This study looks at how safe and effective a medicine called Alpha-1 Antitrypsin (AAT) is in preventing a disease called graft-versus-host disease (GVHD). GVHD happens when transplanted cells attack the body. Participants in this study are patients who receive a type of transplant called hematopoietic cell transplant (HCT) for blood-related cancers like leukemia or lymphoma. Some patients will get AAT, and some will get a placebo, which is a treatment with no active medicine, to see which works better. The study is "double-blind," meaning neither the doctors nor the patients know who is getting AAT or the placebo to ensure fair results.

• The study involves multiple visits and is conducted at several locations.
• Participants will be randomly assigned to groups, and the study is expected to last several months.
• There may be risks involved, as with any medical study, and participants must meet specific health criteria to join.