Prothena Corp Public Ltd Co Q4 FY2023 Earnings Call

Good day ladies and gentlemen and welcome to the Prothena Biosciences Fourth Quarter and Full Year 2023 Financial Results Conference Call. My name is Crysta and I will be your coordinator for today. At this time, all participants are in a listen-only mode. We will be facilitating a question and answer session towards the end of today’s call. I would now like to turn the presentation over to Mark Johnson, Vice President of Investor Relations at Prothena. Please proceed.

Thank you, operator. Good afternoon, everyone and welcome to today’s call to review Prothena's business progress, fourth quarter and full year 2023 financial results and our 2024 financial guidance. Please review the press release we issued earlier today, which is available on our website at prothena.com and is also attached to a Form 8-K filed today with the SEC. In addition, we are using supplemental slides which are available on our Investor website Events and Presentation section. On today's call, Dr. Gene Kinney, our President and Chief Executive Officer will provide opening remarks including an overview of Prothena's corporate and development strategy; then Brandon Smith, our Chief Operating Officer will provide an update on our pre-commercial progress for our wholly-owned Birtamimab program which is in Phase 3 for the treatment of patients with MAYO Stage IV AL Amyloidosis. Hideki Garren, our Chief Medical Officer will provide an update on our ongoing clinical programs. Tran Nguyen, our Chief Financial Officer and Chief Strategy Officer, will then discuss our 2023 financial results and 2024 financial guidance before turning it back to Gene for closing remarks at which point we will open the call up for a Q&A session. Before we begin, I would like to remind you that during today's presentation, we will be making forward-looking statements that are subject to certain risks, uncertainties and other factors that could cause actual results to differ materially from those referred to in any forward-looking statements. For a discussion of the risks and uncertainties associated with our forward-looking statements, please see our press release issued today, as well as our most recent filings with the SEC. We disclaim any obligation to update our forward-looking statements. With that, I'd like to turn the call over to Gene.

Thank you, Mark, and thank you all for joining us today to review our 2023 financial results and business highlights. Let’s begin on Slide 5. Our mission at Prothena is to create transformational therapies addressing significant unmet medical needs for the millions of patients and their loved ones that are affected by devastating diseases caused by protein dysregulation. That mission is enabled by our deep scientific expertise, which serves as a unifying thread connecting our corporate strategy, our portfolio development and the dedication that propels our team every day. We continue to advance our mission, which has fueled our robust late-stage clinical pipeline moving us closer to becoming a fully integrated commercial biotechnology company. As a result of our commitment to our mission, we have created a robust portfolio of therapeutic drug candidates targeting both neurodegenerative and rare peripheral amyloid diseases as shown on Slide 6. Our portfolio includes four wholly-owned programs and five partnered programs. This intentional mix allows us to advance a comprehensive portfolio by leveraging the benefits of working with key strategic partners on some programs while still maintaining the full upside potential for our wholly-owned programs where we feel that we have unique insight and expertise. I'll discuss four of our ongoing clinical programs on the next slide: PRX012, Birtamimab, Prasinezumab, and NNC6019. But first I'd like to highlight the exciting progress across our earlier-stage program. In July of 2023, we presented compelling preclinical results in a late breaker poster presentation at AAIC for PRX123, our dual Aβ-tau vaccine program and by year-end 2023, PRX123 received IND clearance and Fast Track designation from the FDA. Our ongoing neuroscience R&D collaboration with CMS made meaningful advancements in 2023 and into this year. BMS 986446, formerly PRX005, is a potential best-in-class antibody for the treatment of Alzheimer's disease that specifically targets key episodes within the microtubule binding region of tau. In 2023, CMS opted into the global rights for this program with an additional milestone payment of $55 million and announced that the Phase 1 data supports advancing the program into a Phase 2 clinical trial in 2024. For PRX019, a potential best-in-class antibody for the treatment of neurodegenerative diseases, we recently received FDA clearance for the IND application for this program as well. This is the second of three programs in our BMS collaboration. We remain well-funded to execute on our strategic objectives taking us well beyond our upcoming clinical readouts. As you will hear about in more detail later in this call, we ended 2023 with a strong cash position of $621 million. Moving now to Slide 7. Our clinical expertise and differentiated approach enables us to advance best-in-class and/or first-in-class therapies that have the potential to transform the treatment landscape for protein dysregulation diseases. Today, I'd like to focus on the four clinical programs that are nearing significant inflection points within the next 12 to 18 months. First I'll discuss our wholly-owned programs PRX012 and Birtamimab, and then move on to our partnered program with Prasinezumab Roche and NNC6019 with Novo Nordisk. PRX012 is our next-generation investigational treatment for Alzheimer's disease, which targets the key epitope at the Amino Terminus of amyloid beta with high binding potency. PRX012 was designed with the patient in mind and we believe it has the potential to be best-in-class transforming the treatment of Alzheimer's disease by meaningfully reducing treatment burden associated with the currently available anti-amyloid therapies. Based on our market research, we understand that a treatment with similar efficacy and safety to currently approved anti-beta therapies, but delivered as a once monthly at-home subcutaneous treatment has the potential to be the dominant player in the market. In 2023, we presented compelling preclinical data at ADPD and AAIC demonstrating that PRX012 binds the amyloid plaques with high avidity. PRX012 is currently being evaluated in a double-blind, placebo-controlled Phase 1 trial with the goal of identifying optimal dose levels for our registration enabling trial. The preclinical data combined with the initial clinical data from our ongoing Phase 1 trial support a once-monthly subcutaneous treatment with a potential best-in-class profile. Birtamimab seeks to address the high risk of early mortality that remains an urgent unmet medical need for patients with Mayo Stage IV AL Amyloidosis. Through its differentiated depleter mechanism, which is designed to clear accumulated amyloid and neutralize toxic light chain aggregates that are thought to cause organ dysfunction and failure. We're conducting the confirmatory Phase 3 AFFIRM AL clinical trial evaluating Birtamimab in patients with Mayo Stage IV Amyloidosis under a special protocol assessment or SPA agreement with the FDA, with a primary endpoint of all-cause mortality at an unprecedented significance level of 0.10. We expect top-line results between the fourth quarter of 2024 and the second quarter of 2025. Prasinezumab is an antibody for the potential treatment of Parkinson's disease designed to target a key epitope within the C-terminus of alpha-synuclein and is the focus of a worldwide collaboration with Roche. Roche is currently conducting the Phase 2b PADOVA clinical trial in patients with early Parkinson's disease. Roche completed enrollment of this trial in the first quarter of 2023, and expects to report top-line data later this year. Finally, NNC6019 is an amyloid depleter antibody for the potential treatment of ATTR cardiomyopathy. Novo Nordisk is currently conducting an ongoing Phase 2 signal detection trial in patients with ATTR cardiomyopathy. The trial has fully recruited its patients with top-line results expected in the first half of next year. This is an exciting year of clinical trial execution for both Prothena and our strategic partners. As we look ahead, we are also thoughtfully building out our commercial leadership and market insights for Birtamimab so to provide a little more context on our pre-commercial efforts, I will now turn the call over to Brandon.

Thanks, Gene. Moving to Slide 9. As we continue to execute on our ongoing confirmatory Phase 3 of the AFFIRM AL clinical trial, we are focused on building out our commercial capabilities to support Birtamimab as our first potential commercial product. Among patients with AL Amyloidosis, who are progressing and fatal disease, newly diagnosed individuals with significant cardiac involvement such as Mayo Stage IV are at the highest risk for early mortality. This remains a serious unmet need for patients and their families. Birtamimab is the only candidate to have shown a survival benefit in patients with Mayo Stage IV AL Amyloidosis in a randomized clinical trial, our previous Phase 3 VITAL trial. The ongoing confirmatory AFFIRM AL trial was designed based on a SPA agreement with the FDA to approve Birtamimab at a p-value of less than or equal to 0.1 for the primary endpoint of all-cause mortality showing an early and sustained impact on mortality is a powerful differentiator and if approved, we are confident that Birtamimab will be welcomed as a major advancement in the field and a key treatment option. Moving to Slide 10. The market dynamics for Birtamimab as our potential first commercial product are quite compelling. Our plan is to independently commercialize Birtamimab, and we believe that we will be able to efficiently reach prescribers for advanced patients with a focused commercial presence. This is a rare disease patient population with a targeted call point where hematologists are supported by specialized cardiologists and primary treating specialists. KOLs in the community at large recognize the urgent need for treatment that improves survival in patients with AL Amyloidosis who are at high risk for early mortality. Based on epidemiology studies, we estimate there are over 20,000 patients with Mayo Stage IV AL Amyloidosis across the major markets including the United States, Europe, China, Brazil, and Japan. This is further supported by our claims data analysis to identify patients who are actively receiving treatment for AL Amyloidosis in the United States. Based on this, we believe there are approximately 4,000 Mayo Stage IV patients in the U.S. In addition, our US and European market research indicates that approximately 75% of patients are treated in about 500 centers of excellence and amyloidosis specialty centers usually within academic hospitals. Our team continues to build upon the existing relationships we've established with KOLs and experts in the field through our extensive clinical programs for Birtamimab. We will continue to collaborate with these KOLs and experts along with the organizations that publish treatment guidelines such as NCCN and the International Society of Amyloidosis to ensure they are fully aware of and informed about Birtamimab. This includes continuing to present our data at top medical congresses and publications in peer-reviewed journals. Today, we are building our commercial leadership team thoughtfully as we prepare for launch. I'll now turn it over to Hideki to review our clinical programs.

Thank you, Brandon. Let's continue with Birtamimab and review the results from the previous VITAL trial, which we published in the ASH peer-reviewed Journal, Blood last year. Importantly, we observed a survival benefit in the subset of approximately 30% of patients who are categorized as Mayo Stage IV at baseline. The Kaplan-Meier curve illustrating the separation is shown here on Slide 12 demonstrating an early and sustained benefit. In this high-risk group, we observed the survival benefits facing Birtamimab reflecting approximately 60% relative reductions in all-cause mortality at a p-value of 0.021. This was further supported by meaningful and significant improvements in function as measured by the six-minute walk test and quality of life as measured by SF-36. Turning to Slide 13, expanding on Brandon's earlier remarks, based on our extensive analysis of VITAL data, as well as further confirmation of the data with external statistical experts and leading physicians in the field, we actively engaged with the FDA to outline the path towards regulatory success for Birtamimab. A SPA was agreed upon between Prothena and the FDA with a confirmatory Phase 3 AFFIRM AL clinical trial to be conducted in patients with AL amyloidosis categorized as Mayo Stage IV at baseline with a pre-agreed upon significance level of alpha less than or equal to 0.10 on a primary endpoint of all-cause mortality. This is a time-to-event trial and patients are randomized two to one on Birtamimab as standard-of-care or placebo plus standard-of-care. At the end of 2023, based on a predetermined number of mortality events, we were able to estimate that top-line results for Mayo would be available between the fourth quarter of 2024 and the second quarter of 2025. We look forward to the results for this trial moving us one step closer to getting the treatment to patients and families in need. Let’s discuss PRX012, our potential best-in-class anti-amyloid beta treatment starting on Slide 14. We believe PRX012 could be a best-in-class anti-amyloid beta treatment for early Alzheimer's disease. To achieve this target product profile, we need to establish escapades convenience and safety. PRX012 was intentionally designed with the antibody attributes required to achieve a similar or better efficacy and safety profile to currently approved anti-amyloid therapies. With the clear differentiation of being administered in a much more convenient and accessible once monthly, at-home, subcutaneous treatment. PRX012 is a humanized IgG1 monoclonal antibody designed to provide a longer half-life and improved anti-amyloid treatments with low immunogenicity. We’ve demonstrated a high potent binding, high affinity and avidity, and a slow off rate allowing for considered target engagement, all of which are optimal for once-monthly subcutaneous treatment. The ongoing PRX012 Phase 1 trial, which we will discuss on Slides 15 and 16, is designed to demonstrate a potential best-in-class profile in the clinic. Moving to Slide 15, Phase 1 is a double-blind placebo-controlled single ascending dose clinical trial evaluating PRX012 in healthy volunteers and participants with early Alzheimer's disease. The trial enrolled approximately eight participants per single ascending dose cohort, randomized 3 to 1 to receive a single subcutaneous dose of PRX012 or placebo in doses ranging from 70 to 400 milligrams. Moving on to the multiple ascending dose cohorts on Slide 16, Ascent 2 is our double-blind placebo-controlled multiple ascending dose clinical trials evaluating PRX012 in people with early Alzheimer's disease. Each matched cohort is randomized 3 to 1 to receive PRX012 or placebo once monthly for six months in multiple ascending dose levels. The objectives of the trial are twofold: one is to evaluate the safety, tolerability, immunogenicity, pharmacokinetics and pharmacodynamics of PRX012 in patients with early Alzheimer's disease; and two is to find the optimum dose level or levels for registration enabling clinical trials. There are a couple of key aspects to the MAD trial design that I would like to highlight today. Participants are assigned to two groups of cohorts based on APOε4 status, which we refer to as cohort A or B. Participants in the A cohorts are either APOε4 non-carriers or heterozygous carriers. Each of these A cohorts is evaluating approximately 32 participants with early Alzheimer's disease and doses ranging from 45 to 400 milligrams. In addition, we are evaluating APOε4 homozygous carriers with separate B cohorts for approximately 12 participants with early Alzheimer's disease in doses ranging from 45 to 200 milligrams. Following the first six months, which is placebo-controlled, participants previously taking PRX012 or placebo are eligible to receive an additional six monthly doses of PRX012 in an open-label extension. We've completed all cohorts and the double-blind portion of the initial 70 mg MAD A cohort. The Phase 1 clinical trial continues as planned, as the initial data supports once monthly, subcutaneous treatment and dose escalation in additional cohorts. We look forward to evaluating the full exposure response relationship of PRX012 and expect to update you later this year. Turning now to Prasinezumab on Slide 17. Prasinezumab is the first Anti-alpha-synuclein antibody to demonstrate slowing the progression of measures of Parkinson's disease in a Phase 2 trial. Our partner Roche previously presented data from the Phase 2 PASADENA trial showing Prasinezumab reduced one year motor progression by 35% as measured by the MDS-UPDRS Part III, a scale of motor dysfunction compared to placebo. Roche continues to provide meaningful updates on the ongoing open-label extension clinical trial, including recently at the Movement Disorder Study Congress in August. Roche compares three year progression of motor signs in the Prasinezumab population with a propensity score-balanced cohort of real-world data from the Parkinson's Progression Markers Initiative, or PPMI. The Prasinezumab population saw a 62% slowing of progression as measured by the MDS-UPDRS Part III in the early start Prasinezumab population, compared to the real-world data cohort. This data continues to support Prasinezumab's potential effects of delaying motor progression in Parkinson's disease. Roche has advanced Prasinezumab into the Phase 2b PADOVA trial, which is a double-blind placebo-controlled trial evaluating 586 patients with early Parkinson's disease. Participants are randomized 1 to 1 to receive Prasinezumab or placebo every four weeks for at least 18 months. Roche announced they've completed enrollment in the first quarter of 2023. The primary endpoint is time to clinically meaningful progression or motor signs of the disease as assessed by a five-point or greater increase in the MDS-UPDRS Part III from baseline. This disease progression may be correlated to a meaningful worsening on the clinical global impression scale. Roche expects to report top-line data from the PADOVA trial later this year. Moving to NNC6019 on Slide 18, NNC6019 has been developed by Novo Nordisk as a potential first-in-class amyloid depleter antibody for the treatment of ATTR cardiomyopathy. This is a rare progressive and fatal disease characterized by deposition of abnormal non-native forms of TTR protein and amyloid in vital organs. NNC6019 is thought to deplete both deposited amyloid and circulating non-native TTR to prevent further depositions to improve organ function. This mechanism of action has potential benefits for ATTR patients at high risk for early mortality due to amyloid deposition in vital organs. Novo Nordisk is progressing this program in an ongoing double-blind placebo-controlled signal detection Phase 2 clinical trial. The trial has completed recruitment and Novo estimates primary completion in the first half of 2025. Now I'd like to turn the call over to Tran Nguyen for a discussion of our 2023 financial performance and our 2024 financial guidance.

Thanks, Hideki. Today, we reported financial results that were favorable to our 2023 financial guidance. Please refer to our press release for a detailed breakdown of our financial results. As Gene mentioned during his opening remarks, our robust portfolio of wholly-owned and strategically partnered programs allows us to leverage partner payments while still maintaining full upside potential of our wholly-owned programs. In 2023, BMS opted in to secure their global rights for the BMS 986446, formerly known as PRX005, for $55 million. In terms of our 2023 financial performance relative to guidance, we had net cash used in operating and investing activity of $136.7 million, which was favorable to our guidance range of $148 million to $161 million. Net loss was $147 million, which was favorable to our guidance range of $153 million to $171 million. As of December 31, 2023, Prothena had $621 million in cash, cash equivalents and restricted cash, which is favorable to our guidance of $600 million. As of February 9, 2024, Prothena had approximately 53.7 million ordinary shares outstanding. Additionally, we continue to have a simple capital structure with zero debt. Turning to our 2024 financial guidance that's on Slide 21. We expect our full year 2024 net cash used in operating and investing activities to be between $208 million and $225 million. We expect to end the year with approximately $405 million in cash, cash equivalents, and restricted cash, which represents the midpoint of the range. The estimated full year 2024 net cash used in operating and investing activities is primarily driven by an estimated net loss of $229 million to $255 million, which includes an estimated $51 million of non-cash share-based compensation expense. With that, I'll turn the call back over to Gene to discuss our upcoming milestones.

Thanks, Tran. Moving to Slide 23. I'd like to acknowledge and thank the patients, their families, physicians, and study site staff who participate in all our clinical trials. Without their support we could not elucidate the potential impacts of the new medicines we’re developing. I'd also like to thank our talented team for their ongoing commitment to advancing protein dysregulation science to make a real impact for the patients and families we serve. As we look ahead, we're excited to have meaningful catalysts across our programs with potential clinical readouts from four ongoing clinical trials within the next 12 to 18 months. These include top-line results from our confirmatory AFFIRM AL Phase 3 trial evaluating Birtamimab in patients with Mayo Stage IV AL amyloidosis, clinical data from our ongoing Phase 1 trial evaluating PRX012 as a potential best-in-class treatment in early Alzheimer's disease, top-line results from the Phase 2b PADOVA trial evaluating Prasinezumab for Parkinson's disease being conducted by Roche, and finally clinical data from the Phase 2 signal detection trial evaluating NNC6019 for the treatment of ATTR cardiomyopathy by Novo Nordisk. I am proud of the progress that Prothena made in 2023 and continued into 2024. We are well-capitalized with a robust cash position and remain focused on advancing our clinical programs as we strive to become a fully integrated commercial biotechnology company. With that, we will now open the call for Q&A.

Your first question comes from the line of Charles Duncan from Cantor Fitzgerald. Please go ahead.

Yeah, hi. Good afternoon, Gene and team. You've got a lot going on and limiting to one question will be a challenge. But I'll try to do that. I wondered if you could provide a little bit more clarity on the patient enrollment in Ascent 2, specifically what patient or what cohorts have been enrolled both A and B in terms of which doses. And I'm wondering if you could provide a sense of what you meant with regard to giving an update later on this year on data. Could you anticipate being possibly in a pivotal program in the later part of 2025?

Thanks for the questions Charles. I appreciate them. So I think first just with respect to timeline, obviously this is an ongoing trial and we plan to share additional data as it becomes substantive. I think, in terms of when we plan to give an update on PRX012, we will plan to provide an update this year, whether that update is to update on timing or data is something that we will still determine. In terms of your question around enrollment in various cohorts, maybe I can ask Hideki to address that question. Hideki?

Thanks, Tran. Enrollment is very strong in our PRX012 Signal trial. The Monitoring Board has authorized a 400 mg cohort, and proceeding cohorts are planned and so this will allow us to facilitate for the next stages.

Your next question comes from the line of Jay Olson from Oppenheimer. Please go ahead.

Oh, hey, thanks for the update and congrats on the progress. We have another question about the PRX012 MAD study. Could you talk about this six-month open-label extension and what do you hope to learn from that? Will patients on low doses switch to high doses? And how will it impact your next steps for 012? Thank you.

Yeah, thanks, Jay. Thanks for the question. Maybe I can just start with the reminder that the study is a double-blind placebo-controlled trial, six months in duration with patients receiving their specified dose level of PRX012 or placebo once a month through subcutaneous administration. Obviously after that six-month period, we do provide the potential for an open-label extension for patients and maybe Hideki can just speak a little bit about that period.

Yeah, so each patient within each cohort will enroll in the open-label extension for six months, as you mentioned. Again, very strong enrollment, and people are very excited about the one-placebo-controlled, where placebo patients will now receive a drug of course that will be the first – the other patients will continue to go on down for 12 months of potential treatment of PRX012, which we are capturing both safety and tolerability and of course PK and pharmacodynamic measurement.

Your next question comes from the line of Michael DiFiore from Evercore ISI. Please go ahead.

Hi guys. Thanks so much for taking my question. Just wanted to zero in on the comparable ARIA rates that we're seeing between the 70 mg dose of PRX012 and placebo. So when you consider how subcutaneous had less ARIA rates compared to its IV version and while lecanemab sub-Q had about equal ARIA rates versus the IV version. How do you reconcile this? And given that the engineering of 012 was optimized off of – and do you foresee similarly low ARIA rates for 012 at higher doses? Thank you.

Yeah, so it's a great question and you've got a lot built in there around the science. I appreciate the question. I think that you're alluding to is really how the biology of ARIA plays into dosing with these anti-amyloid agents. As you say, there is evidence across the anti-amyloid field that there is a dose-response relationship between, certainly it's almost on a linear basis with respect to amyloid reduction. But in the case of ARIA, there’s a little difference between antibodies, and I think that's what we’re seeing. So you're making a point between bapineuzumab and lecanemab and I think those are astute observations. As you say with the bapineuzumab work, I think there is approximately equivalent exposures on an AAC basis what was observed at least in the published literature was lesser ARIA with that molecule while lecanemab’s data is a little more comparable. What that indicates to us is really that it is molecule-dependent and we need to understand as we see multiple dose level cohorts with our molecule PRX012, and we look forward to determining that as we explore the exposure response relationship that you mentioned from the 45 mg monthly dose level through to the 400 mg monthly dose level. With that said, I think you also asked a little question just in terms of what consistency meant with placebo and maybe Hideki can comment on that piece.

Yeah, thanks, Gene. Just to remind you we're running a double-blind placebo-controlled trial and have reported in the 70 mg dose that factor as well as ARIA rate consistent with placebo. The data allows us to provide a response index to explore a full dose response curve with once monthly dose. Again just to remind you we have the ability to up the program and all these cohorts are active.

Your next question comes from the line of Neena Bitritto-Garg from Deutsche Bank. Please go ahead.

Hey guys. Thanks for taking my question. Just to piggyback on the ARIA discussion here, I'm just wondering if you can tell us a little bit about—was the comment on ARIA being consistent with placebo? Is that true for both the cohort A and the cohort B patients so far? So both the APOε4 non-carriers and heterozygous as well as the homozygous? And then I was just wondering if you could also talk a little bit about some of the differences in activity that you're expecting between the 70 mg dose versus 200 and 400 and why you selected 200 and 400 for both SAD and MAD? I know you talked a lot about collection of 70 mg as being based off of the average to 10 mg per dose, but just wondering how we should think about the higher doses. Thanks.

Yeah, thanks Neena for the question. Maybe I can start then hand it to Hideki to jump in here. I think first with respect to your question about the data that informs what we've said about this molecule to-date which just again as a reminder, we indicated that with the A cohort which is the 70 mg monthly cohort, we've seen evidence of what we would characterize as encouraging reduction in amyloid beta. Obviously, that helps us to understand that we believe this is a once-monthly subcutaneous drug. And obviously, ARIA rates as you mentioned, consistent with placebo, what goes into informing that is obviously the data from a single dose study, as well as the cohorts that the 70 mg cohort I am referring to in the multiple dose study. The additional ongoing cohorts remain blinded. It is a double-blind placebo-controlled study. I think the other question was really just around the selection of the dose levels and I think maybe I’ll ask Hideki to speak to that other than to say that these dose levels are being explored are the ones that were anticipated to be explored, and we are continuing to conduct this study as we had anticipated and it’s moving forward at an encouraging pace.

Yeah, thanks Gene. So as you mentioned we are continuing to explore in a Phase 1 study and that’s the purpose of Phase 1 study. I just remind you that the 70 mg is encouraging amyloid reduction and consistent ARIA rate with placebo and that allowed us to explore the full dose response from 45 mg to 400 mg. Again just to remind you that high binding once monthly subcutaneous administration has potential to be best-in-class.

Your next question comes from the line of Yasmeen Rahimi from Piper Sandler. Please go ahead.

Hi team, this is Yas. Thanks for taking our questions. Just kind of diving more into the details of the ARIA rates given that you're enrolling both APOε4 homozygous and heterozygous patients. We know that this drives sometimes differences in ARIA rates. How do the expectations regarding both safety and efficacy across these populations?

Yeah, no. Thanks for the question. I think there are kind of two questions built into that one in terms of how we're thinking about ARIA across the entirety of the patient population. I think the second is really just around how we think about this trial design. Let me start with ARIA and obviously, as we talked about, ARIA rates were being specific to our patient level cohorts; we are reporting data out as one would in a Phase study relative to placebo. The point you're making about testing separately APOε4 homozygous carriers in these B cohort is something that we're learning from the field. We are learning from each other I think on the clinical side, as well as the preclinical side. One of the lessons that has become clear is that APOε4 homozygosity does tend to lead itself to a higher ARIA rate, and in the context of clinical trials, that can lead to in some cases misdosing or skip dosing. Obviously, that's less than ideal as we start to think forward to efficacy-driven studies and registrational studies. So we chose in the context of the Phase 1 Study to be a little bit more deliberate in evaluating these APOε4 homozygous patients. We want doses that are optimized for the entirety of the population, not just portions of the population. We think that as we continue to iterate in this field across multiple companies, it takes a village to develop therapeutics in this space. We are seeing this as a continuous learning process, and we are also striving for patient safety and remaining cognizant of efficacy-driven endpoints and dosing the provided for treating patients within these cohorts.

Yeah, I think one thing to add in terms of the time to event endpoint is that it captures a five-point or greater increase in progression in the scale, which we found Roche for these to be clinically meaningful. They're also working on other clinical functional endpoints within the trial to correlate with the primary outcomes. We look forward to the continued discussion with regulators and of course the data later this year.

And we have time for one more question today and it comes from Ananda Ghosh from H.C. Wainwright. Please go ahead.

Yeah, hi. I just wanted to get your opinion on some of these concepts which I don't think the street understands very well with respect to the ARIA-focused program. So what has been, how do we think that the pharmacokinetic and maximum concentrations, and in a relative fractional occupancy when you are looking at data which comes from the kind of a subcutaneous data and with respect to your idea on the PRX drug development program. So any ideas with respect to those two factors would be very helpful to understand how to think about PRX012 development going forward.

Yeah, no, I appreciate the question and it's an important question. You brought up lecanemab and I think their relevance as immunotherapeutics targeting anti-beta antibodies. What we see with those antibodies as you look between the Phase 2 dataset and Phase 3 data sets is a relationship between removal of plaque and the dose-response or exposure-response relationship. In the case of lecanemab, this relationship is close to linear. However, that is not true with every anti-beta antibody; other antibodies show much more of an all-or-none effect, and I pointed to – from that perspective around plaque clearance. With respect to ARIA, we continue to believe that ARIA is a mechanistically-driven event, meaning if you are removing plaque, you're going to increase the risk of ARIA. But as I said, there is a relationship between that and the differences among antibodies. We continue to believe our data from multiple dose level cohorts from our ongoing Phase 1 trial will inform the relationship between PRX012 exposure and ARIA rates. As we collect additional dose level cohort data, we expect to provide substantive updates in the future.

Thank you, everyone. This is all the time we have today. I'll now turn it over to Gene Kinney, Chief Executive Officer for closing remarks.

Thank you very much, operator, and I want to thank you all for joining us on the call today. We appreciate your interest in Prothena and we look very much forward to sharing further updates on our program. Have a good afternoon.

Thank you for participating in today's conference call. This concludes the presentation and you may now disconnect. Good day.