Seres Therapeutics, Inc. Price & Performance (MCRB)

Thank you, and good morning. Our press release with the company's fourth quarter and full year 2024 financial results and business update became available at seven a. M. Eastern Time this morning and can be found on the Investors and News section of the company's website. The company has also posted an updated corporate presentation to the website. I'd like to remind you that we'll be making forward looking statements including statements about the timing and results of our clinical studies and data readouts, future product candidates, clinical development plans and commercial opportunities, interactions with regulatory agencies, receipt of future payments related to the valve sale, operating plans and future cash runway our ability to generate additional capital, our planned strategic focus, our efforts to secure partnership and anticipated timing of any of the foregoing and other statements which are not historical fact. Actual results may differ materially. Additionally, these statements are subject to certain risks and uncertainties, which are discussed under the Risk Factors section of our recent SEC filings. Any forward looking statements made on today's call represent our views as of today only. We may update these statements in the future, but we disclaim any obligation to do so.

On today's call with prepared remarks, I'm joined by Eric Schaff, Seres President and CEO Matthew Hen, CSO Lisa Von Mualke, CMO Marilla Thorel, CFO and Terry Young, Chief Commercial and Strategy Officer. And with that, I'll pass the call over to Eric.

Thank you, Carlo, and good morning, everyone. This has been a productive period for Seres, highlighted by substantial progress advancing our lead program SER-one 55 as a novel biotherapeutic to prevent life threatening bloodstream infections including those that can harbor antimicrobial resistance. [indiscernible] We are developing SER-one 55 initially for ALLO HSAT recipients who are at high risk of infection. Our excitement around SER-one 55 is based on the highly encouraging clinical results we reported late last year, from a placebo controlled Phase Ib study [indiscernible] in patients undergoing ALLO HSCT for the treatment of hematologic malignancies. This study showed a clinically meaningful seventy seven percent relative risk reduction in bloodstream infection rate for those patients administered 155. BSIs represent a frequent and serious complication and a growing risk to immune compromised patients undergoing HSCT which can result in adverse impacts on patient outcomes. I would like to highlight the progress we have made since obtaining these initial clinical data over the past several months. [indiscernible] Earlier this year, we released exploratory translational biomarker results from the completed SER-one 55 Phase 1b study. Matt will cover these data in more detail in a moment, but at a high level, the biomarker data reinforce the drug's mechanisms of action and are consistent with a significant BSI reduction in safety profile observed in the clinical study.

The data indicate that BSI risk is reduced by promoting epithelial barrier integrity which can decrease the likelihood of translocation of bacteria and the entry of pro inflammatory molecules from the gastrointestinal tract into the bloodstream. Our data also suggests 55 is positively impacting systemic immune and inflammatory responses [indiscernible] support the opportunity for our biotherapeutics to provide benefit to patients living with serious gut related inflammatory and immune diseases such as inflammatory bowel disease, ulcerative colitis and Crohn's disease. [indiscernible] These remain large and underserved patient groups and the therapeutic and commercial opportunities could be substantial. We have also made substantial progress in working with the FDA to advance SER-one hundred and fifty five. In December of last year, the FDA granted breakthrough therapy designation to SER-one 55 for the reduction of bloodstream infections in adults undergoing ALLO HSCT. In recent months, we have been engaged with the FDA regarding the further development of SER-one 55 in AL ALLO HSCT. The FDA has shared its preference for a SER-one 55 Phase two study as well as other parameters relating to the study design including support for the proposed primary efficacy endpoint of reduction in bloodstream infections at 30 post HSCT for our next study.

We also obtained confirmation of FDA's expectations on key elements of our biotherapeutic manufacturing processes specifications, and release testings. Based on the guidance received, we are currently working to refine the clinical study protocol for our next study which Lisa will expand upon. We intend to seek additional guidance from the FDA consistent with prioritized engagement expected with the breakthrough therapy designation. While we plan further engagement with the FDA, we continue to move with urgency to operationally prepare for the SER-one 55 next study. [indiscernible] are in the process of selecting a clinical research organization to lead study execution and we are manufacturing drug supply. At this juncture, it would be premature to provide timing guidance regarding initiation of the next SER-one 55 study. However, while we are still developing study protocol and plans, we can share initial projections of time to key study milestones after study initiation. Given the tractable standalone Phase two anticipated study size, and the experience we gained from the prior SER-one 55 Phase Ib, we believe we could expeditiously enroll patients and obtain clinical results. Based on the size of a potential Phase two standalone study, our preliminary operational plans and anticipated enrollment rates we believe we could obtain interim results within twelve months at informing next steps to support product approval and additional development opportunities.

We also project obtaining full top line data approximately nine months thereafter. Additionally, we continue to consider various and our other promising 55 opportunity and who would provide financial support and other capabilities to enable us to maximize the broad potential of SER-one 55. We are also seeking the perspectives of for further SER-one 55 development [indiscernible] which will help inform our path forward. We look forward to providing updates as our work advances. I will now pass the call over to Lisa.

Thanks, Eric. As Eric shared, we have continued to receive constructive feedback from the FDA to clarify further development plans for SER-one 55 as part of a Type B breakthrough therapy designation engagement. By pursuing a deliberate and thoughtful dialogue with the agency, we believe that we ensure that we are moving the program forward in a manner that is aligned with the FDA.

The FDA recommended that further development include a Phase two study to facilitate and refine the design of a registrational trial and data set. In a next study, the agency indicated support for a reduction in bloodstream infections at thirty days post HSCT as the primary endpoint. Notably, in our prior Phase 1b study, this was the period in which all BSIs occurred. We are pleased with this outcome and expect to replicate many elements from our prior successful SER-one 55 Phase 1b study in our next protocol. In addition, the FDA confirmed their ongoing expectations for chemistry, manufacturing and control parameters. [indiscernible] Based on the feedback obtained, our team continues to which could be either a standalone Phase two study or a Phase two as part of a seamless Phase two-three. [indiscernible] In either case, we anticipate the study will include an adaptive design with a meaningful interim analysis have reached the primary endpoint. Informing the study path forward and potential indication expansion. We plan to submit a draft study protocol to the FDA to with input expected from potential development partners. [indiscernible] and to seek further clarity on our proposed study design from the agency. Now before I pass the call to Matt to discuss our recent SER-one 55 exploratory biomarker results, I'd like to remind you of the clinical results we shared a few months ago.

In September, we announced encouraging top line clinical data from Cohort two on our Phase 1b study of SER-one 55 in ALLO HSCT. This segment of the study utilized a randomized, double blinded, one to one placebo controlled design to evaluate further safety, drug Seres engraftment and the incidence of bacterial bloodstream infections. As well as outcomes of such as incidence of febrile neutropenia and cumulative antibiotic exposure. From an efficacy perspective in the SER-one 55 arm, two out of twenty patients experienced a BSI. Versus six out of fourteen in the placebo arm. Resulting in a highly meaningful relative risk reduction approximately seventy seven percent. This is an important result especially given that bloodstream infections are a leading cause of death in ALLO HSCT patients. During the one hundred day observation period, febrile neutropenia occurred at a lower incidence in SER-one hundred and fifty five treated patients versus placebo patients. With thirteen out of twenty sixty five percent experiencing sebrile neutropenia compared to eleven percent of fourteen or seventy eight point six percent respectively. In clinical practice, HSCT patients who experience a BSI or febrile neutropenia are typically aggressively treated with broad spectrum antibiotics. [indiscernible] our study, we observed a meaningfully lower mean cumulative exposure to systemic antibacterial and antimicrobial therapy with SER-one hundred and fifty five treated patients being administered these drugs for a mean duration of nine point two days versus twenty one point two days for placebo patients.

Additionally, SER-one hundred and fifty five was generally well tolerated No serious adverse events were attributed to SER-one hundred and fifty five and no SER-one hundred and fifty five species were identified in any cultures, from any subjects. The favorable safety profile of SER-one hundred and fifty five is especially important given the highly immunocompromised state of the target patient population. In summary, our data show important potential clinical benefits associated with SER-one hundred and fifty five across multiple measures, along with a favorable safety profile. All of which we believe support the potential of this live biotherapeutic to fundamentally transform outcomes for many patient groups at risk. For bloodstream infections. Finally, members of our team recently which is sponsored by the American Society for Transplantation and Cellular Therapy and the Center for International Blood and Marrow Transplant Research. At this conference, one of the principal investigators in our Phase 1b study presented a summary of the study outcome. The feedback we received from KOLs at the conference underscore the significant need to address BSIs as well as the meaningful outcomes observed in our Phase 1b study. With that, I'll turn the call over to Matt. Thank you, Lisa. Our lead program SER-one 55 is a live biotherapeutic product designed to decolonize specific GI pathogens.

Improve epithelial barrier integrity, to prevent bacterial bloodstream infections, including those involving pathogen and to induce immune homeostasis in patients undergoing ALLO HSCT Our mechanistic goals were to reduce the likelihood of harmful bacteria and inflammatory products moving from the gut into the bloodstream and also to reduce systemic inflammatory responses. The SERCER155 Phase Ib study was designed to be a translationally rich [indiscernible] Included the analysis of various exploratory biomarkers selected to enable a deeper understanding of the mechanisms of action of SER-one 55, the drug's clinical pharmacology and how we may apply our novel drug modality towards the treatment of additional diseases. We recently presented biomarker results in a poster presentation at the Tandem Conference. Notably, the SER-one 55 Phase Ib placebo controlled study exploratory biomarker data in ALLO HSCT recipients reinforces the drug's mechanism of action and are consistent with clinical results showing a significant reduction in BSIs and the observed safety profile. Exploratory translational biomarker assessments in included fecal albumin and established biomarker of epithelial barrier integrity as well as systemic inflammatory biomarkers measured in plasma that included interferon gamma, TNF alpha, IL-seventeen, and IL-eight. These assessments were evaluated during the HSCT peri transplant period which is the period from the end of the first treatment course of SER-one hundred and fifty five through to neutrophil engraftment.

Following SER-one hundred and fifty five administration, [indiscernible] and in the peri transplant period, SER-one hundred and fifty five was a associated with lower levels of fecal albumin and lower concentrations of certain plasma biomarkers of systemic inflammation specifically interferon gamma, TNF alpha, IL-seventeen and IL-eight. More specifically, there was a statistically significant decrease in fecal albumin, The presence of fecal albumin in fecal matter which is produced in the liver and normally circulates in the bloodstream indicates a breakdown in the epithelial barrier and the gut bloodstream and that translocation of Beaman from the blood to the intestinal tract has occurred. Fecal albumin concentrations in the SER-one 55 arm following the first treatment course of treatment were lower than levels observed in healthy subjects. The healthy subjects cohort while placebo subjects were significantly higher than the SER-one 55 in healthy subjects. This is consistent with barrier damage induced by HSCT conditioning in the placebo arm and not in the SER-one 55 arm. Fecal albumin levels remain low in SER-one 50 patients and are similar to healthy control subjects throughout the PARI transplant window. Concentrations of IL-seventeen and IL-eight were significantly lower in SER-one 55 treated subjects compared to placebo following the first treatment course and concentrations remained generally lower in the SER-one 55 arm compared to placebo through HSCT conditioning. 55 arm were significantly lower than placebo at the time point following neutrophil engraftment.

And concentrations of both 55 treated patients were lower than placebo patients following HSCT conditioning but differences were not statistically significant. These exploratory translational biomarker data provide further mechanistic evidence of the potential of SER-one 55 to reduce BSIs to the promotion of epithelial barrier integrity. Thereby preventing translocation of bacteria and pro inflammatory molecules from the GI tract into the bloodstream and to positively impact systemic inflammatory responses. Based on the totality of the clinical and biomarker results we have obtained, we believe that ALLO HSTT represents only a portion of substantial opportunity available with our biotherapeutic approach. Firstly, BSIs are a major challenge for many patient groups and SER-one patient groups and 55 and our other biotherapeutic such as 47 could represent an important and novel approach that could transform how many groups of medically vulnerable patients including immunocompromised cancer treatment and cirrhosis patients are managed. [indiscernible] Additionally, the mechanistic data we obtained from the exploratory biomarker results support the potential utility of our live biotherapeutics address various gut related inflammatory and immune diseases such as IBD, which includes ulcerative colitis, and Crohn's disease. In each disease, gut epithelial barrier compromise has been identified as a core component of underlying pathology and the inflammatory host pathways denoted earlier are linked to disease.

We are developing 47 for compromised patients living with metabolic disease. SER-one hundred and forty seven is designed to prevent gut Seres infections and associated downstream infections and spontaneous bacterial peritonitis in chronic liver disease. While our focus this year is primarily on 55, we continue to advance IND enabling work for one hundred and forty seven with modest resource investments. We also continue to explore research collaborations to help advance our early stage pipeline programs.

With that, I'll now pass the call to Terry.

Thanks, Matt, and good morning, everyone. As we've discussed, bacterial bloodstream infections are a medically significant and life threatening complication experienced by multiple patient groups including allogeneic and autologous stem cell transplant recipients, CAR T recipients, other cancer patients with neutropenia, individuals with chronic liver disease, solid organ transplant recipients, as well as patients in the intensive care unit and long term acute care facilities.

Our analysis indicates that the commercial opportunity in ALLO HSTT alone could be sizable and that there is considerable ability to extend this opportunity via indication expansion to some of these adjacent patient populations. To better characterize the opportunity in ALLO HSCT, we recently completed multiple rounds of market research with U. S. Healthcare and payers. The results confirmed a high unmet need to prevent BSIs and a desire for better prophylactic options. The results were supportive of a strong value proposition and a robust commercial opportunity for 55. Both HCPs and payers indicated an awareness of the high clinical burden of BSIs driven by the frequency of occurrences and poor associated outcomes. Both groups cited a lack of efficacious prophylactic therapies, and expressed significant ongoing concerns around the risk of BSIs sebron neutropenia. Sepsis and antibiotic resistant infections in this already vulnerable patient population. Specific to SER-one hundred and fifty five, the proposed risk reductions of BSIs and related endpoints were seen as clinically meaningful and incited enthusiasm amongst respondents. [indiscernible] U. S. Payers also shared their expectation that SER-one 55 would primarily be reimbursed via the outpatient pharmacy benefit given the timing and route of administration, which allows for dosing out outside of the inpatient hospital setting.

Notably, in our Phase 1b study, one hundred percent of patients received their first dose of SER-one hundred and fifty five outside of the hospital setting. The reimbursement pathway for SER-one 55 along with the very high incremental costs for patients who do experience BSIs post transplant. Are indicators of strong pricing potential in the category. There are an estimated 9,300 AlloHS CT procedures conducted annually in The U. S. The European Society for reporting approximately 20,000 procedures in 2023. With a higher number of reported procedures than The U. S, and the presence of shared market dynamics, with The U. S, such as unmet need and a high cost of care for these patients. We also see a robust opportunity for 55 in Europe. To summarize, we are excited about the initial 55 opportunity to prevent infections in ALLO HSCT patients. Beyond this anchor population, we have the opportunity to extend across hematologic malignancies as well as to other areas outside of oncology. We believe that with this strategy, 55 and our additional bi therapeutics could deliver multiple highly significant blockbuster opportunities. With that, I'll now pass the call to Marella. Thanks, Terry, and good morning, everyone. First, I will briefly recap the terms of the VAST sale transaction which closed in September and then share our quarterly and full year financial results.

With the VAST transaction, Seres received a payment of $155,000,000 at closing, which represented consideration of $175,000,000 less approximately $20,000,000 related to the settlement of net payables to Nestle from Seres. Included in the upfront consideration was a $60,000,000 prepaid milestone and $15,000,000 related to an equity investment in Seres common stock by Nestle. A portion of these proceeds were used to retire our debt with Oak Tree and we are now debt free. Series received the first installment payment of $50,000,000 in January of twenty twenty five and we are due to receive an additional $25,000,000 less approximately $1,500,000 in employment related payments in July of this year. Provided we remain in material compliance with the terms of the transition services agreement which we expect to do. Additionally, our operations are simpler and our cash burn is lower following the transaction. Company's headcount is approximately 100 team members and we have fewer facilities having transferred certain leases to Nestle. Turning to the results, Seres reported a net loss from continuing operations of $15,700,000 for the fourth quarter of twenty twenty four as compared to a net loss from continuing operations of $34,700,000 for the same period in 2023. We reported a net loss from continuing operations of $125,800,000 for the full year 2024 as compared to a net loss from continuing operations of $190,100,000 for 2023.

The year to year reduction in net loss was due primarily to lower operating expenses of [indiscernible] sale recognized in the fourth quarter of twenty twenty four related to a lower than estimated vAST collaboration loss in the quarter, partially offset by approximately $14,000,000 of net other expenses, representing a $23,400,000 loss on debt retirement partially offset by $6,300,000 of income from Nestle in the fourth quarter related to TSA services. Research and development or R and D expenses for the fourth quarter of twenty twenty four were $12,800,000 compared with $23,000,000 for the fourth quarter of twenty twenty three. For the full year 2024, R and D expenses were $64,600,000 compared with $117,600,000 in 2023. The year to year decrease in R and D expenses was primarily driven by lower personnel expenses and a decrease in platform investments as the company 55.

General and administrative or G and A expenses for the fourth quarter of twenty twenty four were were $12,500,000 compared with $14,000,000 for the fourth quarter of twenty twenty three. For the full year 2024, G and A expenses were $53,200,000 compared with $77,500,000 in 2023. The year to year decrease in G and A expenses was primarily a result of reduced personnel and contractor expenses and other cost management activities. Manufacturing services expenses a new category in 2024, were $3,000,000 $3,500,000 for the fourth quarter and year ended 12/31/2024. These costs relate to the provision of manufacturing services under the transition services agreement with Nestle. The associated reimbursement received from Nestle expense and income net as mentioned earlier. Notably, many of the transition service service activities will be fully complete as of the March. Certain activities such as IT transition have been extended through May and consistent with the original transition plan, manufacturing support is provided through the end of this year. Moving now to our cash position, As of 12/31/2024, we had $30,800,000 in cash and cash equivalents. This does not include the previously mentioned $50,000,000 installment payment that we received from Nestle in January of this year.

As part of the VAST transaction. Based on existing cash and anticipated second installment payment to be received in July of this year, ongoing transaction related obligations and current operating plans, we expect to fund operations into the first quarter of twenty twenty six. We continue to evaluate opportunities to maximize maximize value creation and as we seek to develop our live biotherapeutic programs in various patient groups. Partnership could deliver both financial and other capabilities and accommodate sharing of development costs while enabling us to potentially realize the commercial value of our products across multiple patient populations. We continue to advance these discussions.

With that, I'll pass the call back to Eric.

Thanks, Marilla. We are excited about the progress we have made especially in our efforts to further the development of Seres. We have obtained confirmatory biomarker data that extend our understanding of this live biotherapeutic supporting the intended mechanisms of action in the clinical setting. The regulatory progress we have made is also notable. We are very pleased to have obtained breakthrough therapy designation as well as the constructive guidance obtained from FDA related to continued development. Our team looks forward to continued dialogue with the agency as we seek the most efficient and expeditious approach to advancing NK-fifteen fifty four. [indiscernible] Before I close, I'd like to extend our appreciation to Lisa, will be transitioning from Seres to another professional opportunity. Lisa has made significant contributions to the Series including leading the clinical development and approval of VAST, overseeing SER-one hundred and fifty five and the Allo HSAT Phase Ib study and our planned next steps for the SER-one 55 program. Lisa has also built a strong clinical and regulatory team and the company is well positioned for ongoing interactions with FDA and preparation for the next SER-one 55 study activities. [indiscernible] Moving forward, Kelly Brady, SVP, Clinical Development and Dennis Doctor.

Dennis Walling, SVP, Clinical Development and Anne Karowski, SVP of Regulatory Affairs will lead the advancement of our SER-one 55 clinical plans and FDA interactions. [indiscernible] Each of these individuals have decades of industry experience and key roles successfully developing FDA approved medicines. I look forward to working closely with Kelly, Dennis and Anne as we further the development of SER-one 55 and our additional biotherapeutic programs.

While our media focuses on SER-one 55 and ALLO HS HSET, the longer term we believe that there are opportunities to broaden the target patient populations for this therapy into other medically vulnerable groups. We continue to engage in discussions with prospective partners and believe both SER-one 55 and our broader portfolio represent attractive collaboration opportunities. We look forward to updating you as we advance our priorities across SER-one 55 and ALLO HSAT and the strategic goals we've outlined this morning. With that, we'll close our remarks. Operator, please open the call up for questions.

Your first question comes from the line of Joseph Tong with TD Cohen. Please go ahead.

Wishes to Lisa on her next step. Maybe just in terms of the feedback that you received from the FDA, it sounds like you got some feedback related to manufacturing and controls. I guess, is there anything that you'll need to implicate do in terms of changing manufacturing between the Phase one and the potential Phase two, Phase two, three And then second, when you think about the types of patients that would be enrolled in the next study, would you consider making any changes versus what you saw in the Phase one? It sounds like you're event rate kind of coincided with that thirty day post HSCT. So might be the right population, but are you anticipating making any changes? Thank you. Hey, Joe, good morning and thanks for the question. So let me start I might ask Lisa to comment on your second question and Chris to weigh in on the CNC side. But let's step back for a second. We don't get into the kind of play by play with the but let me offer a couple of thoughts in general. We had received comprehensive feedback from the FDA including their suggestion that we consider the next study for 155 to be a Phase two.

Right? And subsequently from that we had asked a set of clarifying questions We have not heard answers to those questions yet. But let me be clear that our expectation then as now is that the next step for us is to submit the clinical protocol, right? And that will be the major next step in unlocking the next the next step in terms of clinical progress. Now we talked about both a standalone Phase two and an adaptive twothree. If the next study is a standalone Phase two, our assessment is that we know what we need to do in order to move forward with that. And if it is an adaptive two-three, then by definition, there will be more work to do and more alignment with FDA that will be required both on the clinical side as well as to your question the CMC side. So we're in the process now of thinking about those relative trade offs and considering those. But let me make one more comment before I pass it off. One is that we're moving, we're not waiting. We're doing those key critical path items to enable us to move forward in the next the next study, whether it's a standalone Phase two or a Seamless 2.3.

And the last thing I would just say is that because we're in a partnership process, our expectation is that a partner will want to have a point of view on some of these questions. So what we think about. Maybe I'll ask Lisa to answer your second part and then Chris if I missed something on the first part.

Yes. So with regard to the population, we think we have the right population. It's a broad population.

In a bigger study, what you could see is us taking steps to make sure we can handle whatever variability and there are multiple through stratifying or through planned analysis. But we think we have the population.

Chris, any other comments on first part? Thanks, Eric. This is Chris McGallagher, Head of Manufacturing Quality.

To your questions about manufacturing, essentially, the feedback from the FDA was confirmatory that our plans moving forward allow us to start manufacturing today. We're already in our manufacturing campaign. And have full confidence that we'll be able to supply the drug for for either of the clinical options.

Perfect. Thank you very much. Thanks for the question, Jeff.

Your next question comes from the line of Tessa Romero with JPMorgan. Please go ahead.

Good morning, team. This is Caroline Poacher on for Tessa Romero with JPMorgan. Thanks for taking our questions and also from us, best best wishes to Lisa. So, in terms of questions, how has the recent FDA feedback and insight you have received thus far fallen relative to your expectations going into these interactions?

And how would a Phase twothree differ from just the Phase two study? And why do you think that FDA recommended the next study via Phase two? Yes, Caroline, let me start and maybe I'll ask Lisa to comment further. I'd start with just a reminder that we received breakthrough therapy designation at the end of last year. We were really pleased with that To us, that suggests a couple of things. One is that the FDA recognizes that this is an area of unmet need. And that the the evidence that was provided or the initial data that was was interesting to them and they see this as an interesting path forward. In terms of how the FDA guidance or the feedback fell relative to our expectations, We thought it was a constructive and robust and comprehensive set of comments for us. And we think that Seres a great deal that we can learn from it and that we will take forward. In terms of Q3, I kind of outlined some of those pieces in the answer to the last question. Ask Lisa to comment further, but there's a trade off in some sense of having certain items locked as part of a two, three seamless design.

As of and perhaps on the other side of that, the benefit of we would hope speed and reduced costs from not having a pause between a two and a three but maybe Lisa can comment further.

Yes. No, as Eric said, the main difference with the Phase two, three seamless is that the requirement to pre specify and lock things in a front. And that obviously can take more time and discussion with the agency to get that all settled.

I think in any case, what the agency was asking for is more data. And I think the existing data set, which was impressive enough to give us breakthrough designation, [indiscernible] still relatively small. And I think more data is something that would be helpful for us in designing the next study as well.

Okay, great. Thank you so much.

Thanks for the question, Caroline.

Your next question comes from the line of Ted Tenthoff with Piper Sandler. Please go ahead.

Great. Thank you very much and congrats on the continued progress. Question really has to do with safety database. I know that that was part of the consideration with Valsam approval. And I was wondering whether you guys have started to discuss the size of the potential safety database based on the prior experience with VAST does that at all increase the agency's comfort with microbiome therapeutics? Or are they really looking this as one off? And obviously, there's differences in population and just size of population, But curious what the conversations have been around the safety database.

Thanks.

Ted, good morning and thanks for the question. So, I'm going to start in I might start with a little bit of a caution that we're very careful not to speak for the FDA. We can offer our thoughts as to what we think they're thinking, but it's really just our perspective. Obviously, you mentioned VAST as a precedent and it's an important one. And in our experience with VAST, it was clear that the FDA was looking for at least 300 patients in terms of exposure. How relevant that is or how much incremental comfort they've had on the modality It's let me ask Lisa for her opinion, but ultimately, I think the FDA that's going to speak most important.

Yes. Generally the discussion on the safety database evolves as the safety profile evolves. And I think we know by guidance and our past life with Faust that they have a sort of minimum threshold of 300. That's a nice number for them. But it really varies too with the population. It's not just the therapy, it's the population. And we ourselves have been really careful and cautious with this population. We're very pleased with what we've seen so far.

And we expect it to continue. But I think we'll have these conversations with the agency as we generate more data.

Makes a lot of sense. Thanks. And Lisa, wishing me all the very best. It's been an absolute pleasure working with you.

Thank you.

Thanks for the questions Ted.

Your next question comes from the line of John Newman with Canaccord Genuity. Please go ahead.

Hi, guys. Thanks for taking my question. And Lisa, it's been a pleasure to work with you as well. A lot of great accomplishments. At Sirius and Best of Life going forward. My question is, wondering if you could give us any sense on the potential size of the next study for 155. Let's just assume at this maybe you run a Phase two. And also, in addition to the thirty day bloodstream infection endpoint, what might be some of the other potential efficacy endpoints that you could look at? I'm curious if you might look at things like acute GVHD maybe with a little bit longer follow-up, etcetera. Thanks. Yes, John, maybe I'll start and then I'll ask Lisa to comment. If in fact we're looking at a standalone Phase two, I think one of the real advantages of that is that, we think that Seres an data back reasonably quickly. And that's one of the reasons that we've designed an interim look that we think could provide meaningful data on both efficacy, safety and help inform how we move forward to to a pivotal study. So whereas we haven't guided our numbers, we did say in our prepared remarks that we think we could potentially hit an interim read within twelve months of starting a study, which is which is pretty tangible.

But in terms of other endpoints that will be of interest, maybe Lisa can comment.

Sure. So in addition to the BSIs, we'll be looking at fever during neutropenia.

Antibiotic use, hospitalization, ICU utilization. We will absolutely follow GVHD rates just as part of our safety assessment. What we know from the field is that the rates are dropping pretty seriously and we saw single digit, low single digit rates in our Phase one study. So it's probably these kinds of rates are not going to be something where we're going to be able to tease out kind of efficacy benefit but we will be able to chart that for safety.

And then, John, I might just add additional Lisa's comments around GBHD and the impact of PTCI, We also have potentially the opportunity to leverage an interim result to think about adjacencies from ALLO HSCT. So we've talked in the past about other areas that we think 155 potentially be helpful and where we think the mechanism could be effective there's a lot that we could have in a relatively short amount of time based on our clinical experience in the first study as well. I expect expectations on enrollment rates in the next study.

Okay. Thank you.

Thanks for the question. I will now turn the call back to management for closing remarks.

So thank you, operator, and thanks all of you for joining us this morning. We appreciate the opportunity to update you on our progress. Hope that everyone has a great week and we will speak again soon. Very much and have a good morning.

Ladies and gentlemen, that concludes today's call. Thank you and have a great day. [indiscernible]