Meningococcal polysaccharide vaccines: A review

Liposomes, transfersomes and niosomes: production methods and their applications in the vaccinal field

One of the most effective strategies to fight viruses and handle health diseases is vaccination. Recent studies and current applications are moving on antigen, DNA and RNA-based vaccines to overcome the limitations related to the conventional vaccination strategies, such as low safety, necessity of multiple injection, and side effects. However, due to the instability of pristine antigen, RNA and DNA molecules, the use of nanocarriers is required. Among the different nanocarriers proposed for vaccinal applications, three types of nanovesicles were selected and analysed in this review: liposomes, transfersomes and niosomes. PubMed, Scopus and Google Scholar databases were used for searching recent papers on the most frequently used conventional and innovative methods of production of these nanovesicles. Weaknesses and limitations of conventional methods (i.e., multiple post-processing, solvent residue, batch-mode processes) can be overcome using innovative methods, in particular, the ones assisted by supercritical carbon dioxide. SuperSomes process emerged as a promising production technique of solvent-free nanovesicles, since it can be easily scaled-up, works in continuous-mode, and does not require further post-processing steps to obtain the desired products. As a result of the literature analysis, supercritical carbon dioxide assisted methods attracted a lot of interest for nanovesicles production in the vaccinal field. However, despite their numerous advantages, supercritical processes require further studies for the production of liposomes, transfersomes and niosomes with the aim of reaching well-defined technologies suitable for industrial applications and mass production of vaccines.

Quantitation of free cyanide using ion exchange chromatography in Neisseria meningitidis serogroups A, C, W, Y and X conjugates used in vaccine manufacture

Polysaccharide vaccines essentially used in the prevention of bacterial infections are known to be good immunogens when conjugated to an immunogenic protein using various cyanylating agents. Analysis of residual cyanide in polysaccharide conjugate vaccines is an ardent task due to the complexity of the sample matrices and the lack of suitable methods. We report a selective ion chromatography method with electrochemical detection using IonPac AS7 column for estimation of residual cyanide in meningococcal serogroups A, C, W, Y and X bulk conjugates in presence of other interfering ions. Gold electrode and Ag/AgCl reference electrode ensures sensitivity and reproducibility of cyanide quantitation. The calibration curve of the method is linear having r² ≥0.990 over the concentration range 1.45 ng/mL to 93.10 ng/mL. The recovery of cyanide in bulk conjugates ranged between 96.0% and 108.9%. The limits of detection and quantitation were 0.50 ng/mL and 1.45 ng/mL which corresponds to 0.31 ng/μg and 0.91 ng/μg of polysaccharide respectively. The method validation and feasibility study were performed using Men W and Men X bulk conjugates respectively with in house residual cyanide specification due to unavailability of pharmacopeia guidelines. The method is reproducible and can accurately quantify residual cyanide in purified meningococcal bulk conjugates.

Production and Characterization of Bacterial Ghost Vaccine against Neisseria meningitidis

Bacterial ghosts (BGS) are empty non-living envelopes produced either genetically or chemically. This study investigated a novel chemical protocol for the production of Neisseria meningitidis ghost vaccine using tween 80 followed by a pH reduction with lactic acid. For our vaccine candidate, both safety and immunogenicity aspects were evaluated. The ghost pellets showed no sign of growth upon cultivation. BGS were visualized by scanning electron microscopy, illustrating the formation of trans-membrane tunnels with maintained cell morphology. Gel electrophoresis showed no distinctive bands of the cytoplasmic proteins and DNA, assuring the formation of ghost cells. In animal model, humoral immune response significantly increased when compared to commercial vaccine (p < 0.01). Moreover, serum bactericidal assay (SBA) recorded 94.67% inhibition compared to 64% only for the commercial vaccine after three vaccination doses. In conclusion, this is the first N. meningitidis ghost vaccine candidate, proven to be effective, economic, and with significant humoral response and efficient SBA values; however, clinical studies should be performed.

Preparation and characterization of polymyxin B- and histidine-coupled magnetic nanoparticles for purification of biologics from acquired endotoxin contamination

Background

Endotoxin is a major process-related impurity that can act as a strong immunostimulant leading to fever and hypotensive shock. Thus, the US FDA and international quality standards strictly direct the biologics manufacturers to control the endotoxin contamination during the purification process. In this work, a developed method for biologics purification from acquired endotoxin contamination is introduced. This is accomplished by the preparation of dextran-coated magnetic nanoparticles using a facile rapid co-precipitation method.

Results

The resulting magnetic nanoparticles (MNPs) are characterized by dynamic light scattering, transmission electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, and vibrating sample magnetometry. The dextran-coated magnetic nanoparticles are further coupled to either polymyxin B or histidine to provide a positively charged ligand which enhances the affinity to the negatively charged endotoxin. Both ligands-coupled MNPs are tested for purification efficiency using the chromogenic kinetic assay. The method conditions are optimized using a two-level factorial design to achieve best purification conditions of the contaminated biologics and indicated endotoxin removal percentage 85.12% and maximum adsorption capacity of 38.5 mg/g, for histidine-coupled MNPs.

Conclusions

This developed method is introduced to serve biologics manufacturers to improve their manufacturing processes through providing a simple purifying tool for biologics from acquired endotoxin contamination.

Graphical Abstract

Yeasts in nanotechnology-enabled oral vaccine and gene delivery

Oral vaccine and gene delivery systems must be engineered to withstand several different physiological environments, such as those present in the oral cavity, stomach, and jejunum, each of which exhibits varying pH levels and enzyme distributions. Additionally, these systems must be designed to ensure appropriate gastrointestinal absorption and tissue/cellular targeting properties. Yeasts-based delivery vehicles are excellent candidates for oral vaccine and oral gene therapies as many species possess cellular characteristics resulting in enhanced resistance to the harsh gastrointestinal (GI) environment and facilitated passage across the mucosal barrier. Yeast capsules can stimulate and modulate host immune responses, which is beneficial for vaccine efficacy. In addition, recombinant modification of yeasts to express cell penetrating proteins and injection mechanisms along with efficient cell adhering capabilities can potentially improve transfection rates of genetic material. In this literature review, we present evidence supporting the beneficial role yeast-based delivery systems can play in increasing the efficacy of oral administration of vaccines and gene therapies.

Meningococcal polysaccharides identification by NIR spectroscopy and chemometrics

Near-infrared (NIR) spectroscopy is an attractive tool for pharmaceutical analyses. The main purpose of this study was to assess the potential of NIR spectroscopy coupled with different multivariate classification tools for the identification of meningococcal polysaccharide serogroups A and C. Moreover, it sought to determine, if the models established on production batches, could be used to correctly identify National Institute for Biological Standards and Control standards. Two different classification tools were investigated: soft independent modeling of class analogy (SIMCA) and partial least squares discriminant analysis (PLS-DA). Models' performance was evaluated by external validation. Although both models were able to correctly classify 100% of meningococcal polysaccharides from serogroups A and C, they performed differently in the presence of similar non-target serogroups W135 and Y. These results demonstrate that NIR spectroscopy, coupled with either SIMCA or PLS-DA, provides a method suitable for the identification of meningococcal polysaccharides A and C.

Solution conformation and flexibility of capsular polysaccharides from Neisseria meningitidis and glycoconjugates with the tetanus toxoid protein

The structural integrity of meningococcal native, micro-fluidized and activated capsular polysaccharides and their glycoconjugates - in the form most relevant to their potential use as vaccines (dilute solution) - have been investigated with respect to their homogeneity, conformation and flexibility. Sedimentation velocity analysis showed that the polysaccharide size distributions were generally bimodal with some evidence for higher molar mass forms at higher concentration. Weight average molar masses Mw where lower for activated polysaccharides. Conjugation with tetanus toxoid protein however greatly increased the molar mass and polydispersity of the final conjugates. Glycoconjugates had an approximately unimodal log-normal but broad and large molar mass profiles, confirmed by sedimentation equilibrium "SEDFIT MSTAR" analysis. Conformation analysis using HYDFIT (which globally combines sedimentation and viscosity data), "Conformation Zoning" and Wales-van Holde approaches showed a high degree of flexibility - at least as great as the unconjugated polysaccharides, and very different from the tetanus toxoid (TT) protein used for the conjugation. As with the recently published finding for Hib-TT complexes, it is the carbohydrate component that dictates the solution behaviour of these glycoconjugates, although the lower intrinsic viscosities suggest some degree of compaction of the carbohydrate chains around the protein.

Issues in pediatric vaccine-preventable diseases in low- to middle-income countries

The highest burden of pediatric vaccine-preventable disease is found in developing nations where resource constraints pose the greatest challenge, impacting disease diagnosis and surveillance as well as the implementation of large scale vaccination programmes. In November 2012, a Working Group Meeting convened in Casablanca to describe and discuss the status with respect to 8 vaccine-preventable diseases (pertussis, pneumococcal disease, measles-mumps-rubella-varicella (MMRV), rotavirus and meningococcal meningitis) to identify and consider ways of overcoming obstacles to pediatric vaccine implementation. Experts from Europe, Russia, the Commonwealth of Independent States, the Middle East, Africa and South East Asia participated in the meeting. A range of region-specific needs and barriers to uptake were discussed. The aim of this article is to provide a summary of the ongoing status with respect to pediatric vaccine preventable disease in the countries represented, and the experts' opinions and recommendations with respect to pediatric vaccine implementation.

Review of meningococcal vaccines with updates on immunization in adults

Meningococcal disease is a serious and global life-threatening disease. Six serogroups (A, B, C, W-135, X, and Y) account for the majority of meningococcal disease worldwide. Meningococcal polysaccharide vaccines were introduced several decades ago and have led to the decline in the burden of disease. However, polysaccharide vaccines have several limitations, including poor immunogenicity in infants and toddlers, short-lived protection, lack of immunologic memory, negligible impact on nasopharyngeal carriage, and presence of hyporesponsiveness after repeated doses. The chemical conjugation of plain polysaccharide vaccines has the potential to overcome these drawbacks. Meningococcal conjugate vaccines include the quadrivalent vaccines (MenACWY-DT, MenACWY-CRM, and MenACWY-TT) as well as the monovalent A and C vaccines. These conjugate vaccines were shown to elicit strong immune response in adults. This review addresses the various aspects of meningococcal disease, the limitations posed by polysaccharide vaccines, the different conjugate vaccines with their immunogenicity and reactogenicity in adults, and the current recommendations in adults.

A peptide-free, liposome-based oligosaccharide vaccine, adjuvanted with a natural killer T cell antigen, generates robust antibody responses in vivo

Due to the prevalence of oligo- and polysaccharides on the surfaces of pathogenic organisms, carbohydrates are primary targets for recognition by antibodies generated by the immune systems of higher organisms. Consequently, substantial effort has been expended in efforts to develop vaccines based on carbohydrate epitopes. Typical approaches involve multivalent presentation of carbohydrate targets on antigenic peptides or proteins, which often involve substantial synthetic commitments and/or vaccines that are heterogeneous and difficult to characterize. We have developed a simple, liposome-based approach to generate multivalent carbohydrate vaccines, and in place of an antigenic peptide or protein, we have used a potent antigen for natural killer T cells. This vaccine, based on the Streptococcus pneumoniae serotype 14 polysaccharide, gave a response superior to that from a clinically used vaccine (Prevnar). The dependence of this response on liposome formation was demonstrated by comparison to a simple mixture of the oligosaccharide and the natural killer T cell adjuvant. The importance of the strength of the adjuvant was observed by use of a potent synthetic adjuvant and a weaker, bacterial derived glycolipid adjuvant. These results demonstrate the effectiveness of this novel and relatively simple means of generating carbohydrate-based vaccines.

Quantitative proton nuclear magnetic resonance evaluation and total assignment of the capsular polysaccharide Neisseria meningitidis serogroup X

Neisseria meningitidis constitutes the main cause of meningococcal disease in infants. Serogroups A, B, C, W135, Y, and X have the higher incidence in young children and teenagers. The use of polyvalent conjugate carbohydrate-based vaccines has decreased the meningococcal infection around the world. Recently, the serogroup X has been found to be responsible of different outbreaks of meningococcal diseases, mainly in "Meningitis Belt" of Africa and the structure of the repetitive unit of the capsular polysaccharide has been confirmed through a monodimensional (13)C NMR study. No further characterization studies have been carried out, especially with the use of other nuclei. In this paper a novel method for quantification of the N. meningitidis serogroup X by proton qNMR is reported. Deep characterization of the serogroup X polysaccharide was also carried out by combination of correlation experiments involving (13)C, (1)H, and (31)P nuclei.

An evaluation of emerging vaccines for childhood meningococcal disease

Background

Meningococcal meningitis is a major cause of disease worldwide, with frequent epidemics particularly affecting an area of sub-Saharan Africa known as the “meningitis belt”. Neisseria meningitidis group A (MenA) is responsible for major epidemics in Africa. Recently W-135 has emerged as an important pathogen. Currently, the strategy for control of such outbreaks is emergency use of meningococcal (MC) polysaccharide vaccines, but these have a limited ability to induce herd immunity and elicit an adequate immune response in infant and young children. In recent times initiatives have been taken to introduce meningococcal conjugate vaccine in these African countries. Currently there are two different types of MC conjugate vaccines at late stages of development covering serogroup A and W-135: a multivalent MC conjugate vaccine against serogroup A,C,Y and W-135; and a monovalent conjugate vaccine against serogroup A. We aimed to perform a structured assessment of these emerging meningococcal vaccines as a means of reducing global meningococal disease burden among children under 5 years of age.

Methods

We used a modified CHNRI methodology for setting priorities in health research investments. This was done in two stages. In the first stage we systematically reviewed the literature related to emerging MC vaccines relevant to 12 criteria of interest. In Stage II, we conducted an expert opinion exercise by inviting 20 experts (leading basic scientists, international public health researchers, international policy makers and representatives of pharmaceutical companies). They answered questions from CHNRI framework and their “collective optimism” towards each criterion was documented on a scale from 0 to 100%.

Results

For MenA conjugate vaccine the experts showed very high level of optimism (~ 90% or more) for 7 out of the 12 criteria. The experts felt that the likelihood of efficacy on meningitis was very high (~ 90%). Deliverability, acceptability to health workers, end users and the effect on equity were all seen as highly likely (~ 90%). In terms of the maximum potential impact on meningitis disease burden, the median potential effectiveness of the vaccines in reduction of overall meningitis mortality was estimated to be 20%; (interquartile range 20-40% and min. 8%, max 50 %). For the multivalent meningococcal vaccines the experts had similar optimism for most of the 12 CHNRI criteria with slightly lower optimism in answerability and low development cost criteria. The main concern was expressed over the cost of product, its affordability and cost of implementation.

Conclusions

With increasing recognition of the burden of meningococcal meningitis, especially during epidemics in Africa, it is vitally important that strategies are taken to reduce the morbidity and mortality attributable to this disease. Improved MC vaccines are a promising investment that could substantially contribute to reduction of child meningitis mortality world-wide.