Stem cells are master cells of the human body which can do one of two things. They can either simply make copies of themselves, or they can produce other types of specialised cells. The very early embryo contains stem cells which slowly specialise to produce all the cells of the body. Adult cells can now also be reprogrammed in the laboratory so that they return to an embryonic-like state and can be used to make all kinds of specialised cells.
The medical importance of stem cells
Stem cells taken from embryos or created by reprogramming adult cells would not be injected directly into the adult body because of a risk that they might go on copying themselves and become cancerous. But they can be induced under special conditions in the laboratory to grow into (in principle) any type of cell in the human body. This would give a ready source of cells to replace ones that normally can’t be replaced once damaged, such as heart and nerve cells.
Take a patient with a spinal cord injury. They might be helped to recover if nerve cells were injected into the spinal cord. Nerve cells might also be able to slow or even stop Parkinson’s disease. Pancreatic cells might bring diabetes under control, and so on. The potential is clearly enormous, but at this early stage in the research it is difficult to know how many of these hopes will indeed become viable therapies. Using embryos in this way is very controversial and the techniques for reprogramming cells are very new. It is not yet known whether reprogrammed cells will be able to do everything that embryo-derived cells can.