Graft-versus-host disease is a serious, life threatening complication of allogeneic stem cell transplantation. It develops, when the new immune system, which arises from the transplanted stem cells (graft), attacks tissues and organs of the recipient (host). It can be classified as acute or chronic, depending on the time of occurrence and/or the pathology.

Graft-versus-host disease is triggered by minor differences in immunological tissue characteristics between the donor and recipient. The new immune system recognizes these differences as foreign structures and subsequently attacks cells of recipient. In the course of graft-versus-host disease, multiple organs and tissues are damaged. The skin, liver and gastrointestinal tract are most commonly affected.

Graft-versus-host disease can lead to permanent impairment of quality of life, and in many cases even to death. Patients with graft-versus-host disease often require prolonged immunosuppressive treatment which increases the risks for infections, organ damage, secondary malignancies and other complications associated with these medications.