A Novel, Multiple-Antigen Pneumococcal Vaccine Protects against Lethal Streptococcus pneumoniae Challenge

Current vaccination against Streptococcus pneumoniae uses vaccines based on capsular polysaccharides from selected serotypes, and has led to non-vaccine serotype replacement disease. We have investigated an alternative serotype-independent approach, using multiple-antigen vaccines (MAV) prepared from S. pneumoniae TIGR4 lysates enriched for surface proteins by a chromatography step after culture under conditions that induce expression of heat shock proteins (Hsp, thought to be immune adjuvants). Proteomics and immunoblots demonstrated that compared to standard bacterial lysates, MAV was enriched with Hsps and contained several recognised protective protein antigens, including pneumococcal surface protein A (PspA) and pneumolysin (Ply). Vaccination of rodents with MAV induced robust antibody responses to multiple serotypes, including non-pneumococcal conjugate vaccine serotypes. Homologous and heterologous strains of S. pneumoniae were opsonised after incubation in sera from vaccinated rodents. In mouse models, active vaccination with MAV significantly protected against pneumonia, whilst passive transfer of rabbit serum from MAV vaccinated rabbits significantly protected against sepsis caused by both homologous and heterologous S. pneumoniae strains. Direct comparison of MAV preparations made with or without the heat-shock step showed no clear differences in protein antigen content and antigenicity, suggesting that the chromatography step rather than Hsp induction improved MAV antigenicity. Overall, these data suggest that the MAV approach may provide serotype-independent protection against S. pneumoniae .