We present the case of a 13-year-old boy with refractory systemic lupus erythematosus (SLE) who achieved drug-free remission after antiCD19 CART cell therapy , but subsequently experienced Epstein–Barr virus (EBV) reactivation leading to relapse of SLE and manifestations of chronic active EBV disease (CAEBVD). The temporal association between EBV resurgence and SLE flare suggests that CARTinduced immunosuppression may permit EBV reactivation, which in turn triggers the return of autoimmunity . This case highlights the need for vigilant monitoring for opportunistic infections, particularly EBV , after CART therapy for autoimmune diseases, as they may contribute to disease relapse.