Disease, graft-versus-host: Graft versus host disease (GVHD) is a rare disorder that occurs when the immune cells from donated bone marrow stem cells or a blood transfusion attack the recipient. The only transplanted tissues that contain enough immune cells (specifically T-lymphocytes) to cause GVHD are the blood, intestines, the bone marrow, and, less commonly, the liver. It can occur with other solid organ transplants as well. This condition typically occurs in patients who have extremely weakened immune systems. Also called GVHD.