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**18** 

*1Thailand 2Australia* 

**Chitosan and Its Modifications: Are They** 

In gene therapy, the most important step is how to effectively deliver the therapeutic gene to the target cells or organ. At present, there are two methods, which are those using a viral and a non-viral vector system. The most common viral vectors that have been used include retroviruses, herpes simplex viruses, lentiviruses, adenoviruses and adenoassociated viruses (Oligino et al., 2000). The advantages of most viral vectors are high transfection efficiency and fast transcription of the foreign material inserted in the viral genome. However, a number of disadvantages have also been described, such as poor target-specificity, low capacity to incorporate foreign deoxyribonucleic acid (DNA) sequence to their genome (Mansouri et al., 2004), toxic and inflammatory effects, wild– type mutations, potential oncogenic effects (Lee et al., 1998), and, in particular, unwanted immune responses. In clinical trials of gene replacement therapy using viral vectors, significant adverse effects have been reported, including a fatal inflammatory response associated with adenoviral vector (Raper et al., 2003), and the development of acute leukaemia in recipients of ex-vivo, adenoviral vector-transduced hematopoietic cells (Woods et al., 2006). Intravenous adenoviral vector has also resulted in high liver toxicity due to uptake by hepatocytes or Kupffer cells of the liver reticular endothelial system,

Due to the limitations and disadvantages of using viral vectors, there has been an ongoing search for an efficient safe vector for gene therapy, which has lead to the development of non-viral gene therapy. They have some advantages over viral methods, including simple large scale production and relatively low host immunogenicity. Previously, low levels of transfection and expression of the gene limited the usefulness of non-viral methods. However, recent advances in vector technology have been useful in yielding molecules and techniques with transfection efficiencies approaching or surpassing those of viral vectors.

Table 1 provides examples of the main non-viral methods of gene delivery.

**1. Introduction** 

immediately following systemic administration.

**2. Non-viral vectors for gene delivery** 

**Possible Vehicles for Gene Therapy?** 

Ureporn Kedjarune-Leggat1 and Peter A. Leggat2 *1Department of Oral Biology and Occlusion, Faculty of Dentistry* 

*2Anton Breinl Centre for Public Health and Tropical Medicine* 

*Prince of Songkla University, Hat Yai, Songkhla* 

*James Cook University, Townsville, Queensland* 

