UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 10-K (Mark One) ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2025 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission File Number: 001-37465 le Seres Therapeutics, Inc. (Exact Name of Registrant as Specified in Its Charter) Delaware 27-4326290 (State or Other Jurisdict ...

Exhibit 99.1 SERES THERAPEUTICS REPORTS FOURTH QUARTER AND FULL YEAR 2025 FINANCIAL RESULTS AND PROVIDES BUSINESS UPDATES Readout of investigator-sponsored SER-155 study in immune checkpoint–related enterocolitis, a frequent and serious side ef ect in cancer patients treated with immune checkpoint inhibitors, on track for Q2 2026 Seres operational focus on advancing live biotherapeutic programs for inflammatory and immune diseases Company working to create meaningful partnerships with collaborators to suppo ...

Core Insights - Seres Therapeutics is advancing its live biotherapeutic programs, particularly focusing on SER-155 for immune checkpoint-related enterocolitis and SER-603 for inflammatory bowel disease, with significant clinical data expected in Q2 2026 [1][2][5] Financial Performance - For the full year 2025, Seres reported a net income from continuing operations of $5.7 million, a significant improvement from a net loss of $125.8 million in 2024, primarily due to lower operating expenses and gains from the sale of VOWST [9] - Research and development expenses decreased to $49.1 million in 2025 from $64.6 million in 2024, reflecting cost management efforts [9] - General and administrative expenses also saw a reduction, totaling $39.2 million in 2025 compared to $53.2 million in 2024 [9] Cash Position - As of December 31, 2025, Seres had $45.8 million in cash and cash equivalents, with expectations to fund operations through Q3 2026 [6] Clinical Development - The company is preparing for Phase 2 trials of SER-155 aimed at preventing serious bloodstream infections in patients undergoing allogeneic hematopoietic stem cell transplant [2][5] - SER-155 is currently involved in an investigator-sponsored trial at Memorial Sloan Kettering Cancer Center, with enrollment completed and clinical data anticipated in Q2 2026 [2][5] Strategic Focus - Seres is actively seeking partnerships and funding to support the advancement of its pipeline programs, indicating a strategic focus on collaboration to enhance resource availability [3][5]

Core Viewpoint - The conference call is focused on providing a corporate update from Seres Therapeutics, highlighting management transitions, strategic plans, and clinical development efforts [2]. Group 1: Management and Leadership - The call features remarks from key executives including Richard Kender, who serves as Executive Chair and Interim CEO, Dr. Matthew Henn, President and Chief Scientific Officer, Kelly Brady, Chief Operating Officer, and Marella Thorell, Chief Financial Officer [3]. Group 2: Forward-Looking Statements - The company will be making forward-looking statements regarding various aspects such as management transitions, strategy, clinical development plans, anticipated data readouts, regulatory interactions, and funding efforts [2].

Summary of Seres Therapeutics Corporate Update Conference Call Company Overview - **Company**: Seres Therapeutics (NasdaqGS: MCRB) - **Focus**: Development of live biotherapeutic products targeting inflammatory and immune diseases, particularly in the context of microbiome therapies Key Points and Arguments Management Transition and Leadership - Richard N. Kender has been appointed as Executive Chair and Interim CEO, emphasizing confidence in the company's scientific foundation and leadership team [2][3] - The leadership team includes Dr. Matthew Henn (President and CSO), Kelly Brady (COO), and Marella Thorell (CFO), all of whom are pivotal in advancing the company's strategic goals [4][5] Product Development and Pipeline - **VOWST**: The first oral microbiome therapeutic, which has validated the company's platform and demonstrated its ability to navigate complex regulatory pathways [5] - **SER-155**: A key program targeting immune checkpoint inhibitor-related colitis (irEC), with clinical data expected in Q2 2026. This condition affects up to 50% of patients receiving immune checkpoint inhibitors [7][15] - **SER-603**: A preclinical stage biotherapeutic aimed at inflammatory bowel disease (IBD), addressing unmet needs for non-immunosuppressive treatment options [8][10] Clinical Trials and Collaborations - Ongoing collaboration with Memorial Sloan Kettering Cancer Center for the SER-155 study, which is fully enrolled with 15 participants [13][14] - SER-155 has received breakthrough therapy designation, facilitating interactions with the FDA for further development [16] Financial Position and Strategy - As of December 31, 2025, Seres had approximately $45.8 million in cash and cash equivalents, with expectations to fund operations through Q3 2026 [18] - The company has implemented cost-reduction measures, including workforce reductions, to extend its cash runway [18] - A focus on securing funding and collaborations to advance the pipeline and create shareholder value [19] Market Opportunity - The potential market for irEC therapies is significant, given the success of immunotherapeutics like Merck's Keytruda, which reached $32 billion in global sales in 2025 [7] - SER-603 aims to address the chronic nature of IBD and the need for safe, durable treatment options, presenting a substantial commercial opportunity [8][10] Additional Important Content - The company is exploring collaborations with entities that have established franchises in IBD to enhance the development of SER-603 [11] - The development of an oral liquid formulation of SER-155 is underway, targeting patients unable to take capsules, which could have broad applicability [11] This summary encapsulates the critical aspects of Seres Therapeutics' corporate update, highlighting the company's strategic direction, product pipeline, financial status, and market opportunities.

Core Insights - Seres Therapeutics is advancing its corporate strategy focused on live biotherapeutic programs targeting inflammatory and immune diseases, particularly inflammatory bowel disease and immune checkpoint-related enterocolitis, with clinical data from the SER-155 study expected in Q2 2026 [1][3][5] Leadership Changes - Richard N. Kender has been appointed as Executive Chair and Interim CEO, bringing over 35 years of biopharma experience, while previous co-CEOs will continue in their roles as Chief Legal Officer and Chief Financial Officer [2][4][5] Clinical Development - SER-155 is ready for Phase 2 trials for patients undergoing allogeneic hematopoietic stem cell transplant to treat hematologic malignancies, with ongoing efforts to secure funding for the program [1][5][11] - The SER-155 study is fully enrolled with 15 participants, and initial clinical data is anticipated in Q2 2026, focusing on safety, efficacy, and pharmacology [11][13] Financial Position - As of December 31, 2025, Seres had approximately $45.8 million in cash and cash equivalents, with expectations to fund operations through Q3 2026 [8][10] Pipeline Updates - The company is also advancing SER-603, a novel live biotherapeutic candidate aimed at treating inflammatory bowel disease, with IND-enabling activities underway [11][13]

Core Viewpoint - Seres Therapeutics Inc. is undergoing a strategic shift to prioritize emerging programs in inflammatory and immune diseases, leading to a decline in its stock price and raising investor concerns about its pipeline and funding strategies [1]. Group 1: Lead Drug Update - The company has finalized the protocol for its Phase 2 study of SER-155 in patients undergoing allogeneic hematopoietic stem cell transplant (allo-HSCT) but is pausing further investment in this program while seeking funding [2]. - Seres is supporting the read-out of clinical results from the fully enrolled Investigator-sponsored SER-155 study in immune checkpoint-related enterocolitis (irEC), with results expected in early Q2 2026 [3]. Group 2: Strategic Focus - The company's future strategy will prioritize advancing early-stage programs, including SER-603, targeting inflammatory and immune indications such as ulcerative colitis, Crohn's disease, and irEC, while discussions for potential collaborations are ongoing [4]. - A workforce reduction of approximately 30% has been announced to extend the cash runway through Q3 2026, allowing the company to focus on early-stage live biotherapeutic programs and pursue collaborations [5]. Group 3: Market Performance - Seres Therapeutics shares were down 16.25% at $11.80 during premarket trading, indicating company-specific concerns despite a generally positive market environment [6][9]. - The stock is trading 24.4% below its 20-day simple moving average (SMA) and 33% below its 100-day SMA, reflecting a bearish trend, with a 12-month decrease of 13.86% [7].

Core Insights - Seres Therapeutics has finalized the protocol for the Phase 2 study of SER-155 in patients undergoing allogeneic hematopoietic stem cell transplant (allo-HSCT) and is pausing further investment while seeking funding for the study [1][3] - The company has reduced its workforce by approximately 30% to extend its cash runway through Q3 2026, allowing for continued development of its live biotherapeutic programs [1][3] - Seres is focusing on advancing early-stage live biotherapeutic programs targeting inflammatory and immune diseases, including SER-603 for ulcerative colitis and Crohn's disease [2][5] Financial and Operational Strategy - The workforce reduction and other cost-saving measures are expected to extend the company's cash runway, providing opportunities to advance its therapeutic programs and pursue collaborations [1][3] - The company anticipates reporting initial clinical results from the fully enrolled SER-155 study in immune checkpoint related enterocolitis (irEC) in early Q2 2026, which could highlight the potential of live biotherapeutics [3][4] Clinical Development - SER-155 has shown a significant reduction in bloodstream infections in a Phase 1b clinical study and has received Breakthrough Therapy and Fast Track designations [6] - The ongoing investigator-sponsored trial at Memorial Sloan Kettering Cancer Center is evaluating SER-155 in 15 participants with irEC, a severe adverse event in patients receiving immune checkpoint inhibitors [4][5] - Data from the SER-155 study could support the use of live biotherapeutics as a non-immunosuppressive treatment option for inflammatory and immune diseases linked to colitis [5][6]

Core Insights - Seres Therapeutics has published new findings on the mechanisms of action and clinical impact of its live biotherapeutic product VOWST, reinforcing the company's approach to developing next-generation live biotherapeutics [1][3][4] Group 1: VOWST Development and Approval - VOWST is the first FDA-approved oral microbiome biotherapeutic, designed to prevent recurrent Clostridioides difficile infection (rCDI), with its approval granted in April 2023 [2] - The product was sold to Nestlé Health Science in September 2024, marking a significant milestone for the company [2][7] Group 2: Clinical Findings and Mechanisms - A study published in Nature Medicine confirmed that higher doses of VOWST lead to enhanced pharmacokinetics, resulting in faster and more robust engraftment of therapeutic species in the gut [3] - Treatment with VOWST significantly altered the intestinal microbiome composition and increased beneficial metabolites, which inhibit C. difficile growth [3] - A complementary analysis in the Journal of Infectious Diseases showed that VOWST demonstrated similar efficacy across patients with first and multiply recurrent CDI, indicating consistent pharmacological effects [4] Group 3: Future Pipeline and SER-155 - The company is advancing its lead candidate SER-155, which has shown a 77% reduction in bacterial bloodstream infections in a Phase 1b study for patients undergoing allogeneic hematopoietic stem cell transplant (allo-HSCT) [5][7] - SER-155 has received Breakthrough Therapy designation for reducing bloodstream infections and Fast Track designation for preventing infections and graft-versus-host disease in allo-HSCT patients [7] - The company aims to explore SER-155 in various medically vulnerable populations, including cancer patients and those in intensive care [7]

Industry Overview - The biotech and drug industry experienced a significant rebound in 2025 after a cautious start, driven by drug pricing agreements and increased M&A activity [1] - The FDA approved 44 novel therapies in 2025, with 26 approvals occurring in the second half of the year, indicating an acceleration in regulatory activity [1][2] Company Analysis: Altimmune (ALT) - Altimmune is focused on developing therapies for liver diseases, with its lead candidate pemvidutide currently in mid-stage studies for metabolic dysfunction-associated steatohepatitis (MASH) [4] - Shares of Altimmune have decreased over 46% year-to-date due to mixed results from the phase IIb IMPACT study, although it met one primary endpoint related to MASH resolution [5] - Recent 48-week results from the IMPACT study showed further improvements in non-invasive tests and significant reductions in liver health biomarkers [6] - Altimmune plans to initiate a late-stage study for pemvidutide in MASH in 2026 after aligning with the FDA on key parameters [7] - The company is also exploring pemvidutide for alcohol use disorder and alcohol-associated liver disease, with data expected next year [8] Company Analysis: ImmunityBio (IBRX) - ImmunityBio focuses on therapies for cancer and infectious diseases, with its marketed drug Anktiva approved for bladder cancer [11] - Shares of ImmunityBio have declined over 16% this year due to a regulatory setback from the FDA regarding a label expansion for Anktiva [12] - Despite the setback, Anktiva generated nearly $75 million in sales this year, a significant increase from $7 million in the previous year, and the company is seeking EU market expansion [13] - ImmunityBio is also developing Anktiva for other cancer indications, with promising data in non-small cell lung cancer and glioblastoma expected to be updated in 2026 [14] - Loss per share estimates for 2026 have improved from $0.37 to $0.33 in the past 60 days [15] Company Analysis: Seres Therapeutics (MCRB) - Seres Therapeutics is developing SER-155, an oral live biotherapeutic aimed at preventing bloodstream infections in patients undergoing stem cell transplantation [16] - Investor interest in SER-155 increased after a phase Ib study showed a 77% relative reduction in bacterial infections compared to placebo [17] - The FDA has provided positive feedback for SER-155's advancement to mid-stage development, with an interim update expected within 12 months of study initiation [18] - Shares of Seres Therapeutics have decreased nearly 12% year-to-date, but loss per share estimates for 2026 have improved from $10.66 to $7.67 in the past 60 days [18]