Although the
prevalence of diarrhea due to V. cholerae O139 has recorded a decrease, efforts on vaccine development
continues to formulate an oral vaccine capable of stimulating the gut mucosal system. We have studied
the mucosal immunogenicity in Bangladeshi adults to a killed whole cell (WC) bivalent cholera vaccine
composed of V. cholerae O139 as well as V. cholerae O1 strains together with the recombinant cholera
toxin B subunit (CTB) (WC-O1/O139/CTB) and compared the immune responses to that obtained with the
licensed monovalent cholera vaccine, Dukoral (WC-O1/CTB). Direct estimation of the WC-O1/O139/CTB
vaccine-specific mucosal responses were carried out using lymphocytes isolated from duodenal biopsies,
intestinal lavage fluid and feces. The vaccine induced robust antibody-secreting cell responses in the
duodenum specific to CTB as well as the O1 and O139 lipopolysaccharide (LPS). Magnitude of response
was higher in the gut than in the circulation in all three antibody isotypes. The CTB and LPS-specific
mucosal antibody responses were also seen in intestinal lavage fluid and fecal extracts. Vibriocidal antibody
responses in plasma were observed to both the V. cholerae O1 and O139 serogroups (76% and 57%
response rates, respectively). Plasma IgA and IgG responses to CTB and IgA responses to both O1 and
O139 LPS were elevated. The immune responses were comparable to that seen to the monovalent WCO1/
CTB recipients in all components studied. Overall, the bivalent cholera vaccine induces strong mucosal
responses and the addition of the O139 component does not interfere with the responses to the licensed
vaccine Dukoral. This sets the ground for testing such vaccines in large field trials in Bangladesh and also
demonstrates that addition of other vibrio components to the existing cholera vaccine does not alter the
responses to the O1 vaccine components.