Inactivated pep27 mutant as an effective mucosal vaccine against a secondary lethal pneumococcal challenge in mice

PURPOSE A pep27 mutant may be able to elicit mucosal immunity against pneumococcal diseases, and could be employed as an inexpensive attenuated vaccine. However, this particular mutant contains an erythromycin-resistance marker. The purpose of the current study is to develop a markerless pep27 mutant and assess whether this inactivated mutant is able to induce mucosal immunity. MATERIALS AND METHODS Mice were vaccinated intranasally with the inactivated markerless pep27 mutant every 2 weeks for a total of three times, after which time serum samples were analyzed for antibody titers. The mice were then challenged with a lethal D39 strain and their survival time was measured. The cross-reactivity of the antisera against pep27 was also compared to other mutant serotypes. RESULTS Intranasal immunization of mice with the inactivated markerless pep27 mutant provides effective protection and rapidly cleared bacterial colonization in vivo. Moreover, antisera raised against the pep27 mutant may cross-react with several other serotype strains. CONCLUSION Intranasal immunization with the inactivated pep27 mutant may be able to provide mucosal immunity, and could represent an efficient mucosal vaccine.