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

Participants will be eligible to receive an FMT on or after Day +30 post-HCT. FMT will be performed using FMP material obtained from OpenBiome. 60 mL of FMP will be administered via NJ tube and 250 mL via colonoscopy. A second FMT may be performed at least 14 days after the initial FMT in GI clinical symptoms have partially improved or have not changed. The second FMT will be administered using the same procedure as in the initial FMT

Inclusion criteria

• Age < 22 years old.
• Received an allogeneic HCT greater than or equal to 30 days prior to enrollment
• Diagnosed with one of the following conditions:

• Steroid-resistant gut a GvHD (defined as GI symptoms that do not improve within 5 days after initial steroid therapy, >/= 1mg/kg of prednisolone) OR
• Steroid-dependent gut a GvHD (defined as the presence of a response to methylprednisolone 2 mg/kg/day but relapsing when an attempt was made to taper steroid treatment).

OR

• Current or prolonged GI dysfunction following HCT, defined as having diarrhea or loose stools >/= 4 weeks with at least one of the following:

• Requiring NG or G-tube feeds
• Requiring TPN or IVF for more than 4 weeks
• Diagnosis of gastroparesis by GI specialist documented in the medical record
• Willing and able to provide informed assent/consent

Exclusion criteria

• Participant is at risk for aspiration pneumonia
• History of anaphylactic allergy to foods that are not excluded from the stool donor diet
• Female participant who is pregnant or nursing
• History of previous FMT
• Intra-abdominal surgery within 4 weeks of enrollment
• At increased risk for peritonitis: presence of intra-abdominal devices (G-or GJ-tubes are acceptable), receiving peritoneal dialysis, or ascites
• Concurrent abdominal radiation therapy
• Any acute or chronic illness/condition as well as medication that in the opinion of the investigator puts the subject at greater risk from FMT or may confound the study results.