Increment of recombinant hepatitis B surface antigen-specific T-cell precursors after revaccination of slow responder children.

The aim of the study was to investigate the in vitro T-cell response to recombinant hepatitis B (rHBsAg) in a group of children (defined as "slow responders") vaccinated at birth, presenting antibody levels < 10 mIU/ml after the vaccination schedule, and developing anti-rHBs antibodies after revaccination. T-cell mediated immune response towards rHBsAg was evaluated in 35 healthy children in "bulk" culture experiments (19 responders and 16 slow responders) and by limiting dilution analysis (nine responders and five slow responders) to quantify the frequency of proliferating T lymphocyte-precursors (PTL-p). Before the booster dose, lymphocytes from slow responder children failed to proliferate to rHBsAg, while a normal proliferation was observed in all responders. A statistically significant difference in rHBsAg-specific PTLp frequencies was observed between the two groups. Among the slow responder group, a significant increase of PTLp was observed after the supplementary vaccine dose.Nevertheless, PTLp frequencies remained significantly lower than those measured in responders. These results suggest a role for follow-up of slow responder children over time, in order to perform booster vaccination when inadequate anti-HBs titre is present.