THE ODDS GROW LONGER

By Christine Gorman

When Dr. David Ho announced last year that he thought he might be able to eliminate the AIDS virus completely from the bodies of his patients by hitting it early and hard with a combination of powerful antiviral drugs, his startling prediction was couched in a big "if." If it turned out that there were previously undiscovered pockets of viral particles in the body, all bets were off.

The bets are off. Reporting in the journal Science, two groups of investigators--one from Johns Hopkins Medical School in Baltimore, Md., the other from the University of California at San Diego--announced last week that they had found a hidden reservoir of HIV that seems perfectly capable of reactivating an infection. A third paper, which will appear in next week's Proceedings of the National Academy of Sciences, comes to the same conclusion. All three studies determined that HIV lurks in some of the so-called memory T cells of the immune system--even after it has been cleared from the bloodstream. "I kind of expected this," says Ho, director of the Aaron Diamond AIDS Research Center in New York City, who worked with the Hopkins group. "It would have been nice not to have this to deal with, but it's here and we have to handle it."

The memory cells turn out to be perfect hiding places for HIV. Like an extraordinarily detailed computer database, they keep track of every foreign particle or microbe that the body has ever come across. If they meet up with the same intruder at a later date, they can trigger an immediate immune response. (That's why you need to be vaccinated only once against such diseases as polio or smallpox.)

Until the memory cells are called into action, however, they exist for years and possibly decades in what is known as a resting phase, never making copies of themselves or any of the viruses that may have infected them. Unfortunately, combination therapy works only against actively reproducing viruses. So by lying low within a few memory cells, HIV can escape the pharmacological onslaught.

Although disappointed by the latest results, AIDS researchers have not conceded defeat. They were pleased to discover that the HIV stored in the memory cells had not mutated: the same collection of antiviral drugs should work on it whenever it comes out of hiding. "The bad news is we can't yet get rid of the virus," says Dr. Robert Siliciano, who led the Hopkins team. "The good news is that as long as people infected with HIV keep taking the triple-drug cocktail, they have an excellent chance of surviving the infection for a long time."

Meanwhile, researchers are trying to figure out how to lure the virus out of hiding. One idea: trigger a mild case of toxic-shock syndrome, hoping that in the immune system's frenzied--and sometimes fatal--reaction, the hidden viruses will be activated. If all the memory cells containing HIV could be stimulated, the viruses hiding within them could be destroyed by the right combination of drugs. Once again, it's a big if.

--By Christine Gorman. Reported by Alice Park/New York and Dick Thompson/Washington

With reporting by Alice Park/New York and Dick Thompson/Washington