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.

Background/Objective: Cationic polymers were shown to assemble with negatively charged proteins yielding nanoparticles (NPs). Poly-diallyl-dimethyl-ammonium chloride (PDDA) combined with ovalbumin (OVA) yielded a stable colloidal dispersion (OVA/PDDA-NPs) eliciting significant anti-OVA immune response. Dendritic cells (DCs), as sentinels of foreign antigens, exert a crucial role in the antigen-specific immune response. Here, we aimed to evaluate the involvement of DCs in the immune response induced by OVA/PDDA. Methods: In vivo experiments were used to assess the ability of OVA/PDDA-NPs to induce anti-OVA antibodies by ELISA, as well as plasma cells and memory B cells using flow cytometry. Additionally, DC migration to draining lymph nodes following OVA/PDDA-NP immunization was evaluated by flow cytometry. In vitro experiments using bone marrow-derived DCs (BM-DCs) were used to analyze the binding and uptake of OVA/PDDA-NPs, DC maturation status, and their antigen-presenting capacity. Results: Our data confirmed the potent effect of OVA/PDDA-NPs inducing anti-OVA IgG1 and IgG2a antibodies with increased CD19⁺CD138⁺ plasma cells and CD19⁺CD38⁺CD27⁺ memory cells in immunized mice. OVA/PDDA-NPs induced DC maturation and migration to draining lymph nodes. The in vitro results showed higher binding and the uptake of OVA/PDDA-NPs by BM-DCs. In addition, the NPs were able to induce the upregulation of costimulatory and MHC-II molecules on DCs, as well as TNF-α and IL-12 production. Higher OVA-specific T cell proliferation was promoted by BM-DCs incubated with OVA/PDDA-NPs. Conclusions: The data showed the central role of DCs in the induction of antigen-specific immune response by OVA-PDDA-NPs, thus proving that these NPs are a potent adjuvant for subunit vaccine design.

Cationic polymers were previously shown to assemble with negatively charged proteins yielding nanoparticles (NPs). Poly-diallyl-dimethyl-ammonium chloride (PDDA) is a cationic polymer able to combine with ovalbumin (OVA) yielding a stable colloidal dispersion of OVA/PDDA NPs eliciting significant anti-OVA immune response. Dendritic Cells (DC), as sentinels of foreign antigens, exert a crucial role in the induction of antigen-specific T cell activation and consequent adaptive immune response. Objective: The present study aimed at evaluating the involvement of DCs in the adaptive immune response induced by OVA/PDDA. Methods/Results: Confirming the potent induction of adaptive immune response against OVA/PDDA, the data showed increased CD19+CD138+ plasma cells and CD19+CD38+CD27+ memory cells in spleens of mice immunized with OVA/PDDA-NPs 28 days before. OVA/PDDA-NPs also induced the migration and maturation of DCs to draining lymph nodes on days 3 and 4 of mice immunization. The in vitro results with bone-marrow differentiated DCs (iBM-DCs) showed an increase of the binding and uptake of OVA/PDDA NPs by these cells compared with soluble OVA. In addition, OVA/PDDA NPs were able to induce DC maturation and upregulation of costimulatory and MHC-II molecules, TNF- and IL-12 production. iBM-DCs incubated with OVA/PDDA NPs promoted high OVA-specific T cell proliferative response. Conclusion: Altogether, the data demonstrated the central role of DCs in the induction of antigen-specific immune response by OVA-PDDA-NPs, thus proving these NPs as potent adjuvants for subunit vaccine design.