Human Cloning: Part 1
HUMAN CLONING: PART 1
Roberto Colombo
Pontifical Academy for Life
Scientific facts help clarify the debate
Six years after publishing the experiments of Ian Wilmut and his associates (Nature, 1997, 385: 810-813) that led to the birth of the first cloned mammal via somatic cell nuclear transfer (SCNT), human cloning continues to be the object of unremitting biological research, lively philosophical, ethical and juridical conjecture, and heated public debate. The more realistic perspective of restricting cloning to certain laboratory or specially-bred animals, or to a limited number of wild species nearing extinction, seems to have averted the initial spectre of a dangerous technological interference by SCNT due to biodiversity, the process of natural selection and the balance among the species.
Thus, most scholars and citizens today are prepared to accept the cloning of animals for purposes such as the pre-clinical experimentation of drugs and transgenesis related to the etio-pathological study of certain diseases and the production of bio-molecules for medical treatment (proteins, for example, such as the α-1-antitrypsin, and coagulation factors VII and VIII), and tissue and organs destined for surgical therapy. On the other hand, there is a deeply disturbing possibility — reinforced at times by non-documented scientific information disseminated by the media — that cloning by SCNT has been or may be applied to humans, with the a-sexual reproduction of human embryos for research or for transfer to a uterus for development and birth.
After a period of animal experimentation, which not only enabled the cloning technique to be perfected but also paved the way to acquiring the first notions of its effects on the growth and survival of the embryo and fetus, the gestation process and the perinatal and postnatal physio-pathological structure of certain cloned mammals, it seems appropriate to return to the serious issue of human cloning and supply additional facts for a deeper philosophical knowledge, moral assessment and juridical consideration. Background is needed because of an improper and deceptive use in public debate of the "so-called" distinction between "reproductive" and "therapeutic" human cloning. The terms were introduced to differentiate between two intended "uses" of one and the same cloning process, SCNT, with the same result: a human embryo.
"Reproductive" cloning refers to the transfer of a cloned embryo to a uterus and its subsequent development to birth; "therapeutic" cloning aims at harvesting autologous embryonic stem cells from the internal cellular mass of the cloned embryo, thus destroying it for therapeutic and research reasons when it has reached the blastocyte stage (about five days after SCNT). In fact, cloning any organism is "reproductive" in the etymological sense, being "re-produced": when successful, "it produces again" an organism of the same species at the initial stage of its embryonic growth. Unless there is a wish surreptitiously to introduce the idea that a human embryo in the initial phases of growth is not a living organism at the beginning of its life-cycle (contrary to experience, reason and scientific literature from more than a century of biological study), whatever use this "product of human cloning" may be intended for, it cannot alter the biological and ontological aspect proper to the "product", nor the moral aspect of the act of cloning that must first be considered independently. The distinction between "reproductive" human cloning and "therapeutic" cloning that claims to have an ethical and juridical dimension confuses the purpose of the procedure with the actual question of the act.
Also misleading is the conviction that "therapeutic" cloning's "final result" is merely the cultivation in vitro of embryonic stem cells (a cell clone), whereas "reproductive" cloning results in a child (an individual born from developing an embryonic clone-organism). The argument forgets that the clone of human stem cells derives from a cloned human organism in the embryonic phase of development which, had it been transferred to a uterus instead of being destroyed, could have developed into a fetus and later, a new baby. Autologous embryonic stem cells in current or planned research are the secondary product of cloning; the first, in every case, continues to be the embryo.
As in the case of other biotechnological interventions in human procreation, "a preliminary point for the moral evaluation of such technical procedures is constituted by the consideration of the circumstances and consequences which those procedures involve in relation to the respect due to the human embryo" (Congregation for the Doctrine of the Faith, Donum Vitae, II). Among these, particularly important for moral judgment are the high percentages of failure in light of live births that are so far recorded in animal cloning, and the effects of SCNT on the somatic integrity and health of the cloned animal.
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A first conclusion emerging from the experimental data is the significant variability in quality of the results obtained by applying the same or a similar cloning technique to animals of different species, even when the work is done by the same team of researchers. Despite repeated attempts, it has not yet been possible to obtain from the intra-oocite transfer of the nuclei of post-fetal cells the birth of rats, dogs, horses or monkeys (Y. Tsunoda and Y. Kato, Differentiation 2002, 69: 158-161). Even the recent cloning of a mule was possible only due to using fibroblasts from fetuses at the 45th day of development, to whose nucleus was transferred a horse oocite whose nucleus had previously been removed. This suggests that the technical possibility that human cloning via SCNT may effectively lead to human birth should not be taken for granted.
In every case, the attempts needed to verify this hypothesis are also unjustifiable from the ontological and professional viewpoint of the biomedical researcher, with regard both to the negative outcome so far obtained on the animal model closest to the human being that was used (Macacus rhesus monkey) and because of the high number of oocytes needed (which could be obtained only by hyperstimulating the ovaries of numerous volunteers, a pharmacological process not exempt from gynaecological complications), and above all, because of the destruction of human embryos to which this would lead: "To use human embryos or fetuses as the object or instrument of experimentation constitutes a crime against their dignity as human beings having a right to the same respect that is due to the child already born and to every human person" (Donum Vitae, I, n. 4).
A second aspect of cloning concerns the procedure's effectiveness in mammals born via SCNT using the nuclei of post-fetal cells: the sheep, cow, rat, pig, goat and recently, the rabbit and cat. In these species the effectiveness of cloning from nuclei of adult animal cells is minimal. Typically, less than 1 percent of embryos resulting from SCNT and 4 percent of those transferred to the uterus achieve proper prenatal development and birth (I. Wilmut et al., Nature 2002, 419: 583-586). In the case of the rhesus monkey, cloning from nuclei of adult tissue cells has so far failed, but using those from embryos with eight cells (more easily reprogrammed, with better results in other species) has led to the birth of only two animals out of 53 cloned embryos transferred to a uterus (0.4%: D.P, Wolf et al., Biology of Reproduction 1999, 60: 199-204).
This tiny number is not only due to the greater difficulty in the in vitro culture of agamic embryos, the percentage of whose survival and growth is in any case lower than that of embryos reproduced by fertilization; it is also linked to a high abortion rate after transfer and implantation in the uterus. In the human being, as in the animal, spontaneous abortions also occur in a number of pregnancies that result from natural conception or from in vitro fertilization (IVF); but whereas in these pregnancies the loss of the embryo occurs most frequently in the first three months, in the case of cloning there is a high risk of abortion throughout the gestation period; this is associated with a consistent perinatal and neonanal mortality rate ("many cloned animals die within 24 hours of birth": I. Wilmut et al., a.c., p. 583). A pathology of the placenta, including vascular insufficiency, is the chief cause of the loss of cloned sheep and cow fetuses in the first months of gestation (J.R. Hill et al., Biology of Reproduction 2000, 63: 1787-1794). In the case of rat clones, placenta-megaly caused by the expansion of the layer of the spongio-trophoblast is frequent (S. Tanaka et al., Biology of Reproduction 2001, 65: 1813-1821). These and other complications, such as toxemia, observed in pregnancies via SCNT are a cause of fetal stress and endanger the health and life of the mother. For example, in a study by J.R. Hill and his collaborators (Theriogenology 1999, 51: 1451-1465), four of the 13 pregnant cows and their fetuses died from complications towards the end of gestation. The consideration that human abortion in the later stages of pregnancy is associated with an increased likelihood of maternal disease and mortality leads to the presumption that human cloning "would also entail a high risk for the health of both the fetus and child, as well as of the mother" (National Academy of Sciences [USA], Scientific and Medical Aspects of Human Cloning, National Academy Press, 2002, p. 40).
Thus, a further biological and clinical problem connected with SCNT emerges. If it is recorded — as certain champions of research into human cloning claim — that many of the animals cloned so far "appear healthy and normal" (according to the review of 335 cases published by J.B. Cibelli et al. [Nature Biotechnology 2002, 20; 13-14], so would the 77 percent of those that survived the first week of extrauterine life), yet "a high incidence of congenital abnormalities is found in comparison with normal reproduction", which are revealed before and after birth, or even only at an older age (J.B. Cibelli et al., op. cit, p. 13; cf. also the National Academy of Sciences [USA], op. cit., pp. 39-42; I. Wilmut et al., op. cit., p. 583; and J.R. Hill, Differentiation 2002, 69: 174-178). Among the defects observed are: excessive birth weight (frequent in the cow and goat), certain pulmonary pathologies (respiratory insufficiency in the sheep, cow and rat; pulmonary hypertension in the cow), immune system deficiencies and infections (cow, sheep), articulatory diseases (juvenile arthritis in the sheep; arthrogryposis in the cow) and obesity not associated with hereditary factors (rat). The LOS (Large Offspring Syndrome) phenotype, characterized at birth by hypertrophy of the placenta and weight excess in the newborn offspring, has been observed in many cloned cattle, rats and sheep, but is also sporadically present in certain animals born by IVF. In the human, it is well known that excessive birth weight increases risk of disease.
Research into the causes of the high incidence of intrauterine deaths and abnormalities among SCNT-cloned animals is only in its early stages, but several explanations have been proposed that appear to correspond with the experimental data available. Some specialists believe the "problems associated [with the failures of cloning] are not all of a technical nature... and it is not clear which of them could be eliminated by an improvement in technique" in the selection and cultivation of the donor somatic cell, of the nuclear transfer and of the activation of the oocite whose nucleus has been removed after transfer (D. Solter, Nature Reviews Genetics 2000, 1: 199-207, p. 204). The microscopic observation of cloned bovine blastocytes has made it possible to identify a relationship between the number of cells in the embryoblast and those in the trophoblast, higher in comparison with the embryo that originated from fertilization, and it is known that fewer cells in the trophoblast diminish the embryogenetic potential and reduce viability after implantation, probably because of abnormal placenta development. At the molecular level, the expression of certain genes that is proper to the trophectoderm is altered by SCNT cloning (C. Wrenzycki et al., Biology of Reproduction 2001, 65: 309-317); that of gene MHC-I in particular could cause an endometrial immunological response with an abortive effect (J.R. Hill et al., Biology of Reproduction 2002, 76: 55-63).
The result of cloning depends on the satisfactory epigenetic reprogramming of the nucleus, which must be converted from a specific tissue to a totipotent state. The donor nucleus must interrupt the programme of genetic expression and rapidly activate the one required for the embryo's development. Correct epigenetic reprogramming provides for the remodelling of the structure of the chromatin, an extended demethylation and remethylation of the DNA, and other precocious embryonic-genetic phenomena. If some of these processes do not occur completely and/or in the time and order required, the embryo's development is jeopardized at one or other of its critical stages (the so-called "epigenetic check-points"), with effects that could also be manifested later in the individual's life. Errors in epigenetic reprogramming, among other things, were observed at the level of the state of methylation of the DNA (for example, in blastocytes and cloned bovine fetuses). Defects were also found in the post-transcriptional regulation of the genes.
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Over and above any further and necessary anthropological or moral considerations, it will be impossible in an ethical evaluation of experimental research in the reproduction of human individuals via cloning to ignore evidence of development that is abnormal or impeded by certain pathologies in many animals cloned by SCNT. "There is no doubt", Pius XII recalled with regard to therapeutic experimentation, "that with a new method, still insufficiently tested" on animals, "before accepting the use of new methods as morally licit, it is impossible to demand the exclusion of every danger, of every risk. This goes beyond human possibilities, it would paralyse all scientific research and frequently be to the detriment of the patient.... Nonetheless, as our explanations have shown, there is a degree of danger that morality cannot permit.... This way of proceeding [in the presence of a danger to the subject] cannot be established as a rule of conduct in normal cases" (Address to Participants in the Premier Congrès International d'Histopathologie du Système Nerveux, 14 September 1952, in: AAS 44 [1952] 779-789, pp. 788-789), not even when the health of the sick person for whom an experimental treatment is recommended is at stake. It must be limited to "desperate cases, when the sick person will die if nothing is done, and when a medicine, means or operation exist which, without excluding every danger, may yet have a certain probability of success" (Address to the Participants in the VIII Congrès de l'Association Médicale Mondiale, 30 September 1954, in: Discorsi e Radiomessaggi 16 [1955] 167-179, p. 172).
This applies a fortiori to scientific research on an unborn human being carried out for purposes other than treating a life-threatening disease that personally afflicts him: cloning certainly cannot qualify as "a strictly therapeutic intervention whose explicit objective is the healing" (John Paul II, Address to the 35th General Assembly of the World Medical Association, 29 October 1983; ORE, 5 December 1983, p. 10) of the person subjected to experimentation, nor for "his individual survival", a condition for which "one must upholdas licit procedures carried out on the human embryo" (Donum Vitae, I, n. 3).
Even the Helsinki Declaration — which inspires the conduct of specialists of every culture and religious orientation since 1964 — after recalling that "medical research which involves human subjects... must be based on a complete knowledge of scientific literature, on other pertinent sources of information and on adequate laboratory experimentation, and, where appropriate, on animals", says that in this same research, "it is the duty of the doctor to protect the life, health, privacy and dignity of the human subject". Indeed, "in research on human subjects considerations associated with the well-being of the human subject must take precedence over the interests of science and society" (52nd General Assembly of the World Medical Association, Declaration of Helsinki: Ethical Principles for Medical Research Involving Human Subjects,6th rev. ed., Edinburgh, 2000).
The sense of responsibility mentioned by the Declaration is also echoed by some distinguished researchers in the field of animal cloning. Cloning "is a somewhat inefficient and unpredictable process" (W. Shi et al., Differentiation 2003, 71: 91-113, p. 91). SCNT "is currently an unreliable technique. We therefore consider that the technology of nuclear transfer should not be used in human beings or in therapeutic application until its technical reliability has been confirmed" (Y. Tsunoda and Y. Kato, op. cit., p. 160); indeed, it would "be unethical to attempt to produce and transfer cloned human embryos when it is well known that with this same procedure in animals there is a high risk of some fetal abnormality" (J.R. Hill, op. cit., p. 175). "We regard as dangerous and irresponsible attempts to clone human beings at a time when the scientific aspects of cloning by nuclear transfer have not been clarified" (R. Jaenisch and I. Wilmut, Science 2001, 291: 2552).
See Part 2.
Taken from:
L'Osservatore Romano
Weekly Edition in English
10 September 2003, page 4
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