Immunization of Female Mice with Glycoconjugates Protects Their Offspring Against Encapsulated Bacteria

The immune system of the newborn is immature, and therefore it is difficult to induce protective immunity by vaccination in the neonatal period. Immunization of mothers during pregnancy against infections caused by encapsulated bacteria could thus be particularly attractive, as infants do not respond to polysaccharide (PS) antigens. Transmission of maternal vaccine-specific antibodies and protection of offspring against pneumococcal bacteremia and/or lung infection were studied in a neonatal murine model of pneumococcal immunization and infections. Adult female mice were immunized with native pneumococcal PS (PPS) of serotypes 1, 6B, and 19F or PPS conjugated to tetanus protein (Pnc-TT), and PPS-specific antibodies were measured in sera of mothers and their offspring. Effective transmission of maternal antibodies was observed, as PPS-specific immunoglobulin G levels in 3-week-old offspring of immunized mothers were 37 to 322% of maternal titers, and a significant correlation between maternal and offspring antibody levels was observed. The PPS-specific antibodies persisted for several weeks but slowly decreased over time. Offspring of Pnc-TT-immunized mothers were protected against pneumococcal infections with homologous serotypes, whereas PPS immunization of mothers did not protect their offspring, in agreement with the low titer of maternal PPS specific antibodies. When adult female mice were immunized with a meningococcal serogroup C conjugate vaccine (MenC-CRM), antibody response and transmission were similar to those observed for pneumococcal antibodies. Importantly, bactericidal activity was demonstrated in offspring of MenC-CRM-immunized mothers. These results demonstrate that this murine model of pneumococcal immunization and infections is suitable to study maternal immunization strategies for protection of offspring against encapsulated bacteria.