How the research could help to treat incurable diseases

An undifferentiated cell that has the potential to develop into one of the specialised tissues of the body, such as heart, lung or nerve cells.

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British experts set to lead world revolution in medical science

What is a stem cell?

An undifferentiated cell that has the potential to develop into one of the specialised tissues of the body, such as heart, lung or nerve cells. Stem cells first appear in early embryos when they are at the stage called a blastocyst – a microscopic ball of about 100 cells – at about six days after fertilisation. They are also found in the umbilical-cord blood of newborn babies and even among some of the rapidly dividing cells of the adult body, such as the bone marrow.

Why is there such a fuss about them?

Scientists say that stem cells promise to revolutionise medicine. They hope that stem cells can be used in transplant operations to repair damaged tissues and organs, such as hearts, lungs, muscles and even brains. Many diseases could be cured in the process, including diabetes, Parkinson's and chronic heart disease.

Why can't we use adult stem cells rather than ones that are derived from embryos?

Scientists believe that stem cells from adults are capable of developing only into a restricted range of specialised tissues. So adult bone marrow stem cells develop into mature blood cells, whereas stem cells from a six-day-old embryo can develop into any one of many dozens of tissues. However, a scientific comparison of the two types of stem cell has yet to be done and some work on adult stem cells has indicated that they have a surprising potential to grow into widely different tissue types.

What use are the stem cells derived from umbilical-cord blood?

These have proven to be invaluable in treating some inherited blood disorders in children and these stem cells may prove far more versatile than adult stem cells, but probably not as potent as embryonic stem cells. But again, the research comparing the potential of all three sources of stem cell has yet to be done.

What has cloning got to do with stem cells?

If stem cells from embryos produce the medical benefits expected of them, the issue of tissue rejection will always hinder their use in transplant operations. One way around this problem is to use stem cells from an early embryo cloned from the skin cell of the same patient.

Didn't an American company announce last December that it had cloned a human embryo?

It did, but the embryo died before stem cells could be extracted. It is not sure whether this "clone" was a genuine clone or an experimental artefact.