ARE cloned animals normal and healthy? The claims and counterclaims that
followed a Japanese report on mouse clones last week show that experts are as
divided as ever on this crucial issue.
“Human cloning advocates are taking this superficial evidence and saying
clones are normal, we’re ready to go ahead,” says Rudolf Jaenisch, a mouse
cloner at Massachusetts Institute of Technology. “It’s a real disservice to the
ھ.”
But Robert Lanza of the Massachusetts-based company Advanced Cell Technology
(ACT) thinks such caution is delaying medical and agricultural advances that
could save millions of lives. “Claims that these data are superficial are just
irresponsible,” he says.
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The Japanese scientists reported that some of the problems with mouse clones
found by Jaenisch and others only occur in animals cloned from embryonic stem
cells, rather than normal or somatic cells (Science, vol 295, p 297).
“This work really vindicates us,” Lanza says. “There’s a misconception out there
that clones have two heads and are all defective. Recent reports should add some
balance back.”
But Jaenisch points out that the Japanese findings only focus on the
survivors, as do most reports claiming clones are healthy. The placentas of the
Japanese mouse clones showed obvious gene malfunctions, he says, and less than 3
per cent of the implanted embryos survived to term. “There may be some other
gene regulation abnormalities during the development of somatic clones,” admits
Fumitoshi Ishino of the Tokyo Institute of Technology, a team member.
And there’s more bad news for cloners. Last week Dolly’s creator, Ian Wilmut
of the Roslin Institute near Edinburgh, announced that the most famous clone of
all has premature arthritis, although it is hard to say whether the technology
that spawned her is to blame.
Wilmut also points out that while ACT has recently produced two dozen
apparently healthy cloned cattle (Science, vol 294, p 1893), the
overall success rate was low. Lanza’s team reported a 73 per cent miscarriage
rate, with a fifth of the clones that survived to term dying soon after
birth.
Part of the problem is knowing when an animal really is healthy. Results from
Jaenisch’s team suggest that ordinary tests might not be sensitive enough to
pick up any subtle genetic defects in the surviving clones. “We need many more
observations and should be cautious about any application,” says Wilmut. Given
the risk of animals suffering, he is not yet convinced that the results justify
the use of cloning to create cattle merely for dairy production, as ACT
plans.
But whichever camp they’re in, nearly all cloners agree on one thing. Given
that the majority of cloned embryos still die during pregnancy or soon after, it
is far too soon to consider creating cloned children. “The data doesn’t at all
justify human reproductive cloning,” says Lanza.
