Poop pills may shield stem cell patients from deadly immune attack

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

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