- A stem cell has been found in adults that can turn into
every single tissue in the body. It might turn out to be the most important
cell ever discovered.
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- Until now, only stem cells from early embryos were thought
to have such properties. If the finding is confirmed, it will mean cells
from your own body could one day be turned into all sorts of perfectly
matched replacement tissues and even organs.
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- If so, there would be no need to resort to therapeutic
cloning - cloning people to get matching stem cells from the resulting
embryos. Nor would you have to genetically engineer embryonic stem cells
(ESCs) to create a "one cell fits all" line that does not trigger
immune rejection. The discovery of such versatile adult stem cells will
also fan the debate about whether embryonic stem cell research is justified.
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- "The work is very exciting," says Ihor Lemischka
of Princeton University. "They can differentiate into pretty much
everything that an embryonic stem cell can differentiate into."
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- Remarkable findings
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- The cells were found in the bone marrow of adults by
Catherine Verfaillie at the University of Minnesota. Extraordinary claims
require extraordinary proof, and though the team has so far published little,
a patent application seen by New Scientist shows the team has carried out
extensive experiments.
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- These confirm that the cells - dubbed multipotent adult
progenitor cells, or MAPCs - have the same potential as ESCs. "It's
very dramatic, the kinds of observations [Verfaillie] is reporting,"
says Irving Weissman of Stanford University. "The findings, if reproducible,
are remarkable."
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- At least two other labs claim to have found similar cells
in mice, and one biotech company, MorphoGen Pharmaceuticals of San Diego,
says it has found them in skin and muscle as well as human bone marrow.
But Verfaillie's team appears to be the first to carry out the key experiments
needed to back up the claim that these adult stem cells are as versatile
as ESCs.
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- Verfaillie extracted the MAPCs from the bone marrow of
mice, rats and humans in a series of stages. Cells that do not carry certain
surface markers, or do not grow under certain conditions, are gradually
eliminated, leaving a population rich in MAPCs. Verfaillie says her lab
has reliably isolated the cells from about 70 per cent of the 100 or so
human volunteers who donated marrow samples.
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- Indefinite growth
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- The cells seem to grow indefinitely in culture, like
ESCs. Some cell lines have been growing for almost two years and have kept
their characteristics, with no signs of ageing, she says.
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- Given the right conditions, MAPCs can turn into a myriad
of tissue types: muscle, cartilage, bone, liver and different types of
neurons and brain cells. Crucially, using a technique called retroviral
marking, Verfaillie has shown that the descendants of a single cell can
turn into all these different cell types - a key experiment in proving
that MAPCs are truly versatile.
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- Also, Verfaillie's group has done the tests that are
perhaps the gold standard in assessing a cell's plasticity. She placed
single MAPCs from humans and mice into very early mouse embryos, when they
are just a ball of cells. Analyses of mice born after the experiment reveal
that a single MAPC can contribute to all the body's tissues.
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- MAPCs have many of the properties of ESCs, but they are
not identical. Unlike ESCs, for example, they do not seem to form cancerous
masses if you inject them into adults. This would obviously be highly desirable
if confirmed. "The data looks very good, it's very hard to find any
flaws," says Lemischka. But it still has to be independently confirmed
by other groups, he adds.
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- Fundamental questions
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- Meanwhile, there are some fundamental questions that
must be answered, experts say. One is whether MAPCs really form functioning
cells.
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- Stem cells that differentiate may express markers characteristic
of many different cell types, says Freda Miller of McGill University. But
simply detecting markers for, say, neural tissue does not prove that a
stem cell really has become a working neuron.
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- Verfaillie's findings also raise questions about the
nature of stem cells. Her team thinks that MAPCs are rare cells present
in the bone marrow that can be fished out through a series of enriching
steps. But others think the selection process actually creates the MAPCs.
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- "I don't think there is 'a cell' that is lurking
there that can do this. I think that Catherine has found a way to produce
a cell that can behave this way," says Neil Theise of New York University
Medical School.
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- http://www.newscientist.com/news/news.jsp?id=ns99991826
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