Graft-versus-host disease

Definition:

A condition that occurs following bone marrow transplants in which the donor's immune cells, in the transplanted marrow, make antibodies against the host's tissues. Also see transplant rejection.

Causes, incidence, and risk factors:

Bone marrow transplants are done when a person has certain types of leukemia or the bone marrow has been invaded by other types of malignancy. In the transplant, bone marrow is destroyed by drugs, radiation or both and is replaced with "compatible" marrow from a donor. While marrow destruction kills the cancer, it also suppresses the persons immune system, thus allowing the new donor marrow to implant without being destroyed by the recipient's immune system.

Graft-versus-host disease occurs when the new donor marrow makes antibodies against the host (person who received the marrow) and tries to destroy the host as if it were a disease or foreign material.

Varying degrees of graft-versus-host disease are viewed as an expected complication of bone marrow transplantation since tissue typing can find close but not perfect tissue matches between donor and recipient (see Histocompatibility antigens). Only identical twins have identical tissue types.