Scientists find way to program key cells

WASHINGTON (Reuters) -- Scientists said on Monday they had taken a first step towards being able to control stem cells -- master cells that have the ability to become any kind of cell in the body.

Doctors hope one day these cells can be directed to grow into organs or tissues for transplant, used to test drugs and potentially toxic chemicals, and studied to give insights into basic human biology.

But first they have to learn how to control them.

"One obvious goal is to control the differentiation of human embryonic stem cells," Dr. Douglas Melton of the Howard Hughes Medical Institute at Harvard University and colleagues in Israel wrote in their report, published in the Proceedings of the National Academy of Sciences.

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Genetic tinkering

If this differentiation could be directed, the cells could be used as a source of brain cells for Parkinson's patients, pancreatic islet cells for diabetes patients, heart cells for heart patients and so on.

The researchers ran a series of tests on the obvious candidates for directing stem cell development -- chemicals known as growth factors, which influence cell growth.

They tested them on what many scientists consider the most promising form of stem cells -- embryonic stem cells. Taken from very early embryos, only a few cells in size, embryonic stem cells have the potential to become any kind of cell in the body at all.

Embryonic stem cells also seem to have the ability to survive indefinitely, making them extremely valuable to laboratory scientists.

The researchers tried out eight different growth factors, including basic fibroblast growth factor, transforming growth factor and epidermal growth factor.

The stem cells had receptors, or molecular doorways, for all of the growth factors, which suggests they would be open to the influence of the compounds.

"Each growth factor has a unique effect," the researchers wrote.

When exposed to one group of growth factors, the stem cells tended to develop into muscle cells, which belong to a family of cell type known as mesodermal cells. When exposed to a second class of factors, the stem cells became mesodermal or ectodermal cells, which include brain, skin, and adrenal tissues.

The third category of growth factors seemed to cause stem cells to develop into any of the three cell types.

No one factor caused cells to become a specific cell type, such as a neuron or a heart cell, so the researchers said they still have a great deal of work to do.

They said the growth factors actually tended to inhibit the cells' development in certain directions, rather than encourage them along a certain road. Therefore, perhaps using specific known inhibitors might work better.

The use of embryonic stem cells is controversial. Opponents say using any cells from a human embryo is unethical and immoral, even if -- as is the case in the United States -- the embryos are left over from attempts at making test-tube babies for infertile couples and were destined to be thrown away.

The U.S. government has determined that it is all right for federally funded researchers to use such cells if they are not directly involved in deriving them from embryos. Privately funded researchers can do as they please.

Opponents of embryonic stem cell research advocate using adult stem cells, which are found circulating in everyone's bodies. But scientists argue that adult stem cells are hard to find and isolate, hard to control and may not be as useful as embryonic stem cells.

Copyright 2000 Reuters. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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