Bone marrow cells could treat the brain

Marker: A neuronal cell derived from bone marrow

Bone marrow cells could be used in new treatments for a range of diseases from stroke to Alzheimer's, scientists believe.

Research on human embryonic stem cells is still essential

Prof Richard Gardner, UK Royal Society

Two groups of researchers have shown that the stem cells found in bone marrow transform themselves naturally into neurons - brain cells that carry nerve impulses - and can install themselves seamlessly into the brain.

It could mean bone marrow transplants, already commonly used to treat cancer, might one day be used to help people with degenerative brain conditions and injuries.

"I really think that it is a very encouraging beginning and it will help people down the road with diseases that we don't have any cure for," said one of the lead scientists, Dr Eva Mezey of the US National Institute of Neurological Disorders and Stroke (NINDS).

Remarkable flexibility

Stem cells are a hot new field of research that promises to change the face of modern medicine.

These special cells are like "master" cells, capable of developing into various cell types. If scientists can learn how to control this development, stem cells could provide new means to regenerate damaged tissues and organs.

But they are not easy to find and the only convenient source so far is the bone marrow, which generates both red blood cells and the white blood cells of the immune system.

However, as scientists now know, stem cells can display remarkable flexibility, producing cell types beyond even what would seem to be their natural remit.

Green cells

Mezey and colleagues demonstrated this by injecting mice with bone marrow stem cells that contained a mutation, or error, that prevented them, as would be expected, from developing into the cells found in the blood.

Instead, the NINDS team found that the transplanted cells migrated to the brains of the rodents where they differentiated into cells that expressed two proteins found exclusively in neurons - good evidence that the bone marrow stem cells had produced brain cells.

Timothy Brazelton and colleagues, at Stanford University, US, harvested bone marrow stem cells from a line of mice engineered to express a green fluorescing protein on their cells.

The team injected the cells into normal mice, and later observed the glowing green cells in the rodents' brains. These cells also expressed several other key proteins that are typical of neurons.

On-going debate

The research will add to the debate about where scientists should source their stem cells.

Some believe only the stem cells taken from early-stage embryos will have the full flexibility to fulfil the potential of the new hoped-for treatments. Others, who find embryo work ethically problematic, point to work like that of NINDS and Stanford as evidence that stem cells taken from adults could do just as well.

Professor Richard Gardner, chairman of the UK's Royal Society working group on therapeutic cloning, said of the latest research: "We welcome these very exciting and interesting results, but the work will need to be independently replicated by other researchers before we can fully assess its significance.

"In any case, these results do not prove that adult human stem cells could ever provide the full range of cell types required for treatments. Research on human embryonic stem cells is still essential."