A clinical trial of Vedolizumab vs. placebo (dummy drug) for the prevention of intestinal Acute Graft Versus Host Disease (aGvHD), in patients undergoing allo-HSCT for a hematologic malignancy, (cancers that affect the blood and/or lymphatic system).

Main Objective: 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 subjects who receive allo-HSCT as treatment for a hematologic malignancy or myeloproliferative disorder.
Primary end point(s): The primary endpoint is intestinal aGvHD-free survival by Day +180 after allo HSCT. Intestinal aGvHD is defined as Stage 1-4 intestinal involvement per Acute Graft versus-Host Disease Clinical Stage criteria.