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

Supramolecular Nanostructures for Vaccines

Although this is an era of pandemics and many devastating diseases, this is also a time when bionanotechnology flourishes, illuminating a multidisciplinary field where vaccines are quickly becoming a balsam and a prevention against insidious plagues. In this work, we tried to gain and also give a deeper understanding on nanovaccines and their way of acting to prevent or cure cancer, infectious diseases, and diseases caused by parasites. Major nanoadjuvants and nanovaccines are temptatively exemplified trying to contextualize our own work and its relative importance to the field. The main properties for novel adjuvants seem to be the nanosize, the cationic character, and the biocompatibility, even if it is achieved in a low dose-dependent manner.

Cationic and Biocompatible Polymer/Lipid Nanoparticles as Immunoadjuvants

Nanostructures have been of paramount importance for developing immunoadjuvants. They must be cationic and non-cytotoxic, easily assembling with usually oppositely charged antigens such as proteins, haptens or nucleic acids for use in vaccines. We obtained optimal hybrid nanoparticles (NPs) from the biocompatible polymer poly(methyl methacrylate) (PMMA) and the cationic lipid dioctadecyl dimethyl ammonium bromide (DODAB) by emulsion polymerization of methyl methacrylate (MMA) in the presence of DODAB. NPs adsorbed ovalbumin (OVA) as a model antigen and we determined their adjuvant properties. Interestingly, they elicited high double immune responses of the cellular and humoral types overcoming the poor biocompatibility of DODAB-based adjuvants of the bilayer type. The results suggested that the novel adjuvant would be possibly of use in a variety of vaccines.

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.

Effect of DODAB Nano-Sized Cationic Bilayer Fragments against Leishmania amazonensis

The dioctadecyldimethylammonium bromide (DODAB) is a double-chained cationic lipid with potent bactericide and fungistatic activities; however, its toxicity on protozoan parasites is still unknown. Here, we show the antileishmanial activity of DODAB nano-sized cationic bilayer fragments on stationary-phase promastigotes and amastigotes of Leishmania amazonensis, the causative agent of cutaneous leishmaniasis. Upon treatment with DODAB, we analyzed the parasite surface zeta-potential, parasite viability, cellular structural modifications, and intracellular proliferation. The DODAB cytotoxic effect was dose-dependent, with a median effective concentration (EC₅₀) of 25 µM for both life-cycle stages, comparable to the reported data for bacteria and fungi. The treatment with DODAB changed the membrane zeta-potential from negative to positive, compromised the parasite's morphology, affected the cell size regulation, caused a loss of intracellular organelles, and probably dysregulated the plasma membrane permeability without membrane disruption. Moreover, the parasites that survived after treatment induced small parasitophorous vacuoles and failed to proliferate inside macrophages. In conclusion, DODAB displayed antileishmanial activity, and it remains to be elucidated how DODAB acts on the protozoan membrane. Understanding this mechanism can provide insights into the development of new parasite-control strategies.

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.

Cationic Nanostructures for Vaccines Design

Subunit vaccines rely on adjuvants carrying one or a few molecular antigens from the pathogen in order to guarantee an improved immune response. However, to be effective, the vaccine formulation usually consists of several components: an antigen carrier, the antigen, a stimulator of cellular immunity such as a Toll-like Receptors (TLRs) ligand, and a stimulator of humoral response such as an inflammasome activator. Most antigens are negatively charged and combine well with oppositely charged adjuvants. This explains the paramount importance of studying a variety of cationic supramolecular assemblies aiming at the optimal activity in vivo associated with adjuvant simplicity, positive charge, nanometric size, and colloidal stability. In this review, we discuss the use of several antigen/adjuvant cationic combinations. The discussion involves antigen assembled to 1) cationic lipids, 2) cationic polymers, 3) cationic lipid/polymer nanostructures, and 4) cationic polymer/biocompatible polymer nanostructures. Some of these cationic assemblies revealed good yet poorly explored perspectives as general adjuvants for vaccine design.

Simple Nanoparticles from the Assembly of Cationic Polymer and Antigen as Immunoadjuvants

Since antigens are negatively charged, they combine well with positively charged adjuvants. Here, ovalbumin (OVA) (0.1 mg·mL^-1) and poly (diallyldimethylammonium chloride) (PDDA) (0.01 mg·mL^-1) yielded PDDA/OVA assemblies characterized by dynamic light scattering (DLS) and scanning electron microscopy (SEM) as spherical nanoparticles (NPs) of 170 ± 4 nm hydrodynamic diameter, 30 ± 2 mV of zeta-potential and 0.11 ± 0.01 of polydispersity. Mice immunization with the NPs elicited high OVA-specific IgG1 and low OVA-specific IgG2a production, indicating a Th-2 response. Delayed-type hypersensitivity reaction (DTH) was low and comparable to the one elicited by Al(OH)₃/OVA, suggesting again a Th-2 response. PDDA advantages as an adjuvant were simplicity (a single-component adjuvant), low concentration needed (0.01 mg·mL^-1 PDDA) combined with antigen yielding neglectable cytotoxicity, and high stability of PDDA/OVA dispersions. The NPs elicited much higher OVA-specific antibodies production than Al(OH)₃/OVA. In vivo, the nano-metric size possibly assured antigen presentation by antigen-presenting cells (APC) at the lymph nodes, in contrast to the location of Al(OH)₃/OVA microparticles at the site of injection for longer periods with stimulation of local dendritic cells. In the future, it will be interesting to evaluate combinations of the antigen with NPs carrying both PDDA and elicitors of the Th-1 response.

Immunological characteristics of Mycobacterium tuberculosis subunit vaccines immunized through different routes

Tuberculosis is chronic infectious disease caused by Mycobacterium tuberculosis (M.tb) that is prevalent worldwide. Several specific antigens, such as Antigen 85B (Ag85B) and 6 kDa early secretory antigenic target (ESAT-6) protein of M.tb, are listed as some of the candidate subunit vaccines against M.tb. ESAT-6, as a virulent factor and differential gene in M.tb, shows insufficient immunogenicity in animal model. In order to investigate the ways to improve the immunogenicity of ESAT-6, we immunized ESAT-6 by subcutaneous and intramuscular routes with different adjuvants. We found that ESAT-6 immunized alone did not induce significant humoral immunity in both immunization routes. However, subcutaneous immunization of ESAT-6 plus incomplete Freund's adjuvant can induce a significant humoral immune response, enhanced proliferation and elevated secretion of IFN-γ from splenocytes. Intramuscular immunization of ESAT-6 plus adjuvant aluminum salt or poly(I:C) did not enhance humoral and cellular immune responses. Therefore, it is concluded that immunization of ESAT-6 subcutaneously plus incomplete Freund's adjuvant induces stronger humoral and cellular immune responses, which can be considered of ESAT-6 as a subunit vaccine in further research against tuberculosis.