San Francisco Chronicle - Wednesday, December 15, 1993
Charles Petit, Chronicle Science Writer

Moreover, it may take only a tiny mutation in a given strain of virus to transform it from one that is vulnerable to immune system attack into one that flares back -- like a fire doused with gasoline.

The ability of the virus to turn the tables on the human immune system is something never seen before in any virus or bacterium, said Dr. Jay Levy, the University of California at San Francisco virologist in whose laboratory the new work was done. The report is in today's issue of the Proceedings of the National Academy of Sciences. The lead author is research virologist Srisakul C. Kliks.

"This indicates, on the molecular level, how some viruses are able to learn to escape the immune system," Levy said. The difference between a virus strain that quickly succumbs to a specific antibody, and one that is either indifferent to it or seems to get worse in its presence, appears to be as minor as a change in a single amino acid molecule among many hundreds in the virus' outer coat, or envelope.

The findings, if confirmed, should help show how the quickly mutating human immunodeficiency virus, or HIV, outwits the immune systems of nearly every person it infects -- often turning virulent after having been kept at bay in an infected person for years.

On the positive side, the new work exposing some of the details of the virus' strategy may help show medical researchers how, eventually, to outwit a pathogen that seems well-designed to attack the biological systems designed to destroy such threats.

Meanwhile, work to manufacture anti-AIDS vaccines is increasing worldwide and is encountering a host of frustrations because of the ability of HIV to quickly change the molecular makeup of its outer envelope.

A vaccine works by exposing a person to molecules or fragments of a virus or bacteria. It thus primes the immune system to develop antibodies and other means to fight off any subsequent exposure to the actual contagion.

`SO MANY VARIANTS'

Levy's work fits in with a host of new studies of HIV and the immune system, said Dr. John McNeil, head of the largest U.S. vaccine development program, centered at the Walter Reed Army Medical Center in Washington.

"There is a lot of uncertainty about what the vaccine has to actually do to defeat this virus," he said. "There are so many variants . . . but whether pessimism is warranted won't be known until we test some actual vaccines."

Among frustrating reports in recent months, McNeil said, has been the discovery that many antibodies induced by vaccines work exceedingly well against samples of HIV grown in a test tube but then fail to have any effect against HIV taken from people with AIDS.

McNeil's program plans large-scale tests of AIDS vaccines in Thailand, largely among prostitutes and others at high risk of exposure, but it may take a year or more before the vaccines are prepared and approved for test by both U.S. and Thai agencies.

Always watch for outdated information. This article first appeared in 1993. This material is designed to support, not replace, the relationship that exists between you and your doctor.

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