So-called therapeutic vaccines, which harness the body's own immune system to control HIV, have long been a goal of research. However, data released at an AIDS vaccine conference in Philadelphia on Friday are the first to hint this may be an effective strategy when combined with standard AIDS drugs.
The idea is to give people a break from their AIDS medicines that could last for weeks, months or even years. Experts caution that much more experimentation is needed to know whether vaccines could be used safely and effectively this way.
These early AIDS vaccines are likely to offer only partial protection against HIV, but could still have a significant impact in North America and Europe, where the epidemic has already slowed, researchers said on Friday.
The race to find a vaccine, which began soon after AIDS was first identified as a disease in the early 1980s, has produced over 90 candidates that are now being tested on human subjects in hopes of halting a worldwide epidemic that has killed 22 million people and infected 36 million others.
Dr. Raphael Dolin of the Harvard University Medical School said at the AIDS Vaccine 2001 conference in Philadelphia that a vaccine that is effective only 30 percent of the time would still help control the spread of HIV in regions of the globe where behavioral changes have already slowed the epidemic, including the United States and Europe.
"It would give you significant protection in areas where the (disease)...is less rampant," he said. "It would also get us into the realm of being able to determine the parameters of human immunity, which we don't know at the moment."
But Dolin said such a vaccine, which would leave 70 percent of a population unprotected, could do relatively little good in hard-hit developing regions such as sub-Saharan Africa, which is home to 26 million HIV and AIDS sufferers.
Drug companies are designing many of the vaccines for use both to prevent AIDS and to treat it.
Furthest along in this kind of dual testing is Aventis Pasteur's ALVAC-HIV, which has been given to more than 1,900 people worldwide and will enter large-scale testing to prevent AIDS next summer. The vaccine consists of a harmless canary pox virus that is genetically engineered to carry several genes that make HIV proteins. The company is sponsoring 14 studies of the vaccine as a treatment for infected people in the United States and Europe.
Normally, when people stop taking their AIDS drugs, the virus can reproduce again rampantly, producing billions of new copies. By exposing the immune system in advance to HIV proteins, experts hope it will mount a vigorous defense against the re-emerging virus, knocking it down to acceptably low levels.
At the meeting, called AIDS Vaccine 2001, Dr. Martin Markowitz of he Aaron Diamond AIDS Research Center in New York City described the first results of this strategy using ALVAC-HIV. The study was conducted on patients who began taking AIDS drugs within four months of catching HIV.
Thirteen of them took four doses of the vaccine before stopping their AIDS medicines, while five others stopped treatment without being vaccinated.
The researchers were disappointed that the virus returned to detectable levels in all the vaccinated volunteers. Nevertheless, virus levels fell back down to low levels in six of the vaccinated patients, compared with just one of those who was not vaccinated.
Markowitz said this is the first study to suggest that inducing an immune response with a vaccine influences patients' health when used in combination with standard AIDS drugs.
"There is clearly an effect of the vaccine that justifies continuing in this direction," he said. "It's a hint of something good."
"The computer models show that if behaviors remain unchanged, a 30-percent effective vaccine would have a marked positive effect on the epidemic," said Donald Francis, president of Brisbane, Calif.-based VaxGen Inc. which has a leading vaccine candidate.
VaxGen's AIDSVAX is a protein agent being tested on 5,400 gay men and at-risk heterosexual women in the United States, Canada and Europe.
It is scheduled to complete the final phase of human clinical trials in October 2002. But as early as next November an interim review of the trials will provide an early glimpse of the vaccine's efficacy.
VaxGen's Francis said he did not expect interim results to show efficacy rates as high as the 60-70 percent level necessary to cut short the trial and speed the vaccine agent into commercial production.
"I think it's a high hurdle to achieve. I don't know how optimistic I would be," he told a news conference.
The goal is to find a strategy that will allow patients to stop taking AIDS drugs, at least temporarily. These combinations of medicines have revolutionized AIDS treatment over the past five years, changing HIV from a death sentence to a manageable infection. Nevertheless, the treatment requires taking several pills a day and can cause a variety of unpleasant side effects, such as odd accumulations of body fat.
Dr. Douglas Richman of the University of California at San Diego said priming the immune system with a vaccine is a more sensible way to accomplish this than simply cycling people on and off treatment, a strategy enthusiastically discussed last year but largely abandoned because of poor results.
"It's conceivable that it could have a dramatic impact or no impact," he said. "You can speculate until the cows come home. We need to do the experiments."
Dr. Lawrence Corey of the University of Washington said a big challenge is trying to invigorate an immune system that is already weakened by HIV.
"There is no proof in any system that a vaccine has any clinical utility," he said. "The consensus iHIV is that there is no consensus."
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