Important note: Information in this article was accurate in 1999. The state of the art may have changed since the publication date.

Reuters NewMedia - Monday, April 26, 1999
Maggie Fox, Health and Science Correspondent

Their findings are bad news for those who had hoped the drugs, which can suppress the virus to near-zero levels, could eventually wipe out the virus within a person's lifetime.

But Robert Siliciano and colleagues at Johns Hopkins University in Baltimore said there might still be ways to tease out and destroy the virus.

"What we are showing is that there is a mechanism by which the virus can persist, essentially, for life, even in patients who are on optimal therapy as we currently define it," Siliciano said in a telephone interview.

"This doesn't mean that eradication is impossible or that the patients are going to fail therapy -- most of the patients are doing extremely well," he added.

Siliciano's team looked at 34 patients who were on the cocktails, known as highly active antiretroviral therapy (HAART) and whose virus was suppressed to undetectable levels.

Researchers had already found that the virus hides in memory T-cells -- the immune system cells that are assigned to recognise a new invader and then remember it in case it ever attacks again, making it easier for the body to respond next time.

"We know that immunologic memory lasts 60 years. For example, if you have a measles infection as a child you are protected 60 years later," Siliciano said.

They did calculations to see if the HIV-infected memory T-cells would last this long and found they probably would -- although no one has had HIV this long so it is impossible to confirm.

Writing in the journal Nature Medicine, they said their findings were one more nail in the coffin of hope that if patients take drugs for long enough, they can become free of the virus.

"Our results challenge the idea that anti-retroviral therapy as it is now given can ever be expected to eradicate the infection," they wrote.

It took a long time to figure this out because the virus cannot be detected by tests unless it is activated -- something it would not, by definition, do in a resting cell.

"These cells escape detection unless you activate them in the test tube," Siliciano said. "If you activate them, the virus comes out."

AIDS experts hope a way can be found to activate these memory T-cells and thus expose the virus hiding in them to HAART. The drugs only work when the virus is actively replicating.

There are a very few patients who have taken HAART for a few years and then stopped it and who so far have not seen the virus rebound. But Siliciano said at least one of them does still have the virus hiding in his memory T-cells.

Some doctors think it was adding the cancer drug hydroxyurea to the mix of drugs that somehow helped boost the patient's immune response so it could keep the virus in check. Siliciano said it is too soon to tell if this is the case.

One of the dilemmas of treating HIV infection is that the virus attacks the very immune cells that would help the body fight off the infection.

In a second paper in Nature Medicine, Dr. Louis Picker of the University of Texas and colleagues said they had found that these memory T-cells decline in number very soon after patients start on HAART -- but they are still there.

Such cells, if not themselves infected, might provide a way to help fight the infection, they wrote.
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