"Gene therapy" is generally thought of as a very new concept, but the idea that genes could be manipulated to treat human disease goes back several decades. The basic concepts and methodologies for manipulating genes have been taken directly from studies of procaryotic organisms and the viruses that infect them. The idea that viral genomes could become a permanent part of cell genomes was first discovered with bacterial viruses around 1956, and later extended to include animal viruses. One of the earliest mammalian gene transfer experiments was performed by W. Szybalski in 1962. Szybalski developed cell lines that carried mutations in genes responsible for salvage of purine bases and showed that DNA from normal cells could be introduced into these mutant cells to restore the normal phenotype. However, there was little interest in their results because at that time procaryotes, DNA synthesis, and the genetic code were the centers of attention. In 1966, E.L.Tatum gave a talk in New York and covered several aspects of gene therapy including the long-range concept that viruses could be used effectively for man's benefit and that genes would be isolated or synthesized and introduced into defective cells of particular organs. He also speculated that since the basis of cancer is altered genes, treatment could be achieved "by modification and regulation of gene activities or by means of gene repair or replacement." By the late 1960s and early 1970s, gene therapy became the subject of an increasing number of articles and meetings.
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