Protection against influenza virus infection by a two-dose regimen of nasal vaccination using vaccines combined with cholera toxin B subunit

Abstract

The effectiveness of the two-dose regimen, composed of a primary intranasal inoculation of influenza A-type virus HA vaccine together with B subunit of cholera toxin (CTB) and the subsequent intranasal inoculation of vaccine alone 4 weeks later, was examined. In mice given a relatively high dose of virus A/PR/8/34 (PR-8, H1N1) HA vaccine (1.5 μg) both as a primary antigen with CTB (1 μg) and as the second antigen, the secondary responses of both antiviral IgA antibodies in nasal wash and haemagglutination-inhibiting (HI) antibody in serum were much higher than those of primary responses and persisted for > 12 weeks after the second inoculation. Even in mice that received reduced amounts of a primary vaccine (0.03 μg) [prepared from virus PR-8, A/Yamagata/120/86 (H1N1) or A/Fukuoka/C29/85 (H3N2) together with reduced amounts of CTB (0.05 μg), the subsequent inoculation of PR-8 vaccine produced both nasal IgA and serum HI antibodies and provided complete protection against homologous A-type virus (PR-8) infection. Moreover, the combination of the reduced amounts of heterologous A-type virus vaccine (A/Yamagata or A/Fukuoka) with CTB for primary inoculation and the secondary heterologous A-type virus vaccine [A/Yamagata, A/Kumamoto/37/79 (H1N1), or A/Fukuoka] resulted in high levels of cross-reactive IgA antibodies and partial cross-protection against PR-8 infection. On the other hand, a second inoculation of B/Ibaraki/2/85 vaccine failed to produce cross-reactive antibodies and to protect against PR-8 infection. These results suggest that a two-dose regimen using A-type virus vaccines together with a small dose of CTB can provide not only complete protection against homologous virus infection, but also partial cross-protection against heterologous A-type virus infection, in parallel with high persistent levels of cross-reactive IgA antibodies.