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Mark Eisner

Thank you, Marianne. We've made significant progress in clinical stage programs, and I'm looking forward to sharing the details with you today.
Let's start with our hepatitis delta program, which continues to be a key focus for us. We're making excellent progress towards initiating our ECLIPSE Phase 3 program in the first half of this year. These studies will form the basis of our marketing applications.
Before we dive into the ECLIPSE program, let me briefly recap our SOLSTICE Phase 2 data, which has given us confidence to move forward with our Phase 3 program. We saw impressive virologic responses across multiple cohorts. To provide some context, when we refer to HDV RNA target not detected or TND, we mean there is no measurable presence of the virus in the blood. This is the most stringent measure of viral suppression we can achieve with current testing methods.
In our de novo combination therapy arm at 24 weeks, 41% of patients achieved HDV RNA levels below the target not detected threshold. Even more impressively, this increased to 64% of patients at week 36.
In our rollover cohort, which provides our longest follow-up data, we saw even more encouraging results. At week 60, four out of five patients or 80% achieved target not detected levels. This suggests the potential for durable and deepening responses with our combination therapy over time.
Importantly, we also observed significant declines in hepatitis B surface antigen levels. At week 24, approximately 90% of participants receiving the combination of tobevibart and elebsiran achieved surface antigen levels below 10 IU per ml. This is a crucial finding because reducing hepatitis B surface antigen is essential for controlling both hepatitis B and hepatitis B virus replication. Additionally, the combination of tobevibart and elebsiran demonstrated a favorable safety profile across all the cohorts.
Our approach has garnered significant regulatory support, which speaks to the potential impact of our therapy. We've received breakthrough therapy designation and fast track designation from the FDA. The EMA has granted us PRIME designation and orphan drug status. These designations could help accelerate our development and review process, potentially bringing this much-needed therapy to patients sooner.
Turning to our hepatitis B program; we are looking forward to sharing functional cure data in the second quarter of this year. This functional cure data will be a crucial milestone for this program. I want to reiterate that we would pursue the development of this program only with a partner.
I'm very excited about the progress we've made in our infectious disease programs. We're on the cusp of potentially changing the treatment landscape for hepatitis delta, and we're looking forward to sharing our hepatitis B functional cure data.
Now let me shift gears to discuss our oncology portfolio to discuss the significant progress we've made with the PRO-XTEN platform. As Marianne mentioned, we've shared compelling data at our investor event in January, and I'd like to dive deeper into those results.
Before we get into the specifics of each program, let me briefly recap the PRO-XTEN platform. This innovative technology allows us to create dual masked T-cell engagers designed to be selectively activated in the tumor microenvironment. The key advantage is the potential for a wider therapeutic window, allowing for higher dosing and improved efficacy with reduced systemic toxicity.
The PRO-XTEN masks are unstructured and hydrophilic, acting as a shield to prevent T-cell engagement in normal tissues expressing the target antigen. Importantly, their fluid nature also allows access to the cleavable linkers, enabling efficient activation when in the protease-rich tumor microenvironment.
The PRO-XTEN masks are universal and have been clinically validated as seen in ALTUVIIIO, an approved therapy for hemophilia. ALTUVIIIO contains three protease cleavage sites that are quickly cleaved in a high protease microenvironment of a clot during the clotting cascade, demonstrating the ability of the PRO-XTEN system to enable efficient and tightly regulated unmasking. We believe this approach could overcome many limitations seen with traditional unmasked T-cell engagers, and the validated nature of the platform gives us confidence in its potential application across our oncology programs.
Let's start with the VIR-5818, our HER2-targeted T-cell engager. We've seen encouraging efficacy signals across multiple HER2-positive tumors, particularly in colorectal cancer. At doses of 400 micrograms per kilogram and above, we observed a 33% confirmed partial response rate in colorectal cancer patients. It is important to note that these patients had exhausted all standard of care options and were heavily pre-treated with many having received multiple prior lines of therapy, including HER2-targeted treatments.
Additionally, one of these three responses was observed in a patient on the every three-week dosing schedule. I'd also like to highlight a compelling case we presented at our recent investor event, which speaks to the potential for durable responses.
A patient with HER2-positive colorectal cancer, who progressed through six prior lines of therapy, including HER2-targeted agents, achieved a partial response. Remarkably, this response has been sustained for over 18 months with the patients still on study as of our last data cutoff.
Crucially, we've observed efficacy in microsatellite stable or MSS colorectal cancer tumors, which typically are resistant to immunotherapies. This suggests VIR-5818's ability to overcome the immunosuppressive tumor microenvironment in these hard-to-treat patients. To put these results in context, it's important to note that for patients who have exhausted multiple lines of treatment, current regimens like LONSURF plus bevacizumab typically show objective response rates in the single digits.
Our early results, therefore, are particularly encouraging in this heavily pretreated population. The safety profile of VIR-5818 has been favorable with no high-grade cytokine release syndrome or CRS and without mandatory prophylactic corticosteroids. We're continuing dose escalation on an every three-week schedule to optimize efficacy while maintaining this favorable safety profile.
We're also exploring combination strategies, including with pembrolizumab. It's worth noting that VIR-5818 utilizes the pertuzumab binding epitope, which enables potential combination strategies with trastuzumab-based therapies in an earlier-line setting.
Turning to VIR-5500, our PSMA-targeted T-cell engager for prostate cancer, we've seen impressive early results in our ongoing Phase 1 dose escalation study. Among the 12 patients treated in the efficacious dose range, 100% experienced PSA declines with 58% achieving PSA50 response and 8% achieving PSA90 response. This is particularly encouraging given the heavily pretreated nature of this population and the early stage of dose escalation.
Like VIR-5818, VIR-5500 in early dose escalation has a favorable safety profile with minimal high-grade adverse events and no Grade 3 or higher CRS. Notably, these results have been achieved without the use of prophylactic corticosteroids or anti-IL-6 therapies, which are often required with other T-cell engagers, including masked T-cell engagers.
Importantly, we have not observed any cases of on-target, off-tumor toxicities such as hearing loss, which have been reported with other PSMA-targeted therapies. We're continuing dose escalation and based on our favorable safety profile, we believe there's significant room to potentially improve efficacy further. As we move to higher doses, we expect to see deeper and more durable responses, which could significantly improve outcomes for patients with prostate cancer.
We're also actively exploring every three-week dosing, which could be a significant advantage, especially in earlier lines of therapy. This potential for less frequent dosing is supported by VIR-5500's pharmacokinetic profile, which shows a half-life of 8 to 10 days. The potential for less frequent dosing combined with the encouraging efficacy and safety profile we've observed could offer meaningful benefit to patients across various stages of prostate cancer treatment. Importantly, these results have been achieved without the need for prophylactic corticosteroids or anti-IL-6 therapies.
For VIR-5525, our EGFR-targeted T-cell engager, we're on track to initiate the Phase 1 study in the first half of this year. This program has potential to address multiple high-value indications, including non-small cell lung cancer, colorectal cancer and head and neck cancer. We're leveraging our learnings from VIR-5818 and VIR-5500 to optimize the study design and dosing strategy. Based on our experience with the PRO-XTEN platform and the successes we've seen with our other T-cell engagers, we're confident in our ability to achieve a broad therapeutic index with VIR-5525.
Looking ahead, we anticipate sharing additional data from our ongoing dose escalation studies for VIR-5818 and VIR-5500. While the exact timing is still to be announced, we expect to present more mature data at higher doses for both programs. This will include results from both weekly and every three-week dosing schedules, which we believe will provide valuable insights into the optimal dosing regimens for these therapies.
In conclusion, I'm very excited about the progress we're making across our oncology portfolio. The early data from our T-cell engager programs are further validating the potential of the PRO-XTEN platform, demonstrating both efficacy and the ability to dose higher than traditional unmasked approaches.
We believe we're well-positioned to redefine the treatment landscape for several challenging solid tumors. Our team remains focused on executing our clinical development plans and unlocking the full potential of these promising therapies.
With that, I'll now hand the call over to Jason.

Jason O'Byrne

Thank you, Mark. I'm really pleased to share that our hard work on rightsizing the cost structure, improving efficiencies, and making thoughtful investment is paying off. Since late 2023, we've taken significant steps to streamline operations and focus on our most promising programs. We've implemented two restructurings, closed two sites and deprioritized certain programs.
Then in September, we executed the agreement with Sanofi to license three dual mask T-cell engagers and the PRO-XTEN technology. While this added modestly to our cost structure, including approximately 50 new team members from Sanofi, it significantly expanded our pipeline and brought in critical expertise in oncology, T-cell engager clinical development, and masking technology. This, combined with our existing expertise in protein engineering and immunology, positions us well for future growth and innovation.
During our budget process last fall, we applied further financial discipline, culminating in our January 8 announcement to advance our HBV program only with a development and commercialization partner. Many of these actions have led to substantial improvements in our financial performance. Let me highlight a few key financial metrics for 2024 compared to 2023.
R&D expenses for 2024 were $507 million compared to $580 million in 2023. This decrease was achieved despite absorbing approximately $103 million in Sanofi transaction expenses related to our licensing agreement. Excluding this one-time transaction-related expense, our R&D spending decreased by approximately $176 million or about 30% year over year, reflecting our continued focus on cost management and program prioritization.
G&A expenses decreased to $119 million in 2024 from $174 million in the prior year. This significant reduction, reflecting a 32% decrease year over year was primarily achieved through multiple cost-saving initiatives implemented since late 2023. As a result, our net loss for 2024 was $522 million compared to $615 million in 2023. Excluding the $103 million Sanofi R&D transaction expense, our net loss for 2024 was $419 million, representing a decline of approximately 32% from the previous year.
We ended 2024 with 408 employees compared to 587 at the end of 2023, representing about a 30% year-over-year reduction. It's important to note that the 408 includes approximately 50 employees, who joined us from Sanofi as part of our licensing agreement.
Now turning to cash. Our 2024 net cash consumption was roughly $532 million. Excluding approximately $179 million of Sanofi transaction-related items, the decrease to cash and investments for 2024 was approximately $354 million.
We're starting 2025 with a strong financial position of $1.1 billion in cash, cash equivalents and investments. It's important to note that this $1.1 billion figure already excludes the $75 million pending EGFR milestone, which is currently in escrow and classified as restricted cash. Based on our current operating plan, we anticipate this will provide runway into mid-2027.
As we look ahead to 2025, I want to emphasize that our capital deployment strategy remains focused on our most promising programs. Our priorities for the year are, first, we'll accelerate ECLIPSE clinical enrollment and initiate activities toward registration; second, we'll invest in VIR-5500 to rapidly advance the program, capitalizing on the very encouraging PSMA data that was shared in January; third, we'll continue enrolling patients in VIR-5818, potentially leveraging the promising early data we see in HER2-positive colorectal cancer; fourth, we'll initiate the Phase 1study for VIR-5525 in patients with EGFR-expressing solid tumors; and finally, for our hepatitis B program, we continue to pursue a partnership strategy. We believe this approach will maximize the value of the asset while allowing us to focus our internal resources on our lead programs.
In closing, I'm confident that our $1.1 billion in cash will fund these priorities into mid-2027 based on our current operating plan. This reflects our ongoing commitment to disciplined capital allocation, ensuring we have the resources to advance our key programs while maintaining financial flexibility.
With that, I'll hand it back to Rich to initiate the Q&A session.

Question and Answer Session

Richard Lepke

Thank you, Jason. This concludes our prepared remarks, and we will now start the Q&A section. (Event Instructions)
I’ll turn it over to you, operator.

Operator

(Operator instructions)
Gena Wang, Barclays.

Hang Hu

Hi. This is Hang Hu on behalf of Gena Wang from Barclays. So we have two questions. First one is for T-cell engager. So you are using the cleavable linker. So can you elaborate the mechanism for the cleavage and how efficient is the cleavage in the tumor microenvironment, for instance, for the single cleavage and for dual cleavage?
And the second question is for HDV. So regarding the ECLIPSE registrational study starts in the first half of the year. So what additional steps you need to start this trial? And we understand this is event driven, but what is your estimated timing to complete the enrollment? Thanks.

Marianne De Backer

Thank you very much for that question. I'll ask Mika to address the first one related to the mechanism of action related to cleavage of the linkers.

Mika Derynck

Yeah. Thank you for that question. So we believe that we're getting efficiently cleavage for both masks. And the reasons for this is that we've seen really nice activity in both the HER2 program as well as the PSMA program, both having the double mask and both having the same PRO-XTEN masking technology as well as both having the same protease linkers on both sides of the linkers.
In addition to that, seeing that activity that appears to be tumor-specific as we've not seen any significant toxicity in the periphery, very minimal CRS, and the absence of prophylactic -- widespread prophylactic corticosteroids, we're really seeing that tumor-specific cleavage. Besides that, the same exact XTEN masking technology is used in an approved drug, ALTUVIIIO, as Mark had mentioned.
This drug is a hemophilia drug. It has the same XTEN mask, and it uses three thrombin cleavage sites. And it is efficiently cleaved, three sites in the setting of a clot where you have efficient thrombin activation, efficient cleavage and clotting as needed as well as not having clotting in the state where there is no clotting -- activated clotting cascade.
So the efficiency of being able to cleave three sites, there's nothing about the XTEN masks in of itself that prevents access to the cleavage sites. Three sites versus two sites versus one site, tumor microenvironment is known to have very high protease activity. So we don't think that the number of sites is really an issue in terms of efficiency of cleavage.

Marianne De Backer

Thank you, Mika. So as to your second question relates to additional steps before starting on the ECLIPSE trial, I will ask Mark to address that.

Mark Eisner

Sure. Thank you for the question. So we are on track to initiate the ECLIPSE program in the first half of this year. The team is working with a high sense of urgency and excitement to get these trials up and running. We're confident that we will be able to initiate these trials in the near-term and efficiently recruit patients because of the high unmet need in HDV and our very compelling SOLSTICE Phase 2 data. So we're working quickly to get these studies up and running, and we will provide some updated guidance at a future point.

Operator

Paul Choi, Goldman Sachs.

Paul Choi

Hi, thank you. Good afternoon, and thank you for taking our questions. My first question is on the 5525 EGFR TCE program. Can you maybe paint for us a picture of what sort of patients you're envisioning for your Phase 1study? Are you going to allow sort of MET treatment experienced patients or patients who have been treated with J&J's RYBREVANT bispecific be enrolled into your study? Any sort of color to understand what population you'll be there would be great.
And my second question is on the hep B program. I realize that the MARCH B data is coming up here next quarter fairly soon. But as you sort of think about go/no-go criteria for the future, even though you plan to partner it, can you maybe just again refresh your views on what you think is sort of clinically meaningful here and what you think would potentially be attractive to a theoretical development partner? Thank you.

Marianne De Backer

Yes. Thank you, Paul. On the hepatitis B program and our go/no-go criteria, I'll ask Mark to address.

Mark Eisner

Sure. Thanks for the question, Paul. So as you said, we will have our functional cure rate data second quarter of this year in particular. Is going to be the functional cure data 24 weeks of treatment. We had compelling results at the end of treatment at 48 weeks in the surface antigen low patients with 39% as loss in the doublet with the tobevibart, elebsiran, and 46% as loss in the triplet including pegylated interferon.
In terms of go/no-go criteria, what we said before is we're looking for a 30% functional cure in the triplet, 20% in the doublet, generally speaking, that's based on our KOL interactions and what could be clinically meaningful. I think it's also maybe worth mentioning that GSK's bepirovirsen had a 16% functional cure, and they're in Phase 3 based on that. So their Phase 3 program will read out early next year, but that kind of gives you a little bit of context for what's been achieved so far.
So we will be partnering this program and engaging with partners once we have the functional cure data. And I hope gives you a little bit of context for what we're looking for.

Mika Derynck

So I can answer the EGFR question. So this is a pretty standard first-in-human Phase 1 study. And in such that patients must have exhausted all current standard of care to be enrolled on study, which means that they must have exhausted standard approved drugs, but we will allow for patients, who may have been on any prior experimental drugs as well.
So we typically do get a smattering of different types of patients. We are enriching for patients who have EGFR as a target that's important such as lung cancer, head and neck, pancreas and colorectal cancer. But other than that, we're probably going to have patients with a variety of different prior treatments.

Operator

Mike Ulz, Morgan Stanley.

Avraham Novick

Hey. It's Avi Novick on the line from Mike. Thank you for taking our questions. So I guess, number one, on 5525, given the strong safety profile you've seen in the Phase 1studies of 5818 and 5500, do you see a read-through to 5525? And do you believe you can possibly more aggressively escalate doses in the upcoming Phase 1 study?
And then my second question is what are you thinking with respect to disclosing data for 5525? Do you think you would maybe plan to do an initial data update as you did for 5818 and 5500 or await for more mature data? Thanks.

Marianne De Backer

Yeah. Thank you for that question. As you know, there have been significant learnings from the HER2 program that were translated the 5500 program and the PSMA program could start at the higher dose and escalate more swiftly compared to the original 5818 program. So we expect that we will continue to learn across the clinical programs and that these learnings will benefit us also as we go into the 5525 program. Anything you want to add here, Mark or Mika?

Mark Eisner

I mean the only thing is that EGFR is broadly expressed in normal tissue, which makes it different from the PSMA program where, of course, there is PSMA expressed outside the prostate. And then the HER2, there is HER2 expressed in lung and heart and other normal tissues, but EGFR is broadly expressed.
So we're looking forward to this program because it will be a really rigorous test of our dual masking approach and the specificity for unmasking the tumor microenvironment, whether we can achieve an excellent therapeutic index in EGFR-positive tumors, as Mika alluded to before.
But to Marianne's point, yes, the learnings from the earlier two programs have and will continue to inform 5525 and further programs. So we do expect to be efficient in how we conduct that.

Mika Derynck

Yeah. And I might just also add in that from the HER2 program, again, the EGFR molecules will use the same PRO-XTEN technology, the same protease linkers, et cetera. But with the HER2 program, we've seen a prior naked HER2 T-cell engager that had a Grade 4 CRS at 0.5 micrograms per kg and IL-6 levels in the 10,000 picomole per ml range, suggesting that there's plenty of normal expression of HER2, enabling that significant CRS.
But when you look at our 818 double masked molecule, we -- our start dose was 1 microgram per kg. So higher than this fully unmasked HER2 drug, GBR 1302, that was in the clinic many years ago. So we do believe with that very wide therapeutic index that we've seen for the HER2 double mask that that will give us confidence on the 5525.

Operator

Roanna Ruiz, Leerink Partners.

Mazahir Alimohamed

Hi, this is [Mazie] Alimohamed on for Roanna Ruiz. Thanks for taking our questions. But first, so given the early clinical response signals in the heavily pretreated patients, what are your thoughts of potentially moving the T-cell engagers into earlier lines of therapy in future trials? And also, could you elaborate on how machine learning and antibody engineering -- your background in that and those capabilities are being applied to optimize the design and efficacy of your T-cell engagers?

Marianne De Backer

Yeah. Thank you for that question. As we move into earlier lines, maybe Mark, you can address that.

Mark Eisner

Sure. So yes, you are correct that in both the HER2 and PSMA programs, the basket trial for HER2, PSMA is all metastatic castration-resistant prostate cancer, but they're heavily pre-treated patient population, very heterogeneous in terms of their clinical features and prior treatment history. So that is where we are starting. For the PSMA program, of course, we are interested in getting into earlier lines of treatment. This is something that we will talk more about in the future time, but clearly, that is of interest.
In terms of your question about the dAIsY machine learning and how to optimize the TCE platform, I think one of the beautiful parts about this deal, bringing in the Amunix platform and the people with it is that we can apply our antibody discovery platform and our dAIsY AI abilities to optimize the next generation of T-cell engagers.
So we are using that to more rapidly identify and optimize the binders for the next generation of T-cell engagers. So I think there's a real synergy there between our peer's antibody discovery and optimization platform that's AI-driven and the T-cell engager platform that we now have in-house.

Marianne De Backer

Yeah. I would just add that our protein engineering platform is really such that we start with a starting point of a protein. It could be an antibody; it could be a BiTE or single or whatever it might be. And then we deploy basically a population of different models to come up with molecules that have increased characteristics, better potency, increased developability, and so on.
And it's a combination of both internal models and external models, so large protein models and a lot of internal data that we have generated over the years that together gives us an output that we can quickly test in biological models and that sort of feeds back into the database.

Operator

Eric Joseph, JPMorgan.

This is Billy on for Eric. Thanks for taking our questions. Quick one on the dosing frequency for the EGFR. You've pushed to go to two, three weeks with the other two. Is this something that you continue with the EGFR?

Mika Derynck

Yeah. So we are looking at both Q week and Q3 week for both the HER2 and the PSMA program, and we are planning to do the same for the EGFR. We're encouraged that the half-life so far for both of our clinical programs are very encouraging and that for the HER2 program appears to be safe and efficacious at both schedules.

Operator

Phil Nadeau, TD Cowen.

Phil Nadeau

Good afternoon. Thanks for taking our questions. Two from us. The most common question we currently get on Vir is about the expectations for a dose response for 5500. I'm sure you get that same question. Can you talk a little bit more about what gives you confidence that higher doses will produce deeper, more durable PSA responses given that there wasn't a clear dose response in the initial data? That's the first question.
Second question on the timing of the next updates for 5500 and 5818, we appreciate it's too early to give a specific timing guidance, but could you speak to what you hope to have in the next update in terms of quality and quantity of data? Will you wait for some certain number of patients in the trials or do you want to wait for the Phase 2 dose? Some sense of kind of what you hope to accomplish before giving us the next update would be helpful. Thank you.

Marianne De Backer

Yeah. Thank you, Phil. I mean we are really trying to, as you mentioned, right, balance communication of data that is really meaningful with the need to draw important conclusions as to our next steps from the data. And as you know, both programs are in dose escalation. We just discussed, we are exploring two different dosing frequency models.
We are exploring in combination with pembro. So a lot of data that needs to read out of safety, efficacy, durability and so on. So as that data develops, we will -- as soon as we have really meaningful updates, of course, share that with you all.
As it relates to the dose response, yes, we do get that question quite often. So either Mark or Mika, you want to address it.

Mark Eisner

Yeah. I think what we tried to emphasize in our investor event in last January is that this is very early in the PSMA program in terms of dose escalation. And we believe we've presented compelling early signs of efficacy in terms of PSMA -- I'm sorry, PSA declines and excellent safety with minimal CRS and minimal toxicity. So we have a lot of room to move on the dose. So we've been escalating the dose both in Q week and Q3 weeks, and we are anticipating to see deeper and more sustained efficacy as we escalate the dose in that program.
The other thing maybe to mention is that we have now shown good compelling early signs of efficacy and safety of both the HER2 and PSMA program. So we're really validated, we think, the platform and the masked, dual masked nature of the platform and the specificity of our ability to unmask these molecules in the tumor while maintaining a very high safety profile.
Maybe just to mention one other thing, which is in that colorectal cancer patient we referred to today and that we presented in our investor event in the HER2 program that when we escalate the dose from 60 micrograms to 600 micrograms per kilo in that patient, we saw a deepening antitumor responses.
So that patient is an example of what can happen as we escalate the dose. Now of course, the PSMA program is even earlier, and we're continuing to escalate the dose. But we anticipate with higher doses, we'll see better efficacy with acceptable safety.

Operator

Alec Stranahan, Bank of America.

Alec Stranahan

Hey, guys. Thanks for taking our questions. Just two quick ones from us. First on 5525, apologies if this was already asked, but just on the need for steroid prophylaxis, do you think you'd approach this similarly to studies for your other two assets or maybe a different approach just given the breadth of the EGFR expression?
And secondly, I appreciate that the additional pre-clinical mask TE targets are undisclosed. But I guess as you're approaching maximizing the value of the PRO-XTEN platform in oncology, is your development process driven more by de-risked targets or areas of high unmet need maybe with a novel target? Thank you.

Marianne De Backer

Thank you, Alex. Maybe I'll address the second question. So since we announced the data on January 8, there has been quite a bit of outreach as it relates to our platform. And so we have for ourselves defined a set of targets that we would believe would be highly valuable as next programs, but we also are getting educated on what some potential partners might be interested in.
So we will certainly share going forward some more insight into how we are thinking about what next pre-clinical programs could be that really take advantage of the PRO-XTEN platform, because we do want to make sure we extract that value out of the platform. And again, with promising data across two clinical programs, we think there's a high belief in the potential there.
As it relates to the need for prophylactic corticosteroids, just clarifying that we did not use any in our prior program and for 5525, the same is true. I don't know Mark, Mika, anything to add?

Mika Derynck

Yeah. So we've built quite a bit of confidence with this platform with the other two drugs, again, not using -- not having to use prophylactic steroids with really minimal CRS and very minimal IL-6 levels. So for the 5525, we are starting that study without any prophylactic steroids.

Operator

Joseph Stringer, Needham.

Joseph Stringer

Hi, thanks for taking our questions. Financial one from us. Can you just remind us of the details of the collaboration agreement with Alnylam on the elebsiran component? I believe it's a cost profit share, but just want to make sure of the details on the cost share.
I guess my question is around the financial impact of this. Does Alnylam have optionality coming up for that asset? And is that potential decision built into some of your OpEx and cash burn assumptions over the next few years? And then as a follow-up, how does that current collaboration agreement impact your potential partnership negotiations for the HBV program? Thank you.

Marianne De Backer

Yes. Thank you for that question. So our collaboration agreement with Alnylam stemming from 2017 is a pure financial arrangement. So there's no operational role that Alnylam is playing in the development nor the commercialization.
Alnylam does have an option to either step into the program and share 50% of the cost that it relates to the electron component of the regimen and then, of course, also share the commensurate percentage of the profit or opt out and have a typical type of milestone and royalty deal. So that is an option that Alnylam still needs to decide on.
The impact from any partnership related to HBV, both are possible. Again, because the nature of the deal with Alnylam is a pure financial one, it doesn't preclude from a large pharma partner to step in and take an operational role on the clinical development and commercialization. Obviously, it would be easier if there was sort of one partner for the program that both are possible.

Jason O'Byrne

Can I just add, yeah, on this? Further details will be in the 10-K on the Alnylam agreement. And just as you think about our runway, we have sort of assumed the worst case in the shorter term, which is that Alnylam opts out. In the shorter term, if they opt in and do a profit share, that would potentially be upside.

Operator

Patrick Trucchio, H.C. Wainwright.

Patrick Trucchio

Thanks. Good afternoon. Just a couple of follow-ups from me on the HDV program. I'm wondering now as more time has passed and you've had more time to kind of digest the data from SOLSTICE if there's been any further learnings that could help inform the ECLIPSE program?
And then separately, I was just curious if you could talk more about the relative importance of demonstrating that robust reduction in HB surface antigen in the hepatitis delta setting and how we should think about this reduction for combination treatment relative to the monotherapy antibody, particularly as we think about long-term outcomes in this chronic treatment setting with delta?

Mark Eisner

Yeah, thanks for the question. So in terms of SOLSTICE, just to recap for everyone, we did see at 24 weeks, 41% of patients reaching complete viral suppression or target not detected at 24 weeks, 64% at 36 weeks, and in the 80% range at 60 weeks in the rollover cohort. So I think we're really seeing unprecedented levels of viral suppression of the delta virus. So we're very excited about that, and we're very keen to move into the ECLIPSE program.
Obviously, we've learned a lot about delta, both in terms of the data, but importantly, about the demographics of the disease, where the patients reside. And I think those learnings have really informed how we've approach site selection, investigator selection and things of that nature. So we're not prepared to share more details about that today, but essentially, that's going to help us, I think, really optimize our Phase 3 program.
In terms of your question about hepatitis B surface antigen reduction, yes, in the combination of tobevibart and elebsiran, we are seeing a 3-log reduction in hepatitis B surface antigen, which is much, much greater than our monotherapy with the antibody tobevibart, which is a 1-log reduction. We think this is really important because it shows the potency and the depth of antiviral effect of our combination therapy. It shows that we are as hepatitis B surface antigen is critical for a delta or a life cycle of forming a virion that this just really taken together with a very profound viral suppression data that we really think we have a very, very good chance of long-term viral suppression for patients.
In terms of long-term outcomes, I can speculate that because we can achieve such deep and durable suppression of delta virus and HBV surface antigen that we hope that will translate into better outcomes for patients, less progression to cirrhosis, less progression to liver cancer and other poor outcomes. Of course, we have to demonstrate that. But the virus does drive those poor outcomes. So we do think that suppressing the virus as well as we can with our combination should lead to better outcomes for patients. So we're very excited about the program, and we're moving with all pace to our Phase 3 initiation.

Operator

This concludes the Q&A session of the call. Thank you for participating. And I'll turn the call back over to Marianne De Backer.

Marianne De Backer

Thank you, operator. As we conclude, I'd like to emphasize the significant strides that we have made in 2024 and our exciting path forward. We've successfully transformed Vir Biotechnology into now a dual platform company with promising advancements, as you have heard, in both infectious diseases and in oncology. Our hepatitis delta program, as Mark just mentioned, is poised to enter Phase 3 trials, while our innovative T-cell engager platform has shown those really encouraging early results across multiple solid tumor types.
Our strong financial position with a runway extending into mid-2027 also provides us with the resources to advance our key programs through critical value and inflection points.
So we remain committed to our mission of harnessing the power of the immune system to transform patients' lives, and we are more confident than ever in our ability to deliver on this promise. Thank you, all, for your continued support and for joining us today. We look forward to updating you on our progress in the coming months.
Operator, you may end the call.

Operator

Ladies and gentlemen, that concludes today's call. Thank you all for joining, and you may now disconnect.