This study explores a new treatment for acute graft-versus-host disease (GVHD), which happens when donor cells attack a patient's healthy body cells after a stem cell transplant. Current treatments use high-dose steroids like prednisone, but they can cause serious issues and may not always work. The study uses the Minnesota risk system to predict how GVHD will respond to steroids, classifying patients into standard or high-risk groups.

The study will test if the drug ruxolitinib can work as well as or better than steroids in treating GVHD. Ruxolitinib is a medicine already used for GVHD when steroids don't work. Patients will be divided randomly into groups to test different doses of ruxolitinib. The goal is to find the best dose that helps patients the most with the fewest side effects, like blood or infection problems.

• Participants must be adults (18+ years).
• Exclusion criteria include prior ruxolitinib use and uncontrolled infections.
• Safety and effectiveness of ruxolitinib will be monitored.