title: Surface-assembled poly(I:C) on PEGylated PLGA microspheres as vaccine adjuvant: APC activation and bystander cell stimulation.
abstract: Biodegradable poly(lactic-co-glycolic acid) (PLGA) microspheres are potential vehicles to deliver antigens for vaccination. Because they lack the full capacity to activate professional antigen presenting cells (APCs), combination with an immunostimulatory adjuvant may be considered. A candidate is the synthetic TLR3 ligand polyriboinosinic acid-polyribocytidylic acid, poly(I:C), which drives cell-mediated immunity. However, poly(I:C) has also been linked to the pathogenesis of autoimmunity, as affected by widespread stimulation of non-hematopoietic bystander cells. To address this aspect, we propose to minimize the poly(I:C) dose as well as to control the stimulation of non-immune bystander cells by poly(I:C). To facilitate the maturation of APCs with minimal poly(I:C) doses, we surface-assembled poly(I:C) onto PLGA microspheres. The microspheres' surface was further modified by poly(ethylene glycol) (PEG) coronas with varying PEG-densities. PLGA microspheres loaded with tetanus toxoid (tt) as model antigen were manufactured by microextrusion-based solvent extraction. The negatively charged PLGA(tt) microspheres were coated with polycationic poly(l-lysine) (PLL) polymers, either PLL itself or PEG-grafted PLL (PLL-g-PEG) with varying grafting ratios (g=2.2 and g=10.1). Stable surface assembly of poly(I:C) was achieved by subsequent incubation of polymer-coated PLGA microspheres with aqueous poly(I:C) solutions. We evaluated the immunostimulatory potential of such PLGA(tt) microsphere formulations on monocyte-derived dendritic cells (MoDCs) as well as human foreskin fibroblasts (HFFs) as model for non-hematopoietic bystander cells. Formulations with surface-assembled poly(I:C) readily activated MoDCs with respect to the expression of maturation-related surface markers, proinflammatory cytokine secretion and directed migration. When surface-assembled, poly(I:C) enhanced its immunostimulatory activity by more than one order of magnitude as compared to free poly(I:C). On fibroblasts, surface-assembled poly(I:C) upregulated class I MHC but not class II MHC. Phagocytosis of PLGA(tt) microsphere formulations by MoDCs and HFFs remained mostly unaffected by PEG-grafted PLL coatings. In contrast, high concentrations of free poly(I:C) led to a marked drop of microsphere phagocytosis by HFFs. Overall, surface assembly on PEGylated PLGA microspheres holds promise to improve both efficacy and safety of poly(I:C) as vaccine adjuvant.
authors.affiliation: Institute of Pharmaceutical Sciences, ETH Zurich, Zurich 8093, Switzerland.
authors.forename: Annina M
authors.initials: AM
authors.lastname: Hafner
authors.affiliation: Division of Immunology and Allergy, CHUV, Lausanne 1005, Switzerland.
authors.forename: Blaise
authors.initials: B
authors.lastname: Corthésy
authors.affiliation: Laboratory for Surface Science and Technology, ETH Zurich, Zurich 8093, Switzerland.
authors.forename: Marcus
authors.initials: M
authors.lastname: Textor
authors.affiliation: Institute of Pharmaceutical Sciences, ETH Zurich, Zurich 8093, Switzerland. Electronic address: hmerkle@pharma.ethz.ch.
authors.forename: Hans P
authors.initials: HP
authors.lastname: Merkle
mesh_terms: D000276:Adjuvants, Immunologic / Q000737:chemistry* / Q000494:pharmacology; D000941:Antigens / Q000737:chemistry* / Q000276:immunology; D002478:Cells, Cultured; D003713:Dendritic Cells / Q000276:immunology; D005347:Fibroblasts / Q000276:immunology; D006801:Humans; D007111:Immunity, Cellular / Q000276:immunology; D019344:Lactic Acid / Q000737:chemistry*; D008863:Microspheres; D009000:Monocytes / Q000276:immunology; D010587:Phagocytosis / Q000276:immunology; D011070:Poly I-C / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry*; D011100:Polyglycolic Acid / Q000737:chemistry*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011107:Polylysine / Q000031:analogs & derivatives* / Q000737:chemistry; D013499:Surface Properties; D013745:Tetanus Toxoid / Q000737:chemistry / Q000276:immunology; D014612:Vaccines / Q000737:chemistry* / Q000276:immunology
chemical_list: D000276:Adjuvants, Immunologic; D000941:Antigens; D013745:Tetanus Toxoid; D014612:Vaccines; C443714:polylysine-graft-(poly(ethylene glycol)); D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011107:Polylysine; D011100:Polyglycolic Acid; D019344:Lactic Acid; D011092:Polyethylene Glycols; D011070:Poly I-C
keywords: Adjuvants; Dendritic cells; Fibroblasts; Immunostimulants; Microspheres; Poly(I:C); Vaccine formulation