Embryonic stem cells
Human embryonic stem cells are derived from five to six-day-old human embryos.
At this stage of development, the embryo is a hollow ball of about 200 to 250 cells, no bigger than a pinhead. It is called a blastocyst.
Within the blastocyst is a small group of 30 to 34 cells, called the inner cell mass. These cells are pluripotent (able to develop into any type of cell) and are the source of all the highly specialised cells found in an adult organism. The remaining cells generate all other tissues such as the foetal membranes and placenta.
Australian Stem Cell Centre
Once the inner mass cells are obtained, they may be used to create pluripotent stem cell lines – cell cultures that can be grown indefinitely in the laboratory. Stem cell lines are important tools for scientists, as the cells are all the same, and new cells do not need to be isolated for every new experiment.
In Australia, it is illegal to conduct any type of research on embryos that are conceived naturally. Embryonic stem (ES) cells are taken from embryos that come from eggs fertilised in an IVF (in vitro fertilisation) clinic. Only embryos not required for implantation are used. They are donated for research purposes only, with informed consent from the donors. They are not derived from eggs fertilised within a woman’s body, and embryos are not created specifically for research purposes.
Because ES cells can become any cell type of the body, they can be used to develop different tissues for cell-based therapies.
Large numbers of ES cells can be grown in the laboratory relatively easily. ES cell lines are sometimes referred to as immortal due to their ability to keep dividing (self-renewing) over many generations. Established cell lines can be maintained in laboratories for further research and generation of cells for cell-based therapies for many years.
Human embryonic stem cells could be used to seek out and destroy a fatal form of brain cancer. Experiments using mice with brain tumours show that ES cells migrate across the brain and can deliver an anti-cancer drug.
ES cells may have great potential in forming the basis of long-term therapies, but issues regarding their safety must be overcome first. It is not yet known how transplanted ES cells would behave inside the body, but scientists are particularly worried that the transferred ES cells might not stop dividing. This uncontrolled growth may generate tumours, and this has already been shown to occur in laboratory cultures. While the cells in these tumours are benign, scientists do not know how they might behave in the body. However, cells differentiated from ES cells have been used in a number of studies and have developed normally. This issue must be fully explored before clinical trials can proceed in people.
Another issue with the use of ES cells in regenerative medicine is that they may trigger immune rejection by the patient’s immune system. Alternatives are being investigated to overcome this, including combining stem cell technology with cloning methods in a process called somatic cell nuclear transfer. This is discussed in the section on stem cells in cloning.
The community has a range of opinions about ES cell research. The overwhelming issue for most people who are opposed to ES cell research is that taking inner mass cells inevitably leads to the destruction of the embryo. For those that view a fertilised egg as a human life, this is most distressing. Others consider the blastocyst to be nothing more than a ball of cells with the potential to become a human. Debate on this issue remains considerable and controversial.