A Study of SER-155 to Treat Diarrhea in People on Immunotherapy

A Single-Arm, Open-Label, Phase 1 Study to Assess Safety and Preliminary Efficacy of Cultivated Multi-Strain Live Bacterial Therapeutic SER-155 for First-Line Treatment of Immunotherapy-Related Enterocolitis

The purpose of this study is to find out whether SER-155 may be a safe first treatment that causes few or mild side effects for people due to irEC.

Study Overview

• Status: Recruiting
• Conditions: Diarrhea; Enterocolitis
• Intervention / Treatment: Biological: SER-155

• Study Type: Interventional
• Enrollment (Estimated): 15
• Phase: Phase 1

Contacts and Locations

• Study Contact: Name: David Faleck, MD; Phone Number: 212-639-8286; Email: faleckd@mskcc.org
• Study Contact Backup: Name: Michael Postow, MD; Phone Number: 646-888-4315; Email: PostowM@mskcc.org

Study Locations

• United States
  • New Jersey
    • Basking Ridge, New Jersey, United States, 07920
      • Recruiting
      • Memoral Sloan Kettering at Basking Ridge (Limited Protocol Activities)
      • Contact: David Faleck, MD; Phone Number: 212-639-8286
    • Middletown, New Jersey, United States, 07748
      • Recruiting
      • Memorial Sloan Kettering Monmouth (All Protocol Activities)
      • Contact: David Faleck, MD; Phone Number: 212-639-8286
    • Montvale, New Jersey, United States, 07645
      • Recruiting
      • Memorial Sloan Kettering Bergen (All Protocol Activities)
      • Contact: David Faleck, MD; Phone Number: 212-639-8286
  • New York
    • Commack, New York, United States, 11725
      • Recruiting
      • Memorial Sloan Kettering Suffolk-Commack (Limited protocol activity)
      • Contact: David Faleck, MD; Phone Number: 212-639-8286
    • Harrison, New York, United States, 10604
      • Recruiting
      • Memorial Sloan Kettering Westchester (Limited Protocol Activities)
      • Contact: David Faleck, MD; Phone Number: 212-639-8286
    • New York, New York, United States, 10065
      • Recruiting
      • Memorial Sloan Kettering Cancer Center (All Protocol Activities)
      • Contact: David Faleck, MD; Phone Number: 212-639-8286
    • Rockville Centre, New York, United States, 11553
      • Recruiting
      • Memorial Sloan Kettering Nassau (Limited Protocol Activities)
      • Contact: David Faleck, MD; Phone Number: 212-639-8286

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Age > 18 years
• Receipt of ICI (single-agent or combination) within the 180 days preceding screening.

Concurrent treatment with cytotoxic chemotherapy or other tumor-directed agents is permitted.

• Grade 2 - 3 diarrhea (i.e., increase of at least 4 bowel movements a day above baseline during the screening window), deemed by the treating provider as likely related to ICI therapy, with or without concomitant symptoms of grade 1 - 2 colitis (e.g.

abdominal pain, bloody or mucoid stools)

• Able to swallow oral medication
• Individuals of childbearing potential willing to use a highly effective method of contraception (failure rate of <1% per year when used consistently and correctly) for 30 days after the last dose of SER-155.
• Willing to provide written informed consent, comply with the protocol, and understand the potential risks and benefits of study enrollment and treatment.

Exclusion Criteria:

• Active GI infection, including untreated viral, bacterial or fungal cause(s) of diarrhea.
• Received immunosuppressive therapies for suspected or confirmed irEC, including systemic corticosteroids (either oral or intravenous) and/or infliximab, vedolizumab or ustekinumab
• Grade 3 colitis symptoms, i.e. severe abdominal pain or peritoneal signs
• Admitted to the hospital for irEC
• Prednisone (or steroid equivalent) dose > 10 mg a day for a non-GI irAE at time of screening
• Pre-existing inflammatory bowel disease (e.g. Crohn's disease or ulcerative colitis) or microscopic colitis
• Pregnant or lactating women
• Any condition that requires ongoing prophylactic or therapeutic antibacterial antibiotics
• Severe neutropenia, as defined by an absolute neutrophil count (ANC) < 500 cells/mm^3, at time of screening
• Treatment with investigational medications used for diarrhea/colitis treatment and microbiome therapeutics within 30 days prior to enrollment
• Known allergy or intolerance to oral vancomycin
• Unable to comply with the protocol requirements
• Any condition that in the opinion of the investigator may increase the risk of study participation and/or may interfere with the interpretation of study results

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Participants with Immune checkpoint inhibitor-related enterocolitis (irEC); Participants with grade 2-3 diarrhea from irEC who have not yet received immunosuppressive therapy for irEC	Biological: SER-155; SER-155 (Cultivated Multi-Strain Live Bacterial Therapeutic, Encapsulated) is an experimental designed ecology of 16 unique, human-commensal bacterial strains encapsulated for oral administration and will be provided by Seres as an investigational drug; Other Names: Cultivated Multi-Strain Live Bacterial Therapeutic, Encapsulated

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Proportion of participants with treatment-related adverse events of special interest	Proportion of participants with treatment-related adverse events of special interest, i.e. blood stream infection	1 year
Proportion of patients with treatment-related adverse events	Proportion of patients with treatment-related adverse events	1 year

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Proportion of patients with immunosuppressive-free clinical response of irEC (immunotherapy-related enterocolitis) at day 15	Proportion of patients with immunosuppressive-free clinical response of irEC (immunotherapy-related enterocolitis) at day 15, defined as at least one grade decrease in diarrhea symptoms without the use of immunosuppressive therapy	Day 15
Proportion of patients with immunosuppressive-free clinical remission of irEC at day 15	Proportion of patients with immunosuppressive-free clinical remission of irEC at day 15, defined as resolution in diarrhea symptoms (grade 0) without the use of immunosuppressive therapy	Day 15
Proportion of patients with immunosuppressive-free clinical response of irEC at day 43	Proportion of patients with immunosuppressive-free clinical response of irEC at day 43	Day 43
Proportion of patients with immunosuppressive-free clinical remission of irEC at day 43	Proportion of patients with immunosuppressive-free clinical remission of irEC at day 43	Day 43
Time to immunosuppressive-free clinical response	Time to immunosuppressive-free clinical response	1 year
Time to immunosuppressive-free clinical remission	Time to immunosuppressive-free clinical remission	1 year
Number of detectable SER-155 strains at day 15	Number of detectable SER-155 strains at day 15	Day 15
Number of detectable SER-155 strains at day 43	Number of detectable SER-155 strains at day 43	Day 43

Collaborators and Investigators

• Sponsor: Memorial Sloan Kettering Cancer Center
• Investigators: Principal Investigator: David Faleck, MD, Memorial Sloan Kettering Cancer Center

Publications and helpful links

Helpful Links

• Memorial Sloan Kettering Cancer Center

Study record dates

Study Major Dates

• Study Start (Actual): January 24, 2025
• Primary Completion (Estimated): January 24, 2027
• Study Completion (Estimated): January 24, 2027

Study Registration Dates

• First Submitted: January 24, 2025
• First Submitted That Met QC Criteria: January 24, 2025
• First Posted (Actual): January 30, 2025

Study Record Updates

• Last Update Posted (Actual): December 2, 2025
• Last Update Submitted That Met QC Criteria: December 1, 2025
• Last Verified: October 1, 2025

More Information

Terms related to this study

• Keywords: Diarrhea; Memorial Sloan Kettering Cancer Center; Enterocolitis; SER-155; 24-231
• Additional Relevant MeSH Terms: Signs and Symptoms, Digestive; Intestinal Diseases; Digestive System Diseases; Gastrointestinal Diseases; Gastroenteritis; Pathological Conditions, Signs and Symptoms; Signs and Symptoms; Diarrhea; Enterocolitis
• Other Study ID Numbers: 24-231

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: Memorial Sloan Kettering Cancer Center supports the international committee of medical journal editors (ICMJE) and the ethical obligation of responsible sharing of data from clinical trials. The protocol summary, a statistical summary, and informed consent form will be made available on clinicaltrials.gov when required as a condition of Federal awards, other agreements supporting the research and/or as otherwise required. Requests for deidentified individual participant data can be made beginning 12 months after publication and for up to 36 months post publication. Deidentified individual participant data reported in the manuscript will be shared under the terms of a Data Use Agreement and may only be used for approved proposals. Requests may be made to: crdatashare@mskcc.org.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No