"[These webpages have a] wealth of information on biotechnology which puts its uses into context for students."
The early human embryo contains many stem cells. Stem cells are undifferentiated themselves, but have the potential to develop into many different types of specialised cells. The very earliest cells in an embryo are known as totipotent – they have the potential to develop into any one of the different types of cells needed to make a complete human being. By the time the embryo is four or five days old and has formed a hollow ball of cells (blastocyst) the stem cells are slightly less flexible. They have become pluripotent – they can form almost all of the cell types needed in future, but not tissue such as the placenta.
Thompson and Gearhart (see what is stem cell research?) realised that embryonic stem cells have the potential to be harvested and cultured in the laboratory to produce huge numbers of undifferentiated cells. Once they had found the conditions which made it possible for embryonic stem cells to survive, they managed to do just that, persuading the cells to reproduce successfully in cultures in the laboratory, without mutating or changing, for up to eight months. This time is likely to get longer and longer. This may seem a strange idea, but long lived cell cultures are widely used by scientists – HeLa cells are commonly cultured in laboratories all over the world and they all come originally from cancer cells from the cervix of a woman who died around sixty years ago!
The next big step is to turn undifferentiated stem cells into useful cells, tissues or organs needed in the body of a patient. By changing the culture conditions of the embryonic stem cells, scientists have persuaded them to differentiate into different types of adult cells, forming clusters of cartilage, bone, nerve and intestinal cells. So far no-one knows how to control exactly which adult cells develop – but that will surely come.
There is hope that developments of this technique will make it possible to grow nerve cells, heart cells, brain cells to repair damaged tissue in Alzheimer’s and Parkinson’s disease, islet cells to produce insulin – the possibilities are almost endless. Because embryonic cells do not trigger the normal immune response in their mother, transplants of tissues from embryonic stem cells may not cause the rejection which has previously beset tissue and organ transplantations. In the future it may be possible to collect stem cells for each of us during embryonic development or from the umbilical cord at birth, stem cells which could then be stored and saved until we needed them in later life.
Another, more immediate, benefit is that scientists can use cells and tissues grown from embryonic stem cells to carry out tests on new medicines. These tests could potentially replace some of the animal tests which are currently required when new medicines are being developedfor human treatment.
However there are some difficulties – scientists don’t know how to control fully the development of embryonic stem cells into all the tissues they want whilst avoiding uncontrolled growth.