Graft-versus-host disease (GVHD) is an acute immune complication that sometimes occurs following a bone marrow transplant. Sergio Giralt, Chief of the Adult Bone Marrow Transplant Service at Memorial Sloan-Kettering Cancer Center, explains that although GVHD can be dangerous, people with certain types of cancer may benefit from some immune response to prevent a cancer from returning. Doctors at Memorial Sloan-Kettering have pioneered a technique for preventing GVHD in people who receive bone marrow that is not a perfect match.