Definition of Graft-versus-host disease:

Graft-versus-host disease (GVHD) is a complication that can occur after a stem cell or bone marrow transplant in which the newly transplanted material attacks the transplant recipient's body.

See also: Transplant rejection

Causes, incidence, and risk factors:

GVHD occurs in a bone marrow or stem cell transplant involving a donor and a recipient. The bone marrow is the soft tissue inside bones that helps form blood cells, including white cells that are responsible for the immune response. Stem cells are normall found inside bone marrow.

Since only identical twins have identical tissue types, a donor's bone marrow is normally a close, but not perfect, match to the recipient's tissues. See: Histocompatibility antigen test

The differences between the donor's cells and recipient's tissues often cause T cells (a type of white blood cells) from the donor to recognize the recipient's body tissues as foreign. When this happens, the newly transplanted cells attack the transplant recipient's body.

Acute GVHD usually happens within the first 3 months after transplant. Chronic GVHD usually starts more than 3 months after transplant, and can last a lifetime.

Rates of GVHD vary from between 30 - 40% among related donors and recipients to 60 - 80% between unrelated donors and recipients. The greater the mismatch between donor and recipient, the greater the risk of GVHD. After a transplant, the recipient usually takes drugs that suppress the immune system, which helps reduce the chances (or severity) of GVHD.