A condition that happens when donor immune cells attack the new host.

Graft-versus-host disease may happen at any time after a transplant. However, it's more common after the marrow has started to make healthy cells. The condition can be mild or severe.

Symptoms depend on which organ is affected. Some symptoms include nausea, vomiting, diarrhea, stomach pain or cramping, and rash.

Treatment includes medicines to suppress the immune system, such as steroids.