Gene therapy can be defined as the introduction of nucleic acid into cells to ameliorate a disease process. To date there have been more than 313 trials with more than 2000 patients enrolled. The majority of these trials are Phase I or Phase II and have target diseases of either cancer or acquired immunodeficiency syndrome using retroviral and retroviral vectors. The choice of molecular target and the means of delivery have varied and chosen on the basis of the specific indication. Until recently the risks associated with treatment had been under appreciated. The first fatality associated with gene therapy occurred in September 1999 in which an adenoviral vector was used in the treatment of a patient with orthnithine transcarbamylase deficiency. Subsequent to this report, other reports have surfaced suggesting that reporting of previous nonfatal reactions may have been minimized. Safety must be considered in relation to the disease process and to alternative treatments available. It may be easier to rationalize placing patients at risk who are facing a fatal disease process without effective alternative therapies. The ultimate goal of gene therapy will be the injection of a vector that has a specific target cell and that will be regulated by physiologic signals. Such a goal will require major improvements in the currently available delivery systems or the development of novel vectors.

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