BLOOD tests could soon pick up the human form of mad cow disease鈥攂efore
any symptoms appear. Two groups of researchers have developed separate ways to
detect low levels of the prion which causes variant CJD. The startling advances
could also lead to animal tests for BSE and scrapie and ways to screen blood
donated for transfusions.
Small amounts of the prion that causes vCJD are thought to circulate in the
blood, but current tests cannot detect it.
Now Claudio Soto and his colleagues from the Serono Pharmaceutical Research
Institute in Geneva have found a way to amplify the offending prion. They do
this by using small amounts of infectious protein to convert much larger amounts
of the normal form.
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Until now, no one had managed to do this in the lab because newly converted
prions form unreactive clumps. Soto uses sound waves to break up the clumps
after each round of conversion. When brain extracts from scrapie-infected
hamsters were passed through five cycles of the treatment, the amount of
converted prion was amplified over 30 times (Nature, vol 411, p 810).
They also amplified prions from human brain samples, but have still to publish
their results. 鈥淲e are confident that with our method we鈥檒l be able to detect it
[in blood],鈥� Soto says.
A team at Oxford University and the Institute for Animal Health in Berkshire
is also blazing a trail to a blood test. Oxford pathologist William James is
using artificial strands of RNA called aptamers, which stick to molecules of
particular shapes. From an initial pool of 1014 molecules, James鈥檚 team
selected an RNA strand that is 100 times better at binding to infectious prions
than to the normal protein. 鈥淚t鈥檚 the first time that anyone has found something
that fits the disease form better than the normal form,鈥� James says.
James鈥檚 team, together with American firm VITEX in Watertown, Massachusetts,
hopes to produce a blood-testing kit that could screen donated blood samples to
make sure they are safe, diagnose people with vCJD before symptoms arise, or
screen livestock so that infectious animals can be removed from the food
chain.
VITEX also plans to remove prions from infected blood samples by this method.
Passing blood through huge columns containing immobilised aptamers would mop up
any infectious molecules on the way through.
This could lead to a treatment for vCJD. 鈥淲e know that aptamers inhibit the
conversion process in vitro,鈥� says James. He believes it may be possible to
design small molecules to do the same thing in the body. These could be used as
drugs to slow down or halt the progression of the disease.