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Immunization with the RrgB321 fusion protein protects mice against both high and low pilus-expressing Streptococcus pneumoniae populations

2011; Elsevier BV; Volume: 30; Issue: 7 Linguagem: Inglês

10.1016/j.vaccine.2011.12.080

1873-2518

Monica Moschioni, Gabriella De Angelis, Carole Harfouche, Esmeralda Bizzarri, Sara Filippini, Elena Mori, Giuseppe Mancuso, Francesco Doro, Michèle A. Barocchi, Paolo Ruggiero, Vega Masignani,

Streptococcal Infections and Treatments

RrgB321, a fusion protein of the three Streptococcus pneumoniae pilus-1 backbone RrgB variants, is protective in vivo against pilus islet 1 (PI-1) positive pneumococci. In addition, antibodies to RrgB321 mediate a complement-dependent opsonophagocytosis of PI-1 positive strains at levels comparable to those obtained with antisera against glycoconjugate vaccines. In the pneumococcus, pilus-1 displays a biphasic expression pattern, with different proportions of two bacterial phenotypes, one expressing and one not expressing the pilus-1. These two populations can be stably separated in vitro giving rise to the enriched high (H) and low (L) pilus expressing populations. In this work we demonstrate that: (i) the opsonophagocytic killing mediated in vitro by RrgB321antisera is strictly dependent on the pilus expression ratio of the strain used; (ii) during the opsonophagocytosis assay pilus-expressing pneumococci are selectively killed, and (iii) no switch towards the pilus non-expressing phenotype can be observed. Furthermore, in sepsis and pneumonia models, mice immunized with RrgB321 are significantly protected against challenge with either the H or the L pilus-expressing population of strains representative of the three RrgB variants. This suggests that the pilus-1 expression is not down-regulated, and also that the expression of the pilus-1 could be up-regulated in vivo. In conclusion, these data provide evidence that RrgB321 is protective against PI-1 positive strains regardless of their pilus expression level, and support the rationale for the inclusion of this fusion protein into a multi-component protein-based pneumococcal vaccine.