Longitudinal study of viral loads and polyfunctional T cell responses towards epstein-barr virus in paediatric liver transplant recipients who developed post-transplant lymphoproliferative disorder

Abstract

This study aims to investigate the long-term viral control and T-cell immunity towards Epstein-Barr virus (EBV) in paediatric liver transplant patients who developed posttransplant lymphoproliferative disorder (PTLD). We performed a longitudinal study on viral loads and T cell functions in six PTLD patients (two boys and four girls) up to 5 years after diagnosis. Median age at diagnosis was 2.4 years (range: 0.8-5.2 years). Primary disease was congenital biliary atresia with a median age of transplantation at 0.6 years (range: 0.5-1.3 years). Median time from date of transplantation to diagnosis of PTLD was 1.3 years (range: 0.3-4.7 years). All patients were seronegative towards EBV prior to transplantation and were maintained on a range of tacrolimus doses for immunosuppression. Three patients entered continual clinical remission after one course of rituximab while two patients had relapsed disease and one had persistent lymphocytosis requiring additional treatment with second course of rituximab or chemotherapy to enter clinical remission. Plasma EBV loads were determined by qPCR. Despite entering clinical remission, persistently elevated plasma loads were found in 4 of 6 patients indicating suboptimal long-term viral control. Two patients were selected for longitudinal profiling of EBV latent cycle and lytic cycle antigen-specific polyfunctional T-cell (PFC) responses from 1-4 years after PTLD diagnosis. Upon stimulation by overlapping peptides of EBNA1, EBNA3a/ 3b/3c and BZLF1, the production of three cytokines (IFN-, TNF-, IL-2) and expression of two cytotoxic markers (perforin, CD107a) were examined. Although CD4+ and CD8+ PFC responses could be detected at 3 years after diagnosis, the PFCs were predominantly perforinnegative and the proportion of PFCs with three-five functions was low ranging from 0-3 percent of total antigen-responsive T-cells. Long-term viral control is suboptimal concurrent with slow development of EBV-specific PFC responses signifying the continual risk of re-emergence of PTLD in this cohort of young PTLD patients.