Prophylactic rituximab administered on day -1 during conditioning significantly reduces early EBV reactivation in pediatric allogeneic HSCT: Real-world evidence from a propensity-matched cohort of 834 patients

Abstract Background: Epstein–Barr virus (EBV) reactivation is a common and serious complication after pediatric allogeneic hematopoietic stem cell transplantation (allo-HSCT), contributing to post-transplant lymphoproliferative disorder (PTLD) and non-relapse mortality (NRM). Rituximab (RTX) is widely used as preemptive therapy for EBV viremia, and prior studies have assessed prophylactic RTX given up to six months before transplant or on Day +5 post-HSCT, with variable efficacy. However, the efficacy of RTX administered on Day –1 during conditioning has not been systematically studied in children.Methods: We retrospectively analyzed pediatric patients who underwent allo-HSCT from October 2010 to January 2025. Patients were grouped by RTX use during conditioning. The primary endpoint was to evaluate whether RTX (375 mg/m² on day –1) during conditioning reduces EBV reactivation after pediatric allo-HSCT. Secondary endpoints included neutrophil and platelet engraftment, transplant-related complications, and immune reconstitution. Propensity scores were generated via logistic regression and used for 1:1 nearest-neighbor matching without replacement (caliper = 0.1). Covariate balance was assessed using standardized mean differences (SMD < 0.1). Competing risk models were applied for outcomes with competing events. Overall survival (OS) and graft-versus-host disease-free, relapse-free survival (GRFS) were analyzed using the Kaplan–Meier method and compared via log-rank tests. Variables with p < 0.1 in univariate analysis were included in multivariable models; p < 0.05 was considered significant.Results: Of 834 pediatric patients, 200 matched pairs (n = 400) were included. Baseline characteristics were well balanced (all SMDs < 0.1). EBV reactivation was significantly lower in the RTX group (10.1% vs. 47.0%, p < 0.001). Multivariable analysis confirmed RTX was independently associated with reduced EBV risk (HR = 0.145, 95% CI: 0.089–0.234, p < 0.001). Among patients with EBV reactivation, RTX recipients had lower peak viral loads (median 11,400 vs. 51,200 copies/mL, p < 0.001). RTX was associated with faster platelet engraftment (p = 0.013), with no significant differences in OS, GRFS, NRM, neutrophil engraftment, GVHD, or CMV reactivation (all p > 0.05). Immune reconstitution was transiently delayed in the RTX group during the first three months post-HSCT, but showed normalization thereafter, indicating a temporary effect on early immune recovery.Conclusions: Prophylactic administration of RTX on Day -1 during conditioning effectively reduces EBV reactivation and viral burden and promotes earlier platelet engraftment in pediatric allo-HSCT, without increasing transplant-related complications. This approach demonstrates promising efficacy and represents a feasible prophylactic option. Further prospective studies are warranted to confirm its role and determine the optimal timing and dosing strategy in this setting.