The approach involves using enzymes to destroy a gene in the immune cells of people with HIV, thereby increasing resistance to the virus

Scanning electron micrograph of a human T cell from the immune system of a healthy donor. Credit:NIAID/NIH - Wikimedia Commons

A clinical trial has shown that a gene-editing technique can be safe and effective in humans. For the first time, researchers used enzymes called zinc-finger nucleases (ZFNs) to target and destroy a gene in the immune cells of 12 people with HIV, increasing their resistance to the virus. The findings were published March 5 in The New England Journal of Medicine.

This is the first major advance in HIV gene therapy since it was demonstrated that the Berlin patient Timothy Brown was free of HIV, says John Rossi, a molecular biologist at the Beckman Research Institute of the City of Hope National Medical Center in Duarte, California. In 2008, researchers reported thatBrown gained the ability to control his HIV infectionafter they treated him with donor bone-marrow stem cells that carried a mutation in a gene calledCCR5. Most HIV strains use a protein encoded byCCR5as a gateway into the T cells of a hosts immune system. People who carry a mutated version of the gene, including Brown's donor, are resistant to HIV.

But similar treatment isnot feasible for most people with HIV: it is invasive, and the body is likely to attack the donor cells. So a team led by Carl June and Pablo Tebas, immunologists at the University of Pennsylvania in Philadelphia, sought to create the beneficialCCR5 mutation in a persons own cells, using targeted gene editing.

Personalized medicine The researchers drew blood from 12 people with HIV who had been taking antiretroviral drugs to keep the virus in check. After culturing blood cells from each participant, the team used a commercially available ZFN to target theCCR5gene in those cells. The treatment succeeded in disrupting the gene in about 25% of each participants cultured cells; the researchers then transfused all of the cultured cells into the participants. After treatment, all had elevated levels of T cells in their blood, suggesting that the virus was less capable of destroying them.

Six of the 12 participants then stopped their antiretroviral drug therapy, while the team monitored their levels of virus and T cells. Their HIV levels rebounded more slowly than normal, and their T-cell levels remained high for weeks. In short, the presence of HIV seemed to drive the modified immune cells, which lacked a functionalCCR5gene, to proliferate in the body. Researchers suspect that the virus was unable to infect and destroy the altered cells.

They used HIV to help in its own demise, says Paula Cannon, who studies gene therapy at the University of Southern California in Los Angeles. They throw the cells back at it and say, Ha, now what?

Long-term action In this first small trial, the gene-editing approach seemed to be safe: Tebas says that the worst side effect was that the chemical used in the process made the patients bodies smell bad for several days.

The trial isnt the end game, but its an important advance in the direction of this kind of research, says Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland. Its more practical and applicable than doing a stem-cell transplant, he says, although it remains to be seen whether it is as effective.

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Gene-Editing Technique Shown to Work as HIV Treatment

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