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Well-Known Member
By Rick Weiss
Washington Post Staff Writer
Thursday, August 14, 2003; Page A04
Scientists in China have, for the first time, used cloning techniques to
create hybrid embryos that contain a mix of DNA from both humans
and rabbits, according to a report in a scientific journal that has
reignited the smoldering ethics debate over cloning research.
More than 100 of the hybrids, made by fusing
human skin cells with rabbit eggs, were allowed
to develop in laboratory dishes for several days
before the scientists destroyed them to retrieve
so-called embryonic stem cells from their
interiors. Although scientists in Massachusetts
had previously mixed human cells and cow
eggs in a similar attempt to make hybrid
embryos as a source of stem cells, those
experiments were not successful.
Researchers said yesterday they were hopeful
that the rabbit work would lead to a new and
plentiful source of embryonic stem cells for
research and, eventually, for medical use. But
theologians and others decried the work as
unethical.
Some wondered aloud what, exactly, such a
creature would be if it were transferred to a
womb to develop to term.
The vast majority of the DNA in the embryos
is human, with a small percentage of genetic
material -- called mitochondrial DNA --
contributed by the rabbit egg. No one knows if
such an embryo could develop into a viable
fetus, though some experiments with other
species suggest it would not.
Congress has been mulling legislation for years
that would outlaw certain human cloning experiments, with some
opposed to any creation of cloned embryos for research and others
sympathetic to research uses as long as the embryos are not allowed to
grow into cloned babies. No law has been passed, however, in part
because of researchers' warnings that the proposed restrictions are so
far-reaching that they would hobble development of new medical
treatments.
The new work, led by Hui Zhen Sheng of Shanghai Second Medical
University, appears in the latest issue of Cell Research and was
highlighted in a news report in the journal Nature. Cell Research is a
peer-reviewed -- if little-known in the United States -- bimonthly
scientific journal affiliated with the Shanghai Institute of Cell Biology
and the Chinese Academy of Sciences. Some researchers yesterday
said they were frustrated by the lack of details in the paper.
The team said it retrieved foreskin tissue from two 5-year-old boys and
two men, and facial tissue from a 60-year-old woman, as a source of
skin cells. They fused those cells with New Zealand rabbit eggs from
which the vast majority of rabbit DNA had been removed. More than
400 of those new, fused entities grew into early embryos, and more
than 100 survived to the blastocyst stage -- the point at which coveted
stem cells begin to form.
The approach could help scientists wishing to mass-produce human
embryos as sources of human embryonic stem cells. Stem cells can
morph into all kinds of tissues and may be able to reverse the effects of
various degenerative diseases. But to make cloned embryos, scientists
need both normal body cells -- such as skin cells -- and egg cells, which
have the unique capacity to "reprogram" the genes in body cells and
make them behave as though they were embryo cells.
Because human egg cells are difficult and costly to retrieve from
women's ovaries -- and because human egg retrieval poses risks to the
donors -- scientists have been wanting to know whether animal eggs
may serve as well. A major question has been whether the remnants of
mitochondrial DNA that typically remain in an animal egg would be
compatible with the nuclear DNA contributed by the human cell.
The new work suggests that the answer to that question is yes,
scientists said -- though with a number of caveats. Most important,
researchers said, the paper stops short of proving beyond a doubt that
the stem cells retrieved from the hybrid embryos are truly capable of
growing for long periods of time in lab dishes, and that they can turn
into every known kind of cell.
Even so, said Douglas Melton, a Harvard University cell biologist and
cloning expert, the work is a big advance because it offers a new
system for exploring the mechanisms by which egg cells get adult cells
to act in embryonic ways. That could provide deep insights into human
development, wound healing and tissue regeneration.
He noted that although this is the first creation of a human "chimeric"
embryo -- a reference to the fabulous chimera of Greek mythology,
which had a lion's head, a goat's body and a serpent's tail -- it is not the
first time scientists have blended human cells into lab animals. Some
mice, for example, have been endowed with human brain cells or
portions of the human immune system for research.
The Chinese work, Melton said, is "extremely interesting, and I hope
they pursue it."
R. Alta Charo, an associate dean of law and professor of bioethics at
the University of Wisconsin at Madison, noted that the work passed
muster with Chinese ethics authorities, who had demanded, among
other things, that the embryos not be allowed to grow more than 14
days.
"Short of putting one of these embryos into a woman's body for
development to term, I don't think this work harms anyone alive,"
Charo said.
She said the experiments should force opponents of cloning research to
identify more clearly than they have until now exactly where they
would draw the line against human embryo cloning -- in effect: How
human does an embryo have to be to have the moral standing these
advocates confer on embryos?
Richard Doerflinger, of the U.S. Conference of Catholic Bishops, said
he felt certain that the human-rabbit embryos were human enough to
deserve protections.
"I think because all the nuclear DNA is human," Doerflinger said,
"we'd consider this an organism of the human species."
http://www.washingtonpost.com/ac2/wp-dyn/A55911-2003Aug13?language=printer
