Preparation, immunogenicity, and protective efficacy, in a murine model, of a conjugate vaccine composed of the polysaccharide moiety of the lipopolysaccharide of Vibrio cholerae O139 bound to tetanus toxoid

The epidemic and pandemic potential of Vibrio cholerae O139 is such that a vaccine against this newly emerged serogroup of V. cholerae is required. ii conjugate made of the polysaccharide moiety (O-specific polysaccharide plu s core) of the lipopolysaccharide (LPS) of V. cholerae O139 (pmLPS) was pre pared by derivatization of the pmLPS with adipic acid dihydrazide and coupl ing to tetanus toxoid (TT) by carbodiimide-mediated condensation. The immun ologic properties of the conjugate were tested using BALB/c mice injected s ubcutaneously three times at weeks interval and then a fourth time weeks la ter, Mice were bled 7 days after each injection and then once each month fo r the following 6 months, LPS and TT antibody levels were determined by enz yme-linked immunosorbent assay using immunoplates coated with either O139 L PS or TT, Both pmLPS and pmLPS-TT conjugate elicited low levels of immunogl obulin M (IgM), peaking 5 weeks after the first immunization. The conjugate elicited high levels of IgG antibodies, peaking 3 months after the first i mmunization and declining slowly during the following 5 months, TT alone, o r as a component of conjugate, induced mostly IgG antibodies, Antibodies el icited by the conjugate recognized both capsular polysaccharide and LPS fro m V. cholerae O139 and were vibriocidal. They were also protective in the n eonatal mouse model of cholera infection. The conjugation of the O139 pmLPS , therefore, enhanced its immunogenicity and conferred T-dependent properti es to this polysaccharide.