Recent development of nonviral gene delivery systems with virus-like structures and mechanisms.

The concept of gene therapy includes not only the addition of normal genes to genetically deficient cells, but also the use of transgenes encoding several peptides that function to enhance the capacity of normal cells or to regulate cell differentiation. The application of gene therapy has been widely considered for various diseases, as well as for the field of tissue engineering. To overcome the problems with viral vectors, a broad range of nonviral systems for gene delivery have been developed, including systems composed of cationic lipids (lipoplexes) and cationic polymers (polyplexes). However, most of these systems are still much less efficient than viral vectors, especially for in vivo gene delivery. Paradoxically, to achieve a maximum transgene expression in the targeted cells, there is no question that natural viruses are the most effective nanocarriers. In this article, we highlight the approaches currently being taken to improve nonviral gene delivery systems so that they better replicate the typical structures and mechanisms of viruses, such as DNA (RNA) condensation in the core, surrounding structures with targeting molecules for specific receptors, as well as the toxic and immunogenic problems which should be avoided, with the ultimate goal of bringing these systems into a clinical setting.