As we go through life, some tissues or organs become damaged or diseased. As a result, they cannot always replace themselves well. If nervous tissue is crushed or damaged in a spinal injury it cannot regrow and the person will remain paralysed for the rest of their life. In a heart attack heart muscle is damaged and destroyed. It is replaced by useless scar tissue. Doctors and scientists have long been looking for a way to replace such tissues and give their patients – literally – a new lease of life.

Scientists can culture tissue cells in the laboratory by providing them with a specialised nutrient medium and the right conditions of oxygen, temperature and pH. For some years now they have been able to take skin cells from a patient and grow large sheets of new skin to replace tissue affected by burns. The technique was relatively limited until at the very end of 1998 two groups scientists working in American universities announced a breakthrough. Both teams, one led by Dr James Thomson at Wisconsin and the other by John Gearhart in Baltimore, developed a technique for culturing embryonic stem cells. Embryonic stem cells have the potential to become almost any of the specialised cells our body needs – they are pluripotent. This breakthrough raised hopes of a major medical breakthrough – the ability to replace diseased or worn out body parts with new healthy tissue.

These human embryonic stem cells were grown by the team at Wisconsin, one of the first groups to find a way of culturing them in the laboratory. The modest-looking cells have the potential to form almost any other cell needed in the human body – we just have to discover how to instruct them to form exactly the type of cells we want!

© University of Wisconsin Board of Regents, reproduced with permission

The new stem cell technology also raised many ethical issues, because the stem cells are derived from human embryos. These ethical concerns in turn drove more research to find and use the stem cells still present in our adult bodies. Now adult stem cells also look as if they may have an important role in replacing and restoring damaged tissue. Although there are still many technical and ethical issues to be sorted out, the new techniques may well revolutionise medicine in the future.