Antibody responses in serum and lung to intranasal immunization with Haemophilus influenzae type b polysaccharide conjugated to cholera toxin B subunit and tetanus toxoid

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Abstract
Aim: Cholera toxin B subunit (CTB) has previously been used as a mucosal carrier for various vaccine candidate antigens. The objective of this study was to see if coupling a bacterial polysaccharide, Haemophilus influenzae type b capsular polysaccharide (HibCPS), to CTB, either directly or through prior coupling to tetanus toxoid (TT), would improve the immunogenicity of HibCPS after nasal immunization. Methods: HibCPS was conjugated to CTB, TT or via TT to CTB, using glutaraldehyde or 1-ethyl-3(3-dimethylaminopropyl)-carbodiimide (EDAC) and N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP). The conjugates were characterized and used for intranasal (IN) and subcutaneous (SC) immunizations of mice. The anti-Hib, -TT and -CTB antibody titers in serum and lungs after the immunizations were measured with ELISA. Results: The HibCTB was poorly immunogenic both given IN and SC compared with HibTT and HibTTCTB, probably because of inefficient coupling. In contrast, the conjugation of CTB to the HibTT conjugate resulted in a preparation which was superior both to the HibTT and the HibCTB conjugates in inducing local IgA and IgG anti-HibCPS antibodies in the lungs. The anti-HibCPS serum IgG titers after IN immunization with the HibTTCTB conjugate were similar to the titers after IN immunization with HibTT, or SC immunization with a commercial HibCRM conjugate vaccine. In contrast to the other conjugates, the HibTTCTB conjugate also gave rise to anti-Hib serum IgA titers. Conclusion: We conclude that appropriate conjugation to CTB increases the mucosal immunogenicity of HibCPS, and that intranasal immunization with such a conjugate can give rise to both local and systemic anti-HibCPS antibody responses.