http://www.boston.com/dailyglobe2/233/science/What_can_stem_cells_really_do_+.shtml
By Raja Mishra, Globe Staff, 8/21/2001
READING - Inside the Fertility Center
of New England in Reading are several waist-high freezers. Inside the freezers
are hundreds of pinpoint-thin straws. And in the straws are human embryos,
each smaller than the period at the end of this sentence.
Some will be implanted in women.
Most end up in the trash. The ongoing national debate on stem cells begins
there.
''See these little gray circles -
that's them,'' said lab supervisor May Fung as she held microscope-enhanced
photos of the embryos, whose rough textures resemble moon rocks.
Fung goes about her task - helping
impregnate women - quietly, shuffling from freezer to microscope to incubator.
But the debate has been anything but quiet, especially since President
Bush earlier this month allowed limited taxpayer funds to support research
on embryonic stem cells. Supporters claim the new field has boundless potential
for medicine. Opponents equate it with murder.
Much of the public is confused about
this quite new sliver of biology - and scientists have not always helped
clarify the issue, mingling optimistic predictions with firm facts. What
follows is a primer on stem cells.
What is a stem cell?
Every person begins as a single cell
- the fertilized egg - and grows into an enormously complex machine, a
unified network of billions and billions of cells. Stem cells are behind
this transformation.
Within that initial cell is all the
information needed to create a person. Hours after fertilization, the cell
divides. Then it divides again and again. Within five days, there is a
cluster of about 150 cells called the blastocyst. In the inner core of
the blastocyst are embryonic stem cells.
As time passes, they will receive
genetic signals to change. Some will become bone cells. Some heart cells.
Others will form the cells of the brain.The body has more than 200 types
of cells. The stem cells in the blastocyst are called ''pluripotent'' -
they can become any one of those types.
And as long as they remain stem cells,
they can divide indefinitely. Once they start to specialize, they cannot.
Scientists extract the mass of stem
cells from the blastocyst for research. They store them in such a way that
they do not specialize. Instead, they keep dividing, producing a mass of
stem cells with the same DNA, called a ''line.'' As long as the line continues
to reproduce, many researchers can draw from this supply for their experiments.
But, in the process of extracting
the cells, the blastocyst is destroyed.
Is a blastocyst a person?
Many believe that life begins the
moment the egg and sperm fuse to form the first cell. At this point, they
believe, the cell is given a soul, otherwise known as ''ensoulment.''
By this reasoning, the blastocyst
is morally just like a person, endowed with the same basic human rights.
To destroy the blastocyst is murder, in their view. And stem cell research,
whatever benefit it may have, comes at the expense of this slaughter, they
feel.
Supporters of embryonic stem cell
research fall into two camps. There are those who believe that an embryo
should not be considered a human life until well into a pregnancy. Some
say after three months; others after six. A smaller group believes life
starts at birth.
There are also stem cell researchers
who believe ensoulment occurs quite early, but later than the blastocyst
stage. They point out that a blastcyst still has potential to become twins.
How, then, can it have a soul? They believe as soon as the stem cells start
on their missions and the faint signs of a person appear, then ensoulment
occurs. In this camp, many believe three weeks into a pregnancy, when the
spine emerges, is the magic threshold.
How can stem cells cure disease?
Most major diseases involve the destruction
of cells - Parkinson's disease, diabetes, liver disease, cancer, spinal
injuries, burns, multiple sclerosis and Alzheimer's disease, to name a
few.
Scientists theorize they can coax
stem cells to become whatever new cells a patient needs. A Parkinson's
victim can get new brain cells. A burn victim, new skin cells. And so on.
Does this really work?
We know plenty about embryonic stem
cells - in mice.
In 1981, scientists first successfully
removed mouse stem cells and stored them in a lab. It wasn't until 1998
that this was repeated with human cells.
In mice, scientists have used the
cells to cure paralysis, diabetes and brain disease. This has generated
enormous hope among researchers. But mouse cures do not mean human cures.
Researchers have had limited success
in coaxing human stem cells to become pancreatic cells, cardiac cells and
blood cells.
How close are the answers?
In reality, we know surprisingly
little about stem cells. Fundamental questions remain: What is the mechanism
by which they specialize? How can we control what they become? How can
we deliver them to patients with precision?
Even if stem cell research takes
off in the coming years, researchers estimate it will be at least five
years before the first clinical tests begin. And many of these will fail.
Can scientists use the existing stem
cells?
Bush said in his televised address
that only stem cell lines already in existence as of three weeks ago could
be used for taxpayer-funded research. No new embryos could be destroyed
for federal research.
Bush said that 60 or so stem cell
lines exist around the world. But that doesn't mean researchers will have
access to all 60 lines.
Some researchers believe the true
number is far lower. The ownership of many of the lines are shrouded in
secrecy. And researchers suspect that many of the lines Bush is counting
on are unusable. The Wisconsin lab that harvested the first five lines
of embryonic stem cells has acknowledged that two of those lines cannot
be used for research.
What happened?
To keep stem cells from specializing
requires a carefully controlled lab environment, all the more difficult
because scientists don't know exactly what makes these cells specialize.
Sometimes the stem cells researchers cultivate spontaneously start specializing.
Their ability to multiply then ends, and the line dies out.
The other problem is a common one
in labs - contamination. A infectious organism can render a line scientifically
useless. And sometimes lines die out for reasons unknown.
What about adult stem cells?
The blastocyst is not the only place
in which stem cells are found. In fact, from conception to death, stem
cells are present.
Stem cells with potential to become
bone marrow cells are found in umbilical cord blood, which is usually discarded
after birth. Already, these cells are used to treat leukemia victims and
other severely ill patients whose immune systems are crippled by chemotherapy.
Many types of stem cells exist in
adults. Embryonic stem cell opponents have seized on this, stating that
embryos do not have to be destroyed to get the cells.
Scientists have identified adult
stem cells in bone marrow, the brain, blood vessels, bone, skin, eyes,
teeth, liver and several other tissue types. But they are very difficult
to find and isolate.
Adult and embryonic stem cells differ
in fundamental ways. Embryonic stem cells can multiply indefinitely, enough
to potentially treat disease. Their adult counterparts proliferate less,
limiting their supply.
Adult cells also have a more limited
ability to specialize. Embryonic cells can become any of the 200 or so
body tissues. But adult cells appear limited by their environment. For
instance, adult stem cells in the blood can transform only into cell types
related to blood. Scientists have had limited success in coaxing adult
stem cells to transform into other types of cells, with skin stem cells
appearing to have great promise. But much of the work has been done in
mice.
Some have proposed that adult stem
cells can be coaxed ''backward'' into embryonic stem cells. This has not
been proved.
There remains much research to be
done into both adult and embryonic stem cells. Most scientists are uncertain
what they will find.
Does the Bush decision mean that
no embryos will be destroyed?
No. Bush's decision did not outlaw
any stem-cell work. He simply declared that no federal research money could
go to scientists who either create or use fresh lines of embryonic stem
cells.
And since the advent of test-tube
fertilization in the 1980s, modern fertility science has been creating
unneeded extra embryos.
On a recent morning, Fung at the
Reading fertility clinic prepared for the moment of truth. A woman had
come in for implantation. Earlier, seven of her embryos were frozen. Then
they were exposed to her husband's semen. They were placed in an incubator
that mimics the conditions inside a woman and, within days, three appeared
to develop promisingly.
The team decided to implant two.
This would increase the chances that one would take. But implanting all
three might result in a multiple pregnancy, which the fertility center
discourages.
The woman lied on the operating table
as a team of embryologists brought the precious cargo to the implantation
doctor. Later, the woman would throw the leftover embryos in the trash.
Until the stem cell debate erupted
recently, this simple act occurred thousands of times a year, mostly unnoticed.
For more information on stem cells,
visit:
http://www.nih.gov/news/stemcell/index.htm
http://www.news.wisc.edu/
http://www.stemcellresearch.org.
This story ran on page C1 of the
Boston Globe on 8/21/2001.
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