Newsday
Cell Versatility: How It May Cure Diseases
by  Earl Lane
Washington Bureau

Washington  --  Human embryonic stem cells, first isolated by
researchers in 1998, hold great medical promise but also have
been the focus from the outset of a contentious political and
ethical debate.

Such cells, obtained from spare embryos slated to be discarded
at fertility clinics, could be used to create custom-designed cells
for use in medical treatment  -- insulin producing cells to cure
diabetes, muscle cells for implant in diseased hearts, brain cells
to treat Parkinson's and Alzheimer's diseases.

Scientists are excited about embryonic stem cells because
of their versatility. Scientists have known that even adults
harbor stem cells in bone marrow and elsewhere that are
capable of replenishing vital tissues. Liver stem cells give rise
to more liver cells, for example. Recent research suggests that
even adult stem cells may be able to develop into more diverse
kinds of tissue than previously thought.

But it is the embryonic stem cells that are considered to be
truly remarkable, able to proliferate indefinitely once isolated
and potentially to turn into any of the dozens of specialized
types of cells  -- skin, hair, muscle, kidney  --  that make up the
human body.

To understand what such cells are, and are not, consider first
what happens when a sperm fertilizes an egg. It creates a single
cell capable of forming an entire organism through many
successive cycles of cell division and specialization.

In the first hours after fertilization, as the egg divides into two
cells and then four, each of those early cells continues to be
non-specialized and "totipotent,” according to a National Institutes
of Health primer on stem cells.

But after about five days, and additional cycles of division, the
cells form a hollow sphere, called a blastocyst, that is ready for
implant on the uterine wall. The outer layer of the sphere will go
on to form the placenta and other tissues, such as the umbilical
cord, needed for fetal development in the womb. The inner cluster
of cells will go on to form virtually every type of cell found in the
human body.

In November 1998, James Thomson and his colleagues at the
University of Wisconsin at Madison reported that they were
able to extract inner cells from blastocysts, grow them in a
culture medium and isolate single cells that then continued
dividing indefinitely while retaining the potential to grow into
a wide variety of specialized cells.

At the same time, Dr. John Gearhart of Johns Hopkins University
in Baltimoreand his colleagues reported isolating a source
of similarly adaptable stem cells from human fetal tissue.

Scientists note that embryonic stem cells, drawn from the inner
mass of the blastocyst, are not the equivalent of embryos.
If implanted in a womb, they will not grow into a baby because
they do not have the potential to make the placenta and other
specialized tissues needed for a successful pregnancy.

But opponents of embryonic stem cell research say it is unethical
to use such cells for medical studies, no matter how promising,
because they are obtained initially from the destruction of surplus
embryos which they regard as sanctified human life.

Since 1995, Congress has banned federal funding of research in
which a human embryo is destroyed or injured. Thomson's research
was privately financed, and a privately financed spinoff from the
University of Wisconsin Medical School has been offering
embryonic stem cell lines for sale to other researchers. Such
privately financed stem cell research can continue.

But experts say a federal role in funding of embryonic stem cell
research would bring more investigators into the field, stimulate
more open exchange of ideas and data and provide more oversight
over developments. The Clinton administration proposed to finesse
the funding issue by continuing to ban use of federal money to
create stem cell lines derived from surplus embryos. But it proposed
allowing federally funded researchers to study and use embryonic
stem cell lines that had been created through private funding and
then made more widely available for publicly funded research.

Opponents of using embryonic stem cells cite the promising
research on the potential of stem cells derived from tissues of
fully grown adults, such as those in the bone marrow that
replenish blood cells throughout a person's life. Animal research
suggests such adult stem cells, previously thought to be
committed to developing only certain types of specialized cells,
may be more versatile. Studies in rats suggest that stem cells
in the bone marrow can produce liver cells, for example. But
scientists say it is by no means clear that various types of adult
stem cells will ever have as much adaptability as those derived
from early embryos.

As one option, the Bush administration reportedly is considering
limiting federally funded researchers to using only the embryonic
stem cell lines that already have been established in the lab. But
scientists say the handful of cell lines already available is not
enough to fully explore the potential of embryonic stem cells,
particularly since studies in mice suggest there are subtle
differences between embryonic stem cell lines that must be
explored. They argue that dozens of stem cell lines must be
established if the research effort is to go forward.

SOURCE: Newsday
http://www.newsday.com/news/daily/cell710.htm

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