Additive effects of fecal microbiota transplantation and infliximab on gut microbiome and metabolome in refractory inflammatory bowel disease patients

Fecal microbiota transplantation (FMT) is an emerging therapy for inflammatory bowel disease (IBD), yet its efficacy in patients refractory to conventional treatments and its underlying mechanisms require further elucidation. We studied 37 IBD patients (15 ulcerative colitis [UC], 22 Crohn's disease [CD]) refractory to conventional therapies and 16 healthy donors. FMT monotherapy from a single donor induced week-4 clinical response in 12 UC and 9 biologic-naïve CD patients, with all responders sustaining remission and most achieving endoscopic remission by week 14. Integrated multi-omics revealed FMT restored microbial diversity and profoundly reorganized host-microbiota-metabolite networks. In nine refractory CD patients (7 infliximab [IFX] non-responders, 2 FMT non-responders), IFX-FMT combination led to week-4 response in 6 patients, all of whom attained clinical and endoscopic remission by week 14, with more complete microbial-metabolic restoration than monotherapy. Our findings establish that FMT induces remission in refractory IBD via ecosystem network rewiring, and that IFX-FMT exhibits additive effects, supporting further trials of microbiome-directed adjunctive strategies. IMPORTANCE: This study provides mechanistic and clinical insights into the therapeutic effects of fecal microbiota transplantation (FMT) in inflammatory bowel disease (IBD), particularly when combined with the anti-tumor necrosis factor (anti-TNF) biologic infliximab (IFX). While both FMT and IFX achieve response in approximately 60% of IBD patients, their combined influence on the gut microbial and metabolic landscape in refractory disease has been poorly understood. Here, we demonstrate that FMT monotherapy restores gut microbial diversity and reconfigures host-microbiota-metabolite networks, correlating with clinical and endoscopic remission in patients refractory to conventional treatments. Furthermore, in Crohn's disease patients unresponsive to either therapy alone, combined IFX-FMT induced more complete microbial and metabolic normalization and achieved remission where monotherapy had failed. These findings reveal ecosystem-level network rewiring as a central mechanism of FMT efficacy and establish the additive potential of combining microbiome-targeted and immunomodulatory therapies. This work supports the development of microbiome-informed adjunctive strategies for severe or refractory IBD, highlighting an actionable path toward personalized, mechanism-based treatment regimens. CLINICAL TRIALS: This study is registered with ClinicalTrials.gov as NCT07149441.