Prevention of Epstein-Barr Virus Reactivation With the ATG-based Haploidentical Protocol Combined With Rituximab in Children Undergoing Allogeneic Hematopoietic Stem Cell Transplantation

The goal of this clinical trial is to learn if adding rituximab to the ATG-based Protocol can prevent Epstein-Barr virus (EBV) from reactivating in children who have received an allogeneic haploidentical hematopoietic stem cell transplant. It will also learn about the safety of adding rituximab. The main questions it aims to answer are: Does giving rituximab twice during the conditioning regimen lower the number of children who have EBV reactivation after transplant? What medical problems or side effects do children experience when they receive rituximab in addition to the ATG-based Protocol? Researchers will compare the group that receives rituximab (two doses before transplant) with a control group that receives no rituximab, to see if the addition of rituximab effectively prevents EBV reactivation. Participants will: Receive either rituximab (two doses during the preconditioning phase) or no extra treatment (control group), depending on which group they are assigned to Have regular follow-up visits for blood tests to monitor their EBV-DNA levels Keep a record of any symptoms or health changes they notice between visits

Inclusion Criteria: * ECOG performance status score of 0-1, or Karnofsky Performance Status (KPS) score \> 80. * Diagnosis of a disease that has an indication for allogeneic hematopoietic stem cell transplantation. * Donor source is a related HLA haploidentical (half-matched) family donor. * Use of an "ATG-based" transplantation conditioning/protocol. * Written informed consent obtained from the patient's legal guardian prior to enrollment in this study. Exclusion Criteria: * Lansky performance score \< 60. * Diagnosis of EBV-associated hemophagocytic lymphohistiocytosis (HLH) or chronic active EBV infection. * Serum EBV DNA level \> 100 U/mL before transplantation. * Use of B-cell depleting immunotherapy (e.g., rituximab, blinatumomab, etc.) within 2 weeks prior to preconditioning. * Known allergy or hypersensitivity to rituximab. * Severe organ dysfunction * The subject or their legal guardian is unwilling or unable to comply with the protocol, or refuses to sign the informed consent document. * Patients deemed by the investigator to be unsuitable for participation in this trial.