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Cloning and Embryo Research

Note This report represents the medical/scientific literature on this subject as of June 1999.

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Resolution 528, introduced at the 1997 Annual Meeting by the Section on Medical Schools and referred to the Board of Trustees by the House of Delegates, asked that: "The American Medical Association (AMA) work with the National Bioethics Advisory Commission and members of Congress and the executive branch to ensure that any legislation regulating human somatic cell nuclear transfer cloning not interfere with other significant important ongoing medical research;" and further, "study the scientific and bioethical implications of research involving the earliest stages of human embryonic development, including somatic cell nuclear transfer cloning."

This report summarizes the scientific basis of cloning and describes its potential risks and benefits for clinical medicine and biomedical research. Regulatory and legislative issues are addressed in the context of not hindering unduly current or future research. Recommendations of the Council of Scientific Affairs conclude the report. The ethical considerations of human cloning are discussed in a companion report from the Council of Ethical and Judicial Affairs (CEJA), Report 2 (A-99), "The Ethics of Human Cloning" (PDF, 40KB)

Introduction

"Clone" (from the Greek "klon," or twig) describes an organism that is a replica of another, whether of a cell or of a whole organism, ie, plant, animal or fungus.

In the past few decades, cloning has also come to refer to the duplication of fragments of deoxyribonucleic acid (DNA) comprising one or more genes. In this report, unless otherwise indicated, "cloning" will refer specifically to the production of genetically identical individuals via somatic cell nucleus transfer. This technique is one of four potential ways of cloning mammals and was the one used to clone the famous lamb Dolly,¹ a scientific accomplishment that is the source of the current public focus on cloning.

On February 27, 1997, Wilmut and colleagues¹ from the Roslin Institute and PPL Therapeutics in Roslin, Scotland, reported the first successful cloning of a mammal using a differentiated cell from adult tissue as the source of genetic material: lamb # 6LL3 (more commonly known as Dolly) was reportedly derived from an adult ewe mammary gland cell fused to an enucleated egg cell or oocyte. This technique is called somatic cell nuclear transfer. Until recently, some doubt remained that Dolly may have originated from a contaminating cultured cell, or a fetal cell present in the udder of the pregnant ewe donor,² instead of an adult differentiated cell. Now that the final confirmation of Dolly s origin has been provided via detailed DNA microsatellite analysis^{3, 4} it appears that Wilmut et al have answered in the affirmative one of the major questions facing developmental biologists today; ie, whether any nuclei from differentiated adult somatic cells retain the capability of directing the development of an entire adult individual under certain conditions. In 1975, Gurdon and colleagues⁵ demonstrated that nuclei of adult skin cells from frogs could support the development of tadpoles when transplanted into oocytes. However, no instance of full development to the adult stage was ever reported.

Despite the scientific importance of Gurdon s finding, it was the first instance of viable duplication of a living adult mammal that attracted public attention. In vitro fertilization already allows cloning of humans at the very early (2- to 4-cell) embryonic stage, but not at any later stage. To the public, the making of Dolly has brought society significantly closer to the material possibility of cloning human beings of any age.

Cloning methods

All multicellular organisms are composed of two major categories of cells: (1) germ cells or gametes, which function in sexual reproduction; and (2) somatic cells, ie, any cell that is not involved in sexual reproduction. Sexual reproduction usually requires the fusion of gametes from different genders. Some simple invertebrates and most plants reproduce asexually. Asexual reproduction involves either parthenogenesis (regrowing an entire organism from a piece of the donor) or cloning (the generation of an entire organism from a somatic cell). Vertebrates do not have the natural ability to reproduce asexually.

Dolly was cloned via a technique referred to as "somatic cell nuclear transfer" or "somatic cell nuclear transplantation." Before describing the technique in more detail, the other possible cloning methods are described. Post-fertilization development in mammals occurs as follows: the fertilized, mammalian egg (or zygote) begins to develop into an embryo by a process called "cleavage," whereby the large zygotic cell is apportioned into numerous smaller cells called "blastomeres" to form a tiny ball, the morula, which then begins to form a separate external and internal layer of cells. A cavity forms inside the morula, leaving a ring of external cells surrounding the fluid-filled cavity containing the internal cells. The inner cell mass is not equally distributed inside the cavity, but rather lies against one side of the outer ring. This is the blastocyst stage of embryonic development. The inner cell mass of the blastocyst ultimately gives rise to the embryo proper.

Early blastomeres are totipotent (from totipotency: the ability to form any cell type in the body⁶), and therefore capable of regenerating an entire organism on their own in utero. It is thus possible to clone mammals by teasing apart the early blastomeres of an early embryo, reimplanting them in the uterus, and allowing each to develop independently. Scientists believe blastomere separation is one of the processes by which monozygotic twins or multiples normally form. It is also possible to divide the blastocyst in two (blastomere halving), to reimplant the two portions in the uterus, and to allow each half to develop independently into a complete organism. This is believed to be another way twins normally form.

Only embryos can be used for the donor cells when cloning is performed by blastomere separation or blastocyst halving, and only a limited number of clones can be produced since the source material is a single embryo. These limitations do not apply to somatic cell nuclear transfer. Such limitations restrict the usefulness of both methods for large-scale cloning of farm animals. In human subjects, scientists have succeeded in increasing the number of pre-implantation embryos produced per oocyte in preparation for in vitro fertilization in cases where oocyte availability is a limiting factor. Other potential advantages of somatic cell nuclear transfer over blastocyst-based methods with regard to clinical applications or biomedical research include: (1) The opportunity to genetically modify donor nuclei for therapeutic purposes prior to cloning; and (2) the ability to use a foreign oocyte without affecting the genetic inheritance of the embryo when the mother's oocyte contains defective mitochondria (see below for more detailed discussion of these advantages).

The fourth potential method for cloning animals is based on a form of parthenogenesis (from the Greek "virgin birth," ie, the ability to develop an embryo without spermatic contribution), which involves the activation of unfertilized eggs to bring about cleavage in the absence of sperm cells. Unfertilized eggs have only half of the normal complement of genetic material; sperm cells provide the other half at fertilization. It would, therefore, be necessary to devise a method for restoring the genetic material to its normal number of chromosomes before development of parthenogenesis as a cloning technique for mammals could occur. Such a method is theoretically feasible; for instance, in mice, eggs containing a full complement of genetic material derived from the egg alone have been produced, and have formed embryos that can develop, albeit not to term thus far.

Apart from whole organisms, it is also possible to clone single cells or fragments of DNA. A single cell is cloned by culturing it in physical isolation and allowing it to divide, producing a line of cells that are genetically identical to one another and to the parent cell. Clonally derived cell lines are essential for studying biological phenomena in a controlled fashion. Variation in the responses to experimental treatment that otherwise occurs due to differences in the genetic background of cells can thus be eliminated. The cloning of DNA fragments, also known as molecular cloning, is the foundation of recombinant DNA technology. It consists of multiplying DNA fragments, usually composed of genes or portions of genes, either in vivo inside a bacterial cell, or in vitro via polymerase chain reaction amplification. In addition to being an essential tool for molecular biology research, DNA cloning forms the basis of gene therapy approaches to the treatment of genetic disorders and cancer. The clonal derivation of cell lines and the multiplication of DNA fragments are two different procedures that are indispensable to both clinical and basic biomedical research. Neither of these procedures bears any direct relation to the cloning of whole organisms, and neither carries any of the ethical or legal implications of cloning, but since the word "cloning" figures in their name, there are grounds for confusion. Precise wording is therefore essential when discussing cloning in legislative or policy contexts.

Development of the somatic cell nuclear transfer technique

Two principal lines of inquiry converged in the experiment that produced Dolly. Researchers in animal breeding have long sought a reliable method for producing large numbers of genetically identical adult animals with desirable qualities. Embryologists and developmental biologists, however, have always been interested in defining the developmental potential of cells at various stages and under various circumstances.

One fundamental question of biology concerns the mechanisms by which a single fertilized cell can give rise to a fully functional adult organism with stereotypical cell composition. During the early stages of development, cells are generated in large numbers via repeated division of the fertilized egg and its descendants. Most cells in the embryo do not initially display overt differentiation, but subsets progressively stop dividing and begin to differentiate. This appears as trademark specializations of cells, such as the extension of axons or dendrites for neurons or the secretion of hormones for endocrine cells. Changes in the pattern of gene expression inside the cell underlie these overt signs of differentiation.

A traditional line of inquiry, carried over from classical embryology to contemporary developmental biology, concerns the timing of cell commitment, ie, when does a particular precursor cell become set on its course of terminal differentiation into a given cell type? Do the changes in patterns of gene expression ever become irreversible? The formal definition of cell commitment is empirically based: a cell is considered to be committed to a particular fate (ie, to becoming a particular cell type) if it persists in adopting that fate regardless of the conditions to which it is experimentally subjected. Investigating cell commitment therefore requires subjecting cells at various stages of their development to as many different experimental conditions as conceivable. For cells that prove to be uncommitted, the next task is to determine the range of their developmental potential, ie, which different cell fates they can adopt, and under which conditions. Ultimately, it should be possible to rank cells of each type, age, and tissue source on a scale from totipotency to irreversible commitment, via states of increasingly restricted developmental potential.

Most of the experiments that test for cells' developmental potential have consisted of transplanting whole cells into different types of tissue, or into similar tissue from different stages of development, and observing whether the cell still adopts the fate it would have assumed in its original location or acquires instead a fate that matches its new environment. This type of experiment, however, does not address the relative roles of the nucleus and the cytoplasm in cell fate determination. All the genes of a cell (except the mitochondrial genome) are located in the nucleus. The cytoplasm of a given cell, which on division is distributed to its daughter cells, itself contains gene products (ie, proteins, growth factors, and other signaling molecules) previously produced by the mother cell's nucleus. One possibility is that some of these factors are responsible for poising the newly formed nucleus of the newborn daughter cell for a given developmental fate. Alternatively, the nucleus of the newborn cell alone determines the fate that cell will adopt. A test of this hypothesis would be to transplant the nucleus of a cell (donor nucleus) into the cytoplasm of an enucleated cell (host cytoplasm). The host cytoplasm must first be enucleated in order to eliminate any confounding effect attributable to the host nucleus. Since an oocyte is certainly totipotent, the best test for its cytoplasm's ability to confer totipotency onto a foreign nucleus is to transplant the foreign nucleus into it. However, this assumes that the donor nucleus is amenable to being made totipotent. Given this situation, it becomes clear that negative results (ie, failure to produce an embryo that undergoes full development) would be difficult to interpret. However, complete development of a so-called "reconstructed embryo" to term, or better, adulthood, after a nuclear transfer experiment of this kind would constitute proof that both (1) the transplanted nucleus retains the potential for totipotency; and (2) the oocyte's cytoplasm can provide all the signals necessary to express the totipotency of the transplanted nucleus. This is precisely the result obtained by Wilmut and colleagues.¹

Experimental evidence from studies on animal cell development suggests that the less differentiated a cell is (or the younger a cell is), the more extensive its developmental potential; sometimes as extensive as totipotency for some embryonic cells. In vivo derived cells are more likely to be totipotent than cultured cells, for reasons that may relate directly to developmental potential, but that might alternatively have to do with decreased viability in vitro. It is, therefore, not surprising that the first successfully cloned mammalian farm animal (a sheep) was derived from a cell of the inner cell mass of an embryo.⁷ Its birth constituted proof that at least some post-cleavage stage embryonic sheep cells are totipotent. The experiment was later successfully repeated using bovine embryonic cells,^8,9 showing that the same was true in at least one other mammalian species. This success was followed by others, using cells previously considered unlikely to be returned to a totipotent state: (1) cloned lambs were derived from embryonic cells that had been cultured for a short time before being used as nuclei donors¹⁰; (2) cloned lambs were derived from a line of cells that had been cultured for a longer time¹¹; and finally (3) cloned lambs, eg, Dolly, were derived from fetal and from adult mammalian cells.¹

One modification that seems to have contributed to the success of Wilmut and colleagues where previous investigators had failed was pre-treatment of the donor cells to force them into a state called G0 (gap phase 0); ie, a quiescent state in which neither DNA replication nor cell division occur.¹¹ Previously, a high incidence of chromosomal damage due to interrupted replication had been observed in transferred nuclei, which probably accounts for failure of reconstructed embryos to develop fully. The apparent totipotency of G0-arrested nuclei also suggests that G0 may be a state that favorably predisposes a nucleus to be "reprogrammed" by the host cytoplasm, whatever its degree of differentiation immediately preceding the induction of quiescence. If proven, this hypothesis may have significant implications for research in cell fate determination and developmental potential of all existing cell types.

In a recent development, Wakayama et al¹² cloned a relatively large number of mice using a modified version of the technique used to produce Dolly. Partly as a result of earlier failed attempts, it was long believed that mice were not amenable to cloning via somatic cell nuclear transfer.¹³ Instead of fusing the donor cell and enucleated oocyte, the investigators injected the donor nucleus directly into the oocyte. This difference in methods is not believed to have been the determining factor for achieving the cloning. Instead, some of the important parameters are thought to be the prolonged lag between nucleus injection and oocyte activation, and the use of a piezo-impact pipette drive unit that minimizes trauma to the oocyte. The rate of success of clones developing to term--2% to 2.8%--was significantly better than for Wilmut et al,^1,12 making the technique reasonably useful, at least for experimental purposes, if not yet for breeding. Of similar concern is the high rate of congenital malformations.¹ Given the advantages of mice as experimental animals, the possibility of cloning them easily promises to facilitate the investigation of various scientific questions and to help resolve some of the issues surrounding mammalian cloning.

Remaining scientific uncertainties

A number of scientific uncertainties remain regarding somatic cell nuclear transfer as a cloning technique, and its feasibility in human beings. First, whereas research in the past few decades has highlighted the similarities in molecular mechanisms across the evolutionary board, from the fruit fly Drosophila to human beings, it also has revealed differences between species in mechanisms that would have been expected to be conserved. Therefore, it is unclear whether the methods employed for sheep and cows might be directly transferable to humans.

Another question concerns cellular aging. In vitro there is a limit to the number of cell divisions a cultured cell can undergo. This can be thought of as a cell's life span, which, given its constancy, seems to be an intrinsic feature of cells as opposed to a simple consequence of a suboptimal growth environment. If cells in vivo also have a predetermined life span, it may be that the older the donor nucleus, the earlier a clone's cells will age, causing as yet unforeseeable problems. Alternatively (and optimistically), it may be that exposure to the egg cytoplasm "resets" a guest nucleus' internal clock. In either case, cloning experiments might occasion a leap in understanding of cellular aging mechanisms. In the meantime, the consequences of cellular aging on a clone's health are uncertain.

An example of scientific uncertainty arises from the fact that the contributions of the male and the female genomes to a zygote's development differ. Sex-specificity of developmental phenomena (an example is genomic imprinting, which "brands" genomes according to their parental origin, male or female) would be eliminated in a clone whose genome is derived from a single parent. The consequences of having a uniparental genome are currently unknown. Human disease secondary to uniparental disomy has been increasingly recognized, eg, Angelman syndrome and occasional cases of recessively inherited disease, such as cystic fibrosis, when only one parent is a documented carrier of the disease allele. Whether a clone would be at a higher risk of accumulating such deleterious mutations is not known. These unresolved scientific issues continue to prompt questions about the safety of cloning by somatic cell nuclear transfer.

Technical issues include how to improve the success rate of nuclear transfer and how to ensure that adult donor cells have not acquired any spontaneous deleterious mutations that would endanger the health of the developing clone. Given the conservation of fundamental mechanisms across species, it is possible to address most of these scientific and technical issues experimentally in animals to learn how to minimize risk and maximize efficiency.

Potential benefits of cloning animals

The study and implementation of somatic cell nuclear transfer in mammals promises several benefits in research, biotechnology, and animal husbandry. In particular, this technique offers an experimental paradigm for addressing otherwise intractable problems of developmental biology, such as the nature of molecular and genetic interactions between the nucleus and the cytoplasm of a zygote during normal development, and the maintenance or restoration of totipotency in nuclei from cells at various degrees of differentiation. In addition to advancing understanding of the earliest stages of life, this knowledge could provide insight into the pathologies of early development, ultimately help in the treatment of human infertility, and yield clues to the development of diseases such as cancer.

Selective mating has been the traditional means of attaining the goals of animal breeding; more recently, breeders have used artificial insemination. As a potential method for generating stocks of domestic animals that display desirable characteristics in a rapid, reliable, and large-scale fashion, somatic cell nuclear transfer would be superior to existing methods in its ability to replicate the original animal precisely. Net improvement in the efficiency and safety of the technique would have to be achieved first. The ability to generate large numbers of identical animals would be of great value for research as well. Inbreeding, the traditional way of producing a strain of identical animals, requires repeated matings of selected animals for several generations. It can be achieved in small mammals such as mice or rats, but is much more difficult in larger animals for a variety of reasons including longer generation time, smaller litter size, etc. Cloning by somatic cell nuclear transfer might help overcome these limitations. Cloning also offers the opportunity to salvage endangered species by increasing the number of animals available for intra-species breeding.

Making "transgenic" animals, ie, animals in which all the cells contain an extra gene introduced by genetic engineering, is a commercially useful goal. Techniques for making mice and other small animals transgenic have been perfected in recent years, mostly for research purposes, but there is as yet no efficient way to make some of the larger farm animals transgenic. The freedom of choosing the source of genetic material for cloning afforded by somatic cell nuclear transfer technology introduces the possibility of achieving this goal. Provided that cells cultured in vitro for a certain length of time prove to be routinely utilizable as nuclei donors for cloning, these cells can be genetically engineered by introduction of a desired gene first. Successful incorporation of the extra gene can be verified in individual cells, which are then used as sources of nuclei for transplantation. The genetic alteration is thus propagated to the entire animal including its germ line and hence to its offspring. Any potential adverse effect of the site of gene insertion would be demonstrable in experimental animals, eg, inadvertent activation of oncogene. Examples of useful genetic modifications include making a cloned animal's cells able to produce proteins that improve the qualities of the animal (eg, growth-enhancing, or disease-resistance proteins) or to manufacture pharmaceutically important human proteins. The making of transgenic lambs that express human coagulation factor IX that can be secreted into the milk has recently been reported,¹⁴ thus proving experimental feasibility of the procedure.

Xenotransplantation is another possible use for transgenic animals. Currently, graft rejection limits transplantation of animal organs into human beings. One possible solution is to express human antigens in the organs of animals such as pigs, which are commonly used as donors. The most efficient method would be to breed stocks from individual animals that have been made transgenic for particular human antigens. The current method of injecting oocytes with genes of interest is neither reliable nor predictable. Using genetically modified nuclei as donors for somatic cell nuclear transfer promises to be a better method for breeding the desired animal stocks.

Another form of genetic manipulation consists of altering an animal s own genes in a targeted fashion. If the desired gene is defective, it can be replaced by a normal copy, or eliminated from the cell using a technique known as gene "knockout" or "targeted disruption." Scientists using this technique in mice and other research animals have succeeded in assessing the consequences of the lack of a particular gene. In addition to their potential commercial and therapeutic uses, farm animals that are transgenic or that feature targeted genetic alterations would also be invaluable research tools.

Finally, experimentation on somatic cell nuclear transfer in various mammals will be necessary for improvement and assessment of the safety and feasibility of the technology.

Potential scientific uses of cloning humans

In spite of societal fears and controversies, scientists must objectively assess the potential uses of somatic cell nuclear transfer and of human cloning using this technique. Described here are the previously unattainable goals that the application of the somatic cell nuclear transfer technique may make possible.

The nucleus is commonly viewed as the most important element in heredity; however, there are inherited human diseases caused by defects in the DNA of mitochondria. An example of an inheritable mitochondrial disease is MELAS (Mitochondrial myopathy Encephalopathy, Lactic Acidosis, Stroke-like episode). Mitochondria in the zygote are always of maternal origin, provided by the cytoplasm of the oocyte. By using another woman s oocyte, with normal mitochondria, a couple in which the woman's mitochondria are defective would have the option of sparing their child the corresponding disease, without having to use an extra-parental source of genetic material. If technically feasible, the fertilized zygotic nucleus might be used as a donor, since exact duplication of either of the parents is not the main goal of nuclear transfer in this situation.

Gene therapy is one of the most promising therapeutic applications of human cloning. The simplest example is that of one parent carrying an autosomal dominant disease gene. The parent who is free of the disease allele can be cloned to guarantee that the child would be unaffected by the disease while still carrying exclusively parental genes. The same procedure could treat autosomal recessive disease genes; however, the child would still be a carrier for the disease. It may become possible to eliminate the mutated allele. This could be performed by growing the adult cells in culture, correcting the genetic disease while the cells are still in the culture (using the genetic technique known as "knockout"), and finally using the nuclei from these cells as donors in the somatic cell nuclear transfer process.

Cloning via somatic cell nuclear transfer could make excellent therapeutic use of the extensive DNA sequence information generated by the Human Genome Project. Currently, for a given genetic syndrome when the possibility of diagnosis exists, the only course for a concerned couple is to conceive and then test the fetus. If the results indicate presence of the mutated gene, the options are either to terminate the pregnancy or to bring it to term in full knowledge of the consequences for both the child and the parents. Human cloning via somatic cell nuclear transfer would allow opportunity to correct a genetic problem before birth. Currently, there are proposals for in utero gene therapy, proposed by W. French Anderson. In preliminary studies, direct injection of retroviral markers appears to confer expression of a foreign gene without modifying the germ line.¹⁵

As a method for assisted reproduction, cloning does not offer significant advantages over currently practiced in vitro fertilization methods, unless self-replication is considered an advantage. It might be helpful to couples in which both individuals are infertile, or the man does not have any functional sperm, by providing the option of cloning one member of the couple instead of seeking gametes from others. It might also allow replication of a child who is terminally ill, a controversial goal currently unattainable by other means.

Organ and tissue transplantation is a major problem that somatic cell nuclear transfer might resolve. The shortage of donors and the problem of host-graft tissue incompatibility are widespread. Unfortunately, mentioning transplantation and human cloning in the same context conjures up the popular fear that human clones would be enslaved and exclusively used as a source of tissue and organs for transplantation. However, besides being an unlikely scenario given existing laws and safeguards, it is also an unnecessary one. A simpler way of producing matched tissues and organs would be to use a clone at its early embryonic stages as a source of cells. Scientists are learning how to treat early cells of the embryo with different factors to predictably direct differentiation into various types of tissues,^16,17 and are making progress in identifying the precise combination of factors that direct the differentiation of each tissue and cell type. Ultimately, it may be possible to generate and maintain in vitro any type of matched tissue (even organs) starting with unspecialized cells removed from a cloned embryo and subsequently treated with the adequate additives. Alternatively, somatic cell nuclear transfer alone could be used to generate appropriate cell lines (stem cells) capable of being directed towards various differentiation paths in vitro, without ever making cloned embryos. Here again, the prospect of using embryos for the proposed purposes is controversial.

Twins and clones: the issue of similarity

One form of natural cloning already exists in human beings: the formation of identical (ie, homozygotic) twins. Homozygotic twins (or multiples such as triplets, quadruplets, etc.) are produced when the first (or immediately subsequent) division of a fertilized egg develops into two (or more) cells that separate and each give rise to a complete individual. Alternatively, twins can arise from division of the blastocyst. Due to its similarity to twin formation, cloning has been called "delayed twinning," because it is a means of producing a twin for an organism at a later point than twinning would naturally occur.

Because important interactions with the environment and life circumstances shape the development of a human being, so-called identical twins are never truly identical. Similarity between twins is much greater in physical appearance and physiology than in personality and mental characteristics. The difference between a cloned human being and his or her clone is likely to be even more marked than between natural twins, given different life circumstances/environment. In addition, they share neither womb nor oocyte cytoplasm.¹⁸

Another commonly expressed fear is that the extreme resemblance between clone and clonee, coupled with the asymmetrical parent-child relationship, would cause special problems that would particularly affect the clone given his or her status as offspring. However, striking physical similarity sometimes occurs between parents and children who are not clones of one another.

Public concerns about cloning

Human twins arise naturally. Scientists were already engaged in human cloning before Dolly, and continue to do so for in vitro fertilization purposes. The novel opportunity that somatic cell nuclear transfer technology offers is for a sentient human being to clone him or herself, thereby changing the terms of the relationship that has so far existed between clone and clonee from a sibling relationship of equals, to an asymmetrical parent/child relationship. This may be the most disturbing perspective to the public, but is certainly not the only one. Public concerns regarding human cloning include emotional, philosophical, religious, and other issues. It is important to begin the process of identifying the issues, consulting with appropriate experts and interested citizen groups, and developing consensus to inform future legislation.

The National Bioethics Advisory Commission's report "Human Beings"¹⁹ is a comprehensive presentation of the arguments on all sides of these issues, based on extensive testimony from an array of experts (scientists, ethicists, theologians, legal experts) and other interested parties (see Appendix.) Public concerns regarding cloning primarily involve two themes: safety of the technology and societal choices.

1. Safety of the technology: In the event that human embryos are successfully cloned and implanted into a woman s uterus, the question of what percentage of these embryos are likely to be born healthy arises. There are numerous reasons why cloning might present a significantly higher risk of birth defects or even of problems that would only manifest later in the life of the cloned individual, as compared to the risks present in natural reproduction. No matter what the source of risk, it would be unacceptable to most people to allow human cloning without exhaustive evaluation of its impact on embryo development. Unlike the system in place for studying new drugs, the option of empirically evaluating risk by conducting a large-scale cloning trial is inconceivable. Therefore, the only reasonable decision would seem be to ban cloning. However, the safe and gradual scientific development of human cloning techniques may be possible. By carefully and simultaneously characterizing large numbers of pre-implantation cloned embryos for gene expression levels and for morphological development, scientists might develop reliable molecular markers (or other predictors) of an embryo s potential to develop and grow normally. The status of these predictors would be assessed every time an embryo is cloned, and only potentially healthy embryos would be considered for implantation. Researchers in human reproductive biology have already successfully undertaken this approach. Scientists at Cornell University Medical College have found that the expression of genes from the insulin-like growth factor family correlates well with the morphological growth potential of donated day-3 human embryos.²⁰

Scientific research on human and animal somatic cell nuclear transfer is necessary to improve the safety of human cloning. It could even be argued that the issue can be resolved only through appropriate experimentation. In this context, the line should probably be drawn at the level of implantation, rather than creation, of embryos. Safety issues must be resolved to the full satisfaction of the public and scientists before uterine implantation of human embryos is allowed. A segment of the public, however, deems the very creation of embryos for research purposes unacceptable, even for the purpose of improving safety of the procedure. Therefore, this approach can only be taken if society decides to go forward with the development of human cloning technology. Meanwhile, scientists are restricted to research on animals and donated human embryos, which is suboptimal to assess the safety of human cloning. A shift in the consensus toward permitting the use of very early human embryos for research purposes, while still restricting further growth and prohibiting implantation, would greatly facilitate the assessment and improvement of the safety of human cloning.

2. Societal choices: Beyond moral issues, the prospect of cloning humans raises questions about societal choices and basic human rights. Public expressions of fear and excitement about cloning often reflect belief in genetic determinism. It is widely believed that genetics are the major determinant of a person's appearance, personality, and even fate. Some believe that this tendency toward excessive genetic determinism might be accentuated by the advent of human cloning. It is feared that by focusing on the striking similarities between clone and clonee, people would tend to attribute more to genetics than to other determinants of human essence, such as the environment. However, observation of the differences that are certain to emerge between clone and clonee may temper belief in genetic determinism. Genetic determinism may also lead to concern about eugenics and the desire to create a "perfect race," and the fear that cloning would further such a goal.

Scenarios describing exceptional circumstances have been used to argue against a definitive ban on human cloning. These include the impending death of a beloved child, or the predicament of parents who are both carriers of a lethal gene. However, while banning cloning may seem cruel toward families faced with such circumstances, some people still believe that the dangers of cloning override any of its potential benefits. Were cloning to be conditionally legalized as a solution to exceptional reproductive problems, another difficult question arises: how to establish guidelines.

Most of the above noted concerns assume widespread usage of human cloning technology. However, even if cloning were legalized and unrestricted, numerous reasons exist to presume that people would resort to it only on rare occasions. First, it would be expensive, since it requires sophisticated manipulations, and its frivolous use would be unlikely to become reimbursable as a health care expense. Second, it is not immediately evident that people would desire the creation of "look-alikes" of themselves, in the absence of a compelling reason (such as an inherited disorder or the impending loss of a loved one). Ultimately, public choices about cloning will be made in the political arena, but in the meantime, exposure should be given to the widest possible range of views.

Public understanding of science/training of scientists

According to a National Science Foundation study, even though public interest in science and technology currently is higher in the United States than in most other countries, popular understanding of basic concepts remains weak. For instance, only 11% of people interviewed could accurately define the word "molecule."²¹ While an international comparison reveals that US adults perform relatively well in scientific literacy tests, understanding complex processes such as cloning requires more than a grasp of basic scientific concepts. For this and other reasons, the communication of science to the public is increasingly difficult, and is compounded by public distrust of the news media and the scientific and medical establishments. Responsibility for improving the quality of science information must be shared by the public, scientists and physicians, and the news media. The role of professional medical and scientific associations, such as our AMA, in this context is to participate, or take the lead, in initiatives to improve science communication and promote the public understanding of scientific issues.

In the context of science communication, scientists and physicians should not be immune to criticism. Generating knowledge and thinking about its social implications have often been kept separate in the past. Professional medical and scientific associations could help by promoting the training of scientists and physicians in social and philosophical issues surrounding new technological advances in their respective fields.

Legal and policy issues

The announcement of Dolly's cloning triggered worldwide official reactions, most warning against the dangers of cloning. President Clinton requested the National Bioethics Advisory Commission (NBAC) undertake a "thorough review of the legal and ethical issues associated with the use of this technology," and report back within 90 days with recommendations on possible federal actions to prevent its abuse.¹⁹ Shortly thereafter, the President announced a moratorium banning the use of federal funds for cloning humans. In June 1997, he proposed a bill to ban the cloning of human beings for at least five years. Legislation was also introduced in Congress (eg, Human Cloning Prohibition Act, 1997: H.R. 923; 1998: S 1599, S 1601, 1611 PCS), and in a dozen states. These bills differed significantly in formulation, and some go so far as proposing to ban the "& use of human somatic cell nuclear transfer technology" or to inadvertently and even explicitly ban any research using cloned cells or tissue as well. The most explicit and most precise bill at this time is S 1611, introduced by Senators Diane Feinstein and Edward Kennedy (Human Cloning Prohibition Act, 1998: S 1611), which is essentially based on the recommendations of the NBAC.¹⁹ This bill is also the most comprehensive: it includes several provisions for protecting research, a recommendation to further review the ethical and scientific issues associated with cloning, and a sunset clause that limits its effectiveness to 10 years. Ideally, any bill that might be introduced would follow the same model, and detail even more explicitly the procedures and techniques that are excluded from prohibition. In May 1997, the state of Michigan passed legislation that makes it a felony to clone a human being; however, it allows all research short of creating a human being through cloning. At present, nine states have outright bans on research on human fetal tissues. Other laws prohibit payment for embryos. Such laws could also extend to cells and tissues derived from embryos

The major issues for public policy on cloning fall into two categories: regulatory and constitutional. The 1995 ban prohibited the use of federal funds for financing research on human fetal cells, including those derived from human embryos; industry, however, is not prohibited from research in this arena.

The Food and Drug Administration (FDA) has claimed oversight on human cloning.^22,23 Others have disputed the FDA s claim, which is based on the agency s ability to regulate medical products. The essential question is whether cloned cells fall under the FDA s jurisdiction versus representing a new form of fertility treatment or medical practice. In response to possible congressional legislation, a coalition of research organizations have circulated a preliminary proposal to create a national review board for all cloning experiments along the lines of the National Institutes of Health-affiliated Recombinant DNA Research Advisory Committee. The latter body has reviewed protocols dealing with experiments using recombinant DNA techniques. The advent of the initial recombinant DNA technology was accompanied by voluntary restrictions that researchers placed on themselves. There is concern, however, that the potential cloning presents is too great for voluntary restrictions to succeed.

The possibility of human cloning also raises legal and constitutional issues. Some state laws, particularly medical malpractice law and laws governing family relationships may have applicability if human beings are cloned.

Other questions include: Will cloning be permissible based on motivation? What would be the acceptable criteria for requesting cloning? What would be the issues of informed consent for the clone and the donor? What sources of tissues would be acceptable (ie, would it be acceptable to clone anyone unable to give informed consent, such as dead persons, young children, or terminally ill persons)? How would such regulations be enforced? What are the implications of variations in international law covering human cloning?²⁴

The above questions emphasize the critical need for serious public reflection in order to reach a national consensus to inform the formulation of public policy. The "timeout" on cloning that has been provided by the current moratorium is an excellent opportunity to initiate consultation with experts and organize public deliberations. The role of our AMA is to help clarify the underlying scientific, medical, ethical, and policy issues, and to help develop a mechanism that protects biomedical research.

Conclusion

The recent success of somatic cell nuclear transfer technology as a method for cloning mammalian farm animals such as sheep, cows and mice, has brought society one step closer to the possibility of cloning human beings. Human cloning presents a number of challenges to society, whether ethical, legal, philosophical, regulatory, or emotional. It also offers tremendous potential benefits, such as the first opportunity to make use of the knowledge generated by the Human Genome Project in order to correct genetic problems before birth. It is important to address each of the reasonable questions raised. This includes careful consideration of whether any proposed argument outweighs potential benefits and warrants unconditional prohibition of the technology. However, simply banning experimentation or the practice of human cloning without any further consideration is not in society s collective interest.

Unconditionally banning research and applications of human cloning is not recommended. Since the procedure is scientifically feasible, it is likely to be developed privately and secretly, outside a proper regulatory framework, which would mean that any benefits of human cloning will only be accessible to a restricted segment of society. If legislation outlaws the use of somatic cell nuclear transfer and the cloning of animals and human tissues, it could easily result in the loss of very useful scientific and medical insight into processes as diverse as developmental biology, cancer biology, transplantation, and the cure or treatment of genetic diseases.

The challenge for scientists, policy makers, and the public lies in appropriate pacing of scientific and technological advances. The pace will be appropriate if it allows for thorough examination of the potential consequences, and the adoption of measures that address these consequences, without unnecessarily hindering highly beneficial biomedical research. The temporary moratorium on human cloning declared by President Clinton, if used as an opportunity to seek consensus on the various concerns surrounding the procedure to establish a regulatory framework and to propose an adequate research program that is not unduly restricted, is a commendable step. During this moratorium on the cloning of a human being there should be extensive government consultation with all concerned groups, hopefully leading to a comprehensive plan for how to realize the potential of this technology.

Recommendations (adopted AMA policy)

The following statements, recommended by the Council on Scientific Affairs, were adopted by the AMA House of Delegates as AMA policy at the 1999 AMA Annual Meeting.

1. The AMA supports efforts to convene a conference of scientists, physicians, bioethicists, and other relevant experts to develop consensus on the scientific and bioethical issues raised by somatic cell nuclear transfer technology. 
2. The AMA will promote efforts to maintain the 5-year moratorium on the cloning of human beings and prevent efforts to restrict current and future biomedical research unduly. 
3. The AMA supports efforts to develop an oversight mechanism similar to the Recombinant DNA Research Advisory Committee, affiliated with the National Institutes of Health, to review all human cloning experiments. 
4. The AMA supports efforts to establish a program for promoting the public understanding of science, and the understanding of social and philosophical issues by scientists.

References

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