Humoral and Cellular Immunity for TBE Vaccination in Allogeneic HSCT Recipients

Patients undergoing allogeneic blood and marrow transplantation (HSCT) experience a prolonged period of dysfunctional immunity. Systematic reimmunization is necessary at appropriate time intervals following transplantation to re-establish immunity. Vaccination practices after HSCT remain varied and data sparse. Tick-borne encephalitis (TBE) is one of the most severe infections of the central nervous system caused by a tick-borne flavivirus. There is no specific treatment, and prevention with the vaccine is the only intervention available. To assess the efficacy of TBE vaccination in adult allogeneic HSCT recipients compared to an age-matched and sex-matched control group of healthy volunteers without previous TBE vaccination, a prospective open-label phase II pilot study on humoral and cellular immune responses after use of TBE vaccine (FSME Immun) will be performed. As primary end point the outcome of the neutralization test (NT) against TBE will be assessed in a total of 26 HSCT patients one year after HSCT and in 26 healthy volunteers, namely four weeks after the second vaccination. Therefore, the number of subjects with NT titres against TBE virus \>10, assumed to be the threshold for antibody-mediated protection will be evaluated. As secondary endpoints, antibody concentrations of TBE enzyme-linked immunosorbent assay before and four weeks after the second and third vaccination and antibody concentrations of NT against TBE four weeks after primary immunization. To evaluate cellular immune responses, lymphocyte proliferations assays and cytokine detection assays will be performed. In a subgroup analysis, these secondary endpoints will be compared between healthy volunteers, HSCT patients without immunosuppressive treatment and HSCT patients receiving immunosuppressive agents. Additionally, immune reconstitution by analysis of peripheral blood lymphocyte subsets and serum immunoglobulin levels will be evaluated prior to vaccination, after twelve weeks and prior t