Important note: Information in this article was accurate in 1998. The state of the art may have changed since the publication date.

Reuters NewMedia, Inc.; Wednesday, July 1, 1998
Jonathan Birt

Although scientists at the University of California San Francisco AIDS Research Institute stressed it was early, they said the theory could play a role in creating a vaccine to fight AIDS.

"This provides great encouragement for the ultimate development of a vaccine to HIV," said Professor Jay Levy. "If such an immune response can be induced we expect protection from HIV infection will result."

The study, presented at the 12th World AIDS Conference, looked at 60 people considered at high risk because of repeated exposure to the HIV virus through sharing needles or having unprotected sexual intercourse with a person known to be HIV-positive.

"These are people who have beat the odds for many years," said Dr. Sharon Stranford, who was in charge of the project.

"In the beginning I didn't believe in protection. I thought some people were just lucky and would seroconvert (the first sign of HIV infection) later, but after studying them for 2 1/2 years, only one out of 60 has seroconverted." Stranford believes exposure to the virus may have induced immunity, with repeated exposure acting like a natural vaccine and boosting the immune sytem without infecting healthy cells.

The individuals in the group all showed a unique immune response in one type of infection-fighting blood cell, CD8, which appeared to suppress reproduction of the virus. A similar type of response is found in people who are HIV-positive but remain healthy, known as "long-term survivors."

A series of experiments showed the CD8 cells in the individuals at high risk, and in people who were infected with HIV, mounted a response against HIV. Tests on the blood of people who were not infected with HIV and had not been exposed to the virus showed no such activity.

Researchers also took care to eliminate the possibility that a genetic difference accounted for the lack of infection in the main study group. Stranford said ony two out of 60 had a genetic defect that gave them protection from some strains of the virus, "so the other 58 have some other process protecting them."

In other news from the conference, an American doctor who reported the first case of transmission of a strain of the HIV virus that is resistant to the most potent drugs said it was a "important warning sign" but no reason to panic. Dr. Frederick Hecht of the University of California and San Francisco General Hospital told the 12th World AIDS Conference Wednesday the middle-aged man was infected with HIV that is resistant to six of the 11 marketed anti-retroviral drugs, including protease inhibitors.

"It is an important warning sign but I don't think people should be panicking," Hecht told Reuters in an interview.

"It is a wake-up call that we need to keep focusing on prevention and need to monitor the transmission of these strains."

HIV strains resistant to an older and less potent class of drugs known as reverse transcriptase inhibitors have been reported before but this is the first time a virus resistant to protease inhibitors (PI) is known to have been passed on.

"Protease inhibitors are the cornerstone of our HIV therapy," said Hecht. "People had hoped that PIs would be significant enough to make it difficult or impossible for the virus to be transmitted."

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