Immunization with the RrgB321 fusion protein protects mice against both high and low pilus-expressing Streptococcus pneumoniae populations.
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 RrgB321 antisera 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.
Novartis Vaccines and Diagnostics, 53100 Siena, Italy. monica.moschioni@novartis.com
Monica
M
Moschioni
Gabriella
G
De Angelis
Carole
C
Harfouche
Esmeralda
E
Bizzarri
Sara
S
Filippini
Elena
E
Mori
Giuseppe
G
Mancuso
Francesco
F
Doro
Michèle A
MA
Barocchi
Paolo
P
Ruggiero
Vega
V
Masignani
D000818:Animals; D045744:Cell Line, Tumor; D005260:Female; D036781:Fimbriae Proteins / Q000235:genetics / Q000276:immunology*; D010861:Fimbriae, Bacterial / Q000235:genetics / Q000276:immunology; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D007106:Immune Sera; D007114:Immunization; D051379:Mice; D008807:Mice, Inbred BALB C; D009895:Opsonin Proteins / Q000276:immunology; D010587:Phagocytosis / Q000276:immunology; D011008:Pneumococcal Infections / Q000235:genetics / Q000276:immunology / Q000517:prevention & control*; D022242:Pneumococcal Vaccines / Q000235:genetics / Q000276:immunology*; D011817:Rabbits; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000276:immunology; D013296:Streptococcus pneumoniae / Q000235:genetics / Q000276:immunology*
D007106:Immune Sera; D009895:Opsonin Proteins; D022242:Pneumococcal Vaccines; D011993:Recombinant Fusion Proteins; D036781:Fimbriae Proteins