Microparticle-mediated transfection of non-phagocytic cells in vitro

DNA-loaded microparticles represent an attractive delivery system to target professional antigen presenting cells (APC) for the delivery of DNA vaccines. Microparticles exhibiting a positively charged surface were prepared by the incorporation of two selected cationic polymers into a poly(D, L-lactide-co-glycolide) polymer (PLGA) core. The toxicity of the different formulations was checked in two cell lines and was found to be comparable to plain PLGA particles. Increased toxicity of some formulations was observed in primary macrophages (Mphi) with high phagocytosis activity. Plasmid DNA was efficiently adsorbed to the microparticle surfaces, and the different formulations were checked for their transfection efficiency in phagocytic and non-phagocytic cells. Interestingly, the most pronounced gene transfer efficiency was observed in a non-phagocytic 293 cell line when compared to a macrophage cell line and primary Mphi. Possible mechanisms include the dissociation of DNA-polymer complex and subsequent transfection of the cells. Microscopic observation of fluorescent-labeled DNA in primary Mphi revealed large amounts of DNA entering the cells, but no detectable DNA inside the nuclei. We conclude that phagocytic professional APC represent a group of cells, which is especially difficult to transfect when compared to other cell types. The administration of DNA in vivo is likely to predominantly result in the transfection of non-lymphoid cells unless there is a possibility to provide efficient targeting and trafficking of the DNA to the nucleus of professional APC. Although DNA-loaded PEI and DAEM microparticles resulted in significant transfection of cells, toxicity and transfection efficiency was not superior to that of DNA complexed with soluble PEI and DAEM.