Stem-cell science cannot deliver miracle cure-alls

Published on Saturday 12 August 2006 01:54

WHEN Dr James Thomson isolated cells from the inner cell mass of the early embryo and developed the first human embryonic stem-cell lines at the University of Wisconsin, nobody could have predicted the flurry of interest that would follow.

Since his discovery in 1998, stem cells have been hailed as the "holy grail" to put an end to a host of diseases including Parkinson's and Alzheimer's diseases, spinal cord injury, stroke, burns, heart disease, diabetes, osteoarthritis and rheumatoid arthritis.

Six years ago, Ronald McKay of the American National Institutes of Health predicted: "In two years people will be routinely reconstituting liver, regenerating heart, building pancreatic islets, putting cells into the brain that get incorporated into the normal circuitry."

These extraordinary claims come from the unique ability of stem cells to transform themselves into all the different cell types that make up our bodies, from skin to brain cells. Scientists and clinicians around the world have been trying to develop therapies in which these cells are introduced into a diseased area to replace tissue that has been lost or damaged.

However, Professor Colin Blakemore, a brain researcher and chief executive of the Medical Research Council (MRC), recently told The Scotsman that stem cells will not provide miracle cures that will banish Alzheimer's disease or strokes. "Stem cells are not the ultimate approach to curing degenerative diseases [of the brain] such as Alzheimer's... nor for stroke", he said.

His justification is that cells die in huge numbers "and I think it is not feasible [for stem cells] to replace them". He also pointed out that even if stem cells are able to fill diseased gaps in the brain, there is no guarantee that they would rebuild functional connections. In the case of Alzheimer's, Prof Blakemore thinks that drug treatments offer the best hope for sufferers.

In reaction to Prof Blakemore's pessimistic view, a spokesman from Alzheimer Scotland commented: "Stem cells can have wider uses than a simple transplantion approach."

Baroness Susan Greenfield, a brain pharmacologist and the director of the Royal Institution of Great Britain, said: "It's unfortunate that stem cells have been overhyped." She described using stem-cell therapy in Parkinson's disease as "not trivial" due to numerous safety factors that have to be taken into account.

In her view, a more promising approach would be to discover the chemical signal that converts stem cells into neurons: "If you knew what the chemical signal was, you could use that as a therapy... which would be more ethical and far less hazardous and expensive than transplanting stem cells."

Prof Blakemore does believe that stem cells may lead to a cure for degenerative diseases, such as Parkinson's or motor neurone disease, where the damage is confined to a particular, small region of the brain. "Animal studies of brain injury have demonstrated benefits on motor control and learning, for reasons that are not yet understood," he said.

In recent years, neurons and glia - the two main cell types that are lost in brain disorders - have been produced from stem cells cultured in the laboratory, fuelling hopes for stem-cell transplantation-based therapies.

Scientists have extended their efforts towards stimulating the brain to produce its own neurons from "endogenous" stem cells already present inside the brain.

Despite these advances, the majority of scientists working in the field believe that experimental stem-cell therapy in humans is still dangerously premature. This is exemplified by the poor survival of transplanted human embryonic stem cells in animal models of Parkinson's disease, which needs to be drastically improved before any human clinical trials can be attempted.

Prof Blakemore's comments coincide with research from the University of California that neural, or brain, stem cells, derived from human embryonic stem-cell lines, suffer from a genetic abnormality that leads to hypoglycaemia in humans.

This could limit the usefulness of federally approved human embryonic stem-cell lines. Stem cells derived from embryos do not appear to suffer from the same problems, although the process of harvesting cells from embryos remains deeply controversial.

Prof Blakemore said: "It would be wrong at this stage to be either foolishly optimistic or totally dismissive about stem-cell therapy.

"One thing is certain: a great deal more research is needed before we shall know exactly what the potential is for new treatments."