Recombinant PhpA Protein, a Unique Histidine Motif-Containing Protein fromStreptococcus pneumoniae, Protects Mice against Intranasal Pneumococcal Challenge

Abstract

The multivalent pneumococcal conjugate vaccine is effective against both systemic disease and otitis media caused by serotypes contained in the vaccine. However, serotypes not covered by the current conjugate vaccine may still cause pneumococcal disease. To address these serotypes and the remaining otitis media due to Streptococcus pneumoniae, we have been evaluating antigenically conserved proteins from S. pneumoniae as vaccine candidates. A previous report identified a 20-kDa protein with putative human complement C3-proteolytic activity. By utilizing the publicly released pneumococcal genomic 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 expressed a 79-kDa fragment (rPhpA-79) that contains a repeated HxxHxH motif and evaluated it for vaccine potential. The antibodies elicited by the purified rPhpA-79 protein were cross-reactive to proteins from multiple strains of S. pneumoniae and were against surface-exposed epitopes. Immunization with rPhpA-79 protein adjuvanted with monophosphoryl lipid A (for subcutaneous immunization) or a mutant cholera toxin, CT-E29H (for intranasal immunization), protected CBA/N mice against death and bacteremia, as well as reduced nasopharyngeal colonization, following intranasal challenge with a heterologous pneumococcal strain. In contrast, immunization with the 20-kDa portion of the PhpA protein did not protect mice. These results suggest that rPhpA-79 is a potential candidate for use as a vaccine against pneumococcal systemic disease and otitis media.

Characterization of an Extracellular Virulence FactorMade by Group A Streptococcus with Homology to the Listeria monocytogenes Internalin Family ofProteins

“…Active immunization of mice with recombinant PhtA, PhtB, and PhtD or passive immunization with rabbit hyperimmune serum raised against PhtA conferred protection against pneumococcal sepsis in a mouse model of infection (1). Similar results were reported by a separate group for their investigation of S. pneumoniae histidine protein A (PhpA), a HxxHxH protein with ϳ76 to 85% sequence identity to PhtA, -B, and -D (83). Both parenteral and intranasal immunization of mice with a 79-kDa recombinant form of PhpA conferred protection against bacteremia following intranasal challenge (83).…”

“…Similar results were reported by a separate group for their investigation of S. pneumoniae histidine protein A (PhpA), a HxxHxH protein with ϳ76 to 85% sequence identity to PhtA, -B, and -D (83). Both parenteral and intranasal immunization of mice with a 79-kDa recombinant form of PhpA conferred protection against bacteremia following intranasal challenge (83). In addition to the identification of the HxxHxH repeats, several observations suggest that investigation of the potential of Slr for use in future vaccine-related studies is warranted.…”

The Streptococcal Blr and Slr Proteins Define a Family of Surface Proteins with Leucine-Rich Repeats: Camouflaging by Other Surface Structures

“…1A). The same motif, for which no function has been identified, has been described for several surface proteins of Streptococcus pneumoniae (1,64). Together, the similarities between Blr and Slr demonstrate that these two proteins are members of a family of streptococcal proteins with LRRs.…”

Prevention of Pneumococcal Disease in Mice Immunized with Conserved Surface-Accessible Proteins

“…Dis.). Immunization of mice with members of the BVH-11 family, i.e., PhtA (BVH-11-3), PhtB/PhpA (BVH-11), or PhtD (BVH-11-2), generated protection against S. pneumoniae (1,31), while a truncated version of BVH-3 (PhtE) was shown to be ineffective (1).…”