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- WASHINGTON (Reuters) - Scientists
had more bad news for HIV patients on Thursday, saying they found that,
within days of infecting someone, the virus manages to find hiding places
that no drug currently in use is able to reach.
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- The finding is another setback to doctors who had hoped
that perhaps HIV could be stopped early, either with quick drug treatment
or by somehow stimulating the body's immune system.
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- Microbiologist Ashley Haase of the University of Minnesota
and colleagues said that within 3 days of getting into the body, the virus
sneaks into cells known as resting T-cells.
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- These cells are good hiding places because they are inactive
and thus not noticed by the immune system. Nor can they be targeted by
drugs, which need some kind of activity by the virus or the cells it infects
in order to work.
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- ``These cells fly below the radar screen of the immune
system,'' Haase, who reported his team's work in the journal Science, said
in a statement.
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- ``They also live a long time and won't be affected by
our current combinations of anti-AIDS drugs.''
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- Resting T-Cells
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- HIV infects immune system cells known as CD4 T-cells.
When it gets inside, it takes over a cell's machinery and makes it crank
out copies of the virus, eventually killing the cell.
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- While it is actively doing this, the body's other immune
cells can detect the activity and move in. And drugs can stop various stages
of the hijacking -- which is why cocktails of HIV drugs can help suppress
the virus.
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- But the virus can also get into inactive T-cells, known
as ''resting'' T-cells. They can exist in the body for years, even decades,
without doing anything. The virus sits inside there too, quiet and unnoticed.
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- It had been thought that it took some time for the virus
to find these latent cells. But Haase's team, working first in monkeys
and then in HIV patients, found it finds its way in within 3 days of infection
-- before a patient has a single symptom.
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- To discover this, Haase's team infected 14 rhesus monkeys
vaginally, to simulate the most common way HIV is passed on around the
world. They killed several of the monkeys one, three, seven and 12 days
after infection and looked to see where they could find the virus in their
bodies.
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- Within three days, the resting CD4 T-cells were infected
and by the 12th day the virus was found throughout the lymphatic systems
and organs of the animals.
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- ``HIV replicates in these cells whether or not they are
demonstrably activated and proliferating and the infected cells that are
not proliferating have lower levels of viral gene expression and are longer-lived,''
the researchers wrote.
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- They looked at patients with HIV infections and found
a similar pattern. At least half the cells infected early on were resting
T-cells, Haase said.
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- ``This study identifies a source of cells that are invulnerable
to current therapies,'' Haase said. In addition, most vaccine techniques
need activated T-cells to work.
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- ``Sobering News''
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- Dr. Anthony Fauci, head of the National Institute of
Allergies and Infectious Diseases (NIAID), said the study helped explain
why people who took strong cocktails of drugs for years were not cured.
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- ``We have shown that you can whittle down the latent
reservoir to virtually undetectable levels, but as soon as we stop the
drugs, 2 1/2 weeks later, boom -- the virus came right back,'' he said
in a telephone interview.
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- This suggested the virus was hiding.
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- ``This paper shows that this occurs literally at the
time of entry of the virus, so it's sobering news,'' he said in a telephone
interview.
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- Fauci added that he never thought there would be a cure
for HIV infection anyway.
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- ``I think that we need to work on ways that we can develop
drugs that target these latently infected cells, and enhance the immune
system so it contains these cells,'' he said.
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- The body does this naturally, for example, with herpes
viruses that infect just about everybody but cause no more trouble than
the occasional cold sore.
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- ``We don't die of disseminated herpes disease because
our immune system is strong enough to contain it,'' Fauci said.
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