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HIV & AIDS Health Center

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AIDS Vaccine Moves Forward

WebMD Health News

March 1, 2002 -- It's not the only AIDS vaccine in development. It's not even the one that's furthest along. Yet it's the one on which most AIDS experts pin their hopes.

Now there's some human data. It's not earthshaking, but it means that development will continue. A report presented this week at a major U.S. AIDS conference shows that the vaccine is safe and that it just might work.

"Of course we need to collect more data ... but it's fair to say we are encouraged by the results to date," says John W. Shiver, PhD, senior director of viral vaccine research at Merck, in a news release. Merck is developing the vaccine.

Everything about the conference report by Merck researcher Emilio Emini, PhD, is unusual. Rarely does very early human trial data get much attention -- and these are the very first human studies of the Merck vaccine. It's even more uncommon practice for a report to be based on a study that isn't even finished yet. Yet interest in the vaccine is so great that Emini was asked to present the findings.

Why the excitement? Merck's HIV vaccine won't keep a person from getting the AIDS virus. It's just supposed to keep people from getting sick if they do get infected. This it does very well -- in monkeys. Other vaccines based on the same so-called "prime-boost" concept also work in animals. But Merck's vaccine is the only one backed by a huge company with the resources and the will to carry out advanced human trials.

The idea behind the prime-boost strategy is to start with a shot of DNA that produces important pieces of HIV. This primes the immune system to start making the weapons -- killer T cells -- thought to work best against HIV. The priming shot would be followed by several booster shots of a harmless virus genetically engineered to produce pieces of HIV. The boosts kick anti-HIV weapons production into high gear.

Merck conducted a series of studies. In the first trial using the shot of DNA, 109 healthy people volunteered to get four injections. Some got fake shots, some got low-dose shots, and others got higher-dose shots. Nobody had any ill effects. About one in five of the low-dose subjects and about two in five of the high-dose subjects developed anti-HIV killer T cells.

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