Recombinant PhpA protein, a unique histidine motif-containing protein fromStreptococcus pneumoniae, protects mice against intranasal pneumococcal challenge

The multivalent pneumococcal conjugate vaccine is effective against both sy stemic disease and otitis media caused by serotypes contained in the vaccin e. However, serotypes not covered by the current conjugate vaccine may stil l cause pneumococcal disease. To address these serotypes and the remaining otitis media due to Streptococcus pneumoniae, we have been evaluating antig enically conserved proteins from S. pneumoniae as vaccine candidates. A pre vious report identified a 20-kDa protein with putative human complement C3- proteolytic activity, By utilizing the publicly released pneumococcal genom ic sequences, we found the gene encoding the 20-kDa protein to be part of a putative open reading frame of approximately 2,400 bp. We recombinantly ex pressed a 79-kDa fragment (rPhpA-79) that contains a repeated HxxHxH motif and evaluated it for vaccine potential. The antibodies elicited by the puri fied rPhpA-79 protein were cross-reactive to proteins from multiple strains of S. pneumoniae and were against surface-exposed epitopes. Immunization,v ith rPhpA-79 protein adjuvanted with monophosphoryl lipid A (for subcutaneo us immunization) or a mutant cholera toxin, CT-E29H (for intranasal immuniz ation), protected CBA/N mice against death and bacteremia, as well as reduc ed nasopharyngeal colonization, following intranasal challenge with a heter ologous pneumococcal strain, In contrast, immunization with the 20-kDa port ion of the PhpA protein did not protect mice. These results suggest that rP hpA-79 is a potential candidate for use as a vaccine against pneumococcal s ystemic disease and otitis media.