Prevention of meningococcal serogroup B infections in children: a protein-based vaccine induces immunologic memory

An Intranasal OMV-Based Vaccine Induces High Mucosal and Systemic Protecting Immunity Against a SARS-CoV-2 Infection

The development of more effective, accessible, and easy to administer COVID-19 vaccines next to the currently marketed mRNA, viral vector, and whole inactivated virus vaccines is essential to curtailing the SARS-CoV-2 pandemic. A major concern is reduced vaccine-induced immune protection to emerging variants, and therefore booster vaccinations to broaden and strengthen the immune response might be required. Currently, all registered COVID-19 vaccines and the majority of COVID-19 vaccines in development are intramuscularly administered, targeting the induction of systemic immunity. Intranasal vaccines have the capacity to induce local mucosal immunity as well, thereby targeting the primary route of viral entry of SARS-CoV-2 with the potential of blocking transmission. Furthermore, intranasal vaccines offer greater practicality in terms of cost and ease of administration. Currently, only eight out of 112 vaccines in clinical development are administered intranasally. We developed an intranasal COVID-19 subunit vaccine, based on a recombinant, six-proline-stabilized, D614G spike protein (mC-Spike) of SARS-CoV-2 linked via the LPS-binding peptide sequence mCramp (mC) to outer membrane vesicles (OMVs) from Neisseria meningitidis. The spike protein was produced in CHO cells, and after linking to the OMVs, the OMV-mC-Spike vaccine was administered to mice and Syrian hamsters via intranasal or intramuscular prime-boost vaccinations. In all animals that received OMV-mC-Spike, serum-neutralizing antibodies were induced upon vaccination. Importantly, high levels of spike-binding immunoglobulin G (IgG) and A (IgA) antibodies in the nose and lungs were only detected in intranasally vaccinated animals, whereas intramuscular vaccination only induced an IgG response in the serum. Two weeks after their second vaccination, hamsters challenged with SARS-CoV-2 were protected from weight loss and viral replication in the lungs compared to the control groups vaccinated with OMV or spike alone. Histopathology showed no lesions in lungs 7 days after challenge in OMV-mC-Spike-vaccinated hamsters, whereas the control groups did show pathological lesions in the lung. The OMV-mC-Spike candidate vaccine data are very promising and support further development of this novel non-replicating, needle-free, subunit vaccine concept for clinical testing.

Development of Extracellular Vesicle Therapeutics: Challenges, Considerations, and Opportunities

Extracellular vesicles (EVs) hold great promise as therapeutic modalities due to their endogenous characteristics, however, further bioengineering refinement is required to address clinical and commercial limitations. Clinical applications of EV-based therapeutics are being trialed in immunomodulation, tissue regeneration and recovery, and as delivery vectors for combination therapies. Native/biological EVs possess diverse endogenous properties that offer stability and facilitate crossing of biological barriers for delivery of molecular cargo to cells, acting as a form of intercellular communication to regulate function and phenotype. Moreover, EVs are important components of paracrine signaling in stem/progenitor cell-based therapies, are employed as standalone therapies, and can be used as a drug delivery system. Despite remarkable utility of native/biological EVs, they can be improved using bio/engineering approaches to further therapeutic potential. EVs can be engineered to harbor specific pharmaceutical content, enhance their stability, and modify surface epitopes for improved tropism and targeting to cells and tissues in vivo. Limitations currently challenging the full realization of their therapeutic utility include scalability and standardization of generation, molecular characterization for design and regulation, therapeutic potency assessment, and targeted delivery. The fields' utilization of advanced technologies (imaging, quantitative analyses, multi-omics, labeling/live-cell reporters), and utility of biocompatible natural sources for producing EVs (plants, bacteria, milk) will play an important role in overcoming these limitations. Advancements in EV engineering methodologies and design will facilitate the development of EV-based therapeutics, revolutionizing the current pharmaceutical landscape.

Neisseria meningitidis B vaccines: recent advances and possible immunization policies

Since the development of the first-generation vaccines based on outer membrane vesicles (OMV), which were able to contain strain-specific epidemics, but were not suitable for universal use, enormous steps forward in the prevention of Neisseria meningitidis B have been made. The first multicomponent vaccine, Bexsero(®), has recently been authorized for use; other vaccines, bivalent rLP2086 and next-generation OMV vaccines, are under development. The new vaccines may substantially contribute to reducing invasive bacterial infections as they could cover most Neisseria meningitidis B strains. Moreover, other potentially effective serogroup B vaccine candidates are being studied in preclinical settings. It is therefore appropriate to review what has recently been achieved in the prevention of disease caused by serogroup B.

Meningococcal serogroup B infections: a search for a broadly protective vaccine

Meningococcal disease is mainly caused by serogroup B in many West European countries. Recently, a highly efficacious vaccine against infections caused by serogroup C has been introduced in the UK and The Netherlands. However, an effective vaccine against serogroup B has not yet become available. Outer membrane vesicle vaccines against serogroup B were previously tested in large Phase III trials but showed a low efficacy in young children. In addition, the high variability of the vaccines' main component, porin A, potentially diminishes its efficacy. Therefore, several approaches in either optimizing these outer membrane vesicle vaccines or searching for novel, highly conserved antigens are currently under investigation. The sequencing of the meningococcal genome has provided new opportunities to detect additional immunogenic epitopes. In this review, the developments in the search for a broadly protective meningococcal serogroup B vaccine will be discussed.

Bexsero: a multicomponent vaccine for prevention of meningococcal disease

Serogroup B meningococcal (MenB) disease remains a serious public health problem for which a cross-protective vaccine effective against a wide range of MenB isolates has not been available. Novartis Vaccines has developed a vaccine for the prevention of MenB disease that contains four antigenic components: factor H binding protein (fHbp), neisserial adhesin A (NadA), Neisseria heparin binding antigen (NHBA) and outer membrane vesicles from a New Zealand epidemic strain (which provides PorA). This vaccine has been submitted for regulatory review in Europe so it is timely to review the design of the vaccine, results to date in clinical studies and the potential strain coverage provided by the vaccine. It is also critical to discuss the key issues for the long-term success of the vaccine which include strain coverage, potential persistence of protection, potential effects on carriage of MenB strains, potential for escape mutants and cost effectiveness.

Population coverage analysis of T-Cell epitopes of Neisseria meningitidis serogroup B from Iron acquisition proteins for vaccine design

Although the concept of Reverse Vaccinology was first pioneered for sepsis and meningococcal meningitidis causing bacterium, Neisseria meningitides, no broadly effective vaccine against serogroup B meningococcal disease is yet available. In the present investigation, HLA distribution analysis was undertaken to select three most promiscuous T-cell epitopes out of ten computationally validated epitopes of Iron acquisition proteins from Neisseria MC58 by using the population coverage tool of Immune Epitope Database (IEDB). These epitopes have been determined on the basis of their binding ability with maximum number of HLA alleles along with highest population coverage rate values for all the geographical areas studied. The comparative population coverage analysis of moderately immunogenic and high immunogenic peptides suggests that the former may activate T-cell response in a fairly large proportion of people in most geographical areas, thus indicating their potential for development of epitope-based vaccine.

Review of meningococcal group B vaccines

No broadly effective vaccines are available for prevention of group B meningococcal disease, which accounts for >50% of all cases. The group B capsule is an autoantigen and is not a suitable vaccine target. Outer-membrane vesicle vaccines appear to be safe and effective, but serum bactericidal responses in infants are specific for a porin protein, PorA, which is antigenically variable. To broaden protection, outer-membrane vesicle vaccines have been prepared from >1 strain, from mutants with >1 PorA, or from mutants with genetically detoxified endotoxin and overexpressed desirable antigens, such as factor H binding protein. Also, recombinant protein vaccines such as factor H binding protein, given alone or in combination with other antigens, are in late-stage clinical development and may be effective against the majority of group B strains. Thus, the prospects have never been better for developing vaccines for prevention of meningococcal disease, including that caused by group B strains.

Immunogenicity and tolerability in infants of a New Zealand epidemic strain meningococcal B outer membrane vesicle vaccine

BACKGROUND

An outer membrane vesicle meningococcal vaccine (MeNZB), was developed for the New Zealand epidemic strain of Neisseria meningitidis B:4:P1.7-2,4.

METHODS

A phase II, randomized, observer blind, controlled study evaluating the safety, reactogenicity, and immunogenicity of MeNZB administered with routine New Zealand immunizations at 6 weeks, 3 months, and 5 months of age (n = 375). Group 1 (n = 250) received 25 mug MeNZB and routine immunizations with a fourth MeNZB dose given at 10 months (n = 51). Group 2 (n = 125) received routine immunizations only. Sero-response was a > or =4-fold rise in vaccine strain serum bactericidal antibody titer compared with baseline or a titer of at least 1:8 for baselines <1:4. Reactogenicity was monitored for 7 days after vaccination.

RESULTS

Sero-response in Group 1 was achieved in 53% (95% Confidence interval [CI]: 46-59, n = 239) and 69% (95% CI: 54-80, n = 45) with geometric mean antibody titers of 9 (95% CI: 7-10) and 22 (95% CI: 12-39) after the third and fourth doses, respectively. No negative interference by MeNZB on routine immunizations was detected. There were no serious adverse events judged to be vaccine related.

CONCLUSIONS

In this group of New Zealand infants, 4 MeNZB doses were required to demonstrate titers comparable with those achieved after 3 doses in older children. MeNZB was safe when used concomitantly with routine New Zealand immunizations to 5 months of age.

Meningococcal outer membrane vesicle vaccines derived from mutant strains engineered to express factor H binding proteins from antigenic variant groups 1 and 2

Meningococcal outer membrane vesicle (OMV) vaccines, which are treated with detergents to decrease endotoxin activity, are safe and effective in humans. However, the vaccines elicit serum bactericidal antibody responses largely directed against PorA, which is antigenically variable. We previously prepared a native (non-detergent-treated) OMV vaccine from a mutant of group B strain H44/76 in which the lpxL1 gene was inactivated, which resulted in penta-acylated lipid A with attenuated endotoxin activity. To enhance protection, we overexpressed factor H binding protein (fHbp) from the antigenic variant 1 group. The vaccine elicited broad serum bactericidal antibody responses in mice against strains with fHbp variant 1 (approximately 70% of group B isolates) but not against strains with variant 2 or 3. In the present study, we constructed a mutant of group B strain NZ98/254 with attenuated endotoxin that expressed both endogenous variant 1 and heterologous fHbp variant 2. A mixture of the two native OMV vaccines from the H44/76 and NZ98/254 mutants stimulated proinflammatory cytokine responses by human peripheral blood mononuclear cells similar to those stimulated by control, detergent-treated OMV vaccines from the wild-type strains. In mice, the mixture of the two native OMV vaccines elicited broad serum bactericidal antibody responses against strains with heterologous PorA and fHbp in the variant 1, 2, or 3 group. By adsorption studies, the principal bactericidal antibody target was determined to be fHbp. Thus, native OMV vaccines from mutants expressing fHbp variants have the potential to be safe for humans and to confer broad protection against meningococcal disease from strains expressing fHbp from each of the antigenic variant groups.

Combination vaccine against invasive meningococcal B and pneumococcal infections: potential epidemiological and economic impact in the Netherlands

BACKGROUND

Streptococcus pneumoniae and Neisseria meningitidis group B are among the main causes of invasive bacterial meningitis infections in infants. Worldwide, these diseases lead to significant mortality, morbidity and costs. The societal impact is especially severe since the majority of cases occur in very young infants. A combination vaccine consisting of 9-valent conjugated pneumococcal and meningococcal B components is currently being developed. The aim of this study was to estimate the potential impact and cost effectiveness from the societal perspective of vaccinating infants in The Netherlands with this combination pneumococcal and meningococcal B vaccine versus no vaccination.

METHODS

A Markov cycle model was developed using epidemiological and healthcare resource use data from 1996 to 2001. This model was used to project the annual costs, benefits and health gains associated with vaccinating all newborns. The base year for the costing was 2003 and all costs and health effects were discounted at 4%. The results of the analysis are expressed in costs per QALY and both probabilistic and univariate sensitivity analyses were used to identify the robustness of the results.

RESULTS

Annually, an average of 755 cases of invasive pneumococcal and meningococcal B infection occurred in infants aged 0-10 years in The Netherlands. Introduction of the combination vaccine would prevent 201 cases of meningococcal B meningitis and 165 cases of invasive pneumococcal disease per year. Additionally, 3410 cases of pneumococcal pneumonia and 46,350 cases of otitis media would be prevented. Vaccination would save 35 lives per year and prevent 71 cases of severe sequelae. This translates into 860 life-years gained, or 1128 QALYs gained. Alongside these health gains, vaccination would prevent euro 17,681,370 of direct medical and indirect costs attributable to meningococcal and pneumococcal infections in The Netherlands. Depending on vaccine price, cost effectiveness varied from euro 3160 (vaccine price per dose euro 20) to euro 32,170 (vaccine price euro 60 per dose) per QALY. Base-case cost effectiveness (vaccine price euro 40) was euro 17,700 per QALY. The model was most sensitive to changes in incidence, vaccine price and duration of protective efficacy.

CONCLUSION

Our results suggest that the introduction of a combination meningococcal B and pneumococcal vaccine into the Dutch infant vaccination programme is potentially cost effective compared with no vaccination.

Crystal Structure of an Anti-meningococcal Subtype P1.4 PorA Antibody Provides Basis for Peptide–Vaccine Design

In various western countries, subtype P1.4 of Neisseria meningitidis serogroup B causes the greatest incidence of meningococcal disease. To investigate the molecular recognition of this subtype, we crystallised a peptide (P1HVVVNNKVATH(P11)), corresponding to the subtype P1.4 epitope sequence of outer membrane protein PorA, in complex with a Fab fragment of the bactericidal antibody MN20B9.34 directed against this epitope. Structure determination at 1.95 A resolution revealed a unique complex of one P1.4 antigen peptide bound to two identical Fab fragments. One Fab recognises the putative epitope residues in a 2:2 type I beta-turn at residues P5NNKV(P8), whereas the other Fab binds the C-terminal residues of the peptide that we consider a crystallisation artefact. Interestingly, recognition of the P1.4 epitope peptide is mediated almost exclusively through the complementarity-determining regions of the heavy chain. We exploited the observed turn conformation for designing conformationally restricted cyclic peptides for use as a peptide vaccine. The conformational stability of the two peptide designs was assessed by molecular dynamics simulations. Unlike the linear peptide, both cyclic peptides, conjugated to tetanus toxoid as a carrier protein, elicited antibody responses in mice that recognised meningococci of subtype P1.7-2,4. Serum bactericidal assays showed that some, but not all, of the sera induced with the cyclic peptide conjugates could activate the complement system with titres that were very high compared to the titres induced by complete PorA protein in its native conformation administered in outer membrane vesicles.

Effect of a booster dose of serogroup B meningococcal vaccine on antibody response to Neisseria meningitidis in mice vaccinated with different immunization schedules

The generation and maintenance of memory antibody response by different primary immunization schedules with the Cuban-produced outer membrane protein based vaccine was investigated in a murine model. We analyzed the duration of the antibody response (IgG-ELISA and bactericidal titer) and the effect of a booster dose on the antibody response. The IgG avidity index was determined in an attempt to find a marker for memory development. This study also included an analysis of IgG subclasses induced by primary and booster immunization. The specificity of bactericidal antibodies was investigated using local strains of the same serotype/serosubtype (4,7:P1.19,15) as the vaccine strain and mutant strains lacking major outer membrane proteins. A significant recall response was induced by a booster dose given 7 months after a primary series of 2, 3 or 4 doses of vaccine. The primary antibody response showed a positive dose-effect. In contrast, a negative dose-effect was found on the booster bactericidal antibody response. There was a significant increase in IgG1 levels after the fourth and booster doses. Three doses of vaccine were required to induce a significant increase in IgG avidity. Two injections of vaccine induced a significant antibody response to PorA protein, while 4 injections induced a larger range of specificities.

Genome-based vaccines

Vaccination is an effective possibility to prevent many bacterial or viral infections, but for several important pathogens still no vaccines are available. The sequences of complete genomes are now decoded for an increasing number of bacterial pathogens and offer the possibility for comprehensive screenings to identify targets for vaccine development. In this article current genomic approaches to identify antigenic proteins of Neisseria meningitidis, Streptococcus pneumoniae, Staphylococcus aureus, and Chlamydia pneumoniae are summarized.

Meningococcal conjugate vaccines

Neisseria meningitidis is a leading cause of bacterial meningitis and sepsis in the US, Europe and in many other parts of the world, including parts of sub-Saharan Africa (known as the African 'meningitis belt'). There are > 500000 cases of meningococcal disease annually with an estimated death toll of 135000 worldwide. Approximately 10 - 15 % of survivors experience significant morbidity in the form of neurological sequelae, including hearing loss, speech disorders, loss of limbs, mental retardation and paralysis. Disease is usually caused by N. meningitidis serogroups A, B, C, Y or W-135. Prevention of meningococcal disease includes isolation, chemoprophylaxis and vaccination with available polysaccharide vaccines. However, the polysaccharide meningococcal vaccines (i.e., A and C; A, C and W-135; or A, C, Y and W-135) initially developed in the 1970s are generally poorly immunogenic in children or require repeated doses and do not produce long-lasting immunity. Conjugate vaccine technology has been very successfully used in childhood vaccines for the prevention of other bacterial meningitis pathogens, including vaccines against Haemophilus influenzae serotype b (Hib) and more recently, the seven- and nine-valent conjugate pneumococcal vaccines. Newly released meningococcal conjugate vaccines against N. meningitidis serogroup C have been highly efficacious in young children and adolescents, with minimal side effects. Conjugate vaccines targeting other important meningococcal serogroups (e.g., N. meningitidis serogroup A, responsible for the large pandemic outbreaks and the majority of disease in sub-Saharan Africa and serogroups Y and W-135) are under development and together with the serogroup C conjugates, have the potential to significantly impact worldwide sporadic and epidemic meningococcal disease. The search for an effective serogroup B meningococcal vaccine remains elusive. This manuscript reviews the conjugate meningococcal vaccines and their potential for meningococcal disease prevention.

Bacterial meningitis in children

This review comprises aspects of the epidemiology, microbiology, pathophysiology, clinical manifestations, diagnosis, management, prognosis, and prevention of bacterial meningitis, with emphasis on the paediatric population. The beginning of this millennium has witnessed the virtual disappearance of Haemophilus invasive disease in some countries, emergence of pneumococcal strains that are resistant to multiple antibiotics, isolation of pneumococci with tolerance to vancomycin, outbreaks and clusters of meningococcal meningitis in several geographical areas, and intense research in development of effective conjugate pneumococcal and meningococcal vaccines. Bacterial meningitis has become an uncommon disease in the developed world. Unfortunately, because of limited economic resources and poor living conditions, many developing countries are still affected by the devastating consequences of this life-threatening systemic infection. Basic and clinical research is needed to discover new antimicrobial and anti-inflammatory agents to improve outcome from disease. Novel strategies are needed to distribute and implement effective vaccines worldwide to prevent bacterial meningitis.

Meningococcal vaccines: a progress report

Neisseria meningitidis causes a wide range of human disease and remains a common cause of septicaemia and meningitis. Meningococcal serogroups A, B, C and Y cause the majority of cases of invasive disease in the US and throughout the world, with epidemics usually caused by serogroups A and C. Most patients with meningococcaemia, with or without meningitis, respond to standard antimicrobial therapy with either penicillin or ampicillin, but the recent emergence of meningococcal strains that are intermediately resistant to penicillin may alter these recommendations in the future. Given the devastating nature of meningococcal disease and emergence of these resistant strains, prevention (specifically through vaccination) remains the best approach to control this serious infection. A polysaccharide meningococcal vaccine is efficacious against disease caused by serogroups A, C, Y and W135, but is not effective in infants and children aged <2 years, and the duration of efficacy decreases markedly during the first 3 years after a single dose of the vaccine. Conjugate meningococcal vaccines have been developed to address these concerns. Initial studies with the meningococcal C conjugate vaccine have shown that the vaccine is safe and immunogenic and provides a T cell-dependent antigen that can be boosted by further doses of vaccine, or following exposure to the homologous organism or cross-reacting antigens. The UK recently implemented routine vaccination with the meningococcal C conjugate vaccine to all infants, and to all persons aged >1 year in a catch-up programme to immunise all school-aged children and young adults up to 20 years of age. Early postlicensure data indicate that this vaccine has shown significant efficacy in reduction of invasive meningococcal disease in these age groups. The full impact of vaccination will be determined once all age groups are immunised.

Cross-reactivity of antibodies against PorA after vaccination with a meningococcal B outer membrane vesicle vaccine

The cross-reactivity of PorA-specific antibodies induced by a monovalent P1.7-2,4 (MonoMen) and/or a hexavalent (HexaMen) meningococcal B outer membrane vesicle vaccine (OMV) in toddlers and school children was studied by serum bactericidal assays (SBA). First, isogenic vaccine strains and PorA-identical patient isolates were compared as a target in SBA, to ensure that the vaccine strains are representative for patient isolates. Geometric mean titers (GMTs) in SBA against patient isolates with subtypes P1.5-2,10 and P1.5-1,2-2 after vaccination with HexaMen were generally lower than those against vaccine strains with the same subtype, although the percentage of vaccine responders (> or =4-fold increase in SBA after vaccination) was not affected. Using various P1.7-2,4 patient isolates, GMTs as well as the number of vaccine responders were higher than for the P1.7-2,4 vaccine strain, indicating that the use of the P1.7-2,4 vaccine strain may have underestimated the immunogenicity of this subtype in HexaMen. Secondly, the cross-reactivity of antibodies induced by MonoMen and HexaMen was studied using several patient isolates that differed from the vaccine subtypes by having minor antigenic variants of one variable region (VR), by having a completely different VR or by having a different combination of VRs. MonoMen induced P1.4-specific antibodies that were cross-reactive with P1.4 variants P1.4-1 and P1.4-3. HexaMen induced a broader cross-reactive antibody response against various patient isolates with one VR identical to a vaccine subtype or a combination of VRs included in HexaMen. Cross-reactivity, measured by a fourfold increase in SBA after vaccination, against these strains ranged from 23 to 92% depending on the subtype of the tested strain and was directed against both VR1 and VR2. The extended cross-reactivity of vaccinee sera induced by HexaMen against antigenic variants has important favorable implications for meningococcal B OMV vaccine coverage.

La inmunización activa frente a Neisseria meningitidis serogrupo B

Serogroup B Neisseria meningitidis causes high morbidity and mortality rates over the world. This article reviews the current vaccination strategies against this microorganism, including vaccines already tested on a large scale, particularly those based on class 1 outer membrane proteins, and vaccines in different stages of development. The latter involve several approaches, such as modification of the polysaccharide capsule composition or conjugation with proteins, and the use of recombinant DNA techniques to obtain vaccines that express the prevalent sero-subtypes in a particular geographical area. The challenges that have emerged with the sequencing of the meningococcus B genome are also addressed.

Influence of serogroup on the presentation, course, and outcome of invasive meningococcal disease in children in the Republic of Ireland, 1995-2000

To test the hypothesis that the infecting meningococcal serogroup modulates the presentation, course, and outcome of invasive meningococcal disease (IMD), we performed a retrospective review of cases of IMD in 407 children from 2 tertiary referral centers and 2 regional centers in Ireland. Patients infected with serogroup C meningococci (n=104) were older than those infected with serogroup B (n=303; median, 2.5 vs. 1.5 years; P=.04); all other demographic and clinical parameters were similar for the 2 groups. Among serogroup B patients, mortality was 3.6% and morbidity was 10%; for serogroup C patients, mortality was 4.8% and morbidity was 12.5% (P=.81 and P=.76, respectively). Serogroup C-associated sequelae more often were multiple (P=.003). Despite the introduction of serogroup C conjugate vaccine into the routine immunization schedule of some countries, ongoing morbidity from IMD is anticipated, because group B disease was very similar to group C disease in this pediatric population.

[Immunization: leaps into the future. The vaccinology at the beginning of the 21th century (II)]

The second part of the article is a review of the perspectives on orphan vaccines, therapeutic immunization and strategies to improve the compliance to the vaccination programmes.