Such trials are in progress for the treatment of brain tumours. There are, however, major problems yet to be overcome before gene therapy can become a common way of treating diseases. Scientists have to learn how to isolate and deliver curative genes. These vectors have to be able to home in on cancer cells and successfully integrate the desired gene into the DNA of these cells. The vectors currently being tested include adenoviruses and retroviruses.
Scientists select a virus that normally infects cells of the desired type.
By making use of the properties of the marker gene, such as sensitivity to a particular antibiotic, it is possible to select out those cells that have successfully integrated the new genes. Genetic research has developed at an astonishing pace over the last 40 years or so. By the 1960s scientists had cracked the genetic code. During the 1980s, gene transfer systems using retroviruses and lymphocytes were first developed. At this stage, gene therapies are considered experimental.