Wednesday, 19 July, 2000, 18:04 GMT 19:04 UK
UK scientists have shown
how cells from transplanted bone marrow can turn into liver tissue.
The finding raises the
prospect of regenerating diseased livers. It may also pave the way for new
gene-therapy treatments. Researchers already knew that so-called stem cells in
bone marrow were responsible for generating blood cells. The new discovery that
stem cells can also turn into liver cells inside patients means that marrow stem
cells could eventually be used to repair damaged livers as well.
Stem cells are special
cells which have not yet become totally specialized to one role in the body. The
techniques developed to isolate these cells are regarded as being among the most
important scientific discoveries made in recent years.
Drug side effects
Professor Nick Wright, of
the Imperial Cancer Research Fund (ICRF), said: "We may be able to
stimulate liver regeneration using cells from the patient's own bone
marrow." And he added:
"This would be particularly useful for patients whose livers have been
damaged due to drug side effects, or through surgery to remove cancers that have
spread to the liver, and where there is insufficient functioning liver
remaining." Professor Wright's
team says that livers that are defective because of a faulty gene could one day
be repaired using stem cells that have been given a working copy of the gene.
But it is the prospect of
being able to generate new liver tissue using the patient's own stem cells that
really excites the scientists.
"We could avoid
problems with current liver transplants where the patient's body rejects the
foreign organ," said Professor Wright.
Patient's blood
The scientists conducted a
genetic analysis of liver cells from female patients who had received
bone-marrow transplants from male donors. Liver cells from male patients who had
been given whole livers from female donors were also examined. Using a DNA probe
that identifies male cells, the scientists found male liver cells in the female
patients, indicating that male bone-marrow stem cells had repopulated the liver.
Male liver cells were also found in a female-donated liver, showing that the
liver had accepted bone-marrow stem cells from the male recipient.
Dr Malcolm Alison, a
research pathologist based at Imperial College School of Medicine, said:
"We already knew from laboratory experiments that liver cells can be
derived from bone-marrow stem cells, but we had to show this happened in humans
as well.
"Adult stem cells
offer great promise in medicine as they may generate the full spectrum of cell
types needed to repair a damaged organ. Working with human blood-forming stem
cells is particularly attractive as they can be harvested rapidly from a
patient's own blood."
Ultimate flexibility
Using adult stem cells
will also avoid the ethical problems associated with even earlier cell types.
Embryonic stem cells can,
in theory, be made to develop into any cell type in the body - they would offer
the ultimate flexibility. But their only source is from aborted tissue or
discarded test-tube embryos, and several campaign groups have vowed to fight any
law change that would permit the widespread harvesting of stem cells in these
areas.
Professor Wright said:
"If we can understand the mechanisms and identify the switches that trigger
adult stem cells into regenerating specific tissues, the future could see a
revolution in transplant medicine."
Around 5,000 people in the
UK are awaiting organ transplants, and for many an organ will almost certainly
not be found in time. Patients will inevitably die waiting for a suitable donor.
"Eventually, adult stem cell technology may overcome this problem," Professor Wright said. "Clearly there is still much work to be done but the potential for therapies is enormous."
The work, reported in the journal Nature, was carried out in London by teams from the Imperial Cancer Research Fund, Imperial College School of Medicine, and the Royal Free Hospital.