**1.4 Non-viral vectors for gene therapy**

Non-viral vectors such as peptide, polymer mediated gene therapy can only produce transient expression of genes, and the transfection efficiency is much lower compared to viral vectors (Al-Dosari & Gao, 2009; Cartier & Reszka, 2002; X. Gao et al., 2007; Niidome & Huang, 2002).
