Humoral immune response to tick-borne encephalitis vaccination in allogeneic blood and marrow graft recipients.

The aim of this prospective study was to characterize the humoral immune response to TBE vaccination after hematopoietic stem cell transplantation (HSCT). Nineteen adult patients 11-13 months after HSCT and 15 age-matched immunocompetent adults received up to three TBE vaccinations. Antibodies against TBE virus were measured by neutralization test (NT). As primary endpoint, the antibody response (NT titer of ≥10 and at least a twofold increase from baseline 4 weeks after second vaccination) was compared between patients and controls using Fisher exact test. Prior vaccination, 15 (79%) HSCT patients still had detectable neutralizing antibodies. At primary endpoint, the antibody response was significantly lower in patients than in controls (35% versus 93%; p < 0.001). The CD4+ cell count was a predictor for an antibody response in patients (p = 0.019). Interestingly, the majority of HSCT patients still had detectable antibodies prior vaccination. Following vaccination, antibody response in HSCT patients was associated with the CD4+ cell count.