Studies: HIV quickly kills immune cells

Monday, March 28, 2005 Posted: 1811 GMT (0211 HKT)

WASHINGTON (Reuters) -- Within days of infection, the AIDS virus destroys more
than half of the immune cells that might recognize and help fight it -- a
finding that may force a re-evaluation of how to tackle the deadly infection,
two teams of U.S. researchers reported Sunday.

Two separate studies in monkeys showed that SIV, the monkey version of the human
immunodeficiency virus or HIV, attacks CD4 memory T-cells right away and wipes
out more than half of them.

"The findings may require a rethink of strategies to design HIV drugs and
vaccines," Dr. Mario Roederer of the National Institute of Allergy and
Infectious Diseases and colleagues said in one of two reports published in the
journal Nature.

The findings will be difficult to replicate in people, because most people do
not know the moment they are infected with the AIDS virus, which gradually
destroys the immune system, leaving patients vulnerable to numerous infections.

But SIV is a good model and works in a similar way.

Both teams worked with monkeys that they infected with SIV. They watched what
happened to their immune cells.

Right away the virus attacked the CD4 T-cells that had the correct configuration
for the virus. Normally during an infection such cells would recognize and latch
onto an invader, helping other components of the immune system destroy it.

But HIV is different because it targets the immune system, and the two studies
show how quickly it makes it impossible for its victims to launch a defense.

Roederer's team used new, sensitive tests to show just how the virus moves so
quickly.

"Specifically, 30 percent to 60 percent of CD4 memory T- cells throughout the
body are infected by SIV at the peak of infection, and most of these infected
cells disappear within four days," they wrote.

"Furthermore, our data demonstrate that the depletion of memory CD4 T-cells
occurs to a similar extent in all tissues. As a consequence, over one-half of
all memory CD4 T-cells in SIV-infected macaques are destroyed directly by viral
infection during the acute phase -- an insult that certainly heralds subsequent
immunodeficiency."

This means any attempt to vaccinate against HIV or to provide efficient
treatment must stop this process right away.

Dr. Ashley Haase of the University of Minnesota Medical School and colleagues
made similar findings. Not only does the virus directly kill the CD4 cells, they
found, but it also causes them to them to commit cell suicide.

There is no cure for HIV infection, which killed more than 3 million people
globally last year and which infects 39 million people, according to the United
Nations.

Drug cocktails can control the infection but it comes back quickly if they are
stopped. More than two dozen vaccines are being tested, but experts do not
expect any of them to prevent HIV infection in substantial numbers of people.




Sandra Tara Balduf (Ane)

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