Strategy of oral vaccination by polymeric nanoparticles : M cell targeting or bioadhesion

Abstract

Oral vaccines delivery is an attractive alternative to parenteral route for vaccination but is limited by destruction and low absorption of the antigen in the gastro-intestinal tract. Development of new formulations encapsulating antigens in polymeric biodegradable nanoparticles is a promising strategy to counter these drawbacks. The objective of this thesis was to compare two delivery strategies: M cell targeted or bioadhesive nanoparticles. The first strategy consisted in encapsulating antigens in nanoparticles targeting M cells by presenting specific M cell ligands at nanoparticle surface. M cells, localised in the follicle associated epithelium on the Peyer’s Patches, are part of the mucosal immune system and specialized in antigen uptake. The core of the nanoparticles was constituted of PLGA, and PLGA-PEG and PCL-PEG were included in the formulation to stabilize it by sterical repulsion and to graft on PEG residue a ligand targeting M cells. As β1 integrins are over-expressed at the apical pole of human M cells, we studied the potential of some ligands of the integrin family to increase nanoparticle transport across the epithelium. The second strategy was to encapsulate the antigen in bioadhesive polymers, like chitosan and trimethylchitosan, to improve the intestinal uptake of antigens by increasing adsorption of the nanoparticles on mucus and intestinal cells. Nanoparticles were formed by ionic gelation between cationic polymers and anionic tripolyphosphate. An in vitro model of the human follicle associated epithelium was developed and used to compare the transport of targeting and bioadhesive nanoparticles. The potential of the different antigen-loaded nanoparticles to induce immune responses was also tested through intra-duodenal immunization in vivo. Bioadhesive chitosan nanoparticles appeared to be more transported through the epithelium than PLGA nanoparticles, with or without targeting ligands, but were not M cells specific. PLGA nanoparticles exposing a RGD peptidomimetic molecule as ligand significantly increased the transport through M-like cells in comparison to normal enterocytes-like cells. Oral immunization induced higher immune response with PLGA nanoparticles targeting M cells β integrins with RGD peptidomimetic. However, presence of chitosan could influence immune response type and played a role of immunopotentiator by enhancing Th1 cytokines secretion. Depending on the type of immune response that needs to be elicited, oral vaccine by PLGA based nanoparticles targeting M cells could be more useful to induce an humoral response whereas chitosan might be more useful to stimulate a cellular immune response oriented Th1. Then a combination of different strategies could be an asset for oral vaccine delivery and it seems necessary to add some mucosal adjuvants and immunopotentiators like ligands targeting the antigen presenting cells to boost the immune responses.(FARM 3) -- UCL, 201