Meningococcal factor H-binding protein vaccines with decreased binding to human complement factor H have enhanced immunogenicity in human factor H transgenic mice

Abstract

Factor H-binding protein (fHbp) is a component of a meningococcal vaccine recently licensed in Europe for prevention of serogroup B disease, and a second vaccine in clinical development. The protein specifically binds human factor H (fH), which down-regulates complement activation and enhances resistance to bactericidal activity. There are conflicting data from studies in human fH transgenic mice on whether binding of human fH to fHbp vaccines decreases immunogenicity, and whether mutant fHbp vaccines with decreased fH binding have enhanced immunogenicity. fHbp can be classified into two sub-families based on sequence divergence and immunologic cross-reactivity. Previous studies of mutant fHbp vaccines with low fH binding were from sub-family B, which account for approximately 60% of serogroup B case isolates. In the present study, we evaluated the immunogenicity of two mutant sub-family A fHbp vaccines containing single substitutions, T221A or D211A, which resulted in 15- or 30-fold lower affinity for human fH, respectively, than the corresponding control wild-type fHbp vaccine. In transgenic mice with high serum concentrations of human fH, both mutant vaccines elicited significantly higher IgG titers and higher serum bactericidal antibody responses than the control fHbp vaccine that bound human fH. Thus, mutations introduced into a sub-family A fHbp antigen to decrease fH binding can increase protective antibody responses in human fH transgenic mice. Collectively the data suggest that mutant fHbp antigens with decreased fH binding will result in superior vaccines in humans.

A meningococcal vaccine antigen engineered to increase thermal stability and stabilize protective epitopes

“…We chose FHbp ID 22, as this sequence variant was prevalent in invasive isolates from Africa (14,20) and the immunogenicity of vaccines containing FHbp ID 22 previously had been tested in mice (6,14,16,21). The L130R substitution increased the T m of the N-terminal domain by 7.7°C (Fig.…”

“…Binding of human FH decreases FHbp immunogenicity (24)(25)(26), and FHbp mutants with decreased binding of FH elicit higher protective antibody responses in human FH transgenic mice (16,24,27). Because R130 is an FH binding residue in variant group 1 proteins (28), we tested binding of human FH to the doublemutant FHbp.…”

“…FHbp mutants with decreased binding of human FH were shown to have enhanced immunogenicity in human FH transgenic mice (15,16,24,27). The stabilized double-mutant FHbp had approximately sevenfold lower affinity for human FH than the WT FHbp (Fig.…”

“…Meningococcal FHbp vaccine antigens in variant groups 1 and 3 were reported to be stable (15,17,18), whereas FHbp in variant group 2 was unstable (15,16). In the present study, we used multiple sequence alignments and a known crystal structure of FHbp in variant group 1 (19) to identify L130 and G133 as residues that might explain the lower thermal stability of FHbp variant group 2.…”

“…These two sequence variants were reported to have low thermal stability for the amino-(N-) terminal domain (15,16), whereas FHbp from variant groups 1 and 3 had high thermal stability (15,17,18). The relatively low thermal stability for FHbp variant group 2 proteins was suggested to limit the vaccine potential of these variants (15).…”