Use of expanded Neisseria meningitidis serogroup B panels with the serum bactericidal antibody assay for the evaluation of meningococcal B vaccine effectiveness

Figures & data

Table 1. Strengths and limitations of methods to evaluate MenB vaccine strain coverage and effectiveness.

	Method	Strength	Limitation
Traditional hSBA [17,18]	Measures complement-mediated killing via meningococcal vaccine-induced antibody	Established in vitro surrogate measure of meningococcal vaccine efficacy/effectiveness routinely used to support vaccine licensure Measures immunogenicity endpoints, such as antibody GMT, percentage of subjects above GMT threshold, 4-fold rise in GMT, etc.	Limited exogenous sources of seronegative human complement; process of identifying sources can be laborious and time consuming Impractical to use to evaluate coverage in large strain panels; may not sufficiently predict vaccine effectiveness across diverse circulating strains
MATS [25–27]	Evaluates in each strain the affinity of vaccine-induced antibodies against fHbp, NadA, and NHBA antigens via a sandwich ELISA combined with genotyping of PorA	Standardized, reproducible antigen typing system that assesses the level of expression and genetic diversity of antigens, allowing prediction of 4CMenB strain coverage	Specific to antigen components in 4CMenB Dedicated ELISA reaction kits are required Cannot be used on non-culture-confirmed IMD cases Underestimates predicted coverage as does not take synergistic effects of multiple antigens into account
MEASURE [18,22]	Flow cytometric method that generates phenotypic fHbp expression data via cross-reactive monoclonal antibody	Reproducible estimation of MenB-FHbp strain coverage	Specific to antigen components in MenB-FHbp Cannot be used on non-culture-confirmed cases Measures only expression level and not antigenic diversity and cross-reactivity
MenDeVAR Index [23,27,28]	Genotyping tool based on information from published MATS, MEASURE, and SBA studies	Allows prediction of vaccine strain coverage for cultured and non-cultured cases Can be used to estimate 4CMenB and MenB-FHbp strain coverage	Conservative estimate because uses published data only and because of criteria used to define antigen cross-reactivity Does not provide a real-time evaluation of coverage
gMATS [24,27]	Genotyping tool to predict 4CMenB strain coverage	Allows prediction of vaccine coverage for cultured and non-cultured cases	Predicted coverage value likely to be underestimated as does not take synergistic effects of multiple antigens into account Does not predict coverage for new alleles or alleles without available MATS data
Enc-hSBA assay against 110-strain panel [29–31]	Assessment of killing activity against 110-strain panel via hSBA assay using endogenous complement present in the serum of each vaccinated individual	Highly standardized method for measuring immunological vaccine effectiveness in clinical trial settings Ability to test large panels of epidemiologically representative NmB strains Accounts for complement activity differences among vaccinees and synergistic effects of multiple vaccine antigens Can be used for any MenB-containing vaccine and to complement data generated using traditional hSBA assay	Results reported as positive or negative only (at 1:4 dilution); not feasible to conduct quantitative measurements such as antibody GMT, etc. Large number of tests have to be performed on a panel of 110 strains Not all strains may be tested with same serum sample because of limited serum volume Persons with complement deficiencies might have impaired bactericidal activity Strain panel may need to be updated according to NmB strains causing outbreak
Traditional hSBA assay against 4 + 10 strains [32]	Quantitative assessment of killing activity of MenB-FHbp against 4 primary + 10 additional NmB strains via traditional hSBA assay, which uses exogenous complement	Relatively low operational burden Assay is established in vitro surrogate measure of meningococcal vaccine efficacy/effectiveness	Limited number (14) of test strains Focus on fHbp antigen only Limited exogenous sources of seronegative human complement; process of identifying sources can be laborious and time consuming
Real-world effectiveness data	Vaccine effectiveness data from clinical trials or the field	Demonstration of effect against disease, as opposed to immune response	Feasible only after vaccine is registered and used in large populations

4CMenB, 4-component meningococcal serogroup B vaccine; ELISA, enzyme-linked immunosorbent assay; enc-hSBA, endogenous complement hSBA; fHbp, factor H binding protein; gMATS, genetic Meningococcal Antigen Typing System; GMT, geometric mean titer; hSBA assay, serum bactericidal antibody assay using exogenous human complement; IMD, invasive meningococcal disease; MATS, Meningococcal Antigen Typing System; MEASURE, Meningococcal Antigen Surface Expression; MenB, meningococcal serogroup B; MenB-FHbp, bivalent factor H binding protein meningococcal serogroup B vaccine; MenDeVAR, Meningococcal Deduced Vaccine Antigen Reactivity; NadA, Neisseria adhesin A; NHBA, Neisserial Heparin-Binding Antigen; NmB, Neisseria meningitidis serogroup B; PorA, Porin A; SBA, serum bactericidal antibody.

Figure 1. Characteristics and standardization process for the endogenous complement hSBA (enc-Hsba)) assay [29,30]. The enc-Hsba assay uses active endogenous complement present in each vaccinee’s serum, i.e. serum samples are not heat-inactivated, maintaining intrinsic complement activity. Each serum sample is tested at a 1:4 dilution. After preparation of the microtiter plate with diluted sera, N. meningitidis serogroup B (NmB) bacteria from fresh log-phase liquid culture are added. Following incubation, aliquots of each well are transferred onto agar and incubated overnight, providing a positive or negative result for bactericidal killing. The assay was validated using NmB indicator strains for each of the four 4CMenB vaccine antigens, assessing robustness (assay stability), specificity, and sensitivity, and was qualified (consistency of results on triplicate testing) using the indicator strains and 110 randomly selected NmB disease-causing strains. This supported the utility of this assay for measuring the immunological effectiveness of MenB-containing vaccines against a large NmB strain panel in clinical trial settings, under conditions that are as close as possible to real-world conditions.Enc-Hsba,, serum bactericidal antibody assay using endogenous human complement; hSBA, serum bactericidal antibody assay using human complement; NmB, Neisseria meningitidis serogroup B.

Table 2. Features of the Neisseria meningitidis serogroup B (NmB) strain panel used in the endogenous complement hSBA (enc-HSBA)) assay against 110-strain panel method and the exogenous complement hSBA (traditional hSBA) assay against four primary and 10 additional (4 + 10) strains [49,57,61].

	Enc-hSBA assay against 110-strain panel	Traditional hSBA assay against 4 + 10 strains
Number of NmB strains	110	14: 4 primary plus 10 additional
NmB strain collection	110 strains randomly selected from 442 strains from US (CDC ABCs panel, 2000–2008)	4 primary: selected from 1,263 strains from US and Europe 10 additional: 9 selected from 1,263 strains, 1 (variant A07) selected from 1,814 US and Europe strains US strains from CDC ABCs panel, 2000–2005; European strains collected 2001–2006
Strain selection criteria	110 strains suitable for laboratory conditions and qualified for use in the enc-hSBA assay	4 primary: adequately reflect fHbp diversity in NmB disease strains; low to medium fHbp surface expression; low baseline hSBA seropositive rates; express fHbp variants heterologous to MenB-FHbp antigens 10 additional: fHbp variant prevalence among IMD strains in Europe or US; difference from primary test strain variants; representativeness of its variant group; technical compatibility in hSBA assay; predominant clonal complex for the variant group, if one existed
Comparison with other strain panels	4,273 strains from US, Canada, Australia, Europe: US (748 strains) Canada (407 strains) Australia (520 strains) 9 European countries (2,598 strains)	1,263 strains from US and Europe
Geographic representativeness of strain panel	Presence of at least one 4CMenB antigen in 110 strains: Overall ~89% US 95% Canada 90% Europe 87% Australia 97%	Overall ~80% (US and Europe)
Time period representativeness of strain panel	Comparison to CDC ABCs strains (2009–2014) shows stability of genetic characteristics over time	Data not available

4CMenB, 4-component meningococcal serogroup B vaccine; CDC ABCs, Centers for Disease Control and Prevention Active Bacterial Core Surveillance; fHbp, factor H binding protein; hSBA assay, serum bactericidal antibody assay using human complement; IMD, invasive meningococcal disease; MenB-FHbp, bivalent factor H binding protein meningococcal serogroup B vaccine; NmB, Neisseria meningitidis serogroup B.

Table 3. Neisseria meningitidis serogroup B (NmB) strains for the hSBA assay, using an exogenous complement, against four primary and 10 additional NmB strains (traditional hSBA 4 + 10 approach), which was used in the clinical development of the MenB-FHbp vaccine [61,,63].

Strain	fHbp variant (peptide id)	fHbp expression (MFI)	Clonal complex	Country of origin	Year of isolation
Primary strains
PMB80	A22 (2.19)	3127	41/44	US	2002
PMB2001	A56 (3.187)	5002	213	France	2002
PMB2948	B24 (1.1)	6967	32	France	2001
PMB2707	B44 (1.15)	11,283	269	UK	2006
Additional strains
PMB3010	A06 (3.47)	3370	461	UK	2001
PMB3040	A07 (2.21)	1379	162	Germany	2004
PMB824	A12 (2.24)	2540	35	US	2001
PMB1672	A15 (2.25)	2995	103	France	2002
PMB1989	A19 (2.16)	1934	8	UK	2002
PMB3175	A29 (3.30)	3839	32	US	2000
PMB1256	B03 (1.14)	3976	41/44	UK	2001
PMB866	B09 (1.13)	2089	269	UK	2005
PMB431	B15 (1.252)	3785	41/44	US	2000
PMB648	B16 (1.4)	2347	41/44	UK	2003

fHbp, factor H binding protein; hSBA assay, serum bactericidal antibody assay using human complement; MenB-FHbp, bivalent factor H binding protein meningococcal serogroup B vaccine; MFI, mean fluorescence intensity on Meningococcal Antigen Typing System (MEASURE); peptide id, peptide identifier (http://pubmlst.org/neisseria/fHbp/).

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