Seres Therapeutics Announces Publications in Nature Medicine and Journal of Infectious Diseases Highlighting Vowst™ Mechanism of Action and Supporting Broader Live Biotherapeutic Strategy

Rhea-AI Summary

Seres Therapeutics (Nasdaq: MCRB) announced two publications in Nature Medicine and the Journal of Infectious Diseases detailing VOWST™ functional mechanism and clinical translation.

The Nature Medicine paper reported dose-related faster engraftment, shifts in gut metabolites (decreased primary/increased secondary bile acids; higher short- and medium-chain fatty acids) that inhibit C. difficile germination and growth. The Journal of Infectious Diseases analysis found similar gastrointestinal microbiome and bile acid profiles in first and multiply recurrent C. difficile patients, with comparable VOWST pharmacology and efficacy across groups.

Seres noted these MbTx platform data supported its pipeline, including lead candidate SER-155, whose randomized Phase 1b showed a 77% reduction in bacterial bloodstream infections and reduced antibiotic use in allo-HSCT patients.

Positive

• FDA approval of VOWST in April 2023 (first oral microbiome therapeutic)
• Nature Medicine: dose-linked faster engraftment and metabolite shifts (bile acids, SCFAs)
• SER-155 Phase 1b reduced bloodstream infections by 77%

Negative

• None.

News Market Reaction – MCRB

+2.37%

1 alert

+2.37% News Effect

+$3M Valuation Impact

$145M Market Cap

0.1x Rel. Volume

On the day this news was published, MCRB gained 2.37%, reflecting a moderate positive market reaction. This price movement added approximately $3M to the company's valuation, bringing the market cap to $145M at that time.

Data tracked by StockTitan Argus on the day of publication.

Key Figures

BSI reduction with SER-155: 77% reduction

1 metrics

BSI reduction with SER-155 77% reduction Randomized, placebo-controlled Phase 1b allo-HSCT study

Market Reality Check

Price: $8.55 Vol: Volume 53,597 is at 0.73x...

normal vol

$8.55 Last Close

Volume Volume 53,597 is at 0.73x the 20-day average of 73,208, indicating subdued trading interest pre-news. normal

Technical Price $15.19 is trading above the 200-day MA $14.14 and sits 49.33% below the 52-week high and 132.62% above the 52-week low.

Peers on Argus

MCRB gained 0.26% with relatively light volume while peers were mixed: ACOG fell...

MCRB gained 0.26% with relatively light volume while peers were mixed: ACOG fell 5.22%, whereas GLSI, CHRS, SGMO, and TIL rose between 0.32% and 7.9%. Scanner data did not flag a coordinated sector momentum move, suggesting a more stock-specific setup.

Historical Context

5 past events · Latest: Nov 24 (Neutral)

Pattern 5 events

Date	Event	Sentiment	Move	Catalyst
Nov 24	Conference participation	Neutral	-4.2%	Announcement of participation in Piper Sandler healthcare conference.
Nov 05	Earnings and update	Negative	-7.6%	Q3 2025 results with going concern doubt despite gain on VOWST sale.
Oct 30	Earnings call notice	Neutral	-6.6%	Scheduling of Q3 2025 results call and webcast details.
Oct 29	Grant and SER-155 data	Positive	-1.6%	Up to $3.6M CARB-X award and 77% BSI reduction data for SER-155.
Oct 14	Clinical data preview	Positive	+2.4%	Plan to present SER-155 Phase 1b post hoc data at IDWeek 2025.

Pattern Detected

Recent news and earnings have often been followed by negative price reactions, including on seemingly constructive pipeline and funding updates.

Recent Company History

Over the past few months, Seres reported several key events. In October–November 2025, the company highlighted SER‑155 Phase 1b data showing a 77% reduction in bacterial bloodstream infections and received up to $3.6M from CARB‑X, yet shares often traded lower after these announcements. Q3 2025-11-05 results showed net income and gains from the VOWST sale but also disclosed substantial doubt about going concern. Today’s publication-driven update on VOWST and SER‑155 continues the focus on clinical validation and microbiome mechanisms within this challenging financial backdrop.

Market Pulse Summary

This announcement highlights peer-reviewed validation of VOWST’s microbiome mechanisms and reinforce...

Analysis

This announcement highlights peer-reviewed validation of VOWST’s microbiome mechanisms and reinforces SER‑155’s potential, including a reported 77% reduction in bacterial bloodstream infections in allo‑HSCT patients. Recent filings, such as the Q3 10-Q, also disclosed gains from the VOWST sale but raised substantial doubt about going concern, underscoring financing risk. Investors monitoring this story may focus on future SER‑155 trial progress, additional clinical publications, and any updates to the company’s operating runway.

Key Terms

mechanism of action, bile acids, short- and medium-chain fatty acids, allo-HSCT, +4 more

8 terms

mechanism of action medical

"functional mechanism and clinical impact of VOWST™."

Mechanism of action describes how a drug, therapy, or medical product produces its effect in the body—the specific steps, targets, and biological processes it engages, like a key fitting into a lock to open a door. Investors care because a clear, well-understood mechanism reduces scientific uncertainty, supports regulatory approval and market confidence, and helps predict safety, effectiveness and additional uses, all of which influence a product’s commercial potential and a company’s valuation.

bile acids medical

"including decreased primary and increased secondary bile acids, as well as elevated"

Bile acids are natural chemicals made by the liver that help break down fats in the gut like a soapy detergent and also act as signals that control metabolism and liver function. Investors care because changes in bile acid levels or drugs that target their pathways can indicate liver or digestive disease, serve as diagnostic markers, or create new treatment markets — all of which can affect a company’s regulatory outlook, sales potential, and valuation.

short- and medium-chain fatty acids medical

"and increased secondary bile acids, as well as elevated short- and medium-chain fatty acids,"

Short- and medium-chain fatty acids are types of fats defined by how many carbon links are in their molecular 'chain': short-chain fats are produced largely by gut microbes, while medium-chain fats appear in certain foods and are absorbed and used by the body more quickly. Investors care because these molecules underpin product claims, medical or wellness therapies, and ingredient markets—like different fuel types companies can develop, sell, or patent, affecting demand, margins and regulatory scrutiny.

allo-HSCT medical

"care for allogeneic hematopoietic stem cell transplant (allo-HSCT) recipients and other"

Allo-HSCT is a medical procedure in which a patient receives blood-forming stem cells from a genetically matched donor to replace a diseased or damaged bone marrow, often used for blood cancers and immune disorders. For investors, it matters because demand and outcomes for this complex, high-cost treatment affect hospital and clinic revenue, the market for supportive drugs and cell therapies, and the commercial value of companies developing safer transplants, donor matching tools, or complications treatments — like replacing a failing engine with a donated one and tracking the market for parts and repairs.

febrile neutropenia medical

"SER-155 reduced bacterial bloodstream infections by 77% and significantly lowered systemic antibiotic use and febrile neutropenia."

A serious medical condition in which a patient develops a fever while their level of infection-fighting white blood cells, called neutrophils, is very low. Think of the body’s defenses as an army: when its front-line soldiers are depleted, even a small invader can cause major problems, leading to hospital stays, treatment delays or extra supportive care. Investors watch febrile neutropenia because its frequency and severity affect demand for therapies, clinical trial outcomes, safety labeling and healthcare costs.

placebo-controlled medical

"In a randomized, placebo-controlled Phase 1b study evaluating SER-155 in patients"

"Placebo-controlled" describes a testing method where one group receives the actual treatment or intervention, while another group receives a harmless, inactive version called a placebo. This approach helps determine whether the real treatment has genuine effects beyond psychological expectations. For investors, understanding this ensures confidence that reported benefits are real and not influenced by bias or false perceptions.

biomarker medical

"Exploratory biomarker data presented at medical meetings has further supported the"

A biomarker is a measurable indicator found in the body, such as in blood or tissues, that provides information about health, disease, or how the body responds to treatment. For investors, biomarkers can signal the potential success or risk of medical products or therapies, influencing the value of related companies and industry trends. They act like signals or clues that help assess the progress of medical advancements and their market impact.

microbiome medical

"purified microbiome therapeutic on the gastrointestinal microbiome", confirmed Seres"

Microbiome is the community of tiny living organisms—bacteria, viruses, fungi and their genes—that live in a particular place, like the gut, skin or soil; think of it as a neighborhood of microscopic life that affects how that environment works. Investors care because changes or products that target the microbiome can alter health outcomes, crop yields or consumer product performance, creating new markets, regulatory risks and potential shifts in revenue for companies.

AI-generated analysis. Not financial advice.

Data demonstrate clinical translation of VOWST mechanisms of action in both first and multiply recurrent CDI patients

Seres MbTx® platform provides high-resolution functional biological understanding of live biotherapeutics and supports the advancement of Seres’ portfolio, including Phase 2-ready lead candidate SER-155

CAMBRIDGE, Mass., Jan. 06, 2026 (GLOBE NEWSWIRE) -- Seres Therapeutics, Inc. (Nasdaq: MCRB), a leading live biotherapeutics company, today announced the publication of two manuscripts in Nature Medicine and the Journal of Infectious Diseases highlighting new insights into the functional mechanism and clinical impact of VOWST™. Together, these publications provide further validation of the Company’s Live Biotherapeutics Products (LBPs) approach and inform the continued development of Seres’ pipeline of next-generation LBPs, including its lead investigational candidate, SER-155.

Seres led the development and FDA approval of VOWST™, a rationally selected consortia of bacteria in oral capsules that was designed to have specific functional pharmacological properties with clinical translation of these MoAs observed in the ECOSPOR III and IV Phase 3 trials. VOWST was the first-ever oral microbiome biotherapeutic licensed by the FDA, with approval in April 2023 for the prevention of recurrent Clostridioides difficile (rCDI) infection. VOWST was sold to Nestlé Health Science in September 2024.

The Nature Medicine article, titled “The impact of an oral purified microbiome therapeutic on the gastrointestinal microbiome”, confirmed Seres pharmacological hypotheses from earlier VOWST studies, with higher VOWST dosing associated with enhanced pharmacokinetics, as assessed by faster and more robust therapeutic species engraftment in the gut. Treatment also significantly altered the composition of the intestinal microbiome and microbe-associated metabolites, including decreased primary and increased secondary bile acids, as well as elevated short- and medium-chain fatty acids, functional changes that inhibit C. difficile spore germination and vegetative growth. Further, in vitro analyses confirmed that VOWST batches induced production of these metabolites that disrupt C. difficile life cycle and growth. Collectively, these findings support VOWST’s role in restoring microbe-associated metabolic functions critical to preventing CDI recurrence.

A complementary publication in the Journal of Infectious Diseases, titled “Comparability of Gastrointestinal Microbiome and Bile Acid Profiles in Patients With First or Multiply Recurrent Clostridioides difficile Infection”, reported a post hoc analysis of the ECOSPOR IV Phase 3 trial, evaluating differences in gastrointestinal microbiome and bile acid profiles between patients experiencing a first recurrence C. difficile infection (frCDI) versus multiply recurrence infection (mrCDI). These data demonstrate that the underlying functional disease etiology is consistent in both first and multiply recurrent CDI patient populations, with VOWST demonstrating similar efficacy and drug pharmacology across the broad patient population.

“We are thrilled to see these high-impact publications highlighting the important role biotherapeutics that comprise commensal bacteria may have in treating human disease,” said Matthew Henn, Ph.D., Chief Scientific Officer at Seres Therapeutics. “These data provide important clinical translation and further demonstrate the promise of live biotherapeutics to target specific microbiome functions that are linked to serious disease, including those that are not effectively treated with other drug modalities. The body of evidence from our clinical trials provides additional momentum for our current pipeline, including our lead candidate SER-155, which we believe has the potential to transform care for allogeneic hematopoietic stem cell transplant (allo-HSCT) recipients and other high-risk patients vulnerable to bloodstream infections.”

The underlying data supporting these publications was developed using Seres MbTx platform, which provides high-resolution assessment of drug pharmacology and functional mechanism of action. These data on bacterial function and pharmacology anchored the preclinical development of SER-155. In a randomized, placebo-controlled Phase 1b study evaluating SER-155 in patients undergoing allo-HSCT, SER-155 reduced bacterial bloodstream infections by 77% and significantly lowered systemic antibiotic use and febrile neutropenia. Exploratory biomarker data presented at medical meetings has further supported the therapy’s intended mechanisms and demonstrate the broader potential of live biotherapeutics in inflammatory and immune-mediated diseases.

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.

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: timing and results of our clinical studies and data readouts; past, current or future products or product candidates and their potential benefits; clinical development plans and commercial opportunities; our clinical development plans for SER-155 and other cultivated live biotherapeutic candidates across medically vulnerable populations; 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; and (14) our ability to manage our recent CEO transition, to retain key personnel and to manage our growth. 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 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:  
IR@serestherapeutics.com

Carlo Tanzi, Ph.D.
Kendall Investor Relations
ctanzi@kendallir.com

FAQ

What did the Nature Medicine paper report about VOWST pharmacology in 2026?

It reported dose-associated faster engraftment and metabolic shifts (decreased primary/increased secondary bile acids; elevated short- and medium-chain fatty acids) linked to anti–C. difficile activity.

How did VOWST perform across first versus multiply recurrent CDI in the Journal of Infectious Diseases analysis?

Post hoc ECOSPOR IV data showed comparable microbiome and bile acid profiles and similar VOWST pharmacology and efficacy in both first and multiply recurrent CDI patients.

What clinical effect did SER-155 show in the Phase 1b trial reported by Seres?

In a randomized placebo‑controlled Phase 1b, SER-155 reduced bacterial bloodstream infections by 77% and significantly lowered systemic antibiotic use and febrile neutropenia.

When was VOWST approved and what is its indication?

VOWST received FDA approval in April 2023 for the prevention of recurrent Clostridioides difficile infection (rCDI).

Did Seres sell VOWST and when?

VOWST was sold to Nestlé Health Science in September 2024.

How do the new publications affect Seres' pipeline and the MCRB program SER-155?

Seres says the MbTx platform data support mechanistic validation of VOWST and anchor preclinical development of SER-155, reinforcing its clinical rationale in allo-HSCT patients.