The Roslin Institute, one of the world's leading centers for research in animal husbandry, is housed in a neat collection of buildings near Edinburgh. Surrounded by gently rolling, impossibly green hills dotted with countless puffs of fleecy white sheep, the place seems an unlikely setting for grand, scientific events. The setting seems more that of a highly successful, modern farm than the high-octane scientific laboratory that it is. Yet, it was here in 1996 and 1997 that a scientific team led by Ian Wilmut, a mammalian embryologist, in collaboration with a team at a neighboring biotech company called PPL Therapeutics, cloned a sheep named Dolly, which overnight became the most famous animal in the world.
In creating Dolly, Wilmut and his colleagues repealed a fundamental biological law: that it is not possible to produce a genetic copy of a mammal from a cell taken from an adult. Dolly was not created via the union of sperm with egg. She was created from the genetic material of a single cell—taken from the mammary gland of a six-year-old Dorset ewe. Of course, a sperm and egg did come together to create Dolly's genome. Her genetic parents are the parents of the Dorset ewe from which she was cloned. Dolly was created in a glass dish when the nucleus of the cell taken from the Dorset sheep was inserted into an ovine egg and transferred to the uterus of a surrogate mother belonging to yet another breed.
On nature's mighty evolutionary tree, the human twig arises from the same branch as does the sheep twig. Since Wilmut could clone sheep, there is a good reason to think that we will eventually be able to clone humans. Is there any more dramatic moment in the history of our species than the discovery that we can circumvent the mechanisms of genetic recombination and reproduction by which we evolved? Unless there is some as-yet-
undetected aspect of human biology that forbids it (which is unlikely), cloning, in combination with gene modification, will eventually launch humans on a scientific and cultural voyage of immense consequences. At some still far-off time, we will truly be able to guide our own evolution. In some respects, Wilmut's experiment is as dramatic as was the proof that the earth revolves around the sun.
All humans and—until Dolly—all mammals begin life as the union of a single sperm and egg. That first cell, the zygote, contains in its nucleus a full set of all the genes needed to create an adult animal. After the first cell division, the daughter cells of the zygote are still totipotent; that is, they are each capable of producing a human. We know this because of the existence of identical twins. Scientists had long thought that totipotency faded quickly. How else could the body plan be established or organs formed? As the first two cells divide to become four and then in turn a cluster of eight and so on, until after three weeks they have organized as an embryo composed of billions of daughter cells, each cell somehow must be repro-grammed to carry out defined tasks—to be a heart cell, a kidney cell, a brain cell. Scientists had good reason to infer that the price of this exquisite specialization was the loss of totipotency. They thought that the genetic programming that must occur to become, say, a heart cell was much too complicated to ever permit such a cell to retrace its history and reconfigure itself with the set of directions needed to create an entire embryo. Although the nucleus of a heart cell has all the genes that make up a complete human genome, most scientists were convinced that many, if not most, of those genes were permanently inactive.
One of the first challenges to the notion of the fixed nature of a cell's genetic program came in 1952 when scientists removed a nucleus of a cell taken from an early frog embryo and transferred it into a frog egg from which all genetic material had been removed. To everyone's surprise, the genetically engineered egg grew into a frog! In 1975 John Gurdon, a British embryologist, repeated the experiment with a nucleus taken from the skin cell of an adult frog. The cloned cells consistently grew into tadpoles, but stubbornly refused to go further. Gurdon's experiments strongly suggested that animals could not be cloned from adult cells. In subsequent years, few scientists decided to risk their careers by assaulting this barrier.
During the late 1980s, several research teams did clone sheep and cows by using nuclear material taken from blastomeres (a cluster of cells from which the embryo arises). This is a different kind of cloning, more akin to the deliberate creation of identical twins. One can think of it as "horizontal" cloning, because the replication event (the creation of the twin) does not involve copying a genome from a parent—an animal which has lived or is living independently. Rather, a cell mass is disaggregated, and multiple copies of the animal that would have arisen from the blastomere are created.
In 1996 Wilmut and his colleagues showed that they could use DNA from a fetal cell, which was sufficiently old that virtually every reproductive biologist thought it had completed the path to irreversible commitment, as the nuclear material for cloning sheep. Their experiment, which gained relatively little attention, was based on a new idea that set the stage for creating Dolly. Wilmut guessed that the secret to successfully cloning mammals from adult cells lay not in the genes but in the cytoplasm which surrounds the nucleus. Drawing on their knowledge of the cell cycle, he and his colleagues induced the cells to enter a quiescent phase (a sort of molecular hibernation during which the DNA would be inactive) which they thought would lead to a loosening of the fixity of the nuclear program. Success with fetal sheep cells emboldened them to repeat and expand their experiments.
What did they actually do? They used hormone injections to make Scottish Blackface ewes superovulate, an intervention quite like the treatment of infertile women to harvest eggs from them for in vitro fertilization. Using a laparoscope, they retrieved the eggs from the ovaries of the Blackface ewes. Next, they placed the eggs under a microscope and used incredibly thin pipettes to puncture them and, quite literally, sucked the nuclei (a tiny sac containing all the genes) out of the cells. They then isolated a nucleus (containing the full complement of DNA) taken from a culture of cells prepared from a biopsy of a physically distinct breed of sheep (the Dorset) and used a mild electrical shock (which creates small holes in the cell wall) to coax that nucleus to move into the genetically empty egg. They cultured the resulting clones for six days, carefully monitoring them for any sign of disorderly development. They then transferred all the apparently healthy cloned embryos into Scottish Blackface ewes that had been hormonally prepared for pregnancy.
They conducted experiments with three populations of cells: some from a 9-day embryo, some from a 26-day fetus, and some from the mam mary gland of a six-year-old ewe. Altogether, they created 385 potential clones by fusing enucleated eggs with embryonic cells or fetal fibroblasts and 277 potential clones from cells created by fusing enucleated eggs with adult mammary epithelial cells. Most ewes did not become pregnant, and of those that did, the vast majority miscarried. Altogether, the host mothers gave birth to only eight lambs. Of these, seven derived from cells that had been created with sheep embryos or fetuses, and thus represented a validation of earlier experiments. Of the 277 fused cells that were created from adult Dorset mammary cells, 29 morulas (pre-embryo cell masses) were put in the surrogate mothers, 13 ewes became pregnant, and one gave birth—to Dolly. Being the genetic clone of a Dorset ewe, Dolly looks nothing like her Scottish Blackface birth mother.
Does Dolly have a genetic mother? Does she have a father? Yes. From a genetic perspective, she is the offspring of the pair of sheep that gave birth to the Dorset ewe from which the cell was taken to launch her. That is, she is the genetic child of the two sheep that are the parents of the animal that provided the cell from which she was cloned (animals that from a generational perspective we would call her grandparents). But Dolly is also the identical twin sister of the sheep which provided the mammary cell that became the source of her genetic constitution. Of course she is identical only from a genetic perspective, not from an environmental one. After all, she was born nearly seven years after her older twin!
This raises the fascinating question of Dolly's age. Is she a yearling or is she (in terms of life expectancy, fertility, and risk of disease) an old sheep? We have learned that just as do whole organisms, cells too have life expectancies, usually measured in terms of expected number of cell divisions before senescence. Dolly developed from a relatively old sheep cell. Determining her biological age—best done by pampering her for the next decade—will be of crucial importance. Early studies suggest (but do not prove) that Dolly will have a shorter life expectancy than would a lamb born on the same day.
As any literate adult who was on the planet in March of 1997 knows, Dolly's birth elicited an unprecedented public response. Suddenly, Ian Wilmut, a mild-mannered fellow, was the best-known biologist in the world. The Scottish lowlands were besieged by the world press, and not a few vans carrying television crews probably shouldered sheep transport lorries off the narrow roads about Roslin. To the furthest corners of the globe, nearly everyone who heard the story seemed to sense that humankind had acquired a vast new power, and many worried that we might not be able to handle it.
News of Dolly triggered two quite different stampedes. One group— politicians, consumer activists, bioethicists, religious leaders, and lawyers—rushed to formulate policies that banned human cloning. The other group—reproductive biologists, scientists who work in animal husbandry, and investment bankers—rushed to conduct other cloning experiments, mostly involving farm animals. President Jacques Chirac of France promptly announced that he would ask the Group of Seven industrialized countries to ban human cloning. He convened a panel of experts to discuss "fears" and "fantasies" raised by the prospect of human cloning. Wolfgang Fruchwald, president of the German Research Association, urged Chancellor Kohl to seek a worldwide ban; the Chinese Academy of Sciences announced it had banned cloning; and in Geneva, Dr. Hiroski Natajima, Director General of the World Health Organization, called human cloning an extreme form of experimentation that should never be done because it violates the dignity of the persons born thereby. President Clinton declared a moratorium on federally funded research relating to human cloning and asked the National Bioethics Advisory Commission to advise him within 90 days. In an unusual twist, Ian Wilmut's appearance before Britain's Parliament (which had a few years earlier enacted a law that has been interpreted to prohibit human cloning) to oppose human cloning was countered by the testimony of Ruth Deech, of the Human Fertilisation and Embryology Authority, who said she could envision rare circumstances in which it might be ethically defensible.
Nicholas Coote, assistant general secretary of the Roman Catholic Bishops Conference, asserted that every human being has the right to two biological parents. He was quick to note, however, that human cloning would not contradict the Church doctrine of unique creation. Otherwise, what moral status could be accorded to naturally arising human identical twins? Jeremy Rifkin, a professional critic of genetics, called for criminal penalties for human cloning and advocated longer prison terms for clon-ers than those handed down to convicted rapists. At MIT, one of the few places that seemed to find some humor in cloning, an April issue of the student paper announced that the university would "use new state-of-the-art cloning techniques to create a race of super beings." The paper also reported that a "superior" university administrator would be the source for cloning future administrative clones. In a news interview, he proclaimed himself the "prototype" who would "be in charge of all the others."
From Denmark to Brazil, scientists rushed to replicate and extend Wilmut's work. Because of the potential economic benefits that could flow from increasing the average milk and meat yield of herds, many scientists attempted to clone cattle. A little more than a year after Dolly, Jose Antonio Visinton, a veterinary scientist at the University of Sao Paulo, announced he had successfully used embryo splitting to clone cows. Rather than replicate a single cell, he had divided early cow blastomeres and transferred them to surrogate mothers, setting the stage for the birth of a small herd of identical twins. This "laboratory twinning" is technically easier to perform than the nuclear transfer technology used to create Dolly.
On July 24,1997, just 5 months after reporting the arrival of Dolly, the teams at Roslin and PPL announced the birth of five lambs cloned from fetal cells into which had been inserted a single human gene (they did not disclose which one for proprietary reasons, but it is almost certainly a gene the protein product of which is crucial to treating an important human disease). Studies of one lamb, named Polly, showed that she had incorporated the human gene into her cells. Even if the gene product is not well expressed, the fact that it is possible to insert human DNA randomly into the genome of a fetal sheep cell and clone an animal from that cell which develops normally has immense implications for the development of new therapies. The birth of Polly is an important milestone in refining methods for the production of transgenic animals (see Chapter 14)—the pharmaceutical factories of the future! It also brings the dream of xenotransplantation (see Chapter 16) a big step closer to reality.
In August of 1997, ABS Global, Inc., a small biotech company in Wisconsin, announced that it had developed a highly efficient approach to cloning animals and that ten cloned Holstein cows would soon be born. The announcement came hard on the heels of one that ABS had made just a day earlier of the birth of the world's first calf created via somatic cell nuclear transfer (e.g., as was Dolly), a male named, appropriately, Gene. The ABS approach capitalized on technical improvements developed by a
Florida scientist named Dr. Steen Willadson, who reasoned that if one turned an adult cell into an embryo cell and then cloned the embryo cell, many more pregnancies would result. In this double cloning process, the Wisconsin group first created a clone in the way Wilmut had, then it sheared cells from the resulting blastomere and again fused them with enucleated eggs. After they began to form an embryo, they were transferred into surrogate mothers who delivered them. Whereas the technique used by Ian Wilmut yielded about one live-born clone for every 60 attempts at pregnancy (1-2%), ABS claimed a success rate approaching 40%.
Besides agricultural improvements, what are other potential uses of cloning in mammals? Two important ones are preservation of endangered species and making progress in xenotransplantation (see Chapter 16). In 1999 a rare African cat was born after in vitro fertilization and transfer into the womb of a domestic house cat. The feline surrogate mother doted on her unexpected kitten, despite the lack of any family resemblance. Can cloning be far behind? There are a number of offbeat potential uses of cloning, such as the suggestion from a cat fancier that cloning would permit one to immortalize pets. This is, of course, not the case, but it might well provide a grieving master with a cloned pet that he or she could not distinguish from its deceased genetic twin.
The overwhelming reaction around the world to the arrival of Dolly has been that nuclear transfer technology (as cloning is termed in the scientific literature) should not be used to create human beings. Sifting through dozens of moral pronouncements, however, one is hard pressed to find rigorous arguments. Rather, there is a widely shared moral revulsion to the notion of cloning humans. What is the source of that revulsion? It seems to be a deeply held belief that every human should have the right to begin life (be conceived) with a unique genetic constitution. For example, the first clause of the statement on cloning by the European Parliament says that "each individual has a right to his or her own genetic identity and that human cloning is, and must continue to be, prohibited." What then of identical twinning (which occurs about once in every 270 births)? Are twins born bereft of a fundamental right? Identical twins are natural clones, the product of a normal conception about which the couple (if they thought about it) assumed that the resulting child would be genetically unique. Thus, identical twins, whether hoped for or not, are never intended because (for now at least) humans attempting to have children cannot act in a manner that improves the chance of achieving that aim. On the other hand, intentional human cloning (whether by splitting an embryo to create octuplets or by nuclear transfer technology) would knowingly and deliberately violate that natural right.
What precisely is the harm to one who is created by a method that denies genetic uniqueness? Identical twins are genetic replicas of each other. Are they in some fashion diminished? How? Psychologists have been studying identical twins for a century and have found very little evidence that the experience is harmful. Quite to the contrary, identical twins typically have a close, supportive relationship, a wonderful asset in our troubled world. Simply put, there is no evidence that one is harmed by being a twin.
Indeed, the argument that one is harmed if one is created in a manner that precludes genetic uniqueness is based on a false assumption: that we are unique because of our genes. In addition to being scientifically erroneous, such an assumption is a capitulation to genetic determinism and a dangerous political idea. Scientist or not, our life experiences should convince each of us that we are the product of an infinitely varied set of interactions with our world. All organisms are at any given moment the embodiment of the history of the interactions of their genetically programmed selves with the environment.
Furthermore, from a genetic perspective, one could even argue that a cloned individual would have a richer and more varied genetic constitution than any individual conceived naturally. Each of his or her cells actually would have genes from three individuals. The nuclear genome would be, like everyone else's, the result of a usual conception between germ cells from two individuals (in this case the parents of its "older twin"). In addition, he or she would inherit mitochondrial DNA (small circles of DNA coding for a few key genes) from a third individual—the donor of the egg into which the nucleus was transferred! Thousands of copies of the circular mitochondrial DNA would be in the cytoplasm of that enucleated egg. Finally, because the genome from which the clone was created existed for years in a somatic cell, it almost certainly acquired a number of mutations that differentiate it from the zygote from which it derived.
The strongest objections to human cloning seem to arise from those with the most fertile imaginations. The potential for some of the imagined abuses is real; for others, however, there is no basis for concern. For example, fears that some person or groups will create battalions of genetic copies of individuals for personal gain or for a destructive goal have no grounding in reality. Cloning requires access to human eggs and women willing to act as surrogates, both of which are and will continue to be scarce. It is possible that scientists will eventually discover a way to modify enucleated cow or pig eggs in order to use them as a suitable home for a human somatic cell nucleus. The scientists would also have to figure out either how to transfer human mitochondrial DNA or convert animal mitochondria to meet the needs of human cells, but this too may be a surmountable challenge. Assuming technical success, this would eliminate one major hurdle to inexpensive cloning. However, it is difficult for me to imagine any regulatory body in any nation permitting the experiments that would have to be undertaken to pave the way for clinical attempts to use animal eggs. With enough money, one can, admittedly, acquire even such precious services as those provided by surrogate mothers, but one could hardly do so in secrecy. Surely, global moral censorship would dissuade all governments and all corporate entities from attempting human cloning, but there are no certain mechanisms to prevent isolated acts by a few individuals.
Discussion of technical issues may obfuscate the key point. If the most fundamental fear is that we are entering a brave new world in which we will be able to replicate human genomes, then we must make sure we grasp the reality of being a clone. Even if one made many copies of an individual and arranged to raise a dozen clones, it is highly doubtful that any of them would wind up living a life substantially like his or her genomic parent. True, clones of Michael Jordan might tend to be tall, handsome, and athletic, but as each would grow up in a profoundly different environment from the one that shaped him, it is impossible to predict a life scenario. Could one of the clones become a basketball superstar? Possibly. But the 25-year wait to find out should dissuade even the most zealous fans from being much interested in cloning.
One can imagine far more grotesque scenarios than cloning humans that could spin out of the ever-accelerating advances in molecular biology. For example, someone might someday attempt to use a combination of gene transfer and cloning to create novel primates with some "human" ca pabilities. This dark vision recalls The Island of Dr. Moreau by H. G. Wells. The classic science fiction tale recounts the accomplishments of a brilliant physician who, self-banished to a remote Pacific Island, has discovered how to circumvent immunological and genetic barriers in order to create "beast men." Such an act would contradict the teachings of virtually every religion and contravene virtually all ethical systems, as well as violating existing regulations and law. No nation claiming membership in the moral community would permit it. But what if research discovered that the transfer of a particular animal gene into human embryos destined to have a particular disease was the only available cure? Would it be unethical (assuming fully informed consent by the potential parents) to perform the gene transfer? Would the treated fetus be any less human?
What is the most likely scenario by which the first human clone born with a genome copied from an adult will arrive in this world? It is possible that a vainglorious reproductive biologist will clone himself just for the sake of being first, but I think it far more likely that human cloning will occur first in a setting that will be highly likely to evoke our sympathy. For example, imagine a 42-year-old woman who has just lost her only child (a six-week-old infant) and her husband in an auto accident. She arranges for a biopsy of the newly dead child and persuades a friend who is an infertility specialist to transfer a nucleus from the child's cell into one of her own eggs, and then to place it in her uterus. Since she did not witness the infant she lost grow to adulthood, the woman would not watch the cloned child's life unfold with any preconceptions. Who would condemn this act? How would it harm humanity?
How will we respond to the arrival of the first human clone? Will it depend on how we learn? If this news story of the decade is presented as an exclusive television interview or Internet webcast featuring an adoring birth mother and a beautiful infant, is not the clone likely to take on permanent celebrity status (with yearly photo stories in People magazine)? I think curiosity and fascination are far more likely to be the dominant responses than is moral revulsion. When the event occurs (and it will), perhaps the society will ultimately regard it as a choice made by a single person (or a couple) for intensely private reasons. If we condemn their act, do we not threaten the general principle of procreative autonomy? Do not most of us passionately believe that marriage and procreation are activities into which the state should rarely, if ever, interfere? Since the world will in no tangible way be harmed by the unusual, perhaps bizarre, choice of a few people to have a child through cloning, then on what basis should we forbid it?
I think that the most powerful argument against human cloning is that there is too great a risk that the child created by cloning will suffer— perhaps severely—when he or she grasps the nature of his origins. It is certainly possible that a human clone would carry no more (and perhaps less) emotional baggage than does a child adopted across racial groups, a child adopted into a gay household, or a child who began life as a donated frozen embryo. Such children are welcomed into our society every day. On balance, it seems the wiser course to err on the side of protecting the potential child and to forbid human cloning for any reason. Of course, forbidding it will not prevent human cloning. It will merely result in a world where it is practiced infrequently and clandestinely. Of course, no matter what the rules, we will still have to anticipate how to respond to the first human clones. The only morally permissible response is to welcome them into the human family.
If creating humans by cloning is absolutely immoral, is it ever permissible to clone human cells that are totipotent, that is, capable of developing into a human, for other purposes? In 1999, hard upon the world-changing discovery that it was possible to isolate cells from human embryos that have totipotency and grow and store them, this became a dominant bioethical issue that reverberated through Congress and the White House.
Since 1981, scientists have been able to isolate and manipulate mouse embryonic stem cells. This provided the technological foundation upon which transgenic animals were created. In particular, transgenic mice have become one of the most valuable of all tools to use in understanding the role of genes in development and disease.
During the 1980s and 1990s, the conventional wisdom was that human embryonic cells lost totipotency very early and permanently. At the end of 1998, however, two privately funded research laboratories reported convincing evidence that they had isolated and cultured human embryonic stem cells and prevented them from becoming highly differentiated. In 1999 more than a dozen research papers were published extending this research. Even though it is in its infancy, the work thus far signals a revolution in medical therapy. In the next few years we could see the emergence of cell transplant therapy in which cultured stem cells are persuaded to differentiate into the proper sort of brain cell to be transplanted into persons with Parkinson disease or to become insulin cells for transplant into diabetic patients. In 20 years or so, the cells, mounted on tissue scaffolds, may become the seeds from which much-needed organs are grown. One can imagine a world with a virtually unlimited supply of organs available for those in need.
Reports of the discovery of human stem cells were instantly entangled in the abortion debate. In the United States and many other nations, it is illegal to use federal funds to perform research that destroys a human embryo. Yet, by far the best source of these extraordinarily valuable stem cells are frozen human embryos stored by infertile couples who no longer wish to attempt pregnancy. The use of tissue obtained from spontaneous abortions is much less attractive to scientists because of the obvious problem of timing, access to the tissue, risks of infection, and other concerns. The use of tissue from planned abortions is an alternative possibility, but it has met with predictably strong opposition.
In 1999 the U.K. imposed a one-year moratorium on experiments with human stem cells to permit public discourse about the ethical issues. France's highest court advised lifting that country's ban on human embryo research. In the United States, the National Bioethics Advisory Commission recommended to President Clinton to permit federal funding of stem cell research. Late in 1999, the NIH issued guidelines that permitted funding of stem cell research but forbade expenditures to derive the needed cell lines from human embryos, thus leaving that task to the private sector. In the halls of Congress, groups lobbying for fetal rights have, somewhat surprisingly, been effectively countered by advocacy groups representing millions of people whose only hope for cure may be stem cell therapy.
The ethical debate over the use of frozen human embryos to serve a highly desirable line of research that could save so many lives recalls the public reaction to the daring act a few years ago by a California couple. When Abe and Mary Ayola, a couple in Walnut, California, learned that their teenage daughter had a fatal form of leukemia for which the only possible cure was a bone marrow transplant, they devoted two years of intense effort to finding a donor. To no avail. Already in their early 40s and feeling that time was running out for them and their daughter, they intentionally conceived a child, hoping that they would win the 1 in 4 bet that the baby would be an immunologically compatible bone marrow donor for their daughter. News of their action evoked sharp criticism from bioethicists who accused them of turning the fetus into a therapeutic object, to which Mrs. Ayola responded, "Our baby is going to have more love than she probably can put up with." The infant did turn out to be an ideal genetic match, and bone marrow taken from her appears to have saved her older sister's life.
Ultimately, the most beneficial use of cloning human cells will probably be the generation of autologous tissue. Perhaps before 2050, we will be able to create our own private organ banks. Some parents are already paying to have cord blood taken from newborn babies and stored. This tissue is rich in stem cells that can be frozen for decades and used if a bone marrow transplant is needed; for example, to treat leukemia. One can imagine a day, decades hence, when cells from an individual will be on call as needed to produce specialized tissues and organs. For example, stem cells might be removed from cord blood and used to create cell lines to treat Parkinson disease and other neurological disorders or grow new organs to replace failing parts. Because this technique does not depend on the creation of embryos, it is not likely to encounter much moral opposition. In the next few years, however, the key research will be done with frozen human embryos. The moral debate will not be resolved, but the political struggle will end in funding the research.
Francis Galton, age 66. (Reprinted, with permission, from Pearson 1924.)
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