Enhanced protective antibody to a mutant meningococcal factor H-binding protein with low-factor H binding
Dan M. Granoff, Serena Giuntini, Flor A. Gowans, Eduardo Lujan, Kelsey Sharkey, Peter T. Beernink
Dan M. Granoff, Serena Giuntini, Flor A. Gowans, Eduardo Lujan, Kelsey Sharkey, Peter T. Beernink
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Research Article Vaccines

Enhanced protective antibody to a mutant meningococcal factor H-binding protein with low-factor H binding

Abstract

Meningococcal factor H-binding protein (FHbp) is an antigen in 2 serogroup B meningococcal vaccines. FHbp specifically binds human and some nonhuman primate complement FH. To investigate the effect of binding of FH to FHbp on protective antibody responses, we immunized infant rhesus macaques with either a control recombinant FHbp antigen that bound macaque FH or a mutant antigen with 2 amino acid substitutions and >250-fold lower affinity for FH. The mutant antigen elicited 3-fold higher serum IgG anti-FHbp titers and up to 15-fold higher serum bactericidal titers than the control FHbp vaccine. When comparing sera with similar IgG anti-FHbp titers, the antibodies elicited by the mutant antigen gave greater deposition of complement component C4b on live meningococci (classical complement pathway) and inhibited binding of FH, while the anti-FHbp antibodies elicited by the control vaccine enhanced FH binding. Thus, the mutant FHbp vaccine elicited an anti-FHbp antibody repertoire directed at FHbp epitopes within the FH binding site, which resulted in greater protective activity than the antibodies elicited by the control vaccine, which targeted FHbp epitopes outside of the FH combining site. Binding of a host protein to a vaccine antigen impairs protective antibody responses, which can be overcome with low-binding mutant antigens.

Authors

Dan M. Granoff, Serena Giuntini, Flor A. Gowans, Eduardo Lujan, Kelsey Sharkey, Peter T. Beernink

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Figure 5

Effect of FHbp vaccination on binding of serum FH to meningococci, bactericidal activity, and C4b deposition.

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Effect of FHbp vaccination on binding of serum FH to meningococci, bacte...
In a subanalysis to control for group differences in IgG titers, 6 macaques in the control WT FHbp group were selected based on the highest postdose 3 IgG anti-FHbp titers and 6 macaques in the mutant vaccine group with the lowest IgG anti-FHbp titers (see Figure 2C). (A) Serum IgG anti-FHbp GMTs of the vaccine groups were not significantly different, P = 0.6. (B) Ratios of FH binding to meningococci (WT strain H44/76) in postdose 3 sera to respective preimmunization sera from individual animals. All sera were tested at a dilution of 1:150. For the WT FHbp vaccine group, the MFI ratio of 1.68 was significantly > 1.0 (P = 0.03 by Wilcoxon signed-rank test compared with a theoretical ratio of 1.0.). For the mutant FHbp vaccine group, there was a trend for inhibition of FH binding by postimmunization serum (median ratio of 0.78, P = 0.16 [2-tailed]). The difference in the median ratios of FH binding in the 2 vaccine groups was significant (P = 0.002). (C and D) Bactericidal titers in postdose 3 sera against WT strains H44/76 with FHbp ID 1 (100% amino acid identity with vaccine) (C), and strain CH860 with FHbp ID 15 (89% identity) (D), for the subset of animals with similar IgG anti-FHbp titers. **P < 0.01, comparing GMT of the 2 vaccine groups against strain CH860 by t test of log10-transformed titers. Respective GMTs against H44/76 were not significantly different (P = 0.10). (E) C4b deposition on live meningococci of strain CH860 activated by macaque serum anti-FHbp antibodies in postdose 3 sera diluted 1:40. The MFI values for each individual animal are shown; the horizontal lines and numbers indicate the median of the individual values for each vaccine group. (**P < 0.01 by Mann-Whitney nonparametric test). (F) Relationship between serum bactericidal titers measured against strain CH860 and C4b deposition (data from D and E). r2 = 0.92, P < 0.0001. Data in A–D for the subanalyses were recalculated from data shown in Figures 2–4. Data in E (C4b deposition) represent the MFI values for each animal based on one assay in which all sera were tested in parallel.