[Improvement of immunogenicity of Streptococcus pneumoniae psaA DNA vaccine by prime and boost strategy].

Objective: To study on the preparation of Streptococcus pneumoniae psaA DNA vaccine and to analyse the immunogenicity by the prime-boost strategy.

Methods: The psaA gene was amplified from the genome of Streptococcus pneumoniae by PCR, and then was inserted into plasmid pVAX1 and pET28a to construct recombinant expression vectors respectively. 293T cells were transiently transfected with pVAX1-psaA, and RT-PCR analysis of total cell RNA extracts showed successful expression of psaA. BALB/c mices (n = 5) were intramuscularly injected with 100 microg psaA DNA vaccine for three times, and then boosted with 50 microg recombinant PsaA protein. The antibody response against PsaA was measured by ELISA.

Results: The psaA gene was amplified and subcloned successfully. The constructed psaA DNA vaccine was confirmed by DNA sequencing, and the recombinant PsaA protein was purified by the one-step Ni(2+) affinity chromatography. Expression of the PsaA was observed in cells transfected with pVAX1-psaA. The animal experiment results showed that the anti-PsaA level of the DNA prime-protein boosting mice was higher significantly than the other groups (t = 87.518, P < 0.05).

Conclusion: The psaA DNA vaccine was prepared successfully, and the immunogenicity of Streptococcus pneumoniae psaA DNA vaccine could be improved significantly by the DNA prime and protein boost strategy.