Studies on the development of mucosal vaccine adjuvant

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Cholera toxin B subunit (CTB) or Escherichia coli heat-labile toxin (LTB) (2mug) , each supplemented with a trace amount of the holotoxin (0.02-20ng) , were examined for the adjuvant effect on antibody responses against influenza inactivated vaccine in BALB/c mice.Each mouse received a primary intranasal (i.n.) inoculation with the vaccine (1.5mug) , prepared from PR8 (H1N1) virus, together with the toxin-containing B subunit and in 4 weeks a second i.n.inoculation of the vaccine alone.The inoculation of the vaccine with the toxin-containing the B subunit induced significantly high primary and secondary anti-HA lgA and lgG Ab responses in the nasal wash and serum, while the vaccine with the B subunit or less than 2 ng of the toxin induced little response.The synergistic adjuvant effect was maximal in the concentration of the B subunit supplemented with 0.2-2 ng of the toxin.Under these conditions, the augmented lgA and lgG Ab responses, which are cross-protective to PR8 HA molecules provided complete cross-protection against PR8 virus challenge in mice immunized with heterologous vaccines within the same subtype.These results suggest that CTB or LTB containing a trace amount of CT or LT can be used as a potent adjuvant for nasal vaccination of human against influenza.