*Purpose: After transplantation immunosuppressive therapy causes an impaired cellular immune response resulting in an increased risk of EBV-associated complications, e.g. post-transplant lymphoproliferative disease (PTLD). Prognostic markers for the outcome of EBV-infections and reactivations are missing. Controlling virus replication, EBV-specific T cells (EBV-Tvis) may serve as a predictive marker to decide on the necessity of therapeutic interventions.

*Methods: EBV-CD4 Tvis were monitored in 53 pediatric kidney recipients with EBV-IgG-positivity at time of transplantation or with EBV-seroconversion after transplantation. After in vitro stimulation with EBV-antigens EBV-CD4 Tvis were analysed by cytokine flow cytometry. EBV-DNA in blood was measured by PCR.

*Results: Within our pediatric study group 34 patients were EBV-IgG-positive at time of kidney transplantation and 19 patients developed a primary EBV-infection with seroconversion after transplantation. Post-transplant EBV-viremia was found in 37 children (20 with EBV-seropositivity at transplantation and 17 with EBV-seroconversion after transplantation). The majority of EBV-IgG-positive children showed -at least temporarily- EBV-CD4 Tvis. In case of asymptomatic primary infections or reactivations with self-limiting EBV-viremia high levels of EBV-CD4 Tvis were found. In contrast, symptomatic EBV-infections or reactivations were characterized by absence or very low levels of EBV-CD4 Tvis combined with long-term viremia and high EBV-DNA load. After start of antiviral therapy and / or reduction of immunosuppression EBV-CD4 Tvis secondarily increased simultaneously with decrease of EBV-DNA in blood. One patient, suffering from PTLD, did not show any significant detection of EBV-CD4 Tvis.

*Conclusions: After pediatric kidney transplantation sufficient levels of EBV-CD4 Tvis are associated with asymptomatic, self-limiting viremia, whereas low EBV-CD4 Tvis are found in case of long-term viremia and symptomatic EBV-infections / reactivations. Serving as a diagnostic marker for the individual EBV-specific immune response, monitoring of EBV-CD4 Tvis may identify patients at risk of EBV-associated complications (e.g. PTLD) and thereby improve post-transplant management by preemptive therapeutic interventions as adaption of immunosuppression or antiviral therapy.

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