2.1.1 Until recently, it was thought that stem cells could rarely be found in adult tissue. However, this view has been conclusively disproved. The last twelve months have seen an explosion of information on adult stem cells (the term is often used to include stem cells from, for example, newborn babies). Adult stem cells have, in fact, been given to patients for decades in the course of bone marrow transplants, and new trials on patients using adult stem cells have had positive results.
2.1.2 It is clearly best if the cells used in transplantation can be taken from the patient him- or herself, to avoid rejection by the body. While embryonic cells have been proposed as a means of avoiding rejection problems, even early embryonic cells have surface molecules which can cause an immune response.2 Supporters and opponents of embryonic stem cell research are in agreement that the ultimate goal should be to use the patient's own cells.
2.1.3 There are various ways in which adult cells can be used. They can be taken from the patient, or a donor, and used without being modified, as in the case of bone marrow transplants for patients with cancer. Alternatively, stem cells from the patient can be subjected to gene therapy before being re-introduced, as in the case of children who were treated recently for Severe Combined Immune Deficiency.3
2.1.4 Stem cells can be induced to carry out a new role in the body, as when a patient with heart disease was given stem cells from muscle in his leg, which then formed a different kind of muscle in his heart.4 It is known that adult bone marrow cells are particularly versatile, and can produce bone, cartilage, tendon, muscle, fat, liver and neural cells. Neural stem cells can also form other cell types, such as blood and muscle cells.
2.1.5 Finally, there are ways of treating stem cells while they are still in the body of the subject. In animal studies, positive results have been obtained by adding the proper growth signal to the injured brains of rats, so that their own stem cells could proliferate.5
2.1.6 Treatments of human patients using adult cells are already yielding results. Successful treatments have been carried out on children with cartilage defects,6 patients with corneal scarring,7 and patients with lupus,8 systemic sclerosis9 and rheumatoid arthritis.10 A number of cancers have been successfully treated using adult cells, including metastatic retinoblastoma, which has a poor prognosis with conventional treatments.11
2.2.1 How do these achievements using adult cells compare with those made using embryonic cells? It should be noted that cells from early embryos have not so far been used on patients, and appear too unspecialised to control, unless modified in some way.12 We are some years away from any treatment using early embryonic cells.
2.2.2 Where stem cells from foetuses have been transplanted into patients along with other tissue the results have not been altogether positive. Even foetal cells can be difficult to control, and it is feared that embryonic stem cell transplants could give rise to cancer. In one case, a man with Parkinson's died after a transplant of foetal cells; it was later found that these cells had given rise to bone, skin and hair in the patient's brain.13
2.2.3 A recent clinical trial did find some improvement in younger Parkinson's patients (those aged 60 or less). However, in 15% of those treated the patient developed permanent uncontrollable movements such as writhing, head-jerking and constant chewing.14 One patient now has to be tube-fed, so severe are his symptoms.
2.2.4 In animal experiments, there have been some favourable results using embryonic cells. However, there are technical problems involved in keeping human embryonic stem cells alive, and in making them differentiate along the right lines. A trial in which cells from human embryos were transplanted into rats found that these cells did not readily differentiate into brain cells. Instead, they stayed together in a disorganized cluster, and nearby cells began to die.15
2.2.5 While it is too early to say whether embryonic or adult stem cells will ultimately prove more effective, there is more current evidence of usefulness in the case of adult cells. Statements to the contrary may owe more to external pressures - political or commercial - than to the scientific data. To quote the journal Science in December 2000, “the human embryonic stem cells and fetal germ cells that made headlines in November 1998 because they can, in theory, develop into any cell type have so far produced relatively modest results. Only a few papers and meeting reports have emerged from the handful of labs that work with human pluripotent cells.”16
2.3.1 Cloning for birth has been carried out in various species of mammal, including sheep, cows, mice, pigs and goats. However, it is very difficult to produce a healthy animal by cloning. Problems arise at every point: in producing embryos by cell nuclear replacement, in bringing these embryos to term, and in obtaining healthy live-born offspring. There is a high rate of miscarriage of clones, throughout the period of gestation, and a high rate of neonatal death. Major fluid retention in the gestating mother has also been observed.
2.3.2 Abnormalities in clones include developmental delays, heart and lung defects, malfunctioning immune systems, and excessive size. Genetic errors in the clone can cause unpredictable problems at any stage. Some mouse clones, after growing to the equivalent age in humans of thirty, suddenly become obese.
2.3.3 Despite these problems, there are those who wish to carry out cloning for birth in human beings. Fertility specialists Panos Zavos and Severino Antinori plan to clone for birth within the next two years. Zavos claims it will be possible to identify abnormalities at the embryo stage, so that abnormal embryos can be discarded. However, experts in animal cloning have suggested that this cannot be done, since there is no test for determining whether genes in the embryo have been properly reprogrammed.
2.4.1 The high rate of serious abnormality in animal clones gives us reason to fear the effect on patients of transplanting into them genetically abnormal cells from an embryonic clone. In general, embryonic cells are unstable and difficult to control because of their pluripotency. Cells from a cloned embryo, prone to genetic abnormality, raise still more difficulties. In any case, the great expense involved in cloning, and the need for a large number of human eggs, would be major impediments to its clinical use.17
Next Page: Status of the human embryo
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