Mucosal delivery of diphtheria toxoid using polymer-coated-bioadhesive liposomes as vaccine carriers

The aim of this study was to prepare stable liposomes coated or loaded with bioadhesive polymers and test their efficacy following oral, nasal (IN) or intramuscular (IM) delivery of diphtheria toxoid (DT) in raising systemic antibody responses. The stability of these liposomes in three different media mimicking gastrointestinal (GI) fluids of the stomach and small intestine was also examined. Fluorescence microscopy of the rat small intestine showed preferential adsorption/association of polymer-coated liposomes versus free FITC-BSA. Finally, the efficacy liposomes composed of dipalmitoylphosphatidylcholine, dicetyl phosphate and cholesterol (DPPC:DCP:CH, 7:3:2 molar ratio) for delivery of DT to mice was assessed. Immunisation through the IM route with these liposomes produced the highest DT specific serum IgG antibody titres; liposomes loaded with chitosan chloride were the only formulation to elicit a specific measurable IgG response when delivered orally with the present protocol. IN delivery of liposomes loaded with PVA resulted in a significantly better IgG antibody response (p < 0.05) when compared to uncoated liposomes.