Immune reconstitution and viral reactivation after allogeneic hematopoietic stem cell transplantation in hematologic malignancies

Objectives To evaluate associations between post-transplant immune reconstitution, Epstein–Barr virus (EBV) and cytomegalovirus (CMV) DNAemia/reactivation, and survival after allogeneic hematopoietic stem cell transplantation (HSCT).Methods We conducted a retrospective observational cohort study of 312 patients with hematologic malignancies who underwent allogeneic HSCT between 2016 and 2024. Bone marrow B-cell proportion and peripheral blood lymphocyte subsets were assessed longitudinally by flow cytometry. EBV and CMV reactivation was monitored by quantitative PCR and analyzed as surveillance-defined reactivation status. Landmark-based logistic regression evaluated associations between immune-reconstitution parameters and viral reactivation; receiver operating characteristic analysis assessed model discrimination, and Cox regression evaluated overall survival determinants.Results CMV and EBV DNAemia/reactivation occurred in 42.0% and 31.4% of patients, respectively, and were significantly correlated (ρ = 0.191, p = 0.028). Higher bone marrow B-cell proportion at sixmonths was associated with lower odds of CMV DNAemia/reactivation (OR = 0.947, 95% CI: 0.901–0.995, p = 0.034). For EBV, an exploratory interaction between 12-month CD8⁺ T-cell recovery and chronic GVHD was associated with EBV DNAemia/reactivation status (p = 0.039). Lower NK-cell levels were observed in patients with EBV and CMV coinfection (p = 0.021 and p = 0.036, respectively). Overall survival was mainly associated with relapse (HR = 5.5, p0.001) and conditioning regimen, whereas viral reactivation was not significantly associated with survival.Discussion Intermediate immune-reconstitution landmarks showed distinct associations with surveillance-defined viral reactivation, particularly six-month B-cell proportion for CMV and CD8⁺ T-cell recovery in the context of chronic GVHD for EBV.Conclusion Longitudinal immune-reconstitution patterns may help characterize persistent post-HSCT immune vulnerability, although prospective studies incorporating viral timing and treatment-exposure data are needed for validation.