Fecal Microbiota Transplantation for the Prevention of Acute Graft Versus Host Disease in Adults Undergoing Allogeneic Hematopoietic Cell Transplantation

Inclusion Criteria: * Age \>= 18 * Signed informed consent * Able to take oral medications * Planned T-replete allogeneic hematopoietic cell transplantation for any indication. History of prior transplantation is allowed * Planned GVHD prophylaxis using one of the following regimens: * Calcineurin inhibitor (tacrolimus or cyclosporine) plus methotrexate * Calcineurin inhibitor (tacrolimus or cyclosporine) plus mycophenolate mofetil (MMF) * Sirolimus plus cyclosporine plus MMF * Post-transplant cyclophosphamide plus calcineurin inhibitor (with or without MMF or sirolimus) * One of the following HCT donor types: * Human leukocyte antigen (HLA)-matched sibling donor * 9/10 or 10/10 HLA-matched unrelated donor * HLA- haploidentical donor * Cord blood * Willing to use at least 1 accepted method of contraception until day 180 after transplant and agree to not donate eggs/sperm for 180 days after * Not pregnant or breast feeding * ELIGIBILITY CRITERIA FOR RANDOMIZATION: Absolute neutrophil count (ANC) recovery to \> 0.5 x 10\^9/L from nadir, without ongoing growth factor support * ELIGIBILITY CRITERIA FOR RANDOMIZATION: Discontinuation of all antibacterial antibiotics (except those used for Pneumocystis jiroveci prophylaxis) for 2 days * ELIGIBILITY CRITERIA FOR RANDOMIZATION: Resolution of all acute toxicities (other than anemia and thrombocytopenia) to Common Terminology Criteria for Adverse Events (CTCAE) grade 2 or lower * ELIGIBILITY CRITERIA FOR RANDOMIZATION: Ability to swallow capsules * ELIGIBILITY CRITERIA FOR RANDOMIZATION: No grade II-IV acute GVHD * ELIGIBILITY CRITERIA FOR RANDOMIZATION: No moderate to severe chronic GVHD * ELIGIBILITY CRITERIA FOR RANDOMIZATION: No concurrent antibiotics to treat infections. Prophylactic antiviral and antifungal antibiotics used to prevent infections are allowed Exclusion Criteria: * Severe food allergy in the form of anaphylaxis or attributable symptoms requiring hospitalization * History of chronic aspiration or conditions predisposing to aspiration (e.g. neuromuscular disorders) * Receiving or planned to receive other experimental agents (including ex vivo T-cell depletion) to prevent GVHD. The use of other experimental agents is prohibited unless approved by the principal investigator (PI) of the other trial