Abstract
Nontypeable Haemophilus influenzae (NTHi) causes respiratory infections that lead to high morbidity and mortality worldwide, encouraging development of effective vaccines. To achieve a protective impact on nasopharyngeal (NP) colonization by NTHi, enhanced immunogenicity beyond that achievable with recombinant-protein antigens is likely to be necessary. Adding a lipid moiety to a recombinant protein would enhance immunogenicity through Toll-like receptor 2 signaling of antigen-presenting cells and Th17 cell response in the nasal-associated lymphoid tissue (NALT). We investigated effects of lipidation (L) of recombinant proteins P6 and OMP26 compared to nonlipidated (NL) P6 and OMP26 and as fusion constructs (L-OMP26ϕNL-P6 and L-P6ϕNL-OMP26) in a mouse model. After intraperitoneal or intranasal vaccination, antibody responses were compared and protection from NP colonization and middle ear infection were assessed. L-P6 and L-OMP26 induced approximately 10- to 100-fold-higher IgG antibody levels than NL-P6 and NL-OMP26. Fusion constructs significantly increased IgG antibody to both target proteins, even though only one of the proteins was lipidated. NP colonization and middle ear bullae NTHi density was 1 to 4 logs lower following vaccination with L-P6 and L-OMP26 than with NL-P6 and NL-OMP26. Fusion constructs also resulted in a 1- to 3-log-lower NTHi density following vaccination. NALT cells from mice vaccinated with lipidated protein constructs had higher levels of interleukin-17 (IL-17), IL-22, and CD4+ T-cell memory. Passive transfer of sera from L-OMP26ϕNL-P6-vaccinated mice to recipient infant mice reduced NP colonization and ear bulla NTHi density. We conclude that L-P6, L-OMP26, and fusion constructs generate enhanced antibody responses and protection from NP colonization and middle ear infection by NTHi in mice.