MCRB

Recently announced 80% of SER-155 recipients achieved immunosuppressive-free clinical response at day 15 for immune checkpoint inhibitor-related enterocolitis (irEC) in the investigator-sponsored trial (IST) conducted by Memorial Sloan Kettering Cancer Center (MSK) IST data support SER-155 as a potential treatment for irEC that may allow patients to continue cancer therapy; Company evaluating irEC clinical development strategy in consultation with KOLs Seres engaging potential partners, seeking capital to advance its SER-155 programs, including for the prevention of bloodstream infections in patients undergoing allo-HCT and those experiencing irEC Seres announces agreement to exit additional leased space early, further reducing ongoing facility-related cash costs, which follows announcement of balance sheet strengthening and facilities cost reduction transactions in June 2026 CAMBRIDGE, Mass., Aug. 05, 2026 (GLOBE NEWSWIRE) -- Seres Therapeutics, Inc. (Nasdaq: MCRB), (Seres or the Company), a leading live biotherapeutics company, today reported second quarter 2026 financial results and provided business updates. "We are very pleased with the recent progress at Seres, including the positive topline data from the investigator-sponsored trial of SER-155 in irEC conducted by MSK, announced last month," said Richard Kender, Executive Chairman and Interim Chief Executive Officer of Seres. "The study demonstrated that 80% of participants achieved an immunosuppressive-free clinical response at day 15, and the accompanying pharmacology data reinforced that our live biotherapeutic operated as designed, including by repairing the mucosal epithelial barrier. SER-155 to treat irEC, a frequent and often severe side effect of widely used immune checkpoint inhibitor (ICI) cancer treatment, represents a meaningful therapeutic and commercial opportunity, as many patients who experience irEC are required to halt their ICI therapy and begin immunosuppressive corticosteroid treatment. We are engaging potential partners, including companies with ICI franchises, as we evaluate the clinical development pathway in this indication and consider sources of financing. In parallel, we continue to pursue partnerships and other financing sources to support development of SER-155 in allo-HCT, and to advance our broader inflammatory and immune portfolio, including SER-603 for inflammatory bowel disease." Marella Thorell, Chief Financial Officer of Seres, added, "Terminating our Sidney Street lease will substantially reduce our future lease obligations and will further lower our ongoing annual fixed costs beginning in 2027. Together with the lease restructuring we announced in June, this transaction reflects our continued focus on rigorous financial discipline, while we maintain the operational infrastructure needed to advance our live biotherapeutic pipeline, including our Phase 2-ready SER-155 program in allo-HCT." Recent Highlights SER-155 in immune checkpoint inhibitor-related enterocolitis (irEC) In July, Seres announced positive topline results from the IST of SER-155 in irEC (NCT06801067) conducted at MSK. The open-label study evaluated SER-155 in 15 participants with moderate-to-severe (Grade 2-3) irEC who were naïve to immunosuppressive therapy. irEC is among the most frequent and severe immune-related adverse reactions in recipients of ICI therapy and, at the moderate-to-severe grade, affects approximately 25% of ICI recipients in the US. In the study, 12 of 15 participants (80%) achieved an immunosuppressive-free clinical response at day 15, the primary efficacy endpoint, defined as at least a 1-grade improvement in diarrhea symptoms without immunosuppressive therapy. SER-155 was generally well tolerated with no safety concerns identified and no serious adverse events assessed as related to SER-155. Participants in the study were on a wide range of ICI types, including PD-1 inhibitors (Keytruda®, Opdivo®, Zynyz®), PD-L1 inhibitors (Imfinzi®, Bavencio®), CTLA-4 inhibitors (Yervoy®, Imjudo®), LAG-3 inhibitor (Opdualag®), and combinations thereof. The promising study results support continued development of SER-155 to treat irEC and the Company is engaging potential partners, including companies with ICI franchises, as it evaluates next steps for the development of SER-155 in irEC. Broader pipeline and portfolio SER-155 remains Phase 2 ready for the prevention of bloodstream infections in patients undergoing allogeneic hematopoietic stem cell transplant (allo-HCT) for the treatment of blood cancer. SER-155 has received Breakthrough Therapy and Fast Track designations for this indication. Efforts to secure funding to advance clinical development for this program continue. The Company continues to advance IND-enabling activities for SER-603, in development for inflammatory bowel disease, and is engaging potential collaborators to support the clinical advancement of this program as a mono and/or combination therapy. Seres continues to progress development of SER-428, an investigational oral liquid formulation based on SER-155 strains supported by a grant from CARB-X (Combating Antibiotic-Resistant Bacteria Biopharmaceutical Accelerator), for dosing in patients who cannot take oral capsules. Seres is designing a Phase 1b open-label trial, in collaboration with Dr. Dan Freedberg at Columbia University, to evaluate SER-428 in medical ICU patients at high risk of infection. Corporate Updates Seres completed the below transactions that will collectively strengthen the Company’s balance sheet and reduce ongoing annual facility cash costs. On July 31, Seres entered into an agreement to terminate the lease for its facility at 200 Sidney Street in Cambridge, MA. This early termination eliminates the Company's remaining obligations under the lease as of December 31, 2026 in exchange for certain consideration and will further significantly reduce ongoing facility-related cash costs beginning in 2027. Additional details regarding the agreement are included in the Company's Report on Form 8-K, which was filed with the Securities and Exchange Commission on August 4, 2026. The accounting for this transaction will be reported in the Company’s third quarter 2026 results. In June, Seres restructured the lease for its facility at 101 CambridgePark Drive in Cambridge, MA, reducing its leased space, rental rate and related operating expenses. The restructured 10-year lease is expected to materially reduce the Company's ongoing annual facility-related cash costs and long-term lease obligations. In June, Seres entered into an amendment to its asset purchase agreement with Nestlé Health Science (Nestlé) under which Nestlé will pay Seres an aggregate $25 million (the Milestone Termination Payment), in two equal installments of $12.5 million on July 1, 2026 (which was received) and $12.5 million which is expected to be received on October 1, 2026, to buy out potential future VOWST net sales-based milestones. Seres sold the VOWST business to Nestlé Health Science in 2024. Second Quarter 2026 Financial Results Net income was $4.6 million for the second quarter of 2026, compared to a net loss of $19.9 million for the same period in 2025. The difference is primarily due to a $25 million Gain on Sale of the VOWST Business recognized in the second quarter of 2026 arising from the Milestone Termination Payment due from Nestlé. Research and development expenses were $9.1 million for the second quarter of 2026, compared with $12.9 million for the same period in 2025, reflecting lower personnel-related expenses, facilities costs, transition services agreement (TSA) costs and SER-155 costs driven by lower activities in these areas and cost reduction efforts. General and administrative expenses were $7.1 million for the second quarter of 2026, compared with $10.3 million for the same period in 2025, due to lower personnel-related expenses, facilities costs, professional services fees, and IT costs, including those related to IT services provided under the TSA. In the second quarter of 2026, there was a $5.8 million impairment charge recorded related to the early termination of a portion of the Company’s leased space at 101 Cambridgepark Drive. There were no manufacturing services expenses in the second quarter of 2026, compared with $1.7 million in the second quarter of 2025, as the Company completed such services under the TSA at the end of 2025. Cash and Cash Runway As of June 30, 2026, Seres had $15.6 million in cash and cash equivalents. Based on Seres’ currently available cash resources, including the $12.5 million Milestone Termination Payment received from Nestlé on July 1, 2026, and the expected receipt of the remaining $12.5 million Milestone Termination Payment from Nestlé on October 1, 2026, and considering future operating plans, the Company expects to fund operations through the first quarter of 2027. This projection excludes proceeds from any potential future partnerships or other sources of capital. About Seres Therapeutics Seres Therapeutics, Inc. (Nasdaq: MCRB) is a clinical-stage biotechnology company developing novel live biotherapeutics products (LBP), designed to address unmet needs in oncology that can lead to interruption to patients' cancer care and/or mortality, and to treat inflammatory and immune (I&I) diseases, by modulating host function to protect and improve mucosal epithelial barrier integrity, induce immune homeostasis and tolerance, and prevent the colonization and overgrowth of pathogens in the gastrointestinal (GI) tract. The Company previously led the development and FDA approval of VOWST™, the first orally administered microbiome therapeutic, which was subsequently divested to Nestlé Health Science. SER-155, an investigational cultivated multi-strain biotherapeutic, which has received Breakthrough Therapy and Fast Track designations, is being advanced for the prevention of bloodstream infections in patients undergoing allogeneic hematopoietic stem cell transplant (allo-HCT), and is Phase 2 ready, pending receipt of funding. SER-155 is also being developed to address immune checkpoint inhibitor-related enterocolitis (irEC) to provide an immunosuppressive-free alternative and enable patients to continue their ICI cancer therapy. Having recently reported promising results from an IST, Seres is evaluating the design of a Phase 2 study in irEC. The Company is advancing IND-enabling studies for SER-603, which is in development for inflammatory bowel disease. Mechanistically, Seres' biotherapeutics target the mucosal epithelial barrier-immune interface and are optimized to modulate host function to increase mucosal epithelium integrity, induce immune homeostasis, and prevent the colonization and overgrowth of harmful bacteria in the GI tract. For more information, please visit www.serestherapeutics.com. Forward-Looking Statements This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including statements about: SER-155 and its intended uses and benefits in irEC; our clinical development plans for SER-155, SER-603 and SER-428; potential accessibility for patients; the timing and results of clinical studies and data readouts; current or future product candidates and their potential impacts and outcomes; engagement with potential partners and financing sources; our ability to access capital to advance our programs; expected receipt of milestone termination payments; our lease restructuring activities and anticipated cost savings and liability reductions; our cash runway; our planned strategic focus; the anticipated timing of any of the foregoing; and other statements that are not historical fact. These forward-looking statements are based on management's current expectations. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements, including, but not limited to, the following: (1) our need for additional funding; (2) our ability to continue as a going concern; (3) we have incurred significant losses, are not currently profitable and may never become profitable; (4) our cost reduction actions may not achieve their intended benefits, including an extended cash runway; (5) our limited operating history; (6) we may not be able to realize the anticipated benefits of the VOWST sale, and may face new challenges as a smaller, less diversified company; (7) we have in the past and may in the future receive notice of the failure to satisfy a continued listing rule from The Nasdaq Stock Market LLC; (8) our novel approach to therapeutic intervention; (9) our reliance on third parties to conduct our clinical trials and manufacture our product candidates; (10) our ability to achieve market acceptance necessary for commercial success; (11) the competition we will face; (12) our ability to protect our intellectual property; (13) impact of our recent management transitions and appointments and our ability to retain key personnel; and (14) disruptions at the FDA or other government agencies. These and other important factors discussed under the caption "Risk Factors" in our Quarterly Report on Form 10-Q for the quarterly period ended June 30, 2026, to be filed with the Securities and Exchange Commission (SEC) on August 5, 2026, as well as our other reports filed with the SEC, could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent management's estimates as of the date of this press release. While we may elect to update such forward-looking statements at some point in the future, except as required by law, we disclaim any obligation to do so, even if subsequent events cause our views to change. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date of this press release. [1] Includes $0, $0, $3,490, and $9,799 for the three and six months ended June 30, 2026 and 2025 related to reimbursement received from SPN (related party) for transition services provided by the Company. Investor and Media Contact:[email protected] Tanzi, Ph.D.Kendall Investor [email protected]

CAMBRIDGE, Mass., June 25, 2026 (GLOBE NEWSWIRE) -- Seres Therapeutics, Inc. (Nasdaq: MCRB), a leading live biotherapeutics company, today announced that it will host a webcast to discuss top-line results from an investigator-sponsored trial (IST) evaluating SER-155 in patients with immune checkpoint inhibitor-related enterocolitis, a serious and frequent side effect of immune checkpoint inhibitor cancer therapy. The IST was conducted at Memorial Sloan Kettering Cancer Center, with which Seres has a long history of collaboration, by Principal Investigator David Faleck, M.D., Director of Inflammatory and Immune-Related Bowel Diseases. The webcast will occur on July 8, 2026, at 8:30 am ET. To access the conference call, please dial 800-715-9871 (domestic) or 646-307-1963 (international) and reference the conference ID number 3327556. To join the live webcast, please visit the “Events and Presentations” tab within the “Investors and News” section of the Seres website at www.serestherapeutics.com. The webcast will be available for replay following the event. About Immune Checkpoint Inhibitors and the Investigator-Sponsored Trial (NCT06801067)Immune checkpoint inhibitors (ICI) have transformed cancer treatment across multiple tumor types, but they frequently trigger immune-mediated adverse events, including enterocolitis. ICIs now represent one of the largest and fastest-growing segments of the oncology market. Immune checkpoint inhibitor-related enterocolitis (irEC) is among the most frequent and severe immune-related adverse events in ICI recipients. Current standard of care for those who suffer from moderate to severe irEC (in the US this approximates 25% of all ICI recipients) requires halting their ICI cancer therapy and initiating an immunosuppressive corticosteroid, further compromising the patient’s immune system. A significant unmet need remains for immunosuppressive-free therapeutic approaches that reduce gastrointestinal inflammation and diarrhea and may allow patients that develop irEC to avoid disruption of their ICI therapy. This investigator-sponsored, open-label trial (IST) (NCT06801067) evaluated SER-155 in 15 participants with Grade 2-3 (moderate to severe) irEC who were naïve to immunosuppressive therapy. The primary efficacy endpoint is the proportion of participants achieving an immunosuppressive-free clinical response on Day 15, defined as at least a 1-grade improvement in diarrhea symptoms, without the need for toxic immunosuppressive therapy such as corticosteroids. The study is also evaluating the safety, tolerability and drug pharmacology of SER-155. The IST is designed to inform if SER-155 may provide an alternate treatment for irEC with the potential to prevent interruption of the patient’s ICI cancer treatment. About Seres TherapeuticsSeres Therapeutics, Inc. (Nasdaq: MCRB) is a clinical-stage biotechnology company developing novel live biotherapeutics, with a focus on therapies that allow patients to maintain their cancer care, and that treat inflammatory and immune diseases. The Company led the development and FDA approval of VOWST™, the first orally administered microbiome therapeutic, which was subsequently divested to Nestlé Health Science. SER-155, which has received Breakthrough Therapy and Fast Track designations, is being advanced for the prevention of bloodstream infections in patients undergoing allogeneic hematopoietic stem cell transplant (allo-HSCT), and is Phase 2 ready, pending receipt of funding. An investigator-sponsored trial of SER-155 in immune checkpoint inhibitor–related enterocolitis (irEC) to further evaluate the potential breadth of the Company’s live biotherapeutic platform is ongoing. The Company is advancing IND-enabling studies for SER-603, which is in development for inflammatory bowel disease. Mechanistically, Seres’ biotherapeutics target the mucosal epithelial barrier-immune interface and are optimized to modulate host function to increase epithelium integrity, induce immune homeostasis, and prevent the colonization and overgrowth of harmful bacteria in the gastrointestinal tract. For more information, please visit www.serestherapeutics.com. Forward-Looking StatementsThis press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including statements about: the anticipated content and timing of upcoming webcasts, conference calls and data readouts; SER-155 and its intended uses and benefits in irEC and other indications; potential accessibility for patients; clinical development plans for SER-155; the timing and results of our clinical studies; the anticipated timing of any of the foregoing; and other statements that are not historical fact.  These forward-looking statements are based on management’s current expectations. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements, including, but not limited to, the following: (1) our need for additional funding; (2) our ability to continue as a going concern; (3) we have incurred significant losses, are not currently profitable and may never become profitable; (4) our cost reduction actions may not achieve their intended benefits, including an extended cash runway; (5) our limited operating history;(6) we may not be able to realize the anticipated benefits of the VOWST sale, and may face new challenges as a smaller, less diversified company; (7) we have in the past and may in the future receive notice of the failure to satisfy a continued listing rule from The Nasdaq Stock Market LLC; (8) our novel approach to therapeutic intervention; (9) our reliance on third parties to conduct our clinical trials and manufacture our product candidates; (10) our ability to achieve market acceptance necessary for commercial success; (11) the competition we will face; (12) our ability to protect our intellectual property; (13) impact of our recent management transitions and appointments and our ability, to retain key personnel; and (14) disruptions at the FDA or other government agencies. These and other important factors discussed under the caption “Risk Factors” in our Quarterly Report on Form 10Q for the quarterly period ended May 5, 2026, as well as our other reports filed with the SEC, could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent management’s estimates as of the date of this press release. While we may elect to update such forward-looking statements at some point in the future, except as required by law, we disclaim any obligation to do so, even if subsequent events cause our views to change. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date of this press release. Investor and Media Contacts:[email protected] Carlo Tanzi, Ph.D.Kendall Investor [email protected]

Agreement with Nestlé Health Science provides $25 million payable to Seres in 2026 as a buy-out of potential future VOWST™ net sales-based milestones Restructured lease materially reduces ongoing annual facility cash costs and long-term lease liability Clinical data from investigator-sponsored SER-155 study in immune checkpoint inhibitor-related enterocolitis expected later this month CAMBRIDGE, Mass., June 05, 2026 (GLOBE NEWSWIRE) -- Seres Therapeutics, Inc. (Nasdaq: MCRB), (“Seres” or the “Company”), a leading live biotherapeutics company, today announced two transactions to strengthen its balance sheet and extend its expected operating cash runway well into the first quarter of 2027. Seres entered into an amendment to the prior asset purchase agreement whereby Nestlé Health Science will now pay Seres a total of $25 million (in two equal installments in July and October 2026) to buy out potential future VOWST™ net sales-based milestones, and a restructured lease agreement for one of Seres’ locations which materially reduces the Company’s leased space and ongoing annual facility cash costs and long-term lease obligations. Seres previously developed VOWST, the first orally administered microbiome-based therapeutic approved by the U.S. Food and Drug Administration for the prevention of recurrence of Clostridioides difficile infection in adults following antibacterial treatment for recurrent CDI. Seres sold the VOWST business to Nestlé Health Science in 2024. “We have taken meaningful actions to strengthen our balance sheet and extend our cash runway well into the first quarter of 2027,” said Richard Kender, Executive Chair and Interim Chief Executive Officer of Seres. “The Company intends to continue to exercise rigorous financial discipline while advancing its live biotherapeutic programs in inflammatory and immune diseases and pursuing partnerships and other sources of capital to support continued pipeline development, including our Phase 2-ready SER-155 program in allo-HSCT. We look forward to the clinical readout expected later this month from the investigator-sponsored study of SER-155 in immune checkpoint inhibitor-related enterocolitis being conducted at Memorial Sloan Kettering Cancer Center, a long-term collaborator with Seres.” “These transactions will improve our financial flexibility, and the lease restructure marks progress in our goal to reduce our leased space to align with our focused corporate strategy,” said Marella Thorell, Chief Financial Officer of Seres. “We are pleased with these outcomes, which will provide near-term capital from the Nestlé agreement and significantly reduce our ongoing annual facility-related cash spending via the restructured lease. Importantly, while reducing fixed costs and preserving capital, we are maintaining the operational infrastructure needed to support our pipeline as we pursue additional sources of funding and strategic opportunities.” As of March 31, 2026, Seres had $29.8 million in cash and cash equivalents. Based on the transactions described herein and current operating plans, Seres expects to fund operations well into the first quarter of 2027. This projection excludes proceeds from any potential future partnerships or other sources of capital. Amendment to Asset Purchase Agreement with Nestlé Health Science Seres sold its interest in the VOWST business to Nestlé Health Science in 2024. Seres has entered into an amendment to the asset purchase agreement whereby Nestlé Health Science will pay Seres an aggregate of $25 million, in two installments of $12.5 million each on July 1, 2026, and October 1, 2026, to buy-out the potential future milestones due to Seres if and upon the achievement of certain VOWST net sales targets. Lease Restructuring Seres has amended its lease with its landlord for the Company’s facility at 101 CambridgePark Drive in Cambridge, Massachusetts, reducing its leased space, rental rate and facility operating expenses. Under the amended arrangement, Seres will lease the retained space for a 10-year term at market-adjusted annual rent and a lower percentage of shared operating expenses for the building as of May 1, 2026, in exchange for the landlord drawing the existing letter of credit, Seres payment of a termination fee and the establishment of a new letter of credit. The restructured lease is expected to materially reduce the Company’s ongoing annual facility-related costs and long-term obligations. Additional details regarding the Nestlé Health Science asset purchase agreement amendment and the lease amendment are included in the Company’s Current Report on Form 8-K which will be filed with the Securities and Exchange Commission today. About Seres Therapeutics Seres Therapeutics, Inc. (Nasdaq: MCRB) is a clinical-stage biotechnology company developing novel live biotherapeutics, with a focus on inflammatory and immune diseases. The Company led the development and FDA approval of VOWST™, the first orally administered microbiome therapeutic, which was subsequently divested to Nestlé Health Science. SER-155, which has received Breakthrough Therapy and Fast Track designations, is being advanced for patients undergoing allogeneic hematopoietic stem cell transplant (allo-HSCT), and is Phase 2 ready, pending receipt of funding. An investigator-sponsored trial of SER-155 is ongoing in immune checkpoint inhibitor–related enterocolitis (irEC) to further evaluate the potential breadth of the Company’s live biotherapeutic platform. SER-603, in development for inflammatory bowel disease, is designed to modulate the gastrointestinal microbiome and support mucosal barrier integrity by targeting inflammatory bacteria and associated metabolites. For more information, please visit www.serestherapeutics.com. Forward-Looking StatementsThis press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including statements about: anticipated payments under the amendment to the asset purchase agreement with Nestlé Health Science; the expected effects and benefits of the restructured lease, including reduced ongoing annual facility-related cash costs and long-term lease obligations; the Company’s expected operating cash runway; the timing and results of clinical studies and data readouts, including the investigator-sponsored study of SER-155 in immune checkpoint inhibitor-related enterocolitis; the advancement of SER-155 and other pipeline programs; the Company’s ability to support its pipeline and to enter into partnerships or obtain other sources of capital; and the anticipated timing of any of the foregoing. These forward-looking statements are based on management’s current expectations. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements, including, but not limited to, the following: (1) our need for additional funding; (2) our ability to continue as a going concern; (3) we have incurred significant losses, are not currently profitable and may never become profitable; (4) our cost reduction actions may not achieve their intended benefits, including an extended cash runway; (5) our limited operating history; (6) we may not be able to realize the anticipated benefits of the VOWST sale, and may face new challenges as a smaller, less diversified company; (7) we have in the past and may in the future receive notice of the failure to satisfy a continued listing rule from The Nasdaq Stock Market LLC; (8) our novel approach to therapeutic intervention; (9) our reliance on third parties to conduct our clinical trials and manufacture our product candidates; (10) our ability to achieve market acceptance necessary for commercial success; (11) the competition we will face; (12) our ability to protect our intellectual property; (13) impact of our recent management transitions and appointments and our ability, to retain key personnel; and (14) disruptions at the FDA or other government agencies. These and other important factors discussed under the caption “Risk Factors” in our Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2026 filed with the Securities and Exchange Commission (SEC) on May 5, 2026, as well as our other reports filed with the SEC, could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent management’s estimates as of the date of this press release. While we may elect to update such forward-looking statements at some point in the future, we disclaim any obligation to do so, even if subsequent events cause our views to change except as required by law. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date of this press release. Investor and Media Contact:  [email protected] Carlo Tanzi, Ph.D.Kendall Investor [email protected]

Clinical readout from investigator-sponsored SER-155 study in immune checkpoint inhibitor-related enterocolitis expected in the coming weeks Seres maintains operational focus on advancing live biotherapeutic programs in inflammatory and immune diseases Company pursuing partnerships and other sources of capital to support continued development of pipeline programs including SER-155 in allo-HSCT CAMBRIDGE, Mass., May 05, 2026 (GLOBE NEWSWIRE) -- Seres Therapeutics, Inc. (Nasdaq: MCRB), (Seres or the Company), a leading live biotherapeutics company, today reported first quarter 2026 financial results and provided business updates. “We are approaching an important clinical milestone with the expected readout in the coming weeks from the investigator-sponsored study at Memorial Sloan Kettering Cancer Center, an institution with whom we’ve collaborated for over a decade, evaluating SER-155 in immune checkpoint inhibitor-related enterocolitis (irEC),” said Richard Kender, Executive Chair and interim Chief Executive Officer of Seres. “irEC is a serious condition which represents a meaningful therapeutic and commercial opportunity, and with positive data we will evaluate potential development pathways and adjacent expansion opportunities. In parallel, we are advancing our inflammatory and immunology portfolio, including SER-603 for inflammatory bowel disease, with IND-enabling work progressing. We have achieved Phase 2 readiness for SER-155 for the prevention of bloodstream infections in patients undergoing allo-HSCT for the treatment of blood cancer and are seeking funding to commence the study. We are continuing disciplined capital allocation while actively pursuing partnerships and other financing sources to support Seres’ pipeline advancement and long-term value creation.” Recent Highlights As highlighted in recent press releases from February and March, Seres is prioritizing its emerging live biotherapeutic programs in inflammatory & immune (I&I) diseases, including SER-155 for immune checkpoint-related enterocolitis (irEC) and SER-603 for inflammatory bowel disease (IBD). Seres is collaborating with Memorial Sloan Kettering Cancer Center on an investigator-sponsored trial evaluating SER-155 in participants with irEC. irEC is among the most frequent and severe immune-related adverse events (irAEs) in recipients of immune checkpoint-inhibitor therapy and can be observed in up to 50% of patients, with rates varying based on cancer drug and treatment regimen. Study enrollment is complete, with 15 patients enrolled, and clinical data are expected in the coming weeks. Positive data from this IST could further inform the expansion of indications well-suited to Seres’ live biotherapeutic approach. The Company continues to advance its preclinical stage live biotherapeutic product candidates, including SER-603. The Company is conducting IND-enabling activities for SER-603 and is engaging potential collaborators to support the clinical advancement of this program as a mono and/or combination therapy for IBD. In May, Seres presented new preclinical data supporting the design and potential of SER-603 at Digestive Disease Week (DDW). The Company’s poster, titled “The Rational Design of SER-603: A Next Generation Cultivated Microbial Consortia to Treat IBD,” which was selected as a DDW ‘Poster of Distinction,’ highlights Seres’ integrated approach to the design of microbiome therapeutics, combining rational strain selection and a novel biomarker-driven patient stratification. In May, Seres’ management will be attending the Memorial Sloan Kettering’s (MSK) Innovation with Lasting Impact Summit which this year focuses on "Drug Discovery & Development and MSK” and will be presenting, along with Dr. Jonathan (Tsoni) Peled an oncologist at MSK specializing in bone marrow transplantation for blood cancers, on Seres’ decade-long research and clinical development collaboration with MSK. SER-155 is Phase 2 ready for the prevention of serious bloodstream infections in patients undergoing allogeneic hematopoietic stem cell transplants (allo-HSCT) for the treatment of blood cancer, and efforts to secure funding to advance clinical development for this program continue. Supported by a grant from CARB-X (Combating Antibiotic-Resistant Bacteria Biopharmaceutical Accelerator), a global nonprofit partnership accelerating the development of new antibacterial products to address drug-resistant bacteria, Seres is progressing development of an oral liquid formulation based on SER-155 strains, referred to as SER-428, for dosing in patients who cannot take oral capsules such as intubated patients in the medical ICU, and other medically vulnerable patients at high risk of AMR infections. Seres has advanced manufacturing of SER-428 and is designing a Phase 1b open label trial, in collaboration with Dr. Dan Freedberg at Columbia University, to evaluate this therapeutic candidate in medical ICU patients at high risk of infection. The Company attended the ESCMID Global Conference in April and presented a poster highlighting biomarker and clinical pharmacology data from the Company’s SER-155 Phase 1b study in allo-HSCT. Data showed that administration of SER-155 induced a significant and durable shift in gastrointestinal (GI) microbiome composition relative to placebo, characterized by high relative abundance of SER-155 species. This shift is associated with improved GI epithelial barrier integrity that could reduce the likelihood of bacterial translocation from the GI to the bloodstream. These pharmacology results are consistent with the intended SER-155 mechanisms of action as well as the observation of significantly lower bloodstream infection incidence (77% relative risk reduction) post allo-HSCT in SER-155-administered participants in Seres’ Phase 1b study. In January, the Company announced the publication of manuscripts in Nature Medicine and the Journal of Infectious Diseases, highlighting new insights into the functional mechanism and clinical impact of VOWST™, which was developed by Seres and sold to Nestlé Health Science (Nestlé) in 2024. These publications further inform the continued development of Seres’ next-generation live biotherapeutics pipeline. Financial Results Net loss was $19.9 million for the first quarter of 2026, compared to net income of $32.7 million for the same period in 2025. Contributing to the net income in the first quarter of 2025 was a $50 million installment payment received from Nestlé, related to certain transition services following the sale of VOWST and $6.3 million in reimbursements from Nestlé for the costs of those services. Operating expenses were approximately $6 million lower in the first quarter of 2026 compared to the first quarter of 2025. Research and development expenses were $13.2 million for the first quarter of 2026, compared with $11.8 million for the same period in 2025, primarily due to higher facilities and manufacturing-related costs that in 2025 were partially reimbursed by Nestlé under the transition services agreement (TSA), partially offset by lower personnel-related expenses. General and administrative expenses were $8.1 million for the first quarter of 2026, compared with $11.9 million for the same period in 2025, reflecting lower personnel and professional services costs, and a reduction in IT costs, including those related to services provided under the TSA. There were no manufacturing services expenses in the first quarter of 2026, compared with $3.5 million in the first quarter of 2025, as the Company completed such services, provided under the TSA, at the end of 2025. Cash and Cash Runway As of March 31, 2026, Seres had $29.8 million in cash and cash equivalents. Based on Seres’ current cash position and operating plans, the Company expects to fund operations through the third quarter of 2026. The Company continues to evaluate opportunities to extend its cash runway. About Seres Therapeutics Seres Therapeutics, Inc. (Nasdaq: MCRB) is a clinical-stage biotechnology company developing novel live biotherapeutics, with a focus on inflammatory and immune diseases. The Company led the development and FDA approval of VOWST™, the first orally administered microbiome therapeutic, which was subsequently divested to Nestlé Health Science. SER-155, which has received Breakthrough Therapy and Fast Track designations, is being advanced for patients undergoing allogeneic hematopoietic stem cell transplant, and is Phase 2 ready, pending receipt of funding. An investigator-sponsored trial of SER-155 is ongoing in immune checkpoint inhibitor–related enterocolitis to further evaluate the potential breadth of the Company’s live biotherapeutic platform. SER-603, in development for inflammatory bowel disease, is designed to modulate the gastrointestinal microbiome and support mucosal barrier integrity by targeting inflammatory bacteria and associated metabolites. For more information, please visit www.serestherapeutics.com. Forward-Looking Statements This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including statements about: the design, timing and results of our preclinical and clinical studies and data readouts; current or future product candidates and their potential impacts and outcomes; clinical development plans and commercial opportunities; communications with, feedback from, or submissions to the FDA; operating plans; cost reduction actions and their anticipated benefits; our cash runway; our ability to secure a strategic, R&D, or other partnership and other funding sources; the advancement of IND-enabling activities; CARB-X funding and its intended uses and benefits and the potential accessibility for patients; our ability to operationalize a study upon receipt of any funding; our planned strategic focus; the anticipated timing of any of the foregoing; and other statements that are not historical fact. These forward-looking statements are based on management’s current expectations. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements, including, but not limited to, the following: (1) our need for additional funding; (2) our ability to continue as a going concern; (3) we have incurred significant losses, are not currently profitable and may never become profitable; (4) our cost reduction actions may not achieve their intended benefits, including an extended cash runway; (5) our limited operating history; (6) the expected payments from the VOWST sale are subject to risks and uncertainties; (7) we may not be able to realize the anticipated benefits of the VOWST sale, and may face new challenges as a smaller, less diversified company; (8) we have in the past and may in the future receive notice of the failure to satisfy a continued listing rule from The Nasdaq Stock Market LLC; (9) our novel approach to therapeutic intervention; (10) our reliance on third parties to conduct our clinical trials and manufacture our product candidates; (11) our ability to achieve market acceptance necessary for commercial success; (12) the competition we will face; (13) our ability to protect our intellectual property; (14) impact of our recent management transitions and appointments and our ability, to retain key personnel; and (15) disruptions at the FDA or other government agencies. These and other important factors discussed under the caption “Risk Factors” in our Annual Report on Form 10-K for the fiscal year ended December 31, 2025 filed with the Securities and Exchange Commission (SEC) on March12, 2026, as well as our other reports filed with the SEC, could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent management’s estimates as of the date of this press release. While we may elect to update such forward-looking statements at some point in the future, we disclaim any obligation to do so, even if subsequent events cause our views to change except as required by law. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date of this press release. [1] Includes $0 and $6,309 for the three months ended March 31, 2026 and 2025 related to reimbursement received from SPN (related party) for transition services provided by the Company. Investor and Media Contact: [email protected] Carlo Tanzi, Ph.D. Kendall Investor Relations [email protected]

Readout of investigator-sponsored SER-155 study in immune checkpoint–related enterocolitis, a frequent and serious side effect 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 support continued development of pipeline programs, including SER-155 for allogeneic hematopoietic stem cell transplant (allo-HSCT) CAMBRIDGE, Mass., March 12, 2026 (GLOBE NEWSWIRE) -- Seres Therapeutics, Inc. (Nasdaq: MCRB), (Seres or the Company), a leading live biotherapeutics company, today reported fourth quarter and full year 2025 financial results and provided business updates. “As highlighted in our recent announcements, we are prioritizing our promising inflammatory and immunology biotherapeutics portfolio, including SER-603 for inflammatory bowel disease,” said Richard Kender, Executive Chair and interim CEO of Seres. “We are on track to report clinical data from the fully enrolled investigator-sponsored study at Memorial Sloan Kettering Cancer Center evaluating SER-155 to treat immune checkpoint inhibitor-related enterocolitis in the second quarter of this year. This serious condition affects up to 50% of immune checkpoint-treated cancer patients, with rates varying based on cancer drug and treatment regimen, and represents a sizable therapeutic and commercial opportunity. Additionally, our SER-155 program for the prevention of serious bloodstream infections in patients undergoing allo-HSCT for blood cancer is Phase 2 ready, and we continue to seek funding to support further development. “To advance these opportunities, we continue to judiciously manage our resources, focusing on progressing our prioritized programs, as we pursue partnerships and other funding sources. We are in discussion with collaborators who could potentially provide Seres with additional financial and other resources to support pipeline advancement and value creation.” Recent Highlights As highlighted in recent press releases from February and March, Seres is prioritizing its emerging programs in inflammatory & immune diseases, including SER-603 for inflammatory bowel disease (IBD) and SER-155 for immune checkpoint-related enterocolitis (irEC). The Company also announced leadership changes, including the appointment of Richard N. Kender as Executive Chair and interim Chief Executive Officer. Seres is collaborating with Memorial Sloan Kettering Cancer Center on an investigator-sponsored trial (IST) evaluating SER-155 in participants with irEC. irEC is among the most frequent and severe immune-related adverse events (irAEs) in recipients of immune checkpoint-inhibitor therapy and can be observed in up to 50% of patients, with rates varying based on cancer drug and treatment regimen. Study enrollment is complete, with 15 subjects enrolled, and clinical data are expected in Q2 2026. Data from this IST could further inform the expansion of indications well-suited to Seres’ live biotherapeutic approach. The Company continues to advance its preclinical stage live biotherapeutic product candidates, including SER-603. The Company is conducting IND-enabling activities for SER-603 and is engaging potential collaborators to support the clinical advancement of this program as a mono- or combination therapy for IBD. Key Phase 2 preparatory activities have progressed to support further development of SER-155 for the prevention of serious bloodstream infections in patients undergoing allo-HSCT for blood cancer. Efforts to seek funding to advance clinical development remain ongoing. In January, the Company announced the publication of manuscripts in Nature Medicine and the Journal of Infectious Diseases, highlighting new insights into the functional mechanism and clinical impact of VOWST™, which was previously sold to Nestle Health Science. These publications further inform the continued development of Seres’ next-generation live biotherapeutics pipeline. Financial Results The Company has classified all historical operating results for the VOWST business within discontinued operations in the consolidated statements of operations for the comparative periods presented. There is no activity in the current period related to discontinued operations. Net income from continuing operations was $5.7 million for the full year 2025, as compared to a net loss from continuing operations of $125.8 million for 2024. The difference in results between 2025 and 2024 were primarily due to: $26.6 million of lower operating expenses in 2025, an increase of $75 million in the gain on sale due to the installment payments received from Nestle in 2025, the $23.4 million loss on extinguishment of debt recognized in 2024 upon repayment of debt following the sale of VOWST, and an increase of $7 million in payments from Nestle related to transition services provided by the Company. Net loss from continuing operations was $15.3 million for the fourth quarter of 2025, as compared to a net loss from continuing operations of $15.6 million for the same period in 2024. Research and development (R&D) expenses for the year ended December 31, 2025, were $49.1 million, compared with $64.6 million for the same period in 2024. The year-over-year decrease of $15.5 million was primarily driven by lower personnel expenses, lower live biotherapeutics platform investments, and lower expenses related to our SER-155 program. R&D expenses for the fourth quarter of 2025 were $11.7 million, compared with $12.8 million for the fourth quarter of 2024. General and administrative (G&A) expenses for the year ended December 31, 2025, were $39.2 million, compared with $53.2 million for the same period in 2024. The year-over-year decrease of $14 million was primarily due to reduced personnel expenses, lower professional fees, and lower facility-related costs and cost management activities. G&A expenses for the fourth quarter of 2025 were $7.5 million, compared with $12.5 million for the fourth quarter of 2024. Manufacturing Services expenses were $6.5 million for the year ended December 31, 2025, as compared to $3.5 million in 2024. These costs relate to the provision of manufacturing services under the transition services agreement with Nestlé. The associated reimbursement received from Nestlé related to these expenses is recognized in other (expense) income, net. Cash and Cash Runway As of December 31, 2025, Seres had $45.8 million in cash and cash equivalents, which includes net proceeds of $12.2 million raised in Q4 2025 through the Company’s at-the-market equity offering program. Based on Seres’ current cash position and operating plans, the Company expects to fund operations through the third quarter of 2026. The Company continues to evaluate further opportunities to extend its cash runway. About Seres Therapeutics Seres Therapeutics, Inc. (Nasdaq: MCRB) is a clinical-stage biotechnology company developing novel live biotherapeutics, with a focus on inflammatory and immune diseases. The Company led the development and FDA approval of VOWST™, the first orally administered microbiome therapeutic, which was subsequently divested to Nestlé Health Science. SER-155, which has received Breakthrough Therapy and Fast Track designations, is being advanced for patients undergoing allogeneic hematopoietic stem cell transplant (allo-HSCT), and is Phase 2 ready, pending receipt of funding. An investigator-sponsored trial of SER-155 is ongoing in immune checkpoint inhibitor–related enterocolitis (irEC) to further evaluate the potential breadth of the Company’s live biotherapeutic platform. SER-603, in development for irritable bowel disease, is designed to modulate the gastrointestinal microbiome and support mucosal barrier integrity by targeting inflammatory bacteria and associated metabolites. For more information, please visit www.serestherapeutics.com. Forward-Looking Statements This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including statements about: the design, timing and results of our clinical studies and data readouts; current or future product candidates and their potential impacts and outcomes; clinical development plans and commercial opportunities; communications with, feedback from, or submissions to the FDA; operating plans; cost reduction actions and their anticipated benefits; our cash runway; our ability to secure a strategic, R&D, or other partnership and/or generate or obtain additional capital, financing or other resources; our ability to operationalize a study upon receipt of any financing; our planned strategic focus; the anticipated timing of any of the foregoing; and other statements that are not historical fact. These forward-looking statements are based on management’s current expectations. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements, including, but not limited to, the following: (1) our need for additional funding; (2) our ability to continue as a going concern; (3) we have incurred significant losses, are not currently profitable and may never become profitable; (4) our cost reduction actions may not achieve their intended benefits, including an extended cash runway; (5) our limited operating history; (6) the expected payments from the VOSWT sale are subject to risks and uncertainties; (7) we may not be able to realize the anticipated benefits of the VOWST sale, and may face new challenges as a smaller, less diversified company; (8) we have in the past and may in the future receive notice of the failure to satisfy a continued listing rule from The Nasdaq Stock Market LLC; (9) our novel approach to therapeutic intervention; (10) our reliance on third parties to conduct our clinical trials and manufacture our product candidates; (11) our ability to achieve market acceptance necessary for commercial success; (12) the competition we will face; (13) our ability to protect our intellectual property; (14) impact of our recent management transitions and appointments and our ability, to retain key personnel; and (15) disruptions at the FDA or other government agencies. These and other important factors discussed under the caption “Risk Factors” in our Annual Report on Form 10-K to be filed with the Securities and Exchange Commission (SEC) on March 12, 2026, as well as our other reports filed with the SEC, could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent management’s estimates as of the date of this press release. While we may elect to update such forward-looking statements at some point in the future, we disclaim any obligation to do so, even if subsequent events cause our views to change. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date of this press release. [1] Includes $0 as of December 31, 2025 and $2,683 as of December 31, 2024 of unbilled receivable from SPN (related party) related to certain costs of the transition services performed by the Company. See Note 3, Discontinued Operations and TSA, for further details. [2] Includes $13,311 and $6,292 for the years ended December 31, 2025 and 2024 related to reimbursement received from SPN (related party) for transition services provided by the Company. Investor and Media Contact: [email protected] Carlo Tanzi, Ph.D. Kendall Investor Relations [email protected]

Following constructive FDA feedback, Seres is finalizing its SER-155 Phase 2 study protocol for the prevention of bloodstream infections in adults undergoing allogeneic hematopoietic stem cell transplant for the treatment of hematological malignancies Efforts are ongoing to obtain capital and other resources to support SER-155 Phase 2 study; pending securing funding, interim clinical results anticipated within 12 months of study initiation Ongoing investigator-sponsored study in immune checkpoint related enterocolitis expected to inform broader SER-155 opportunity; initial study results anticipated in early 2026 Seres recently implemented actions to reduce operating costs; based on these actions and current operating plans, Seres expects to fund operations through Q2 2026 CAMBRIDGE, Mass., Nov. 05, 2025 (GLOBE NEWSWIRE) -- Seres Therapeutics, Inc. (Nasdaq: MCRB), (Seres or the Company), a leading live biotherapeutics company, today reported third quarter 2025 financial results and provided business updates. “Following constructive feedback from the FDA, we are working to finalize our SER-155 Phase 2 study protocol for the prevention of bloodstream infections in adults undergoing allogeneic hematopoietic stem cell transplant (allo-HSCT) for hematological malignancies,” said Thomas DesRosier and Marella Thorell, co-Chief Executive Officers of Seres. “As we prepare for the next phase of SER-155 development, we continue our efforts aimed at securing the funding needed to conduct the Phase 2 study. We expect to be ready to rapidly operationalize the study once financing is in place, and we expect to obtain interim efficacy and safety results within 12 months of the study start. If these results are consistent with our prior successful Phase 1b study, and supportive of continued development, we believe this milestone should be a significant value-creating event for the Company and shareholders. Based on our on-going engagement with the medical community and assessment of the commercial landscape, we remain highly enthusiastic about the broad potential for SER-155—in allo-HSCT and other medically vulnerable populations.” Mr. DesRosier and Ms. Thorell continued, “In addition to SER-155 development in allo-HSCT, we are expanding our understanding of the broader SER-155 therapeutic opportunity through an ongoing investigator-sponsored study in immune checkpoint related enterocolitis, initiated by the investigator at Memorial Sloan Kettering Cancer Center, and we look forward to obtaining initial efficacy results in early 2026. Additionally, during the third quarter, we implemented cost-reduction measures, including decreasing our workforce. Considering these actions and our current operating plans, we expect to fund operations through the second quarter of 2026, providing flexibility to advance our strategic priorities.” Recent Highlights SER-155 and Bloodstream Infection (BSI) Prevention Efforts are ongoing to obtain capital and other resources to support the SER-155 Phase 2 study. The Company is evaluating a range of potential deal structures that could leverage Seres’ live biotherapeutics expertise and success, as demonstrated by bringing VOWST™, the first FDA-approved oral microbiome therapeutic, from early development through FDA approval. The Company received constructive feedback from the FDA during the third quarter and is working to finalize the planned Phase 2 study protocol for SER-155 in allo-HSCT, which previously received Breakthrough Therapy designation. The study is expected to enroll approximately 248 participants and incorporate an adaptive design and an interim data analysis when approximately half of the enrolled participants have reached the primary endpoint. The Company expects to obtain the interim clinical results within 12 months following study initiation, which it believes will facilitate timely engagement with the FDA on the design of a Phase 3 study, and inform development in adjacent medically vulnerable patient populations. The Company believes that positive results from the Phase 2 study, if achieved, could create significant value and enable advancement into a single Phase 3 trial to support registration. In the third quarter, CARB-X (Combating Antibiotic-Resistant Bacteria Biopharmaceutical Accelerator), a global non-profit partnership accelerating antibacterial products to address drug-resistant bacteria, awarded Seres a grant of up to $3.6 million, representing the second grant the Company has received from CARB-X. The funds will support the development of an oral liquid formulation of SER-155, potentially expanding patient access for medically vulnerable populations who cannot be dosed with oral capsules. In October, Seres presented an oral presentation at IDWeek 2025. The presentation included new post-hoc analysis from the completed SER-155 Phase 1b study describing differences between the SER-155 and placebo groups, including the bacterial and fungal organisms causing BSIs, BSI event clinical outcomes, antibacterial prophylaxis use, and patterns of antimicrobial resistance (AMR) among the bacterial BSI organisms. These new data illustrated that BSIs occurred despite antibacterial prophylaxis, and that BSI bacteria exhibited AMR. Resistance to multiple antibacterial agents was observed only in the BSI bacteria from placebo-treated participants, two of whom had fatal outcomes related to their BSIs. These new data further support the potential of SER-155 as an innovative alternative approach to the significant unmet medical need for prevention of BSIs in HSCT patients, especially those BSIs associated with AMR that increase the risk of morbidity and mortality. Development of Biotherapeutics for the Treatment of Inflammatory and Immune Diseases The Company is collaborating with Memorial Sloan Kettering Cancer Center on an investigator-sponsored trial (IST) which is evaluating SER-155 in participants with immune checkpoint related enterocolitis (irEC). Enrollment is anticipated to be completed by the end of 2025, with clinical readout expected in early 2026. IrEC is among the most frequent and severe immune-related adverse events (irAEs) in recipients of immune checkpoint-inhibitor therapy and can be observed in up to 50% of patients, with rates varying based on cancer drug and treatment regimen. Immune checkpoint inhibitors can cause a wide range of irAEs with links to T cell biology and epithelial barrier inflammation, both of which are biological functions shown in our preclinical and clinical pharmacology data to be positively impacted by SER-155. Supportive data from this IST could provide further support for the expansion of indications that may be well suited for our biotherapeutic approach. Seres continues to explore potential R&D partnerships to advance development of its investigational live biotherapeutics in inflammatory and immune diseases, including ulcerative colitis and Crohn’s disease. Financial Results The Company has classified all historical operating results for the VOWST business within discontinued operations in the consolidated statements of operations for the comparative periods presented (three and nine months ended September 30, 2024). There is no activity in the current period related to discontinued operations. Seres reported net income from continuing operations of $8.2 million for the third quarter of 2025, as compared to a net loss from continuing operations of $51.0 million for the same period in 2024. The net income of $8.2 million is comprised primarily of a $22.5 million loss from operations offset by a $27.2 million gain on sale of VOWST resulting primarily from the $25 million installment payment received, as expected, from Nestle during the third quarter. The net loss of $51.0 million in 2024 is primarily comprised of a $29.2 million loss from operations plus a $23.4 million loss on the extinguishment of the Oaktree debt, which was retired at completion of the VOWST sale in September 2024. Research and development (R&D) expenses for the third quarter of 2025 were $12.6 million, compared with $16.5 million for the third quarter of 2024. The decrease in R&D expenses was primarily driven by a decrease in personnel and related costs, a decrease in platform investments, and a reduction in clinical expenses resulting from completion of the SER-155 Phase 1b study. General and administrative (G&A) expenses for the third quarter of 2025 were $9.5 million, compared with $12.7 million for the third quarter of 2024. The decrease in G&A expenses was primarily a result of lower personnel and related expenses, including IT-related expenses. Manufacturing services expenses were $0.7 million for the third quarter of 2025. These costs relate to the provision of manufacturing services under the Transition Services Agreement (TSA) with Nestlé, which began in the fourth quarter of 2024. The reimbursement received from Nestlé related to these expenses is recognized in other income. Cash Runway As of September 30, 2025, Seres had $47.6 million in cash and cash equivalents. Based on the Company’s current cash position, VOWST transaction-related obligations, and current operating plans, the Company expects to fund operations through the second quarter of 2026. The Company continues to evaluate further opportunities to extend its cash runway. Conference Call Information Seres’ management will host a conference call today, November 5, 2025, at 8:30 a.m. ET. The conference call may be accessed by calling 1-800-715-9871 (international callers dial 1-646-307-1963) and referencing the conference ID number 8471287. To join the live webcast, please visit the “Investors and News” section of the Seres website at www.serestherapeutics.com. A webcast replay will be available on the Seres website shortly after the event and will be archived for at least 21 days. About SER-155 SER-155 is an investigational, oral, live biotherapeutic designed to decolonize gastrointestinal (GI) pathogens, improve epithelial barrier integrity, and induce immune homeostasis, to prevent bacterial bloodstream infections, including those that can harbor antimicrobial resistance (AMR), as well as other pathogen associated negative clinical outcomes, in patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT). SER-155 has been evaluated in a Phase 1b placebo-controlled study in patients undergoing allo-HSCT, which demonstrated a significant reduction in both bacterial bloodstream infections (BSIs) (77% relative risk reduction) and systemic antibiotic exposure, as well as lower incidence of febrile neutropenia. SER-155 has received Breakthrough Therapy designation for the reduction of bloodstream infections in adults undergoing allo-HCST and Fast Track designation for reducing the risk of infection and graft-versus-host disease in patients undergoing allo-HCST. The early development of the program was supported by Combating Antibiotic-Resistant Bacteria Biopharmaceutical Accelerator (CARB-X), a global non-profit partnership accelerating antibacterial products to address drug-resistant bacteria. About Seres Therapeutics Seres Therapeutics, Inc. (Nasdaq: MCRB) is a clinical-stage company focused on improving patient outcomes in medically vulnerable populations through novel live biotherapeutics. Seres led the successful development and approval of VOWST™, the first FDA-approved orally administered microbiome therapeutic, which was sold to Nestlé Health Science in September 2024. The Company is developing SER-155, which has received Breakthrough Therapy designation for the reduction of bloodstream infections in adults undergoing allo-HSCT and Fast Track designation for reducing the risk of infection and graft-versus-host disease in adults undergoing allo-HSCT, and which has demonstrated a significant reduction in bloodstream infections and related complications (as compared to placebo) in a Phase 1b clinical study in patients undergoing allo-HSCT. SER-155 and the Company's other pipeline programs are designed to target multiple disease-relevant pathways and are manufactured from standard clonal cell banks via cultivation, rather than from the donor-sourced production process used for VOWST. In addition to allo-HSCT, the Company intends to evaluate SER-155 and other cultivated live biotherapeutic candidates in other medically vulnerable patient populations including autologous-HSCT patients, cancer patients with neutropenia, CAR-T recipients, individuals with chronic liver disease, solid organ transplant recipients, as well as patients in the intensive care unit and long-term acute care facilities. For more information, visit www.serestherapeutics.com. Forward-Looking Statements This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including statements about: the design, timing and results of our clinical studies and data readouts; current or future product candidates and their potential benefits; clinical development plans and commercial opportunities; communications with, feedback from, or submissions to the FDA; operating plans; cost reduction actions and their anticipated benefits; our cash runway; our ability to secure a strategic, R&D, or other partnership and/or generate or obtain additional capital, financing or other resources; our ability to operationalize a study upon receipt of any financing; our planned strategic focus; the anticipated timing of any of the foregoing; and other statements that are not historical fact. These forward-looking statements are based on management’s current expectations. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements, including, but not limited to, the following: (1) our need for additional funding; (2) our ability to continue as a going concern; (3) we have incurred significant losses, are not currently profitable and may never become profitable; (4) our cost reduction actions may not achieve their intended benefits, including an extended cash runway; (5) our limited operating history; (6) the expected payments from the VOSWT sale are subject to risks and uncertainties; (7) we may not be able to realize the anticipated benefits of the VOWST sale, and may face new challenges as a smaller, less diversified company; (8) we have in the past and may in the future receive notice of the failure to satisfy a continued listing rule from The Nasdaq Stock Market LLC; (9) our novel approach to therapeutic intervention; (10) our reliance on third parties to conduct our clinical trials and manufacture our product candidates; (11) our ability to achieve market acceptance necessary for commercial success; (12) the competition we will face; (13) our ability to protect our intellectual property; (14) our ability to manage our recent CEO transition, to retain key personnel and to manage our growth; and (15) disruptions at the FDA or other government agencies. These and other important factors discussed under the caption “Risk Factors” in our Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission (SEC) on August 6, 2025 and our Quarterly Report on Form 10-Q to be filed with the SEC on November 5, 2025, as well as our other reports filed with the SEC, could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent management’s estimates as of the date of this press release. While we may elect to update such forward-looking statements at some point in the future, we disclaim any obligation to do so, even if subsequent events cause our views to change. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date of this press release. Investor and Media Contact: [email protected] Carlo Tanzi, Ph.D. Kendall Investor Relations [email protected]

CAMBRIDGE, Mass., Oct. 30, 2025 (GLOBE NEWSWIRE) -- Seres Therapeutics, Inc. (Nasdaq: MCRB), a leading live biotherapeutics company, today announced that management will host a conference call and live audio webcast on November 5, 2025 at 8:30 a.m. ET to discuss third quarter 2025 financial results and provide business updates. To access the conference call, please dial 800-715-9871 (domestic) or 646-307-1963 (international) and reference the conference ID number 8471287. To join the live webcast, please visit the “Investors and News” section of the Seres website at www.serestherapeutics.com. A webcast replay will be available on the Seres website shortly after the event and will be archived for approximately 21 days. About Seres Therapeutics Seres Therapeutics, Inc. (Nasdaq: MCRB) is a clinical-stage company focused on improving patient outcomes in medically vulnerable populations through novel live biotherapeutics. Seres led the successful development and approval of VOWST™, the first FDA-approved orally administered microbiome therapeutic, which was sold to Nestlé Health Science in September 2024. The Company is developing SER-155, which has received Breakthrough Therapy designation for the reduction of bloodstream infections in adults undergoing allo-HSCT and Fast Track designation for reducing the risk of infection and graft-versus-host disease in adults undergoing allo-HSCT, and which has demonstrated a significant reduction in bloodstream infections and related complications (as compared to placebo) in a Phase 1b clinical study in patients undergoing allo-HSCT. SER-155 and the Company's other pipeline programs are designed to target multiple disease-relevant pathways and are manufactured from standard clonal cell banks via cultivation, rather than from the donor-sourced production process used for VOWST. In addition to allo-HSCT, the Company intends to evaluate SER-155 and other cultivated live biotherapeutic candidates in other medically vulnerable patient populations including autologous-HSCT patients, cancer patients with neutropenia, CAR-T recipients, individuals with chronic liver disease, solid organ transplant recipients, as well as patients in the intensive care unit and long-term acute care facilities. For more information, please visit www.serestherapeutics.com. Investor and Media Contact: [email protected] Carlo Tanzi, Ph.D. Kendall Investor Relations [email protected]