Development of new vaccine strategies against Streptocarpus pneumoniae
2014-12-15T10:40:01Z (GMT) by
In this thesis I have shown that peptide mimotopes of both serotype 6B and 9V pneumococcal polysaccharide, following vaccination, can induce specific and anti-CPS antibodies and can protect mice against developing pneumococcal disease. This was achieved using previously described monoclonal antibodies (mAb) directed against the capsular polysaccharide of S. pneumoniae serotype 6B and 9V. These mAbs were shown to protect mice in passive immunisation experiments, and were then used to screen phage-displayed peptide libraries. In total four peptide mimics of serotype 9V pneumococcal polysaccharide and seven mimics of serotype 6B pneumococcal polysaccharide were identified. The peptides were conjugated to keyhole limpet haemocyanin (KLH) and were used to immunise mice. Two peptides, MP7 and MP13, were found significantly protect mice against a lethal challenge with S. pneumoniae and induce anti- capsule specific antibodies. This project showed that the poor immunogenicity of capsular polysaccharide could be improved using peptide mimics.;Secondly, this thesis confronts the problem of high vaccine production costs by developing a transgenic plant capable of manufacturing pneumococcal polysaccharide. The four genes involved in type 3 pneumococcal capsular polysaccharide synthesis are closely linked on the bacterial chromosome, arranged within a single locus (cassette). I cloned a copy of the serotype 3 capsule synthase gene, cps3S, into a plant expression vector, which was transformed into tobacco plants by Agrobacterium-mediated gene transfer. After cultivating a second generation of transgenic plants, we have shown the stable integration of the cps3S gene and production of type 3 pneumococcal polysaccharide. This discovery aims to confront the high vaccine production costs associated with pneumococcal vaccines.