by
Sylvia Pagan Westphal, Boston
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.
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.
Ethical dilemma: Why most researchers insist embryonic stem cell studies must continue
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.
"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."
Remarkable findings
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.
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."
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.
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.
Indefinite growth
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.
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.
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 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.
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.
Fundamental questions
Meanwhile, there are some fundamental questions that must be answered, experts say. One is whether MAPCs really form
functioning cells.
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.
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.
"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.
19:00 23 January 02
New Scientist
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