The advance, described online in the journal Cell Stem Cell, is
the first time researchers have achieved "therapeutic cloning" of
adults. Technically called somatic-cell nuclear transfer,
therapeutic cloning means producing embryonic cells genetically
identical to a donor, usually for the purpose of using those cells
to treat disease.
But nuclear transfer is also the first step in reproductive cloning,
or producing a genetic duplicate of someone — a technique that has
sparked controversy since the 1997 announcement that it was used to
create Dolly, the clone of a ewe. In 2005, the United Nations called
on countries to ban it, and the United States prohibits the use of
federal funds for either reproductive or therapeutic cloning.
The new study was funded by a foundation and the South Korean
If confirmed by other labs, it could prove significant because many
illnesses that might one day be treated with stem cells, such as
heart failure and vision loss, primarily affect adults.
Patient-specific stem cells would have to be created from older
cells, not infant or fetal ones. That now looks possible, though far
from easy: Out of 39 tries, the scientists created stem cells only
once for each donor.
Outside experts had different views of the study, which was led by
Young Gie Chung of the Research Institute for Stem Cell Research at
CHA Health Systems in Los Angeles.
Stem cell biologist George Daley of the Harvard Stem Cell Institute
called it "an incremental advance" and "not earth-shattering."
Reproductive biologist Shoukhrat Mitalipov of Oregon Health and
Science University, who developed the technique the CHA team
adapted, was more positive. "The advance here is showing that
(nuclear transfer) looks like it will work with people of all ages,"
he said in an interview.
A year ago, Mitalipov led the team that used nuclear transfer of
fetal and infant DNA to produce stem cells, the first time that had
been accomplished in humans of any age.
In therapeutic cloning, scientists use a zap of electricity to fuse
a grown cell, usually a skin cell, with an ovum whose own DNA has
been removed. The egg divides and multiplies, and within five or six
days it develops into an embryo shaped like a hollow sphere.
The interior cells are "pluripotent" stem cells, which have the
potential to develop into any kind of human cell.
If the embryo were implanted in a uterus, it could develop into a
clone of the DNA donor, which is how Dolly was created. "Without
regulations in place, such embryos could also be used for human
reproductive cloning, although this would be unsafe and grossly
unethical," said Dr Robert Lanza, chief scientist of
Massachusetts-based biotech Advanced Cell Technology and a co-author
of the new study.
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The goal is to grow these embryonic stem cells in lab dishes and
coax them to turn into specialized cells for therapeutic use against
an illness the DNA donor has, such as Parkinson's disease, heart
disease, multiple sclerosis or type-1 diabetes. Because the cells
are genetically identical to the donor's, they would not be rejected
by the immune system.
Despite more than 15 years of trying, scientists' single success at
producing human stem cells through this cloning technique came a
year ago. Mitalipov's team at Oregon had fused fetal and infant
cells with donated eggs whose DNA had been removed and got them to
develop into about 150-cell embryos.
One key to Mitalipov's success was letting the engineered eggs rest
for 30 minutes before zapping them to start dividing.
Chung and his colleagues waited two hours before triggering the egg
to start dividing, which Lanza believes was a key to their success:
"It gives you time for the massive amount of genetic reprogramming
required" to turn back the calendar on adult DNA so that it can
direct the development of an embryo, he said in an interview.
It worked: They generated two healthy embryos, one from each adult
donor, aged 35 and 75.
If each stem-cell line has to be created from scratch for each
patient, the low success and expected high costs means that "only a
few wealthy old men could do it," said Lanza. A big barrier to
producing patient-specific stem-cell lines for tens of millions of
people this way is that few women want to donate eggs, a sometimes
But it may not be necessary to make a unique cell line for each
patient. Many people have genetically similar immune systems, Lanza
said, so just "100 human embryonic stem cell lines would generate a
complete match for over half the (U.S.) population," he said.
(Reporting by Sharon Begley; editing by Douglas Royalty)
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