Effect of physico-chemical modification on the immunogenicity of Haemophilus influenzae type b...

Haemophilus influenzae type b (Hib) poly-ribosyl-ribityl phosphate (PRP) oligosaccharide-CRM(197) conjugate vaccines from two different manufacturers (Hib A and Hib B) were subjected to adverse storage conditions and used to establish correlates between physico-chemical characteristics and immunogenicity. There were manufacturer-specific differences in the effect of freezing or freeze-thawing on the carrier protein conformation and the anti-CRM(197) or anti-PRP IgG response in rabbits whereas both conjugates showed similar stability when stored at elevated temperatures. Both oligosaccharide-CRM(197) conjugate vaccines formed apparent 'aggregates' of non-specifically associated higher molecular weight material when subjected to elevated temperatures or repeated freeze-thawing. Following subcutaneous injection of samples into CBA mice and New Zealand White rabbits, the amount of IgG raised against CRM(197) was significantly lower for samples incubated at 37 or 55 degrees C compared with those kept at 4 degrees C, consistent with the less well-folded conformation of the carrier protein observed at elevated temperatures. Moreover, there was a parallel reduction in the amount of IgG raised against PRP and the level of bactericidal antibodies induced by vaccines A and B stored at 55 degrees C consistent with the observed depolymerisation of the oligosaccharide chains. Carrier protein conformational changes resulting from storage under adverse conditions did not affect the immunogenicity to Hib PRP in laboratory animals unless associated with loss of bound saccharide presumably because the carrier protein retains continuous T(H) cell epitopes which are unaffected by conformational changes.