Neisseria lactamica antigens complexed with a novel cationic adjuvant

Commensal Neisseria cinerea outer membrane vesicles as a platform for the delivery of meningococcal and gonococcal antigens to the immune system

An affordable, accessible, and broadly protective vaccine is required to tackle the re-occurring bacterial meningococcal epidemics in Sub-Saharan Africa as well as an effective control of multi-drug resistant strains of gonococcus. Outer membrane vesicles (OMVs) secreted from Gram-negative bacteria represent an attractive platform for antigen delivery to the immune system and therefore for development of multi-component vaccines. In this study, we describe the generation of modified OMVs (mOMVs) from commensal biosafety-level 1 (BSL-1) Neisseria cinerea ATCC® 14685TM, which is phylogenetically close to the pathogenic bacteria Neisseria meningitidis and Neisseria gonorrhoeae. mOMVs were prepared from N. cinerea engineered to express heterologous antigens from N. meningitidis (factor H binding protein (fHbp) and Neisseria Heparin Binding Antigen (NHBA-2)) and from N. gonorrhoeae (NHBA-542). Mice immunised with the mOMVs produced antibodies against fHbp and NHBA. The work indicates that mOMV from N. cinerea can be used as a platform to induce immune responses against antigens involved in the protective immune response against meningococcal and gonococcal diseases.

Study of avidity-ELISA: Comparison of chaotropic agents, incubation temperature and affinity maturation after meningococcal immunization

The avidity index (AI) measures the binding strength between the antibody and the antigen, reflecting the affinity maturation. It can be measured by a modified ELISA, adding a chaotropic agent to disrupt the antigen x antibody interaction. However, details of the protocols used affect the final results. We compared the AI of mice sera after a three-dose immunization with meningococcal antigens using different adjuvants. The AI was assessed using potassium thiocyanate (KSCN) and urea as chaotropic agents, incubated at 4 °C, room temperature (RT) and 37 °C. KSCN presented statistically different results when the incubation was set at 4 °C vs RT and 4 °C vs 37 °C, thus, the mean AI obtained were lower. For Urea, 4 °C vs 37 °C presented relevant differences. Using whole-cells suspensions or OMVs as coating antigen provided similar results in some protocols. Thus, the affinity maturation was assessed after each immunization dose and adjuvant use (aluminium hydroxide and dimethyldioctadecylammonium bromide) supported affinity maturation. It is important to study the AI as a functional parameter of humoral response, and both KSCN and Urea are suitable chaotropic agents, however, the protocols should be standardized considering the nature of the antigen, the chaotropic activity and overall laboratory conditions. Adjuvants are important tools to improve antibody avidity following immunization.

Intranasal and Intramuscular Immunization with Outer Membrane Vesicles from Serogroup C Meningococci Induced Functional Antibodies and Immunologic Memory

BACKGROUND

Immunization is the key to prevent invasive meningococcal disease (IMD), caused by Neisseria meningitidis. Outer membrane vesicles (OMVs) can be used as meningococcal antigens.

METHODS

Isogenic mice A/Sn (H2^a) were immunized with low antigenic doses of OMVs of an N. meningitidis C:2a:P1.5 strain, via intranasal/intramuscular route, adjuvanted by cholera toxin subunit B (CTB) or via intramuscular route only, adjuvanted by aluminium hydroxide (AH). Mice were followed until old age and humoral and cellular responses were assessed by ELISA, Immunoblotting, Dot-blot, Serum-bactericidal assay, Immunohistochemistry and ELISpot.

RESULTS

OMV+CTB and OMV+AH groups presented statistically higher antibodies titers, which persisted until middle and old ages. IgG isotypes point to a Th2 type of response. Avidity indexes were considered high, regardless of adjuvant use, but only groups immunized with OMVs and adjuvants (OMV+CTB and OMV+AH) presented bactericidal activity. The antibodies recognized antigens of molecular weights attributed to porin and cross-reactivity proteins. Although the spleen of old mice did not present differences in immunohistochemistry marking of CD68+, CD4+, CD79+ and CD25+ cells, splenocytes of immune groups secreted IL-4 and IL-17 when stimulated with OMVs and meningococcal C polysaccharide.

CONCLUSION

We concluded that both adjuvants, CTB and AH, improved the immunogenicity of low doses of OMVs and contributed to a persistent immune response. Even though AH is well established in the vaccinology area, CTB seems to be a promising adjuvant candidate for meningococcal vaccines: it is suitable for mucosal delivery and supports a Th2 type of response. Therefore, OMVs are still a relevant vaccine platform.

Immunological Effects of Dimethyldioctadecylammonium Bromide and Saponin as Adjuvants for Outer Membrane Vesicles from Neisseria meningitidis

The meningococcal disease is a global health threat, but is preventable through vaccination. Adjuvants improve meningococcal vaccines and are able to trigger different aspects of the immune response. The present work evaluated the immune response of mice against Neisseria meningitidis outer membrane vesicles (OMV) complexed with the adjuvants aluminium hydroxide (AH), via subcutaneous route; and dimethyldioctadecylammonium bromide (DDA) or Saponin (Sap), via intranasal/subcutaneous routes. ELISA demonstrated that all adjuvants increased IgG titers after the booster dose, remaining elevated for 18 months. Additionally, adjuvants increased the avidity of the antibodies and the bactericidal titer: OMVs alone were bactericidal until 1:4 dilution but, when adjuvanted by Alum, DDA or Sap, it increased to 1/32. DDA and Sap increased all IgG isotypes, while AH improved IgG1 and IgG2a levels. Thus, Sap led to the recognition of more proteins in Immunoblot, followed by DDA and AH. Sap and AH induced higher IL-4 and IL-17 release, respectively. The use of adjuvants improved both cellular and humoral immune response, however, each adjuvant contributed to particular parameters. This demonstrates the importance of studying different adjuvant options and their suitability to stimulate different immune mechanisms, modulating the immune response.

Immunogenicity of antigens from outer membrane vesicles of Neisseria meningitidis associated with bilayer fragment of dioctadecyldimethylammonium in Swiss adult mice

Purpose

In the present study, meningococcal serogroup B outer membrane vesicles (OMVs) were associated with bilayer fragments of a cationic lipid, dioctadecyldimethylammonium (DDA-BF), used as adjuvant, in an antigenic preparation tested in adult female outbred mice. This adjuvant was compared to the traditional adjuvant aluminum hydroxide.

Materials and Methods

The potential in generating humoral response was evaluated by enzyme-linked immunosorbent assay (ELISA). Individual serum was collected and immunoglobulin G (IgG), IgG1, IgG2a, and IgG2b were quantified. Analyses were carried out 15 and 60 days after immunization. Antibodies avidity index were also analyzed by ELISA. Immunoblot and dot-ELISA were carried out to evaluate specific reaction for homologous strains and cross-reactive antigens present in other meningococcal strains isolated in 2011–2012 year, in Brazil. Delayed type hypersensitivity was used as indicative of cellular immunity and compared between two experimental groups, 24 hours after homologous strain challenge.

Results

The OMVs of Neisseria meningitidis, and N. lactamica (related species) were characterized by electrophoretic separation of proteins in 13% polyacrylamide gel. The strains presented antigens in the range of 8 to 130 kDa, showing a heterogeneous protein migration pattern. In the group immunized with OMVs/DDA-BF, we found no significant production of total IgG 15 days after the first immunization. On the other hand, 60 days after first immunization both adjuvants act benefiting total IgG production similarly. The antibodies of the IgG isotype produced by animals immunized after one or two doses after first immunization, showed intermediate and high avidity, independent on the adjuvant used. In both experimental groups the swelling of the footpads was significantly higher than those of the controls, suggesting that only one dose was enough to stimulate the generation of cellular immunity.

Conclusion

The use of this cationic adjuvant for N. meningitidis OMVs preparation revealed good potential for future new antigen preparation for N. meningitidis vaccine.

Study of different routes of immunization using outer membrane vesicles of Neisseria meningitidis B and comparison of two adjuvants

Outer membrane vesicles (OMVs) of Neisseria meningitidis contain important antigens to trigger an immune response against meningococci and have been studied as vaccines compounds. The immune response to a vaccine may be affected by its constitution and route of administration. Therefore, Swiss mice were immunized by different routes with OMVs of N. meningitidis B with dimethyl dioctadecyl ammonium bromide in bilayer fragments (DDA-BF) or aluminum hydroxide (AH) as adjuvants. The adjuvants and different routes were compared regarding the immune responses by ELISA, western blot, delayed type hypersensitivity (DTH) and histopathologic analysis. The antigenic preparation generated humoral and cellular immune responses. In quantitative analyzes, in general, AH was superior to DDA-BF. However, analysis such as IgG avidity index, bactericidal activity and immunoblot, revealed no important differences regarding the adjuvant or route of immunization. Regarding the parameters tested, it was not possible to define a superiority between the adjuvants and routes of immunization proposed by this study.

Prevalence, sequence type, and quinolone resistance of Neisseria lactamica carried in children younger than 15 years in Shanghai, China

OBJECTIVE

Neisseria lactamica has an important influence on carriage and antimicrobial susceptibility of N. meningitidis, a major pathogen of septicemia and meningitis. In China, quinolone resistance is highly prevalent in N. meningitidis but unknown in N. lactamica. This study investigates the carriage rate, sequence type, and ciprofloxacin resistance of N. lactamica in children in China.

METHODS

During 2014-2016, throat swabs were collected from 2,239 children in Shanghai. The ciprofloxacin minimum inhibitory concentrations of the isolates were determined by the agar dilution method.

RESULTS

The overall carriage rate of N. lactamica was higher (8.9%) than that of N. meningitidis (0.9%) and peaked at two years (37.1%). The resistance frequency of N. lactamica to ciprofloxacin was 98.5% (197/200). There were 65 sequence types (STs). Clonal complex (cc) 640 (45.5%) dominated, while ST-14031 was predominant (37%, 74/200). All isolates possessed a GyrA mutation; 17 isolates (8.5%) harbored additionally a ParC mutation. Assigned to 39 different alleles, the gyrA sequences from these N. lactamica isolates formed an N. lactamica cluster, which also included eight alleles from N. meningitidis.

CONCLUSION

The N. lactamica isolates in China showed distinct characteristics with lower genetic diversity and a much higher prevalence of quinolone resistance than in other countries.

Dioctadecyldimethylammonium bromide (DODAB-BF) as a new adjuvant for maternal-fetal immunization in mice against Neisseria meningitidis: evaluation of humoral response

Neisseria meningitidis bacterium is a Gram-negative diplococcus. Among their serogroups, the B is one of the main causes of invasive meningococcal disease. Newborns and children are particularly susceptible to this infection because of their immune systems that are still maturing and relatively inexperienced. Thus, further studies on the use of maternal immunization for protection against this disease are needed. The purpose of this study was to evaluate the potential immunogenic antigens from the outer membrane of N. meningitidis serogroup B in outbred mice and the influence of maternal immunization in the offspring, and analyze the adjuvant effect of bilayer fragments of dioctadecyldimethylamonium bromide (DODAB-BF) and hydroxide aluminium (alum) in enhancing antibodies production and transference to offspring. IgG and IgG1, IgG2a and IgG2b subclasses of antibodies in serum from immunized mice and controls were quantified and compared. Immunization by subcutaneous and intramuscular routes exhibited evidence of IgG, and both adjuvants promoted the production of IgG1 and IgG2b that were transferred to the offspring. These antibodies also showed specificity with the outer membrane vesicles from homologous strain and were capable to cross react with different strains. The use of DODAB-BF seems to enhance immune response on mothers and offspring and may have immunological advantages.

Evaluation of intranasal and subcutaneous route of immunization in neonatal mice using DODAB-BF as adjuvant with outer membrane vesicles of Neisseria meningitis B

BACKGROUND

The Neisseria meningitidis bacterium is a Gram-negative diplococcus that can be classified into different serogroups according to the capsular structure. Six of them (A, B, C, W, X, Y) are responsible for causing Invasive Meningococcal Disease (IMD). The strategies for the development of a vaccine for serogroup B have been directed to the use of outer membrane vesicles (OMVs). The aim of this study was to evaluate the immunogenicity of antigenic determinants from OMVs of N. meningitidis B complexed with two different adjuvants: DODAB-BF and aluminum hydroxide (alum), comparing the evaluation of intranasal and subcutaneous route of immunization.

METHODS

We used prime-boost immunization for the first time in outbred neonatal mice evaluating the cellular and humoral immune response.

RESULTS

Immunoblot, ELISA DOT-ELISA and ELISpot were used universal methods of antibody detection, in order to detect the humoral and cellular immune response in male and female mice. Immunoblot analyzes the specificity of antibodies with the homologous N. meningitidis strain. ELISA served to quantify and compare the titers of antibodies in the serum of mice immunized with DODAB-BF + OMVs and alum + OMVs for IgG, IgG1, and IgG2a. Intranasal immunization produced a mixed response in the T helper cells Th1 and Th2, while subcutaneous immunization exhibited a Th1 profile. The DOT-ELISA identified cross-reactivity with DODAB-BF to different serogroups of N. meningitidis (B, C, W, and Y) that was not observed with alum. ELISpot analyzed IFN-γ- and IL-4 and the results showed the response directly to Th1 and Th2 profile.

CONCLUSION

Our findings indicate that DODAB-BF can be an alternative adjuvant for mucosal cell activation with OMVs of N. meningitidis B and that DODAB-BF was similar to aluminum hydroxide as an adjuvant for subcutaneous immunization.