Organ transplant recipients are chronically immunosuppressed and their T-cell function is impaired. Ensuing diseases are mostly infections and are similar to those occurring in other conditions associated with T-cell impairment, such as AIDS. In addition, organ transplant recipients are at great risk for developing melanoma and nonmelanoma skin cancers. Bone marrow and stem cell graft recipients are at risk for graft-versus-host disease (GVHD).