San Francisco Chronicle - The Voice of the West, 901 Mission Street, San Francisco, CA 94119 - Tuesday, July 9, 1996 - Page A1
David Perlman, Chronicle Science Editor

The report is a sobering counterpoint to a mood of cautious optimism among most of the 15,000 participants at the world's largest AIDS meeting -- a mood caused mainly by news of dramatic new therapies with drug combinations that, at least temporarily, appear able to nearly banish HIV from the body.

For six years, Dr. Francine E. McCutchan, a molecular biologist at the Walter Reed Army Institute of Research in Rockville, Md., has been studying the genetic structure of the 10 or so subtypes of HIV that are most common in much of the world, including the United States. That broad category of the virus is called HIV-1. Another variant, HIV-2, is found primarily in western Africa.

In a major report delivered in Vancouver to the 11th International Conference on AIDS, McCutchan said she and colleagues around the world have discovered that the genetic diversity of HIV-1 is increasing rapidly as its subtypes combine with one another over and over again.

As she reflected on the way influenza viruses tend to similarly recombine -- forcing scientists to introduce new vaccines virtually every year -- McCutchan warned that the new mosaic subtypes of the AIDS virus may profoundly challenge drug and vaccine developers.

STILL SOME HOPE

Still, McCutchan expressed hope that some of the recombinant subtypes may well preserve some crucial characteristics -- and possible vulnerabilities -- such as the proteins studding the viral membranes that are potential targets for drugs and vaccines.

It has long been known that the AIDS virus can mutate with extraordinary speed -- that is, although the tiny virus possesses only nine genes, the chemical structure of those genes can shift spontaneously, lessening the impact of outside influences such as drug therapy.

Mutation, in fact, often occurs while a drug is doing its job, only to have the wily virus quickly change the molecular makeup of its genes and thus escape the drug's onslaught.

Recombination is a different process, however. In it, two subtypes of the virus actually exchange some of their genetic material, creating a variant more different than could be caused simply by internal mutations. McCutchan and her colleagues refer to these mongrel HIV types as mosaics.

This is not all bad news: Some of those mosaics, McCutchan told the scientists, physicians, health care workers and AIDS activists attending the conference, "may be particularly effective targets" for the proposed drugs whose molecular structures are being tinkered with by researchers.

`RESHUFFLING' CAPABILITIES

But posing a more difficult problem, McCutchan said, is the fact that "a rapid reshuffling" of virus properties that affect their biology and effects on the immune system has created a wealth of "raw material" that could enable HIV to adapt even more effectively to new drugs or vaccines.

Recombinant subtypes of HIV already are responsible for the rapidly expanding epidemic in Southeast Asia, she said. In the global spread of HIV subtypes, McCutchan reported, one sample of the virus first isolated in patients in Thailand has already been analyzed in Africa. Another subtype already isolated in several African countries has cropped up in Russia, while several recombined forms of the same subtype have been isolated in Gabon and Nigeria and are now spreading globally. Virus samples collected most recently from Europe, Asia and the Western Hemisphere all show varied intermixing of the subtypes, she said.

Meanwhile, other researchers said yesterday that, although AIDS strikes mainly heterosexuals in most of the world's poorest nations, a generation of young gay men risks a new wave of HIV infection by engaging in dangerous sex.

First spotted in San Francisco a few years ago, the pattern has now been documented across the United States, Europe and Canada.

"The epidemic of HIV among young gay men is not only an individual tragedy but is certainly also a major public health concern," said John de Wit, a psychologist at the University of Utrecht in the Netherlands.

In some parts of the United States, as many as one in 10 gay men younger than 25 carries the virus, and the risk seems to be especially high for people of color.

The research suggests that young gay men are two to three times more likely than older gay men to become infected with HIV. In San Francisco, about 3 percent of young homosexuals are infected with the virus annually.

Surveys in other U.S. cities show that gay black youngsters are about twice as likely as whites the same age to be infected this way.
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