Graft-versus-host disease (GVHD) is a complication that can occur after certain stem cell or bone marrow transplants. GVHD may occur after a bone marrow, or stem cell, transplant in which someone receives bone marrow tissue or cells from a donor. This type of transplant is called allogeneic. The new, transplanted cells regard the recipient's body as foreign. When this happens, the cells attack the recipient's body.