Vedolizumab in the Prophylaxis of Intestinal Acute Graft Versus Host Disease (aGVHD) in Participants Undergoing Allogeneic Hematopoietic Stem Cell (Allo-HSCT) Transplantation

The purpose of this study is to evaluate the efficacy of vedolizumab when added to background aGvHD prophylaxis regimen compared to placebo and background aGvHD prophylaxis regimen on intestinal aGvHD-free survival by Day +180 in participants who receive allo-HSCT as treatment for a hematologic malignancy or myeloproliferative disorder.

The drug being tested in this study is called vedolizumab. Vedolizumab is being tested to treat people who are undergoing allo-HSCT transplantation. This study will look at the efficacy and safety of vedolizumab in the prophylaxis of intestinal aGvHD in participants undergoing allo-HSCT transplantation.

The study will enroll approximately 558 participants. Participants will be randomly assigned (by chance, like flipping a coin) in 1:1 ratio to one of the two treatment groups-which will remain undisclosed to the participant and study doctor during the study (unless there is an urgent medical need) along with background GvHD prophylaxis regimen:

* Vedolizumab 300 mg
* Placebo (dummy inactive intravenous infusion)

This multi-center trial will be conducted Worldwide. The overall time to participate in this study is 12 months.

Eligibility Criteria:
Inclusion Criteria:

1. Must be \>= 18 years of age and, in selected countries, adolescents aged 12 years and greater and weighing \>=30 kilogram (kg) at time of randomization.
2. Must undergo deoxyribose nucleic acid (DNA)-based human leukocyte antigen (HLA) matching and be 8 of 8 or 7 of 8 HLA-matched (singe allele or antigen mismatch at HLA-A, -B, and -C, and HLA-DRB1 is allowable) unrelated hematopoietic stem cell transplantation (HSCT) from either peripheral blood or bone marrow stem cells for a hematologic malignancy or myeloproliferative disorder.
3. For whom a myeloablative conditioning or reduced intensity conditioning (RIC) is planned.
4. Allo-HSCT eligible (meeting institutional criteria)-participants planned medical care should include aGvHD prophylaxis with a combination of calcineurin inhibitor (CNI) (cyclosporine \[CYS\] or tacrolimus \[TAC\]) and methotrexate (MTX) or CNI and mycophenolate mofetil (MMF). With the exception of antithymocyte globulin (ATG) (antithymocyte globulin-Fresenius \[ATG-F\] or thymoglobulin), all other therapies, approved or investigational, for GvHD prophylaxis are excluded.
5. Eastern Cooperative Oncology Group (ECOG) performance status of \<= 2 for participants aged \>=18 years at randomization or \>=60 % using the Karnofsky performance status for adolescent participants aged \>=16 years at randomization or the Lansky performance status for adolescent participants aged 12 to \< 16 years at randomization.

Exclusion Criteria:

1. Had prior allo- HSCT.
2. Planned umbilical cord blood transplant or planned to receive posttransplant cyclophosphamide, in vivo or ex vivo T cell-depleted hematopoietic stem cells (HSCs) with the exception of ATG (ATG-F or thymoglobulin).
3. Planned allo-HSCT for nonmalignant hematological disorders (example, aplastic anemia, sickle cell anemia, thalassemias, Fanconi anemia or immunodeficiency).