AIDS Vaccine: Safe, but Does It Work?

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The first experimental AIDS vaccine to enter human testing in the United States has caused no ill effects in volunteers up to 21 months after administration and has triggered potentially protective immune responses in some of those who received the shots, according to an analysis published this week.

The study, performed on healthy men and women deemed at low risk of acquiring AIDS, was designed to determine safety rather than efficacy, leaving scientists uncertain whether the vaccine can actually protect against the AIDS virus, HIV But the researchers express satisfaction with the trial, saying it proves they can overcome the unique challenges inherent in the design and implementation of AIDS vaccine testing.

Under the direction of the National Institute of Allergy and Infectious Diseases' AIDS Clinical Trials Network in Rockville, Md., scientists from seven U.S. universities and two private companies collaborated to test the experimental vaccine, made by MicroGeneSys inc. of West Haven, Conn. The vaccine contains a synthetic protein fragment that mimics a protein called gp160 found on the outer surface of HIV

The researchers saw no signs of toxicity in any of the volunteers, who received up to four doses of the vaccine over an 18-month period. The most sensitive blood tests showed that 30 of the 33 AIDS vaccine recipients had developed gp160-specific antibodies after the third inoculation, given six months after the initial shot.

But the antibody response appears somewhat weak. And when the researchers used a different analytical method, they confirmed the presence of gp160 antibodies in only nine individuals. Disappointingly, antibody levels dropped steadily over the next year; only four recipients retained antibodies 18 months after the first injection, as measured by the most sensitive test.

Moreover, the mere presence of antibodies provides no guarantee that a person can fend off HIV For evidence of that ability, scientists measured the antibodies' ability to "neutralize" HIV in test tubes. …