectivity for solid tumors. And here is the first clinical proof-of-concept for our XmAb [ 2+1 ] CD3 format xaluritamig, which targets STEAP1.Our partner, Amgen, presented very promising efficacy intolerability data, at ESMO last October in late line prostate cancer, usually considered a cold tumor for immunotherapy. This target was challenging due to the limited accessible binding regions outside the cell membrane and non-tumor expression. So, we're very encouraged to see this early data for the molecule in the [ 2+1 ] format. Amgen's announced they are nearing completion of the Phase I study and are planning additional studies in earlier lines of therapy, so we'll be eagerly awaiting their updates.Now, our own lead XmAb [ 2+1 ] CD3 bispecific is XmAb819, targeting ENPP3 in renal cell carcinoma. We chose ENPP3 as a target because it has exactly the kind of expression and profile we want for a CD3 solid tumor target, much higher expression on tumor than normal tissues and nearly uniformly high expression on clear cell renal cell carcinoma. Plus, it has potential for use in select patients in range of other tumors.Also, we think renal cell carcinoma has a need for new mechanisms beyond checkpoint inhibitors and TKIs, and directly cytotoxic antibody could be well positioned. 819's design gives us the selectivity we wanted in vitro, and we're continuing to advance in dose escalation with both IV and subcutaneous dosing, and expect to make significant progress this year towards target dose levels.I'll shift now to XmAb808, our new T-cell engager mechanism, CD28 targeting. The goal here is to activate T-cells via the Signal 2 pathway, which powerfully amplifies and sustains T-cell responses. We designed 808's bispecific format and affinities to try to drive this activation in a tumor-specific way by requiring sufficient binding to its tumor antigen, B7-H3, to turn on CD28 signaling.A key part of our approach is a lower potency CD28 binding domain that we think could give us control of CD28 signaling and improved tolerability. We picked B7-H3 because it offers high expression across a range of tumor types, creating an opportunity to potentially treat multiple cancers in combination with either checkpoint inhibitors or CD3 bispecifics. CD28 targeting has generated a lot of interest among clinicians and across the industry in the current Phase I study in combination with pembrolizumab, is progressing well in escalation.Now, our latest CD3 bispecific is set to enter the clinic imminently. XmAb541 targets CLDN6, which is highly expressed on the majority of ovarian cancers and also on several other tumor types. Though it has a very promising expression profile, it is a selectivity design challenge because there are multiple closely homologous claudins. We think we addressed it with careful binding domain engineering and our [ 2+1 ] format.XmAb541 INDs are open and we expect to be in patients the first half of this year. We're planning to apply lessons learned for solid tumor CD3 dosing from both internal and external programs to move the study quickly.Now, I'm going to turn it over to Nancy for the vudalimab update.

[Nancy Valente, executive]

Thanks, Bassil. I'm excited about the encouraging new data we have to share from the prostate cancer monotherapy cohort.If we could go to the next slide. This cohort is part of the overall vudalimab program, which consists of 4 studies. Based on the outcome of the Phase I study, we moved into 2 tumor-specific expansions initially: the study 717-04 in metastatic castrate-resistant prostate cancer in combination with standard of care chemo and other agents; and study 717-05 that included patients with gynecologic malignancies and a monotherapy metastatic castrate-resistant prostate cancer cohort, which I'm going to further describe.The next slide. The prostate monotherapy cohort required patients [ had ] [ RECIST ] measurable disease, including visceral sites or lymph nodes, and the patients had to have progressed after all other appropriate therapy. Vudalimab was given every 3 weeks based -- as a flat dose based on our PK analysis of earlier studies.You can see that this study enrolled a heavily pre-treated patient population that had exhausted available standard-of-care therapies. With a median of 4 prior therapies, 100% received prior antiandrogen therapy, all but one received prior chemotherapy, and 86% were ECOG-1 performance status. As noted, the study protocol required patients with measurable disease at baseline, which is why we see a high rate of visceral metastases and high median baseline PSA.Reduction in target lesions and disease control are encouraging for such a heavily pre-treated patient population, as you can see on the right, with a RECIST response rate of 35% and a disease control rate of 50% and the spider plot shows we have several lasting responses and one patient with stable disease [ past ] 48 weeks. [ Deep ] PSA reduction was also seen in 3 patients giving a PSA90 rate of 25% and a fourth patient with a nearly 50% PSA, who is still on study.To describe one especially poor prognostic patient who responded well to vudalimab, this patient had 3 liver [ meds ], a total disease burden of 12 centimeters and a PSA at baseline of 180 nanograms per mil, and achieved a confirmed PR, a PSA90, and was in response for over 22 weeks.The treatment-emergent adverse events highlight the tolerability has been generally well managed by dose modifications with only 2 treatment discontinuations. Unfortunately, there has been one case of Grade 5 immune-related mediated hepatitis. The patient's treatment course was complex and this is the only known Grade 5 immune-mediated hepatitis event in over 240 patients that we've treated with vudalimab to-date.Reviewing specific immune-related adverse events, generally, the events are what we'd expect with checkpoint inhibitor therapy. The rate of Grade 3 events that you can see on the right, were generally limited and specific to several patients. Overall, we are encouraged by the tolerability profile of the Q3 week flat dosing schedule with vudalimab.In summary, we have observed encouraging single-agent activity in heavily pre-treated patient population. This is consistent with the data from the Phase I study in prostate cancer where we had patients with 6 and 10-months duration of response. Vudalimab's safety profile is consistent with other checkpoint inhibitors and we observed limited treatment discontinuations.Now, I will turn this over to Dane to share comparative data to place these results in context.

[Dane Leone, executive]

Thanks, Nancy. As you can see on the next slide, these emerging data support us enrolling more patients into the monotherapy cohort. When you put the data into the context of the broader novel therapeutic landscape under development, it really is clear why we and our investigators during our discussion at ASCO GU were so encouraged about continuing the study.When you compare the baseline characteristics of our patients versus our peer studies, vudalimab monotherapy cohort is among the most heavily pre-treated, and has the most advanced disease upon enrollment, as shown by nearly all having ECOG-1 and all having measurable disease. Comparatively, only the xaluritamig dose escalation study has enrolled similar patients that are very late line in poor performance status.Despite the remarkably advanced patient population, patients treated with vudalimab have comparable RECIST response rate versus the peer studies in this table, and experienced deep PSA90 responses. Importantly, we think that RECIST response and deep PSA response are required for translating into effective durability of response, and ultimately survival outcomes for these patients.Regarding tolerability, using the Q3 week flat dose schedule of vudalimab has supported a manageable safety profile compared to our peers. Overall, considering the early nature of the vudalimab monotherapy cohort, we are encouraged by the clinical benefit for these advanced prostate cancer patients that have been treated well beyond current standard of care, and we look forward to evaluating a larger cohort of patients by year-end.Now, on the next slide. Beyond prostate cancer, we are executing on the start of our frontline non-small cell lung cancer study of vudalimab plus chemotherapy, and we are excited that the study is underway, with the first patient dose in the fourth quarter of last year.And with that, I'll turn back to Bassil for a view of our corporate goals for 2024.

[Bassil Dahiyat, executive]

Thanks, Dane. Here's a look at our priorities for 2024. We're starting with a strong balance sheet and as you can see, we're looking forward to this year really bringing the focus to our solid tumor bispecifics pipeline, where we have a lot going on for our CD3 and CD28 T-cell engagers and for vudalimab. Of course, we're doing discovery work on additional CD3 and CD28 bispecifics and we'll select our next IND candidate later this year.Operator, we'll now open this call to questions.

[Operator]

[Operator Instructions] Our first question comes from Jonathan Chang of or Leerink Partners.

[Dylan Drakes, analyst]

This is Dylan Drake on for Jonathan. Thanks for taking our questions. First of all, would you be able to comment on how investors should be thinking about when we might be able to see initial clinical data from the ENPP3 study?

[Bassil Dahiyat, executive]

Sure. I'll take that one. So we're not commenting on data just yet. And what we're trying to do is characterize with a sufficient patient number and follow-up the sort of outlines of the effective dose level as we pull together a dosing regime. These are CD3 bispecifics, so you want to have that -- you want to have your priming and step-up doses.We've made great progress and we really hope that this year we'll have a lot more knowledge about it. And then when we get close to having the decision to disclose, we will tell you. So we're not guiding anything there yet.

[Dylan Drakes, analyst]

And if I could just sneak in one more. You guys set the stage pretty well with your comparative table there. But looking ahead to the go-forward decisions for both the mono and combination xaluritamig approaches, how would you guys set the bar?

[Bassil Dahiyat, executive]

Yes. I guess maybe the mono first. I mean, Nancy, Dane, you guys want to take that? What's the bar for advanced comparables?

[Dane Leone, executive]

Yes. Sure. Great question. When we look at the patients that we've enrolled into the monotherapy cohort, we'll continue to enroll -- these are patients that are as late line as you can get and have exhausted every standard of care therapy available to them. As such, what we've really decided to do in engaging the signal that we'll have as we hopefully get a cohort of 20 to 30 patients enrolled over the course of this year is look at some of the contemporary studies where cabazitaxel has been used as a control arm.And in those studies, namely the control arm for therapy, or the very recently reported part 2 of CheckMate 650, you've seen a RECIST response rate for cabazitaxel on that 11% to 24% range, and a PSA50 response rate of 24% to 37%. This is why we're quite encouraged with what we're seeing in the cohort now with clinical activity of vudalimab monotherapy.And hopefully, with a larger cohort, more follow-up, we can then try and extrapolate what would be needed in terms of survival outcomes. And cabazitaxel, for reference, has generally come out around 8 months for a radiographic progression-free survival. And right now, based on some of the durability, seems like we're in pretty good shape.

[Dylan Drakes, analyst]

Now, then for the combo cohort, I guess we've got different baselines there to look at?

[Dane Leone, executive]

Yes. In the combination cohort with docetaxel, you really have to think about what docetaxel might be able to do in what would be post and during receptor inhibitor exposure for these patients. And again, the landscape will continue to change with PLUVICTO, but historically, if you're looking at the TAX 327 study, you'd be looking at a PSA50 response range of 40% to 50% and a fairly low RECIST response rate of somewhere around 10%.That said, the survival curves are a bit better for that line in that setting with docetaxel monotherapy. But that's kind of what you have to think about when you're doing the combination study with docetaxel at this point.

[Operator]

Our next question comes from the line of Etzer Darout from BMO Capital Markets.

[Etzer Darout, analyst]

I guess maybe on the safety profile of vudalimab, if there's anything you can or will incorporate into the study to maybe kind of mitigate this autoimmune hepatitis? Is this something that is just unique to this patient or is -- there are other things sort of going on that you need to understand? And then also on XmAb564, just wondered the decisions to sort of pause that, was that data-driven, or whatever other contributing factors, if you could comment on that to [ pausing ] that study?

[Nancy Valente, executive]

Yes.

[Bassil Dahiyat, executive]

Sure. So I'll talk -- I'll gun through the XmAb564. Then maybe Nancy can take the question on the vudalimab safety profile. So for 564, it was really driven by our -- as much as anything, by our decision to focus on our T-cell engagers, our resources, our capital, and our people and looking at how the class cytokines generally, and IL-2 Treg driving cytokines in particular has evolved. There's still, I think a lot of outstanding data coming in the next year from other companies about efficacy, about how much potential does this class have.And with our study having progressed and given us a reasonable look at our [ PK/PD ] and safety, we think that, that's the time to consider resources and wait and see how the field evolves. Well positioned -- we're well positioned to ramp up again, but it's about focus now. And for 2024, pipeline focus is the key for Xencor. So it was really more just strategy-driven. With that, maybe, Nancy, if you want to touch on the question on vudalimab?

[Nancy Valente, executive]

Yes. So I'll go back to the patient with the hepatitis death, and that's the only immune-related hepatitis death we've seen across our program with more than 240 patients treated both in the monotherapy and combination setting. The patient had responded to therapy, but did have other treatment-emergent adverse events before that, including diabetes mellitus and diabetic ketoacidosis, a thyroiditis, a hyperkalemia, a lipase increase. So a bit of a complex course here. We have looked across the entire program, and we don't see anything concerning relating hepatitis.As far as the protocol and the investigators, we have emphasized to the investigators to be watchful for this and communicated with them. The protocol does include the NCCN guidelines for treatment, and it's also consistent with ASCO guidelines and other society guidelines like the gastric GI guidelines for monitoring and treatment. And so, we do include screening at baseline for any diseases that might contribute to hepatitis. And we have frequent laboratory monitoring.

[Operator]

Our next question comes from Gregory Renza of RBC Capital Markets.

[Kurt Kharouf, analyst]

This is Kurt for Greg. Just to confirm if this monotherapy data was from a particular molecular subtype since I think that was how the trial used to be characterized? And if I may -- secondarily, from the data comparison table, I think the PSA90 looks competitive but PSA50 looks a little lower. Just curious if you have any hypothesis on why the data looks that way?

[Bassil Dahiyat, executive]

So I'll touch on the specifics of the trial and the population. So I think, just to be careful, there's 2 studies ongoing now where we're studying prostate cancer with vudalimab. The monotherapy study, the one we discussed today, is not subdivided by molecular subtype. It's people with clinically defined high-risk disease, which includes extra pelvic and visceral metastases. So that's a population that's independent of molecular subtype in that regard.The other study, our combination with chemo study, that study is subdivided by molecular subtype. That's a different study. We didn't discuss data for that one today. We're enrolling still accrued patients and more follow-up, and we hope to have a lot more clarity later in the year on that program.And also, I guess, first half of next year really bring it altogether. So that -- just -- I just want to make sure that this is not from the molecular subtype dividing study. Maybe on the comparison table, Dane, you want to answer that one on the PSAs?

[Dane Leone, executive]

Yes. Sure. That's a great question that -- we looked at quite extensively once we had this data cut and were able to review the data with our investigators during ASCO GU. What seems to be [ is ] somewhat of an artifact of taking patients that are required to have measurable disease at baseline, versus other studies that also include [ bone ] only. And as you can see on that table, most of our peer studies outside -- maybe one with a similar mechanism of action, is more of a mixed patient population.And what we see in those studies is you will get more PSA50s that don't necessarily correlate to a RECIST response as some of those patients do not have measurable disease at baseline. In our cohort, to really get clinical benefit, those patients will need either a RECIST response or a PSA90. So I think there's 2 things there. One is PSA50 for patients that are this advanced in their disease course, are relevant for survival outcomes, very debatable. But what is definitely needed is those RECIST responses and PSA90s.

[Operator]

Our next question comes from the line of Kaveri Pohlman from BTIG.

[Kaveri Pohlman, analyst]

My questions are mostly on vudalimab. So first on the safety profile. Can you tell us how the safety profile looks in comparison with [ Ipi/Nivo ] combination and how you are thinking about the dose that will be used going forward? And my second question is, also for the go/no-go decision. How many patients you plan to enroll in monotherapy and combination cohorts for that? And is efficacy the only factor you're considering to make these decisions?And the last one is also from the same trial. Any color you can provide on how many patients had [ bone ] disease? And were there any responses observed in those patients?

[Bassil Dahiyat, executive]

So that's a set of questions. I think maybe the one that's more just generically descriptive is your first one, vudalimab safety versus [ Ipi/Nivo ] which is a broad kind of amorphous question, but we'll take a crack at it and what our dose going forward is. Nancy, do you want to jump in on that one?

[Nancy Valente, executive]

Yes. I mean, overall, what we've seen so far is a safety profile. It looks similar to other checkpoint inhibitors. So we haven't seen anything that says that this is different -- markedly different in some way that wouldn't be unfavorable to the product. I guess I could say that overall. I mean, there's a lot of data out there on Ipi single monotherapy checkpoint inhibitors as well as combinations. So broadly, we're similar to that. Do you want to...?

[Bassil Dahiyat, executive]

Yes. And on the dose going forward, note that in our lung cancer study, the newest study we started, as well as in the monotherapy prostate study which was the second newest, we have switched to Q3 week schedule using flat doses. And I think that's given us a good feeling that the Q3 week might have some benefits over the Q2 week [ weight-based ] dosing.With regard to [ Ipi/Nivo ], even though we've got over 240 patients, now it's still hard to parse out those subtle differences. We don't see the kind of colitis that often [ bedevils ] Ipi therapy at high doses. And note we're giving much higher doses of our drug than the current sort of Ipi regime of 1 milligram per kilogram. So I think that's maybe the best we can say comparatively across such a range of studies and what not. But generally very checkpoint-like.And then on your second question, go/no-go number of patients that we'd hope to have for both the combo and the mono, so by first half next year we're looking at on the order of I guess roughly 30 patients in each of those settings. The chemo study in particular, in the main cohort, which is our no targetable mutations cohort, which is our now docetaxel combo, and then on our monotherapy study as well. So in that -- we're aiming for 20 patients. Hopefully, we'll get pretty close to that and be able to make decisions. Was that -- was your...

[Kaveri Pohlman, analyst]

Bone response.

[Dane Leone, executive]

I think it would be helpful. Maybe, Nancy, you could just explain the difference between measurable disease and non-measurable disease at baseline, because I think that might be helpful for everyone.

[Nancy Valente, executive]

Sure. I mean, measurable disease means it has very basically 2 dimensions, and it's got to be a metastatic site in an organ, or a measurable lymph node bigger than a normal lymph node. Non-measurable would typically be bone-only disease, or if a patient had bone-only disease. Our patients had measurable disease, and they could have also had bone disease on top of that. I can tell you 2 of the 4 responders had bone disease in addition to their other measurable disease. So, we have seen responses in bony -- in patients who had bony disease.

[Operator]

Our next question comes from the line of Brian Cheng from JPMorgan.

[Lut Ming Cheng, analyst]

Maybe first one is just on the 3 confirmed responders. I think just kind of piggybacking on what was the question prior to this. What was the background of the 3 confirmed responders? Can you just kind of give us what -- how many lines they have and kind of give us a sense of what their historical responses were to prior [ AR ] or even -- I see that they had -- some patients had radiation. So just curious like what were [ their ] responses like? And I have a follow-up.

[Bassil Dahiyat, executive]

Yes. I mean, Nancy, you could take that. You know all the details. I'd say they were really, really heavily pre-treated in rough shape when we got them.

[Nancy Valente, executive]

Yes. They had to be progressing through prior therapies. They had to have at least 2 prior therapies. They're -- I'm looking at the background and they had anywhere from 3 to like 7 prior therapies, including XRT. I'm just looking at...

[Bassil Dahiyat, executive]

Yes. That's a lot of detail, Brian. So we're picking up our notes.

[Nancy Valente, executive]

Yes. So, one patient had 3 prior therapies, not including any radiation. Second patient had 3 prior therapies. The third patient had 6 prior therapies, not including -- so none of these are with radiation or counting that. And then last patient had 2 prior therapies. They all included -- one -- They all included docetaxel or one included carboplatin. 2 had prior radiotherapy. Let me just see. That's -- I can't really bet on their prior responses, but maybe in an upcoming presentation we could drill down into each individual occasions.

[Bassil Dahiyat, executive]

Yes, yes.

[Bassil Dahiyat, executive]

But suffice to say, they'd seen a lot of prior therapy, Brian.

[Lut Ming Cheng, analyst]

And then a follow-up here is, as you're looking at this data, and I think the last time we saw the combo data might be back in -- let's see -- I think, back in 2022. How should we think about the low-hanging fruit piece? What is the lowest-hanging subset of the mCRPC patient that investors should think of when it comes to vudalimab? And is it high risk, is it genetically defined? How do you think about the low-hanging fruit either with combo or monotherapy?

[Dane Leone, executive]

Yes. I think it's a great question that we're obviously going to have a fuller answer to as we get these cohorts enrolled over the course of this year and can really look for a reliable signal, hopefully in 30 patients per cohort for monotherapy and for the combination. But the way we're thinking about it now is we just had an update on part 2 of CheckMate 650 at ASCO GU, where Ipi/Nivo was tried in every foreseeable combination relative to cabazitaxel.The emergent signal that we have in a small [ end ] right now is better than anything that was achieved in that study in a comparable patient population post-taxane patients. So that's step 1. We think we have something differentiated that hasn't been done with an IO therapy before in this heavily pre-treated patients, even going back to the table that we have looking across all of our peer studies.And then step 2 is more of a question, I think you're asking of how we see the treatment landscape evolving. As everyone knows, PLUVICTO is probably going to be used more and more. They had a good 2023 of commercial uptake in the United States, and so that has to be on our minds as we look through future development. But the interesting point here is the toxicity profile of vudalimab is non-overlapping with PLUVICTO. So that's one.And secondly, there's emerging evidence presented and published late last year that treatment of PLUVICTO might actually sensitize the tumor microenvironment to checkpoint targeted therapy. And this all has to be proven out in the clinic within larger studies. And step one for us is still defining what we think the clinical profile is of vudalimab monotherapy for these heavily treated metastatic patients with measurable disease.But once we understand that, I think there's a number of options how to move forward in an intelligent manner for development of this drug. So we're excited for what we're seeing. Again, early days here. So, we don't want to get over our [ skis ], but we'll look for a confirmation of this signal as we move throughout the year.

[Operator]

Our next question comes from the line of Alec Stranahan from Bank of America.

[Unknown Analyst]

This is [indiscernible] for Alec. Just a first, quick question. I think this was briefly mentioned before, but just wanted to check, I didn't catch everything. But what would be like a good benchmark, or like a comparator for us to look at in comparison to the vudalimab monotherapy data presented today? That's my first question. Second question on quality-of-life data. When can we expect to see some color regarding that, if you're keeping track of it and could you maybe provide some -- shed some light on what you're currently observing in the clinic in terms of quality-of-life and some patient-reported outcomes?

[Bassil Dahiyat, executive]

Yes. We're not -- sorry. Dane, you want to take both of them or?

[Dane Leone, executive]

Yes. I think -- I mean that question is really a question of when we have a totality of a cohort in discussion with our clinical investigators. Is the clinical experience overall for these patients something that we should move forward? And -- so to that effect, the totality of the data, we don't know at this point, right? We want to see, hopefully, 30 patients in each of these cohorts, the monotherapy cohort and the docetaxel combination cohort, to have that conversation with our clinical investigators. So it's a great question and that's really what we're hoping to answer.In terms of the first part of the question, that's why we provided the data table and the slides. Because each of these studies that we're looking at are peer studies, are exciting, right? We're excited about xaluritamig and the clinical response there. But they're also limited in terms of their size and their scope and the comparability of the patients that were enrolled.So, we don't want to make apples-and-oranges comparisons of novel agents for the treatment of these prostate cancer patients right now. But I think what we could say is a number of these programs -- xaluritamig, I think is undeniable. And hopefully, our vudalimab monotherapy program as well seem to be surpassing what you could probably expect for a late line chemotherapy from contemporary studies as we mentioned the cabazitaxel response rates and the CheckMate 650 study and the therapy study.And then once you get to earlier lines of therapy, I think it is a toxicity profile. And again, if it does seem that PLUVICTO is sensitizing the tumor microenvironment for IO therapy, we have a therapy that does not have overlapping [ hemetox ] and could be an interesting idea to explore down the road.

[Operator]

Our next question comes from the line of Tara Bancroft from TD Cowen.

[Tara Bancroft, analyst]

So my question is more of a general question. So are there any other combos besides chemo that you're considering or really excited about that could increase the robustness of this data? And then, in -- specifically referring to the chemo combo, how do you think safety will look in that combination? Is there any update that you can provide on how that's going now in the 1704 study?

[Bassil Dahiyat, executive]

So I guess on the first one, other combos other than the chemo, we think chemo is a very important one in this setting because it is the predominantly used therapy post androgen still. I think it's really interesting to imagine post-PLUVICTO treatment maybe not in concert, given the intriguing immune priming activity that PLUVICTO perhaps has from some small studies recently published and they got a [ UCSF ].So I think those are the 2 top things on our mind now. But I think in the future, as we see our CD28 technology evolve, our XmAb808 program is, of course, aimed partially, at least at prostate maybe even predominantly at the moment. And as that one evolves in combo with pembro, we're certainly keeping our eye on how to maybe use that with vudalimab if the stars align, right?So that's maybe the other big one that we're thinking of. The future might hold combinations with CD3 bispecifics, with molecules like vudalimab. I think that's something people are looking at, or just starting to happen in the clinic now. I'm aware of some CD3 solid tumor molecules that are being tested with checkpoints. That's maybe a little bit further off in the future, though.And then I guess your second question was on what can we say about safety from the ongoing [ 04 ] study, given that we're not sharing specific data. So maybe, Nancy, do you want to comment?

[Nancy Valente, executive]

Yes. Absolutely. So maybe I can share also that, since we last presented data, we amended the protocol -- the combination protocol in prostate cancer to remove the carboplatin in all, but the aggressive variant. And we're really focused on the taxane, specifically docetaxel as first-line chemotherapy. And so far, based on feedback from investigators, we seem to be seeing better tolerability with these new regimens than the prior one.

[Bassil Dahiyat, executive]

Operator, we have any other questions?

[Operator]

No. That looks like that's clear.

[Bassil Dahiyat, executive]

Great. Well thanks, everybody, for joining us today, and have a wonderful evening. We look forward to our next update.

[Operator]

Thank you for participation in today's conference. This does conclude the program. You may now disconnect.