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. 2018 Mar 13;9(2):e00036-18.
doi: 10.1128/mBio.00036-18.

Predicting the Susceptibility of Meningococcal Serogroup B Isolates to Bactericidal Antibodies Elicited by Bivalent rLP2086, a Novel Prophylactic Vaccine

Lisa K McNeil  1 , Robert G K Donald  1 , Alexey Gribenko  1 , Roger French  1 , Nathaniel Lambert  1 , Shannon L Harris  1 , Thomas R Jones  1 , Sheng Li  2 , Gary Zlotnick  1 , Ulrich Vogel  3 , Heike Claus  3 , Raquel Abad  4 , Julio A Vazquez  4 , Ray Borrow  5 , Jamie Findlow  5 , Muhamed-Kheir Taha  6 , Ala-Eddine Deghmane  6 , Dominique A Caugant  7 , Paula Kriz  8 , Martin Musilek  8 , Xin Wang  9 , Jeni Vuong  9 , Leonard W Mayer  9 , Michael W Pride  1 , Kathrin U Jansen  1 , Annaliesa S Anderson  10
Affiliations

Predicting the Susceptibility of Meningococcal Serogroup B Isolates to Bactericidal Antibodies Elicited by Bivalent rLP2086, a Novel Prophylactic Vaccine

Lisa K McNeil et al. mBio. .

Abstract

Bivalent rLP2086 (Trumenba), a vaccine for prevention of Neisseria meningitidis serogroup B (NmB) disease, was licensed for use in adolescents and young adults after it was demonstrated that it elicits antibodies that initiate complement-mediated killing of invasive NmB isolates in a serum bactericidal assay with human complement (hSBA). The vaccine consists of two factor H binding proteins (fHBPs) representing divergent subfamilies to ensure broad coverage. Although it is the surrogate of efficacy, an hSBA is not suitable for testing large numbers of strains in local laboratories. Previously, an association between the in vitro fHBP surface expression level and the susceptibility of NmB isolates to killing was observed. Therefore, a flow cytometric meningococcal antigen surface expression (MEASURE) assay was developed and validated by using an antibody that binds to all fHBP variants from both fHBP subfamilies and accurately quantitates the level of fHBP expressed on the cell surface of NmB isolates with mean fluorescence intensity as the readout. Two collections of invasive NmB isolates (n = 1,814, n = 109) were evaluated in the assay, with the smaller set also tested in hSBAs using individual and pooled human serum samples from young adults vaccinated with bivalent rLP2086. From these data, an analysis based on fHBP variant prevalence in the larger 1,814-isolate set showed that >91% of all meningococcal serogroup B isolates expressed sufficient levels of fHBP to be susceptible to bactericidal killing by vaccine-induced antibodies.IMPORTANCE Bivalent rLP2086 (Trumenba) vaccine, composed of two factor H binding proteins (fHBPs), was recently licensed for the prevention of N. meningitidis serogroup B (NmB) disease in individuals 10 to 25 years old in the United States. This study evaluated a large collection of NmB isolates from the United States and Europe by using a flow cytometric MEASURE assay to quantitate the surface expression of the vaccine antigen fHBP. We find that expression levels and the proportion of strains above the level associated with susceptibility in an hSBA are generally consistent across these geographic regions. Thus, the assay can be used to predict which NmB isolates are susceptible to killing in the hSBA and therefore is able to demonstrate an fHBP vaccine-induced bactericidal response. This work significantly advances our understanding of the potential for bivalent rLP2086 to provide broad coverage against diverse invasive-disease-causing NmB isolates.

Keywords: Neisseria meningitidis serogroup B; factor H binding protein; flow cytometry; meningococcal antigen surface expression (MEASURE) assay; vaccine.

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Figures

FIG 1
FIG 1
MAb MN86-994-11-1 is specific for fHBP and correlates with total cellular fHBP expression. (A) Antibody specificity was confirmed by obtaining positive MN86-994-11 detection with NmB WT isolates (black line) and no detection on corresponding fHBP NmBΔfHBP isolates (dashed line), similar to the mouse IgG negative control (gray histogram). (B) Three different isolates expressing A22 fHBP variants and three different isolates expressing B09 fHBP variants were used to measure fHBP surface expression in a flow cytometry assay with MN86-994-11-1. (C) Correlation of surface expression of fHBP (MFI, log10) as assessed in the MEASURE assay with MN86-994-11-1 antibody versus total cellular fHBP as quantitated in whole-cell lysates by fluorescent Western immunoblotting with polyclonal bivalent fHBP A and B rabbit sera. Thirty-eight isolates expressing the following nine different fHBP variants (number of isolates of each variant tested) were tested: A05 (4), A12 (1), A22 (7), A29 (3), B03 (4), B09 (3), B16 (3), B24 (8), and B44 (5). Log-transformed data with R2 values are shown. Linear regression analysis was used to estimate levels of fHBP equivalent to respective MFIs.
FIG 2
FIG 2
Mapping of the MN86-994-11 binding epitope on fHBP (rP2086) structural models. A schematic depiction of the binding residues of MN86-994-11-1 on fHBP is shown. A, rP2086-A05; B, rP2086-B01. Positions of the segments showing a decrease in deuterium accumulation in the presence of antibody MN86-994-11 are shown in yellow with the first and last residues of each segment highlighted.
FIG 3
FIG 3
The MAb MN86-994-11-1 binding epitope is conserved among subfamily A and B fHBP variants present in the strain pool (n = 1,814). Peptide sequences of the MN86-994-11-1 K180-to-L198 binding site in subfamily A and B antigens defined by deuterium exchange mapping (Fig. 2) are compared. The number of variants represented by each sequence is indicated along with the mean MFI for each variant example and its corresponding frequency in the strain pool. An fHBP-B01 isolate (asterisk) is absent from the collection, but the epitope (shared with fHBP-B44) is included to permit comparisons with other fHBP variants for MAb MN86-994-11 binding affinity (see Table 1).
FIG 4
FIG 4
fHBP expression is detected on >95% of the isolates in the NmB invasive-isolate set (n = 1,814). fHBP surface expression levels of subfamily A (n = 550) and B (n = 1,264) isolates in the NmB invasive-isolate set (n = 1,814) are shown. (A) Correlation of serogroup B capsular polysaccharide MFIs (y axis) with the fHBP expression level MFI (x axis) as measured by the broadly cross-reactive fHBP MAb MN86-994-11-1. Subfamily A isolates are represented by blue squares, and subfamily B isolates are shown as green diamonds. (B) Isolates were binned on the basis of the level of fHBP expression (MFI) in the MEASURE assay. The y axis represents the frequency of isolates in each binned group. The background category includes strains with an MN86-994-11-1 MFI of <3 times the mouse IgG (negative control) MFI or an MFI of <100.
FIG 5
FIG 5
fHBP expression levels are distributed similarly in European Union (EU) and United States isolates. fHBP surface expression levels in the United States (n = 432) and European Union (n = 1,382) subsets of the prevalence-based collection of invasive NmB isolates (n = 1,814) are shown. (A) Subfamily A isolates from the United States (n = 149) and the European Union (n = 401). (B) Subfamily B isolates from the United States (n = 283) and the European Union (n = 981). Isolates were binned on the basis of their level of fHBP expression (MFI) in the MEASURE assay. The y axis represents the frequency of isolates in each binned group. Background denotes an MFI of <3 times the mouse IgG (negative control) MFI and/or an MFI of <100.
FIG 6
FIG 6
GMTs of individual serum samples from a phase 1 study are similar to those of serum pools in hSBAs with NmB isolates that express fHBP subfamily A or B variants. The susceptibility of subfamily A and B isolates to vaccine immune serum samples was evaluated, and the mean fHBP surface MFIs were determined by MEASURE assay with MAb MN86-994-11 (mean value of three experiments ± the standard deviation). Preimmune and immune serum samples from five individual subjects were pooled, and the hSBA activities of the pools were compared with those of individual serum samples (GMTs with 95% confidence intervals).
FIG 7
FIG 7
NmB fHBP surface expression level (MFI) and susceptibility to killing in an hSBA by bivalent fHBP immune serum. fHBP surface expression is determined by the binding of broadly cross-reactive MAb MN86-994-11-1 to NmB isolates in the MEASURE assay. The 109 NmB isolates were also tested in the hSBA with pooled human pre- and postvaccination bivalent rLP2086 immune serum samples. (A) For each of the 109 isolates, the postvaccination hSBA titer is plotted versus the level of fHBP surface expression. In cases where more than one assay was conducted with the same strain, the GMT was used. The symbol associated with each isolate conveys both the fHBP subfamily expressed and whether or not the isolate is killed (>4-fold increase in titer comparing pre- and postvaccination serum pools) with immune serum samples in an hSBA (B) Isolates were ordered from high to low fHBP surface expression and separated into killed and not killed groups on the basis of the ≥4-fold rise in hSBA titers between pre- and postvaccination serum pools. Green diamonds represent killed isolates, and red triangles represent isolates that were not killed. The dotted line marks the MFI threshold of 1,000.
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