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 May
28th, 2002
In
"Body Building," Alan meets scientists working to repair injured
and diseased tissues by growing replacements for them in the
lab. This work depends on stem cells, special cells with the
potential to become any other type of cell - from a beating
heart cell to a conductive nerve cell to a light-sensitive
retina cell. So far, researchers have made a great deal of
progress working with animal cells and tissues. But growing
tissue for human patients requires human stem cells. Since
the most useful stem cells come from human embryos, stem cell
research has been at the center of a high-profile political
debate. What's at stake? FRONTIERS sorts it out.
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Limitless
Potential
Like
a child with a bright future, stem cells possess the ability
to become anything they want to be when they grow up. Every
cell in your body contains the same DNA blueprint, the genetic
operating instructions for your entire body. Yet cells from
your liver cannot perform the same tasks as the cells in your
heart, your eye or your skin. That's because as your cells
divide, they differentiate, becoming expert at specific tasks
as special genes "switch off" other genes. So, the genes for
how to be a heart cell are switched off in your liver cells,
while the genes for how to be a liver cell are switched off
in your heart cells.
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John McDonald works to repair spinal cord injuries using
stem cells to regenerate nerve cells.
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In stem cells, however, all the genes are still switched on.
The cell retains its original potential and is therefore said
to be "totipotent." In theory, scientists could coax such
a cell into becoming any of the body's 200-plus types of cells.
Researcher Douglas Melton, chair of molecular and cellular
biology at Harvard University, hopes to coax stem cells into
becoming the pancreatic cells that are missing in people with
juvenile diabetes, also known as Type 1 diabetes.
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In U.S. politics, few topics are more divisive than
the issue of when life begins and the treatment of human
embryos.
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"What
we would like to do is make the insulin-producing cells and
transplant them into diabetic persons," says Melton. "They
would no longer need to do blood checks or take insulin injections
and would thereby be cured of the disease."
This
type of therapy could mean the end of countless other diseases
such as Parkinson's, Alzheimer's and osteoporosis, to name
just a few. According to Melton, any disease caused by the
lack or destruction of one specific type of cell - pancreatic
cells in diabetes, neurons in Alzheimer's, bone cells in osteoporosis
- is a prime target for stem cell theapy.
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| Douglas
Melton works to "cure" diabetes by replacing
missing pancreas cells.
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James
A. Thompson of the University of Wisconsin, Madison, and his
colleagues managed to isolate and culture the first human
embryonic stem cells in 1997. Five years later, big scientific
questions remain. Melton and his colleagues, for instance,
don't yet know how to instruct the totipotent stem cells to
become the specific cells missing in a diabetic person, the
pancreatic beta cell.
"Normally, if you take an embryonic stem cell, it will make
all kinds of things, sort of willy-nilly," says Melton. "We're
trying to figure out how to control it, sort of get its attention
and tell it to become a [pancreatic] beta cell."
Further research would likely resolve this question. But Melton
and other U.S.-based scientists may never have the chance
to unlock the deeper mysteries of stem cells. That's because
stem cells are harvested from four-day-old human embryos,
which are destroyed in the process. Some of these embryos
were aborted fetuses, donated to science with informed consent.
Many were the discarded surplus embryos created for the purposes
of in vitro fertilization (IVF), also donated by parents with
informed consent. Other techniques make use of cutting-edge
cloning technology, requires harvesting human eggs from willing
participants. These circumstances push the research out of
the laboratory and into the political arena. And in U.S. politics,
few topics are more divisive than the issue of when life begins
and the treatment of human embryos. 
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