To many, it is one of the most exciting developments in modern
medicine. To others, it is an ethically unacceptable practice. The
conflict of beliefs has always meant that the use of stem cells from
human embryos to treat a range of debilitating and incurable disorders
has remained controversial.

Now scientists have made a breakthrough that could offer a medical
solution without the controversy, by undermining the case for using
embryonic stem cells at all.

New evidence suggests that cells derived from a patient's own bone
marrow may regenerate damaged nerves in the brain, a task once
considered impossible. It is an important breakthrough in the
treatment of illnesses such as Parkinson's, multiple sclerosis and
Alzheimer's disease. brain INJURY

The work has potential to challenge embryonic stem cell research
because these stem cells have come not from embryos but from the bone
marrow of a mature adult.

It is the latest evidence to emerge from several lines of research
that have pointed to the power of adult stem cells to "reinvent"
themselves rather than to be narrowly predestined to develop into just
one type of body tissue.

The findings, published in the journal Cell Transplantation, will
reopen the debate over the ethics of experimenting on stem cells taken
from human embryos given that adult stem cells appear to possess the
same all-round ability to develop into specialised tissues.
Anti-abortion groups and the Vatican have fiercely opposed the use of
human embryos in stem cell research.

Stem cells have become one of the most exciting areas of medical
research because of their ability to be cultured in the laboratory and
stimulated with chemicals to become any one of the scores of
specialised tissues of the body.

Scientists envisage a day when stem cells can be used to repair
damaged organs rather than using potentially toxic drugs, a transplant
or palliative care for the terminally ill.

Several sources of stem cells have been identified, such as "spare"
IVF embryos less than 14 days old or adult bone marrow that is
constantly regenerating to produce fresh blood cells. The question has
been whether adult stem cells are just as good as embryonic stem cells
in terms of "pluripotency" ­ the ability of a cell to become any
specialised cell of the body.

Work on animals shows the power of cultured embryonic stem cells to
develop into any tissue, but adult stem cells were traditionally
thought to be more fixed in terms of what they could become ­ bone
marrow should only develop into blood cells for instance. But the
latest research, led by Walter Low, professor of neurosurgery at the
University of Minnesota Medical School, shows bone marrow extracted
from adult mice can develop into fully functioning, specialised brain
cells.

Professor Low injected bone marrow cells from a mouse into early
embryos, which were implanted into other mice who gave birth to live
young. The offspring were found to have taken up the "foreign" bone
marrow stem cells and used them to make cells in all regions of the
brain.

The transplanted stem cells developed into nerve cells, which normally
conduct electrical impulses, glial cells, which provide support to the
nerve cells, and cells that produce the fatty myelin sheath around the
nerve cells, which is damaged in patients with multiple sclerosis.

Catherine Verfaillie, a colleague of Professor Low, said the bone
marrow stem cells developed into all the cells known to be implicated
in Parkinson's disease, Huntington's disease, ataxia and Alzheimer's
disease. "This tells us that these adult stem cells are capable of
becoming nerve cells that communicate with other nerve cells within
the brain and form proper neural circuits that permit the mice to
function normally," Dr Verfaillie said.

A number of studies have already indicated that adult bone marrow
cells may have the ability to develop into non-blood tissue.
Scientists from the US National Institute of Neurological Diseases and
Stroke in Bethesda, Maryland, found for instance that post-mortem
tests on women who had received bone marrow transplants from men
possessed brain cells containing the male Y chromosome. The
implications were that male bone marrow stem cells had migrated to the
women's brains to become nerve cells, said Eva Mezey, who led the
study. "We have had trouble convincing some members of the scientific
community that this could happen," Dr Mezey said.

Opponents of the use of human embryos in stem cell research are likely
to use the findings to support their belief that there is no real need
to experiment with human embryos.

Josephine Quintavalle, a lawyer and campaigner, said that she would
use the latest work on adult cells to challenge whether scientists
needed to use human embryos at all. "Adult stem cells are infinitely
better than embryonic stem cells," she said. "The bias in the UK has
been to use embryonic stem cells simply because we have the most
permissive environment in the world for this sort of research."

Many British scientists and scientific organisations ­ such as the
Royal Society ­ believe research on both adult and embryonic stem
cells needs to be done in parallel before any decisions are taken to
ban the latter.

A report on stem cells by a House of Lords committee concluded: "It is
unlikely that either adult stem cells or embryonic stem cells alone
will provide the basis for all stem cell-based therapies; it is
therefore necessary to keep both routes to therapy open to ensure
maximum medical benefit."

Professor Low said further work was needed to ensure that the adult
stem cells in his study were genuinely developing into specialised
brain cells rather than merely fusing with them.

Professor Austin Smith, of Edinburgh University, found evidence to
suggest that adult stem cells tended to fuse with other cells, which
could make them potentially cancerous.

"This suggests a need for caution with regard to the therapeutic use
of adult tissue stem cells. If they only make other tissues by fusing
with existing cells rather than producing new cells, their utility for
tissue repair and regenerative medicine will be greatly reduced,"
Professor Smith said.

"If nothing else, our study indicates that calls for a halt to
embryonic stem cell research are not scientifically justified," he
added.

Professor Low said his findings were unlikely to be the result of
adult stem cells fusing with existing cells ­ but he could not yet
rule it out.

Further research this year should establish beyond doubt whether adult
stem cells are truly capable of regenerating damaged brains, he said.
Until then, he added, further work on embryonic stem cells and adult
bone marrow cells was still necessary to compare the remarkable
attributes of both types of cell