Cloning

2. Potential applications

Cell therapy. One of the potential therapeutic applications of CNR is in the field of cell therapy. Stem cells are cells that have the capacity to give rise to different cell types and therefore to develop in different tissues of the body. Embryonic stem cells (ESC) have the capacity to differentiate in all human tissues (except for extra-embryonic tissues, such as placenta and umbilical cord – normally ESC are called ‘pluripotent’ in virtue of this ‘plural potentiality’). Thus it is hoped that ESC can be used to repair or rebuild any damaged or malfunctioning bodily system if introduced into the appropriate part of the body. This is how it might work. A zygote would be created through CNR, and the nucleus of a cell taken from the person who needs the transplantation would be used. The zygote would be grown to the blastocyst stage. At this stage the embryo presents itself as a hollow cavity containing ESC. These may be easily harvested and cultured in vitro, and made limitlessly available, given their capacity to replicate. ESC thus created would be particularly suitable for transplantation as these cells are genetically ‘matched’ to that of the recipient by creating the new cells from the nucleus of a cell taken from the recipient him- or herself.

It is sometimes argued that ‘individual’ treatment, such as that described above, is unrealistic due to the high costs of the procedure and to the need for a continuing supply of human oocytes for CNR. A less speculative therapeutic application than the creation of compatible tissues on an individual basis is thought to be creation of ESC banks through CNR. From these banks, cells and tissues that appear more compatible with those of the patient would be selected.

If the potential of CNR for cell therapy is fully utilized, the benefits for humanity would be great (DOH 2000: 23). Among the diseases that might be treatable in this way are Alzheimer’s disease, spinal cord injuries, multiple sclerosis, stroke, Parkinson’s disease, diabetes, cancer, osteoporosis, muscular dystrophy (for full details, see DOH 2000: 26). It is important to stress that if CNR could be used to create compatible closely matching tissues, this would overcome two major problems: (1) shortage of tissues, and (2) immunological rejection, when the recipient’s immune system recognizes the transplanted tissue (or organ) as ‘foreign’ and rejects it. Immuno-suppressant drugs are used to minimize the risk of rejection, but these are not always effective and must normally be taken for the entire duration of the patient’s life, leaving them vulnerable to infections.

Creation of compatible organs. The creation of compatible organs through CNR is one of the major potential therapeutic applications of the technique, although it is currently regarded as highly speculative. Again, the capacity of stem cells to form any part of the human organism would be harnessed to create ‘tailor-made’ organs which, because they are formed from cells which are clones of the intended recipient, would be compatible and immune to the body’s normal mechanisms for rejecting ‘foreign’ tissue. The procedure would be the same as described above, up to the point of harvesting ESC. Ideally, ESC might be induced to differentiate in the laboratory, that is, to specialize into specific types of cells, and then grown until a full organ could be available for transplant. In a future scenario, this procedure would obviate the major problem of shortage of organs – people in need of an organ could have ‘their own’ spare organs created by this means – as well as the problem of immunological rejection.

Treatment of mitochondrial disease. Mitochondria are energy-producing structures present in the cytoplasm of every cell. Mitochondria are not transferred from the male gametes during fertilization, and only the mitochondria present in the oocyte will be inherited by the embryo. Mitochondria are thus only inherited from the mother. Mitochondrial alterations are relatively rare but result in very serious diseases. Through CNR, it would be possible to replace the mother’s mitochondrial DNA with that of a healthy donor. This technique would involve a donated oocyte, from which the nucleus would be removed, and the nucleus of the mother’s egg (the nucleus of the cell does not contain cytoplasm), which would be introduced into the denucleated, donated, healthy oocyte. With this technique a ‘new’ oocyte would be created, with the healthy nucleus of the mother and the healthy cytoplasm of a donor. This ‘new’ oocyte would preserve the vast majority of DNA of the mother, alongside a small amount of (mitochondrial) DNA from the donor. The ‘new’ oocyte would then be ready for in vitro fertilization with the father’s sperm.

Differently from the CNR technique discussed above, the embryo in this case would preserve the genetic material of two individuals (the mother, who supplies the nucleus, and the father), and in addition it would have a small amount of DNA from a third person (mitochondrial DNA from the donor of the oocyte). The embryo, therefore, will not be the ‘identical copy’ of any of the three persons involved in the process.

Creation of embryos for research. The feasibility of the above procedures rests on embryo research. Embryos may be made available by in vitro fertilization (IVF) clinics (supernumerary or spare embryos), and they may also be created specifically for research purposes through either IVF or CNR. The international community is divided on the ethics of creating embryos for research purposes (see §§4,5 and References and further reading). It is often considered more ethical to use spare embryos obtained from IVF treatment. However, CNR would be necessary to investigate the behaviour of adult stem cells and also to assess whether tissue that is compatible with an individual recipient may be created (DOH 2000: 40). The ethical issues surrounding embryo creation through CNR are reported below in §4.

Differentiation, de-differentiation and re-differentiation of stem cells. Until recently it was believed that the process of differentiation of stem cells was irreversible, that is that a cell, once specialized, could not be ‘brought back’ to its unspecialized stage. Experiments on animals have instead demonstrated that it is possible, in some cases, to de-differentiate specialized adult cells. Adult cells of a specific type may de-differentiate to pluripotency and then specialize again to generate a different cell type from the one they were originally programmed to generate; or a cell may change into a different cell type without going through the de-differentiation phase (this process is sometimes called ‘transdifferentiation’) (House of Lords 2002: 14). Once these processes are fully understood, it may be possible to produce tissues and organs that are compatible with the recipient (given that the cells utilized in the therapy would belong to them), without creating embryos and harvesting ESC. This would resolve problems of shortage of organs and of immunological rejection and would satisfy those who believe that creating and killing embryos is unethical (see §5). However, the vast majority of the scientific community believes that research on adult stem cells does not currently make research on ESC redundant, and CNR research is held to be the only realistic means fully to understand the processes of differentiation and de-differentiation of human cells.

Reproduction. In theory CNR could be utilized for reproductive purposes. In this case the embryo created through CNR would be implanted in a viable womb and grown to term. CNR would have in this case similar potential applications to IVF. It would enable single parents or gay couples to have children genetically related to themselves without unwanted DNA, gender selection in cases of gender-related diseases, and infertile couples to have children without using donor gametes.

These potential applications of CNR are currently regarded as highly speculative by the scientific community. Given the technical problems discussed in §3, the reproductive use of CNR would require a degree of experimentation on human beings that is currently regarded as unacceptable, and this is likely to mean that CNR will be not regarded, at least for the foreseeable future, as a viable method of reproduction.

Other applications. CNR could be used to clone genetically modified animals, a prospect that may offer important benefits for human health. The idea is to create animals whose milk, for example, might become a means to administer medicines or proteins or even vaccinations, and then clone these animals so that their genetic characteristics are not lost during reproduction.