The purpose of the present study was to investigate the usefulness of the ternary complex with protamine and γ-polyglutamic acid (γ-PGA), which are biodegradable materials for foods and medical products, as a safe gene delivery vector. We formed cationic binary complexes (plasmid DNA (pDNA)/protamine complexes) with high transfection efficiency. The binary complex showed slight toxicity probably related to its total cationic charge. Then, we formed ternary complexes (pDNA/protamine/γ-PGA

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... es) by addition of anionic polymer, γ-PGA, and they showed no cytotoxicity. The transfection efficiency of the pDNA/protamine/γ-PGA complexes was as high as that of the pDNA/protamine complexes, although their zeta potentials were different. Inhibition study of the gene expressions in B16-F10 cells suggested that pDNA/protamine complexes were taken up by caveolae-mediated endocytosis and macropinocytosis. On the other hand, pDNA/protamine/ γ-PGA complexes were taken up by clathrin-mediated endocytosis and macropinocytosis. Thus, we succeeded in developing the ternary complex as a safe gene delivery vector with biocompatible materials.