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AIDS-Vaccine Test To Be Expanded On Upbeat Results
September 23, 2005
Researchers said clinical tests of an experimental AIDS vaccine from Merck & Co. are exceeding expectations, leading them to double enrollment in the trial to 3,000.
The trial is being conducted in healthy volunteers to determine their immune response to the vaccine. The trial may indicate whether these immune reactions can prevent or control AIDS. Such results won't be available until at least 2008. A practical AIDS vaccine is thought to be at least a decade away.
Researchers said they were encouraged that the vaccine, called MRKAd5, was eliciting a stronger-than-expected immune response. The vaccine uses an adenovirus -- a common-cold virus -- as a missile armed with man-made copies of three AIDS virus genes. These genes are designed to rally the body's "killer" T-cells, which seek and destroy human cells infected by HIV, the human immunodeficiency virus that causes AIDS.
Lawrence Corey, principal investigator of the HIV Vaccine Trials Network, a Seattle-based research group supported by the National Institutes of Health, said MRKAd5 has boosted such killer cells by 50-fold to 100-fold -- an immune reaction he called comparable with successful vaccines for diseases like smallpox or measles. But it doesn't elicit antibodies, another key element of immune protection. The trial began in January.
In a promising sign, volunteers got a strong immune response even if they previously had developed antibodies to the adenovirus because of prior cold infections.
"It's very good news," Dr. Corey said. If this trial eventually shows evidence of preventing or controlling HIV, he said, "it will be a major finding for the field."
The Merck vaccine uses genes from AIDS virus strains found in North and South America. AIDS vaccines will need to include genes from virus strains all over the world. Such a vaccine is being developed at the Vaccine Research Center of NIH.
The trial, launched in January, is a collaboration of Merck, the HIV Vaccine Trials Network and the National Institute of Allergy and Infectious Diseases, a unit of NIH.
The HIV Vaccine Trials Network is overseeing 15 active vaccine trials out of dozens being conducted in the hope of halting the epidemic, which affects about 40 million people and killed 3.1 million in 2004.
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