الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Lentiviral vectors have many advantageous characteristics making them a good choice in the field of gene therapy, such as comparatively large coding capacity, lower immunogenicity upon in vivo administration compared to other gene delivery vehicles like adenoviral or adeno-associated viral (AAV) vectors, transduction of non-dividing cells and stable gene expression because of their integration into the host chromosome. However, integration can cause insertional mutagenesis by disturbing the expression of any gene in which integration takes place. For instance, Leukaemia was observed in a clinical trial because of insertional mutagenesis (Hacein-Bey-Abina et al., 2003a). Innovative ways by which insertional mutagenesis of lentiviral vectors can be reduced while retaining efficient transduction are needed to be applied in clinical applications.
Integrase (IN) is the viral enzyme responsible for the integration of retroviruses. This enzyme is encoded by the pol gene and translated together with other proteins (Reverse transcriptase and protease) as one gag-pol polyprotein, which is then cut by the viral enzyme, protease to yield individual enzymes (Hindmarsh and Leis, 1999). Viral integration has many steps starting with vector 3’ end processing (cutting a dinucleotide from both 3’ ends), and then strand transfer in which IN transfers viral DNA to the 5’ phosphorylated ends of a double-stranded cut in the host DNA where it is integrated, and lastly, gap repair most likely through cellular proteins (Craigie, 2001). Viral integration is not an efficient process (Wu, 2008) and with both retroviruses and retroviral vectors a significant amount of double-stranded vector DNA is transformed into episomal bodies by nuclear proteins (Gianni et al., 1975, Hsu et al., 1978, Shank et al., 1978, Li et al., 2001).
Using integration-deficient lentiviral vectors (IDLVs) containing IN mutations can greatly reduce the level of vector integration. IN has several functions besides integration such as taking part in viral morphogenesis, reverse transcription, and nuclear localization. Class II mutations affect viral functions other than integration while class I mutations affect integration only (Engelman et al., 1995, Leavitt et al., 1996, Engelman, 1999)