Cellular and humoral immune responses to a tetanus toxoid booster in perinatally HIV-1-infected children and adolescents receiving highly active antiretroviral therapy (HAART)

Background: Human immunodeficiency virus type 1 (HIV-1) infected children treated with highly active antiretroviral therapy (HAART) may develop a significant reduction of plasma viremia associated with an increase in CD4+ T-cell counts. Functional capacity of this reconstituted immune system in response to recall antigens is important to maintain protective immunity to vaccine-preventable diseases. We therefore determined cellular and humoral immune responses to tetanus toxoid (TT) booster in perinatally HIV-1-infected children and adolescents receiving HAART. Methods: Immune responses were prospectively evaluated pre- and post-tetanus booster using lymphocyte proliferation assay (LPA) stimulation index (SI≥3.0) and tetanus antibody (TAb≥0.15) in 15 patients. The median interval from primary tetanus immunization series was 6 years (range 2-12 years). We compared patients by their virological response to HAART (complete responders, CR, n=7; incomplete responders, ICR, n=8). Results: There were no significant differences in median age 12.6 years (CR: 12.9; ICR: 10.6) or median CD4 T-cell pre-booster (CR: 35%/819; ICR: 26%/429) between groups. Tetanus LPA responses were observed in one patient prior to booster and in seven patients post-booster. In contrast, 38% of patients had protective TAb pre-booster, but 92% developed protective TAb post-booster. All of the CR and 5/6 ICR patients developed protective TAb. Conclusions: HIV-1-infected children and adolescents had modest LPA responses to tetanus following booster, similar to HIV-1-infected adults. However, the majority of patients developed protective TAb levels after booster and maintained the response. Shorter intervals may need to be considered for TT immunization boosters in HIV-1-infected pediatric patients, as only 38% had protective TAb at baseline.