Ectopic EBV infection in T cells following allogeneic hematopoietic stem cell transplantation: Clinical outcomes and immunological characterization

Abstract Background: Epstein-Barr virus (EBV) infection is a common complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT), with the potential to progress to life-threatening post-transplant lymphoproliferative disorder (PTLD). While EBV primarily targets B cells, emerging clinical evidence demonstrates its capacity for ectopic infection of T cells, which may lead to severe complications such as EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH) and chronic active EBV infection (CAEBV). In allo-HSCT setting, EBV infection of T cells has also been documented, however its clinical significance remains poorly understood, the relationship between T-cell tropic EBV infection and the development of EBV-PTLD is unclear, and the immunological profiles of affected patients have not been systematically characterized. Aims: This study aimed to: (1) evaluate the impact of EBV infection in T cells on post-allo-HSCT outcomes, and (2) delineate the immunological features associated with this high-risk subset of patients. Methods: A total of 147 allo-HSCT patients with EBV infection were enrolled. Lymphocyte subsets were isolated by flow cytometry, and EBV DNA levels were quantitatively assessed. Patients were stratified into two groups based on the infected cell type: T-cell infection group (n = 105) and non–T-cell infection group (n = 42). Clinical parameters—including peak EBV titer, duration of EBV persistence, PTLD development, and transplant outcomes—were compared. Multivariate Cox regression analysis was used to identify risk factors for T-cell infection. High-dimensional immunophenotyping using a 40-marker CyTOF panel was conducted on peripheral blood samples to evaluate differences in immune reconstitution between the two groups. Results: The median time to EBV reactivation was 52 days post-HSCT. Of the cohort, 92 patients (62.6%) developed PTLD, while 55 (37.4%) exhibited asymptomatic EBV DNAemia. The T-cell infection group showed a significantly higher cumulative incidence of PTLD compared to the non–T-cell infection group (69.5% vs. 45.2%, P = 0.010). However, there were no significant differences between the groups in 1-year overall survival (73.3% vs. 81.0%), non-relapse mortality (21.9% vs. 11.9%), incidence of acute graft-versus-host disease (aGVHD) (27.6% vs. 42.9%), or relapse rate (11.4% vs. 16.7%). Early post-transplant EBV DNAemia was identified as an independent risk factor for T-cell infection (P < 0.05). CyTOF analysis revealed markedly impaired interferon-γ (IFN-γ) production in both CD4⁺ and CD8⁺ T cells, indicating T-cell exhaustion in patients with T-cell EBV infection. Conclusion: EBV infection of T cells is associated with a significantly increased risk of PTLD and is characterized by functional exhaustion of T cells. Early EBV reactivation serves as a predictive marker for this high-risk subset, underscoring the need for refined monitoring strategies and targeted immunotherapeutic interventions.