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Monday, 9 October, 2000, 22:20 GMT 23:20 UK
Step forward in stem cell control
Stem cell graphic BBC
Scientists have reached another milestone in their quest to create "spare part" tissues for transplant using human embryonic stem cells.

Researchers in the US and Israel have discovered a way to direct the early development of these special cells in the lab.

The international team used eight different growth factors - body chemicals that influence cell development - to encourage embryonic stem cells into becoming the three primary cell types known as ectoderm, endoderm and mesoderm.

It is these cell lines that go on to form the different tissues in the body, including muscle, bone, skin and nerves.

Immune system

Scientists think that if they can obtain full control of this process they will be able to "grow up" replacement tissues to treat a range of degenerative diseases in which specific cell types have become damaged.

If the technology is married to that of cloning, it may even be possible to create perfect-match tissue that is not rejected by the patient's immune system.

The scientists, from the Hebrew University, Jerusalem, and the Howard Hughes Medical Institute, at Harvard University, Cambridge, Massachusetts, report their findings in the Proceedings of the National Academy of Sciences.

In one experiment, growth factors were used to encourage human embryonic stem cells to develop mainly into a cell type known as mesodermal, which eventually forms muscle, blood and skeleton.

Inhibiting development

In another experiment, the stem cells were directed into becoming mesodermal or ectodermal cells. Ectodermal cells include those of the skin and brain.

A third category of growth factors permitted stem cells to grow into any of the three basic layers of cells: mesodermal, ectodermal or endodermal. Endodermal cells include those of the liver and pancreas.

The team found that most of the growth factors worked by inhibiting, rather than promoting, certain kinds of cell development.

This suggested that control of embryonic stem cell development might also be achieved by using compounds that block the action of growth factors, they said.

Ethical debate

The authors wrote: "These results represent an initial step toward achieving fully directed cell differentiation and open the way to combining growth factor incubation with selection methods."

The use of human embryonic stem cells in research has become a highly controversial topic. The cells are sourced from unwanted IVF embryos or aborted foetuses.

This has prompted a major ethical debate which has intensified because of the desire of scientists to also use cloning technology in their studies.

In the UK, an expert panel spent almost a year examining the moral and technical issues relating to stem cells and their use in so-called therapeutic cloning and recommended research should be permitted.

Politicians will have the final say.

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