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AIDS Vaccine Nears Crucial Test

Tat Toxoid Vaccine Promises to Cut Need for AIDS Drugs
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WebMD Health News

Oct. 29, 2002 -- Not many experts thought it would get this far. But now tests in HIV-infected patients suggest that a totally different approach to AIDS therapy and AIDS vaccines just might work. It's called Tat toxoid, the brainchild of controversial French AIDS researcher Daniel Zagury. Co-inventor Robert Gallo has been saying for years that it could be the next big breakthrough in AIDS research. But many experts don't see it that way. Will they have to change their minds? That remains to be seen -- but now a crucial test shows that Tat toxoid raises very interesting immune responses in people already infected with HIV. "This is the first step toward using this as a component of a vaccine both in the AIDS treatment and prevention settings," James Tartaglia, PhD, program director for the Aventis Pasteur HIV program, tells WebMD. Aventis researchers reported the findings at this week's Cent Gardes Symposium on HIV and AIDS Vaccines. Tat is a piece of the AIDS virus. Infected cells make a lot of Tat, and this excess Tat gets into the bloodstream. It is not harmless. HIV needs Tat in order to reproduce. But that's not all Tat does. Tat helps HIV infect new cells. It also speeds AIDS by helping HIV disable the immune system. Some researchers think Tat is just a nuisance. Other, like Tartaglia, think it's absolutely necessary for HIV to do its dirty work. That's where Tat toxoid comes in. Invented by French researchers, it is a Tat look-alike. It doesn't do anything to help HIV. But when used as a vaccine, it stimulates the immune system to make antibodies that attack real Tat. If, indeed, Tat is as bad as Gallo and others say it is, these antibodies could be a huge breakthrough. They offer a way to attack the Achilles' heel of HIV. The new study tested Tat toxoid in HIV-infected people taking AIDS drug cocktails. All had their HIV infection under control. All those who got the vaccine along with a powerful immune-boosting agent made lots of antibodies against Tat. In the test tube, these antibodies powerfully disrupted HIV replication. There was strong evidence that most of the patients were making potent anti-Tat immune responses. "It is very good to see Tat toxoid inducing these activities," Tartaglia says. "Regarding potential clinical outcome, as of yet we don't know. These patients will be allowed to participate in a new clinical trial with the intent of stopping their HIV drugs." It's an exciting idea. How exciting? Tat expert Kuan-Teh Jeang, MD, PhD, is head of the molecular virology section at the National Institute of Allergy and Infectious Diseases. "I think everything they are showing makes sense, is probably true, and probably correct," Jeang tells WebMD. "The biggest problem is the assumption they are using about how Tat works. Is this really true in human beings? That remains to be seen. I don't think in the year 2002 either they or I or anybody else can definitively say what those Tat molecules secreted from HIV-infected cells are doing in terms of HIV replication and HIV disease."

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