Interactions between cationic liposomes and an antigenic protein: the physical chemistry of the immunoadjuvant action

DODAB vesicles containing lysophosphatidylcholines: The relevance of acyl chain saturation on the membrane structure and thermal properties

The saturated LPC18:0 and unsaturated LPC18:1 lysophosphatidylcholines have important roles in inflammation and immunity and are interesting targets for immunotherapy. The synthetic cationic lipid DODAB has been successfully employed in delivery systems, and would be a suitable carrier for those lysophosphatidylcholines. Here, assemblies of DODAB and LPC18:0 or LPC18:1 were characterized by Differential Scanning Calorimetry (DSC) and Electron Paramagnetic Resonance (EPR) spectroscopy. LPC18:0 increased the DODAB gel-fluid transition enthalpy and rigidified both phases. In contrast, LPC18:1 caused a decrease in the DODAB gel-fluid transition temperature and cooperativity, associated with two populations with distinct rigidities in the gel phase. In the fluid phase, LPC18:1 increased the surface order but, differently from LPC18:0, did not affect viscosity at the membrane core. The impact of the different acyl chains of LPC18:0 and 18:1 on structure and thermotropic behavior should be considered when developing applications using mixed DODAB membranes.

Cationic Nanostructures as Adjuvants for Vaccines

Spherical or discoidal lipid polymer nanostructures bearing cationic charges successfully adsorb a variety of oppositely charged antigens (Ag) such as proteins, peptides, nucleic acids, or oligonucleotides. This report provides instructions for the preparation and physical characterization of four different cationic nanostructures able to combine and deliver antigens to the immune system: (1) dioctadecyl dimethylammonium bromide (DODAB) bilayer fragments (DODAB BF); (2) polystyrene sulfate (PSS) nanoparticles (NPs) covered with one cationic dioctadecyl dimethylammonium bromide bilayer (DODAB) named (PSS/DODAB); (3) cationic NPs of biocompatible polymer poly(methyl methacrylate) (PMMA) prepared by emulsion polymerization of the methyl methacrylate (MMA) monomer in the presence of DODAB BF (PMMA/DODAB NPs); (4) antigen NPs (NPs) where the cationic polymer poly(diallyl dimethyl ammonium chloride) (PDDA) directly combined at nontoxic and low dose with the antigen (Ag); when the oppositely charged model antigen is ovalbumin (OVA), NPs are named PDDA/OVA. These nanostructures provide adequate microenvironments for carrying and delivering antigens to the antigen-presenting cells of the immune system.

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.

Rational design of adjuvants for subunit vaccines: The format of cationic adjuvants affects the induction of antigen-specific antibody responses

A range of cationic delivery systems have been investigated as vaccine adjuvants, though few direct comparisons exist. To investigate the impact of the delivery platform, we prepared four cationic systems (emulsions, liposomes, polymeric nanoparticles and solid lipid nanoparticles) all containing equal concentrations of the cationic lipid dimethyldioctadecylammonium bromide in combination with the Neisseria adhesin A variant 3 subunit antigen. The formulations were physicochemically characterized and their ability to associate with cells and promote antigen processing (based on degradation of DQ-OVA, a substrate for proteases which upon hydrolysis is fluorescent) was compared in vitro and their vaccine efficacy (antigen-specific antibody responses and IFN-γ production) and biodistribution (antigen and adjuvant) were evaluated in vivo. Due to their cationic nature, all delivery systems gave high antigen loading (> 85%) with liposomes, lipid nanoparticles and emulsions being <200 nm, whilst polymeric nanoparticles were larger (~350 nm). In vitro, the particulate systems tended to promote cell uptake and antigen processing, whilst emulsions were less effective. Similarly, whilst the particulate delivery systems induced a depot (of both delivery system and antigen) at the injection site, the cationic emulsions did not. However, out of the systems tested the cationic emulsions induced the highest antibody responses. These results demonstrate that while cationic lipids can have strong adjuvant activity, their formulation platform influences their immunogenicity.

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.

Liposomal vaccine formulations as prophylactic agents: design considerations for modern vaccines

Vaccinology is one of the most important cornerstones in modern medicine, providing better quality of life. The human immune system is composed of innate and adaptive immune processes that interplay when infection occurs. Innate immunity relies on pathogen-associated molecular patterns which are recognized by pathogen recognition receptors localized in antigen presenting cells. After antigen processing and presentation, CD4+ T cell polarization occurs, further leading to B cell and CD8+ activation and humoral and cell-mediated adaptive immune responses. Liposomes are being employed as vaccine technologies and their design is of importance to ensure proper immune responses. Physicochemical parameters like liposome size, charge, lamellarity and bilayer fluidity must be completely understood to ensure optimal vaccine stability and efficacy. Liposomal vaccines can be developed to target specific immune cell types for the induction of certain immune responses. In this review, we will present promising liposomal vaccine approaches for the treatment of important viral, bacterial, fungal and parasitic infections (including tuberculosis, TB). Cationic liposomes are the most studied liposome types due to their enhanced interaction with the negatively charged immune cells. Thus, a special section on the cationic lipid dimethyldioctadecylammonium and TB is also presented.

Structural insights on biologically relevant cationic membranes by ESR spectroscopy

Cationic bilayers have been used as models to study membrane fusion, templates for polymerization and deposition of materials, carriers of nucleic acids and hydrophobic drugs, microbicidal agents and vaccine adjuvants. The versatility of these membranes depends on their structure. Electron spin resonance (ESR) spectroscopy is a powerful technique that employs hydrophobic spin labels to probe membrane structure and packing. The focus of this review is the extensive structural characterization of cationic membranes prepared with dioctadecyldimethylammonium bromide or diC14-amidine to illustrate how ESR spectroscopy can provide important structural information on bilayer thermotropic behavior, gel and fluid phases, phase coexistence, presence of bilayer interdigitation, membrane fusion and interactions with other biologically relevant molecules.

The effect of an oligonucleotide on the structure of cationic DODAB vesicles

The effect of a small single-stranded oligonucleotide (ODN) on the structure of cationic DODAB vesicles was investigated by means of differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS) and electron spin resonance (ESR) spectroscopy. ODN adsorption induced coalescence of vesicles and formation of multilamellar structures with close contact between lamellae. It also increased the phase transition temperature by 10 °C but decreased transition cooperativity. The ODN rigidified and stabilized the gel phase. In the fluid phase, a simultaneous decrease of ordering close to the bilayer surface and increase in bilayer core rigidity was observed in the presence of the ODN. These effects may be due not only to electrostatic shielding of DODAB head groups but also to superficial dehydration of the bilayers. The data suggest that oligonucleotides may induce the formation of a multilamellar poorly hydrated coagel-like phase below phase transition. These effects should be taken into account when planning ODN delivery employing cationic bilayer carriers.

Stable assemblies of cationic bilayer fragments and CpG oligonucleotide with enhanced immunoadjuvant activity in vivo

The cationic lipid dioctadecyldimethylammonium bromide (DODAB) and the CpG oligonucleotide (CpG) have been separately used as potent immunoadjuvants driving Th1 responses. Here DODAB bilayer fragments (BF) and CpG (5'-TTGACGTTCG-3') assemblies have their physical properties and immunoadjuvant activity determined using ovalbumin (OVA) as a model antigen. At 0.1 mg/mL OVA, the dependence of DODAB BF/OVA size and zeta-potential on time and [DODAB] establishes 0.1 mM DODAB as suitable for obtaining stable and cationic DODAB BF/OVA assemblies. At 0.1 mM DODAB, 0.1 mg/mL OVA and 0.006 mM CpG, the zeta-potential is zero. At [CpG]>0.006 mM, good colloidal stability for the anionic assemblies is due to charge overcompensation. At 0.020 mM CpG, these DODAB BF/OVA/CpG assemblies are highly effective in vivo generating responses similar to those elicited by the stable and cationic DODAB BF/OVA. The anti-OVA DTH reaction and the secretion of IFN-gamma and IL-12 are 6, 42 and 9 times larger for the DODAB BF/OVA/CpG-immunized mice than the same responses by OVA-immunized mice, respectively. This work shows for the first time that charge of small assemblies is not important to determine the immune response.

Cationic lipid enhances assembly of bacterial cell division protein FtsZ: a possible role of bacterial membrane in FtsZ assembly dynamics

The assembly of FtsZ plays an important role in bacterial cell division. Lipids in the bacterial cell membrane have been suggested to play a role in directing the site of FtsZ assembly. Using lipid monolayer and bilayer (liposome) systems, we directly examined the effects of cationic lipids on FtsZ assembly. We found that cationic lipids enhanced the assembly of FtsZ in association with an increase in the GTPase activity of FtsZ. The system consisting of lipid monolayer and bilayer (liposome) may mimic the bacterial membrane and therefore, the data might indicate the influence of bacterial membrane on the assembly of FtsZ protofilaments.

Silica-based cationic bilayers as immunoadjuvants

Background

Silica particles cationized by dioctadecyldimethylammonium bromide (DODAB) bilayer were previously described. This work shows the efficiency of these particulates for antigen adsorption and presentation to the immune system and proves the concept that silica-based cationic bilayers exhibit better performance than alum regarding colloid stability and cellular immune responses for vaccine design.

Results

Firstly, the silica/DODAB assembly was characterized at 1 mM NaCl, pH 6.3 or 5 mM Tris.HCl, pH 7.4 and 0.1 mg/ml silica over a range of DODAB concentrations (0.001–1 mM) by means of dynamic light scattering for particle sizing and zeta-potential analysis. 0.05 mM DODAB is enough to produce cationic bilayer-covered particles with good colloid stability. Secondly, conditions for maximal adsorption of bovine serum albumin (BSA) or a recombinant, heat-shock protein from Mycobacterium leprae (18 kDa-hsp) onto DODAB-covered or onto bare silica were determined. At maximal antigen adsorption, cellular immune responses in vivo from delayed-type hypersensitivity reactions determined by foot-pad swelling tests (DTH) and cytokines analysis evidenced the superior performance of the silica/DODAB adjuvant as compared to alum or antigens alone whereas humoral response from IgG in serum was equal to the one elicited by alum as adjuvant.

Conclusion

Cationized silica is a biocompatible, inexpensive, easily prepared and possibly general immunoadjuvant for antigen presentation which displays higher colloid stability than alum, better performance regarding cellular immune responses and employs very low, micromolar doses of cationic and toxic synthetic lipid.

The effects of salt on the physicochemical properties and immunogenicity of protein based vaccine formulated in cationic liposome

Recently, we have developed a simple and potent therapeutic cancer vaccine consisting of a cationic lipid and a peptide antigen. In this report, we expanded the utility of this formulation to protein based vaccines. First, we formulated the human papillomavirus (HPV) 16 E7 protein (E7) in different doses of DOTAP liposome. The results showed that these formulations failed to regress an established tumor. However, when sodium chloride (30 mM) was added to the DOTAP (100 nmol)/E7 (20 microg) formulation, anti-tumor activity was generated in the immunized mice. Correlatively, 30 mM NaCl in the DOTAP/E7 protein formulation increased the particle size from approximately 350 to 550 nm, decreased the protein loading capacity (from 95 to 90%), and finally increased the zeta potential (from 29 to 38 mV). Next, a model protein antigen ovalbumin (OVA) was formulated in different doses of DOTAP liposomes. Similarly, the results showed that 20 microg OVA formulated in 200 nmol DOTAP with 30 mM NaCl had the best OVA-specific antibody response, including both IgG(1) and IgG(2a), suggesting both Th1 and Th2 immune responses were generated by this formulation. In conclusion, we have expanded the application of cationic DOTAP liposome formulation to protein based vaccines and also identified that small amounts of salt could change the physicochemical properties of the vaccine formulation and enhance the activity of the DOTAP/protein based vaccine. The enhancement of immune responses by salt is possibly due to its interference of the electrostatic interaction between the cationic lipid and the protein antigen to facilitate the antigen release from the carrier and at the same time activate the antigen presenting cells.

The adjuvant mechanism of cationic dimethyldioctadecylammonium liposomes

Cationic liposomes are being used increasingly as efficient adjuvants for subunit vaccines but their precise mechanism of action is still unknown. Here, we investigated the adjuvant mechanism of cationic liposomes based on the synthetic amphiphile dimethyldioctadecylammonium (DDA). The liposomes did not have an effect on the maturation of murine bone-marrow-derived dendritic cells (BM-DCs) related to the surface expression of major histocompatibility complex (MHC) class II, CD40, CD80 and CD86. We found that ovalbumin (OVA) readily associated with the liposomes (> 90%) when mixed in equal concentrations. This efficient adsorption onto the liposomes led to an enhanced uptake of OVA by BM-DCs as assessed by flow cytometry and confocal fluorescence laser-scanning microscopy. This was an active process, which was arrested at 4 degrees and by an inhibitor of actin-dependent endocytosis, cytochalasin D. In vivo studies confirmed the observed effect because adsorption of OVA onto DDA liposomes enhanced the uptake of the antigen by peritoneal exudate cells after intraperitoneal injection. The liposomes targeted antigen preferentially to antigen-presenting cells because we only observed a minimal uptake by T cells in mixed splenocyte cultures. The adsorption of antigen onto the liposomes increased the efficiency of antigen presentation more than 100 times in a responder assay with MHC class II-restricted OVA-specific T-cell receptor transgenic DO11.10 T cells. Our data therefore suggest that the primary adjuvant mechanism of cationic DDA liposomes is to target the cell membrane of antigen-presenting cells, which subsequently leads to enhanced uptake and presentation of antigen.

Synergism between active listeriolysin O and dimethyldioctadecylammonium bromide to activate CD8+ T cells

Purified recombinant listeriolysin O (LLO) was assessed for its ability to induce T cell responses in mice. Intraperitoneal immunisation with LLO, as a fusion with glutathione-S-transferase (GST), induced the production of LLO-specific CD8(+) T cells, but not LLO-specific CD4(+) T cells. The generation of this response could be blocked by pre-treatment with cholesterol, indicating a requirement for LLO pore formation. An increase in the LLO-specific response of both CD8(+) and CD4(+) T cells could be detected following the addition of dimethyldioctadecylammonium bromide (DDA), although the generation of this response was not dependent upon LLO pore formation, suggesting that DDA might change the presentation pathway of LLO leading to activation of the CD8(+) T cells. However, this response was dependent upon the presence of structurally intact LLO, suggesting a requirement for the innate recognition of LLO in the activation of the CD4(+) and CD8(+) T cells. Therefore, DDA and LLO can act synergistically to induce the production of a CD8(+) T cell response.

Low nephrotoxicity of an effective amphotericin B formulation with cationic bilayer fragments

OBJECTIVES

Evaluation of nephrotoxicity of a novel amphotericin B (AMB) formulation with dioctadecyldimethylammonium bromide (DODAB) bilayer fragments (DOD/AMB).

METHODS

Dose-dependent cytotoxicity of DOD/AMB was evaluated in vitro against cultured kidney epithelial cells in culture. For in vivo experiments, Swiss Webster female mice were injected intraperitoneally for 10 consecutive days with 0.4 mg/kg/day AMB in the form of traditional bile salt desoxycholate (DOC)/AMB or DOD/AMB. Body and spleen weight, and biochemical and histopathological data were obtained at days 11 and 180 after injection.

RESULTS

Nephrotoxicity of the novel formulation was lower than that of Fungizone (DOC/AMB), which is the traditional AMB formulation using DOC. Dose-dependent cytotoxicity of DOD/AMB was lower than that exhibited by DOC/AMB. At day 11, DODAB and DOD/AMB caused loss of body weight and increase in spleen weight, which were not observed for DOC/AMB, although the changes were reversible and weights returned to control values at day 180. Ten days after injection, biochemical parameters for hepatic and renal function remained unaltered. At day 180, renal cortex histopathology revealed leucocytic infiltration and moderate hydropic degeneration of the renal tubules in the DODAB and DOD/AMB groups, in contrast to more severe lesions observed for the DOC/AMB group such as tubular cystic degeneration and glomerular injury, which were absent for the former groups.

CONCLUSIONS

The DOD/AMB formulation exhibited differential cytotoxicity and low nephrotoxicity, but there were also important aspects of general toxicity that will require evaluation with full-scale toxicity protocols.

Achievement of a synergistic adjuvant effect on arthritis induction by activation of innate immunity and forcing the immune response toward the Th1 phenotype

OBJECTIVE

To apply and analyze the mechanisms of action of dimethyldioctadecylammonium bromide (DDA), a powerful adjuvant that does not have the side effects of the conventionally used Freund's adjuvants, in proteoglycan-induced arthritis (PGIA) and collagen-induced arthritis (CIA).

METHODS

PGIA and CIA were generated using standard immunization protocols with cartilage proteoglycan aggrecan (PG) or human type II collagen (CII) emulsified with Freund's complete adjuvant (CFA), and compared with PGIA and CIA generated using immunization protocols in which the same antigens were used in combination with the adjuvant DDA. Immune responses to immunizing and self PGs and CII, and the incidence, severity, and onset of arthritis were monitored throughout the experiments. In addition, a new, inexpensive, and powerful method of inducing arthritis using crude cartilage extracts is described.

RESULTS

A significantly reduced onset period and a more severe arthritis were achieved in BALB/c mice immunized with cartilage PGs in DDA. PGs from bovine, ovine, and porcine cartilage, which otherwise have no effect or have only a subarthritogenic effect, and crude extracts of human osteoarthritic cartilage induced a 100% incidence with a very high arthritis score in BALB/c mice. The overall immune responses to either CII or PG were similar in antigen/CFA-immunized and antigen/DDA-immunized animals, but the Th1/Th2 balance shifted significantly toward a Th1 bias in DDA-injected animals with either PGIA or CIA.

CONCLUSION

DDA, which was first used in autoimmune models, is a potent nonirritant adjuvant, which eliminates all undesired side effects of the Freund's adjuvants. DDA exerts a strong stimulatory effect via the activation of nonspecific (innate) immunity and forces the immune regulation toward Th1 dominance. These lines of evidence also suggest the possibility that seemingly innocuous compounds may exert an adjuvant effect in humans and may create the pathophysiologic basis of autoimmunity in susceptible individuals via the activation/stimulation of innate immunity.

Effects of synthetic lipids on solubilization and colloid stability of hydrophobic drugs

Aqueous miconazole (MCZ) aggregates were solubilized and/or colloidally stabilized by bilayer-forming synthetic amphiphiles such as dioctadecyldimethylammonium bromide (DODAB) or sodium dihexadecylphosphate (DHP) dispersions. Particle sizing, light absorption and scattering from drug particles, zeta-potential determination, and drug aggregation kinetics from turbidity changes in the presence or absence of lipid dispersions were obtained over a range of drug and lipid concentrations. The very low solubility of MCZ in water made possible the determination of size distributions for drug particles in water and comparison to those in the presence of DODAB or DHP nanosized bilayer fragments or entire and closed bilayer vesicles. Large drug aggregates disappeared upon incubation with nanosized bilayer fragments produced by ultrasonic dispersion with tip. Light-absorption spectra for MCZ in a poor solvent (water), in a good organic solvent (methanol), and in different lipid dispersions showed that solubilization depended on the presence of bilayer fragments. MCZ was poorly soluble in dispersions formed of closed bilayers (vesicles) of DODAB or DHP in the gel state and in phosphatidylcholine (PC) vesicles in the liquid-crystalline state. Increased hydrophobicity at the borders of bilayer fragments explained MCZ solubilization. At [MCZ]>0.4 mM, kinetics of drug aggregation, zeta-potential measurements, and size minimization were obtained upon addition of minute amounts of oppositely charged bilayer fragments ([DHP]=0.05 mM), making possible determination of a remarkable stabilizing effect of drug particles by coverage with anionic bilayer fragments. High drug colloid stability in the presence of charged bilayer fragments was achieved by two different means: (1). at large drug concentrations and small concentrations of bilayer fragments, coverage of large drug particles with bilayer fragments; (2). at large amounts of bilayer fragments, drug solubilization in its monomeric form at the borders of bilayer fragments. Inexpensive, synthetic bilayer fragments offered a large area of hydrophobic nanosurfaces dispersed and electrostatically stabilized in water, opening new prospects for drug solubilization and colloid stabilization of insoluble drug particles.

Heat shock protein micro-encapsulation as a double tool for the improvement of new generation vaccines

The modern vaccinology encompasses the recombinant DNA technology, protein and carbohydrate chemistry to obtain safe molecularly defined vaccines. Nevertheless most of the vaccines are poorly immunogenic because a large number of antigens are membrane proteins and consequently they are not present in their active conformation in the vaccine. Others are not as potent because they contain only B epitopes and therefore, cannot stimulate cellular memory. We have been studying the characteristics of the recombinant heat shock protein 18kDa-hsp from Mycobacterium leprae as an alternative carrier protein with a T epitope source to enhance the activity of these second generation vaccines. Here we proved that the 18kDa-hsp acted as carrier, without masking the activity of the carried antigen, with similar immune stimulatory effect when compared with ODN1668. Supramolecular aggregates of 18kDa-hsp and Mice serum albumin (MSA) were obtained using glutaraldehyde as cross linker. The Neisseria meningitides serogroup C polysaccharide (PSC, a B epitope) and the carrier protein 18kDa-hsp were co-encapsulated within Soybean phosphatidylcholine liposomes (SPC: Cho : alpha-Toc, 22 : 5 : 0.18 molar ratio, respectively). These liposomes were prepared in MPB buffer (20 mM phosphate, 295 mM mannitol pH 7.2) in the presence or absence of the ODN1668, TCCATGACGTTCCTGATGCT. When mice were injected with 18kDa-hsp-MSA no antibody against the MSA was observed. This means that the 18kDa-hsp acted as carrier, without masking the carried protein immune activity. Stable liposomes of 150 nm were obtained using mannitol as a cryoprotector. Genetically selected mice when injected with liposomes containing PSC and 18kDa-hsp displayed an antibody titer of 12. In contrast, in those mice injected with free PSC there was no response. The 18kDa-hsp adjuvant effect on the PSC liposomal formulation was comparable to that observed when ODN1668 was co-encapsulated with PSC. Confirming our expectations we observed that the formulation containing 18kDa-hsp conferred a memory response to the carried antigen--the Neisseria meningitidis serogroup C polysaccharide.

Interactions between cationic liposomes and drugs or biomolecules

Multiple uses for synthetic cationic liposomes composed of dioctadecyldimethylammonium bromide (DODAB) bilayer vesicles are presented. Drugs or biomolecules can be solubilized or incorporated in the cationic bilayers. The cationic liposomes themselves can act as antimicrobial agents causing death of bacteria and fungi at concentrations that barely affect mammalian cells in culture. Silica particles or polystyrene microspheres can be functionalized by coverage with DODAB bilayers or phospholipid monolayers. Negatively charged antigenic proteins can be carried by the cationic liposomes which generate a remarkable immunoadjuvant action. Nucleotides or DNA can be physically adsorbed to the cationic liposomes to be transferred to mammalian cells for gene therapy. An overview of the interactions between DODAB vesicles and some biomolecules or drugs clearly points out their versatility for useful applications in a near future.