This exploratory clinical study focuses on the use of EBV-AST cell infusion for treating EBV-DNA viremia following allogeneic hematopoietic stem cell transplantation (Allo-HSCT). The study aims to determine the maximum tolerated dose (MTD) or optimal biological dose (OBD) of EBV-AST cells and assess their safety, tolerability, and preliminary efficacy in treating EBV-DNA viremia. The study will involve a 3+3 dose escalation design to evaluate three different dosages of EBV-AST cell infusion. The study is expected to provide important insights into the clinical application of cell-based therapies for EBV infections.