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

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.