Gastrointestinal (GI) infection caused by the bacterium Clostridioides difficile is a common complication of inflammatory bowel disease (IBD), a condition caused by an aberrant host immune response to the GI microbiota. C. difficile infection (CDI) typically occurs after disruption of the GI microbiota, making the immune response to microbiota during IBD a major risk factor. This is particularly important in pediatric populations where 47% may suffer from an IBD-CDI co-occurrence. Fecal microbiota transplant (FMT) is a successful experimental treatment for IBD and CDI. It is thought to work by restoring a healthy-functioning microbiome to the IBD-CDI patient, however the specific host and bacterial factors that define FMT’s success remains unknown. We will recruit pediatric IBD-CDI patients to define host immune responses to FMT treatment. Using a novel IBD-CDI mouse model, we will then attribute host responses to FMT therapy and microbiota composition. This translational research will advance our mechanistic knowledge of FMT efficacy and ultimately impact FMT safety and governance. We will present our findings at international conferences including Canadian Digestive Diseases Week and aim to publish them in high-impact journals.