UPN 381 developed fevers and hepatosplenomegaly 11 weeks after an unrelated T-cell–depleted SCT (A). This patient received a donor leukocyte infusion at the time of diagnosis, at which time there were 40,000 copies of EBV/μg DNA in the peripheral blood. After the infusion, there was a progressive increase in the amount of EBV-specific cytotoxicity against the donor BLCL (B). This patient died secondary to pulmonary failure, complicated by persistent EBV-LPD in the liver and lungs.