Viral Jujitsu: A new gene therapy has a way of turning the AIDS virus against itself.

The war against AIDS is one of attrition. Antiretroviral drugs can slow the proliferation of the human immunodeficiency virus, delaying the day when the patient experiences full-blown AIDS. But they do not eliminate the virus, which can revive lethally after lying dormant for decades. Now an experimental gene therapy has emerged that may come a little closer toward actually curing AIDS. It works by turning HIV's own virulence against itself. The new therapy, produced by the small biotech firm Virxsys of Gaithersburg, Md., embeds a genetically engineered weapon called a lentiviral vector in the body's own disease-fighting T cells. (A vector is something that transfers genetic material into a cell; in this case it is a defanged version of HIV itself.) The lentiviral vector efficiently delivers its genetic payload into cell chromosomes, where it can stay for a long period of time. Virxsys' vector sets a deadly trap for the marauding HIV.

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When HIV begins infecting T cells laced with the lentiviral vector, the vector's RNA seeks out and binds with the HIV to activate proteins that chew up the virus' reproductive genes as soon as it begins to replicate. Potential patients will get an intravenous dose of about 10 billion T cells, grown in petri dishes with the vector inside them. Once inside the body, the "weaponized" T cells divide, creating a flotilla of anti-HIV vectors. "With the correct dose, it may be possible to cure patients with AIDS by creating an army of T cells that can inhibit and resist HIV infection," explains the vector's discoverers, Boro Dropulic, founder and chief scientist of Virxsys. Virxsys is backed by $23 million from Signature Capital. The therapy may also thwart HIV's insidious ability to mutate its way around antiretroviral drugs. The current crop of AIDS drugs, such...