Current research methods of transfection, which deliver foreign DNA into cells, have taken advantage of the use of non-viral vectors due to recent advantages that researchers have been able to exploit. The cell transfection process encounters a number of problems due to the cell's defense mechanisms. Vectors must be able to not only enter the cell beyond the cell membrane, but they must also be able to make their way into the cell's nucleus to access the target genetic material. The problem with traditional transfection methods is that they are unable to enter the cell with high efficiency without triggering an immune response. This, combined with the inability to prolong gene expression in vivo even after transfection, results in a very expensive and ineffective method of introducing a foreign plasmid into the cell. Viral vectors had previously been used with some success in vitro, but because they lack a high degree of transfection efficiency and duration of gene expression, their use for transfection could not yield substantial practical applications. Another problem is that these laboratory-engineered viruses had low success rates in vivo due to the activation of an immune response. New techniques are being discovered by modifying nonviral vectors in new ways, producing increasingly effective ways to deliver DNA into cells with the hope of clinical application and advancing gene therapy. The research conducted by Figueroa et al. (2013) made progress in the nonviral gene delivery method using gold nanoparticles (AuNPs). In their work they developed an exceptionally efficient transfection method by experimentally improving some desirable traits of the polyamidoamine gold nanoparticle (AuPAMAM) c...... middle of paper...... of efficacy when mTat and PEI are combined to exploit the positive traits of each vector for transfection. Cytotoxicity results from transfected mice in vivo found that there was no significant difference in cell viability between mTat, PEI, or the mTat/PEI complex. These results demonstrated the remarkable ability to significantly increase both transfection efficiency and gene expression in vivo without conferring any increase in cytotoxicity. Cell penetrating peptides (CPPs), including mTat, have been shown to be effective in rapidly crossing cell membranes and are capable of entering the cell based on their small and amphipathic nature (Bolhassani, 2011). By controlling the cargo carried by the CPP and the target to which it delivers it, these vectors can have myriad in vivo uses, including selective destruction of tumor cells and other gene therapy techniques.