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

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.