Letermovir Prophylaxis in Children With EBV-Positive T/NK-Cell Lymphoproliferative Disease and Refractory/Relapsed EBV-Associated Hemophagocytic Lymphohistiocytosis

Inclusion Criteria

• •Diagnosed with EBV-positive T/NK lymphoproliferative disease (EBV-T/NK LPD) according to ICC 2022 criteria, or diagnosed with refractory/relapsed EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH) according to the 2004-HLH diagnostic criteria;
• •Undergoing first allogeneic hematopoietic stem cell transplantation (allo-HSCT) at the study center;
• •Age \< 18 years;
• •CMV seropositive (IgG+) prior to transplantation;
• •Presence of at least one high-risk factor for CMV infection: haploidentical transplantation, HLA-mismatched transplantation, receipt of ATG (including ATLG/ALG) in conditioning, sustained corticosteroid use post-conditioning, donor/recipient CMV serostatus mismatch, or positive NGS result pre-transplant.