Antibody dynamics after tick-borne encephalitis and measles-mumps-rubella vaccination in children post early thymectomy

Objective: In a previously published prospective controlled cohort study, thymectomized children, who had thymectomy in early childhood due to open heart surgery, completed a three-dose immunization regimen in order to analyze the clinical impact of immunological alterations in thymectomized patients after exposure to a new antigen (tick-borne encephalitis virus (TBEV) vaccine). In the previous study, thymectomized children showed significantly lower TBEV IgG antibody levels after the second vaccination when compared to healthy age-matched controls, but a normal response after the third vaccination. Methods: The present study was aimed to analyze the TBEV-specific IgG antibody response 3 years after the third TBE vaccination in 22 thymectomized patients compared to 37 non-thymectomized healthy controls from the previously published cohort, to identify patients with waning antibody titers. Additionally, the serum samples were tested for measles, mumps and rubella IgG antibody concentrations after immunization with live-virus-attenuated vaccine administered post thymectomy. The TBEV-, measles- und rubella-specific IgG antibody avidity was analyzed by an adapted ELISA. Results: Although there was a great inter-individual variety in the TBEV-specific IgG concentrations, thymectomized patients showed equal levels compared to healthy controls. The humoral immune response to measles, mumps and rubella was normal in thymectomized patients. There was no difference in avidity maturation of TBEV-, measles- und rubella-specific IgG antibodies between patients and healthy controls. Conclusion: Despite a delayed primary humoral immune response to new vaccine antigens, thymectomized patients are able to produce and maintain an appropriate memory immune response to TBEV vaccine and live-virus-attenuated vaccines administered post thymectomy. These follow-up data underline the hypothesis of a normal memory function but a diminished primary humoral immune response to new antigens in thymectomized patients, which may also have an impact in later life with increased risk of morbidity or mortality due to infectious diseases with new pathogens.