Facts and Figures

• Cloning is the use of technology to make an exact gen-etic copy of a living organism. The term may also be used to apply to making a copy of simple cells, a gene or a segment of DNA. Reproductive cloning is the cloning of a human being. Therapeutic cloning involves the use of embryonic stem cells for therapeutic purposes. Cloning is controversial. Australian legislation prohibits all cloning of humans.

• Reproductive cloning is largely condemned by the inter-national scientific community. Some commentators believe that human cloning could one day become a reality, because our increasing acceptance of genetic technologies may desensitise us to the ethical dilemmas involved. At the present time, however, there are significant scientific, technological and ethical barriers to reproductive cloning.

• Possible applications of stem cell research and ther-apeutic cloning include: treatment of a person with disorders such as Parkinson’s disease and dementia – the embryonic stem cells, generated from the cells of the individual, would be immunologically compatible; the study of early human development; screening of drugs that may cause birth defects; pharmacogenomic research on disease-specific stem cells to provide information on new and targeted drug treatments; disease-specific stem cell lines would provide the opportunity to learn about the mechanism of disease and make preliminary treatment trials more accessible.

• Stem cells are the human body’s master cells. They are found in the embryo, which is the earliest stage of development following fertilisation, but before implantation. They are also found in cord blood, in the fetus and infant, and in some adult tissues. Stem cells play a critical role in normal growth and development by providing new cells for growth and for replacing and repairing used and damaged tissues. Medical researchers believe stem cell research has the potential to change the way human disease is treated, by allowing stem cells to be used to repair specific tissues or to grow organs.

• Adult stem cells are a type of stem cell found in organs and tissues in babies, children and adults. Most adult stem cells have, so far, been shown to replenish the particular organ or tissue from which it is derived and are more specialised than the unspecialised clump of cells found in an early embryo. For instance the bone marrow stem cell replenishes all the different types of cells of the blood, but has not been shown to be able to replenish cells in the liver or brain. The term “adult stem cell” is misleading, and is used to distinguish such cells (which are often from babies or even the fetus) from “embryonic stem cells”.

• Embryonic stem cells are derived from fertilised embryos that are less than a week old. They have not differentiated, which means they are not yet committed to a specific function. However, they have the ability to develop into almost any cell type found in the body and are important for producing normal cells to potentially repair or replace diseased or damaged tissues. These embryos are donated by couples undergoing IVF. Many couples prefer to see a surplus embryo used for research rather than thrown away. They have to give informed consent and researchers who wish to use them must pass a rigorous government test in order to obtain a licence.

• Embryonic stem (ES) cells were first isolated in humans only recently (1998) and the research is still in its infancy. Of the many different sources of stem cells, only those from embryos have the potential to become almost any of the body’s cell types. They are also able to proliferate limitlessly in the culture dish and these properties have led researchers in the field to claim that the technologies that may develop could have significant medical potential. The ability of ES cells to replicate without limit is particularly important, since meeting the global demand for replacement tissues would require the production of vast amounts of cells. However, the use of ES cells as a source of transplant tissue, unlike adult and cord blood stem cells, raises concerns because ES cells in mice can cause tumours when transplanted. This issue must be addressed before these cells can be used safely in clinical therapy.

• Therapeutic cloning is also called somatic cell nuclear transfer (SCNT). The technique involves taking the nucleus (which contains genetic material) from the skin cell of a patient and inserting it into an egg whose nucleus has been removed. With the right triggers, this new cell will develop into an embryo. Scientists can extract stem cells from it, and use those cells to grow tissue. This might allow stem cells to be made from a patient that could be reintroduced into the patient’s body without rejection by the person’s immune system. It could also enable scientists to understand more thoroughly the triggers and process of that disease.

• Reproductive cloning is also sometimes referred to as human cloning. At the moment, no one has shown any evidence that it is possible. However, if the embryo produced through SCNT were to be implanted into a woman’s uterus, there is a tiny chance it would develop into a baby, as happened for Dolly the sheep. Not only would this be illegal in Australia, but according to most doctors and scientists it would be unethical. Animal experiments show the vast majority of clones abort and many of those born are abnormal.

• It is difficult to predict the pace of future research. Nonetheless, it seems very unlikely that we will be able to answer all of the questions about stem cells within the next 10 years. It might be several decades before we achieve a full understanding of how stem cells develop and maintain specialisation, and how to use this information for the benefit of future clinical medicine.