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Gene Therapy for Controlling HIV Shows Early Promise

Small study hints treatment could someday help patients fight AIDS virus without drugs

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HIV researchers have been studying the CCR5 protein for years. It's long been known, Levine said, that the protein allows HIV to gain entry into cells. And people who have a particular mutation in both copies of their CCR5 gene (inherited from both parents) are protected from HIV infection.

CCR5 research has gained momentum in the past several years -- particularly after the famous case of the "Berlin patient," who is considered the first person to be cured of HIV.

That patient, whose real name is Timothy Ray Brown, was HIV-positive back in 2007, when he underwent a bone marrow transplant to treat leukemia. His bone marrow donor carried two copies of the CCR5 mutation, and the transplant not only cured his cancer, but also knocked his HIV levels below the threshold of detection. He has been off of HIV drugs since 2008.

For the current study, Levine and his colleagues tried to mimic that CCR5 mutation using what's called a zinc-finger nuclease -- which is basically an artificial enzyme that can snip DNA at a specific site.

That effectively knocked out the CCR5 gene in 11 percent to 28 percent of patients' T-cells before they were re-infused.

Levine said one of the more immediate goals now is to make the process more efficient. Right now, the technology knocks out both copies of CCR5 in some cells, but only one copy in others.

"Ideally, you'd like both copies knocked out," Levine said.

Of the four patients in this study whose viral levels declined after stopping their medication, one had undetectable HIV levels when the drug treatment was restarted. Levine's team later found that the patient naturally carried one copy of the CCR5 mutation.

So that patient, Levine said, essentially got a "head start," because there was no need for both CCR5 copies to be knocked out.

For her part, Johnston agreed that boosting the efficiency of the CCR5 knockout technique will be key. She said it also has to be tested in larger and more diverse groups of people with HIV, and researchers need to understand how the immune system responds over the long term.

And the "holy grail," Johnston said, would be to apply gene therapy to the bone marrow stem cells that give rise to the immune system, and not only T-cells.

Worldwide, more than 33 million people are living with HIV/AIDS, and 97 percent of them are in low- to middle-income countries, according to the U.S. Department of Health and Human Services.

If this or any other gene therapy were found to control HIV without the use of drugs, there would still be the questions of how to get it to people, and how to pay for it.

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