Sublingual immunization with adenovirus F protein-based vaccines stimulates protective immunity against botulinum...

Sublingual (s.l.) vaccination is an efficient way to induce elevated levels of systemic and mucosal immune responses. To mediate mucosal uptake, ovalbumin (OVA) was genetically fused to adenovirus 2 fiber protein (OVA-Ad2F) to assess whether s.l. immunization was as effective as an alternative route of vaccination. Ad2F-delivered vaccines were efficiently taken up by dendritic cells and migrated mostly to submaxillary gland lymph nodes, which could readily stimulate OVA-specific CD4(+) T cells. OVA-Ad2F + cholera toxin (CT)-immunized mice elicited significantly higher OVA-specific serum IgG, IgA and mucosal IgA antibodies among the tested immunization groups. These were supported by elevated OVA-specific IgG and IgA antibody-forming cells. A mixed T(h)-cell response was induced as evident by the enhanced IL-4, IL-10, IFN-γ and TNF-α-specific cytokine-forming cells. To assess whether this approach can stimulate neutralizing antibodies, immunizations were performed with the protein encumbering the β-trefoil domain of C-terminus heavy chain (Hcβtre) from botulinum neurotoxin A (BoNT/A) as well as when fused to Ad2F. Hcβtre-Ad2F + CT-dosed mice showed the greatest serum IgG, IgA and mucosal IgA titers among the immunization groups. Hcβtre-Ad2F alone also induced elevated antibody production in contrast to Hcβtre alone. Plasma from Hcβtre + CT- and Hcβtre-Ad2F + CT-immunized groups neutralized BoNT/A and protected mice from BoNT/A intoxication. Most importantly, Hcβtre-Ad2F + CT-immunized mice were protected from BoNT/A intoxication relative to Hcβtre + CT-immunized mice, which only showed ∼60% protection. This study shows that s.l. immunization with Ad2F-based vaccines is effective in conferring protective immunity.