ANALYSIS: DICK AHLSTROM/Science EditorFew issues in scientific research have attracted the attention given to stem cells but why are they so controversial?
THE OPINION by the Irish Council for Bioethics on embryonic stem cell research will renew the long and ongoing debate about the use of these human tissues for scientific study.
It may also serve to polarise views on whether 'Irish scientists should be allowed to experiment on cells recovered from very early embryos given the council strongly supports Irish involvement in this important research.
Yet the public response to the issue is often ambivalent given the complexity of both the science involved and the difficult ethical issues it throws up.
People may voice concerns about the experimentation and the resultant destruction of an otherwise viable embryo, but many acknowledge they would accept medical treatments derived from this work.
This contradiction is seen in the widespread objection to the genetic modification of food plants, yet the near complete acceptance of genetic engineering as a method for producing antibiotics, life-saving insulin and other drugs.
The central ethical concern relates to the source of the stem cells, a days-old embryo. Properly called a blastocyst rather than an embryo, stem cells begin to form inside this structure when it is still microscopic in size. These can only be collected for study by destroying the blastocyst.
This is the pivotal issue that makes stem cell research so controversial. Those opposed to embryonic stem cell research - including a number of prominent research scientists - argue that any medical benefits gained from the work would be completely negated by the destruction of potential human life.
Those in favour of stem cell research counter that the blastocyst before implantation in the womb is nothing more than a collection of cells, is not yet a viable human and could ultimately help cure intractable human diseases.
If the ethical conundrum could temporarily be parked, then there is less disagreement about why embryonic stem cells are so singularly important and potentially beneficial.
After blastocyst implantation, the stem cells start to respond to the presence of growth factors and other signals, transforming them from their original "starter" state to become any of the 200-odd cell types within the body.
The terms used for this phenomenon describe the embryonic stem cell as "pluripotent" and the process of change as "differentiation".
Medical researchers believe that if they can understand the complex cell signalling that leads to differentiation, then they can produce replacement cells on demand for medical treatments.
Stem cell cultures could be coaxed to become nerve tissue to repair a damaged spinal cord or heart cells to replace cells lost through heart attack. Parkinson's disease, multiple sclerosis, Alzheimer's disease and diabetes may all be curable if the promise of stem cell research delivers.
The ethical complexities do not go away, however, and so scientists have sought other sources for stem cells other than embryos, and have found them.
The body constantly renews itself with old worn out cells dying to be replaced by new cells. But there are also a limited number of so-called "adult" stem cells there to help in this process.
Researchers have found these almost wherever they have looked for them.
The bone marrow contains stem cells that can become any type of blood cell and the liver contains its own stem cells that become liver cells.
The problem is that adult stem cells are not pluripotent; they can only become one of the cell types associated with where they are found.
Yet they still offer great promise for medical treatments and, more importantly, the recovery of adult stem cells does not depend on the destruction of a blastocyst.
The world of stem cell research was turned on its head several months ago, however, with the discovery of a process whereby ordinary skin cells from a mouse could be "reprogrammed" to become stem cells.
Work since has shown that these new artificial stem cells are virtually indistinguishable from true embryonic stem cells and are apparently pluripotent.
Much work remains to be done before these cells could be used in medical treatments, however. The conversion process as it now exists requires the inclusion of a gene that could produce cancer once in the body.
The Japanese and US discoverers of this cell reprogramming technique strongly argue, however, that current embryonic stem cell research must continue, at least until stem cell reprogramming can be proven.
And by extension, adult stem cell research should also continue, in the hope that this method could deliver treatments that do not carry ethical baggage.
While all of these techniques hold promise, there are no guarantees that any of them will ultimately treat disease.
But as ever with research, if you don't look, you won't find, and not looking can never be an option.