Important note: Information in this article was accurate in 1999. The state of the art may have changed since the publication date.
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United Press International - Tuesday, April 27, 1999
Larry Schuster, UPI Science Editor
Researchers at Yerkes ("Yerk'-EEZ") Regional Primate Research Center in Atlanta say today their three-year study in macaques found the vaccine was able to substantially contain the AIDS virus, though, it was not able to eradicate it.
The vaccine reduced the level of virus replication in the monkeys by a minimum of least 1,000 and up to 10 million. They were able to contain a virus, that was a combination human AIDS virus and related monkey immunodeficiency virus, during a 62-week period.
"I just couldn't believe the results when I first saw them," said Harriet L. Robinson, chief of microbiology and immunology at Yerkes and the project's lead researcher. "I just didn't believe we could do this well."
Until now, Robinson said, only vaccines featuring live, though weakened virus with risk for causing disease in humans were able to contain severe viral challenges in monkeys as well as this vaccine.
Robinson told United Press International she is very optimistic, that when tailored and simplified for use in humans, her approach will be useful as a preventive vaccine for those not infected. And for people with functioning immune systems who are infected who are on the standard aggressive drug therapies, she was optimistic her vaccine approach will be able to reduce the need for drugs.
She said her goal is to have the vaccine enter human trials in a year.
Scientists who commented on the work said the approach does represent an important advance on two fronts.
It uses elements of human immunodeficiency virus and the related simian or monkey immunodeficiency virus that scientists consider harmless. And the positive response occurred without depending on neutralizing antibodies, one of the two major immune responses.
Peggy Johnston, associate director for vaccine and prevention research, at the National Institute of Allergy and Infectious Diseases, which funded the research, told United Press International one of the most exciting aspects of the research was the protection recorded in the absence of the neutralizing antibodies. The antibodies target the invading virus itself, a task which has become a nearly futile because of the wildly mutating nature of the virus which allows it to escape antibody defenses. Instead, the Yerkes vaccine triggered a response of cytotoxic T lymphocytes, which target cells that are infected with the virus.
The two features of the Yerkes vaccine -- its safety and success despite lack of neutralizing antibodies -- have attracted some positive attention for the vaccine approach.
"This is one of a short list of what needs to move into human trials," Johnston said. The short list of such high priority vaccine candidates totals about three or four, she said.
The vaccine included purified DNA that codes for four proteins associated with the virus: The capsid that surrounds the, nucleic acid -- the genetic code of the virus; a protein involved with replication; a protein involved with the envelope; and a protein that cells generate early in the infection process.
The monkeys that did best first received an intradermal inoculation in a purified form, followed by an inoculation with a harmless pox virus that was engineered to contain the same DNA segments.
AIDS vaccine clinical trials began in 1987. Currently, there are only two vaccines in the most advanced phase of human trials, in which the vaccines are being tested for efficacy. One of the vaccines, by VaxGen Inc., of Brisbane, Calif., is being tested as a preventive vaccine. The second candidate, in the same advanced phase of human trials is being developed by Immune Response Corp. for use as a therapeutic vaccine, Carlsbad, Calif.
About 20 AIDS vaccines are currently in human prevention and/or therapeutic trials worldwide. Altogether, U.S. AIDS researchers estimate that 55 AIDS vaccines have been evaluated in prevention and/or therapeutic clinical trials worldwide since the start of the epidemic.
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