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Scientists Find Way to "Disarm" AIDS Virus
By Kate
Kelland, Reuters
September 19, 2011
World
Activists
distribute red ribbons and light up candles as
they commemorate victims
Scientists have found a way to prevent
HIV from damaging the immune system and say
their discovery may offer a new approach to
developing a vaccine against AIDS.
Researchers from the United States and Europe
working in laboratories on the human
immunodeficiency virus (HIV) found it is unable
to damage the immune system if cholesterol is
removed from the virus's membrane.
"It's like an army that has lost its weapons but
still has flags, so another army can recognize
it and attack it," said Adriano Boasso of
Imperial College London, who led the study.
The team now plans to investigate how to use
this way of inactivating the virus and possibly
develop it into a vaccine.
Usually when a person becomes infected with HIV,
the body's innate immune response puts up an
immediate defense. But some researchers believe
HIV causes the innate immune system to
overreact. This weakens the immune system's next
line of defense, known as the adaptive immune
response.
For this study -- published on Monday in the
journal Blood -- Boasso's team removed
cholesterol from the membrane around the virus
and found that this stopped HIV from triggering
the innate immune response. This in turn led to
a stronger adaptive response, orchestrated by a
type of immune cells called T cells.
AIDS kills around 1.8 million people a year
worldwide. An estimated 2.6 million people
caught HIV in 2009, and 33.3 million people are
living with the virus.
Major producers of current HIV drugs include
Gilead Bristol Myers Squibb, Merck, Pfizer and
GlaxoSmithKline.
Scientists from companies, non-profits and
governments around the world have been trying
for many years to make a vaccine against HIV but
have so far had only limited success.
A 2009 study in Thailand involving 16,000
volunteers showed for the first time that a
vaccine could prevent HIV infection in a small
number of people, but since the efficacy was
only around 30 percent researchers were forced
back to the drawing board.
An American team working on an experimental HIV
vaccine said in May that it helped monkeys with
a form of the AIDS virus control the infection
for more than a year, suggesting it may lead to
a vaccine for people.
HIV is spread in many ways -- during sex, on
needles shared by drug users, in breast milk and
in blood -- so there is no single easy way to
prevent infection. The virus also mutates
quickly and can hide from the immune system, and
attacks the very cells sent to battle it.
"HIV is very sneaky," Boasso said in a
statement. "It evades the host's defenses by
triggering overblown responses that damage the
immune system. It's like revving your car in
first gear for too long -- eventually the engine
blows out.
He said this may be why developing a vaccine has
proven so tricky. "Most vaccines prime the
adaptive response to recognize the invader, but
it's hard for this to work if the virus triggers
other mechanisms that weaken the adaptive
response."
HIV takes its membrane from the cell that it
infects, the researchers explained in their
study. This membrane contains cholesterol, which
helps keep it fluid and enables it to interact
with particular types of cell.
Normally, a subset of immune cells called
plasmacytoid dendritic cells (pDCs) recognize
HIV quickly and react by producing signaling
molecules called interferons. These signals
activate various processes which are initially
helpful, but which damage the immune system if
switched on for too long.
Working with scientists Johns Hopkins
University, the University of Milan and
Innsbruck University, Boasso's team found that
if cholesterol is removed from HIV's envelope,
it can no longer activate pDCs. As a result, T
cells, which orchestrate the adaptive response,
can fight the virus more effectively.
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