Potential medical benefits

In my view, the potential medical benefits of stem cell research are huge. In the first instance, the generation of such cells which can, by various manipulations, be modified to produce lines of muscle cells, nerve cells, bone cells, kidney cells, liver cells and many more will be invaluable for the treatment of many diseases of these individual organs. A certain amount of work has been done in the last few years using, for example, neurones derived from aborted fetuses in order to inject those which produce dopamine into the brains of patients with parkinsonism, and similar work has been done, to a limited degree, using neurones derived from the caudate nucleus trans-planted into the brains of patients with Huntington's disease. Such transplants have proved to be effective to a limited extent, but. the control of such treatment has proved difficult, and indeed neuronal transplants in Parkinson's disease have been stopped in the United States recently following a particular case in which the transplants proved so effective as to produce excessive quantities of dopamine which in turn resulted in intolerable and uncontrollable involuntary movements. The hope for the future is that populations of stem cells can be created and carefully titrated so that the dose, if one may use that term, of stem cells used in transplantation procedures can be carefully controlled. It is not out of the question that in the very long term, the creation of whole organs for transplantation might become feasible through research, but this lies a very long way into the future.

There are three potential mechanisms by which embryonic material can be used for the creation of stem cells. The first is by the use of spare embryos donated during the process of in vitro fertilisation; in one recent year, 10,000 such spare embryos were donated for research purposes. I do not personally see the need to create embryos specifically for the production of stem cells, since so many spare embryos are likely to be available through current and future in vitro fertilisation programmes.

The second process by which stem cells can be created is by nuclear transplantation into an adult cell derived from the recipient (e.g. a skin cell, for example); this technique is similar to that employed in creating 'Dolly the sheep'. One advantage of this technique is that stem cells so created might be immunologically compatible with the tissues of the host. I should say at this point that I am totally opposed to reproductive cloning using this kind of technique, not least because it is at present speculative and somewhat ineffective. No fewer than 220 attempts were made before 'Dolly the sheep' was eventually born, and the potential risk of fetal malformations using this method is at present very high. Nevertheless, the method could well prove to produce an acceptable and ready supply of stem cells. Recent work suggests that it may even be possible to produce parthenogenetic stem cells derived from female ova which are unfertilised, but such work is in a very early stage.

The third and very important possibility relates to nuclear transplantation for the prevention of mitochondrial disease. In my professional career as a neurologist with an interest in neuromuscular disease, I saw many patients with mitochondrial disorders, many of which are devastating and ultimately fatal. Many produce progressive muscular weakness and wasting, but in addition a wide range of metabolic abnormalities may result, including progressive blindness (Leber's optic atrophy), severe lactic acidosis and/ or hypermetabolism, and even stroke-like episodes. Mitochondria, being present in the cytoplasm of ova but not in sperm, are therefore transmitted almost exclusively by the female and hence a woman carrying abnormal mitochondrial genes may well pass on these devastating conditions to her children. 99.8 per cent. of the woman's DNA resides in the nucleus of the cell, but about 0.2 per cent. resides in the mitochondria and some 54 mito-chondrial genes have now been characterised. If the nucleus of an ovum derived from a mother who would otherwise pass on devastating mitochondrial disease to her offspring can be transplanted into a donated ovum from a normal woman from which the nucleus had been removed, then a cell created in this way which could be fertilised by the patient's sperm would contain 99.8 per cent. of the woman's DNA in the nucleus, but normal mitochondria lying in the cytoplasm and derived from the donor egg. The benefits of this technique for treating rare mito-chondrial diseases, many of which, as I have said, are progressive and fatal, are potentially huge.