Intranasal vaccination with recombinant P6 protein and adamantylamide dipeptide as mucosal adjuvant confers efficient protection against otitis media and lung infection by nontypeable Haemophilus influenzae.

Abstract

Nontypeable Haemophilus influenzae (NTHi) is a leading etiologic agent of otitis media in children and recurrent respiratory infections in patients with chronic obstructive pulmonary disease. The highly conserved outer membrane protein P6 constitutes a promising vaccine candidate antigen. However, the small amount of P6 produced by this fastidious microorganism renders large-scale production difficult. Controversial data also exist concerning the suitability of recombinant P6 (rP6) as a vaccine antigen. Therefore, we performed a comparative evaluation of the immunogenicity and efficacy of native P6 and rP6 in mice intranasally vaccinated with adamantylamide dipeptide (AdDP) as an adjuvant. High titers of P6-specific serum antibodies were elicited in mice vaccinated with either native P6 or rP6, which cross-recognized both antigens. However, rP6 stimulated stronger mucosal responses. Mice vaccinated with rP6 were protected against both pulmonary and middle-ear infections (P<.01). This demonstrates that rP6 plus AdDP constitutes a promising vaccine formulation against the most relevant forms of disease caused by NTHi.