Qualitative and Quantitative Immune Response to Bacterial Capsular Polysaccharides and Their Conjugates in Mouse and Man

Capsular polysaccharides (CP), antigens present on the surfaces of Gram-negative and Gram-positive bacteria that cause invasive diseases, serve as bacterial virulence factors and protective antigens. Capsules have been shown to interfere with antibody binding and complement-mediated phagocytosis. In contrast, non-encapsulated bacteria activate complement and are rapidly cleared from the blood without the need for specific antibodies [28]. CP vaccines against several different bacterial pathogens have been successfully developed and are being used in sub-groups of the population who are at risk for infection [27]. Currently, several different CP conjugate vaccines are in development and clinical evaluation for active immunization and for the generation of antibodies for passive immunization. Development of these vaccines has involved the use of different conjugation methodologies and different carrier proteins. Further development of these vaccines will eventually result in the expansion of vaccination programs to include larger populations and the use of multivalent combined vaccines requiring a multiple injection vaccination regimen. In this paper, an overview of CP vaccines will be presented, as will a discussion of the issues that may arise as a result of the development of new vaccines. Possible strategies to resolve such issues will also be discussed.