Affinity-purified human immunoglobulin G that binds a lacto-N-neotetraose-dependent lipooligosaccharide structure is bactericidal for serogroup B Neisseria meningitidis

Neisseria gonorrhoeae lipooligosaccharide glycan epitopes recognized by bactericidal IgG antibodies elicited by the meningococcal group B-directed vaccine, MenB-4C

Introduction

Outer membrane vesicles (OMVs) of Neisseria meningitidis in the group B-directed vaccine MenB-4C (BexseroR) protect against infections with Neisseria gonorrhoeae. The immunological basis for protection remains unclear. N. meningitidis OMV vaccines generate human antibodies to N. meningitidis and N. gonorrhoeae lipooligosaccharide (LOS/endotoxin), but the structural specificity of these LOS antibodies is not defined.

Methods

Ten paired human sera obtained pre- and post-MenB-4C immunization were used in Western blots to probe N. meningitidis and N. gonorrhoeae LOS. Post-MenB-4C sera (7v5, 19v5, and 17v5), representing individual human variability in LOS recognition, were then used to interrogate structurally defined LOSs of N. meningitidis and N. gonorrhoeae strains and mutants and studied in bactericidal assays.

Results and discussion

Post-MenB-4C sera recognized both N. meningitidis and N. gonorrhoeae LOS species, ~10% of total IgG to gonococcal OMV antigens. N. meningitidis and N. gonorrhoeae LOSs were broadly recognized by post-IgG antibodies, but with individual variability for LOS structures. Deep truncation of LOS, specifically a rfaK mutant without α-, β-, or γ-chain glycosylation, eliminated LOS recognition by all post-vaccine sera. Serum 7v5 IgG antibodies recognized the unsialyated L1 α-chain, and a 3-PEA-HepII or 6-PEA-HepII was part of the conformational epitope. Replacing the 3-PEA on HepII with a 3-Glc blocked 7v5 IgG antibody recognition of N. meningitidis and N. gonorrhoeae LOSs. Serum 19v5 recognized lactoneotetrose (LNT) or L1 LOS-expressing N. meningitidis or N. gonorrhoeae with a minimal α-chain structure of Gal-Glc-HepI (L8), a 3-PEA-HepII or 6-PEA-HepII was again part of the conformational epitope and a 3-Glc-HepII blocked 19v5 antibody binding. Serum 17v5 LOS antibodies recognized LNT or L1 α-chains with a minimal HepI structure of three sugars and no requirement for HepII modifications. These LOS antibodies contributed to the serum bactericidal activity against N. gonorrhoeae. The MenB-4C vaccination elicits bactericidal IgG antibodies to N. gonorrhoeae conformational epitopes involving HepI and HepII glycosylated LOS structures shared between N. meningitidis and N. gonorrhoeae. LOS structures should be considered in next-generation gonococcal vaccine design.

Phase I safety and immunogenicity study of a Brazilian serogroup B vaccine

Meningococcal disease by serogroup B has been a public health problem in Brazil in the last decades. The Brazilian Oswaldo Cruz Foundation has been working to develop a vaccine with detergent-treated outer membrane vesicles (OMV) and detoxified endotoxin (dLOS) from Neisseria meningitidis serogroup B prevalent strains. A phase I study, enrolling 26 adults (18–44 years of age) was performed using experimental vaccines combining B components and aluminum hydroxide as adjuvant. It was a dose escalation study testing vaccines made of 25, 50, and 100 µg OMV protein/mL (sum of both strains) and dLOS in half amount of total protein concentration, with three doses given two months apart. Adverse events were mild/moderate with frequency increasing with the amount of antigens. Pain in the site of injection was the most frequent reaction in all doses, reported in more than the 85% across vaccine groups. Considering all injections, cephalea was the most common systemic adverse event, detected in 11.1%, 17.2% and 32.1%, respectively with doses of 12.5 μg, 25 μg and 50 μg. High titers of total IgG (ELISA) were observed for the vaccine components before vaccination. Protective levels of bactericidal antibodies (titer ≥1:4) for both vaccine strains were also present. Considering a 4-fold increase of IgG titers compared to pre-immune values (seroconversion), 50%-70% of those who received intermediate and highest doses of antigens presented satisfactory response for OMV of N44/89 strain. The lowest dose vaccine induced no seroconversion for strain N44/89, and 11% for strain N603/95. For the three vaccines doses, 25% of seroconversion, in total IgG against LOS, was observed. Increased antibody bactericidal activity was observed for both strains in higher antigen concentrations. For IgG against LOS, all vaccine formulations showed 25% of seroconversion. In conclusion, MenB-Bio experimental vaccines were well tolerated and immunogenic, thus allowing phase II studies.

Postbooster Antibodies from Humans as Source of Diphtheria Antitoxin

Diphtheria antitoxin for therapeutic use is in limited supply. A potential source might be affinity-purified antibodies originally derived from plasma of adults who received a booster dose of a vaccine containing diphtheria toxoid. These antibodies might be useful for treating even severe cases of diphtheria.

Innate immune response to lipooligosaccharide: pivotal regulator of the pathobiology of invasive Neisseria meningitidis infections

Infections due to Neisseria meningitidis afflict more than one million people worldwide annually and cause death or disability in many survivors. The clinical course of invasive infections has been well studied, but our understanding of the cause of differences in patient outcomes has been limited because these are dependent on multiple factors including the response of the host, characteristics of the bacteria and interactions between the host and the bacteria. The meningococcus is a highly inflammatory organism, and the lipooligosaccharide (LOS) on the outer membrane is the most potent inflammatory molecule it expresses due to the interactions of the lipid A moiety of LOS with receptors of the innate immune system. We previously reported that increased phosphorylation of hexaacylated neisserial lipid A is correlated with greater inflammatory potential. Here we postulate that variability in lipid A phosphorylation can tip the balance of innate immune responses towards homeostatic tolerance or proinflammatory signaling that affects adaptive immune responses, causing disease with meningitis only, or septicemia with or without meningitis, respectively. Furthermore, we propose that studies of the relationship between bacterial virulence and gene expression should consider whether genetic variation could affect properties of biosynthetic enzymes resulting in LOS structural differences that alter disease pathobiology.

Analysis of Bacterial Lipooligosaccharides by MALDI-TOF MS with Traveling Wave Ion Mobility

Lipooligosaccharides (LOS) are major microbial virulence factors displayed on the outer membrane of rough-type Gram-negative bacteria. These amphipathic glycolipids are comprised of two domains, a core oligosaccharide linked to a lipid A moiety. Isolated LOS samples are generally heterogeneous mixtures of glycoforms, with structural variability in both domains. Traditionally, the oligosaccharide and lipid A components of LOS have been analyzed separately following mild acid hydrolysis, although important acid-labile moieties can be cleaved. Recently, an improved method was introduced for analysis of intact LOS by MALDI-TOF MS using a thin layer matrix composed of 2,4,6-trihydroxyacetophenone (THAP) and nitrocellulose. In addition to molecular ions, the spectra show in-source "prompt" fragments arising from regiospecific cleavage between the lipid A and oligosaccharide domains. Here, we demonstrate the use of traveling wave ion mobility spectrometry (TWIMS) for IMS-MS and IMS-MS/MS analyses of intact LOS from Neisseria spp. ionized by MALDI. Using IMS, the singly charged prompt fragments for the oligosaccharide and lipid A domains of LOS were readily separated into resolved ion plumes, permitting the extraction of specific subspectra, which led to increased confidence in assigning compositions and improved detection of less abundant ions. Moreover, IMS separation of precursor ions prior to collision-induced dissociation (CID) generated time-aligned, clean MS/MS spectra devoid of fragments from interfering species. Incorporating IMS into the profiling of intact LOS by MALDI-TOF MS exploits the unique domain structure of the molecule and offers a new means of extracting more detailed information from the analysis. Graphical Abstract ᅟ.

Lipooligosaccharide Structures of Invasive and Carrier Isolates of Neisseria meningitidis Are Correlated with Pathogenicity and Carriage

The degree of phosphorylation and phosphoethanolaminylation of lipid A on neisserial lipooligosaccharide (LOS), a major cell-surface antigen, can be correlated with inflammatory potential and the ability to induce immune tolerance in vitro. On the oligosaccharide of the LOS, the presence of phosphoethanolamine and sialic acid substituents can be correlated with in vitro serum resistance. In this study, we analyzed the structure of the LOS from 40 invasive isolates and 25 isolates from carriers of Neisseria meningitidis without disease. Invasive strains were classified as groups 1-3 that caused meningitis, septicemia without meningitis, and septicemia with meningitis, respectively. Intact LOS was analyzed by high resolution matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Prominent peaks for lipid A fragment ions with three phosphates and one phosphoethanolamine were detected in all LOS analyzed. LOS from groups 2 and 3 had less abundant ions for highly phosphorylated lipid A forms and induced less TNF-α in THP-1 monocytic cells compared with LOS from group 1. Lipid A from all invasive strains was hexaacylated, whereas lipid A of 6/25 carrier strains was pentaacylated. There were fewer O-acetyl groups and more phosphoethanolamine and sialic acid substitutions on the oligosaccharide from invasive compared with carrier isolates. Bioinformatic and genomic analysis of LOS biosynthetic genes indicated significant skewing to specific alleles, dependent on the disease outcome. Our results suggest that variable LOS structures have multifaceted effects on homeostatic innate immune responses that have critical impact on the pathophysiology of meningococcal infections.

Lack of lipid A pyrophosphorylation and functional lptA reduces inflammation by Neisseria commensals

The interaction of the immune system with Neisseria commensals remains poorly understood. We have previously shown that phosphoethanolamine on the lipid A portion of lipooligosaccharide (LOS) plays an important role in Toll-like receptor 4 (TLR4) signaling. For pathogenic Neisseria, phosphoethanolamine is added to lipid A by the phosphoethanolamine transferase specific for lipid A, which is encoded by lptA. Here, we report that Southern hybridizations and bioinformatics analyses of genomic sequences from all eight commensal Neisseria species confirmed that lptA was absent in 15 of 17 strains examined but was present in N. lactamica. Mass spectrometry of lipid A and intact LOS revealed the lack of both pyrophosphorylation and phosphoethanolaminylation in lipid A of commensal species lacking lptA. Inflammatory signaling in human THP-1 monocytic cells was much greater with pathogenic than with commensal Neisseria strains that lacked lptA, and greater sensitivity to polymyxin B was consistent with the absence of phosphoethanolamine. Unlike the other commensals, whole bacteria of two N. lactamica commensal strains had low inflammatory potential, whereas their lipid A had high-level pyrophosphorylation and phosphoethanolaminylation and induced high-level inflammatory signaling, supporting previous studies indicating that this species uses mechanisms other than altering lipid A to support commensalism. A meningococcal lptA deletion mutant had reduced inflammatory potential, further illustrating the importance of lipid A pyrophosphorylation and phosphoethanolaminylation in the bioactivity of LOS. Overall, our results indicate that lack of pyrophosphorylation and phosphoethanolaminylation of lipid A contributes to the immune privilege of most commensal Neisseria strains by reducing the inflammatory potential of LOS.

Neisseria meningitidis serogroup B lipooligosaccharide genotyping reveals high prevalence of L2 strains in Spain and unexpected relationship with factor H-binding protein expression

Neisseria meningitidis may be classified according to the lipooligosaccharide immunotype. We show that this classification can be achieved by PCR genotyping of the genes involved in the lipooligosaccharide inner-core biosynthesis, lpt3, lpt6, lgtG and lot3. Genotyping data correlated well (90-100%) with mass spectrometry data and was, therefore, applied to screen a random subset of recent N. meningitidis serogroup B isolates from Europe. Analysis of the proportion of the different lipooligosaccharide types highlighted the predominance of L3 strains. Surprisingly, high rates of L2 type strains were found in Spain (17%, versus 2.5% in Germany and 1.9% in the United Kingdom). Therefore, we also investigated further these Spanish L2 strains in an attempt to explain such prevalence despite the known sensitivity of L2 immunotype to complement. We explored the hypothesis that these strains express high amounts of factor H-binding protein (fHbp), but we found, on the contrary, that L2 strains express low or undetectable amounts of fHbp. Our findings suggest that, in addition to a genetic analysis, a multivalent approach may be necessary to estimate the effectiveness of a N. meningitidis serogroup B vaccine.

Improvement of immunogenicity of meningococcal lipooligosaccharide by coformulation with lipidated transferrin-binding protein B in liposomes: implications for vaccine development

Among various meningococcal antigens, lipooligosaccharide (LOS) and recombinant lipidated transferrin-binding protein B (rlip-TbpB) are considered to be putative vaccine candidates against group B Neisseria meningitidis. In the present work, we report the development of a new liposome-based vaccine formulation containing both rlip-TbpB and L8 LOS. The endotoxic activity of the liposomal LOS was evaluated in vitro using the Limulus Amebocyte Lysate assay and compared to the endotoxic activity of free LOS. Above a 250:1 lipid/LOS molar ratio, liposomes were shown to effectively detoxify the LOS as the endotoxic activity of the LOS was reduced by more than 99%. Immunogenicity studies in rabbits showed that the presence of rlip-TbpB dramatically increased the immunogenicity of the LOS. While the formulation raised a strong anti-TbpB response, it elicited a higher anti-LOS IgG level than the liposomal LOS alone. Sera from rabbits immunized with rlip-TbpB/liposomal LOS displayed increased ability to recognize LOS on live bacteria expressing the L8 immunotype and increased anti-LOS-specific bactericidal activity compared to sera from rabbits immunized with liposomal LOS alone. Measurement of interleukin-8 (IL-8) produced by HEK293 cells transfected with Toll-like receptor (TLR) after stimulation with rlip-TbpB showed that the protein is a TLR2 agonist, which is in accordance with the structure of its lipid. Furthermore, an in vivo study demonstrated that the lipid moiety is not only required for its adjuvant effect but also has to be linked to the protein. Overall, the rlip-TbpB/LOS liposomal formulation was demonstrated to induce an effective anti-LOS response due to the adjuvant effect of rlip-TbpB on LOS.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2007-2008

This review is the fifth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2008. The first section of the review covers fundamental studies, fragmentation of carbohydrate ions, use of derivatives and new software developments for analysis of carbohydrate spectra. Among newer areas of method development are glycan arrays, MALDI imaging and the use of ion mobility spectrometry. The second section of the review discusses applications of MALDI MS to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, biopharmaceuticals, glycated proteins, glycolipids, glycosides and various other natural products. There is a short section on the use of MALDI mass spectrometry for the study of enzymes involved in glycan processing and a section on the use of MALDI MS to monitor products of the chemical synthesis of carbohydrates with emphasis on carbohydrate-protein complexes and glycodendrimers. Corresponding analyses by electrospray ionization now appear to outnumber those performed by MALDI and the amount of literature makes a comprehensive review on this technique impractical. However, most of the work relating to sample preparation and glycan synthesis is equally relevant to electrospray and, consequently, those proposing analyses by electrospray should also find material in this review of interest.

Human lipooligosaccharide IGG that prevents endemic meningococcal disease recognizes an internal lacto-N-neotetraose structure

Antibodies that initiate complement-mediated killing of Neisseria meningitidis as they enter the bloodstream from the oropharynx protect against disseminated disease. Human IgGs that bind the neisserial L7 lipooligosaccharide (LOS) are bactericidal for L3,7 and L2,4 meningococci in the presence of human complement. These strains share a lacto-N-neotetraose (nLc4) LOS α chain. We used a set of mutants that have successive saccharide deletions from the nLc4 α chain to characterize further the binding and bactericidal activity of nLc4 LOS IgG. We found that the nLc4 α chain conforms at least four different antigens. We separately purified IgG that required the nLc4 (non-reducing) terminal galactose (Gal) for binding and IgG that bound the truncated nLc3 α chain that lacks this Gal residue. IgG that bound the internal nLc3 α chain killed both L3,7 and L2,4 strains, whereas IgG that required the nLc4 terminal Gal residue for binding killed L2,4 stains but not L3,7 strains. These results show that the diversity of LOS antibodies in human serum is as much a function of the conformation of multiple antigens by a single glycoform as of the production of multiple glycoforms. Differences in sensitivity to killing by human nLc4 LOS IgG may account for the fact that fully two-thirds of endemic group B meningococcal disease in infants and children is caused by L3,7 strains, but only 20% is caused by L2,4 stains.

Importance of antibodies to lipopolysaccharide in natural and vaccine-induced serum bactericidal activity against Neisseria meningitidis group B

Analysis of the specificity of bactericidal antibodies in normal, convalescent, and postvaccination human sera is important in understanding human immunity to meningococcal infections and can aid in the design of an effective group B vaccine. A collection of human sera, including group C and group B convalescent-phase sera, normal sera with naturally occurring cross-reactive bactericidal activity, and some postvaccination sera, was analyzed to determine the specificity of cross-reactive bactericidal antibodies. Analysis of human sera using a bactericidal antibody depletion assay demonstrated that a significant portion of the bactericidal activity could be removed by purified lipopolysaccharide (LPS). LPS homologous to that expressed on the bactericidal test strain was most effective, but partial depletion by heterologous LPS suggested the presence of antibodies with various degrees of cross-reactivity. Binding of anti-L3,7 LPS bactericidal antibodies was affected by modification of the core structure, suggesting that these functional antibodies recognized epitopes consisting of both core structures and lacto-N-neotetraose (LNnT). When the target strain was grown with 5'-cytidinemonophospho-N-acetylneuraminic acid (CMP-NANA) to increase LPS sialylation, convalescent-phase serum bactericidal titers were decreased by only 2- to 4-fold, and most remaining bactericidal activity was still depleted by LPS. Highly sialylated LPS was ineffective in depleting bactericidal antibodies. We conclude that natural infections caused by strains expressing L3,7 LPS induce persistent, protective bactericidal antibodies and appear to be directed against nonsialylated bacterial epitopes. Additionally, subsets of these bactericidal antibodies are cross-reactive, binding to several different LPS immunotypes, which is a useful characteristic for an effective group B meningococcal vaccine antigen.

Design and evaluation in mice of a broadly protective meningococcal group B native outer membrane vesicle vaccine

A vaccine based on native outer membrane vesicles (NOMV) that has potential to provide safe, broad based protection against group B strains of Neisseria meningitidis has been developed. Three antigenically diverse group B strains of N. meningitidis were chosen and genetically modified to improve safety and expression of desirable antigens. Safety was enhanced by disabling three genes: synX, lpxL1, and lgtA. The vaccine strains were genetically configured to have three sets of antigens each with potential to induce protective antibodies against a wide range of group B strains. Preliminary immunogenicity studies with combined NOMV from the three strains confirmed the capacity of the vaccine to induce a broad based bactericidal antibody response. Analysis of the bactericidal activity indicated that antibodies to the LOS were responsible for a major portion of the bactericidal activity and that these antibodies may enhance the bactericidal activity of anti-protein antibodies.

The meningococcal vaccine candidate neisserial surface protein A (NspA) binds to factor H and enhances meningococcal resistance to complement

Complement forms an important arm of innate immunity against invasive meningococcal infections. Binding of the alternative complement pathway inhibitor factor H (fH) to fH-binding protein (fHbp) is one mechanism meningococci employ to limit complement activation on the bacterial surface. fHbp is a leading vaccine candidate against group B Neisseria meningitidis. Novel mechanisms that meningococci employ to bind fH could undermine the efficacy of fHbp-based vaccines. We observed that fHbp deletion mutants of some meningococcal strains showed residual fH binding suggesting the presence of a second receptor for fH. Ligand overlay immunoblotting using membrane fractions from one such strain showed that fH bound to a ∼17 kD protein, identified by MALDI-TOF analysis as Neisserial surface protein A (NspA), a meningococcal vaccine candidate whose function has not been defined. Deleting nspA, in the background of fHbp deletion mutants, abrogated fH binding and mAbs against NspA blocked fH binding, confirming NspA as a fH binding molecule on intact bacteria. NspA expression levels vary among strains and expression correlated with the level of fH binding; over-expressing NspA enhanced fH binding to bacteria. Progressive truncation of the heptose (Hep) I chain of lipooligosaccharide (LOS), or sialylation of lacto-N-neotetraose LOS both increased fH binding to NspA-expressing meningococci, while expression of capsule reduced fH binding to the strains tested. Similar to fHbp, binding of NspA to fH was human-specific and occurred through fH domains 6–7. Consistent with its ability to bind fH, deleting NspA increased C3 deposition and resulted in increased complement-dependent killing. Collectively, these data identify a key complement evasion mechanism with important implications for ongoing efforts to develop meningococcal vaccines that employ fHbp as one of its components.

Neisseria meningitidis is an important cause of bacterial meningitis and sepsis worldwide. The complement system is a family of proteins that is critical for innate immune defenses against this pathogen. In order to successfully colonize humans and cause disease, the meningococcus must escape killing by the complement system. In this study we show that meningococci can use one of its surface proteins called Neisserial surface protein A (NspA) to bind to a host complement inhibitory protein called factor H (fH). NspA is a protein vaccine candidate against group B meningococcal disease. Binding of fH limits complement activation on the bacterial surface and enhances the ability of the meningococcus to resist complement-dependent killing. Capsular polysaccharide expression decreases fH binding to NspA, while truncation of the core glycan chain of lipooligosaccharide increases fH binding to meningococcal NspA. Loss of NspA results in enhanced complement activation on the bacterial surface and increased complement-dependent killing of meningococci. Our findings have disclosed a novel function for NspA and sheds further light on how this pathogen evades killing by the complement system.

The oligosaccharide of gonococcal lipooligosaccharide contains several epitopes that are recognized by human antibodies

Recently, we isolated human IgG from normal human sera (NHS) using lipooligosaccharide (LOS) from gonococcal strain JW31R as an affinity ligand. We provided evidence that the oligosaccharide (OS) moiety of LOS was immunogenic in humans and that NHS contains functional antibodies that bind to the branched OS. The present study aimed to identify bactericidal antibodies that bind to partial core OS structures or their adjacent sites expressed in the 3,4-branched and 2,3:3,4-dibranched neisserial LOSs. Using 15253 LOS from serum-resistant gonococcal strain 15253 as an affinity ligand, we isolated IgG2 and found that this preparation contained at least three different species. (i) One IgG2 species recognized a cross-reactive epitope that is expressed on 3,4-branched and 2,3:3,4-dibranched neisserial LOSs. (ii) Another IgG2 species was specific for JW31R LOS from a pyocin-resistant gonococcal strain; this IgG-defined epitope was not shared with the aforementioned branched LOSs. (iii) The third IgG2 species bound to the "Salmonella minnesota" Rb and Re mutant lipopolysaccharides (LPSs); this IgG2 recognizes a KDOalpha2-4KDO residue at the reducing end of the carbohydrate moiety of each LPS. The IgG2 was also found to be functional and facilitated the killing of strain 15253. The current results show that neisserial LOS contains several epitopes within its OS moiety that are recognized by human antibodies.

Review of meningococcal group B vaccines

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

Application of an ELISA-elution assay to dissociate digoxin-antibody complexes in immunoaffinity chromatography

In this study, we used a modified enzyme-linked immunosorbent assay (ELISA)-elution technique as a screening tool to select specific elution conditions. We examined 12 different elution conditions for the removal of antibodies from a complex on an ELISA plate; 0.2 mol/l glycine-HCl (pH 2.5), 1.0 mol/l acetic acid (pH 2.5), 25% methanol (pH 2.5) and 3 mol/l NaSCN showed a higher elution efficiency. We conducted affinity chromatography with these four conditions for the purification of anti-digoxin antibodies from hyperimmune sera with a digoxin-specific column using omega-aminoalkyl derivatives of Sepharose 4B, whose elution efficiency was similar to that of ELISA. We also monitored the relative specific activities during elution from the digoxin-specific column. The optimum, general-purpose dissociation reagent for this immunoaffinity system was identified as 25% methanol (pH 2.5) with an elution efficiency and relative specific activity of 88.40% and 62.25%, respectively. The high purity of the purified antibodies was demonstrated with sodium dodecyl sulphate-polyacrylamide gel electrophoresis.

Genetically modified L3,7 and L2 lipooligosaccharides from Neisseria meningitidis serogroup B confer a broad cross-bactericidal response

Currently available Neisseria meningitidis serogroup B (MenB) vaccines are based on outer membrane vesicles (OMVs) that are obtained from wild-type strains. They are purified with the aim of decreasing the lipooligosaccharide (LOS) content and hence reduce the reactogenicity of the vaccine even though LOS is a potential protective antigen. In <2-year-old children, these MenB vaccines confer protection only against strains expressing homologous PorA, a major and variable outer membrane protein. Our objective was to develop a safe LOS-based vaccine against MenB. To this end, we used modified porA knockout strains expressing genetically detoxified (msbB gene-deleted) L2 and L3,7 LOSs, allowing the production of LOS-enriched OMVs. The vaccine-induced antibodies were found to be bactericidal against nearly all invasive strains, irrespective of capsular serogroup. In addition, we have also demonstrated that LOS lacking the terminal galactose (with a lgtB mutation; truncated L3 LOS), but not LOS produced without the galE gene, induced a bactericidal antibody response in mice similar to that seen for LOS containing the full lacto-N-neotetraose (L3,7 LOS). In conclusion, a bivalent detoxified LOS OMV-based vaccine demonstrated the potential to afford a broad cross-protection against meningococcal disease.