The purpose of this study is to see if fecal microbiota transplantation (FMT) will prevent the future development of CDI. This is also known as fecal bacteriotherapy or stool transplant.

This is a randomized, open-label, controlled study designed to assess the efficacy of autologous fecal microbiota transplantation (auto-FMT) for prevention of Clostridium difficile infection (CDI) in patients who have undergone allogeneic hematopoietic stem cell transplantation (allo-HSCT). Patients will be enrolled prior to allo-HSCT; feces will be collected and stored from all participating subjects prior to the initiation of conditioning regimens, analyzed by deep 16S rRNA gene sequencing, and tested by assay for intestinal pathogens including Clostridium difficile. Later in the course of transplantation, following engraftment (defined as the first day of three consecutive days, that the absolute blood neutrophil count is at above f 500 mm3), subjects will undergo fecal testing for presence of Bacteroidetes by 16S PCR. Subjects will be eligible for study if they have a microbiologically diverse pre-transplant colonic microbiota, and if the post-engraftment specimen contains Bacteroidetes at a prevalence equal to or below (0.1%)

Inclusion Criteria:

• Planned to undergo allo-HSCT
• Age ≥ 18 years

Exclusion Criteria:

• As determined by the study investigators or consenting professionals, prolonged antibiotic treatment, as prevention or suppression of an ongoing infection, where treatment involves gut-perturbing antianaerobic antibiotics
• Has severe colitis of any etiology or a history of inflammatory bowel disease (IBD).