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8-Humans: First GE human embryonic stem cells produced

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TITLE:  Scientists Replace Stem Cell Genes
SOURCE: The Washington Post, USA, by Rick Weiss
DATE:   Feb 10, 2003

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Scientists Replace Stem Cell Genes

Scientists working with human embryonic stem cells have for the first
time successfully spliced out individual genes from the medically
promising but politically contentious cells and substituted different
genes in their place.

The work is a step toward the biomedical goal of being able to rebuild or
regenerate parts of the human body by transplanting either stem cells or
tissues grown from stem cells into patients, scientists said. Precise
genetic changes in those formative human cells might enhance their
therapeutic potential or make them more compatible with patients' immune

Some scientists suggested the success might someday make it unnecessary
to pursue "therapeutic cloning," in which cloned embryos would be created
as a source of therapeutic tissues that match the genetic signature of
the patient.

But the work could escalate concerns among those who fear that stem cell
technology will lead to the creation of "designer babies."

Applying genetic engineering techniques to humans is "defensible as long
as it's used to cure diseases, but we have to be aware that techniques
like these can be abused, too," said John Robertson, a bioethicist at the
University of Texas School of Law.

The new work, published in today's issue of the journal Nature
Biotechnology, resembles similar studies decades ago in mice. That was
when scientists discovered how to "knock out" and replace individual
genes in mouse embryo cells.

The technique, called homologous recombination, revolutionized molecular
and cellular biology.

By growing animals with those precise genetic changes and seeing what
went wrong as they developed, scientists could start to see what
individual genes did. They also were able to replace "broken" genes in
mouse embryos.

The work with human embryonic stem cells was done by University of
Wisconsin researcher James A. Thomson, the scientist who discovered the
cells in 1998, and his colleague Thomas P. Zwaka.

They used electrical charges and chemicals to make the cells' membranes
porous enough to allow the cells to take in customized genes. Under
proper conditions, the new genes find and replace their counterparts in
the cell DNA.

In one experiment, they knocked out a gene that in humans causes Lesch-
Nyhan syndrome, a rare and fatal genetic disease. They said they hope
such work can shed light on the molecular underpinnings of the disease
and perhaps someday lead to cures. But others noted that just because a
broken cell can be fixed does not mean a cure will be forthcoming soon.

Despite years of efforts, Johns Hopkins University stem cell researcher
John Gearhart said, scientists have not been able to make lines of mouse
stem cells that are compatible in all mice.

He suggested that therapeutic cloning research, controversial though it
is, will remain important in the search for treatments for human disease.