Graft-versus-host disease (GVHD) is a possible side-effect of the transplant. In GVHD, some cells in the donor marrow attack cells in the patient's body. This causes skin, liver, and bowel problems, and may damage other parts of the body. Often, these problems are fairly mild, but they can be severe or even cause death. Severe GVHD is likely to occur in about 10% of patients.