CHARACTERIZATION OF CARBOHYDRATE BASED VACCINES Variables influencing the immunogenicity and physicochemical properties of glycoconjugate vaccinesMany aspects can influence the immunogenicity of conjugate vaccines and the main variables investigated so far are the size of the saccharide moiety, the saccharide:protein ratio in the purified conjugate, the conjugation strategy, the nature of the spacer and the protein carrier. The size of the saccharide moiety and saccharide/protein ratio were investigated in different works such as Seppälä and Mäkelä in one of the first studies on the effect of size and chemistry on the immunogenicity of dextrans-protein conjugates found that dextrans of low molecular weight conjugated to chicken serum albumin, induced strong anti-dextran responses in mice, while increasing the dextrans' size resulted in reduced immunogenicity.47 Peeters et al. showed that a synthetic tetramer of Hib capsular polysaccharide repeating unit, conjugated to a protein carrier, induced in adult mice and non-human primates antibody levels comparable to a commercial Hib conjugate and higher than those induced by a trimer, indicating that for Hib a minimum of eight sugars is needed for a proper immunological response.48 Laferriere et al. found little influence of the carbohydrate chain length on the immunogenicity of pneumococcal conjugate vaccines in mice.49 Pozsgay et al. studied the immunogenicity in mice of synthetic Shigella dysenteriae type 1 LPS oligosaccharides conjugated to human serum albumin (HSA). The authors found that octa-, dodeca-, and hexadecasaccharide fragments induced high levels of lipopolysaccharide binding IgG antibodies in mice after three injections and were superior to a tetrasaccharide conjugate. The influence of the carbohydrate/protein ratio was different for the three conjugates. The octasaccharide-HSA conjugate with the highest density evoked a good immune response, while in the case of dodeca- and hexadecasaccharide conjugates, the median density was optimal.50 These studies suggest that oligosaccharide chain length and hapten loading might be interconnected in determining the immunogenicity of glycoconjugate vaccines. The spacer is a short linear molecule that is generally linked to the polysaccharide chain or to the protein or to both moieties, depending on the chemistry, used to facilitate the coupling between the protein and sugar. There are evidences in the literature which suggest that rigid, constrained spacers like cyclohexyl maleimide, elicit a significant amount of undesirable antibodies, with the risk of driving the immune response away from the targeted epitope on the hapten.51 52 The use of a flexible alkyl type maleimido spacer has been reported as a way to overcome the previous observed immunogenicity of cyclic maleimide linkers.53 A number of protein carriers have been used so far in preclinical and clinical evaluation of conjugate vaccines. 54 55 56 57 58 59 60Proteins such as diphtheria and tetanus toxoids, which derive from the respective toxins after chemical detoxification with formaldehyde, were initially selected as carrier because of the safety track record accumulated with tetanus and diphtheria vaccination. CRM197, a non-toxic mutant of diphtheria toxin61 which instead does not need chemical detoxification, has been extensively used as carrier for licensed Hib, pneumococcal, meningococcal conjugate vaccines and for other vaccines being developed. An outer membrane protein complex of serogroup B meningococcus has been used by Merck as carrier for their Hib conjugate vaccine.62 GSK in their multivalent pneumococcal conjugate vaccine introduced the use of the Hib-related protein D as carrier for most of the polysaccharides included into the vaccine.63 64 The team of John Robbins made extensive use of the recombinant non toxic form of Pseudomonas aeruginosa exo-toxin as carrier for Staphylococcus aureus type 5 and 8 as well as for Salmonella
| Identifer | oai:union.ndltd.org:CCSD/oai:tel.archives-ouvertes.fr:tel-00825838 |
| Date | 26 October 2012 |
| Creators | Tontini, Marta |
| Publisher | Université de Cergy Pontoise |
| Source Sets | CCSD theses-EN-ligne, France |
| Language | English |
| Detected Language | English |
| Type | PhD thesis |
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