Development of cellular immune response after infant pneumococcal conjugate vaccinations.

Prevenar®, a seven-valent pneumococcal conjugate vaccine has been registered for use in a so-called 3+1 vaccination schedule consisting of a three dose primary series followed by a booster vaccination. It has been introduced in the Dutch National Immunization Program in April 2006 for vaccination at 2, 3, 4 and 11 months of age.

Prevenar vaccination provides immediate protection against pneumoccocal related diseases through the induction of functional antibodies, which however only have a short half-life indicating the need for a memory response. Both the induction and maintenance of functional serum antibody titres have a cellular basis which is still poorly understood.

In general, antigens trigger naïve B-cells to expand and differentiate into two types of affinity matured B-cells: antibody secreting plasma B cells and memory B-cells. Since plasma cells are unlikely to persist for more than 6-8 weeks (Gourley TS et al, 2004) maintenance of steady state antibody levels over periods of years requires a continuous low level of differentiation of memory B cells into plasma cells. Factors such as recurrent antigen exposure for example through carriage might be involved in this process.
Prevenar is thought to induce immediate protection through stimulation of antibody production by polysaccharide specific plasma B cells, sustained protection is conferred by a memory B cell pool which induces an accelerated increase in antibody titres during secondary immune responses seen after re-infection or boosting.
An improved understanding of the immunobiology of the B-cell response to conjugate vaccines, such as Prevenar, is essential to develop immunization strategies that provide sustained protection.

Prevenar® is thought to induce immediate protection through stimulation of antibody production by polysaccharide specific plasma B cells, sustained protection is conferred by a memory B cell pool which induces an accelerated increase in antibody titres during secondary immune responses seen after re-infection or boosting.

- inclusion: 6 months

- evaluation: 3 months

4 groups of children, in all groups the children will have 1 blood collection. The children in group 4 (n=25) receive a challenge vaccination of Prevenar® at 24 months of age.