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EVALUATION OF THE EFFICACY OF THE IMMUNIZATION WITH PspA (PNEUMOCOCCAL SURFACE PROTEIN A) IN A CO-COLONIZATION MODEL WITH DIFFERENT STRAINS OF STREPTOCOCCUS PNEUMONIAE
 

Tostes RO, Oliveira MLS, da Silva JB, Ho PL, Miyaji EN

Laboratório de Biotecnologia Molecular I, Centro de Biotecnologia, Instituto Butantan, Brasil

Introduction: Streptococcus pneumoniae is a major cause of morbidity and mortality worldwide. The currently available vaccines are based on the response to the capsular polysaccharide and they have some disadvantages, such as high production cost and restricted serotype coverage. Pneumococcal surface protein A (PspA) is one of the leading candidates for a protein vaccine against pneumococcal diseases. PspA shows variability and the great majority of strains express PspA from family 1 (clades 1 and 2) or family 2 (clades 3, 4 and 5). Objectives: The purpose of this study is to evaluate the efficacy of the nasal immunization with recombinant PspAs from different clades in a mouse model of co-colonization of the nasopharynx with two strains, one expressing PspA from family 1 and another expressing PspA from family 2. Methods: C57BL/6 mice were immunized twice intranasally with recombinant PspAs from clades 1 to 5 (rPspA1, rPspA2, rPspA3, rPspA4 and rPspA5) using the whole-cell pertussis vaccine (wP) as adjuvant. Mice were then challenged with a mixture of the strains 491/00 (serotype 6B, PspA1) and 472/96 (serotype 6B, PspA4, trimethoprim resistant) and bacteria were recovered from nasal washes 5 days after challenge on blood-agar plates.  A challenge experiment with a mixture of a serotype 6B strain (PspA3, spectinomycin resistant) and a serotype 23F strain (PspA2) was also performed. In this experiment, we have evaluated whether it is possible to quantify 6B and 23F strains through qPCR using serotype specific primers. Results and Discussion: In the experiment with the challenge with the mixture of two different 6B strains, only mice immunized with rPspA1 showed statistically significant reduction in colonization with the PspA1 expressing strain when compared to the control group immunized with the adjuvant wP, whereas only animals immunized with rPspA4 showed statistically significant reduction in the PspA4 expressing strain when compared to the control group immunized with the adjuvant wP. One initial experiment with the challenge with the 6B and 23F strains showed statistically significant reduction in colonization with the 6B strain expressing PspA3 in the group immunized with rPspA4 when compared to the control group saline. Though no statistical difference was observed for the 23F strain expressing PspA2, there was a trend towards reduction in colonization in the groups immunized with PspA1, PspA3 and PspA4. These results indicate that a formulation with mixture of rPspA1 and rPspA4 may provide broad coverage. We have performed experiments for the quantification of the 6B and 23F strains in the nasal washes through qPCR and we could only find a good correlation between the CFU recovered on blood-agar plates and the qPCR results for the 6B strain. Quantification of the 23F strain thus needs further improvement.

Supported by Capes, CNPq, FAPESP
CEUAIB 1158/13



4 - IMMUNOLOGY AND VACCINES 21th Annual Scientific Meeting of Instituto Butantan.