Polysaccharide-based vaccine delivery systems: Macromolecular assembly, interactions with antigen presenting cells, and in vivo immunomonitoring.

Using a strategy of macromolecular assembly, a colloidal vaccine delivery system was obtained from chitosan and dextran sulfate and loaded with an antigenic protein (p24, the capsid protein of HIV-1). The colloidal polyelectrolyte complexes (PECs) were obtained by charge neutralization of the polyanion and polycation at a charge ratio (n(+)/n(-)) of 2 (CHDS). The conditions of assembly were tuned to maintain the colloidal properties of the carrier in high salt environment. The relative molar masses of the two polyions and the degree of acetylation (DA) of chitosan were essential parameters to achieve this goal, and this could be related to the nanometric scale organization of the colloids observed by Small Angle X-rays Scattering experiments. The binding of p24 to the colloidal carrier was achieved and the release of the antigen was investigated. Antigen presenting cells [dendritic cells (DCs)], obtained from monocytes, could internalize the colloids. Immature DCs (iDCs) were not matured by the colloidal PECs either loaded or not loaded with p24, as proved by Fluorescent Activated Cell Sorting (FACS) analysis. Despite this lack of in vitro interaction, a specific immune response was observed in mice with a high production of antibodies, after subcutaneous injection. The analysis of the interleukin production shows that both the cellular and the humoral responses were stimulated. This work brings a physico-chemical insight on polysaccharide-based antigen delivery systems and opens up new perspectives for their use as vaccine carriers.