Graft-versus-host disease is a common complication following an allogeneic tissue transplant. It is commonly associated with stem cell or bone marrow transplant but the term also applies to other forms of tissue graft. Immune cells in the tissue recognize the recipient as "foreign". The transplanted immune cells then attack the host's body cells. GVHD can also occur after a blood transfusion if the blood products used have not been irradiated.