Selection of family 1 PspA molecules capable of inducing broad-ranging cross-reactivity by complement deposition and opsonophagocytosis by murine peritoneal cells

Abstract

PspA is one of the most well studied pneumococcal proteins and a promising candidate for a future protein-based anti-pneumococcal vaccine. Nevertheless, its structural and serological variability suggests the inclusion of more than one PspA molecule in order to broaden protection. Since different PspAs exhibit variable levels of cross-reactivity, the selection of the protein combination with the highest coverage potential is an essential step for PspA-based vaccine development. This work investigated the level of cross-reactivity within family 1 PspAs, and established a complement based antibody mediated opsonophagocytic assay for measuring the level of cross-protection. Among a panel of ten family 1 PspA molecules, two of them, one belonging to clade 1 and another from clade 2, induced antibodies capable of enhancing complement deposition and mediating the phagocytic killing by mouse peritoneal macrophages of all pneumococci bearing PspA family 1 strains tested, regardless of their serotype. Therefore, we suggest the inclusion of either one in a PspA-based vaccine, as a representative of family 1. Furthermore, our results suggest that opsonophagocytosis by mouse peritoneal cells can be an efficient means of evaluating the induction of protective immune responses in mice across a large number of strains.

A Combination of Recombinant Mycobacterium bovis BCG Strains Expressing Pneumococcal Proteins Induces Cellular and Humoral Immune Responses and Protects against Pneumococcal Colonization and Sepsis

“…Previously, we selected a PspA molecule able to induce antibodies with broad cross-reactivity (29) and demonstrated the potential use of this PspA molecule in fusion with PdT (30). Recently, in order to improve the immunogenicity of this fusion protein, we constructed a recombinant BCG (rBCG) strain expressing the PspA-PdT fusion protein (rBCG PspA-PdT) (31).…”

Conjugation of Polysaccharide 6B from Streptococcus pneumoniae with Pneumococcal Surface Protein A: PspA Conformation and Its Effect on the Immune Response

“…The strains carrying PspA clade 1 and serotype 3 were shown to be highly pathogenic, causing rapid sepsis and death in the mice, while tests using serotypes different from serotypes 3, 6A, and 6B did not cause disease in the animals (data not shown). In the absence of a suitable pneumococcal disease model, the OPA was the assay of choice for evaluating the functional activity of anti-PspA antibodies (27,40).…”

“…Following incubation, the samples were washed once with PBS and then incubated with 4 ϫ 10 5 peritoneal cells diluted in opsono-buffer at 37°C for 30 min with shaking (200 rpm). Peritoneal cells were obtained as previously described (40). The reaction was stopped by cooling on ice for 5 min.…”

Review: Current and new generation pneumococcal vaccines

“…167 Because they induce protective antibodies reactive with clades 1-5 in mice, Psp4 and PspA5 appear to be the optimum immunogenic variants for inclusion in a protein-based vaccine. 168 Additionally, a combination of one or both of these with a clade 1 PspA protein has also been proposed, either as the individual recombinant proteins or as a hybrid protein consisting of the immunogenic N-terminal regions of each. in association with Sanofi-Pasteur, which was evaluated in a dose-escalation study in adults.…”