Gene therapy is an experimental medical procedure that attempts to correct a genetic mutation (missing or changed genes) so that properly functioning genes are restored to cells. When gene therapy works, the correct instructions for building proteins (chemicals that direct and control chemical reactions in the body) are once again available to cells, and the body returns to normal or healthier function.
Scientists first began discussing the possibility of this method to cure diseases in the 1960s. In 1970, American doctor Stanfield Rogers at Oak Ridge National Laboratory in Tennessee tried to use gene therapy to treat two sisters who had a genetic disorder called argininemia. With this genetic disorder, the body lacks an enzyme (a type of protein) called arginase. People with this disorder can have seizures and mental impairment. Rogers tried to treat the sisters by using a virus to carry the healthy gene into their cells. In this case, the gene therapy was unsuccessful.
In 1977, scientists were able to use gene therapy techniques to deliver a gene into the cells of mammals. American doctor W. French Anderson performed one of the first studies of gene therapy in humans in 1990 on a four-year-old girl who had a rare genetic immune system disorder called severe combined immunodeficiency (SCID). The immune system fights off infections from bacteria and viruses, and the disorder made it difficult for her body to stay healthy. Anderson and his team genetically altered her white blood cells and then returned them to her body. The new white blood cells strengthened the girl's immune system and made it possible for her to survive.
Another setback to gene therapy occurred in 1999. An eighteen-year-old patient named Jesse Gelsinger was involved in a gene therapy trial for a genetic disease called ornithine transcarboxylase deficiency (OTCD). This rare disease prevents the liver from breaking down ammonia, which can build up in the body and become toxic. Gelsinger died from organ failure four days after starting treatment. Researchers believe his immune system reacted to the virus that carried the new gene into his cells.
In 2000, French researcher Alain Fischer was able to cure children of a similar kind of immune system disorder. Fischer used retroviruses as gene carriers. Retroviruses are a type of virus that uses ribonucleic acid (RNA) as its genetic material, instead of DNA. Retroviruses produce an enzyme (a protein that controls a biochemical reaction) that builds DNA upon a strand of RNA. The most well known of these retroviruses is the human immunodeficiency virus (HIV), the virus responsible for acquired immune deficiency syndrome (AIDS). Fischer inserted a retrovirus carrying the normal gene into the children's blood stem cells. Several months later, two of the children in the trial developed a disease similar to leukemia (a type of cancer that starts in the cells that make blood cells). As a result, the U.S. Food and Drug Administration (FDA) halted the use of retroviruses in the United States.
Although research in this field has moved slowly, it still moved forward. In 2003, the first officially licensed gene therapy was available in China. Several types of gene therapy are waiting for approval from the U.S. Food and Drug Administration.