Immunogenicity of conjugate vaccines consisting of pneumococcal capsular polysaccharide types 6B, 14, 19F, and 23F and a meningococcal outer membrane protein complex.

In an effort to prepare pneumococcal (Pn) capsular polysaccharide (Ps) vaccines that would be immunogenic in infants, covalent conjugates were prepared for Pn types 6B, 14, 19F, and 23F. Each Ps type was covalently bound to an outer membrane protein complex from Neisseria meningitidis serogroup B and evaluated for immunogenicity in mice and infant monkeys. The conjugates induced specific anti-Ps antibody responses in mice and in infant rhesus and African green monkeys; a conjugate of 6B and outer membrane protein complex was immunogenic at Ps doses as low as 20 ng. Although low levels of the Pn group-common cell wall polysaccharide were present in all type-specific Ps preparations, anti-cell wall polysaccharide responses induced by covalent conjugates were < 1% of the total anti-Ps response after two doses of vaccine. In contrast, the anti-cell wall polysaccharide response of a noncovalent conjugate represented 41% of the anti-Ps response after two doses. Relative T-cell dependence, a requirement for the human target population of infants less than 18 months old, was demonstrated for all four Pn Ps conjugates in an athymic mouse model. Therefore, these Pn Ps-outer membrane protein complex conjugate vaccines are excellent candidates for evaluation in human infants.