Typing complex meningococcal vaccines to understand diversity and population structure of key vaccine antigens

The serogroup B meningococcal outer membrane vesicle-based vaccine 4CMenB induces cross-species protection against Neisseria gonorrhoeae

There is a pressing need for a gonorrhea vaccine due to the high disease burden associated with gonococcal infections globally and the rapid evolution of antibiotic resistance in Neisseria gonorrhoeae (Ng). Current gonorrhea vaccine research is in the stages of antigen discovery and the identification of protective immune responses, and no vaccine has been tested in clinical trials in over 30 years. Recently, however, it was reported in a retrospective case-control study that vaccination of humans with a serogroup B Neisseria meningitidis (Nm) outer membrane vesicle (OMV) vaccine (MeNZB) was associated with reduced rates of gonorrhea. Here we directly tested the hypothesis that Nm OMVs induce cross-protection against gonorrhea in a well-characterized female mouse model of Ng genital tract infection. We found that immunization with the licensed Nm OMV-based vaccine 4CMenB (Bexsero) significantly accelerated clearance and reduced the Ng bacterial burden compared to administration of alum or PBS. Serum IgG and vaginal IgA and IgG that cross-reacted with Ng OMVs were induced by 4CMenB vaccination by either the subcutaneous or intraperitoneal routes. Antibodies from vaccinated mice recognized several Ng surface proteins, including PilQ, BamA, MtrE, NHBA (known to be recognized by humans), PorB, and Opa. Immune sera from both mice and humans recognized Ng PilQ and several proteins of similar apparent molecular weight, but MtrE was only recognized by mouse serum. Pooled sera from 4CMenB-immunized mice showed a 4-fold increase in serum bactericidal50 titers against the challenge strain; in contrast, no significant difference in bactericidal activity was detected when sera from 4CMenB-immunized and unimmunized subjects were compared. Our findings directly support epidemiological evidence that Nm OMVs confer cross-species protection against gonorrhea, and implicate several Ng surface antigens as potentially protective targets. Additionally, this study further defines the usefulness of murine infection model as a relevant experimental system for gonorrhea vaccine development.

Potential Cross-Reactive Immunity to SARS-CoV-2 From Common Human Pathogens and Vaccines

The recently emerged SARS-CoV-2 causing the ongoing COVID-19 pandemic is particularly virulent in the elderly while children are largely spared. Here, we explored the potential role of cross-reactive immunity acquired from pediatric vaccinations and exposure to common human pathogens in the protection and pathology of COVID-19. To that end, we sought for peptide matches to SARS-CoV-2 (identity ≥ 80%, in at least eight residues) in the proteomes of 25 human pathogens and in vaccine antigens, and subsequently predicted their T and B cell reactivity to identify potential cross-reactive epitopes. We found that viruses subject to pediatric vaccinations do not contain cross-reactive epitopes with SARS-CoV-2, precluding that they can provide any general protection against COVID-19. Likewise, common viruses including rhinovirus, respiratory syncytial virus, influenza virus, and several herpesviruses are also poor or null sources of cross-reactive immunity to SARS-CoV-2, discarding that immunological memory against these viruses can have any general protective or pathological role in COVID-19. In contrast, we found combination vaccines for treating diphtheria, tetanus, and pertussis infectious diseases (DTP vaccine) to be significant sources of potential cross-reactive immunity to SARS-CoV-2. DTP cross-reactive epitopes with SARS-CoV-2 include numerous CD8 and CD4 T cell epitopes with broad population protection coverage and potentially neutralizing B cell epitopes in SARS-CoV-2 Spike protein. Worldwide, children receive several DTP vaccinations, including three-four doses the first year of life and one at 4-6 years of age. Moreover, a low antigenic Tdap dose is also given at ages 9-14. Thereby, children may well be protected from SARS-CoV-2 through cross-reactive immunity elicited by DTP vaccinations, supporting testing in the general population to prevent COVID-19.

Diversification in immunogenicity genes caused by selective pressures in invasive meningococci

We studied population genomics of 486 Neisseria meningitidis isolates causing meningitis in the Netherlands during the period 1979-2003 and 2006-2013 using whole-genome sequencing to evaluate the impact of a hyperendemic period of serogroup B invasive disease. The majority of serogroup B isolates belonged to ST-41/44 (41 %) and ST-32 complex (16 %). Comparing the time periods, before and after the decline of serogroup B invasive disease, there was a decrease of ST-41/44 complex sequences (P=0.002). We observed the expansion of a sub-lineage within ST-41/44 complex sequences being associated with isolation from the 1979-2003 time period (P=0.014). Isolates belonging to this sub-lineage expansion within ST-41/44 complex were marked by four antigen allele variants. Presence of these allele variants was associated with isolation from the 1979-2003 time period after correction for multiple testing (Wald test, P=0.0043 for FetA 1-5; P=0.0035 for FHbp 14; P=0.012 for PorA 7-2.4 and P=0.0031 for NHBA two peptide allele). These sequences were associated with 4CMenB vaccine coverage (Fisher's exact test, P<0.001). Outside of the sub-lineage expansion, isolates with markedly lower levels of predicted vaccine coverage clustered in phylogenetic groups showing a trend towards isolation in the 2006-2013 time period (P=0.08). In conclusion, we show the emergence and decline of a sub-lineage expansion within ST-41/44 complex isolates concurrent with a hyperendemic period in meningococcal meningitis. The expansion was marked by specific antigen peptide allele combinations. We observed preliminary evidence for decreasing 4CMenB vaccine coverage in the post-hyperendemic period.

Methods to evaluate serogroup B meningococcal vaccines: From predictions to real-world evidence

Serogroup B meningococci (MenB) remain a prominent cause of invasive meningococcal disease (IMD). The protein-based multicomponent 4CMenB and the bivalent MenB-FHbp are the only currently available vaccines against MenB-caused IMD. Efficacy studies are not possible, due to the low incidence of IMD. Therefore, the vaccines' immunogenicity has been evaluated against several target strains chosen to quantify complement-mediated killing induced by each vaccine component in the serum bactericidal antibody assay. However, due to the wide genetic diversity and different expression levels of vaccine antigens across MenB strains, vaccine performance may differ from one strain to another. Here, we review the methods used to predict MenB strain coverage for 4CMenB and MenB-FHbp. Phenotypic assays such as the meningococcal antigen typing system (MATS, 4CMenB-specific) and the flow cytometric meningococcal antigen surface expression assay (MEASURE; MenB-FHbp-specific) were developed. Genomic approaches are also available, such as genetic MATS (gMATS) and the Bexsero antigen sequence type (BAST) scheme, both 4CMenB-specific. All methods allow tentative predictions of coverage across MenB strains, including that afforded by each vaccine antigen, and are rapid and reproducible. Real-world data on vaccine effectiveness are needed to confirm predictions obtained by these methods.

Meningococcal carriage in young adults six years after meningococcal C conjugate (MCC) vaccine catch-up campaign in Salvador, Brazil

Meningococcal carriage studies are important to improve the knowledge of disease epidemiology as well as to support appropriate vaccination strategies. We conducted a cross-sectional study to determine the prevalence and genotypic characteristics of meningococci collected from young adults in Salvador, Brazil six years after a meningococcal C conjugate vaccine catch-up campaign. From August through November 2016, oropharyngeal swabs were collected from 407 students aged 1824 years attending a private college in Salvador, Brazil. Neisseria meningitidis was identified by standard microbiology methods and real time PCR. Genetic characteristics of meningococci were assessed by rt-PCR and/or whole genome sequencing. We also investigated potential factors associated with carriage. N. meningitidis was detectable in 50 students, 39 by both culture and rt-PCR, 7 by culture alone and 4 by rt-PCR alone, resulting in an overall meningococcal carriage prevalence of 12.3% (50/407). Carriage was independently associated with male sex (adjusted PR: 1.97; 95% CI: 1.12-3.46; p = 0.018) and attending bars or parties at least once per month (aPR: 3.31; 95% CI: 1.49-7.38; p = 0.003). Molecular tests identified 92% (46/50) N. meningitidis as non-groupable, of which 63% (29/46) had the capsule null genotype; 14 NG isolates contained disrupted capsule backbones and belonged to the following genogroups: 7 B, 3 Z, 3 E and 1 W. One isolate belonged to genogroup C tested only by PCR; 3 isolates contained a complete B capsule backbones, 2 of which were determined to be NG by slide agglutination serogrouping. While most meningococcal carriage isolates were non-groupable, there was a high degree of genetic diversity present in the collection, as evidenced by 25 unique STs being detected. The carriage prevalence of meningococcal serogroup C was low among young adults. Continuous vaccination is important to maintain reduced meningococcal carriage and transmission, inducing herd protection.