effect of physicochemical modification on the immunogenicity of haemophilus influenzae type b oligosaccharidecrm197 conjugate vaccines haemophilus influenzae type b hib polyribosylribityl phosphate prp oligosaccharidecrm197 conjugate vaccines from two different manufacturers hib a and hib b were subjected to adverse storage conditions and used to establish correlates between physicochemical characteristics and immunogenicity there were manufacturerspecific differences in the effect of freezing or freezethawing on the carrier protein conformation and the anticrm197 or antiprp igg response in rabbits whereas both conjugates showed similar stability when stored at elevated temperatures both oligosaccharidecrm197 conjugate vaccines formed apparent aggregates of nonspecifically associated higher molecular weight material when subjected to elevated temperatures or repeated freezethawing following subcutaneous injection of samples into cba mice and new zealand white rabbits the amount of igg raised against crm197 was significantly lower for samples incubated at 37 or 55 degrees c compared with those kept at 4 degrees c consistent with the less wellfolded 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 th cell epitopes which are unaffected by conformational changes