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- WASHINGTON (AP) - The Scottish scientists who cloned Dolly have now produced
Molly and Polly, two lambs cloned with a human gene so their milk will
contain a blood-clotting protein that can be extracted for use in treating
human hemophilia.
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- Molly and Polly were born in July and
Dr. Ian Wilmut of the Roslin Institute
- in Scotland said his team should know
by spring if the lambs' milk will
- contain useful quantifies of factor IX,
a protein that helps blood to clot.
-
- Wilmut and his team announced the cloning
achievement in a report in the
- journal Science to be published Friday.
-
- Experts say the creation of Molly and
Polly is the logical next step following
- last year's cloning of Dolly, the first
mammal cloned from an adult cell. The
- new work could prove that cloning is
an efficient way to create herds of cows
- or flocks of sheep that act as drug-making
factories.
-
- Wilmut said Molly and Polly were produced
with the same technique, called
- nuclear transfer, used to make Dolly,
but the original cell used to produce
- the lambs came from a sheep fetus instead
of from an adult animal.
-
- In nuclear transfer, scientists remove
the nucleus from an egg and replace it
- with the nucleus from another cell. The
egg is then placed into the uterus of
- a surrogate mother that gives birth to
an offspring that has only the genes of
- the original cell.
-
- In Dolly, the original cell came from
an adult ewe's udder.
-
- For Molly and Polly, Wilmut said his
team took the original cell from a
- 26-day-old sheep fetus. Into this cell,
the researchers inserted a human gene
- for factor IX, linked to a sheep gene
that increases milk production. They
- also put into the cell a marker, a gene
that causes resistance to an
- antibiotic.
-
- The manipulated cell was then nurtured
so it replicated to thousands of cells.
-
- Wilmut said the team then added an antibiotic
to identify those cells that
- included the antibiotic-resistant gene.
These cells were separated from the
- rest.
-
- A total of 425 of these gene-modified
cells were then placed into eggs that
- had had their nucleus removed. These
eggs were cultured for five to six days,
- growing to an early embryo stage.
-
- Wilmut said 62 embryos were then implanted
into surrogate mother sheep.
-
- From these, six lambs were born. Three
contained both the human gene and the
- marker gene. One of these lambs died,
leaving only Molly and Polly.
-
- ``The new lambs are identical to each
other and identical to the original
- fetus except for the new gene that we
introduced,'' said Wilmut.
-
- Wilmut said the lambs will be allowed
to grow normally and then given shots in
- the spring to induce lactation. This
will enable the researchers to test their
- milk for the human factor IX. He said
the lambs will mature by October and
- will be mated so they will produce lambs
in February of 1999.
-
- ``By then, we should have a good idea
of the milk volume and the yield of the
- useful protein from these animals,''
said Wilmut.
-
- The selective breeding of Molly and Polly
and their offspring could lead to a
- whole flock of sheep, all of which produce
human factor IX in their milk, he
- said.
-
- The lambs are the first animals cloned
to produce human drugs in their milk,
- but other techniques have been used to
create drug-making animals. Several
- companies are now testing cystic fibrosis
and heart attack drugs that come
- from the milk of genetically engineered
sheep or goats. These animals,
- however, were produced by injecting genes
into a fertilized egg and then
- implanting the egg in a surrogate mother,
a technique less efficient than the
- Roslin Institute's cloning. Only about
2 percent of such eggs grow to live
- animals and only a small percentage of
the survivors actually contain the
- target genes.
-
- Bruce Altrock, a researcher at Amgen
Inc., a leading U.S. pharmaceutical gene
- research lab, said producing Molly and
Polly ``is a significant development,''
- but that the Roslin researchers have
yet to prove the lambs will produce
- useful levels of drug in their milk.
-
- Dr. Robert Foote, an animal gene researcher
at Cornell University, said the
- Roslin scientists may have developed
a short-cut to making animals that
- produce drugs. Others have done it with
more expensive, less efficient
- techniques, he said, ``but this is the
first time it has been accomplished
- with cloning techniques.''
-
- He said, however, that the experiment's
value will be known only after the
- scientists prove Molly and Polly develop
as normal sheep and retain their
- ability to make useful amounts factor
IX in their milk.
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