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Wednesday, 1 May, 2002, 23:41 GMT 00:41 UK
HIV 'targets key defence cells'
HIV cells
Researchers say the findings could one day lead to vaccines
The HIV virus targets those specific immune cells designed to fight it, researchers have found.

The study, by US scientists, found those immune cells are two to five times more likely to be infected with HIV than others designed to attack other diseases.

It confirms what researchers had until now only suspected.

The researchers, from the US National Institute of Allergy and Infectious Diseases (NIAID) Vaccine Research Center, say the finding helps them understand how the virus works - and could one day lead to vaccines.

This finding not only helps us better understand how the virus causes disease, it should also aid in developing effective HIV vaccines

Dr Anthony Fauci, NIAID
UK experts said the study, published in the journal Nature, would also help doctors understand why some proposed treatments for HIV did not work, helping them target their research elsewhere.

The immune cells, called CD4+Tcells, help the body fight infection and disease. They are HIV's primary target.

The virus reduces the body's ability to protect against disease by depleting these cells.

Infection rates

The US researchers isolated three kinds of CD4+ T cells from 12 HIV positive people.

They looked at HIV-fighting cells, cells which fight cytomegalovirus (a virus which can cause illness in people with weakened immune systems - such as those with HIV), and a mixed group.

In each case, HIV infected a much greater percentage of HIV-specific cells than cells in the other two groups.

The other two kinds of cells showed no significant differences in HIV infection rates.

Laboratory research supported two reasons for the pattern.

The first says that when the immune system initially confronts HIV, the specific CD4+ T cells are immature, or "na´ve".

They soon multiply into a mature HIV-fighting cells but are very vulnerable to viral infection during this process - so they could be infected with HIV from the start , meaning a constantly high rate of infection among this group.

The reason HIV infects mature cells may be because they rush to fight HIV and bear the brunt of exposure to the virus compared with cells which fight other conditions, the researchers said.

Therapy breaks

Dr Richard Koup, who worked on the study, added: "For years we have known that the immune system does not produce a good CD4+ T cell response against HIV, and we have postulated that this might be because HIV preferentially infects HIV-specific CD4+ cells.

"This study is the first to show that this phenomenon actually happens in the body."

Dr Anthony Fauci, director of NIAID, said: "This finding not only helps us better understand how the virus causes disease, it should also aid in developing effective HIV vaccines."

One particular treatment pattern that is affected by these findings is the concept of structured therapy interruptions, where patients take a break from their medications.

Patients like the treatment because they can have a rest from the intensive regime of combination therapies used to treat HIV.

Keith Alcorn, senior editor of the UK's National Aids Manual, which provides information about HIV and its treatment to patients and professionals, said the theory behind interrupted therapy was that a break meant a "burst" of virus in the body, which the immune system could recognise and develop specific cells to fight.

He said: "The idea is that a patient could have longer and longer periods off treatment."

But the US research shows the HIV virus targets the specific immune cells that taking a break is supposed to stimulate.

Mr Alcorn said: "This research explains why that particular approach of treatment interruption was never going to work."

He added the research suggested the best hope for a vaccine was a DNA "prime boost" vaccine, which stimulated the response of a different type of immune cell not infected by HIV.

See also:

06 May 02 | Health
HIV 'singled out for destruction'
31 Jan 02 | Health
HIV numbers to rise sharply
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