Studies on the potential of microparticles entrapping pDNA-poly(Aminoacids) complexes as vaccine delivery systems

Poly(D,L-lactide-co-glycolide) (PLGA) microparticles containing plasmid DNA (pDNA) have potential uses as vaccine delivery systems. Nevertheless, the established double emulsion and solvent evaporation method used to produce them is characterised by a low encapsulation efficiency (about 20%) and nic ks the supercoiled DNA. The aim of this work was to develop an encapsulation process to optimise th e overall encapsulation efficiency and the supercoiled DNA content, to obta in a carrier suitable for mucosal delivery of DNA vaccines. Our strategy wa s to reduce the global negative charge of DNA which was unfavourable to its incorporation into the polymer by condensing it with cationic poly(aminoac ids) which were previously reported to improve cell transfection. In this s tudy, after characterisation of the compaction of DNA plasmid encoding for a Green Fluorescent Protein, we demonstrated that resulting complexes were successfully encapsulated into PLGA microparticles presenting a mean size a round 4.5 mum. The preliminary step of complexation enhances the yield of t he process by a factor 4.1 and protects the supercoiled form. In a bacteria transformation assay, we demonstrated that extracted pDNA (naked or comple xed) remained in a transcriptionally active form after encapsulation. Bovin e macrophages in culture phagocytosed microparticles loaded with uncomplexe d/complexed with poly(L-lysine) pDNA. The production of the Green Fluoresce nt Protein demonstrated that these carriers could deliver intact and functi onal plasmid DNA probably by escaping from lysosomal degradation.