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Category: Bacterial Pathogenesis; Immunology
Conjugation Chemistry, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815820/9781555814083_Chap11-1.gif /docserver/preview/fulltext/10.1128/9781555815820/9781555814083_Chap11-2.gifAbstract:
Most bacteria that cause invasive disease, especially those that cause bacteremia, are protected from innate host immunity because they express polysaccharides (PSs) on their cell surfaces. The bacterial capsular PSs are composed of thousands of carbohydrate repeat units resulting in polydisperse polymers that can have molecular masses into the millions of daltons. Multivalent pneumococcal conjugate vaccines present additional complexities with regard to their syntheses, as each serotype is chemically distinct, effectively requiring the optimization of the manufacture of seven or more individual vaccines. Various proteins and peptide molecules have been demonstrated, in preclinical studies, to be effective carriers for PSs and oligosaccharides, but only a small number of protein carriers have been investigated in humans. Surface-exposed proteins and toxins from human pathogenic bacteria have been used as carriers, as they contain one or more of the T-cell epitopes. In order to convert PSs into T-cell-dependent antigens, the protein must be chemically linked to the carbohydrate; that is, there must be covalent links between the two components. Protein solubility at the required pH, concentration, and temperature is an important determinant of the suitability of a protein for use in a particular conjugation scheme. The conjugation step is generally the slowest chemical step and risks damage to the components. Efforts should be made to improve conjugation efficiencies to levels at which the residual unconjugated components, especially free PSs, do not interfere with inductions of protective immune responses. The use of efficient, mild conjugation chemistry would allow for higher yields of vaccine.
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General overview of the protein (Pr)-PS conjugation process.
Reaction schemes for reductive amination (A) and cyanylation (B) using CDAP. Prot, protein.
Comparison of conjugation methods that have been used for PCV