Seres Therapeutics (NASDAQ: MCRB) details 2025 profit, cash runway and SER-155 progress
Rhea-AI Filing Summary
Seres Therapeutics reported fourth quarter and full year 2025 results and outlined its microbiome pipeline strategy. For 2025, the company generated $0.8 million in grant revenue and recorded $5.7 million in net income from continuing operations, driven largely by an $80.7 million gain on the sale of its VOWST business and lower operating expenses of $94.8 million versus $121.3 million in 2024.
As of December 31, 2025, Seres held $45.8 million in cash and cash equivalents and expects this to fund operations through the third quarter of 2026, while it seeks partnerships and other financing. The company is prioritizing live biotherapeutic programs for inflammatory and immune diseases, including SER-155, which showed a 77% relative risk reduction in bloodstream infections in a Phase 1b allo-HSCT study and is Phase 2 ready, and SER-603 for inflammatory bowel disease. An investigator-sponsored SER-155 trial in immune checkpoint inhibitor–related enterocolitis is fully enrolled, with data expected in the second quarter of 2026.
Positive
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Insights
One-time gains and cost cuts drove 2025 profit, while Seres still depends on new funding and partnerships to advance its microbiome pipeline.
Seres Therapeutics moved from large losses to
The balance sheet showed
Strategically, Seres is concentrating on live biotherapeutics for inflammatory and immune diseases. SER-155 delivered a
UNITED STATES
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CURRENT REPORT
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| Item 2.02. | Results of Operations and Financial Condition. |
On March 12, 2026, Seres Therapeutics, Inc. (the “Company”) announced its financial results for the quarter and year ended December 31, 2025 and provided operational updates. The full text of the press release issued in connection with the announcement is furnished as Exhibit 99.1 to this Current Report on Form 8-K (the “Current Report”).
| Item 7.01. | Regulation FD Disclosure. |
On March 12, 2026, the Company posted an updated corporate presentation in the “Investors and News” portion of its website at www.serestherapeutics.com. A copy of the slide presentation is attached as Exhibit 99.2 to this Current Report and incorporated herein by reference.
The information in Items 2.02 and 7.01 of this Current Report, including Exhibits 99.1 and 99.2 attached hereto, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.
| Item 9.01. | Financial Statements and Exhibits. |
(d) Exhibits
The following Exhibits 99.1 and 99.2 relate to Items 2.02 and 7.01, respectively, and shall be deemed to be furnished, and not filed:
| Exhibit No. |
Description | |
| 99.1 | Seres Therapeutics, Inc. Press Release issued March 12, 2026 | |
| 99.2 | Seres Therapeutics, Inc. Corporate Presentation as of March 2026 | |
| 104 | Cover Page Interactive Data File (embedded within the Inline XBRL document) | |
SIGNATURES
Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.
| SERES THERAPEUTICS, INC. | ||||||
| Date: March 12, 2026 | By: | /s/ Thomas J. DesRosier | ||||
| Name: | Thomas J. DesRosier | |||||
| Title: | Executive Vice President and Chief Legal Officer | |||||
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 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 - 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. |
| • | SER-155 Phase 2 key preparatory activities have advanced to support further development for the prevention of serious bloodstream infections in patients undergoing allo-HSCT for blood cancer. Efforts to secure funding to commence the study 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 $15.7 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.
SERES THERAPEUTICS, INC.
CONSOLIDATED BALANCE SHEETS
(Unaudited, in thousands, except share and per share data)
| December 31, | ||||||||
| 2025 | 2024 | |||||||
| Assets |
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| Current assets: |
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| Cash and cash equivalents |
$ | 45,766 | $ | 30,793 | ||||
| Accounts receivable due from SPN - related party |
360 | 2,068 | ||||||
| Accounts receivable |
157 | — | ||||||
| Prepaid expenses and other current assets (1) |
3,093 | 5,813 | ||||||
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|
|||||
| Total current assets |
49,376 | 38,674 | ||||||
| Property and equipment, net |
7,635 | 11,534 | ||||||
| Operating lease assets |
72,483 | 80,903 | ||||||
| Restricted cash |
8,668 | 8,668 | ||||||
| Other non-current assets |
31 | 31 | ||||||
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| Total assets |
$ | 138,193 | $ | 139,810 | ||||
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| Liabilities and Stockholder’s Equity |
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| Current liabilities: |
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| Accounts payable |
$ | 1,682 | $ | 4,079 | ||||
| Accrued expenses and other current liabilities |
3,972 | 10,719 | ||||||
| Accrued liabilities due to SPN - related party |
3,278 | 17,750 | ||||||
| Operating lease liabilities |
10,390 | 8,674 | ||||||
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|
|
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| 19,322 | 41,222 | |||||||
| Operating lease liabilities, net of current portion |
72,576 | 82,966 | ||||||
| Other long-term liabilities |
2,077 | 1,838 | ||||||
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|
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| Total liabilities |
93,975 | 126,026 | ||||||
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| Commitments and contingencies (Note 10) |
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| Stockholders’ equity: |
||||||||
| Preferred stock, $0.001 par value; 10,000,000 shares authorized at December 31, 2025 and 2024; no shares issued and outstanding at December 31, 2025 and 2024 |
— | — | ||||||
| Common stock, $0.001 par value; 360,000,000 shares authorized at December 31, 2025 and 2024, respectively; 9,556,446 and 8,650,227 shares issued and outstanding at December 31, 2025 and 2024, respectively |
10 | 9 | ||||||
| Additional paid-in capital |
1,016,611 | 991,874 | ||||||
| Accumulated deficit |
(972,403 | ) | (978,099 | ) | ||||
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|
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| Total stockholders’ equity |
44,218 | 13,784 | ||||||
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| Total liabilities and stockholders’ equity |
$ | 138,193 | $ | 139,810 | ||||
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| [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. |
SERES THERAPEUTICS, INC.
CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS)
(Unaudited, in thousands, except share and per share data)
| Year Ended December 31, | ||||||||||||
| 2025 | 2024 | 2023 | ||||||||||
| Revenue: |
||||||||||||
| Grant revenue |
789 | — | — | |||||||||
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| Total revenue |
789 | — | — | |||||||||
| Operating expenses: |
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| Research and development expenses |
$ | 49,060 | $ | 64,600 | $ | 117,597 | ||||||
| General and administrative expenses |
39,156 | 53,183 | 77,500 | |||||||||
| Manufacturing services |
6,544 | 3,532 | — | |||||||||
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| Total operating expenses |
94,760 | 121,315 | 195,097 | |||||||||
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| Loss from operations |
(93,971 | ) | (121,315 | ) | (195,097 | ) | ||||||
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| Other income (expense): |
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| Gain on sale of VOWST Business |
80,685 | 5,684 | — | |||||||||
| Interest income |
2,227 | 3,967 | 7,301 | |||||||||
| Interest expense |
— | — | (2,468 | ) | ||||||||
| Other income (expense), net (2) |
16,755 | (14,107 | ) | 134 | ||||||||
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| Total other income (expense), net |
99,667 | (4,456 | ) | 4,967 | ||||||||
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| Net income (loss) from continuing operations |
$ | 5,696 | $ | (125,771 | ) | $ | (190,130 | ) | ||||
| Net income from discontinued operations, net of tax |
$ | — | $ | 125,907 | $ | 76,406 | ||||||
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| Net income (loss) |
$ | 5,696 | $ | 136 | $ | (113,724 | ) | |||||
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| Net income (loss) from continuing operations per share attributable to common stockholders - basic |
$ | 0.64 | $ | (16.20 | ) | $ | (29.71 | ) | ||||
| Net income from discontinued operations per share attributable to common stockholders - basic |
$ | — | $ | 16.20 | $ | 11.94 | ||||||
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| Net income (loss) per share attributable to common stockholders - basic |
$ | 0.64 | $ | — | $ | (17.77 | ) | |||||
| Net income (loss) from continuing operations per share attributable to common stockholders - diluted |
$ | 0.64 | $ | (16.20 | ) | $ | (29.71 | ) | ||||
| Net income from discontinued operations per share attributable to common stockholders - diluted |
$ | — | $ | 16.20 | $ | 11.94 | ||||||
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| Net income (loss) per share attributable to common stockholders - diluted |
$ | 0.64 | $ | — | $ | (17.77 | ) | |||||
| Weighted average common shares outstanding - basic |
8,858,975 | 7,769,910 | 6,400,339 | |||||||||
| Weighted average common shares outstanding - diluted |
8,869,742 | 7,769,910 | 6,400,339 | |||||||||
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| Other comprehensive income: |
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| Unrealized gain on investments, net of tax of $0 |
— | — | 10 | |||||||||
| Currency translation adjustment |
— | — | 2 | |||||||||
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| Total other comprehensive income |
— | — | 12 | |||||||||
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| Comprehensive income (loss) |
$ | 5,696 | $ | 136 | $ | (113,712 | ) | |||||
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| [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:
IR@serestherapeutics.com
Carlo Tanzi, Ph.D.
Kendall Investor Relations
ctanzi@kendallir.com
Seres Company Overview March 2026 Seres Therapeutics, Inc. © 2026 Exhibit 99.2
Disclaimers Forward Looking Statements This communication contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this communication that do not relate to matters of historical fact should be considered forward-looking statements, including statements about: the timing and results of our current or planned clinical trials, studies and data readouts; current or future products or product candidates and their potential benefits; our clinical development plans; communications with, feedback from, or submissions to the FDA; future product candidates; our ability to secure additional capital, financing, or other resources; our drug candidates and their potential impacts and outcomes, including the potential market and commercial opportunity for SER-155, if approved; operating plans, cost reductions actions, and our future cash runway, including potential payments due from Nestlé related to the VOWST sale; our planned strategic focus; the 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 these 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 limited operating history; (5) the expected payments from the VOSWT sale are subject to risks and uncertainties; (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; and (13) the impact of our recent management transitions and appointments and our ability to retain key personnel. 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 communication. 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 communication.
Seres continues on successful journey to lead on delivering on the therapeutic potential of live biotherapeutics (LBPs) 2011 Seres founded 2015 SER-109 Breakthrough Therapy Designation -- Seres goes public $133M IPO 2023 SER-109 FDA approval and launch* -- 2020 SER-109 positive Phase 3 topline -- 88% sustained clinical response rate CDI recurrence up to 8 weeks 2024 SER-155 positive Phase 1b topline and Breakthrough Therapy Designation -- 77% relative risk reduction in bloodstream infections Seres has delivered an approved drug and additional clinical candidates in a novel therapeutic modality that address diseases in an innovative way SER-109 efficacy RESEARCH LETTER SER-109 durability Reduced antibiotic resistance gene carriage 2025-26 High profile publications on VOWST & SER-155 MoA VOWST & SER-155 mechanisms of action* (*2 manuscripts in final review) 2026+ Leverage clinical translation of novel MoAs to advance Inflammatory & Immune disease pipeline *VOWST asset sale to Société des Produits Nestlé S.A. completed 30-Sep-2024;sale provides future sales-based milestone payments Differentiated Biotherapeutics platform
Focused strategy to advance novel live biotherapeutics and deliver shareholder value Advancing promising preclinical live biotherapeutic programs for inflammatory and immune diseases Supporting pending readout of investigator-sponsored SER-155 study in immune checkpoint–related enterocolitis, expected in Q2 2026 SER-155 program is Phase 2 ready for patients undergoing allogeneic hematopoietic stem cell transplant (allo-HSCT) to treat hematologic malignancies (cancers of the blood, bone marrow, and lymph nodes) Seres efforts ongoing to seek funding to support continued development toward meaningful milestones
Program Lead Indication & Development Stage Therapeutic Objectives Potential Additional Indications SER-155 Allogeneic HSCT: Phase 2 Ready: Phase 1b Cohort 2 (placebo controlled) data and exploratory biomarker data announced Immune checkpoint related enterocolitis (irEC) IST readout expected in Q2 2026 Allo-HSCT: Reduce incidence of serious bacterial infections (e.g., BSIs) and febrile neutropenia IrEC: Reduce Grade 2, 3 diarrhea and immunosuppressive drug use Autologous HSCT Blood cancers CAR-T SER-603 Ulcerative colitis and Crohn’s disease: Preclinical: IND-enabling studies Target the mucosal barrier-immune interface to promote protective responses in vulnerable patients Chronic inflammatory diseases (e.g., inflammatory bowel disease) SER-147 Chronic liver disease: Preclinical: IND-enabling studies Reduce incidence of serious bacterial infections (e.g., SBP, BSIs) and related complications Solid organ transplant ICU patients Long-term care patients Reduces risk of recurrent C. diff infections (88% sustained clinical response rate for preventing CDI recurrence) Well tolerated safety profile Near-term foci on advancing colitis programs (IBD & irEC) to key value inflection and advancing SER-155 allo-HSCT Breakthrough Therapy program into Phase 2 Pipeline: Seres live biotherapeutics (LBPs) target infection and mucosal barrier-immune associated diseases and leverage years of clinical progress and data clinical proof of concept BSI: bloodstream infection; SBP: spontaneous bacterial peritonitis
Accessed the vast functional potential of millions of years of co-evolution between microbes and their hosts to prevent and treat diseases Clinical translation on targeting key drivers of disease Mucosal Epithelial Barrier-Immune Interface: Protect and induce regeneration of epithelial barrier in the gastrointestinal tract Regulate immune pathways to reduce GI inflammation and induce local and systemic immune homeostasis without suppression Inhibition of “Undesirable” Microbes Prevent colonization, overgrowth and/or domination with pathogenic & inflammatory bacteria, including antimicrobial resistant bacteria Seres has… Accessed the vast functional potential of millions of years of co-evolution between microbes and their hosts to prevent and treat diseases Track-record of realizing ambitious, impactful therapeutic goals: First company to go from novel concept through clinical development and regulatory approval to commercialization of oral microbiome biotherapeutic (VOWST™) Achieved two Breakthrough Therapy Designations (VOWST & SER-155) and established regulatory precedent for drug pharmacology & manufacturing Proven ability to discover and develop LBPs with strong discovery engine that can deliver additional candidates across multiple unmet medical needs AI-enabled MbTx® Platform can interrogate microbe-host functional interactions specifically and at scale, with demonstrated clinical translation for previously inaccessible biology and disease targets Industry Leadership: Discovery to Approval
Consortia of live commensal bacteria can be used as therapeutics Change in microbiome function Bile acids Short-chain fatty acids Tryptophan metabolites Other Restructure microbiome composition Engraftment of drug strains Disrupted Microbiome with functional deficiencies (Disease susceptible) Change in host function Consortia of bacterial strains optimized to produce therapeutically active metabolites that target multiple disease-relevant pathways Live Biotherapeutics (LBP) PK PD
Seres’ biotherapeutics and pipeline candidates are expected to have well tolerated safety profile, reducing development risk Sources: Nanayakkara et al, CA Cancer J Clin 2021; Penack et al, Blood Adv 2020; Zheng et al, Infect Dis Ther 2021 Based on GI bacteria naturally found in healthy humans, and not associated with disease VOWST product profile includes well tolerated safety without drug-related serious adverse events Well tolerated safety profile in multiple clinical trials and patient populations, including medically vulnerable allo-HSCT recipients Safety profile has potential to mitigate a primary cause of drug development failure
Seres has full stack of live biotherapeutics platform capabilities & experience in novel live biotherapeutic modality Field-leading Microbiome biomarker & drug target identification --- strains, metabolites/peptides, genes Seres has built field-leading biological, clinical microbiome, and manufacturing capabilities with proven ability to design, develop, and receive FDA approval in a novel modality Demonstrated Clinical Translation & Identification of Patient Subpopulations --- novel drug modality PK/PD/MoAs; receipt of breakthrough designation; patient centricity Efficient Lead Candidate Design, Screening, Optimization --- expansive strain library with screening & models adapted for novel drug modality Proven Regulatory Expertise --- Pioneered regulatory path for novel drug modality with FDA approval Exceptional Clinical Trial Execution --- Proprietary know-how on trial design, enrollment in challenging populations, drug pharmacology & sample collection Demonstrated Novel Therapeutic GMP Manufacturing & Quality --- spans broad biological breadth with demonstrated commercial success and clean inspection history
MbTx platform: a discovery and product optimization engine, designed to mine and harness microbe-host functional interactions to address disease Strain Library Seres' curated collection of bacteria that represent broad biological breadth paired with high-resolution screening data – 40,000+ strains, 1000s of drug-ready & deeply characterizes strains Multi’omic & Experimental Functional Screening Seres' functional data on bacterial strains and consortia from genomic, in vitro cell-based assays & in vivo models Clinical Data Powered Discovery High-resolution mapping of microbes, genes & metabolites/peptides with clinical outcomes and drug pharmacology – 1000s of patients across clinical trials Curated Public Literature Indexed repository of microbiome literature and patient datasets MbTx AI Knowledge- base AI Enabled Data Mining & Prediction Agentic AI with knowledge graph of integrated data sets that link microbial strains, genes and metabolites to host pathways and disease with ML analytics INPUTS Clinically actionable OUTPUTS Novel Targets & Leads Therapeutically active strains and microbe-produced compounds to modulate previously inaccessible host targets Optimized Live Biotherapeutics (LBPs) Candidates LBPs optimized for potency, used as mono- or combination-therapy, grounded in a pharmacological framework Precision Medicine Microbe-based biomarkers for patient selection & prediction of response to LBPs & biologics Small-Molecule Metabolism (future research opportunity) Potential for prediction of pharmaceutical drug metabolism (not currently pursued) Drug Pharmacology Standardized and qualified preclinical and clinical assays for data generation on PK/PD of LBPs
Manufacturing Platform: Delivers defined consortia in oral formulations using cost-effective production processes which reflect regulatory benchmarks for LBPs Novel formulations enabling consistent drug product composition, drug stability for distribution, and targeted drug delivery Quality systems to ensure product quality and stability, extending prior regulatory successes, including developing product release specifications with the FDA and to enable clinical trial supply to the US, Canada, Australia, and New Zealand Highly intensive strain bioprocessing leveraging flexible, single-use manufacturing technology for cost-effective production Strain isolation and characterization pipeline to rapidly identify cGMP-suitable medium components
SER-155
Value Proposition Transformational efficacy and placebo-like safety profile to address frequent, deadly blood stream & AMR infections linked to mortality in allo-HSCT recipients and other blood cancer patients Target Indication & Addressable Patient Initial development in allo-HSCT (~10K US / ~40K worldwide per year) Indication expansion planned to autologous HSCT (~60K WW / yr), CAR-T recipients Further indication expansion to prevent infections in broader population w/ blood cancers (~500K WW / yr) Development Stage & Milestones Live biotherapeutic optimized to target: GI pathogen reduction, including antimicrobial resistant strains Improved gut barrier integrity to prevent pathogen translocation Reconstitution of immune homeostasis Mechanism of Action Oral 2 capsules once daily for 10 days pre-transplant* *Follows 4-day course of oral vancomycin used to open up an ecological niche for drug strain establishment in G.I Dosing / Route of Administration Significant reduction SER-155 in bloodstream infections vs. standard of care (antibiotics) 77% relative risk reduction in bloodstream infections observed in Phase 1b study (43% placebo vs. 10% SER-155; p<0.05) Significant reduction in systemic antibiotic use Reduction in febrile neutropenia Reduction in mortality and hospitalization Efficacy (Phase 1b) No serious adverse events attributed to drug (none observed in Phase 1b study) No secondary infections with strains in SER-155 (none observed in Phase 1b study) AEs similar to placebo, largely gastrointestinal in nature Safety (Phase 1b) Program Differentiation Modality prevents infections effectively with novel mechanisms that combats antimicrobial resistance instead of generating it Demonstrated placebo-like safety profile in a vulnerable patient population Gut barrier integrity and anti-inflammatory effects have potential to address infectious consequences of blood cancer treatment broadly Target Product Profile: Preventing Bloodstream Infections in Allo-HSCT SER-155 Oncology Infection: Protect epibarrier integrity and clinically reduce bloodstream & antimicrobial resistant infections in blood cancer patients Status: Phase 1b complete; Phase 2 ready Multi-billion net sales opportunity across indications (e.g., allo-HSCT, autologous-HSCT, blood cancers, CAR-T recipients)
Allogeneic hematopoietic stem cell transplant (allo-HSCT) regimen can result in life-threatening complications Only ~60% survival 3 years post-transplant Significant immune compromised patient population ~10% transplant mortality for adults in first 100 days post-transplant Infections are leading cause of death Gut microbiome disruption frequently observed globally (US, Germany, Japan) Allo-HSCT treatment regimen -14 0 +100 Days Conditioning Immunosuppression Chemotherapy Anti-infectives Increased risk of infection, GvHD Allo-HSCT infusion Extensive GI microbiome disruption Sources: CIBMTR 2023 US summary slides; Passweg et al BMT 2025; Penack et al, Blood Adv 2020; Khan et al, Blood 2021; Peled et al, NEJM 2020; Stein-Thoeringer et al, Science 2019; Bleakley & Riddell, Nat Rev Cancer 2004
Bloodstream infections (BSIs) are a leading cause of death post-transplant and are increasing in incidence with uptake of PTCy treatment BSI risk increasing due to recent adoption of post-transplant cyclophosphamide (PTCy) for GvHD prophylaxis BSI prevalence high despite standard of care use of antibacterial prophylaxis Majority of BSIs in first 30 days post-HSCT are gut-seeded 50-80% febrile neutropenia incidence Incidence Bacterial BSI in first 30 days post-HSCT Salas et al 2024 Impact Infection is leading cause of death in first 100 days post-HSCT for adults ~7.5% mortality rate from bloodstream infections Complications including infection associated with longer hospital stay and ICU utilization, driving substantial cost increase PTCy Non-PTCy Sources: Gill et al, Microorganisms 2023; Sava et al, Bone Marrow Transplantation 2022; Carreira et al, Transplant Cell Ther 2022; Youssef et al, Pediatric Transplantation 2020; Song et al, Infect Drug Resist 2023; Bolaños-Meade J et al, NEJM 2023; Salas et al, Transplant Cell Ther 2024; Rearigh et al, Annals of Hematology 2020; CIBMTR 2023 US summary slides; Perales et al Biol Blood Marrow Transplant 2017; Taplitz et al, J Clin Oncol 2018; 2024 Seres physician market research
Source: Seres primary market research 2024 (Trinity survey of hematologists and infectious disease specialists) Concern driven by high risk of morbidity and mortality in a compromised patient population HCPs have high level of concern for BSIs LOW HIGH 1 2 3 4 5 6 7 Major unmet needs for BSIs Top need: effective prophylaxis – current agents not seen as successful Protection against antimicrobial resistance Reduction of hospitalizations and readmissions resulting from infections Infectious disease and hematology-oncology physicians are highly concerned about BSIs in allo-HSCT patients; effective prophylaxis is a major unmet need
Significant efficacy and placebo-like safety profile in Phase 1b study in allo-HSCT Substantial reduction in pathogen domination in Phase 1b Rapid protection of epithelial barrier integrity in Phase 1b Gut pathogen domination associated with bloodstream infections and mortality SER-155 prevents the loss of GI epithelial barrier integrity due to chemotherapy. Additional benefit observed on IFN-g, TNF-α, IL-17, & IL-8 % patients with bloodstream infections Significant reductions (p < 0.05) for bloodstream infections* and systemic antibiotic use relative to Pbo Numerically lower incidence rate of febrile neutropenia 77% Relative risk reduction *Placebo includes prophylactic antibiotic use as standard of care SER-155 Placebo Healthy Key Data: SER-155 Placebo-controlled Phase 1b reduction in bloodstream infections with mechanism of action (MoA) clinical translation *95% 2-sided Clopper-Pearson confidence interval of incidence is applied. Odds ratio for incidence between treatment groups (SER-155 and placebo) with 95% 2-sided confidence interval and the corresponding p-value calculated based on the Fisher’s Exact test
SER-155 is Phase 2 ready for patients undergoing allo-HSCT to treat hematologic malignancies and design provides opportunity for adjacent indication expansion Expansion: Auto HSCT Cancer neutropenia AML Phase 2 Allo-HSCT Auto HSCT has strong biologic adjacencies to allo-HSCT with similar treatment and conditioning regimens Allo-HSCT phase 2 interim analysis data could trigger advancement of a SER-155 auto-HSCT study With assumption for one pivotal registrational study in auto triggered by allo IA, initial BLA approval for both allo and auto together may be possible FN and BSI data at phase 2 interim analysis could accelerate clinical evaluation in Cancer neutropenia/AML Received Fast Track and Breakthrough Designation FDA in agreement with Phase 2 study design FDA open to expedited path to engage and start Phase 3 if the interim analysis shows overwhelming efficacy Finalized Protocol submitted to FDA January 2026 Clinical Site infrastructure in place and key manufacturing steps advanced
US annual diagnoses or transplants Unmet needs addressed by SER-155 Allo-HSCT ~9,300 Prevent mortality and cost of post-transaction infections Autologous HSCT ~13,500 Prevent mortality and costs of post-transplant infections Broader leukemia & lymphoma population* ~87,000 initial focus Reduce morbidity, mortality, and costs of infections & FN from chemotherapy *Includes acute myeloid leukemia, multiple myeloma, and aggressive B cell non-Hodgkin lymphomas (diffuse large B-cell lymphoma, mantle cell, Burkitt’s lymphoma) Sources: CIBMTR, US NCI SEER, Thandra et al 2021 report of WHO data, Niederwieser et al Haematologica 2022; WHO Global Cancer Observatory; American Cancer Society WW annual diagnoses or transplants ~40,000 ~60,000 ~500,000 SER-155 in allo-HSCT commercial opportunity is meaningful and has indication expansion potential (10x addressable population) creating multi-billion dollar opportunity
Viral prophylaxis provides precedent on commercial opportunity in medically vulnerable patients Prevymis - increasingly used for viral infection prophylaxis (e.g., allo-HSCT and solid organ transplant populations) $785M ‘24 WW sales (~30% growth over '23) Reduces CMV infection in allo-HSCT recipients Lowers mortality rate Allo-HSCT is a very costly procedure (~$400K US year 1 allo-HSCT per patient cost) Transplant-related complications (e.g., infections) raise cost by ~$180K Infections result in longer hospital stays, readmissions, increased ICU utilization Sources: CMS.gov; Broder et al, Am Drug Health Benefits 2017; Perales et al, Biol Blood Marrow Transplant 2017; Merck SEC filings Cost of infections in 2015 dollars estimated at $177K by Perales, et.al. and inflated to 2025 costs (usinflationcalculator.com)
Value Proposition First-in-class microbiome therapeutic designed to treat irEC as a result of immune checkpoint inhibitor (ICI) therapies by addressing mucosal healing and reducing inflammation, with the potential to reduce or eliminate the need for high dose systemic corticosteroids (which carry the risk of toxicity and ICI efficacy impact). Target Indication & Addressable Patient Patients on ICI experiencing irEC ~500,000 patients on ICI globally, with ~50-100,000 experiencing irEC irEC shares substantial pathophysiologic overlap with IBD, enabling clinical and commercial synergies Development Stage & Milestones SER-155: demonstrated preclinically and clinically to improve GI mucosal epithelial barrier integrity and favor Treg development in the GI while maintaining immune tone systemically. Mechanism of Action Oral capsules taken once daily taken for 12 days or until resolution of symptoms and resumption of ICI Dosing / Route of Administration Induce Immunosuppressive-free clinical response and remission of colitis symptoms Efficacy (TPP) No serious adverse events attributed to drug AEs similar to placebo, largely gastrointestinal in nature Safety (TPP) Program Differentiation Development strategy leverages prior clinical experience with SER-155 to enable rapid PoC data No effective alternatives to immunosuppressive therapies, causing disruption of ICI treatment LBPs can uniquely address gut epithelial barrier integrity, offering novel solution Target Product Profile: SER-155 Status: Phase 1b Investigator sponsored trial, with readout expected Q2 2026 SER-155 irEC: Treat immune-related enterocolitis resulting from ICI therapies
SER-603
Value Proposition An inflammatory microbiome drives non-response to advanced therapies. Live biotherapeutics and unique biomarkers can predict response to biologics and can be leveraged to improve response rates and durability through combination therapy and precision medicine Target Indication & Addressable Patient Moderate to severe ulcerative colitis (UC) in combination w/ current standard of care (~300-400K US; TPP shown) Moderate to severe Crohn's disease in combination w/ current standard of care Mild to moderate UC and Crohn's disease as monotherapy Development Stage & Milestones Biomarker: differential remission in UC patients with pro-inflammatory vs. non-inflammatory microbe-associated features; independent validation w/ public datasets SER-603: Live biotherapeutic that targets: Improve GI barrier integrity to reduce translocation of inflammatory molecules Production of anti-inflammatory metabolites to drive Treg development and reduce cytokine-driven inflammatory response Mechanism of Action Single oral capsules once daily Combination with systemic anti-inflammatory therapy (e.g., anti-IL-23, anti-TL1A) Dosing / Route of Administration 12%+ improvement in clinical remission rate vs. standard of care monotherapy; ~15% improvement in response to advanced therapy, with larger increase in biomarker+ patients Efficacy (TPP) No serious adverse events attributed to drug (monotherapy or combination therapy) AEs similar to placebo, largely gastrointestinal in nature Safety (TPP) Program Differentiation Lead optimization and development strategy leverages prior clinical experience No effective biomarkers predictive of treatment response despite patient heterogeneity; program as demonstrated ability to predict responses Standards of care and industry pipeline not amenable to combination use due to long-term safety concerns LBPs can uniquely address gut epithelial barrier integrity a current gap Target Product Profile: Combination therapy in IBD Status: Lead Optimization; IND-enabling studies SER-603 IBD: Improve response & durability to inflammatory bowel disease (IBD) drugs
Key challenges in IBD suggest new therapeutic solutions are needed Efficacy ceiling experienced by many patients due to non-response or poor durability of response Safety concerns limit the potential for combining advanced therapies that are immunosuppressive Current therapies don’t directly target the epithelial barrier, a critical target for limiting inflammation Patient heterogeneity in IBD patients is a core challenge and key reason many drugs may not work or lack durability. Disrupted gut microbiome is a major driver of IBD heterogeneity, pathogenesis, and nonresponse to advanced therapies UC Crohn’s Placebo SER-603 offers a potentially more effective and safer approach to addressing these gaps Sources: Hanauer et al, Gastroenterology 2006; Sandborn et al, NEJM 2005; Hanauer et al, Lancet 2002; D'Haens et al, Lancet 2022; Sandborn et al Gastro 2012; Sandborn et al, Gastro 2014; Sandborn et al, NEJM 2021; Sandborn et al, NEJM 2017; Sands et al, NEJM 2019; Feagan et al, NEJM 2013; Long et al, Lancet 2026; D'Haens et al, NEJM 2023; Danese et al, Lancet 2022; Rutgeerts et al, NEJM 2005
SER-603 designed to target inflammatory drivers of Inflammatory Bowel Disease (IBD) that current standards of care cannot IBD is a mucosal barrier-immune disease Seres IBD Program Inflammatory microbiome Overabundance of pathogenic and inflammatory bacteria Loss of GI barrier integrity Barrier damage allows translocation of inflammatory bacteria and molecules Inflammatory immune responses Induce inflammatory responses in APCs and CD4+ T cells Nominated & validated novel, microbial-linked biomarkers that are predictive of response to current IBD therapies Demonstrated in preclinical models that SER-603, a novel cultivated LBP, can target all three drivers of disease without immunosuppression as a monotherapy and can improve response to advanced therapies in combination Supported by Crohn's & Colitis Foundation IBD Ventures award Engaged with potential partners on potential research collaboration SER-603 targets upstream of current IBD therapies and without immune suppression
Monotherapy Proof of Concept: SER-603 addresses microbiome-driven inflammation in preclinical disease models of IBD Th1 cells Th17 cells SER-603 intervention reduces fecal lipocalin from inflammatory microbiome SER-603 intervention reduces Th1 and Th17 CD4+ T cells * ** Biomarker-based inflammatory microbiome Inflamm. Microbiome + SER-603 Biomarker-based inflammatory microbiome Inflamm. Microbiome + SER-603 GF IL10-/-mice Biomarker (+) microbiome test article ~4-5 weeks of colonization Evaluate treatment effect of SER-603 to address inflammatory microbiome SER-603: LBP designed to treat IBD SER-603 intervention SER-603 only Oral SER-603 intervention
Combination Therapy Proof of Concept: SER-603 increases the efficacy of anti-TNF�� therapy in a preclinical model of microbiome-driven inflammation GF IL10-/-mice Biomarker (+) microbiome test article ~4-5 weeks of colonization Evaluate treatment effect of SER-603 in combination with anti-TNF�� to address disease driven by inflammatory microbiome SER-603 & Anti-TNF�� SER-603 + anti-TNF�� is superior to anti-TNF�� alone in reducing lipocalin SER-603 + anti-TNF�� is superior to anti-TNF�� alone in reducing Th1 and Th17 CD4+ T cells SER-603 + anti-TNFa intervention SER-603 alone (negative control) Anti-TNFa only Mice randomized and anti-TNFa ± SER-603 intervention started next day Th1 cells Th17 cells * * * ** * ***
Biomarker Validation: Identified bacterial features can predict response to therapy in clinical datasets 8% of Seres biomarker (+) patients experience remission, suggesting patients that have an inflammatory microbiome are very unlikely to respond to Ustekinumab, and may be candidates for combination therapy. 68% of Seres Biomarker (-) patients experience remission suggesting patients that do NOT have an inflammatory microbiome are more likely to respond to ustekinumab. Selection of Biomarker (-) patients increases remission after ustekinumab 50% of CD patients remit after ustekinumab in each cohort ~30% of patients Biomarker (+) Inflammatory microbiome ~70% of patients Biomarker (-) Non-inflammatory microbiome Seres Biomarker can predict response to therapy Wang et. al. 2025 - significant impact of microbiome on ustekinumab efficacy Selection of Biomarker (+) patients identifies patients for combination therapy
SER-147
Value Proposition Leverage clinically proven mechanism with potentially transformative efficacy and placebo-like safety profile to reduce infection and other decompensating events in chronic liver disease patients Target Indication & Addressable Patient Decompensated cirrhosis ~500K US patients ~2.3M European patients Solid organ transplant recipients (kidney, liver) Inpatient populations at high infection risk (ICU, long-term acute care) Development Stage & Milestones Live biotherapeutic optimized to target: Reduction spontaneous bacterial peritonitis Improve GI barrier integrity to reduce pathogen & inflammatory molecule translocation Restore bile acids metabolism & reduce bacterial ureases Mechanism of Action One oral capsule once daily for 30 days Dosing / Route of Administration 50% relative reduction in spontaneous bacterial peritonitis and/or bloodstream infections 50% reduction in episodes of acute hepatic encephalopathy Reduction in mortality and hospitalization Efficacy (TPP) No serious adverse events attributed to drug No secondary infections with strains in live biotherapeutic AEs similar to placebo, largely gastrointestinal in nature Safety (TPP) Program Differentiation Potential to address multiple causes of decompensation in cirrhosis patients; drug optimized to target SBP Modality prevents infections effectively with a mechanism that combats antimicrobial resistance instead of generating it (cf., antibiotics) Potential to derisk drug modality potential in metabolic disease (e.g., HE) Target Product Profile: Preventing Infections in Chronic Liver Disease patients Status: Preclinical: IND-enabling studies SER-147 Cirrhosis Infection: Protect epibarrier integrity and clinically reduce spontaneous bacterial peritonitis in liver disease
Significant protection of epithelial barrier integrity against inflammatory-cytokine driven damage Reduces abundance of pathogens causing most common infections in cirrhosis patients Declining E. coli titers Multi-log reduction in E. coli in in vitro model (above); data for additional antimicrobial resistant pathogens in vivo (data not shown) SER-147 protects against IFN-g induced barrier damage in a dose responsive manner Neg. control composition SER-147 lead candidate Key Data: Preclinical demonstration of reduction in SBP bacteria and protection of epithelial barrier
Path Forward
Summary and path forward SER-155 Phase 1b placebo-controlled results in allo-HSCT promising, Phase 2 ready Final Phase 2 study protocol submitted to FDA; commencement of study is funding dependent Administration of SER-155 associated with 77% relative risk reduction for BSIs, significant reduction in systemic antibiotic exposure, and lower incidence of febrile neutropenia vs placebo Exploratory biomarker data support SER-155 MOA and potential role for Seres’ platform to provide clinical benefit to patients with inflammatory & immune diseases (e.g., UC & Crohn’s disease) Capital Strategy & Financial position Efforts aimed at obtaining funding through partnerships or other sources to support development of pipeline candidates in inflammatory and immune diseases and SER-155 Phase 2 study are on-going ~$45.8M in cash/cash equivalents at December 31, 2025; cash runway projected through Q3 2026 VOWST asset sale to Nestle closed in September 2024; $75M installment payments received from Nestle in 2025; $275M potential future net sales related milestones Pipeline of novel live biotherapeutics in areas with large commercial potential Focusing on emerging pipeline targeting inflammatory and immune diseases, including evaluating SER-603 to treat IBD (e.g. UC, Crohn’s) Supporting Memorial Sloan Kettering IST for treatment of immunotherapy-related enterocolitis (irEC) – data expected in Q2 2026 Pipeline aims to bring transformative medicines to a wider set of patients with significant unmet medical needs including Phase 2 ready SER-155 for allo-HSCT
Appendix --- SER-155 allo-HCT Phase 1b Study Results
SER-155 Phase 1b study evaluated safety, pharmacology, and efficacy in adult allo-HSCT recipients SER-155 COHORT 1 Open-label (n=15 enrolled) COHORT 2 Placebo-controlled 1:1 (n=45 enrolled) SER-155 Placebo results reported May 2023 results announced Sept. 2024 Primary Endpoints: Safety and tolerability SER-155 bacterial strain engraftment Key Secondary Endpoints through HSCT Day 100: Incidence of bloodstream infections (BSI), GI infections, and acute GvHD ≥ Grade 2 Incidence and duration of febrile neutropenia Bacterial pathogen abundance
SER-155 Safety: SER-155 was generally well tolerated with no treatment-related SAEs Treatment-emergent adverse events (TEAEs) All but one subject in the placebo arm experienced at least 1 TEAE Most common for SER-155 treated subjects (≥50% and with Δ ≥5% greater than placebo): diarrhea (86% vs. 74% placebo), nausea (62% vs. 53% placebo) 1/40 (3%) subject experienced a TEAE leading to treatment discontinuation (active = 0; placebo = 1) 3/40 (8%) subjects experienced a TEAE leading to study discontinuation (active = 1; placebo = 2) Serious adverse events (SAEs) 19/40 (48%) subjects experienced an SAE: 11/21 (52%) SER-155-treated subjects vs. 8/19 (42%) placebo-treated subjects; none considered related to SER-155 (no SUSARs) Most common SAE SOC: infections & infestations (24% active vs. 37% placebo) 3 deaths prior to Day 100 (active = 1; placebo = 2), 1 death after Day 100 (active), none considered related to SER-155 Adverse events of special interest (AESIs) AESIs (bloodstream infections, GI infection, invasive infection): 14/40 (35%) subjects Rates of AESIs were lower in SER-155 arm vs placebo arm (29% vs 42% respectively) No SER-155 species were identified in culture from any subject
SER-155 Efficacy: SER-155 associated with 77% relative risk reduction in bacterial BSIs and reduction in systemic antibiotic exposure Bloodstream infections Significant decrease in bacterial bloodstream infections in SER-155-treated subjects vs. placebo with 77% relative risk reduction Numerically lower incidence rate of febrile neutropenia in SER-155-treated subjects vs. placebo Febrile neutropenia Antibiotic exposures Significantly lower mean cumulative exposure (days) and exposure rate to systemic antibacterials / antimycotics for SER-155-treated subjects vs. placebo
Bloodstream infections from HSCT Day 0 to Day 100: Lower incidence in SER-155 treated subjects vs. placebo Bloodstream infections from Day 0 to Day 100 (# patients) SER-155 n=20 n (%) Placebo n=14 n (%) Subjects with confirmed BSI 2 (10.0) 6 (42.9) 95% confidence interval (1.2, 31.7) (17.7, 71.1) Odds ratio 0.15 95% confidence interval (0.01, 1.13) p-value 0.0423 mITT-1 population Organisms in SER-155 patients: Finegoldia magna; E. coli/Strep mitis Organisms in placebo patients: E.coli; Enterococcus faecium/staph haemolyticus/Candida krusei; Staph aureus; Staph haemolyticus; Pseudomonas aeruginosa; E coli
Cumulative exposure to systemic treatment antibacterials / antimycotics through HSCT Day 100: Lower incidence in SER-155 treated subjects vs. placebo Cumulative Antibacterial or Antimycotic Exposure (HSCT Days) SER-155 n=20 n (SD) Placebo n=14 n (SD) Mean (SD) 9.2 (5.44) 21.1 (20.31) Median 9.0 14.0 Min, Max 0, 19 0, 74 Cumulative exposure is the sum of all days a subject received systemic antibacterials and/or antimycotics between HSCT Day 0 through Day 100; counting once per day regardless of number of agents taken. 95% confidence interval and p-value based on independent samples t-test of the difference in mean days between SER-155 and placebo Mean Difference (95% CI) -11.9 (-23.85, -0.04) p-value 0.0494 mITT-1 population
Cumulative exposure rate to systemic treatment antibacterials / antimycotics through HSCT Day 100: Lower incidence in SER-155 treated subjects vs. placebo Cumulative Antibacterial or Antimycotic Exposure Rate SER-155 n=20 Rate (SD) Placebo n=14 Rate (SD) Mean (SD) 0.090 (0.0530) 0.305 (0.2898) Median 0.089 0.244 Min, Max 0.00, 0.18 0.00, 0.90 Cumulative exposure rate is calculated as the sum of all days a subject received systemic antibacterials and/or antimycotics on or after HSCT Day 0 (counting once per day, regardless of number of antibacterial/antimycotic medications taken in a day) through HSCT Day 100 over the total number of days a subject was on the study from HSCT Day 0 to the earliest of EOS, or HSCT Day 100. 95% confidence interval and p-value are based on independent samples t-test of the difference in mean days or mean rate of cumulative exposure between SER-155 and Placebo Mean Difference (95% CI) -0.2 (-0.38, -0.05) p-value 0.0163 mITT-1 population
FAQ
How did Seres Therapeutics (MCRB) perform financially in 2025?
Seres Therapeutics reported $0.8 million in grant revenue and $5.7 million net income from continuing operations in 2025. Profitability mainly reflected an $80.7 million gain on the VOWST business sale and reduced operating expenses, rather than strong recurring revenue growth.
What is Seres Therapeutics’ (MCRB) cash position and runway?
As of December 31, 2025, Seres Therapeutics held $45.8 million in cash and cash equivalents. Based on current operating plans, the company expects this cash to fund operations through the third quarter of 2026, while it evaluates additional funding opportunities.
What are the key clinical programs Seres Therapeutics (MCRB) is prioritizing?
Seres Therapeutics is focusing on live biotherapeutics for inflammatory and immune diseases, particularly SER-155 and SER-603. SER-155 is Phase 2 ready for allo-HSCT patients and showed a 77% relative risk reduction in bloodstream infections, while SER-603 targets inflammatory bowel disease.
When will new SER-155 clinical data be available for Seres Therapeutics (MCRB)?
An investigator-sponsored trial of SER-155 in immune checkpoint inhibitor–related enterocolitis is fully enrolled, with a data readout expected in Q2 2026. These results will further characterize SER-155’s potential in treating this serious cancer therapy–related complication.
How did the VOWST business sale affect Seres Therapeutics’ (MCRB) 2025 results?
The divestiture of the VOWST business significantly impacted 2025 results through an $80.7 million gain. This one-time gain, combined with lower operating expenses, shifted Seres from large prior-year losses to positive net income from continuing operations in 2025.
What are the main risk factors highlighted by Seres Therapeutics (MCRB)?
Seres cites risks including its need for additional funding, historical losses and lack of current profitability, reliance on third parties for trials and manufacturing, competitive pressures, regulatory uncertainties, and challenges retaining key personnel, as detailed in its Form 10-K risk factor section.
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