Ectopic Epstein-Barr virus infection in T cells identifies reduced therapeutic responsiveness and immune dysfunction after allogeneic haematopoietic stem cell transplantation.

OBJECTIVES

Epstein-Barr virus (EBV) reactivation after allogeneic haematopoietic stem cell transplantation (allo-HSCT) is typically monitored by plasma viral load, but this fails to capture cellular reservoirs. Lineage-specific testing, although usually performed in high-risk patients, may identify biologically distinct disease states. We aimed to evaluate the clinical and biological significance of lineage-specific EBV quantification especially ectopic EBV infection in T cells in allo-HSCT recipients with EBV reactivation.

METHODS

We analysed 144 allo-HSCT recipients with EBV reactivation who underwent lineage-specific EBV quantification, assessed whether T-cell tropic EBV burden identifies a phenotype with reduced responsiveness to rituximab therapy, an increased risk of posttransplant lymphoproliferative disorder (PTLD), and specific features of underlying immune dysfunction.

RESULTS

Among the tested high-risk patients with high EBV loads and clinical symptoms, 66.6% exhibited T-cell tropic EBV infection. Compared with non-T-cell tropic infection, T-cell tropism was associated with higher rituximab courses and lower complete response rates (67% vs. 81%, p 0.029), suggesting insufficient efficacy of CD20-directed therapy. Patients with T-cell tropic infection had a significantly higher 1-year cumulative incidence of PTLD compared with the non-T-cell tropic group (77% vs. 41.6%; p <0.001). Single-cell RNA sequencing and mass cytometry analyses revealed an exhausted T-cell phenotype with diminished stemness in T-cell tropic EBV-infected patients.

CONCLUSIONS

These findings suggest that T-cell EBV quantification distinguishes a therapeutically challenging subtype of EBV reactivation characterized by immune dysfunction and reduced responsiveness to rituximab-based therapy. Incorporating assessment of cellular viral reservoirs into posttransplant EBV monitoring strategies may facilitate early risk stratification and support timely therapeutic escalation beyond rituximab alone.