Fecal Microbiota Transplant and Dietary Fiber Supplementation for the Treatment of Gut Graft Versus Host Disease

Inclusion Criteria:

* 18 years of age or older
* History of allogeneic hematopoietic stem cell transplant in the past 365 days
* Post-engraftment, defined by time period following three consecutive days of sustained neutrophil engraftment with an absolute neutrophil count of at least 500 cells/mm\^3
* Mild to severe acute GI GvHD, at least stage 1, as measured by one of the following:

  * Modified Glucksberg criteria for GI GvHD averaged over 3 consecutive days and without another explanation for diarrhea such as laxative use or infection. In patients who have already had GI biopsy, biopsy histology must be compatible with GVHD, although biopsy is not required
  * Biopsy evidence of GI GVHD in the upper or lower GI tract

Exclusion Criteria:

* History of previous serious adverse events associated with FMT
* History of bowel perforation in the last 90 days
* History of gastrointestinal resection in the last 90 days
* History of small bowel obstruction without surgical intervention in the last 30 days, or 90 days with surgery, or history of large bowel obstruction in last 90 days
* History of diverticulitis in the last 60 days
* History of celiac disease confirmed by serologic testing or small bowel biopsy
* History of severe dietary allergy as designated by World Allergy Organization Subcutaneous Immunotherapy Systemic Reaction Grading System grade 2 or more
* Subjects who are cytomegalovirus (CMV) seronegative at the time of enrollment as indicated by clinical testing unless the fecal microbiota transplant (FMT) donor is CMV seronegative with negative plasma polymerase chain reaction (PCR) assays for CMV.
* Known allergies to loperamide, sodium chloride, glycerol, theobroma oil, hide bovine gelatin, sodium lauryl sulfate, colorants FD\&C, titanium dioxide, polyethylene glycol, sodium sulfate, sodium bicarbonate, sodium phosphate, benzalkonium chloride, disodium EDTA or potassium chloride.
* Currently pregnant, planning to become pregnant or breastfeeding during the study period. Women of childbearing potential (those who are not post-menopausal or post-hysterectomy) must be negative for pregnancy per urine pregnancy test at enrollment
* Individuals with the ability to conceive children who are not willing to abstain from sexual activity or use an effective form of birth control during the duration of the study
* Unwilling or unable to participate in study procedures including oral intake of FMT, colonoscopy, fiber supplementation, collection of stool samples and completion study surveys
* Cannot reasonably and safely participate in the study in the opinion of the investigators