Safety, Dosage, and Microbiome Engraftment Study of MGT-006 for Ulcerative Colitis (ROOT Study)

The study is a multicenter, randomized, exploratory Phase 1b/2a study planned at approximately 30 sites in Japan and the United States. The study is intended to evaluate the safety and tolerability of repeated oral administration of MGT-006, select an appropriate pretreatment approach, and explore dose and regimen options for further development. In Phase 1b, participants will be randomized in three cohots, MGT-006 without pretreatment antibiotics or to oral vancomycin or AFM (Amoxicillin/Fosfomycin/Metronidazole) pretreatment followed by MGT-006. Randomization will be stratified by country. The planned sample size is approximately 18 participants, with additional enrollment permitted as needed to obtain at least six evaluable participants per group meeting the protocol-defined adherence criteria. Progression to Phase 2a is conditional on the safety and microbiome engraftment review specified in the protocol. The sponsor will make the transition decision taking into account the independent Data Safety Monitoring Board's recommendations, as applicable. Approximately 36 participants across three MGT-006 dose groups are provisionally planned for Phase 2a. The number of groups, doses, dosing regimens, sample size, and treatment duration may be modified based on Phase 1b findings and will be specified in an amended protocol before initiation of Phase 2a. Treatment administration is open-label. Endoscopic efficacy assessments will be performed centrally without knowledge of treatment allocation. Safety data will be reviewed by an independent Data Safety Monitoring Board. Analyses will be descriptive and exploratory; the study is not designed for confirmatory hypothesis testing or to ensure statistical power for between-group comparisons.