Graft-versus-Host Disease (GVHD) is a common condition after a bone marrow or stem cell transplant that uses cells from a donor (an allogeneic transplant). The donor cells are called the “graft” and the patient is called the “host”. When the donor’s immune cells (the graft) are transplanted in the patient’s body (the host) they often unleash an immune system attack against the patient’s organs and tissues which can be mild, moderate or severe.