Feasibility, Safety, and Potential Efficacy of Fecal Microbiota Transplantation (FMT) for Gastrointestinal Dysfunction in Children Following Hematopoietic Cell Transplant (HCT).

This study tests whether fecal microbiota transplantation (FMT) — transferring healthy gut bacteria from a donor — can safely help children who have persistent gut problems after receiving a bone marrow (stem cell) transplant for a blood disorder or cancer. These gut problems include a condition called graft-versus-host disease (GvHD) and prolonged diarrhea. **You may be eligible if...** - You are under 22 years old - You received an allogeneic (donor) bone marrow or stem cell transplant at least 30 days ago - You have gut graft-versus-host disease (GvHD) that has not responded well to steroids, or you have had ongoing gut problems (diarrhea, feeding tube dependency, or inability to eat) for at least 4 weeks after your transplant **You may NOT be eligible if...** - You tested negative for CMV or EBV antibodies (a donor compatibility issue) - You are pregnant or nursing - You have had a previous FMT - You have had abdominal surgery within the past 4 weeks - You have conditions that increase the risk of infection in the abdomen (such as ascites or peritoneal dialysis) Talk to your doctor to see if this trial is right for you.