[Gene transfer systems and gene therapy]

One of the most important developments in medicine is gene therapy. But before it can be accepted to be used widely, certain technical problems should be overcome, especially the methods of gene delivery. In order to modify a specific cell type or tissue, the therapeutic gene must be efficiently delivered to the cell, in such a way that the gene can be expressed at the appropriate level and for a sufficient duration. There are currently availible two gene delivery vehicles. The first consists of viral vectors, which take advantage of a variety of naturally occurring viruses to shuttle the foreign cargo to be integrated permanently into the host's chromosome. The second is non-viral vectors, which rely on direct delivery of either naked DNA or mixture of genes with cationic lipids (liposome). There have been over 600 clinical trials of gene therapy protocols. The majority of clinical trials of gene therapy have been involved in the treatment of cancer and most of them have been at phase I clinical trials. Phase II stage of gene therapy had started of the end of 1996.