NEW YORK (AP) — For the first time,
researchers have used the cloning technique that produced Dolly the
sheep to create healthy monkeys, bringing science an important step
closer to being able to do the same with humans.
Since Dolly's birth in 1996, scientists have
cloned nearly two dozen kinds of mammals, including dogs, cats,
pigs, cows and polo ponies, and have also created human embryos
with this method. But until now, they have been unable to make
babies this way in primates, the category that includes monkeys,
apes and people.
"The barrier of cloning primate species is now
overcome," declared Muming Poo of the Chinese Academy of Sciences
in Shanghai.
In a paper released Wednesday by the journal
Cell, he and his colleagues announced that they successfully
created two macaques. The female baby monkeys, about 7 and 8 weeks
old, are named Zhong Zhong and Hua Hua.
"It's been a long road," said one scientist
who tried and failed to make monkeys and was not involved in the
new research, Shoukhrat Mitalipov of Oregon Health & Science
University. "Finally, they did it."
Poo said the feat shows that the cloning of
humans is theoretically possible. But he said his team has no
intention of doing that. Mainstream scientists generally oppose
making human babies by cloning, and Poo said society would ban it
for ethical reasons.
Instead, he said, the goal is to create lots
of genetically identical monkeys for use in medical research, where
they would be particularly valuable because they are more like
humans than other lab animals such as mice or rats.
The process is still very inefficient — it
took 127 eggs to get the two babies — and so far it has succeeded
only by starting with a monkey fetus. The scientists failed to
produce healthy babies from an adult monkey, though they are still
trying and are awaiting the outcome of some pregnancies. Dolly
caused a sensation because she was the first mammal cloned from an
adult.
The procedure was technically challenging.
Essentially, the Chinese scientists removed the DNA-containing
nucleus from monkey eggs and replaced it with DNA from the monkey
fetus. These reconstituted eggs grew and divided, finally becoming
an early embryo, which was then placed into female monkeys to grow
to birth.
The scientists implanted 79 embryos to produce
the two babies. Still, the approach succeeded where others had
failed. Poo said that was because of improvements in lab techniques
and because researchers added two substances that helped reprogram
the DNA from the fetus. That let the DNA abandon its job in the
fetus, which involves things like helping to make collagen, and
take on the new task of creating an entire monkey.
The Chinese researchers said cloning of fetal
cells could be combined with gene editing techniques to produce
large numbers of monkeys with certain genetic defects that cause
disease in people. The animals could then be used to study such
diseases and test treatments. The researchers said their initial
targets will be Alzheimer's and Parkinson's.
Mitalipov, noting the Chinese failed to
produce healthy babies from adult cells, said he suspects attempts
to clone babies from a human adult would also fail. "I don't think
it would be advisable to anyone to even think about it," he
said.
Jose Cibelli, a scientist at Michigan State
University, said it might be technically possible someday, but
"criminal" to try now because of the suffering caused by the many
lost pregnancies the process entails.
If the procedure became efficient enough in
monkeys, he said, society could face "a big ethical dilemma" over
whether to adapt it for humans. The key step of transferring DNA
might be combined with gene editing to correct genetic disorders in
embryos, allowing healthy babies to be born, he said.
Of course, the familiar image of human cloning
involves making a copy of someone already born. That might be
possible someday, but "I don't think it should be pursued," said
researcher Dieter Egli of Columbia University. "I can't think of a
strong benefit."
Henry Greely, a Stanford University law
professor who specializes in the implications of biomedical
technologies, said the strongest argument he can think of would be
the desire of grieving parents to produce a genetic duplicate of a
dead child. But he doubts that's a compelling enough reason to
undertake the extensive and costly effort needed to get such a
procedure approved, at least for "decades and decades."
Marcy Darnovsky, executive director of the
Center for Genetics and Society in Berkeley, California, called it
unethical to subject that new child to "the psychological and
emotional risks of living under the shadow of its genetic
predecessor." Human cloning could also require many women to donate
eggs and to serve as surrogates, she said.
At the moment, because of safety concerns,
federal regulators in the U.S. would not allow making a human baby
by cloning, and international scientific groups also oppose it,
said biomedical ethics expert Insoo Hyun of Case Western Reserve
University in Cleveland.
People for the Ethical Treatment of Animals
condemned the monkey-cloning experiments.
"Cloning is a horror show: a waste of lives,
time and money — and the suffering that such experiments cause is
unimaginable," PETA Senior Vice President Kathy Guillermo said in a
statement.
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