The PsaA Antigen Of Streptococcus Pneumoniae And Its Application As A Protein Carrier In Conjugates Vaccine

Streptococcus pneumoniae carriage can lead to a wide range of localized and systemic diseases such as otitis media, sinusitis, conjunctivitis, pneumonia, septicemia and meningitis. In recent years, with the development of study on Streptococcus pneumoniae, Pneumococcal surface adhesinA (PsaA), pneumococcal surface protein A (PspA) and pneumolysin (Ply) have all been shown to contribute to pneumococcal virulence, use of these common proteins in a vaccine is a logical alternative to the use of polysaccharide vaccines to ensure not only complete serotype coverage for S.pneumoniae, but also a more vigorous immune response since these proteins generate a T-dependent response with immunologic memory. The conjugates vaccine (rPsaA as a carrier protein conjugated with meningococcal polysaccharide) becomes the main direction at present. Objective: The gene expression and the purification of the pneumococcal surface adhesin A (PsaA) protein and its application as a protein carrier in conjugates vaccine. Method: The gene encoding for the PsaA protein was amplified from the genomic DNA of Streptococcus pneumoniae using PCR. Then the PCR product was respectively cloned into the prokaryotic expression vector pET28a and the eukaryotic expression vector pPIC9K. After that, the recombinant was respectively transformed into host cell E. coli BL21 (DE3) and host cell Pichiapastoris GS115. The expression of the recombinant protein (rPsaA) was respectively induced by IPTG and methanol and purified by using DEAE anion-exchange chromatography. The rPsaA was successfully conjugated with Group A Meningococcal Polysaccharide (GAMP). The mice were immunized subcutaneously with the conjugate and the immune responses against GAMP and PsaA were detected by ELISA. Results: The recombinant PsaA was expressed as a 37-kD soluble protein without His-Tag. The rPsaA was successfully conjugated with GAMP. In addition to the immune response against PsaA, The antibody response against GAMP was significant improved in the mice immunized with conjugate vaccine in comparison with those immunized with GAMP alone. Conclusions: The recombinant protein PsaA without His-Tag was obtained and conjugated with GAMP. The strong antibody responses against PsaA and GAMP were obtained in the immunized mice at the same time which may provide the protection against pneumonia and meningitis simultaneously.