A stem cell has been found in adults that can turn into any tissue in the body. 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.

If it works, there will be no need to clone people in order to get matching stem cells from the resulting embryos. ?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.? The cells were discovered in the bone marrow of adults by Catherine Verfaillie at the University of Minnesota. The cells are called multipotent adult progenitor cells (MAPCs). ?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 is the first to carry out the experiments needed to back up the claim that these adult stem cells are as versatile as embryonic cells.

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, were 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 bone marrow samples. The cells seem to grow indefinitely in culture, just like stem cells from embryos. Some cell lines have been growing for almost two years and have kept their characteristics, with no signs of aging. Given the right conditions, MAPCs can turn into muscle, cartilage, bone, liver and different types of neurons and brain cells.

Verfaillie?s group placed single MAPCs from mice into very early mouse embryos, when they were just a ball of cells. Analyses of mice born after the experiment revealed that a single MAPC contributed to all the body?s tissues.

MAPCs have many of the properties of embryonic stem cells (ESCs), but they are not identical. Unlike ESCs, they do not form cancerous masses if you inject them into adults. One question that needs to be answered is whether MAPCs form functioning cells. Stem cells may express markers characteristic of many different cell types, says Freda Miller of McGill University. But detecting markers for neural tissue, for example, doesn?t prove that a stem cell has become a working neuron.

If MAPCs can replace ESCs, the ethical debate about using embryonic stem cells to save the lives of people who are already alive will be over. The debate about whether to clone individuals in order to produce stem cells for their future use will end as well. ?The data looks very good, it?s very hard to find any flaws,? says Lemischka.

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