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Stem cell therapy

Updated Thursday, 3rd August 2006

Learn more about stem cell therapy

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Ronald Reagan, whose widow believes stem cell research could have eased his later years Copyrighted  image Icon Copyright: BBC

Ethical boundaries are being tested almost daily due to the continual advancement of medical research. Instead of using surgery to transplant whole organs or tissues, techniques have been developed in which cells are transferred between individuals. These cell therapies have varying degrees of success depending on the origin of the cells and they have also aroused very different levels of ethical concern. For example, bone marrow transplants have become routine medical procedures.

Bone marrow transplants
The cells that are transferred are called adult bone marrow stem cells and they divide repeatedly to form all the white cells and red blood cells in the body. In most cases, the bone marrow transplant is from a closely related donor which means that the recipient’s immune system must first be suppressed or destroyed, to prevent the donated stem cells from being attacked as ‘non-self’. But the very property that makes these stem cells so powerful therapeutically, also causes a major problem - the transplanted stem cells develop into a functioning immune system, repopulating and replacing the patient’s white cells, which were destroyed by medical treatment.

Fetal cell implants
The rejection problem can be overcome by a controversial technique based on the use of fetal cell implants taken from the organs of aborted fetuses. The medical benefits of using fetal cell implants in non-related individuals to compensate for cellular deficiencies are very wide ranging. Because fetal cells have not yet developed the ability to distinguish between ‘self’ and ‘non-self’ so they become tolerant of their new host - the fetal graft survives but does not attack the patient’s tissues. The use of cells from fetal organs for therapeutic purposes raises some specific ethical concerns. Organs for transplantation have been removed, with parental permission, soon after the death of very young babies without public objection, but there has been a furore when the origin of the donated tissue is an aborted fetus. This source of transplant material opens up the question of how these cells are obtained. Fears have been expressed that abortion clinics could turn into centres that serve as ‘factory farms’ for fetal transplant material.

Fetal stem cells
A medical breakthrough occurred in 1999, a technique that generated a new and potentially inexhaustible supply of fetal stem cells. Fetal cells can be grown for limited lengths of time outside the body. Fetal stem cells, rather like bone marrow stem cells, can continue dividing indefinitely in the lab. These fetal stem cells are undifferentiated, i.e. unspecialised, and given appropriate chemical signals, are capable of differentiating to form every cell type that exists within the human body.

For this reason, fetal stem cells are referred to as totipotent cells (‘all potentialities’) and means that they have the potential to be used for direct transplantation into patients and might allow the development of replacement tissues grown in the laboratory. Fetal stem cells were originally isolated from aborted human fetuses and from ‘extra’ embryos generated during in vitro fertilisation (IVF) programmes.

In IVF programmes, eggs are removed from the woman and fertilised with tissue cultures, usually her partner’s sperm.

The cell divides to form a tiny ball of cells which is transplanted back into the woman’s uterus before it reaches the 14-day stage, which is the legal limit in the UK for keeping human embryos outside the body. Usually a larger number of embryos are generated than is safe to put back into the woman. These ‘extra’ embryos have either been discarded or ‘deep frozen’ for possible future re-implantation. In 2001, the UK government passed legislation allowing licensed research institutes to conduct experiments on these embryos within the existing 14-day limit.

The use of aborted fetuses and spare embryos raises ethical dilemmas, but these debates were overtaken at the end of 2000 by news of another scientific breakthrough. It was discovered that fetal stem cells could easily be extracted from blood in a mother’s umbilical cord. Millions of these totipotent cells can be obtained from a single umbilical cord, which would otherwise be incinerated.

Dolly the sheep
Most cells in the body from birth onwards – the somatic cells – contain a complete set of genetic instructions to make a complete animal but until 1987 scientists believed that the DNA in somatic cells in adult animals had undergone irreversible modifications or mutations associated with ageing such that it was impossible to use these cells as a starting point to produce a complete healthy animal. The birth of Dolly the sheep in 1997 overturned this concept.

How was Dolly the sheep created?
Dolly was created by taking the nucleus containing genetic material from a single somatic cell of an adult sheep and transferring it into an unfertilised sheep egg from which the donor’s nucleus has been removed. The new cell which was engineered by this process then divided as though it was a fertilised egg and developed along the same pathway as normal sheep embryos. The nuclear transfer converted the genetic material from one adult sheep into a new embryo which was then implanted into the uterus of a surrogate ewe. There Dolly developed normally and was born naturally.

This technique is called reproductive cloning and has subsequently been used to generate cows, mice and monkeys all from DNA taken from adult cells.

Although thousands of cloned embryos have been created, the success rate in producing healthy animals has been very low. This is due to the embryos either not implanting in the surrogate mother (a problem with human IVF too) or the resulting fetus aborts or develops with serious abnormalities.

The implications for this scientific advancement are many, including the potential agricultural and pharmaceutical uses of cloned animals. The benefits for humans who are suffering serious illnesses may be the most immediate result. For example, transferring a human gene to a cow or sheep may induce the animal to secrete a human protein in its milk which can be harvested for therapeutic use: blood clotting factors, human insulin and various enzymes are among the proteins already in production.

Legal position on cloning
In 1998 the Human Fertilisation and Embryology Authority (HFEA) and the Human Genetics Advisory Commission expressed an opinion that although the Human Fertilisation and Embryology Act of 1990 covered most of the issues relating to the human cloning, new legislation might be required explicitly to ban it. In relation to embryo research an amendment to the 1990 act was passed which allowed some limited research in this field to take place.

Concerns raised have focused on the extent of the interference with human biology and the biology of other species, the origins of the material transferred, the issue of informed consent and possible psychological damage to those concerned.

This article is based on extracts from Human Evolution and Health: An Evolutionary Approach, edited by Basiro Davey, Tim Halliday and Mark Hirst and published by the Open University Press. It was originally published in 2001

 

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