Control of the transfection efficiency of human dermal fibroblasts by adjusting the characteristics of jetPEI®/plasmid complexes/polyplexes through the cation/anion ratio

Abstract Primary cells are in general more difficult to transfect than most animal cells. Here we report on the efficient transfection of human dermal fibroblasts with jetPEI ® /DNA complexes (polyplexes). The polycation/DNA ratio was varied with respect to both transfection efficiency and cell viability and the different DNA-polyplexes were characterized by different physicochemical methods, namely ζ-potential measurement, light scattering and scanning electron microscopy. Interestingly these data point to the fact that our DNA-polyplexes possess a core-shell structure in the wet state. We find that the range of jetPEI ® /DNA ratios, expressed as N/P (nitrogen-to-phosphate) ratio, at which high transfection and high cell viability is observed is quite narrow. Transfection efficiency is high for N/P-ratios below 15 and cell viability is high at high N/P-ratios, the optimum of both occurs in the range of 10 to 15. The transfection maximum is observed at over 80% of transfected cells in the range of N/P-ratio of 7.5 to 10, whereas the generally recommended N/P-ratio for jetPEI ® /DNA transfection experiments is 5. At a N/P-ratio of 15, transfection is still as high as at a N/P-ratio of 5, but viability is almost twice as high. We found that the cytotoxicity of the polyplexes is related to their size, and is very small for particles of small size. Our data suggest that the morphologies of the polyplex-particles discussed here are better described by a core-shell structure rather than a conventional homogeneous “scrambled egg” structure.