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By MALCOLM RITTER AP Science Writer

NEW YORK (AP) - Can an experimental drug developed to treat epilepsy block the AIDS virus? A preliminary lab study suggests it's possible, and researchers are eager to try it in people.

Scientists experimented with the drug after uncovering details of how they believe HIV cripples the immune system to bring on AIDS.

When tested in human tissues in the laboratory, the drug "works beautifully" to prevent HIV from destroying key cells of the immune system, said Dr. Warner Greene of the Gladstone Institutes in San Francisco. Those results appear in a paper by Greene and others published online Thursday by the journal Nature.

In that work, and a companion study published in Science, Greene and colleagues focus on how HIV kills vital CD4 cells of the disease-fighting immune system.

Researchers have long known it infects some CD4 cells and turns them into virus-producing factories, killing them in the process. But far more cells die without undergoing that transformation. What is going on in these "bystander"CD4 cells?

The new work provides evidence that HIV enters these cells but fails to produce a full-blown infection, and in response the cells trigger a lethal attack on themselves by the immune system.

It's "more of a suicide than a murder," Greene said. "I believe this is the major mechanism through which CD4 cells are depleted, which is the hallmark of AIDS."

The epilepsy drug, which is not on the market, blocks an enzyme that the research identified as playing a key role in that immune system attack.

Prior studies of the drug in people show it is safe, Greene said. So the researchers are talking to the drug company about testing it in people infected with HIV. No timeline for such studies has been set, he said.

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Drug blocks HIV in lab study, human tests planned