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Failed AIDS vaccine intrigues scientists

Drug seems to work well in small number of blacks who participated in the large trial.

©Associated Press

February 25, 2003

SAN FRANCISCO -- The failure of an experimental AIDS vaccine in its first major test has shattered hopes of developing a shield against infection in the near future and demonstrated just how far scientists are from bringing the disease under control.

Still, the results made public Monday contained an intriguing finding: The vaccine appeared to work well in the small number of blacks who participated. Scientists said more study is needed to draw any conclusions.

The drug's developer, Vaxgen Inc., said that overall there was no meaningful difference in protection between the 3,330 volunteers who received the genetically engineered vaccine and the 1,679 volunteers who received a placebo. All participants were at high risk of contracting the disease through sex.

Dozens of companies, universities and researchers are racing to develop their own vaccines. Among them: Merck & Co., GlaxoSmithKline and Aventis Pasteur.

But because the vaccine, called AIDSVax, was the first to be tested in a so-called Phase 3 clinical trial, usually the final testing stage for marketing approval, interest in the results has been intense.

Officials had been willing to give the drug approval even if it worked in just one in three people. But even that level was not attained.

VaxGen, based in Brisbane, Calif., has spent $200-million developing AIDSvax and said it remains hopeful the vaccine will someday help slow the spread of AIDS. Results from another big human experiment in Thailand are expected to be released later this year. The Thailand experiment involved IV drug abusers.

Company executives conceded doubts that the Food and Drug Administration would approve the vaccine anytime soon.

"The disappointment comes from working in AIDS. This is no doubt a challenging little bug," said Dr. Donald Francis, who co-founded the company in 1995. "It's not surprising that we would have another challenge here. But the door is open, and we can see some light streaming in."

The fact that the vaccine advanced to such large trials was largely the result of the doggedness of Francis, a former epidemiologist and virologist at the Centers for Disease Control and Prevention who was one of the first medical experts to see the dangers of AIDS when the disease became known more than 20 years ago.

AIDSvax is made from a protein called gp120, the same protein that protrudes from the surface of HIV and helps the virus dock with cells of the body's immune system. The protein in the vaccine is made in genetically engineered hamster ovary cells. Since the vaccine consists of only one protein and not the whole virus, it cannot give someone AIDS. But it is designed to provoke the immune system into making antibodies that will latch on to the gp120 protein in the real virus.

Most mainstream AIDS researchers have said they do not believe the approach will succeed. For one thing, HIV mutates rapidly and there are a number of subtypes of the virus, which themselves may have many different strains.

VaxGen stock fell $6.16, or 47 percent, to close at $6.86 Monday on the Nasdaq Stock Market. At one point during the day, VaxGen was down to as little as $3.

The company's stock has been extremely volatile during the last year as rumors about the experiment's results swirled. It has traded as high as $23.25.

The trial took place at 59 sites, mostly in the continental United States, with some in Canada, Puerto Rico and the Netherlands. It involved 5,400 volunteers, mostly men, none of whom were infected with HIV at the start of the trial.

About 5,100 of the participants were gay men who said they had sex with many other men. The other 300 were women who were considered at high risk of infection through sexual contact.

Two-thirds of the participants were given a series of seven shots over three years, while the other third were given the same number of placebo injections. The goal was to see if the people who received the vaccine would have a lower rate of infection. In the overall population of participants, 5.8 percent of those who received the placebo became infected, compared with 5.7 percent of those who received the vaccine. The difference was not statistically significant.

But among black, Asian and other minorities the rate of infection was only 3.7 percent in the vaccinated group, compared with 9.9 percent in the placebo group.

The company said those results were statistically significant and showed the vaccine has value. But others warned that the sample of minorities was too small.

"I am concerned that people will come to the conclusion that we can make a determination about protection," said Chris Collins, executive director of the AIDS Vaccine Advocacy Coalition in New York.

Francis said the company intends more study and cautioned against reading too much into the results. But he speculated that genetic reasons may be behind the different infection rates between whites and blacks, which would open a fertile field of study.

Other experts also found the results, if inconclusive, at least intriguing.

"If we determine the basis why blacks respond better than whites, then we've really done something," said Dr. Tom Merrigan, director of Stanford University's Center of AIDS Research.

Experts and activists believe a vaccine is the most promising way to slow the worldwide AIDS epidemic, which has already killed more than 20-million people and infected 42-million more.

"If we can get vaccines and make them cheap, that's going to control AIDS in the Third World," Merrigan said.

-- Information from the New York Times was used in this report.

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