Preparation, characterization, and immunogenicity of Haemophilus influenzae type b polysaccharide-protein conjugates.

Abstract

A method is presented for covalently bonding H. influenzae type b capsular polysaccharide (HIB Ps) to several proteins. The method is efficient and relies upon the use of adipic dihydrazide as a spacer between the capsular polysaccharide and the carrier protein. In contrast to the poor immunogenicity of the purified HIB Ps in mice and rabbits, the HIB Ps-protein conjugated induced serum anti-type b antibodies having bactericidal activity at levels shown to be protective in humans when low doses were injected s.c. in a saline solution. The antibody response in mice was related to the dose of the conjugates, increased with the number of injections and could be primed by the previous injection of the carrier protein. The HIB Ps-protein conjugates were immunogenic in 3 different mouse strains. The importance of the carrier molecule for the enhanced immunogenicity of the HIB Ps-protein conjugates was shown by the failure of HIB Ps hybrids prepared with the homologous polysaccharide or pneumococcus type 3 polysaccharide to induce antibodies in mice. Rabbits injected with the HIB Ps-protein conjugates emulsified in Freund''s adjuvant produced high levels of serum anti-type b antibodies which induced a bactericidal effect upon H. influenzae type b organisms. The HIB Ps component of the polysaccharide protein conjugates probably is converted to a thymic-dependent immunogen. This method may be used to prepare protein-polysaccharide conjugates with HIB Ps and other polysaccharides to be considered for human use.