The first human trials of gene therapy began in 1990 using a strategy of ex vivo gene therapy. In this approach, the patient cells were harvested and cultivated in the laboratory and incubated with vectors to modify their genes. The cells were then harvested and transplanted back into the patient from whom they derived. The first therapeutic trials utilizing this approach attempted to treat two genetic disorders, including children with an inherited form of immune deficiency as well as children and adults with extremely high levels of serum cholesterol. The first model for in vivo gene therapy was based on an attenuated version of the adenovirus in the treatment of cystic fibrosis.
Adenoviruses have a natural tropism for lungs in that they are associated with respiratory diseases.
Many other types of diseases are currently being investigated as candidates for gene therapy including cardiovascular diseases such as AIDS, and cancer. Occasionally, genes will become mutated, be it from radiation or chemicals. The body has a number of mechanisms for repairing genes should they become altered. Sometimes, though, the repair machinery fails to correct genetic flaws and a mutation creeps into cells. If this occurs in the cells which create sperm and eggs, called germ-line cells, the mistake is passed along to the next generation.