Traffic of poly(lactic acid) nanoparticulate vaccine vehicle from intestinal mucus to sub-epithelial immune competent cells

Mucosal immunization is designed to induce strong immune responses at portal of pathogen entry. Unfortunately, mechanisms underlying the fate of the vaccine vector co-administered with antigens are still partially uncovered and limit further development of mucosal vaccines. Hence, poly(lactic acid) (PLA) nanoparticles being a versatile vaccine vehicle, we have analyzed the fate of these PLA nanoparticles during their uptake at intestinal mucosal sites, both in vivo and ex vivo, to decipher the mechanisms involved during this process. We first designed specific fluorescent PLA nanoparticles exhibiting strong colloidal stability after encapsulation of either 6-coumarin or CellTrace BODIPY® before monitoring their transport through mucosa in the mouse ligated ileal loop model. The journey of the particles appears to follow a three-step process. Most particles are first entrapped in the mucus. Then, crossing of the epithelial barrier takes place exclusively through M-cells, leading to an accumulation in Peyer’s patches (PP). Lastly, we noticed specific interaction of these PLA nanoparticles with underlying B cells and dendritic cells (DCs) of PP. Furthermore, we could document that DCs engulfing some nanoparticles could exhibit a TLR8+ specific expression. Specific targeting of these two cell types strongly supports the use of PLA nanoparticles as a vaccine delivery system for oral use. Indeed, following oral gavage of mice with PLA nanoparticles, we were able to observe the same biodistribution patterns, indicating that these nanoparticles specifically reach immune target required for oral immunization.