- LONDON (Reuters) - Scientists
have figured out how a primate virus similar to HIV evades the immune system
in the first weeks of infection, a discovery they say could pave the way
for the development of a new AIDS vaccine. The HIV virus that causes AIDS
is particularly cunning because it replicates and mutates so quickly that
it can outsmart the body"s normal defense mechanisms.
- SIV, a monkey virus, is very similar to HIV but it infects
monkeys much more quickly than its human equivalent. Scientists at the
University of Wisconsin and the Wisconsin Regional Primate Research Center
in Madison have shown that SIV in monkeys evades a massive immune response
early in the infection by replicating and mutating into a new variant.
The new strain is not recognized by the killer T cells sent by the body"s
immune system to destroy the initial virus.
- "What we have discovered is that in the course of
a normal infection there is a hitherto unknown and unexpected massive killer
cell response in the acute phase of the infection," David Watkins,
one of the researchers, said in a telephone interview. "These results
show that infected individuals do make immune responses that the virus
cannot tolerate. The challenge will be to mimic these responses in an HIV
vaccine," he said. Although drugs have prolonged the lives of AIDS
patients, experts believe that the only way to fight the pandemic that
has killed 19 million people is with a vaccine. More than 70 AIDS vaccines
are in various stages of development and testing around the world.
- VACCINE TO PRODUCE A KILLER CELL RESPONSE
- The scientists, whose research was published in the science
journal Nature Wednesday, discovered that the change in the virus occurs
in the region of a viral protein called TAT, which could be an important
target for a new AIDS vaccine. "This is the first real direct evidence
that the important immune response that is controlling the virus is this
killer cell response," Watkins explained. The scientists are convinced
the immune response is there because several weeks after the macaque monkeys
had been injected with SIV they could not find any trace of the original
virus, only a mutated form.
- "We put in virus A but at four to eight weeks, after
the infection, the only replicating virus is virus B, implying that the
killer cells had actually got rid of the first virus," Watkins explained.
The researchers believe that the TAT-specific killer T-cells can get rid
of the virus in the monkeys and that a vaccine incorporating TAT could
induce a similar response in humans. "If vaccines can induce these
killer T cell responses before infection occurs, the opportunity for the
virus to subsequently escape from these immune responses would be greatly
reduced," Watkins said.
- The researchers have started to vaccinate monkeys with
regions of the TAT protein that they have shown are recognized by T cells.
"This should induce a massive killer T cell response at the onset
of infection," Watkins said. If the monkey trials are successful,
the scientists hope to begin human trials in the United States and Canada
by the end of the year.
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