Important note: Information in this article was accurate in 1998. The state of the art may have changed since the publication date.

Reuters NewMedia, Inc.; Thursday June 4 2:07 AM EDT
Maggie Fox, Health and Science Correspondent

But many AIDS experts were skeptical about whether the vaccine, developed by California-based VaxGen Inc., would actually work to prevent HIV infection in very many people.

The company, however, was euphoric. "I think that this is a real turning point," Dr. Robert Nowinski, an HIV expert who helped found the company, said in a telephone interview.

"This can't be reversed. Somewhere along the line, a vaccine is going to be formulated and this epidemic is going to be ended."

The Phase III clinical trials -- usually the last step before the FDA considers whether to allow a company to market a drug or vaccine -- will involve 5,000 volunteers in 40 cities across North America.

There are more than 40 HIV vaccines in trials now but this one, known as AIDSVAX, is the first to make it this far.

The vaccine uses gp120, one of the surface proteins on the coat of the HIV virus. The idea is that using one of the unique proteins would be enough to stimulate the body's immune system to recognize and attack the viral invaders.

"The vaccine builds a wall of immunity," Nowinski said. "The concept is to train or prime the immune system so that the instant the virus comes into the body there is an immediate reaction. The virus is wiped out before it has a chance to establish a beachhead."

Earlier efforts using gp-120, or any of several other surface proteins, have not worked very well. But VaxGen has combined gp-120 from two different strains of the virus and thinks this one might work better.

"The gp-120 protein is the major protein that everyone believes induces antibody response," Nowinski said.

He said earlier versions did not work because researchers did not clearly understand that there are different strains of HIV. "The major modification that was made was expanding into another strain of virus," he said.

He said the vaccine clearly worked in chimpanzees -- but chimps do not get AIDS like humans do. And it will be years before anyone knows whether the vaccine works.

"You take a high-risk population, like for example in the United States we are doing sexual transmission, so we have men who have sex with men and women whose partners are HIV-positive," Nowinski said.

"One group gets a vaccine and one gets placebo, and then they go about their normal lives. You see if you cut down the transmission rate as result of having vaccinated them."

VaxGen said it is also preparing Phase III clinical trials in Thailand. There are five known strains of HIV, but only three main ones. The vaccine tested in the United States uses the strain found commonly in the Americas, Europe and Australia, while the strain being tested in Thailand is found in east Asia.

VaxGen said it will also work on formulations to protect against the strain typical in China, India and Africa.

Experts agree that, long-term, a vaccine is the only answer to HIV. Cocktails of strong drugs can keep the virus at bay, but they are very expensive, have severe side-effects and are hard to take. Most people cannot afford them.

Several other AIDS vaccine researchers have expressed doubt about whether AIDSVAX will work. "It's a very, very long shot to expect anything that's measurable," Dr. David Baltimore, president of the California Institute of Technology and a top AIDS researcher, told the Wall Street Journal.

But Jose Zuniga, spokesman for the International Association of Physicians in AIDS Care, which is pressing for trials of a vaccine that uses a live but weakened form of the virus, welcomed the tests of AIDSVAX.

"We consider that any trial looking at an AIDS vaccine is a worthy investment," he said. "I think it also sends a signal that the FDA is willing to go out on a limb and push the envelope."

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