A method for predicting whether a patient will be a long-term survivor on treatment of a disease by adoptive cell transfer (ACT), is disclosed comprising: (i) analysing a blood-derived sample obtained from the patient for one or more prognostic markers of long-term survival on treatment of a disease by ACT, and; (ii) based on the analysis of step (i), predicting whether the patient will be a long-term survivor on treatment of the disease by ACT, wherein the disease is preferably a disease caused or exacerbated by infection with Epstein-Barr virus (EBV), such as EBV-positive nasopharyngeal carcinoma (NPC). Also disclosed are methods for treating a patient by ACT, methods for selecting a patient for treatment by ACT, and methods for selecting a patient for treatment of a disease by ACT, preferably EBV-positive NPC.