What is Transfusion-associated graft-versus-host disease?

Transfusion-associated graft-versus-host disease is a rare complication of blood transfusion, in which the immunologically competent donor T lymphocytes mount an immune response against the recipient's lymphoid tissue. These donor lymphocytes engraft, recognize recipient cells as foreign and mount an immune response against recipient tissues. Donor lymphocytes are usually identified as foreign and destroyed by the recipient's immune system. However, in situations where the recipient is severely immunocompromised, or when the donor and recipient HLA type is similar , the recipient's immune system is not able to destroy the donor lymphocytes. This can result in transfusion associated graft-versus-host disease.