Functional impacts of the diversity of the meningococcal factor H binding protein

Estimated strain coverage of serogroup B meningococcal vaccines: A retrospective study for disease and carrier strains in Greece (2010-2017)

Invasive meningococcal disease (IMD) is associated with high case fatality rates and long-term sequelae among survivors. Meningococci belonging to six serogroups (A, B, C, W, X, and Y) cause nearly all IMD worldwide, with serogroup B meningococci (MenB) the predominant cause in many European countries, including Greece (~80% of all IMD). In the absence of protein-conjugate polysaccharide MenB vaccines, two protein-based vaccines are available to prevent MenB IMD in Greece: 4CMenB (Bexsero™, GlaxoSmithKline), available since 2014; and MenB-FHbp, (Trumenba™, Pfizer), since 2018. This study investigated the potential coverage of MenB vaccines in Greece using 107 MenB specimens, collected from 2010 to 2017 (66 IMD isolates and 41 clinical samples identified solely by non-culture PCR), alongside 6 MenB isolates from a carriage study conducted during 2017-2018. All isolates were characterized by multilocus sequence typing (MLST), PorA, and FetA antigen typing. Whole Genome Sequencing (WGS) was performed on 66 isolates to define the sequences of vaccine components factor H-binding protein (fHbp), Neisserial Heparin Binding Antigen (NHBA), and Neisseria adhesin A (NadA). The expression of fHbp was investigated with flow cytometric meningococcal antigen surface expression (MEASURE) assay. The fHbp gene was present in-frame in all isolates tested by WGS and in 41 MenB clinical samples. All three variant families of fHbp peptides were present, with subfamily B peptides (variant 1) occurring in 69.2% and subfamily A in 30.8% of the samples respectively. Sixty three of 66 (95.5%) MenB isolates expressed sufficient fHbp to be susceptible to bactericidal killing by MenB-fHbp induced antibodies, highlighting its potential to protect against most IMD in Greece.

Phenotypic and genotypic characterization of meningococcal isolates in Tunis, Tunisia: High diversity and impact on vaccination strategies

OBJECTIVES

The aim of this study was to characterize Neisseria meningitidis (Men) isolates in Tunisian paediatric patients with invasive meningococcal disease (IMD) in order to target therapeutic and preventive strategies.

METHODS

Fifty-nine isolates of Men and four cerebrospinal fluid samples that were culture-negative but Men-positive by PCR (NC-MenPPCR) (2009-2016) were collected from IMD patients. Isolates were analysed for their antimicrobial susceptibility. Whole-genome sequencing (WGS) was used to characterize isolates and multilocus sequence typing for NC-MenPPCR. Coverage of Men serogroup B (MenB) was determined by Genetic Meningococcal Antigen Typing System (gMATS) and fHbp expression by ELISA.

RESULTS

MenB was the predominant type (88.9%). The majority of isolates (81%) had reduced susceptibility to penicillin G with altered penA alleles. The clonal complex CC461 (27.1%) was the most frequent. Among the MenB vaccine targets neisserial heparin binding antigen (NHBA) and fHbp, the predominant variants were NHBA118 (30.8%) and fHbp peptide 47 (25%), respectively. The nadA gene was present in 17.3% of isolates. Using gMATS, 36.5% of MenB were predicted to be covered by the 4CMenB vaccine. ELISA showed that 92.4% of the MenB were expected to be killed by anti-fHbp antibodies.

CONCLUSIONS

MenB was the leading serogroup in IMD, and more than 90% had a sufficient level of fHbp expression for vaccine coverage. The study results will be useful for the Tunisian vaccination programme.

Distribution of Neisseria meningitidis serogroup b (NmB) vaccine antigens in meningococcal disease causing isolates in the United States during 2009-2014, prior to NmB vaccine licensure

OBJECTIVES

Two Neisseria meningitidis serogroup B (NmB) vaccines are licensed in the United States. To estimate their potential coverage, we examined the vaccine antigen diversity among meningococcal isolates prior to vaccine licensure.

METHODS

NmB vaccine antigen genes of invasive isolates collected in the U.S. from 2009 to 2014 were characterized by Sanger or whole-genome sequencing.

RESULTS

During 2009-2014, the predominant antigen types have remained similar to those reported in 2000-2008 for NmB and 2006-2008 for NmC, NmY, with the emergence of a few new types. FHbp of subfamily B or variant 1 (B/v1) remained prevalent among NmB whereas FHbp of subfamily A or variant 2 and 3 (A/v2-3) were more prevalent among non-NmB. FHbp peptide 1 (B24/1.1) remains the most prevalent type in NmB. Full-length NadA peptide was detected in 26% of isolates, primarily in NmB and NmW. The greatest diversity of NhbA peptides was detected among NmB, with p0005 as the most prevalent type.

CONCLUSIONS

The prevalence and diversity of the NmB vaccine antigens have remained stable with common antigen types persisting over time. The data collected prior to NmB vaccine licensure provide the baseline to understand the potential impact of NmB vaccines on antigen diversity and strain coverage.

Whole-Genome Characterization of Epidemic Neisseria meningitidis Serogroup C and Resurgence of Serogroup W, Niger, 2015

In 2015, Niger reported the largest epidemic of Neisseria meningitidis serogroup C (NmC) meningitis in sub-Saharan Africa. The NmC epidemic coincided with serogroup W (NmW) cases during the epidemic season, resulting in a total of 9,367 meningococcal cases through June 2015. To clarify the phylogenetic association, genetic evolution, and antibiotic determinants of the meningococcal strains in Niger, we sequenced the genomes of 102 isolates from this epidemic, comprising 81 NmC and 21 NmW isolates. The genomes of 82 isolates were completed, and all 102 were included in the analysis. All NmC isolates had sequence type 10217, which caused the outbreaks in Nigeria during 2013–2014 and for which a clonal complex has not yet been defined. The NmC isolates from Niger were substantially different from other NmC isolates collected globally. All NmW isolates belonged to clonal complex 11 and were closely related to the isolates causing recent outbreaks in Africa.

The Phosphocarrier Protein HPr Contributes to Meningococcal Survival during Infection

Neisseria meningitidis is an exclusively human pathogen frequently carried asymptomatically in the nasopharynx but it can also provoke invasive infections such as meningitis and septicemia. N. meningitidis uses a limited range of carbon sources during infection, such as glucose, that is usually transported into bacteria via the phosphoenolpyruvate (PEP):sugar phosphotransferase system (PTS), in which the phosphocarrier protein HPr (encoded by the ptsH gene) plays a central role. Although N. meningitidis possesses an incomplete PTS, HPr was found to be required for its virulence. We explored the role of HPr using bioluminescent wild-type and ΔptsH strains in experimental infection in transgenic mice expressing the human transferrin. The wild-type MC58 strain was recovered at higher levels from the peritoneal cavity and particularly from blood compared to the ΔptsH strain. The ΔptsH strain provoked lower levels of septicemia in mice and was more susceptible to complement-mediated killing than the wild-type strain. We tested whether meningococcal structures impacted complement resistance and observed that only the capsule level was decreased in the ΔptsH mutant. We therefore compared the transcriptomic profiles of wild-type and ΔptsH strains and identified 49 differentially expressed genes. The HPr regulon contains mainly hypothetical proteins (43%) and several membrane-associated proteins that could play a role during host interaction. Some other genes of the HPr regulon are involved in stress response. Indeed, the ΔptsH strain showed increased susceptibility to environmental stress conditions. Our data suggest that HPr plays a pleiotropic role in host-bacteria interactions most likely through the innate immune response that may be responsible for the enhanced clearance of the ΔptsH strain from blood.

Evolutionary Events Associated with an Outbreak of Meningococcal Disease in Men Who Have Sex with Men

Meningococci spread via respiratory droplets, whereas the closely related gonococci are transmitted sexually. Several outbreaks of invasive meningococcal disease have been reported in Europe and the United States among men who have sex with men (MSM). We recently identified an outbreak of serogroup C meningococcal disease among MSM in Germany and France. In this study, genomic and proteomic techniques were used to analyze the outbreak isolates. In addition, genetically identical urethritis isolates were recovered from France and Germany and included in the analysis. Genome sequencing revealed that the isolates from the outbreak among MSM and from urethritis cases belonged to a clade within clonal complex 11. Proteome analysis showed they expressed nitrite reductase, enabling anaerobic growth as previously described for gonococci. Invasive isolates from MSM, but not urethritis isolates, further expressed functional human factor H binding protein associated with enhanced survival in a newly developed transgenic mouse model expressing human factor H, a complement regulatory protein. In conclusion, our data suggest that urethritis and outbreak isolates followed a joint adaptation route including adaption to the urogenital tract.

Expression of factor H binding protein in meningococcal strains can vary at least 15-fold and is genetically determined

Factor H binding protein (fHbp) is a lipoprotein of Neisseria meningitidis important for the survival of the bacterium in human blood and a component of two recently licensed vaccines against serogroup B meningococcus (MenB). Based on 866 different amino acid sequences this protein is divided into three variants or two families. Quantification of the protein is done by immunoassays such as ELISA or FACS that are susceptible to the sequence variation and expression level of the protein. Here, selected reaction monitoring mass spectrometry was used for the absolute quantification of fHbp in a large panel of strains representative of the population diversity of MenB. The analysis revealed that the level of fHbp expression can vary at least 15-fold and that variant 1 strains express significantly more protein than variant 2 or variant 3 strains. The susceptibility to complement-mediated killing correlated with the amount of protein expressed by the different meningococcal strains and this could be predicted from the nucleotide sequence of the promoter region. Finally, the absolute quantification allowed the calculation of the number of fHbp molecules per cell and to propose a mechanistic model of the engagement of C1q, the recognition component of the complement cascade.

Neisseria meningitidis factor H-binding protein fHbp: a key virulence factor and vaccine antigen

Neisseria meningitidis is a leading cause of meningitis and sepsis worldwide. The first broad-spectrum multicomponent vaccine against serogroup B meningococcus (MenB), 4CMenB (Bexsero(®)), was approved by the EMA in 2013, for prevention of MenB disease in all age groups, and by the US FDA in January 2015 for use in adolescents. A second protein-based MenB vaccine has also been approved in the USA for adolescents (rLP2086, Trumenba(®)). Both vaccines contain the lipoprotein factor H-binding protein (fHbp). Preclinical studies demonstrated that fHbp elicits a robust bactericidal antibody response that correlates with the amount of fHbp expressed on the bacterial surface. fHbp is able to selectively bind human factor H, the key regulator of the alternative complement pathway, and this has important implications both for meningococcal pathogenesis and for vaccine design. Here, we review the functional and structural properties of fHbp, the strategies that led to the design of the two fHbp-based vaccines and the data generated during clinical studies.

Genetic diversity and levels of expression of factor H binding protein among carriage isolates of Neisseria meningitidis

The prevention of meningococcal disease may be improved by recombinant vaccines such as 4CMenB and rLP2086 that target the factor H binding protein (fHbp), an immunogenic surface component of Neisseria meningitidis present as one of three variants. Whether such vaccines decrease carriage of invasive isolates and thus induce herd immunity is unknown. We analyzed the genetic diversity and levels of expression of fHbp among 268 carriage strains and compare them to those of 467 invasive strains. fhbp gene sequencing showed higher proportions of variants 2 and 3 among carriage isolates (p<0.0001). Carriage isolates expressed lower levels of fHbp (p<0.01) but that remain high enough to predict targeting by antibodies against fHbp particularly in group B isolates belonging to the frequent hypervirulent clonal complexes in Europe and North America (cc32, cc41/44, cc269). This suggests that fHbp targeting meningococcal vaccines might reduce, at least in part, the acquisition of some hyperinvasive isolates.