A universal vaccine for serogroup B meningococcus

Methods to evaluate the performance of a multicomponent meningococcal serogroup B vaccine

Meningococcal serogroup B (MenB) vaccine licensure was based on the assessment of vaccine-induced immune responses by human serum bactericidal antibody (hSBA) assay against a small number of antigen-specific strains complemented by strain coverage predictions. However, the evaluation of vaccine strain coverage is challenging because of genotypic and phenotypic diversity in surface-exposed MenB strain antigens. This narrative review considers the principal methods applied to assess the performance of a multicomponent MenB vaccine at different stages of its development. Traditional hSBA assay against a limited panel of strains is useful at all stages, while predicted strain coverage methods, such as the meningococcal antigen typing system, are used independent of clinical trials. A new method, the endogenous complement hSBA assay, has been developed to evaluate a vaccine's ability to induce a bactericidal immune response in clinical trials, in conditions that approximate real-world settings through the use of each vaccinee's serum as a source of complement and by testing against a panel of 110 epidemiologically representative MenB strains. Each assay, therefore, has a different scope during the vaccine's development and all complement each other, enabling comprehensive evaluation of the performance of multicomponent MenB vaccines, in advance of real-world evidence of vaccine effectiveness and vaccine impact.

Identification of immunogenic outer membrane vesicle vaccine antigen components using a meningococcal protein microarray

Outer membrane vesicle (OMV)-based vaccines have been employed worldwide in response to epidemic meningococcal disease outbreaks caused by Neisseria meningitidis. The complex composition of OMVs raises challenges in the identification of antigens which contribute to a protective immune response. Here, we measured total IgG antibody binding profiles to a dedicated antigen microarray using human sera from an open-label Phase II trial (NCT00962624) of 4CMenB (Bexsero), a licensed vaccine containing an OMV component. Significant IgG responses were observed against specific Outer Membrane Proteins (OMPs) from OMV antigens, including FetA, PorB, BamA and PorA. Partial Least Squares Regression was used to correlate IgG antibody reactivity profiles with the human complement-dependent killing of meningococci. We show that this approach is a powerful method to identify the potential contributions of OMV antigens - notably OpcA, FetA, PorA and PorB- towards serum bactericidal activity in human vaccinee serum against indicator strains, a recognised correlate of protection against invasive meningococcal disease.

Meningococcal vaccine 4CMenB elicits a robust cellular immune response that targets but is not consistently protective against Neisseria gonorrhoeae during murine vaginal infection

Retrospective epidemiological studies suggest that the licensed serogroup B meningococcal vaccine 4CMenB (Bexsero) provides some protection against the closely related pathogen Neisseria gonorrhoeae in humans. This result has been replicated in murine models of gonococcal colonization, with a gonococci-reactive humoral response and more rapid clearance of vaginal infection. However, immunization with 4CMenB consistently elicits a robust humoral response but does not protect all individuals; hence, the correlates of protection remain undefined. Herein, we exploit the fact that 4CMenB promotes gonococcal clearance in only a subset of immunized mice to perform a broad analysis of the adaptive response in animals that are or are not protected. We observe that 4CMenB vaccination induces high levels of anti-neisserial antibodies in both serum and the vaginal lumen, and a robust cellular response highlighted by an increase in both conventional naïve and memory populations as well as unconventional lymphocyte subsets. Multiplex and flow cytometry results show that 4CMenB vaccination generates a robust, multi-faceted cytokine response that spans numerous T cell subsets (TH1, TH2, Treg, and TH17) and that non-T non-B lymphocytes play an important role in this response, as indicated by an unbiased principal component analysis. Together, this work provides the first comprehensive analysis of the robust humoral and complex cellular response to 4CMenB so as to reveal the effector mechanisms that may contribute to immunity against vaginal gonococcal infection.IMPORTANCEGonorrhea, a sexually transmitted infection caused by the human-specific pathogen Neisseria gonorrhoeae (Ngo), is a growing public health concern due to its rise in prevalence and increasing antibiotic resistance against first-line agents. There is currently no vaccine available for this important bacterium due, in part, to our lack of understanding of immune correlates of protection. Interestingly, a human-approved vaccine (4CMenB; Bexsero) against a related pathogen (N. meningitidis; a cause of meningitis) has demonstrated some protection against gonorrhea in epidemiologic studies. Herein, we provide the first detailed analysis of cellular and antibody-mediated immune responses to this vaccine in animals protected against gonococcal colonization. These findings provide new understanding regarding immune correlates of protection against N. gonorrhoeae, providing new insight into immune protection and helping guide the development of a much-needed vaccine.

Optimization of methods for isolation and purification of outer membrane vesicles (OMVs) from Neisseria lactamica

Outer membrane vesicles (OMVs) are nanoparticles released by Gram-negative bacteria during growth, mainly under stress conditions. OMV-based vaccines have played an important role in vaccination against Neisseria meningitidis serogroup B (MenB), stimulating research into novel approaches for developing more effective vaccines. OMVs released by the bacterium Neisseria lactamica have emerged as a promising platform for new vaccine development, especially as carriers in subunit vaccines. Despite their importance, some challenges remain in obtaining and purifying OMVs. The most commonly employed methods for OMV isolation and purification are ultracentrifugation (UC) and size exclusion chromatography (SEC). However, these techniques could present limitations for large-scale production and often result in low yields. This study investigated techniques such as tangential flow filtration (TFF), membrane chromatography, and mixed-mode (multimodal) chromatography as potential replacements for UC and SEC. Among the TFF methods evaluated, the sample obtained on the membrane with a 300-kDa cutoff showed a profile more similar to UC but with more than double the total protein recovery. Sartobind® Q membrane chromatography was ineffective for OMV purification, in the conditions evaluated, with a recovery of 8.7%. Conversely, multimodal Capto™ Adhere chromatography recovered 59.0%, while Capto™ Core 400 yielded a recovery of 72.0%, proving to be more effective for purification when analyzed by high-performance liquid chromatography (HPLC). Thus, combining TFF with a 300-kDa membrane followed by Capto™ Core 400 chromatography can be applied as strategy for large-scale applications offering high recovery and purity. KEY POINTS: • Evaluation of TFF, membrane and multimodal chromatography techniques for OMV purification. • Improved Neisseria lactamica OMV yields combining TFF and multimodal chromatography. • A process for OMV purification from a non-pathogenic organism feasible to scale up.

Advancing vaccine development in genomic era: a paradigm shift in vaccine discovery

The issue of antibiotic resistance is increasing with time because of the quick rise of microbial strains. Overuse of antibiotics has led to multidrug-resistant, pan-drug-resistant, and extensively drug-resistant bacterial strains, which have worsened the situation. Different techniques have been considered and applied to combat this issue, such as developing new antibiotics, practicing antibiotic stewardship, improving hygiene levels, and controlling antibiotic overuse. Vaccine development made a substantial contribution to overcoming this issue, although it has been underestimated. In the recent era, reverse vaccinology has contributed to developing different kinds of vaccines against pathogens, revolutionizing the vaccine development process. Reverse vaccinology helps to prioritize better vaccine candidates by using various tools to filter the pathogen's complete genome. In this review, we will shed light on computational vaccine designing, immunoinformatic tools, genomic and proteomic data, and the challenges and success stories of computational vaccine designing.

New High-Throughput Method for Aluminum Content Determination in Vaccine Formulations

OBJECTIVE

This manuscript describes an innovative, non-destructive, high-throughput method for the quantification of aluminum hydroxide in aluminum-adjuvanted vaccines, eliminating the need of reagents and providing real-time results. The method is based on a spectrophotometric principle, and several model proteins were studied and tested with the aim to simulate the behavior of aluminum-adjuvanted antigens.

METHODS

As a proof of concept, the MenB vaccine was used, and the titration of aluminum hydroxide (AH) with ethylenediaminetetraacetic acid (EDTA) was used as an orthogonal reference, as it is one of the current release methods for the content determination of aluminum-hydroxide-adjuvanted vaccine drug products (DPs). The factors influencing the spectrophotometric analysis, such as different plate 96/well containers, variation in the sedimentation of the suspension due to component addition errors during formulation, and batch-to-batch variation were studied to assess the method's robustness. Five concentration levels (ranging from 2.0 to 4.0 mg/mL AH) with two different batches of aluminum hydroxide were each measured with independent preparations performed by three different operators, for a total of four sessions/operator and 20 formulations/session. An in-depth statistical study was carried out with generated data to assess the precision (in terms of intermediate precision and repeatability), accuracy, linearity, and specificity of the method.

RESULTS

The novel spectrophotometric method and the official release one (potentiometric) yielded comparable results, demonstrating the potential of this new method as a release test for AH-adjuvanted products. A simple calibration curve enabled the measurement of samples in a 96-well plate in just a few minutes.

CONCLUSIONS

We developed a novel method for Aluminum concentration determination in Aluminum-containing pharmaceutical products, like alum-adjuvanted vaccines. This method is fast, completely automatable, and as precise and accurate as already-in-place release methods.

NIAID Workshop Report: Systematic Approaches for ESKAPE Bacteria Antigen Discovery

On 14-15 November 2023, the National Institute of Allergy and Infectious Diseases (NIAID) organized a workshop entitled "Systematic Approaches for ESKAPE Bacteria Antigen Discovery". The goal of the workshop was to engage scientists from diverse relevant backgrounds to explore novel technologies that can be harnessed to identify and address current roadblocks impeding advances in antigen and vaccine discoveries for the ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). The workshop consisted of four sessions that addressed ESKAPE infections, antigen discovery and vaccine efforts, and new technologies including systems immunology and vaccinology approaches. Each session was followed by a panel discussion. In total, there were over 260 in-person and virtual attendees, with high levels of engagement. This report provides a summary of the event and highlights challenges and opportunities in the field of ESKAPE vaccine discovery.

Molecular and Immunological Properties of a Chimeric Glycosyl Hydrolase 18 Based on Immunoinformatics Approaches: A Design of a New Anti-Leishmania Vaccine

Leishmaniasis is a chronic inflammatory zoonotic illness caused by protozoan flagellates belonging to the Leishmania genus. Current data suggest that over 1 billion people worldwide are susceptible to infection, primarily in tropical and subtropical countries, where up to 2 million new cases are reported annually. Therefore, the development of a vaccine is crucial to combating this disease. This study employed immunoinformatics approaches to design a multiepitope anti-Leishmania vaccine, GH18-cpLeish, based on a cluster of six glycosyl hydrolases 18. We identified six helper T lymphocyte (HTL) epitopes and twenty-six cytotoxic T lymphocyte (CTL) epitopes with IC50 values <50 nM, indicating high affinity. Additionally, we also identified 20 continuous and twenty-six discontinuous B-cell epitopes. Analysis for allergenicity and toxicity showed no potential to induce these phenomena. All data obtained from in silico tools suggest that physicochemical and biological studies indicate that the GH18-cpLeish chimeric protein is a promising candidate for an anti-Leishmania vaccine. Docking analysis showed that the Pep1-cpLeish::TLR1, Pep1-cpLeish::TLR2, Pep1-cpLeish::/TLR3, and Pep1-cpLeish::/TLR4 complexes maintained a stable form. The best interaction cluster score was observed in the complex Pep1-cpLeish::TLR2 (center = -622.6 and lowest energy = -841.7 kcal.mol-1) followed by the complexes Pep1-cpLeish::TLR4 (center = -590.3 and lowest energy = -590.3 kcal.mol-1), Pep1-cpLeish::TLR3 (center = -589.1 and lowest energy = -657.0 kcal.mol-1), and Pep1-cpLeish::TLR1 (center = -504.1 and lowest energy = -602.9 kcal.mol-1), respectively. This study suggests that GH18-cpLeish may be suitable for constructing second-generation anti-Leishmania and even third-generation vaccines, given that its gene sequence is optimized for this purpose.

Refinement and optimisation of Neisseria gonorrhoeae NHBA and MetQ vaccine candidates

Neisseria gonorrhoeae has a significant impact on reproductive health with an estimated 82 million new cases of infection per year worldwide. Due to the ongoing emergence of multidrug-resistant N. gonorrhoeae strains, the high number of asymptomatic cases, and the risk of disease sequelae, the development of a gonococcal vaccine is urgently needed. We have previously described two potential gonococcal vaccine antigens, cNHBA (C-terminal fragment of the Neisseria Heparin Binding Antigen) and MetQ (methionine-binding protein). This study aimed to optimise these antigens for improved immune responses and to facilitate vaccine production, by investigating cNHBA fusions with the full-length MetQ protein or N-terminal and C-terminal MetQ fragments (Met1 and Met2, respectively) adjuvanted with aluminium hydroxide. The cNHBA and MetQ fragments and fusion antigens were all immunogenic in mice, generating a predominantly IgG1 response. Antibodies mediated bacterial killing via both serum bactericidal activity (SBA) and opsonophagocytic activity (OPA), and reduced adherence to cervical and urethral epithelial cells. Among the antigen fusions tested, MetQ-cNHBA and cNHBA-Met2 generated the highest SBA, OPA and adherence blocking titres and are proposed as promising optimised antigens for N. gonorrhoeae vaccine development.

Urgent Need to Understand and Prevent Gonococcal Infection: From the Laboratory to Real-World Context

Neisseria gonorrhoeae is widespread globally. Primary prevention is unsuccessful and antimicrobial resistance threatens optimal management. There is no specific vaccine and natural infection studies show that N gonorrhoeae can avoid and suppress immune responses. In addition to extensive variation in expression and specificity of many gonococcal surface antigens, it induces a robust inflammatory response through the Th17 pathway with a large influx of neutrophils and inflammatory cytokines but evades macrophages. The Th1- and Th2-mediated response is suppressed, resulting in low, short-lived antibody titers. Real-world evidence suggests that gonorrhea cases are reduced among recipients of Neisseria meningitidis group B vaccines containing outer membrane vesicles (OMVs). Although the first randomized trial of an OMV-containing MenB vaccine against N gonorrhoeae infection did not show statistically significant vaccine efficacy, ongoing trials might shed further light. Several candidate vaccine antigens for a gonococcal-specific vaccine are being evaluated preclinically but only one has reached clinical trials.

Characterisation and Immunogenicity of Neisseria cinerea outer membrane vesicles displaying NadA, NHBA and fHbp from Neisseria meningitidis serogroup B

More affordable and effective vaccines against bacterial meningitis caused by Neisseria meningitidis serogroup B are still required for global prevention. We have previously shown that modified outer membrane vesicles (mOMVs) from commensal Neisseria cinerea can be used as a platform to induce immune responses against meningococcal antigens. The aim of the present study was to use a combination of two genetically engineered mOMVs to express multiple antigens from N. meningitidis known to be involved in protective immunity to meningococcal meningitis (different variants of factor H binding protein (fHbp), Neisseria Heparin Binding Antigen (NHBA) and Neisseria Adhesin A (NadA)). Antigen expression in the mOMVs was confirmed by Western blotting; detoxification of the lipooligosaccharide (LOS) was confirmed by measuring human Toll-like receptor 4 (hTLR4) activation using in vitro cell assays. Mice immunised with a combination of two mOMVs expressing fHbp, NHBA and NadA produced antibodies to all the antigens. Furthermore, serum bactericidal activity (SBA) was induced by the immunisation, with mOMVs expressing NadA displaying high SBA titres against a nadA+ MenB strain. The work highlights the potential of mOMVs from N. cinerea to induce functional immune responses against multiple antigens involved in the protective immune response to meningococcal disease.

Neisserial adhesin A (NadA) binds human Siglec-5 and Siglec-14 with high affinity and promotes bacterial adhesion/invasion

Neisserial adhesin A (NadA) is a meningococcal surface protein included as recombinant antigen in 4CMenB, a protein-based vaccine able to induce protective immune responses against Neisseria meningitidis serogroup B (MenB). Although NadA is involved in the adhesion/invasion of epithelial cells and human myeloid cells, its function in meningococcal physiology is still poorly understood. To clarify the role played by NadA in the host-pathogen interaction, we sought to identify its cellular receptors. We screened a protein microarray encompassing 2,846 human and 297 mouse surface/secreted recombinant proteins using recombinant NadA as probe. Efficient NadA binding was revealed on the paired sialic acid-binding immunoglobulin-type lectins receptors 5 and 14 (Siglec-5 and Siglec-14), but not on Siglec-9 therein used as control. The interaction was confirmed by biochemical tools with the determination of the KD value in the order of nanomolar and the identification of the NadA binding site by hydrogen-deuterium exchange coupled to mass spectrometry. The N-terminal domain of the Siglec-5 that recognizes the sialic acid was identified as the NadA binding domain. Intriguingly, exogenously added recombinant soluble Siglecs, including Siglec-9, were found to decorate N. meningitidis surface in a NadA-dependent manner. However, Siglec-5 and Siglec-14 transiently expressed in CHO-K1 cells endorsed NadA binding and increased N. meningitidis adhesion/invasion while Siglec-9 did not. Taken together, Siglec-5 and Siglec-14 satisfy all features of NadA receptors suggesting a possible role of NadA in the acute meningococcal infection.IMPORTANCEBacteria have developed several strategies for cell colonization and immune evasion. Knowledge of the host and pathogen factors involved in these mechanisms is crucial to build efficacious countermoves. Neisserial adhesin A (NadA) is a meningococcal surface protein included in the anti-meningococcus B vaccine 4CMenB, which mediates adhesion to and invasion of epithelial cells. Although NadA has been shown to bind to other cell types, like myeloid and endothelial cells, it still remains orphan of a defined host receptor. We have identified two strong NadA interactors, Siglec-5 and Siglec-14, which are mainly expressed on myeloid cells. This showcases that NadA is an additional and key player among the Neisseria meningitidis factors targeting immune cells. We thus provide novel insights on the strategies exploited by N. meningitidis during the infection process, which can progress to a severe illness and death.

Diversity and selection analyses identify transmission-blocking antigens as the optimal vaccine candidates in Plasmodium falciparum

BACKGROUND

A highly effective vaccine for malaria remains an elusive target, at least in part due to the under-appreciated natural parasite variation. This study aimed to investigate genetic and structural variation, and immune selection of leading malaria vaccine candidates across the Plasmodium falciparum's life cycle.

METHODS

We analysed 325 P. falciparum whole genome sequences from Zambia, in addition to 791 genomes from five other African countries available in the MalariaGEN Pf3k Database. Ten vaccine antigens spanning three life-history stages were examined for genetic and structural variations, using population genetics measures, haplotype network analysis, and 3D structure selection analysis.

FINDINGS

Among the ten antigens analysed, only three in the transmission-blocking vaccine category display P. falciparum 3D7 as the dominant haplotype. The antigens AMA1, CSP, MSP119 and CelTOS, are much more diverse than the other antigens, and their epitope regions are under moderate to strong balancing selection. In contrast, Rh5, a blood stage antigen, displays low diversity yet slightly stronger immune selection in the merozoite-blocking epitope region. Except for CelTOS, the transmission-blocking antigens Pfs25, Pfs48/45, Pfs230, Pfs47, and Pfs28 exhibit minimal diversity and no immune selection in epitopes that induce strain-transcending antibodies, suggesting potential effectiveness of 3D7-based vaccines in blocking transmission.

INTERPRETATION

These findings offer valuable insights into the selection of optimal vaccine candidates against P. falciparum. Based on our results, we recommend prioritising conserved merozoite antigens and transmission-blocking antigens. Combining these antigens in multi-stage approaches may be particularly promising for malaria vaccine development initiatives.

FUNDING

Purdue Department of Biological Sciences; Puskas Memorial Fellowship; National Institute of Allergy and Infectious Diseases (U19AI089680).

Diversity and selection analyses identify transmission-blocking antigens as the optimal vaccine candidates in Plasmodium falciparum

Background

A highly effective vaccine for malaria remains an elusive target, at least in part due to the under-appreciated natural parasite variation. This study aimed to investigate genetic and structural variation, and immune selection of leading malaria vaccine candidates across the Plasmodium falciparum's life cycle.

Methods

We analyzed 325 P. falciparum whole genome sequences from Zambia, in addition to 791 genomes from five other African countries available in the MalariaGEN Pf3k Rdatabase. Ten vaccine antigens spanning three life-history stages were examined for genetic and structural variations, using population genetics measures, haplotype network analysis, and 3D structure selection analysis.

Findings

Among the ten antigens analyzed, only three in the transmission-blocking vaccine category display P. falciparum 3D7 as the dominant haplotype. The antigens AMA1, CSP, MSP119 and CelTOS, are much more diverse than the other antigens, and their epitope regions are under moderate to strong balancing selection. In contrast, Rh5, a blood stage antigen, displays low diversity yet slightly stronger immune selection in the merozoite-blocking epitope region. Except for CelTOS, the transmission-blocking antigens Pfs25, Pfs48/45, Pfs230, Pfs47, and Pfs28 exhibit minimal diversity and no immune selection in epitopes that induce strain-transcending antibodies, suggesting potential effectiveness of 3D7-based vaccines in blocking transmission.

Interpretations

These findings offer valuable insights into the selection of optimal vaccine candidates against P. falciparum. Based on our results, we recommend prioritizing conserved merozoite antigens and transmission-blocking antigens. Combining these antigens in multi-stage approaches may be particularly promising for malaria vaccine development initiatives.

Funding

Purdue Department of Biological Sciences; Puskas Memorial Fellowship; National Institute of Allergy and Infectious Diseases (U19AI089680).

Promising developments in gonococcal vaccines

PURPOSE OF REVIEW

While effective vaccines to prevent invasive infections by Neisseria meningitidis have been deployed around the world, development of a vaccine to prevent Neisseria gonorrhoeae has lagged. After multiple failed vaccine candidates, vaccine development for N. gonorrhoeae is showing promise for the first time in several decades. This review highlights recent progress in the field.

RECENT FINDINGS

Vaccines containing outer-membrane vesicles (OMV) have been used to manage outbreaks of the serogroup B N. meningitidis in a number of countries. Epidemiologic studies indicate these vaccination campaigns were associated with reductions in reported N. gonorrhoeae infections. Recently, a serogroup B N. meningitidis vaccine containing both recombinant antigens and OMV has been licensed through much of the world. Epidemiologic studies also demonstrate associations between 4CMenB immunization and reduced N. gonorrhoeae infections. Additionally, mathematical modeling studies have begun to identify potential strategies for vaccine deployment to maximize reduction of infections.

SUMMARY

After several decades with little progress towards an effective gonococcal vaccine, large observational studies have provided evidence that a new generation of group B N. meningitidis vaccines containing OMV have serendipitously restarted the field. Ongoing clinical trials will soon provide definitive evidence regarding the efficacy of these vaccines in preventing N. gonorrhoeae infection.

DNA nanostructures as biomolecular scaffolds for antigen display

Nanoparticle-based vaccines offer a multivalent approach for antigen display, efficiently activating T and B cells in the lymph nodes. Among various nanoparticle design strategies, DNA nanotechnology offers an innovative alternative platform, featuring high modularity, spatial addressing, nanoscale regulation, high functional group density, and lower self-antigenicity. This review delves into the potential of DNA nanostructures as biomolecular scaffolds for antigen display, addressing: (1) immunological mechanisms behind nanovaccines and commonly used nanoparticles in their design, (2) techniques for characterizing protein NP-antigen complexes, (3) advancements in DNA nanotechnology and DNA-protein assembly approach, (4) strategies for precise antigen presentation on DNA scaffolds, and (5) current applications and future possibilities of DNA scaffolds in antigen display. This analysis aims to highlight the transformative potential of DNA nanoscaffolds in immunology and vaccinology. This article is categorized under: Biology-Inspired Nanomaterials > Nucleic Acid-Based Structures Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

On-Demand Vaccine Production via Dock-and-Display of Biotinylated Antigens on Bacterial Extracellular Vesicles

Engineered outer membrane vesicles (OMVs) derived from Gram-negative bacteria are a promising vaccine technology for developing immunity against diverse pathogens. However, antigen display on OMVs can be challenging to control and highly variable due to bottlenecks in protein expression and localization to the bacterial host cell's outer membrane, especially for bulky and complex antigens. Here, we describe methods related to a universal vaccine technology called AvidVax (avidin-based vaccine antigen crosslinking) for rapid and simplified assembly of antigens on the exterior of OMVs during vaccine development. The AvidVax platform involves remodeling the OMV surface with multiple copies of a synthetic antigen-binding protein (SNAP), which is an engineered fusion protein comprised of an outer membrane scaffold protein linked to a biotin-binding protein. The resulting SNAPs enable efficient decoration of OMVs with a molecularly diverse array of biotinylated subunit antigens, including globular and membrane proteins, glycans and glycoconjugates, haptens, lipids, nucleic acids, and short peptides. We detail the key steps in the AvidVax vaccine production pipeline including preparation and isolation of SNAP-OMVs, biotinylation and enrichment of vaccine antigens, and formulation and characterization of antigen-loaded SNAP-OMVs.

Bioinformatics Analysis of Global Diversity in Meningococcal Vaccine Antigens over the Past 10 Years: Vaccine Efficacy Prognosis

Neisseria meningitidis (N. meningitidis) serogroup B (MenB) is the leading cause of invasive meningococcal disease worldwide. The pathogen has a wide range of virulence factors, which are potential vaccine components. Studying the genetic variability of antigens within a population, especially their long-term persistence, is necessary to develop new vaccines and predict the effectiveness of existing ones. The multicomponent 4CMenB vaccine (Bexsero), used since 2014, contains three major genome-derived recombinant proteins: factor H-binding protein (fHbp), Neisserial Heparin-Binding Antigen (NHBA) and Neisserial adhesin A (NadA). Here, we assessed the prevalence and sequence variations of these vaccine antigens in a panel of 5667 meningococcal isolates collected worldwide over the past 10 years and deposited in the PubMLST database. Using multiple amino acid sequence alignments and Random Forest Classifier machine learning methods, we estimated the potential strain coverage of fHbp and NHBA vaccine variants (51 and about 25%, respectively); the NadA antigen sequence was found in only 18% of MenB genomes analyzed, but cross-reactive variants were present in less than 1% of isolates. Based on our findings, we proposed various strategies to improve the 4CMenB vaccine and broaden the coverage of N. meningitidis strains.

Immunogenicity and Pre-Clinical Efficacy of an OMV-Based SARS-CoV-2 Vaccine

The vaccination campaign against SARS-CoV-2 relies on the world-wide availability of effective vaccines, with a potential need of 20 billion vaccine doses to fully vaccinate the world population. To reach this goal, the manufacturing and logistic processes should be affordable to all countries, irrespective of economical and climatic conditions. Outer membrane vesicles (OMVs) are bacterial-derived vesicles that can be engineered to incorporate heterologous antigens. Given the inherent adjuvanticity, such modified OMVs can be used as vaccines to induce potent immune responses against the associated proteins. Here, we show that OMVs engineered to incorporate peptides derived from the receptor binding motif (RBM) of the spike protein from SARS-CoV-2 elicit an effective immune response in vaccinated mice, resulting in the production of neutralizing antibodies (nAbs) with a titre higher than 1:300. The immunity induced by the vaccine is sufficient to protect the animals from intranasal challenge with SARS-CoV-2, preventing both virus replication in the lungs and the pathology associated with virus infection. Furthermore, we show that OMVs can be effectively decorated with the RBM of the Omicron BA.1 variant and that such engineered OMVs induce nAbs against Omicron BA.1 and BA.5, as measured using the pseudovirus neutralization infectivity assay. Importantly, we show that the RBM438-509 ancestral-OMVs elicited antibodies which efficiently neutralize in vitro both the homologous ancestral strain, the Omicron BA.1 and BA.5 variants with a neutralization titre ranging from 1:100 to 1:1500, suggesting its potential use as a vaccine targeting diverse SARS-CoV-2 variants. Altogether, given the convenience associated with the ease of engineering, production and distribution, our results demonstrate that OMV-based SARS-CoV-2 vaccines can be a crucial addition to the vaccines currently available.

Malaria Genomics, Vaccine Development, and Microbiome

Recent advances in malaria genetics and genomics have transformed many aspects of malaria research in areas of molecular evolution, epidemiology, transmission, host-parasite interaction, drug resistance, pathogenicity, and vaccine development. Here, in addition to introducing some background information on malaria parasite biology, parasite genetics/genomics, and genotyping methods, we discuss some applications of genetic and genomic approaches in vaccine development and in studying interactions with microbiota. Genetic and genomic data can be used to search for novel vaccine targets, design an effective vaccine strategy, identify protective antigens in a whole-organism vaccine, and evaluate the efficacy of a vaccine. Microbiota has been shown to influence disease outcomes and vaccine efficacy; studying the effects of microbiota in pathogenicity and immunity may provide information for disease control. Malaria genetics and genomics will continue to contribute greatly to many fields of malaria research.

A chimeric protein-based vaccine elicits a strong IgG antibody response and confers partial protection against Shiga toxin-producing Escherichia coli in mice

Background

Shiga toxin-producing Escherichia coli (STEC) is a foodborne pathogen that causes gastrointestinal infections, ranging from acute diarrhea and dysentery to life-threatening diseases such as Hemolytic Uremic Syndrome. Currently, a vaccine to prevent STEC infection is an unmet medical need.

Results

We developed a chimeric protein-based vaccine targeting seven virulence factors of STEC, including the Stx2B subunit, Tir, Intimin, EspA, Cah, OmpT, and AggA proteins. Immunization of mice with this vaccine candidate elicited significant humoral and cellular immune responses against STEC. High levels of specific IgG antibodies were found in the serum and feces of immunized mice. However, specific IgA antibodies were not detected in either serum or feces. Furthermore, a significantly higher percentage of antigen-specific CD4+ T cells producing IFN-γ, IL-4, and IL-17 was observed in the spleens of immunized mice. Notably, the immunized mice showed decreased shedding of STEC O157:H7 and STEC O91:H21 strains and were protected against weight loss during experimental infection. Additionally, infection with the STEC O91:H21 strain resulted in kidney damage in control unimmunized mice; however, the extent of damage was slightly lower in immunized mice. Our findings suggest that IgG antibodies induced by this vaccine candidate may have a role in inhibiting bacterial adhesion and complement-mediated killing.

Conclusion

This study provides evidence that IgG responses are involved in the host defense against STEC. However, our results do not rule out that other classes of antibodies also participate in the protection against this pathogen. Additional work is needed to improve the protection conferred by our vaccine candidate and to elucidate the relevant immune responses that lead to complete protection against this pathogen.

In vaccinated individuals serum bactericidal activity against B meningococci is abrogated by C5 inhibition but not by inhibition of the alternative complement pathway

Introduction

Several diseases caused by the dysregulation of complement activation can be treated with inhibitors of the complement components C5 and/or C3. However, complement is required for serum bactericidal activity (SBA) against encapsulated Gram-negative bacteria. Therefore, C3 and C5 inhibition increases the risk of invasive disease, in particular by Neisseria meningitidis. As inhibitors against complement components other than C3 and C5 may carry a reduced risk of infection, we compared the effect of inhibitors targeting the terminal pathway (C5), the central complement component C3, the alternative pathway (FB and FD), and the lectin pathway (MASP-2) on SBA against serogroup B meningococci.

Methods

Serum from adults was collected before and after vaccination with the meningococcal serogroup B vaccine 4CMenB and tested for meningococcal killing. Since the B capsular polysaccharide is structurally similar to certain human polysaccharides, 4CMenB was designed to elicit antibodies against meningococcal outer membrane proteins.

Results

While only a few pre-vaccination sera showed SBA against the tested B meningococcal isolates, 4CMenB vaccination induced potent complement-activating IgG titers against isolates expressing a matching allele of the bacterial cell surface-exposed factor H-binding protein (fHbp). SBA triggered by these cell surface protein-specific antibodies was blocked by C5 and reduced by C3 inhibition, whereas alternative (factor B and D) and lectin (MASP-2) pathway inhibitors had no effect on the SBA of post-4CMenB vaccination sera.

Discussion

Compared to the SBA triggered by A,C,W,Y capsule polysaccharide conjugate vaccination, SBA against B meningococci expressing a matching fHbp allele was remarkably resilient against the alternative pathway inhibition.

An adenoviral-vectored vaccine confers seroprotection against capsular group B meningococcal disease

Adenoviral-vectored vaccines are licensed for prevention of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and Ebola virus, but, for bacterial proteins, expression in a eukaryotic cell may affect the antigen's localization and conformation or lead to unwanted glycosylation. Here, we investigated the potential use of an adenoviral-vectored vaccine platform for capsular group B meningococcus (MenB). Vector-based candidate vaccines expressing MenB antigen factor H binding protein (fHbp) were generated, and immunogenicity was assessed in mouse models, including the functional antibody response by serum bactericidal assay (SBA) using human complement. All adenovirus-based vaccine candidates induced high antigen-specific antibody and T cell responses. A single dose induced functional serum bactericidal responses with titers superior or equal to those induced by two doses of protein-based comparators, as well as longer persistence and a similar breadth. The fHbp transgene was further optimized for human use by incorporating a mutation abrogating binding to the human complement inhibitor factor H. The resulting vaccine candidate induced high and persistent SBA responses in transgenic mice expressing human factor H. The optimized transgene was inserted into the clinically relevant ChAdOx1 backbone, and this vaccine has now progressed to clinical development. The results of this preclinical vaccine development study underline the potential of vaccines based on genetic material to induce functional antibody responses against bacterial outer membrane proteins.

OpcA and PorB are novel bactericidal antigens of the 4CMenB vaccine in mice and humans

The ability of Neisseria meningitidis Outer Membrane Vesicles (OMV) to induce protective responses in humans is well established and mainly attributed to Porin A (PorA). However, the contribution of additional protein antigens to protection remains to be elucidated. In this study we dissected the immunogenicity of antigens originating from the OMV component of the 4CMenB vaccine in mice and humans. We collected functional data on a panel of strains for which bactericidal responses to 4CMenB in infants was attributable to the OMV component and evaluated the role of 30 OMV-specific protein antigens in cross-coverage. By using tailor-made protein microarrays, the immunosignature of OMV antigens was determined. Three of these proteins, OpcA, NspA, and PorB, triggered mouse antibodies that were bactericidal against several N. meningitidis strains. Finally, by genetic deletion and/or serum depletion studies, we demonstrated the ability of OpcA and PorB to induce functional immune responses in infant sera after vaccination. In conclusion, while confirming the role of PorA in eliciting protective immunity, we identified two OMV antigens playing a key role in protection of infants vaccinated with the 4CMenB vaccine against different N. meningitidis serogroup B strains.

Effective Multivalent Oriented Presentation of Meningococcal NadA Antigen Trimers by Self-Assembling Ferritin Nanoparticles

The presentation of viral antigens on nanoparticles in multivalent arrays has emerged as a valuable technology for vaccines. On the nanoparticle surface, highly ordered, repetitive arrays of antigens can mimic their geometric arrangement on virion surfaces and elicit stronger humoral responses than soluble viral antigens. More recently, bacterial antigens have been presented on self-assembling protein nanoparticles and have elicited protective antibody and effective T-helper responses, further supporting the nanoparticle platform as a universal approach for stimulating potent immunogenicity. Here, we present the rational design, structural analysis, and immunogenicity of self-assembling ferritin nanoparticles displaying eight copies of the Neisseria meningitidis trimeric adhesin NadA. We engineered constructs consisting of two different NadA fragments, head only and head with stalk, that we fused to ferritin and expressed in Escherichia coli. Both fusion constructs self-assembled into the expected nanoparticles as determined by Cryo electron microscopy. In mice, the two nanoparticles elicited comparable NadA antibody levels that were 10- to 100-fold higher than those elicited by the corresponding NadA trimer subunits. Further, the NadAferritin nanoparticles potently induced complement-mediated serum bactericidal activity. These findings confirm the value of self-assembling nanoparticles for optimizing the immunogenicity of bacterial antigens and support the broad applicability of the approach to vaccine programs, especially for the presentation of trimeric antigens.

Oral vaccination with novel Lactococcus lactis mucosal live vector-secreting Brucella lumazine synthase (BLS) protein induces humoral and cellular immune protection against Brucella abortus

This work aimed to provide recombinant Lactococcus lactis as a potential live vector for the manufacture of recombinant Brucella abortus (rBLS-Usp45). The sequences of the genes were collected from the GenBank database. Using Vaxijen and ccSOL, the proteins' immunogenicity and solubility were evaluated. Mice were given oral vaccinations with recombinant L. lactis. Anti-BLS-specific IgG antibodies were measured by ELISA assay. Cytokine reactions were examined using real-time PCR and the ELISA technique. The BLS protein was chosen for immunogenicity based on the vaccinology screening findings since it had maximum solubility and antigenic values ​​of 99% and 0.75, respectively. The BLS gene, digested at 477 bp, was electrophoretically isolated to demonstrate that the recombinant plasmid was successfully produced. Protein-level antigen expression showed that the target group produced the 18 kDa-sized BLS protein, whereas the control group did not express any proteins. In the sera of mice given the L. lactis-pNZ8148-BLS-Usp45 vaccine 14 days after priming, there was a significant level of BLS-specific IgG1, IgG2a (P < 0.001) compared to the PBS control group. Vaccinated mice showed higher levels of IFN-γ, TNFα, IL-4, and IL-10 in samples obtained on days 14 and 28, after receiving the L. lactis-pNZ8148-BLS-Usp45 and IRBA vaccines (P < 0.001). The inflammatory reaction caused less severe spleen injuries, alveolar edema, lymphocyte infiltration, and morphological damage in the target group's spleen sections. Based on our findings, an oral or subunit-based vaccine against brucellosis might be developed using L. lactis-pNZ8148-BLS-Usp45 as a novel, promising, and safe alternative to the live attenuated vaccines now available.

Effectiveness of a Meningococcal Group B Vaccine (4CMenB) in Children

BACKGROUND

In September 2015, the four-component, protein-based meningococcal serogroup B vaccine (4CMenB; Bexsero) became available for private purchase in Spain.

METHODS

We conducted a nationwide matched case-control study to assess the effectiveness of 4CMenB in preventing invasive meningococcal disease in children. The study included all laboratory-confirmed cases of invasive meningococcal disease in children younger than 60 months of age between October 5, 2015, and October 6, 2019, in Spain. Each case patient was matched with four controls according to date of birth and province. 4CMenB vaccination status of the case patients and controls was compared with the use of multivariate conditional logistic regression.

RESULTS

We compared 306 case patients (243 [79.4%] with serogroup B disease) with 1224 controls. A total of 35 case patients (11.4%) and 298 controls (24.3%) had received at least one dose of 4CMenB. The effectiveness of complete vaccination with 4CMenB (defined as receipt of at least 2 doses, administered in accordance with the manufacturer's recommendations) was 76% (95% confidence interval [CI], 57 to 87) against invasive meningococcal disease caused by any serogroup, and partial vaccination was 54% (95% CI, 18 to 74) effective. Complete vaccination resulted in an effectiveness of 71% (95% CI, 45 to 85) against meningococcal serogroup B disease. Vaccine effectiveness with at least one dose of 4CMenB was 64% (95% CI, 41 to 78) against serogroup B disease and 82% (95% CI, 21 to 96) against non-serogroup B disease. With the use of the genetic Meningococcal Antigen Typing System, serogroup B strains that were expected to be covered by 4CMenB were detected in 44 case patients, none of whom had been vaccinated.

CONCLUSIONS

Complete vaccination with 4CMenB was found to be effective in preventing invasive disease by serogroup B and non-serogroup B meningococci in children younger than 5 years of age.

A modular vaccine platform enabled by decoration of bacterial outer membrane vesicles with biotinylated antigens

Engineered outer membrane vesicles (OMVs) derived from Gram-negative bacteria are a promising technology for the creation of non-infectious, nanoparticle vaccines against diverse pathogens. However, antigen display on OMVs can be difficult to control and highly variable due to bottlenecks in protein expression and localization to the outer membrane of the host cell, especially for bulky and/or complex antigens. Here, we describe a universal approach for avidin-based vaccine antigen crosslinking (AvidVax) whereby biotinylated antigens are linked to the exterior of OMVs whose surfaces are remodeled with multiple copies of a synthetic antigen-binding protein (SNAP) comprised of an outer membrane scaffold protein fused to a biotin-binding protein. We show that SNAP-OMVs can be readily decorated with a molecularly diverse array of biotinylated subunit antigens, including globular and membrane proteins, glycans and glycoconjugates, haptens, lipids, and short peptides. When the resulting OMV formulations are injected in mice, strong antigen-specific antibody responses are observed that depend on the physical coupling between the antigen and SNAP-OMV delivery vehicle. Overall, these results demonstrate AvidVax as a modular platform that enables rapid and simplified assembly of antigen-studded OMVs for application as vaccines against pathogenic threats.

Recent Advances in Genomics-Based Approaches for the Development of Intracellular Bacterial Pathogen Vaccines

Infectious diseases continue to be a leading cause of morbidity and mortality worldwide. The majority of infectious diseases are caused by intracellular pathogenic bacteria (IPB). Historically, conventional vaccination drives have helped control the pathogenesis of intracellular bacteria and the emergence of antimicrobial resistance, saving millions of lives. However, in light of various limitations, many diseases that involve IPB still do not have adequate vaccines. In response to increasing demand for novel vaccine development strategies, a new area of vaccine research emerged following the advent of genomics technology, which changed the paradigm of vaccine development by utilizing the complete genomic data of microorganisms against them. It became possible to identify genes related to disease virulence, genetic patterns linked to disease virulence, as well as the genetic components that supported immunity and favorable vaccine responses. Complete genomic databases, and advancements in transcriptomics, metabolomics, structural genomics, proteomics, immunomics, pan-genomics, synthetic genomics, and population biology have allowed researchers to identify potential vaccine candidates and predict their effects in patients. New vaccines have been created against diseases for which previously there were no vaccines available, and existing vaccines have been improved. This review highlights the key issues and explores the evolution of vaccines. The increasing volume of IPB genomic data, and their application in novel genome-based techniques for vaccine development, were also examined, along with their characteristics, and the opportunities and obstacles involved. Critically, the application of genomics technology has helped researchers rapidly select and evaluate candidate antigens. Novel vaccines capable of addressing the limitations associated with conventional vaccines have been developed and pressing healthcare issues are being addressed.

Characterization of invasive meningococcal disease case isolates in Atlantic Canada, 2014 to 2020: spatial-temporal variations of clones and predicted meningococcal B vaccine coverage

Introduction. Invasive meningococcal disease (IMD) caused by Neisseria meningitidis may show temporal and geographical changes in both the epidemiology and the characteristics of the strains involved.Gap statement. A study that examined invasive N. meningitidis causing IMD in Atlantic Canada from 2009 to 2013 was published in 2014. Data from subsequent years have not been described.Aim. This study examined the molecular epidemiology of IMD in four Atlantic Provinces of Canada as well as potential serogroup B (MenB) vaccine coverage.Methods. Individual IMD case isolates recovered from 2014 to 2020 were analysed for serotype and serosubtype antigens as well as by whole-genome sequencing (WGS) for prediction of potential MenB vaccine coverage.Results. Of the 56 IMD isolates, 42, 8, 5 and 1 were MenB, serogroup Y, serogroup W (MenW) and serogroup C, respectively. Geographical differences in the distribution of MenB clones revealed concentration of sequence type (ST)-269 clonal complex (cc) and ST-60 cc in Newfoundland and Labrador, while ST-41/44 cc (particularly ST-154) was predominantly found in New Brunswick and Nova Scotia. Core genome multi-locus sequence typing (cgMLST) also separated the New Brunswick and Nova Scotia ST-154 isolates into two clusters, with differences in their nhba and penA alleles. Furthermore, cgMLST also separated the ST-269 cc isolates in Atlantic Canada into the ST-1611 and the ST-269/ST-8924 clusters, with the latter showing high similarity to the ST-269 that first emerged in the Province of Quebec. Genetic Meningococcal Antigen Typing System showed that 54.8 % of MenB were predicted to be covered by the MenB vaccine Bexsero, with a further 38.1 % potentially covered by virtue of the presence of genes that encoded factor H-binding protein variant 1 proteins. Meningococcal deduced vaccine antigen reactivity predicted from WGS data showed that 95.3 % of MenB were covered by Trumenba. Four cases of IMD due to MenW ST-11 cc were also identified, with the first case found in 2018.Conclusions. This study provided evidence concerning the dynamics of N. meningitidis strains causing IMD in Atlantic Canada, with both geographical and temporal differences found. MenB vaccine appeared to provide good coverage of MenB IMD, especially towards the predominant strain of ST-154.

The Defensive Interactions of Prominent Infectious Protozoan Parasites: The Host's Complement System

The complement system exerts crucial functions both in innate immune responses and adaptive humoral immunity. This pivotal system plays a major role dealing with pathogen invasions including protozoan parasites. Different pathogens including parasites have developed sophisticated strategies to defend themselves against complement killing. Some of these strategies include the employment, mimicking or inhibition of host's complement regulatory proteins, leading to complement evasion. Therefore, parasites are proven to use the manipulation of the complement system to assist them during infection and persistence. Herein, we attempt to study the interaction´s mechanisms of some prominent infectious protozoan parasites including Plasmodium, Toxoplasma, Trypanosoma, and Leishmania dealing with the complement system. Moreover, several crucial proteins that are expressed, recruited or hijacked by parasites and are involved in the modulation of the host´s complement system are selected and their role for efficient complement killing or lysis evasion is discussed. In addition, parasite's complement regulatory proteins appear as plausible therapeutic and vaccine targets in protozoan parasitic infections. Accordingly, we also suggest some perspectives and insights useful in guiding future investigations.

Modern vaccine development via reverse vaccinology to combat antimicrobial resistance

With the continuous evolution of bacteria, the global antimicrobial resistance health threat is causing millions of deaths yearly. While depending on antibiotics as a primary treatment has its merits, there are no effective alternatives thus far in the pharmaceutical market against some drug-resistant bacteria. In recent years, vaccinology has become a key topic in scientific research. Combining with the growth of technology, vaccine research is seeing a new light where the process is made faster and more efficient. Although less discussed, bacterial vaccine is a feasible strategy to combat antimicrobial resistance. Some vaccines have shown promising results with good efficacy against numerous multidrug-resistant strains of bacteria. In this review, we aim to discuss the findings from studies utilizing reverse vaccinology for vaccine development against some multidrug-resistant bacteria, as well as provide a summary of multi-year bacterial vaccine studies in clinical trials. The advantages of reverse vaccinology in the generation of new bacterial vaccines are also highlighted. Meanwhile, the limitations and future prospects of bacterial vaccine concludes this review.

Salmonella enterica serovar Choleraesuis vector delivering a dual-antigen expression cassette provides mouse cross-protection against Streptococcus suis serotypes 2, 7, 9, and 1/2

A universal vaccine protecting against multiple serotypes of Streptococcus suis is urgently needed to improve animal welfare and reduce the consumption of antibiotics. In this study, a dual antigen expression cassette consisting of SS2-SaoA and SS9-Eno was delivered by a recombinant Salmonella Choleraesuis vector to form the vaccine candidate rSC0016(pS-SE). SaoA and Eno were simultaneously synthesized in rSC0016(pS-SE) without affecting the colonization of the recombinant vector in the lymphatic system. In addition, the antiserum of mice immunized with rSC0016(pS-SE) produced a broader and potent opsonophagocytic response against multiple serotypes of S. suis. Finally, rSC0016(pS-SE) provided mice with a 100% protection against a lethal dose of parent S. suis serotype 2 and serotype 9, and provided 90% and 80% protection against heterologous S. suis serotype 7 or 1/2. These values were significantly higher than those obtained with rSC0016(pS-SaoA) or rSC0016(pS-Eno). Together, this study serves as a foundation for developing a universal vaccine against multiple serotypes of S. suis.

Inclusion of a dual signal sequence enhances the immunogenicity of a novel viral vectored vaccine against the capsular group B meningococcus

BACKGROUND

Disease caused by the capsular group B meningococcus (MenB) is the leading cause of infectious death in UK infants. A novel adenovirus-based vaccine encoding the MenB factor H binding protein (fHbp) with an N-terminal dual signal sequence induces high titres of protective antibody after a single dose in mice. A panel of N-terminal signal sequence variants were created to assess the contribution of components of this sequence to transgene expression kinetics of the encoded antigen from mammalian cells and the resultant effect on immunogenicity of fHbp.

RESULTS

The full-length signal sequence (FL SS) resulted in superior early antigen expression compared with the panel of variants, as measured by flow cytometry and confocal imaging, and supported higher bactericidal antibody levels against the expressed antigen in mouse sera < 6 weeks post-immunisation than the licensed four component MenB vaccine. The FL SS also significantly increased antigen-specific T cell responses against other adenovirus-encoded bacterial antigens in mice.

CONCLUSIONS

These findings demonstrate that the FL SS enhances immunogenicity of the encoded antigen, supporting its inclusion in other viral vectored bacterial antigen transgenes.

Correlates of protection for meningococcal surface protein vaccines; current approaches for the determination of breadth of coverage

INTRODUCTION

The two currently licensed surface protein non capsular meningococcal serogroup B (MenB) vaccines both have the purpose of providing broad coverage against diverse MenB strains. However, the different antigen compositions and approaches used to assess breadth of coverage currently make direct comparisons complex.

AREAS COVERED

In the second of two companion papers, we comprehensively review the serology and factors influencing breadth of coverage assessments for two currently licensed MenB vaccines.

EXPERT OPINION

Surface protein MenB vaccines were developed using different approaches, resulting in unique formulations and thus their breadth of coverage. The surface proteins used as vaccine antigens can vary among meningococcal strains due to gene presence/absence, sequence diversity and differences in protein expression. Assessment of the breadth of coverage provided by vaccines is influenced by the ability to induce cross-reactive functional immune responses to sequence diverse protein variants; the characteristics of the circulating invasive strains from specific geographic locations; methodological differences in the immunogenicity assays; differences in human immune responses between individuals; and the maintenance of protective antibody levels over time. Understanding the proportion of meningococcal strains which are covered by the two licensed vaccines is important in understanding protection from disease and public health use.

Biological Nanoparticles in Vaccine Development

Vaccines represent one of the most successful public health initiatives worldwide. However, despite the vast number of highly effective vaccines, some infectious diseases still do not have vaccines available. New technologies are needed to fully realize the potential of vaccine development for both emerging infectious diseases and diseases for which there are currently no vaccines available. As can be seen by the success of the COVID-19 mRNA vaccines, nanoscale platforms are promising delivery vectors for effective and safe vaccines. Synthetic nanoscale platforms, including liposomes and inorganic nanoparticles and microparticles, have many advantages in the vaccine market, but often require multiple doses and addition of artificial adjuvants, such as aluminum hydroxide. Biologically derived nanoparticles, on the other hand, contain native pathogen-associated molecular patterns (PAMPs), which can reduce the need for artificial adjuvants. Biological nanoparticles can be engineered to have many additional useful properties, including biodegradability, biocompatibility, and are often able to self-assemble, thereby allowing simple scale-up from benchtop to large-scale manufacturing. This review summarizes the state of the art in biologically derived nanoparticles and their capabilities as novel vaccine platforms.

Multi-epitope based vaccine design against Staphylococcus epidermidis: A subtractive proteomics and immunoinformatics approach

Staphylococcus epidermidis has emerged as a major contributor of nosocomial infections across the world. With the increased rate of emerging resistant and previously undefined infectious diseases, there is a growing need to develop a novel vaccine possessing required immunogenic properties. The adopted reverse vaccinology approach identified "IMPNQILTI" of LysM domain protein, "YSYTYTIDA" of staphylococcal secretory antigen SsaA, and "YNYDANTGQ" neutral metalloproteinaseas potential peptides for vaccine design. The 9-mer epitope of target proteins is antigenic, virulent, surface-exposed, non-allergenic, and conserved across various strains of S. epidermidis. Protein-protein interactions study indicated the involvement of target proteins in major biological pathways for S. epidermidis pathogenesis. Protein-peptide docking was performed, and population coverage analysis showed significant interactions of T-cell epitopes with the HLA-binding molecules while covering 90.58% of the world's population. Further, a multi-epitope vaccine of 177 amino acids long was constructed. Docking with Toll-like receptor (TLR-2) molecule confirmed the effective interaction of the vaccine with the receptor. The vaccine efficiency in generating an effective immune response in the host was evaluated by immune simulation. Finally, in silico cloning confirmed that the constructed vaccine can be efficiently expressed in E. coli. However, the designed vaccine needs experimental validation to determine the effectiveness and immunogenicity profile, which will ensure an active immunity against S. epidermidis.

Synergistic activity of antibodies in the multicomponent 4CMenB vaccine

INTRODUCTION

: Vaccines based on multiple antigens often induce an immune response which is higher than that triggered by each single component, with antibodies acting cooperatively and synergistically in tackling the infection.

AREAS COVERED

An interesting example is the antibody response induced by the 4CMenB vaccine, currently licensed for the prevention of Neisseria meningitidis serogroup B (MenB). It contains four antigenic components: Factor H binding protein (fHbp), Neisseria adhesin A (NadA), Neisserial Heparin Binding Antigen (NHBA) and Outer Membrane Vesicles (OMV). Monoclonal and polyclonal antibodies raised by vaccination with 4CMenB show synergistic activity in complement-dependent bacterial killing. This review summarizes published and unpublished data and provides evidence of the added value of multicomponent vaccines.

EXPERT OPINION

: The ability of 4CMenB vaccine to elicit antibodies targeting multiple surface-exposed antigens is corroborated by the recent data on real world evidences. Bactericidal activity is generally mediated by antibodies that bind to antigens highly expressed on the bacterial surface and immunologically related. However, simultaneous binding of antibodies to various surface-exposed antigens can overcome the threshold density of antigen-antibody complexes needed for complement activation. The data discussed in this review highlight the interplay between antibodies targeting major and minor antigens and their effect on functionality.

Clinical trial registration: www.clinicaltrials.gov identifiers of studies with original data mentioned in the article: NCT00937521, NCT00433914, NCT02140762 and NCT02285777.

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.

Multi-Antigen Outer Membrane Vesicle Engineering to Develop Polyvalent Vaccines: The Staphylococcus aureus Case

Modification of surface antigens and differential expression of virulence factors are frequent strategies pathogens adopt to escape the host immune system. These escape mechanisms make pathogens a "moving target" for our immune system and represent a challenge for the development of vaccines, which require more than one antigen to be efficacious. Therefore, the availability of strategies, which simplify vaccine design, is highly desirable. Bacterial Outer Membrane Vesicles (OMVs) are a promising vaccine platform for their built-in adjuvanticity, ease of purification and flexibility to be engineered with foreign proteins. However, data on if and how OMVs can be engineered with multiple antigens is limited. In this work, we report a multi-antigen expression strategy based on the co-expression of two chimeras, each constituted by head-to-tail fusions of immunogenic proteins, in the same OMV-producing strain. We tested the strategy to develop a vaccine against Staphylococcus aureus, a Gram-positive human pathogen responsible for a large number of community and hospital-acquired diseases. Here we describe an OMV-based vaccine in which four S. aureus virulent factors, ClfA_Y338A, LukE, SpA_KKAA and Hla_H35L have been co-expressed in the same OMVs (CLSH-OMVs_Δ60). The vaccine elicited antigen-specific antibodies with functional activity, as judged by their capacity to promote opsonophagocytosis and to inhibit Hla-mediated hemolysis, LukED-mediated leukocyte killing, and ClfA-mediated S. aureus binding to fibrinogen. Mice vaccinated with CLSH-OMVs_Δ60 were robustly protected from S. aureus challenge in the skin, sepsis and kidney abscess models. This study not only describes a generalized approach to develop easy-to-produce and inexpensive multi-component vaccines, but also proposes a new tetravalent vaccine candidate ready to move to development.

Putative novel B-cell vaccine candidates identified by reverse vaccinology and genomics approaches to control Acinetobacter baumannii serotypes

In the last decade, Multi-drug resistance (MDR)-associated infections of Acinetobacter baumannii have grown worldwide. A cost-effective preventative strategy against this bacterium is vaccination. This study has presented five novel vaccine candidates against A. baumannii produced using the reverse vaccinology method. BLASTn was done to identify the most conserved antigens. PSORTb 3.0.2 was run to predict the subcellular localization of the proteins. The initial screening and antigenicity evaluation were performed using Vaxign. The ccSOL omics was also employed to predict protein solubility. The cross-membrane localization of the protein was predicted using PRED-TMBB. B cell epitope prediction was made for immunogenicity using the IEDB and BepiPred-2.0 database. Eventually, BLASTp was done to verify the extent of similarity to the human proteome to exclude the possibility of autoimmunity. Proteins failing to comply with the set parameters were filtered at each step. In silico, potential vaccines against 21 A. baumannii strains were identified using reverse vaccinology and subtractive genomic techniques. Based on the above criteria, out of the initial 15 A. baumannii proteins selected for screening, nine exposed/secreted/membrane proteins, i.e., Pfsr, LptE, OmpH, CarO, CsuB, CdiB, MlaA, FhuE, and were the most promising candidates. Their solubility and antigenicity were also examined and found to be more than 0.45 and 0.6, respectively. Based on the results, LptE was selected with the highest average antigenic score of 1.043 as the best protein, followed by FimF and Pfsr with scores of 1.022 and 1.014, respectively. In the end, five proteins were verified as promising candidates. Overall, the targets identified herein may be utilized in future strategies to control A. baumannii worldwide.

Looking beyond meningococcal B with the 4CMenB vaccine: the Neisseria effect

Infections with Neisseria meningitidis and Neisseria gonorrhoeae have different clinical manifestations, but the bacteria share up to 80-90% genome sequence identity. The recombinant meningococcal serogroup B (MenB) vaccine 4CMenB consists of four antigenic components that can be present in non-B meningococcal and gonococcal strains. This comprehensive review summarizes scientific evidence on the genotypic and phenotypic similarities between vaccine antigens and their homologs expressed by non-B meningococcal and gonococcal strains. It also includes immune responses of 4CMenB-vaccinated individuals and effectiveness and impact of 4CMenB against these strains. Varying degrees of strain coverage were estimated depending on the non-B meningococcal serogroup and antigenic repertoire. 4CMenB elicits immune responses against non-B meningococcal serogroups and N. gonorrhoeae. Real-world evidence showed risk reductions of 69% for meningococcal serogroup W clonal complex 11 disease and 40% for gonorrhea after 4CMenB immunization. In conclusion, functional antibody activity and real-world evidence indicate that 4CMenB has the potential to provide some protection beyond MenB disease.

The potential utility of liposomes for Neisseria vaccines

INTRODUCTION

Species of the genus Neisseria are important global pathogens. Neisseria gonorrhoeae (gonococcus) causes the sexually transmitted disease gonorrhea and Neisseria meningitidis (meningococcus) causes meningitis and sepsis. Liposomes are self-assembled spheres of phospholipid bilayers enclosing a central aqueous space, and they have attracted much interest and use as a delivery vehicle for Neisseria vaccine antigens.

AREAS COVERED

A brief background on Neisseria infections and the success of licensed meningococcal vaccines are provided. The absence of a gonococcal vaccine is highlighted. The use of liposomes for delivering Neisseria antigens and adjuvants, for the purposes of generating specific immune responses, is reviewed. The use of other lipid-based systems for antigen and adjuvant delivery is examined briefly.

EXPERT OPINION

With renewed interest in developing a gonococcal vaccine, liposomes remain an attractive option for delivering antigens. The discipline of nanotechnology provides additional nanoparticle-based options for gonococcal vaccine development. Future work would be needed to tailor the composition of liposomes and other nanoparticles to the specific vaccine antigen(s), in order to generate optimal anti-gonococcal immune responses. The potential use of liposomes and other nanoparticles to deliver anti-gonococcal compounds to treat infections also should be explored further.

Quest for Novel Preventive and Therapeutic Options Against Multidrug-Resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) is a critical healthcare challenge due to its ability to cause persistent infections and the acquisition of antibiotic resistance mechanisms. Lack of preventive vaccines and rampant drug resistance phenomenon has rendered patients vulnerable. As new antimicrobials are in the preclinical stages of development, mining for the unexploited drug targets is also crucial. In the present study, we designed a B- and T-cell multi-epitope vaccine against P. aeruginosa using a subtractive proteomics and immunoinformatics approach. A total of five proteins were shortlisted based on essentiality, extracellular localization, virulence, antigenicity, pathway association, hydrophilicity, and low molecular weight. These include two outer membrane porins; OprF (P13794) and OprD (P32722), a protein activator precursor pra (G3XDA9), a probable outer membrane protein precursor PA1288 (Q9I456), and a conserved hypothetical protein PA4874 (Q9HUT9). These shortlisted proteins were further analyzed to identify immunogenic and antigenic B- and T-cell epitopes. The best scoring epitopes were then further subjected to the construction of a polypeptide multi-epitope vaccine and joined with cholera toxin B subunit adjuvant. The final chimeric construct was docked with TLR4 and confirmed by normal mode simulation studies. The designed B- and T-cell multi-epitope vaccine candidate is predicted immunogenic in nature and has shown strong interactions with TLR-4. Immune simulation predicted high-level production of B- and T-cell population and maximal expression was ensured in E. coli strain K12. The identified drug targets qualifying the screening criteria were: UDP-2-acetamido-2-deoxy-d-glucuronic acid 3-dehydrogenase WbpB (G3XD23), aspartate semialdehyde dehydrogenase (Q51344), 2-amino-4-hydroxy-6-hydroxymethyldihydropteridine pyrophosphokinase (Q9HV71), 3-deoxy-D-manno-octulosonic-acid transferase (Q9HUH7), glycyl-tRNA synthetase alpha chain (Q9I7B7), riboflavin kinase/FAD synthase (Q9HVM3), aconitate hydratase 2 (Q9I2V5), probable glycosyltransferase WbpH (G3XD85) and UDP-3-O-[3-hydroxylauroyl] glucosamine N-acyltransferase (Q9HXY6). For druggability and pocketome analysis crystal and homology structures of these proteins were retrieved and developed. A sequence-based search was performed in different databases (ChEMBL, Drug Bank, PubChem and Pseudomonas database) for the availability of reported ligands and tested drugs for the screened targets. These predicted targets may provide a basis for the development of reliable antibacterial preventive and therapeutic options against P. aeruginosa.

Correlates of protection for meningococcal surface protein vaccines: lessons from the past

INTRODUCTION

Recombinant surface protein meningococcal serogroup B (MenB) vaccines are available but with different antigen compositions, leading to differences between vaccines in their immunogenicity and likely breadth of coverage. The serology and breadth of coverage assessment for MenB vaccines are multifaceted areas, and a comprehensive understanding of these complexities is required to appropriately compare licensed vaccines and those under development.

AREAS COVERED

In the first of two companion papers that comprehensively review the serology and breadth of coverage assessment for MenB vaccines, the history of early meningococcal vaccines is considered in this narrative review to identify transferable lessons applicable to the currently licensed MenB vaccines and those under development, as well as their serology.

EXPERT OPINION

Understanding correlates of protection and the breadth of coverage assessment for meningococcal surface protein vaccines is significantly more complex than that for capsular polysaccharide vaccines. Determination and understanding of the breadth of coverage of surface protein vaccines are clinically important and unique to each vaccine formulation. It is essential to estimate the proportion of MenB cases that are preventable by a specific vaccine to assess its overall potential impact and to compare the benefits and limitations of different vaccines in preventing invasive meningococcal disease.

The Emerging World of Membrane Vesicles: Functional Relevance, Theranostic Avenues and Tools for Investigating Membrane Function

Lipids are essential components of cell membranes and govern various membrane functions. Lipid organization within membrane plane dictates recruitment of specific proteins and lipids into distinct nanoclusters that initiate cellular signaling while modulating protein and lipid functions. In addition, one of the most versatile function of lipids is the formation of diverse lipid membrane vesicles for regulating various cellular processes including intracellular trafficking of molecular cargo. In this review, we focus on the various kinds of membrane vesicles in eukaryotes and bacteria, their biogenesis, and their multifaceted functional roles in cellular communication, host-pathogen interactions and biotechnological applications. We elaborate on how their distinct lipid composition of membrane vesicles compared to parent cells enables early and non-invasive diagnosis of cancer and tuberculosis, while inspiring vaccine development and drug delivery platforms. Finally, we discuss the use of membrane vesicles as excellent tools for investigating membrane lateral organization and protein sorting, which is otherwise challenging but extremely crucial for normal cellular functioning. We present current limitations in this field and how the same could be addressed to propel a fundamental and technology-oriented future for extracellular membrane vesicles.

High coverage of diverse invasive meningococcal serogroup B strains by the 4-component vaccine 4CMenB in Australia, 2007-2011: Concordant predictions between MATS and genetic MATS

Meningococcal serogroup B (MenB) accounts for an important proportion of invasive meningococcal disease (IMD). The 4-component vaccine against MenB (4CMenB) is composed of factor H binding protein (fHbp), neisserial heparin-binding antigen (NHBA), Neisseria adhesin A (NadA), and outer membrane vesicles of the New Zealand strain with Porin 1.4. A meningococcal antigen typing system (MATS) and a fully genomic approach, genetic MATS (gMATS), were developed to predict coverage of MenB strains by 4CMenB. We characterized 520 MenB invasive disease isolates collected over a 5-year period (January 2007-December 2011) from all Australian states/territories by multilocus sequence typing and estimated strain coverage by 4CMenB. The clonal complexes most frequently identified were ST-41/44 CC/Lineage 3 (39.4%) and ST-32 CC/ET-5 CC (23.7%). The overall MATS predicted coverage was 74.6% (95% coverage interval: 61.1%-85.6%). The overall gMATS prediction was 81.0% (lower-upper limit: 75.0-86.9%), showing 91.5% accuracy compared with MATS. Overall, 23.7% and 13.1% (MATS) and 26.0% and 14.0% (gMATS) of isolates were covered by at least 2 and 3 vaccine antigens, respectively, with fHbp and NHBA contributing the most to coverage. When stratified by year of isolate collection, state/territory and age group, MATS and gMATS strain coverage predictions were consistent across all strata. The high coverage predicted by MATS and gMATS indicates that 4CMenB vaccination may have an impact on the burden of MenB-caused IMD in Australia. gMATS can be used in the future to monitor variations in 4CMenB strain coverage over time and geographical areas even for non-culture confirmed IMD cases.

Deconvolution of intergenic polymorphisms determining high expression of Factor H binding protein in meningococcus and their association with invasive disease

Neisseria meningitidis is a strictly human pathogen and is the major cause of septicemia and meningitis worldwide. Factor H binding protein (fHbp) is a meningococcal surface-exposed lipoprotein that binds the human Complement factor H allowing the bacterium to evade the host innate immune response. FHbp is also a key antigen in two vaccines against N. meningitidis serogroup B. Although the fHbp gene is present in most circulating meningococcal strains, level of fHbp expression varies among isolates and has been correlated to differences in promoter sequences upstream of the gene. Here we elucidated the sequence determinants that control fHbp expression in globally circulating strains. We analyzed the upstream fHbpintergenic region (fIR) of more than 5800 strains representative of the UK circulating isolates and we identified eleven fIR sequence alleles which represent 88% of meningococcal strains. By engineering isogenic recombinant strains where fHbp expression was under the control of each of the eleven fIR alleles, we confirmed that the fIR sequence determines a specific and distinct level of expression. Moreover, we identified the molecular basis for variation in expression through polymorphisms within key regulatory regions that are known to affect fHbp expression. We experimentally established three expression groups, high–medium–low, that correlated directly with the susceptibility to killing mediated by anti-fHbp antibodies and the ability of the meningococcal strain to survive within human serum. By using this sequence classification and information about the variant, we predicted fHbp expression in the panel of UK strains and we observed that strains with higher expressing fIR alleles are more likely associated with invasive disease. Overall, our findings can contribute to understand and predict vaccine coverage mediated by fHbp as well as to shed light on the role of this virulence factor in determining an invasive phenotype.

Complement plays a key role in the immunity against Neisseria meningitidis. The meningococcus uses the Factor H binding protein (fHbp), to bind a negative regulator of the alternative complement pathway, factor H, to its surface thus preventing complement deposition and lysis. The use of fHbp as an antigen in two licensed vaccines highlights its public health relevance. Therefore the levels of this antigen produced by the bacterium are pivotal on the one hand for the survival of N. meningitidis in blood and on the other hand for the susceptibility to vaccine-induced killing antibodies. Here, we identify the predominant nucleotide sequences that drive distinct levels of the fHbp antigen in circulating meningococcal strains. We cluster them into distinct groups with increasing levels and observe that strains expressing higher fHbp amounts are associated with invasive disease. Our findings show that the nucleotide sequence of the fHbp promoter can be used for the prediction of antigen levels of any given strain and consequently for both the assessment of its sensitivity to killing by fHbp antibodies and its likelihood to cause invasive disease.

Low efficacy of vaccination against serogroup B meningococci in patients with atypical hemolytic uremic syndrome

Background: The C5 complement inhibitor eculizumab is first-line treatment in atypical hemolytic uremic syndrome (aHUS) going along with a highly increased risk of meningococcal infections. Serogroup B meningococci (MenB) are the most frequently encountered cause for meningococcal infections in Europe. Efficacy of the protein-based MenB-vaccine Bexsero in aHUS has not been determined and testing is only possible in patients off-treatment with eculizumab as a human complement source is required.

Methods: Patients with aHUS were vaccinated with two doses of the protein-based MenB-vaccine Bexsero. Serum bactericidal antibody (SBA) titers against factor H binding protein (fHbp) of MenB were determined in 14 patients with aHUS off-treatment with eculizumab.

Results: Only 50% of patients showed protective human serum bactericidal antibody (hSBA) titers (≥1:4) against MenB following two vaccinations. Bactericidal antibody titers were relatively low (≤1:8) in three of seven patients with protective titers. While 71% of patients were on immunosuppressive treatment for either thrombotic microangiopathy or renal transplantation at either first or second vaccination, all four patients not receiving any immunosuppressive treatment showed protective bactericidal antibody response. Time between second vaccination and titer measurement was not significantly different between patients with protective titers compared with those with non-protective titers, while time between first and second vaccination was significantly longer in patients with protective titers going along with a tendency for reduction in immunosuppressive treatment.

Conclusions: Efficacy of vaccination against MenB is insufficient in patients with aHUS. Response to vaccination seems to be hampered by immunosuppression. Therefore, implementation of adequate antibiotic prophylaxis seems pivotal.

Comprehensive Bioinformatic Assessments of the Variability of Neisseria gonorrhoeae Vaccine Candidates

A protective vaccine is the only viable way to stop the spread of gonorrhea in the face of rising antibiotic resistance. However, the notorious phase and antigenic variation of Neisseria gonorrhoeae surface proteins remains one of the challenges in vaccine development. To facilitate vaccine advancement efforts, we carried out comprehensive bioinformatic analyses of sequence variation by comparing 34 gonorrhea antigen candidates among >5,000 clinical N. gonorrhoeae isolates deposited in the Neisseria PubMLST database. Eight protein antigens showed exceptional conservation by having a single allele variant distributed in >80% of isolates. An additional 18 vaccine candidates were represented by ≤3 alleles in >50% of N. gonorrhoeae isolates globally. Phylogenetic analyses highlighted closely related antigen variants and additionally showed that AniA and FetB were the closest between N. gonorrhoeae and N. meningitidis Up to 44% of N. meningitidis alleles for both antigens have premature stop codons, suggesting differential expression. Mapping polymorphisms to the available three-dimensional structures of 12 antigens revealed low-frequency surface polymorphisms. PorB and TbpB possessed numerous high-prevalence polymorphic sites. While TbpA was also highly variable, conserved loops were nonetheless identified. A high degree of sequence conservation, the distribution of a single antigen variant among N. gonorrhoeae strains globally, or low-frequency sequence polymorphisms in surface loops make ACP, AniA, BamA, BamE, MtrE, NspA, NGO0778, NGO1251, NGO1985, OpcA, PldA, Slam2, and ZnuD promising candidates for a gonorrhea vaccine. Finally, the commonly used N. gonorrhoeae FA1090 strain emerges as a vaccine prototype, as it carries antigen sequence types identical to the most broadly distributed antigen variants.IMPORTANCE Neisseria gonorrhoeae, the Gram-negative bacterium responsible for the sexually transmitted infection gonorrhea, is categorized as a high-priority pathogen for research and development efforts. N. gonorrhoeae's "superbug" status, its high morbidity, and the serious health impact associated with gonorrhea highlight the importance of vaccine development. One of the longstanding barriers to developing an effective vaccine against N. gonorrhoeae is the remarkable variability of surface-exposed antigens. In this report, we addressed this roadblock by applying extensive bioinformatic analyses to 34 gonorrhea antigen candidates among >5,000 clinical N. gonorrhoeae isolates. Our studies are important, as they reveal promising, conserved gonorrhea vaccine candidates and aid structural vaccinology. Moreover, these approaches are broadly applicable to other infectious diseases where surface antigen variability impedes successful vaccine design.