Retroviruses Rejected for Gene Therapy

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 opposite of what normally happens in humans where RNA is made on sections of DNA). The most well known of these retro viruses 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 all gene therapy that used retroviruses in the United States.

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.

Although gene therapy research moved slowly, it still moved forward. In 2003, the first officially licensed gene therapy was

Gene therapy: Treating disease by replacing nonfunctional genes or supplying genes that do function properly.

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