• Moderna for the human microbiome.
• CRISPR Therapeutics for gut health.

• VOWST (SER-109): An orally administered microbiome therapeutic approved for the prevention of recurrence of *Clostridioides difficile* infection (CDI) in adults following antibacterial treatment for recurrent CDI.

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Thomas J. DesRosier, Co-President, Co-Chief Executive Officer, Executive Vice President, Chief Legal Officer and Secretary

Thomas J. DesRosier joined Seres Therapeutics in May 2016. Prior to his current role, he served as Chief Legal and Administrative Officer at ARIAD Pharmaceuticals and held the same position at Cubist Pharmaceuticals, where he notably led the negotiation of Cubist's acquisition by Merck. He also served as Senior Vice President and General Counsel, North America for Sanofi, a role he assumed after Sanofi acquired Genzyme Corporation, where he was Senior Vice President and Chief Legal Officer. Earlier in his career, Mr. DesRosier held senior legal positions at Wyeth Pharmaceuticals, Genetic Institute, and E.I. DuPont de Nemours.

Marella Thorell, Co-President, Co-Chief Executive Officer, Executive Vice President, Principal Accounting Officer and Chief Financial Officer

Marella Thorell was appointed Executive Vice President and Chief Financial Officer of Seres Therapeutics in March 2024 and was named co-Chief Executive Officer in July 2025. She brings over 25 years of experience in finance and operations within both public and private biotechnology companies. Her previous roles include Chief Financial Officer of Evelo Biosciences, Chief Accounting Officer at Centessa Pharmaceuticals, and Chief Financial Officer of Palladio Biosciences, which was acquired by Centessa. She also served as Chief Financial Officer and Chief Operating Officer of Realm Therapeutics, which was acquired by ESSA Pharma in 2019. Centessa Pharmaceuticals was formed by Medicxi through the merger of multiple private biotech companies.

Matthew Henn, Executive Vice President and Chief Scientific Officer

Matthew Henn is the Executive Vice President and Chief Scientific Officer at Seres Therapeutics. He has been instrumental in the discovery and clinical development of numerous microbiome therapeutics, including Seres' product candidates, and has authored over 65 peer-reviewed publications. Before co-founding Seres in 2012, Dr. Henn served as the Director of Viral Genomics and Assistant Director of the Genome Sequencing Center for Infectious Diseases at the Broad Institute of MIT and Harvard.

Terri Young, Executive Vice President, Chief Commercial and Strategy Officer

Terri Young serves as the Executive Vice President, Chief Commercial and Strategy Officer at Seres Therapeutics. Prior to joining Seres, Dr. Young was Vice President, Global Commercial Strategy at Sage Therapeutics, where she was responsible for developing global commercial capabilities, including marketing, insights and analytics, and new product planning. She previously held commercial leadership positions at Bristol-Myers Squibb, culminating in her role as Vice President and General Manager, Cardiovascular, where she oversaw the global ELIQUIS® business. Earlier in her career, Dr. Young held marketing and sales roles at GlaxoSmithKline.

Seres Therapeutics' primary products address significant medical needs with the following estimated market sizes:

• VOWST (formerly SER-109) for recurrent Clostridioides difficile infection (rCDI): The addressable patient population for recurrent Clostridioides difficile infection in the U.S. is approximately 170,000 cases annually. The global Clostridium difficile infections market was valued at USD 9.82 billion in 2024 and is projected to reach USD 16.88 billion by 2032, expanding at a Compound Annual Growth Rate (CAGR) of 7.00% from 2025 to 2032. Another estimate for the global Clostridium difficile infection treatment market size is US$ 1.24 billion by the end of 2024, expected to climb to US$ 2.28 billion by the end of 2034, with a CAGR of 6.3% between 2024 and 2034.
• SER-155 for preventing bacterial bloodstream infections in allogeneic hematopoietic stem cell transplant (allo-HSCT) patients: While a specific dollar figure for the addressable market for SER-155 is not provided, Seres Therapeutics indicates a "multi-billion-dollar expansion potential" for SER-155. The market opportunity for SER-155 is considered significant, with research suggesting rapid and deep utilization if approved, also in other patient groups at high risk of bloodstream infections. This product has received Breakthrough Therapy designation from the FDA for reducing bloodstream infections in adults undergoing allo-HSCT.

Seres Therapeutics (MCRB) is focused on several key drivers for future revenue growth over the next 2-3 years, primarily centered around its lead investigational product, SER-155, and its broader live biotherapeutic pipeline.

1. Advancement and Commercialization of SER-155: The primary expected driver of future revenue growth for Seres Therapeutics is the successful clinical development and eventual commercialization of SER-155. This oral live biotherapeutic is being developed for the prevention of bloodstream infections (BSIs) in adults undergoing allogeneic hematopoietic stem cell transplant (allo-HSCT). SER-155 has received Breakthrough Therapy and Fast Track designations from the FDA, and Seres is actively preparing to initiate a Phase 2 study following encouraging Phase 1b data showing a 77% relative risk reduction in BSIs. The company views SER-155 as addressing a significant unmet medical need with substantial commercial opportunities, potentially extending beyond allo-HSCT patients to other vulnerable populations at risk of bloodstream infections.
2. Strategic Partnerships and Collaborations: Seres Therapeutics is actively pursuing strategic partnerships, out-licensing deals, mergers, and other transaction structures to secure capital and resources. These collaborations are crucial for funding the clinical advancement of SER-155 and other live biotherapeutic product candidates. Successful partnerships could generate upfront payments, milestone payments, and a share of future product revenues, significantly contributing to the company's financial stability and growth.
3. Expansion of the Live Biotherapeutic Pipeline: Beyond SER-155, Seres is engaged in developing a broader portfolio of live biotherapeutic product candidates. These programs are designed to target multiple disease-relevant pathways, particularly in inflammatory and immune diseases. The successful progression of these other pipeline assets through clinical development and toward commercialization could establish new revenue streams in the medium to long term.
4. Development of New Formulations for SER-155: The company received a grant of up to $3.6 million from CARB-X to support the development of a liquid formulation of SER-155. If successful, a liquid formulation could broaden patient access and expand the market for SER-155, thereby increasing potential revenue. This represents a product line extension that could enhance the overall commercial potential of SER-155.

Share Issuance

• Seres Therapeutics implemented a 1-for-20 reverse stock split effective April 21, 2025, approved by stockholders on April 10, 2025.
• Stockholders approved the 2025 Incentive Award Plan on April 10, 2025, which allows for the issuance of 44,604,870 shares.
• The number of issued and outstanding shares increased from 8,650,227 at December 31, 2024, to 8,764,664 at September 30, 2025.

Inbound Investments

• Seres completed the sale of its VOWST business to Nestlé Health Science, which included a $100 million upfront payment, with approximately $20 million used to settle net obligations. The transaction also includes potential future milestone payments of up to $275 million.
• A $25 million installment payment from Nestlé was received in July 2025.
• In the third quarter of 2025, Seres received a grant of up to $3.6 million from CARB-X (Combating Antibiotic-Resistant Bacteria Biopharmaceutical Accelerator) to support the development of an oral liquid formulation of SER-155.