Product review on the IMD serogroup B vaccine Bexsero®

Bexsero® is a multicomponent vaccine composed of four major proteins of Neisseria meningitidis: the fHbp, NHBA, NadA and PorA. This vaccine was licensed against invasive meningococcal disease (IMD) due to serogroup B isolates. When administered alone, Bexsero® showed a safety profile similar to other childhood vaccines. It provides an excellent immunogenicity but that requires booster doses in infants and young children. Although the vaccine does not seem to impact on acquisition of carriage of serogroup B isolates, it confers protection against isolates of serogroup B harboring distinct but cross-reactive variants of fHbp, NadA and NHBA. Primary vaccination schemes in infancy underwent a rapid increase after a toddler booster suggesting an anamnestic response and the establishment of a memory response. As Bexsero® targets sub-capsular proteins that can be conserved regardless the capsule, the vaccine can be effective against non-B isolates such as isolates of serogroups W and X.

An Intranasal Vaccine Based on Outer Membrane Vesicles Against SARS-CoV-2

The prevailing pandemic of SARS-CoV-2 highlights the desperate need of alternative vaccine-platforms, which are safe, effective, and can be modified to carry antigens of emerging pathogens. The current SARS-CoV-2 vaccines based on mRNA and adenoviral vector technology meet some of these criteria but still face limitations regarding administration route, mass production, stability, and storage. Herein, we introduce a novel SARS-CoV-2 vaccine candidate based on bacterial outer membrane vesicles (OMVs). Vibrio cholerae and enterotoxigenic Escherichia coli (ETEC) have been genetically modified to produce increased amounts of detoxified OMVs decorated with the receptor binding domain (RBD) of the SARS-CoV-2 Spike protein. Intranasal immunization with RBD-decorated OMVs induced not only a robust immune response against the bacterial outer membrane components but also detectable antibody titers against the Spike protein. Cell culture infection assays using a Spike-pseudotyped lentivirus confirmed the presence of SARS-CoV-2 neutralizing antibodies. Highest titers against the SARS-CoV-2 Spike protein and most potent neutralization activity were observed for an alternating immunization regimen using RBD-decorated OMVs from ETEC and V. cholerae in turn. These results highlight the versatile vaccine applications offered by OMVs via expression of heterologous antigens in the donor bacterium.

Interactions Between Pathogenic Burkholderia and the Complement System: A Review of Potential Immune Evasion Mechanisms

The genus Burkholderia contains over 80 different Gram-negative species including both plant and human pathogens, the latter of which can be classified into one of two groups: the Burkholderia pseudomallei complex (Bpc) or the Burkholderia cepacia complex (Bcc). Bpc pathogens Burkholderia pseudomallei and Burkholderia mallei are highly virulent, and both have considerable potential for use as Tier 1 bioterrorism agents; thus there is great interest in the development of novel vaccines and therapeutics for the prevention and treatment of these infections. While Bcc pathogens Burkholderia cenocepacia, Burkholderia multivorans, and Burkholderia cepacia are not considered bioterror threats, the incredible impact these infections have on the cystic fibrosis community inspires a similar demand for vaccines and therapeutics for the prevention and treatment of these infections as well. Understanding how these pathogens interact with and evade the host immune system will help uncover novel therapeutic targets within these organisms. Given the important role of the complement system in the clearance of bacterial pathogens, this arm of the immune response must be efficiently evaded for successful infection to occur. In this review, we will introduce the Burkholderia species to be discussed, followed by a summary of the complement system and known mechanisms by which pathogens interact with this critical system to evade clearance within the host. We will conclude with a review of literature relating to the interactions between the herein discussed Burkholderia species and the host complement system, with the goal of highlighting areas in this field that warrant further investigation.

Streptococcus equi-derived extracellular vesicles as a vaccine candidate against Streptococcus equi infection

Streptococcus equi subspecies equi is a pathogenic bacterium that causes strangles, a highly contagious respiratory infection in horses and other equines. The limitations of current vaccines against S. equi infection warrants the development of an affordable, safe, and effective vaccine. Because gram-positive extracellular vesicles (EVs) transport various immunogenic antigens, they are attractive vaccine candidates. Here, we purified the EVs of S. equi ATCC 39506 and evaluated them as a vaccine candidate against S. equi infection in mice. As an initial step, comparative proteomic analysis was performed to characterize the functional features of the EVs. Reverse vaccinology and knowledge-based annotations were then used to screen potential vaccine candidates (PVCs) for S. equi ATCC 39506. Finally, 32 PVCs were found to be enriched in the EV fraction, suggesting the usefulness of this fraction as a vaccine. Importantly, a significantly higher survival rate after S. equi infection was detected in mice immunized with S. equi-derived EVs via the intraperitoneal route than in mice immunized with heat-killed bacteria. Of note, immunoprecipitation-mass spectrometry results validated various immunogenic antigens within the EV proteome. In conclusion, our results suggest that S. equi-derived EVs can serve as a vaccine candidate against S. equi infection.

Interactions Between Pathogenic Burkholderia and the Complement System: A Review of Potential Immune Evasion Mechanisms

The genus Burkholderia contains over 80 different Gram-negative species including both plant and human pathogens, the latter of which can be classified into one of two groups: the Burkholderia pseudomallei complex (Bpc) or the Burkholderia cepacia complex (Bcc). Bpc pathogens Burkholderia pseudomallei and Burkholderia mallei are highly virulent, and both have considerable potential for use as Tier 1 bioterrorism agents; thus there is great interest in the development of novel vaccines and therapeutics for the prevention and treatment of these infections. While Bcc pathogens Burkholderia cenocepacia, Burkholderia multivorans, and Burkholderia cepacia are not considered bioterror threats, the incredible impact these infections have on the cystic fibrosis community inspires a similar demand for vaccines and therapeutics for the prevention and treatment of these infections as well. Understanding how these pathogens interact with and evade the host immune system will help uncover novel therapeutic targets within these organisms. Given the important role of the complement system in the clearance of bacterial pathogens, this arm of the immune response must be efficiently evaded for successful infection to occur. In this review, we will introduce the Burkholderia species to be discussed, followed by a summary of the complement system and known mechanisms by which pathogens interact with this critical system to evade clearance within the host. We will conclude with a review of literature relating to the interactions between the herein discussed Burkholderia species and the host complement system, with the goal of highlighting areas in this field that warrant further investigation.

Effect of complement Factor H on antibody repertoire and protection elicited by meningococcal capsular group B vaccines containing Factor H binding protein

Bacteria produce surface ligands for host complement regulators including Factor H (FH), which allows the bacteria to evade immunity. Meningococcal Factor H binding protein (FHbp) is both a virulence factor and a vaccine antigen. Antibodies to FHbp can neutralize its function by inhibiting binding of FH to the bacteria and confer robust complement-mediated protection. However, in the presence of human or primate FH, antibodies to FHbp do not inhibit FH binding and the protective antibody responses are decreased. This immune suppression can be overcome by modification of the FHbp antigen to decrease FH binding, which modulates the antibody repertoire to inhibit FH binding and increase protection. When FHbp is present at sufficient density on the bacterial surface, two or more antibodies can synergize to activate the complement system. Thus, modification of FHbp antigens to decrease FH binding expands the anti-FHbp antibody repertoire and increases the potential for synergistic activity.

A Meningococcal Outer Membrane Vesicle Vaccine with Overexpressed Mutant FHbp Elicits Higher Protective Antibody Responses in Infant Rhesus Macaques than a Licensed Serogroup B Vaccine

MenB-4C (Bexsero; GlaxoSmithKline Biologicals) is a licensed meningococcal vaccine for capsular B strains. The vaccine contains detergent-extracted outer membrane vesicles (dOMV) and three recombinant proteins, of which one is factor H binding protein (FHbp). In previous studies, overexpression of FHbp in native OMV (NOMV) with genetically attenuated endotoxin (LpxL1) and/or by the use of mutant FHbp antigens with low factor H (FH) binding increased serum bactericidal antibody (SBA) responses. In this study, we immunized 13 infant macaques with 2 doses of NOMV with overexpressed mutant (R41S) FHbp with low binding to macaque FH (NOMV-FHbp). Control macaques received MenB-4C (n = 13) or aluminum hydroxide adjuvant alone (n = 4). NOMV-FHbp elicited a 2-fold higher IgG anti-FHbp geometric mean titer (GMT) than MenB-4C (P = 0.003), and the anti-FHbp repertoire inhibited binding of FH to FHbp, whereas anti-FHbp antibodies to MenB-4C enhanced FH binding. MenB-4C elicited a 10-fold higher GMT against strain NZ98/254, which was used to prepare the dOMV component, whereas NOMV-FHbp elicited an 8-fold higher GMT against strain H44/76, which was the parent of the mutant NOMV-FHbp vaccine strain. Against four strains with PorA mismatched to both of the vaccines and different FHbp sequence variants, NOMV-FHbp elicited 6- to 14-fold higher SBA GMTs than MenB-4C (P ≤ 0.0002). Two of 13 macaques immunized with MenB-4C but 0 of 17 macaques immunized with NOMV-FHbp or adjuvant developed serum anti-FH autoantibodies (P = 0.18). Thus, the mutant NOMV-FHbp approach has the potential to elicit higher and broader SBA responses than a licensed group B vaccine that contains wild-type FHbp that binds FH. The mutant NOMV-FHbp also might pose less of a risk of eliciting anti-FH autoantibodies.IMPORTANCE There are two licensed meningococcal capsular B vaccines. Both contain recombinant factor H binding protein (FHbp), which can bind to host complement factor H (FH). The limitations of these vaccines include a lack of protection against some meningococcal strains and the potential to elicit autoantibodies to FH. We immunized infant macaques with a native outer membrane vesicle (NOMV) vaccine with genetically attenuated endotoxin and overproduced mutant FHbp with low binding to FH. The NOMV-FHbp vaccine stimulated higher levels of protective serum antibodies than a licensed meningococcal group B vaccine against five of six genetically diverse meningococcal strains tested. Two of 13 macaques immunized with the licensed vaccine, which contains FHbp that binds macaque FH, but 0 of 17 macaques given NOMV-FHbp or the negative control developed serum anti-FH autoantibodies Thus, in a relevant nonhuman primate model, the NOMV-FHbp vaccine elicited greater protective antibodies than the licensed vaccine and may pose less of a risk of anti-FH autoantibody.

Impact of a website based educational program for increasing vaccination coverage among adolescents

Data regarding the use of technology to improve adolescent knowledge on vaccines are scarce. The main aim of this study was to evaluate whether different web-based educational programmes for adolescents might increase their vaccination coverage. Overall, 917 unvaccinated adolescents (389 males, 42.4%; mean age ± standard deviation, 14.0 ± 2.2 years) were randomized 1:1:1 into the following groups: no intervention (n = 334), website educational program only (n = 281), or website plus face to face lesson (n = 302) groups. The use of the website plus the lesson significantly increased the overall knowledge of various aspects of vaccine-preventable disease and reduced the fear of vaccines (p < 0.001). A significant increase in vaccination coverage was observed for tetanus, diphtheria, acellular pertussis and conjugated meningococcal ACYW vaccines in the 2 groups using the website (p < 0.001), and better results were observed in the group that had also received the lesson; in this last group, significant results were observed in the increase in vaccination coverage for meningococcal B vaccine (p < 0.001). Overall, the majority of the participants liked the experience of the website, although they considered it important to further discuss vaccines with parents, experts and teachers. This study is the first to evaluate website based education of adolescents while considering all of the vaccines recommended for this age group. Our results demonstrate the possibility of increasing vaccination coverage by using a website based educational program with tailored information. However, to be most effective, this program should be supplemented with face-to-face discussions of vaccines at school and at home. Thus, specific education should also include teachers and parents so that they will be prepared to discuss with adolescents what is true and false in the vaccination field.

A deeper mining on the protein composition of VA-MENGOC-BC®: An OMV-based vaccine against N. meningitidis serogroup B and C

The protein composition of an Outer Membrane Vesicle (OMV) preparation that constitutes the active pharmaceutical ingredient of VA-MENGOC-BC®, an effective vaccine against Neisseria meningitidis serogroups B, and C is presented. This preparation has a high lipid content and five abundant membrane proteins (FetA, PorA, PorB, RmpM, and Opc), constituting approximately 70% of the total protein mass. The protein composition was determined by combining the use of the Hexapeptide Ligand Library and an orthogonal tandem fractionation of tryptic peptides by reverse-phase chromatography at alkaline and acid pH. This approach equalizes the concentration of tryptic peptides derived from low- and high-abundance proteins as well as considerably simplifying the number of peptides analyzed by LC-MS/MS, enhancing the possibility of identifying low-abundance species. Fifty-one percent of the proteins originally annotated as membrane proteins in the genome of the MC58 strain were identified. One hundred and sixty-eight low-abundance cytosolic proteins presumably occluded within OMV were also identified. Four (NadA, NUbp, GNA2091, and fHbp), out of the five antigens constituting the Bexsero® vaccine, were detected in this OMV preparation. In particular, fHbp is also the active principle of the Trumenba® vaccine developed by Pfizer. The HpuA and HpuB gene products (not annotated in the MC58 genome) were identified in the CU385 strain, a clinical isolate that is used to produce this OMV. Considering the proteins identified here and previous work done by our group, the protein catalogue of this OMV preparation was extended to 266 different protein species.

Meningococcal carriage in Dutch adolescents and young adults; a cross-sectional and longitudinal cohort study

OBJECTIVES

Current information on rates and dynamics of meningococcal carriage is essential for public health policy. This study aimed to determine meningococcal carriage prevalence, its risk factors and duration in the Netherlands, where meningococcal C vaccine coverage is >90%. Several methods to identify serogroups of meningococcal carriage isolates among adolescent and young adults were compared.

METHODS

Oropharyngeal swabs were collected from 1715 participants 13-23 years of age in 2013-2014; 300 were prospectively followed over 8 months. Cultured isolates were characterized by Ouchterlony, real-time (rt-) PCR or whole-genome sequencing (WGS). Direct swabs were assessed by rt-PCR. Questionnaires on environmental factors and behaviour were also obtained.

RESULTS

A meningococcal isolate was identified in 270/1715 (16%) participants by culture. Of MenB isolates identified by whole genome sequencing, 37/72 (51%) were correctly serogrouped by Ouchterlony, 46/51 (90%) by rt-PCR of cultured isolates, and 39/51 (76%) by rt-PCR directly on swabs. A sharp increase in carriage was observed before the age of 15 years. The age-related association disappeared after correction for smoking, level of education, frequent attendance to crowded social venues, kissing in the previous week and alcohol consumption. Three participants carried the same strain identified at three consecutive visits in an 8-month period. In these isolates, progressively acquired mutations were observed.

CONCLUSIONS

Whole genome sequencing of culture isolates was the most sensitive method for serogroup identification. Based upon results of this study and risk of meningococcal disease, an adolescent meningococcal vaccination might include children before the age of 15 years to confer individual protection and potentially to establish herd protection.

The Capricious Nature of Bacterial Pathogens: Phasevarions and Vaccine Development

Infectious diseases are a leading cause of morbidity and mortality worldwide, and vaccines are one of the most successful and cost-effective tools for disease prevention. One of the key considerations for rational vaccine development is the selection of appropriate antigens. Antigens must induce a protective immune response, and this response should be directed to stably expressed antigens so the target microbe can always be recognized by the immune system. Antigens with variable expression, due to environmental signals or phase variation (i.e., high frequency, random switching of expression), are not ideal vaccine candidates because variable expression could lead to immune evasion. Phase variation is often mediated by the presence of highly mutagenic simple tandem DNA repeats, and genes containing such sequences can be easily identified, and their use as vaccine antigens reconsidered. Recent research has identified phase variably expressed DNA methyltransferases that act as global epigenetic regulators. These phase-variable regulons, known as phasevarions, are associated with altered virulence phenotypes and/or expression of vaccine candidates. As such, genes encoding candidate vaccine antigens that have no obvious mechanism of phase variation may be subject to indirect, epigenetic control as part of a phasevarion. Bioinformatic and experimental studies are required to elucidate the distribution and mechanism of action of these DNA methyltransferases, and most importantly, whether they mediate epigenetic regulation of potential and current vaccine candidates. This process is essential to define the stably expressed antigen target profile of bacterial pathogens and thereby facilitate efficient, rational selection of vaccine antigens.

Accelerating Vaccine Formulation Development Using Design of Experiment Stability Studies

Vaccine drug product thermal stability often depends on formulation input factors and how they interact. Scientific understanding and professional experience typically allows vaccine formulators to accurately predict the thermal stability output based on formulation input factors such as pH, ionic strength, and excipients. Thermal stability predictions, however, are not enough for regulators. Stability claims must be supported by experimental data. The Quality by Design approach of Design of Experiment (DoE) is well suited to describe formulation outputs such as thermal stability in terms of formulation input factors. A DoE approach particularly at elevated temperatures that induce accelerated degradation can provide empirical understanding of how vaccine formulation input factors and interactions affect vaccine stability output performance. This is possible even when clear scientific understanding of particular formulation stability mechanisms are lacking. A DoE approach was used in an accelerated 37(°)C stability study of an aluminum adjuvant Neisseria meningitidis serogroup B vaccine. Formulation stability differences were identified after only 15 days into the study. We believe this study demonstrates the power of combining DoE methodology with accelerated stress stability studies to accelerate and improve vaccine formulation development programs particularly during the preformulation stage.

Improving the immunogenicity of a trivalent Neisseria meningitidis native outer membrane vesicle vaccine by genetic modification

Trivalent native outer membrane vesicles (nOMVs) derived from three genetically modified Neisseria meningitidis serogroup B strains have been previously evaluated immunologically in mice and rabbits. This nOMV vaccine elicited serum bactericidal activity (SBA) against multiple N. meningitidis serogroup B strains as well as strains from serogroups C, Y, W, and X. In this study, we used trivalent nOMVs isolated from the same vaccine strains and evaluated their immunogenicity in an infant Rhesus macaque (IRM) model whose immune responses to the vaccine are likely to be more predictive of the responses in human infants. IRMs were immunized with trivalent nOMV vaccines and sera were evaluated for exogenous human serum complement-dependent SBA (hSBA). Antibody responses to selected hSBA generating antigens contained within the trivalent nOMVs were also measured and we found that antibody titers against factor H binding protein variant 2 (fHbpv2) were very low in the sera from animals immunized with these original nOMV vaccines. To increase the fHbp content in the nOMVs, the vaccine strains were further genetically altered by addition of another fHbp gene copy into the porB locus. Trivalent nOMVs from the three new vaccine strains had higher fHbp antigen levels and generated higher anti-fHbp antibody responses in immunized mice and IRMs. As expected, fHbp insertion into the porB locus resulted in no PorB expression. Interestingly, higher expression of PorA, an hSBA generating antigen, was observed for all three modified vaccine strains. Compared to the trivalent nOMVs from the original strains, higher PorA levels in the improved nOMVs resulted in higher anti-PorA antibody responses in mice and IRMs. In addition, hSBA titers against other strains with PorA as the only hSBA antigen in common with the vaccine strains also increased.

Global incidence of serogroup B invasive meningococcal disease: a systematic review

Use of recently licensed vaccines against Neisseria meningitidis serogroup B (NmB) will depend partly on disease burden estimates. We systematically reviewed NmB incidence and mortality worldwide between January, 2000, and March, 2015, incorporating data from 37 articles and 12 websites. Most countries had a yearly invasive NmB incidence of less than 2 per 100,000 people. Within these relatively low incidence rates (compared with common causes of invasive bacterial diseases), substantial variation was detected between countries, with a notably higher incidence in Australia, Europe, North America, and South America. China and India had reports only of sporadic cases, and except for South Africa, sub-Saharan Africa showed a near absence of disease. In countries with consistently collected data, NmB incidence has tended to decrease, even as the proportion of invasive meningococcal disease cases caused by serogroup B has increased. With few exceptions, case-fatality ratios were fairly consistent, ranging between 3% and 10%. In high-income countries, incidence rates of NmB were relatively low compared with other vaccine-preventable diseases and might be decreasing. High case-fatality ratios, substantial disease-related morbidity, and the threat of outbreaks could nevertheless make NmB an attractive target for preventive and reactive immunisation programmes. The low availability of data from low-income and middle-income countries suggests the need for improved surveillance before vaccination strategies are designed.