Person:

Eckhoff, Grace

Background: Protective immunity against cholera is serogroup specific. Serogroup specificity in Vibrio cholerae is determined by the O-specific polysaccharide (OSP) of lipopolysaccharide (LPS). Generally, polysaccharides are poorly immunogenic, especially in young children. Methodology Here we report the evaluation in mice of a conjugate vaccine for cholera (OSP:TThc) made from V. cholerae O1 Ogawa O-Specific Polysaccharide–core (OSP) and recombinant tetanus toxoid heavy chain fragment (TThc). We immunized mice intramuscularly on days 0, 21, and 42 with OSP:TThc or OSP only, with or without dmLT, a non-toxigenic immunoadjuvant derived from heat labile toxin of Escherichia coli. Principal Findings We detected significant serum IgG antibody responses targeting OSP following a single immunization in mice receiving OSP:TThc with or without adjuvant. Anti-LPS IgG responses were detected following a second immunization in these cohorts. No anti-OSP or anti-LPS IgG responses were detected at any time in animals receiving un-conjugated OSP with or without immunoadjuvant, and in animals receiving immunoadjuvant alone. Responses were highest following immunization with adjuvant. Serum anti-OSP IgM responses were detected in mice receiving OSP:TThc with or without immunoadjuvant, and in mice receiving unconjugated OSP. Serum anti-LPS IgM and vibriocidal responses were detected in all vaccine cohorts except in mice receiving immunoadjuvant alone. No significant IgA anti-OSP or anti-LPS responses developed in any group. Administration of OSP:TThc and adjuvant also induced memory B cell responses targeting OSP and resulted in 95% protective efficacy in a mouse lethality cholera challenge model. Conclusion: We describe a protectively immunogenic cholera conjugate in mice. Development of a cholera conjugate vaccine could assist in inducing long-term protective immunity, especially in young children who respond poorly to polysaccharide antigens.

Vibrio cholerae is a non-invasive Gram-negative enteric pathogen that causes cholera, a severe dehydrating diarrheal illness of humans. Cholera is responsible for substantial morbidity and mortality in both endemic and epidemic settings. Current oral killed vaccines do not provide protection that lasts as long as natural cholera infection, and current cholera vaccines have greatly reduced efficacy in children, the population most affected by cholera in endemic areas. Protection against cholera appears to be mediated by immune responses that target the O-specific polysaccharide (OSP) of V. cholerae. Here we report analysis of the immunogenicity and protective efficacy in mice of a cholera conjugate vaccine containing V. cholerae O1 Inaba OSP conjugated to a recombinant immunogenic fragment of tetanus toxoid heavy chain (rTTHc). OSP-rTTHc induced prominent anti-OSP responses in these animals. Serum from vaccinated mice also provide protection in the infant mouse model of cholera infection. Our results suggest that a cholera conjugate might have development potential for evaluation in humans.