Epitope Mapping of Human Polyclonal Antibodies to the fHbp Antigen of a Neisseria Meningitidis Vaccine by Hydrogen-Deuterium Exchange Mass Spectrometry (HDX-MS).

Antigen-antibody interactions play a key role in the immune response post vaccination and the mechanism of action of antibody-based biopharmaceuticals. 4CMenB is a multicomponent vaccine against Neisseria meningitidis serogroup B in which factor H binding protein (fHbp) is one of the key antigens. In this study, we use hydrogen/deuterium exchange mass spectrometry (HDX-MS) to identify epitopes in fHbp recognized by polyclonal antibodies (pAb) from two human donors (HDs) vaccinated with 4CMenB. Our HDX-MS data reveal several epitopes recognized by the complex mixture of human pAb. Furthermore, we show that the pAb from the two HDs recognize the same epitope regions. Epitope mapping of total pAb and purified fHbp-specific pAb from the same HD reveals that the two antibody samples recognize the same main epitopes, showing that HDX-MS based epitope mapping can, in this case at least, be performed directly using total IgG pAb samples that have not undergone Ab-selective purification. Two monoclonal antibodies (mAb) were previously produced from B-cell repertoire sequences from one of the HDs and used for epitope mapping of fHbp with HDX-MS. The epitopes identified for the pAb from the same HD in this study, overlap with the epitopes recognized by the two individual mAbs. Overall, HDX-MS epitope mapping appears highly suitable for simultaneous identification of epitopes recognized by pAb from human donors and to thus both guide vaccine development and study basic human immunity to pathogens, including viruses.

Development and Validation of Multiplex Assays for Mouse and Human IgG and IgA to Neisseria gonorrhoeae Antigens.

There is an urgent need for vaccines against Neisseria gonorrhoeae, the causative agent of gonorrhea. Vaccination with an outer membrane vesicle-based Neisseria meningitidis vaccine provides some protection from N. gonorrhoeae; however, the mechanisms underlying this cross-protection are unknown. To address this need, we developed multiplexed bead-based assays for the relative quantification of human and mouse IgG and IgA against N gonorrhoeae antigens. The assays were evaluated for analyte independence, dilutional linearity, specificity, sensitivity, intra- and interassay variability, and robustness to sample storage conditions. The assay was then used to test samples from mice and humans immunized with an N meningitidis outer membrane vesicle vaccine.

Cost-effectiveness of 4CMenB vaccination against gonorrhea: importance of dosing schedule, vaccine sentiment, targeting strategy, and duration of protection.

BACKGROUND: Observational evidence suggests the 4CMenB meningococcal vaccine may partially protect against gonorrhea, with one dose being two-thirds as protective as two. We examined the cost-effectiveness of vaccinating men-who-have-sex-with-men (MSM) in England, with one- or two-dose primary vaccination. METHODS: Integrated transmission-dynamic health-economic modeling explored the effects of targeting strategy, first- and second-dose uptake levels, and duration of vaccine protection, using observational estimates of vaccine protection. RESULTS: Vaccination with one or two primary doses is always cost-saving, irrespective of uptake, although vaccine sentiment is an important determinant of impact and cost-effectiveness. The most impactful and cost-effective targeting is offering "Vaccination-according-to-Risk" (VaR), to all patients with gonorrhea plus those reporting high numbers of sexual partners. If VaR is not feasible to implement then the more-restrictive strategy of "Vaccination-on-Diagnosis" (VoD) with gonorrhea is cost-effective, but much less impactful. Under conservative assumptions, VaR(2-dose) saves £7.62M(95%CrI:1.15-17.52) and gains 81.41(28.67-164.23) QALYs over 10 years; VoD(2-dose) saves £3.40M(0.48-7.71) and gains 41.26(17.52-78.25) QALYs versus no vaccination. Optimistic versus pessimistic vaccine-sentiment assumptions increase net benefits by ∼30%(VoD) or ∼60%(VaR). CONCLUSIONS: At UK costs, targeted 4CMenB vaccination of MSM gains QALYs and is cost-saving at any uptake level. Promoting uptake maximizes benefits and is an important role for behavioral science.

An open-label randomised controlled trial evaluating the efficacy of a meningococcal serogroup B (4CMenB) vaccine on Neisseria gonorrhoeae infection in gay and bisexual men: the MenGO study protocol.

BACKGROUND: Gonorrhoea is an ongoing public health concern due to its rising incidence and the emergence of antibiotic resistance. There are an estimated 82 million new Neisseria gonorrhoeae infections each year, with several populations at higher risk for gonococcal infection, including gay and bisexual men (GBM). If left untreated, infection can lead to serious morbidity including infertility, sepsis and increased risk of HIV acquisition. Development of a gonorrhoea vaccine has been challenging, however there is observational evidence that serogroup B meningococcal vaccines, used to protect against the closely related bacteria Neisseria meningitidis, could provide cross-protection against N. gonorrhoeae. METHODS: The MenGO (Meningococcal vaccine efficacy against Gonorrhoea) study is a phase III open-label randomised control trial in GBM to evaluate the efficacy of the four-component meningococcal serogroup B vaccine, 4CMenB, against gonorrhoea. A total of 130 GBM will be recruited at the Gold Coast Sexual Health Clinic, Australia, and randomised to either receive 2 doses of 4CMenB or no intervention. Participants will be followed up for 24 months with testing for N. gonorrhoeae and other sexually transmissible infections every three months. Demographics, sexual behaviour risk, antibiotic use, and blood samples for analysis of N. gonorrhoeae-specific immune responses, will be collected during the study. The primary outcome is the number of N. gonorrhoeae infections in participants over 2 years measured by nucleic acid amplification test (NAAT). Secondary outcomes are vaccine-induced N. gonorrhoeae-specific immune responses, and adverse events in trial participants. DISCUSSION: This trial will determine if the 4CMenB vaccine is able to reduce N. gonorrhoeae infection. If shown to be effective, 4CMenB could be used in gonococcal prevention. Analysis of 4CMenB-induced immune responses will increase understanding of the type of immune response needed to prevent N. gonorrhoeae, which may enable identification of a potential correlate of protection to aid future gonorrhoea vaccine development. TRIAL REGISTRATION: The trial has been registered on the Australian and New Zealand Clinical Trials Registry (ACTRN12619001478101) on 25 October 2019.

B Part of It School Leaver Study: A Repeat Cross-Sectional Study to Assess the Impact of Increasing Coverage With Meningococcal B (4CMenB) Vaccine on Carriage of Neisseria meningitidis.

BACKGROUND: Recombinant protein-based vaccines targeting serogroup B meningococci protect against invasive disease but impacts on carriage are uncertain. This study assessed carriage prevalence of disease-associated meningococci in 2018-2020 as the proportion of vaccinated adolescents increased following introduction of a school-based 4CMenB immunization program. METHODS: Eligible participants who completed high school (aged 17-25) in South Australia in the previous year had an oropharyngeal swab taken and completed a risk factor questionnaire. Disease-associated meningococci (genogroups A, B, C, W, X, Y) were detected by meningococcal and genogroup-specific polymerase chain reaction. RESULTS: The analysis included 4104 participants in 2018, 2690 in 2019, and 1338 in 2020. The proportion vaccinated with 4CMenB increased from 43% in 2018, to 78% in 2019, and 76% in 2020. Carriage prevalence of disease-associated meningococci in 2018 was 225/4104 (5.5%). There was little difference between carriage prevalence in 2019 (134/2690, 5.0%; adjusted odds ratio [aOR], 0.82; 95% confidence interval [CI], .64-1.05) and 2020 (68/1338, 5.1%; aOR, 0.82; 95% CI, .57-1.17) compared to 2018. CONCLUSIONS: Increased 4CMenB uptake in adolescents was not associated with decline in carriage of disease-associated meningococci. 4CMenB immunization programs should focus on direct (individual) protection for groups at greatest risk of disease. CLINICAL TRIALS REGISTRATION: NCT03419533.

Impact of Meningococcal B Vaccine on Invasive Meningococcal Disease in Adolescents.

BACKGROUND: From 2017, a statewide cluster randomized trial was conducted in South Australia to assess the impact of the meningococcal B vaccine 4CMenB on pharyngeal Neisseria meningitidis carriage in adolescents. Senior schools were randomized to receive the vaccine in 2017 (intervention) or 2018 (control). In this study we report the vaccine impact of 4CMenB on serogroup B invasive meningococcal disease (IMD) in 16- to 19-year-old adolescents in South Australia. METHODS: This observational time series analysis of serogroup B IMD cases compares the 14 years prior to the commencement of the trial (2003-2016) with the 2 years following 4CMenB vaccination of the 2017 adolescent cohort. RESULTS: Approximately 62% of year 10 and 11 students (15-16 years old) in South Australia enrolled in the trial. A total of 30 522 year 10-12 students received at least 1 dose of 4CMenB. The number of serogroup B IMD cases in 16- to 19-year old adolescents in South Australia increased on average by 10% per year from 2003 to 2016 (95% confidence interval [CI], 6%-15%, P < .001), peaking with 10 cases in 2015. Serogroup B IMD cases reduced to 5 in 2017-2018 and 1 in 2018-2019, below the expected numbers of 9.9 (95% prediction interval [PI], 3.9-17.5) and 10.9 (95% PI, 4.4-19.1), respectively. This translated to an overall reduction in the number of serogroup B IMD cases of 71% (95% CI, 15%-90%, P = .02). There were no serogroup B IMD cases in vaccinated adolescents. CONCLUSIONS: Vaccinating adolescents with 4CMenB was associated with a reduction in group B meningococcal disease in South Australia. CLINICAL TRIALS REGISTRATION: NCT03089086.

First Real-world Evidence of Meningococcal Group B Vaccine, 4CMenB, Protection Against Meningococcal Group W Disease: Prospective Enhanced National Surveillance, England.

BACKGROUND: 4CMenB is a protein-based meningococcal B vaccine, but the vaccine antigens may be present on non-group B meningococci. In September 2015, the UK implemented 4CMenB into the national infant immunization program, alongside an emergency adolescent meningococcal ACWY (MenACWY) program to control a national outbreak of group W (MenW) disease caused by a hypervirulent strain belonging to the ST-11 clonal complex. The adolescent program aimed to provide direct protection for adolescents and indirect protection across the population. METHODS: Public Health England conducts meningococcal disease surveillance in England. MenW cases confirmed during 4 years before and 4 years after implementation of both vaccines were analyzed. Poisson models were constructed to estimate direct protection against MenW disease offered by the infant 4CMenB program along with the indirect impact of the adolescent MenACWY program in children eligible for 4CMenB but not MenACWY. RESULTS: Model estimates showed 69% (adjusted incidence rate ratio [aIRR], .31; 95% CI, .20-.67) and 52% (aIRR, .48; 95% CI, .28-.81) fewer MenW cases than predicted among age-cohorts that were fully- and partly-eligible for 4CMenB, respectively. There were 138 MenW cases in <5-year-olds. 4CMenB directly prevented 98 (95% CI, 34-201) cases, while the MenACWY program indirectly prevented an additional 114 (conservative) to 899 (extreme) cases over 4 years. Disease severity was similar in 4CMenB-immunized and unimmunized children. CONCLUSIONS: This is the first real-world evidence of direct protection afforded by 4CMenB against MenW:cc11 disease. 4CMenB has the potential to provide some protection against all meningococcal serogroups.

Cost-Effectiveness of 4CMenB Infant Vaccination in England: A Comprehensive Valuation Considering the Broad Impact of Serogroup B Invasive Meningococcal Disease.

OBJECTIVES: This cost-effectiveness analysis (CEA) of 4CMenB infant vaccination in England comprehensively considers the broad burden of serogroup B invasive meningococcal disease (MenB IMD), which has not been considered, or was only partially considered in previous CEAs. METHODS: A review of previous MenB vaccination CEAs was conducted to identify aspects considered in the evaluation of costs and health outcomes of the disease burden of MenB IMD. To inform the model structure and comprehensive analysis, the aspects were grouped into 5 categories. A stepwise analysis was conducted to analyze the impact of each category, and the more comprehensive consideration of disease burden, on the incremental cost-effectiveness ratio (ICER). RESULTS: MenB IMD incidence decreased by 46.0% in infants and children 0-4 years old within 5 years after introduction of the program. Stepwise inclusion of the 5 disease burden categories to a conventional narrow CEA setting reduced the ICER from £360 595 to £18 645-that is, considering the impact of all 5 categories, 4CMenB infant vaccination is cost-effective at a threshold of £20 000 per QALY gained. CONCLUSIONS: When considering comprehensively the MenB IMD burden, 4CMenB infant vaccination can be cost-effective, a finding contrary to previous CEAs. This analysis allows policy decision-makers globally to infer the impact of current disease burden considerations on the cost-effectiveness and the comprehensive assessment necessary for MenB IMD. Although this comprehensive CEA can help inform decision making today, it may be limited in capturing the full disease burden and complex interactions of health and economics of MenB IMD.

A re-assessment of 4CMenB vaccine effectiveness against serogroup B invasive meningococcal disease in England based on an incidence model.

BACKGROUND: The four-component serogroup B meningococcal 4CMenB vaccine (Bexsero, GSK) has been routinely given to all infants in the United Kingdom at 2, 4 and 12 months of age since September 2015. After 3 years, Public Health England (PHE) reported a 75% [95% confidence interval 64%; 81%] reduction in the incidence of serogroup B invasive meningococcal disease (IMD) in age groups eligible to be fully vaccinated. In contrast, vaccine effectiveness (VE) evaluated in the same immunization program applying the screening method was not statistically significant. We re-analyzed the data using an incidence model. METHODS: Aggregate data-stratified by age, year and doses received-were provided by PHE: serogroup B IMD case counts for the entire population of England (years 2011-2018) and 4CMenB vaccine uptake in infants. We combined uptake with national population estimates to obtain counts of vaccinated and unvaccinated person-time by age and time. We re-estimated VE comparing incidence rates in vaccinated and non-vaccinated subjects using a Bayesian Poisson model for case counts with person-time data as an offset. The model was adjusted for age, time and number of doses received. RESULTS: The incidence model showed that cases decreased until 2013-2014, followed by an increasing trend that continued in the non-vaccinated population during the immunization program. VE in fully vaccinated subjects (three doses) was 80.1% [95% Bayesian credible interval (BCI): 70.3%; 86.7%]. After a single dose, VE was 33.5% [12.4%; 49.7%]95%BCI and after two doses, 78.7% [71.5%; 84.5%]95%BCI. We estimated that vaccination averted 312 cases [252; 368]95%BCI between 2015 and 2018. VE was in line with the previously reported incidence reduction. CONCLUSIONS: Our estimates of VE had higher precision than previous estimates based on the screening method, which were statistically not significant, and in line with the 75% incidence reduction previously reported by PHE. When disease incidence is low and vaccine uptake is high, the screening method applied to cases exclusively from the population eligible for vaccination may not be precise enough and may produce misleading point-estimates. Precise and accurate VE estimates are fundamental to inform public health decision making. VE assessment can be enhanced using models that leverage data on subjects not eligible for vaccination.

Randomized Trial of 2 Schedules of Meningococcal B Vaccine in Adolescents and Young Adults, Canada1.

Emergency vaccination programs often are needed to control outbreaks of meningococcal disease caused by Neisseria meningitidis serogroup B (MenB) on college campuses. Such campaigns expend multiple campus and public health resources. We conducted a randomized, controlled, multicenter, observer-blinded trial comparing immunogenicity and tolerability of an accelerated vaccine schedule of 0 and 21 days to a longer interval of 0 and 60 days for 4-component MenB vaccine (MenB-4C) in students 17-25 years of age. At day 21 after the first MenB-4C dose, we observed protective human serum bactericidal titers >4 to MenB strains 5/99, H44/76, and NZ 98/254 in 98%-100% of participants. Geometric mean titers increased >22-fold over baseline. At day 180, >95% of participants sustained protective titers regardless of their vaccine schedule. The most common adverse event was injection site pain. An accelerated MenB-4C immunization schedule could be considered for rapid control of campus outbreaks.

The meningococcal vaccine antigen GNA2091 is an analogue of YraP and plays key roles in outer membrane stability and virulence.

GNA2091 is one of the components of the 4-component meningococcal serogroup B vaccine (4CMenB) vaccine and is highly conserved in all meningococcal strains. However, its functional role has not been fully characterized. Here we show that nmb2091 is part of an operon and is cotranscribed with the nmb2089, nmb2090, and nmb2092 adjacent genes, and a similar but reduced operon arrangement is conserved in many other gram-negative bacteria. Deletion of the nmb2091 gene causes an aggregative phenotype with a mild defect in cell separation; differences in the outer membrane composition and phospholipid profile, in particular in the phosphoethanolamine levels; an increased level of outer membrane vesicles; and deregulation of the zinc-responsive genes such as znuD. Finally, the ∆2091 strain is attenuated with respect to the wild-type strain in competitive index experiments in the infant rat model of meningococcal infection. Altogether these data suggest that GNA2091 plays important roles in outer membrane architecture, biogenesis, homeostasis, and in meningococcal survival in vivo, and a model for its role is discussed. These findings highlight the importance of GNA2091 as a vaccine component.-Seib, K. L., Haag, A. F., Oriente, F., Fantappiè, L., Borghi, S., Semchenko, E. A., Schulz, B. L., Ferlicca, F., Taddei, A. R., Giuliani, M. M., Pizza, M., Delany, I. The meningococcal vaccine antigen GNA2091 is an analogue of YraP and plays key roles in outer membrane stability and virulence.

Fatal Nongroupable Neisseria meningitidis Disease in Vaccinated Patient Receiving Eculizumab.

Patients receiving eculizumab have an increased risk for meningococcal disease, but most reported cases are attributable to encapsulated meningococcal strains. We describe a case in which a nongroupable meningococcal strain, which rarely causes disease in healthy persons, caused fatal disease in an eculizumab recipient despite meningococcal vaccination.

Genomic Surveillance of 4CMenB Vaccine Antigenic Variants among Disease-Causing Neisseria meningitidis Isolates, United Kingdom, 2010-2016.

In September 2015, 4CMenB meningococcal vaccine was introduced into the United Kingdom infant immunization program without phase 3 trial information. Understanding the effect of this program requires enhanced surveillance of invasive meningococcal disease (IMD) Neisseria meningitidis isolates and comparison with prevaccination isolates. Bexsero Antigen Sequence Types (BASTs) were used to analyze whole-genome sequences of 3,073 prevaccine IMD N. meningitidis isolates obtained during 2010-2016. Isolates exhibited 803 BASTs among 31 clonal complexes. Frequencies of antigen peptide variants were factor H binding protein 1, 13.4%; Neisserial heparin-binding antigen 2, 13.8%; Neisseria adhesin A 8, 0.8%; and Porin A-VR2:P1.4,10.9%. In 2015-16, serogroup B isolates showed the highest proportion (35.7%) of exact matches to >1 Bexsero components. Serogroup W isolates showed the highest proportion (93.9%) of putatively cross-reactive variants of Bexsero antigens. Results highlighted the likely role of cross-reactive antigens. BAST surveillance of meningococcal whole-genome sequence data is rapid, scalable, and portable and enables international comparisons of isolates.

Phase Variation of NadA in Invasive Neisseria meningitidis Isolates Impacts on Coverage Estimates for 4C-MenB, a MenB Vaccine.

A recombinant NadA protein is one of the four major protective antigens of 4C-MenB (Bexsero), a vaccine developed for serogroup B Neisseria meningitidis (MenB). The meningococcal antigen typing system (MATS) is utilized as a high-throughput assay for assessing the invasive MenB strain coverage of 4C-MenB. Where present, the nadA gene is subject to phase-variable changes in transcription due to a 5'TAAA repeat tract located in a regulatory region. The promoter-containing intergenic region (IGR) sequences and 5'TAAA repeat numbers were determined for 906 invasive meningococcal disease isolates possessing the nadA gene. Exclusion of the 5'TAAA repeats reduced the number of IGR alleles from 82 to 23. Repeat numbers were associated with low and high levels of NadA expression by Western blotting and enzyme-linked immunosorbent assay (ELISA). Low-expression repeat numbers were present in 83% of 179 MenB isolates with NadA-2/3 or NadA-1 peptide variants and 68% of 480 MenW ST-11 complex isolates with NadA-2/3 peptide variants. For isolates with vaccine-compatible NadA variants, 93% of MATS-negative isolates were associated with low-expression repeat numbers, whereas 63% of isolates with MATS relative potency (RP) scores above the 95% confidence interval for the positive bactericidal threshold had high-expression repeat numbers. Analysis of 5'TAAA repeat numbers has potential as a rapid, high-throughput method for assessing strain coverage for the NadA component of 4C-MenB. A key application will be assessing coverage in meningococcal disease cases where confirmation is by PCR only and MATS cannot be applied.

Adverse events following immunisation with a meningococcal serogroup B vaccine: report from post-marketing surveillance, Germany, 2013 to 2016.

Background and aimIn January 2013, a novel vaccine against Neisseria meningitidis serogroup B, the multicomponent meningococcal serogroup B vaccine (4CMenB), was approved by the European Medicines Agency. We aimed to evaluate the safety profile of this vaccine. Methods: All adverse events following immunisation (AEFI) reported from Germany since the vaccine's launch in Germany in November 2013 through December 2016 were reviewed and analysed. Results: Through December 2016, a total of 664 individual case safety reports (ICSR) notifying 1,960 AEFI were received. A majority of vaccinees for whom AEFI were reported were children 2 to 11 years of age (n = 280; 42.2%) followed by infants and toddlers aged 28 days to 23 months (n = 170; 25.6%). General disorders and administration site conditions was the System Organ Class (SOC) with the majority of AEFI (n = 977; 49.8%), followed by nervous system disorders (n = 249; 12.7%), and skin and subcutaneous tissue disorders (n = 191; 9.7%). Screening of patient records for immune-mediated and neurological diseases did not raise any safety signal in terms of an increased proportional reporting ratio (PRR). Conclusions: The safety profile described in the Summary of Product Characteristics, in general, is confirmed by data from spontaneous reporting. No safety concerns were identified.

Community outbreak of serogroup B invasive meningococcal disease in Beaujolais, France, February to June 2016: from alert to targeted vaccination.

In February and March 2016, four cases of serogroup B invasive meningococcal disease (IMD) occurred over 3 weeks in a small area north of Lyon in the Auvergne-Rhône-Alpes region, France. There were no deaths but two cases had sequelae. This community outbreak was caused by a rare meningococcal strain of the clonal complex ST-32, covered by the 4CMenB/Bexsero vaccine. The incidence rate for serogroup B IMD in this area was 22.5 per 100,000 inhabitants, which is above the epidemic threshold (10/100,000). The number of cases observed was significantly higher than expected in the age group of 0-24 year-olds (standardised incidence ratio: 96). These results suggested the potential emergence of this invasive strain in this sub-population. In accordance with French recommendations, it was decided to vaccinate the population aged between 2 months and 24 years, living, working or studying in the epidemic area. The vaccination campaign took place from April to September 2016. Vaccination coverage was estimated at 47% for one dose and 40% for two doses. The lowest coverage estimations were observed for the age groups younger than 3 and 15-19 years. Enhanced epidemiological and microbiological surveillance reported a fifth case in June 2016, outside the epidemic area.

Discordant Effects of Licensed Meningococcal Serogroup B Vaccination on Invasive Disease and Nasal Colonization in a Humanized Mouse Model.

Background: The multicomponent meningococcal serogroup B vaccine (4CMenB) is an outer membrane vesicle and recombinant protein-based vaccine licensed to protect against serogroup B meningococcal disease. It remains unknown whether this vaccine will prevent carriage or transmission, key aspects in long-term vaccine success and disease eradication. Methods: Using a "humanized" transgenic mouse model of nasal colonization, we took a systematic approach to estimate the potential for carriage prevention against antigenically diverse Neisseria meningitidis strains and to compare this protection to an invasive meningococcal disease challenge model. Results: The 4CMenB vaccine prevented morbidity and mortality after lethal invasive doses of all meningococcal strains tested. Immunization effectively prevented carriage with only 1 of 4 single antigen-matched strains but reduced or prevented nasal colonization by all 4 isolates with multiple cross-reacting antigens. Each immunized mouse had substantial immunoglobulin G targeting the challenge strains, indicating that antibody correlates with protection against sepsis but not nasal carriage. Conclusions: Immunization with the 4CMenB vaccine elicits a robust humoral response that correlates with protection against invasive challenge but not with prevention of asymptomatic colonization. This suggests that widespread use of this vaccine will reduce morbidity and mortality rates in immunized individuals, with the potential to contribute to herd protection against a subset of strains.

Binding of Complement Factor H (FH) Decreases Protective Anti-FH Binding Protein Antibody Responses of Infant Rhesus Macaques Immunized With a Meningococcal Serogroup B Vaccine.

BACKGROUND: The meningococcal vaccine antigen, factor H (FH)-binding protein (FHbp), binds human complement FH. In human FH transgenic mice, binding decreased protective antibody responses. METHODS: To investigate the effect of primate FH binding, we immunized rhesus macaques with a 4-component serogroup B vaccine (4CMenB). Serum FH in 6 animals bound strongly to FHbp (FHbp-FH(high)) and, in 6 animals, bound weakly to FHbp (FHbp-FH(low)). RESULTS: There were no significant differences between the respective serum bactericidal responses of the 2 groups against meningococcal strains susceptible to antibody to the NadA or PorA vaccine antigens. In contrast, anti-FHbp bactericidal titers were 2-fold lower in FHbp-FH(high) macaques against a strain with an exact FHbp match to the vaccine (P = .08) and were ≥4-fold lower against 4 mutants with other FHbp sequence variants (P ≤ .005, compared with FHbp-FH(low) macaques). Unexpectedly, postimmunization sera from all 12 macaques enhanced FH binding to meningococci. In contrast, serum anti-FHbp antibodies elicited by 4CMenB in mice whose mouse FH did not bind to the vaccine antigen inhibited FH binding. CONCLUSIONS: Binding of FH to FHbp decreases protective anti-FHbp antibody responses of macaques to 4CMenB. Even low levels of FH binding skew the antibody repertoire to FHbp epitopes outside of the FH-binding site, which enhance FH binding.