The preservation of phenotype and functionality of dendritic cells upon phagocytosis of polyelectrolyte-coated PLGA microparticles

Biodegradable microparticles (MP) represent a promising and efficient delivery system for parenteral vaccination. Recently, MP have also been explored as tool for the ex vivo antigen loading of professional antigen-presenting cells such as dendritic cells (DC) to be used as cellular vaccines. The purpose of this study was to investigate various polycationic coatings on poly(lactide-co-glycolide) (PLGA) MP, with regard to their effect on phenotypic and functional maturation of monocyte-derived DC (MoDC) that had previously been loaded with the MP in vitro. The preparation and concomitant coating of the PLGA was performed by means of a solvent extraction/evaporation method using a recently developed microextrusion-based technique. The polyelectrolytes tested for MP coating encompassed aminodextran, chitosan, poly(ethylene imine) (PEI), poly(l-lysine) and protamine. Uncoated and differently coated PLGA MP were fed to immature MoDC, which ingested efficiently the different MP types irrespective of their surface coating. The MP-loaded immature MoDC were then matured with the help of a cytokine/PGE-2 maturation cocktail. Here, the presence of the ingested MP did not affect the MoDC maturation in terms of expression of the surface markers CD80, CD83, CD86, HLA-DR and MMR, irrespective of the MP surface coating. Importantly, none of the PLGA MP types alone induced significant maturation of MoDC in the absence of the maturation cocktail. MP-loaded and subsequently matured MoDC expressed high levels of the chemokine receptor CCR7, whose functional activity was evidenced by the migration of MoDC towards CCL21, irrespective of the presence of ingested MP. Further, MP-loaded and subsequently matured MoDC also secreted comparable amounts of IL-10 and IL-12p70, irrespective of the presence of ingested MP except for PEI-coated PLGA MP, which enhanced significantly the secretion of IL-12p70 in mature MoDC. In conclusion, phenotypic and functional maturation of MoDC by means of a maturation cocktail remained unchanged irrespective of the presence of previously ingested differently coated PLGA MP. This offers interesting perspectives for using these particulate systems together with entrapped antigens for ex vivo loading of MoDC in view of cellular immunotherapy.