Historical Background and Scientific Foundations

Transcription

1 Human Cloning Biotechnology: In Context, 2012 Introduction A clone is an exact genetic copy. Bacteria and plants can be cloned naturally, but animal cloning is much more difficult. When Dolly the sheep was cloned in 1997, however, it showed that animal cells could be reprogrammed under certain experimental conditions, and achieving this in one mammalian species suggested cloning would be possible in others, including humans. Human cloning can refer to either therapeutic cloning or reproductive cloning. Both can, in theory at least, be achieved using the same technology, nuclear transfer, used to create other clones in other species. In therapeutic cloning, a human embryo is created from a somatic cell, such as a skin cell, and the cells in this embryo are then used to make cells and tissues of various types, such as blood cells or neural cells, that can be used to repair the body. In human reproductive cloning, a process in which nuclear transfer would also be the first step, the goal would be to create an embryo that could develop to term rather than being harvested for its cells. As of 2011, there have been no scientifically verifiable cases of human reproductive cloning. Words to Know Human embryonic stem cells Human embryonic stem cells are just one source of stem cells. They are found, as the name suggests, in the human embryo and have the capacity to develop into all the cells and tissues of the human body. Parthenogenesis The development of a whole organism from an unfertilized egg, which is the main type of reproduction in some organisms, including several insect species, such as some aphids, and certain reptiles and fish. Somatic cell nuclear transfer The process by which animal cloning is achieved, involving transfer of a somatic, or body, cell to an egg from which the nucleus has been removed. The transferred somatic cell begins to divide and develop into an embryo. Stem cell A stem cell is a cell that is characterized by its potential to develop into many other cell types and its ability to keep renewing itself through cell division. Totipotent Stem cells that have the ability to develop into any cell type and create a whole organism are said to be totipotent. Plant cells and animal embryonic stem cells are totipotent. Historical Background and Scientific Foundations Since the nineteenth century, scientists have been intrigued by the question of whether cells are capable of growing into a whole organism. Plant cells are totipotent, with an entire plant being generated easily

2 from a leaf or stem cutting. Moreover, the unfertilized eggs of some small invertebrates, and certain fish and lizard species, are capable of parthenogenesis. In 1962 British developmental biologist John Gurdon (1933 ) achieved cloning in tadpoles when he inserted cells from the intestine of an adult frog into frog eggs lacking a nucleus. The cloned tadpoles did not, however, survive to adulthood, but these early attempts at nuclear transfer laid the groundwork for further work in animal cloning. In 1995, after many attempts, researchers at the Roslin Institute near Edinburgh, Scotland, announced the birth of two cloned sheep, Megan and Morag, from embryonic cells transferred into empty sheep eggs. This was a landmark, showing that the differentiation of an embryo could be reversed. A natural next step was to see if the clock could be similarly reversed in adult cells. Nuclear transfer was used again to clone Dolly the sheep, born in 1996, from an udder cell. Three sheep were involved in the creation of Dolly. The egg came from a Scottish Blackface with the original nucleus removed. A Finn Dorset ewe donated a sample of udder cells, which were placed in a glass dish and given enough nutrients to keep them alive, but not enough to let them grow and divide in the usual way. This approach stopped the cells from developing and made them revert to a primitive stem cell state. One of these cells was then inserted into the egg and a pulse of electric current was applied to it to start off the development making the egg behave as if it had been fertilized. The egg was then placed into the womb of a third sheep who was Dolly s mother in the sense of carrying, nurturing, and giving birth to the developing fetus. However, Dolly did not have a mother, or a father, in the usual sense of the word. Analysis of her DNA showed that her genetic blueprint was that of the udder cell of the Finn Dorset sheep. Had she been conceived in the usual way, her genetic blueprint would have come half from her mother (the egg) and half from her father (the sperm). Since Dolly, many other animals have been cloned mice, goats, rabbits, cows, pigs, dogs, cats, monkeys, and a gaur (a type of wild ox that is an endangered species). There is no scientific reason why the nuclear transfer approach could not be used to clone a human. In 2004 Hwang Woo-Suk (1953 ), of Seoul National University, South Korea, announced the cloning of a number of human embryos but later admitted that the claim had been fabricated. Thus far, human cloning has not been achieved, although many scientists believe it is sure to happen at some point in the future unless prohibited by law or industry ethics agreements. Note that the clone is not an exact copy of the somatic cell donor, because the empty egg has lost its nucleus, but it will still contain the original mitochondria, which carry a small number of genes. These will also be present in the clone, as well as the genes from the donor somatic cell. In Context: Disputed Claims of Human Cloning In 2001, a company called Advanced Cell Technology successfully cloned human embryonic cells that were allowed to undergo several rounds of division. While not yet recognizable as an embryo, the experiment demonstrated that the process was possible. With the realization that cloning was achievable, public concern about the possibility that a human could be cloned grew. The debate was further fueled by one group's highly disputed, and scientifically dubious, claim to have produced a human clone. In May 1997, an international religious cult called the Raelians announced it was creating a company called Clonaid to sponsor research in human cloning. By 2001 the company

3 claimed to have cloned a human embryo, a baby called Eve, allegedly born in Clonaid refused, however, to allow genetic tests to prove its case. The company's CEO promised to deliver proof of the successful clone in 2003, but produced only a photograph. Without any scientific proof, the vast majority of reproductive scientists also dismissed the cult's claims to have produced other living clones. Impacts and Issues Human therapeutic cloning could play an important role in regenerative medicine by providing embryonic stem cells for treatment that are derived from the patient s own cells. For instance, patients requiring a bone marrow transplant would no longer have to wait for a compatible donor. They could be treated with their own bone marrow stem cells, derived from a nuclear transfer experiment. Other potential applications of regenerative medicine include brain repair in stroke, Parkinson s disease, and Alzheimer s disease, repair of the heart after a heart attack, and supply of insulin-producing cells to the pancreas to treat Type 1 Diabetes. Many of these treatments are still at the research stage, but some are already being used in clinical trials to treat patients using stem cells from various sources. Regenerative medicine opens up the possibility of renewing and repairing the human body as it ages and promises to be a viable alternative to drug therapies. However, there are ethical objections to human therapeutic cloning because it involves creating an embryo solely for someone else s use. It will never be implanted into a woman s womb, so it can never have a life of its own. Some people argue that an embryo is not a person until it has been implanted in the womb.

4 Others believe that life begins at conception, so an embryo of any age is a person. For these people, therapeutic cloning is unacceptable, whatever benefit it brings, because it is against human dignity. Additionally, animal cloning has also proved to be very inefficient, with 277 attempts needed to create Dolly. There is no reason to think that human cloning would be any more successful, so a large supply of donated human eggs would be required. When women donate eggs, it is usually as part of an in vitro fertilization (IVF) program intended to create a baby. Egg donation is not a trivial process, because it involves administration of powerful drugs and a surgical egg retrieval procedure, so there are some risks to the woman. It may not, therefore, be practical or ethical to use human eggs for nuclear transfer until the success rate of the process improves. This has led some scientists to propose the use of cow eggs instead, and a few laboratories around the world have permission to research interspecies nuclear transfer. The new procedure is controversial because it creates a chimeric or hybrid embryo with a mixture of cow and human cells. The second possible fate of a cloned human embryo, if one could be created, is to grow and develop into a baby. Reproductive cloning has a number of potential applications. Bereaved parents could replace a dead child or an infertile woman could use a cell from anywhere in her body to create a baby. Cloning plants and animals has now been widely used to reproduce high value crops and valuable farm animals or racehorses. Perhaps, if they had access to the technology, powerful businesspeople or politicians would try to clone armies of obedient workers or disciplined soldiers. It is also possible that tissue preserved from deceased celebrities could be used to clone new copies of them. Also concerning is the prospect of people creating a clone that could be killed for its organs if they were in need of a transplant, which could be considered a more extreme version of therapeutic cloning. The numerous possibilities offered by human cloning mean it is important to have discussions about where the boundaries lie. Currently, human reproductive cloning is outlawed in countries that have legislated cloning science, whereas research on therapeutic cloning is allowed in some countries. Besides the general ethical arguments over whether reproductive cloning is right or wrong, there are also practical and safety issues to be considered. For instance, the embryo would need to be implanted in the womb of a so-called surrogate mother. A woman would have to consent to have her womb used in this way. Then there is the health of the clone itself to consider. Dolly the sheep suffered from arthritis and excessive weight, although she did give birth to some normal lambs. Studies on other animal clones have shown they are often much bigger than normal and have abnormally large organs, which leads to breathing, circulation, and other medical problems. Often it is said that cloning is wrong because it is unnatural. However, organ transplants and IVF were thought unnatural when they were first introduced, and many of the same arguments, now being used against cloning, were advanced. In 2011, a number of public surveys in the United States and United Kingdom indicated that most (but not all) people accepted transplantation and assisted reproduction. Further Readings Books Brown, Terry. Gene Cloning and DNA Analysis: An Introduction, 5th ed. Oxford, UK: Blackwell Science, 2006.

5 Caplan, Arthur and Glenn McGee, eds. The Human Cloning Debate. Berkeley: Berkeley Hills Books, Harris, John. On Cloning. New York: Routledge, Wilmut, Ian, and Roger Highfield. After Dolly: The Promise and Perils of Cloning. New York: W.W. Norton, Web Sites U.S. Department of Energy (DOE) Genomes Programs. Cloning Fact Sheet. genomics.energy.gov. (accessed September 9, 2011). Full Text: COPYRIGHT 2012 Gale, Cengage Learning. Source Citation Aldridge, Susan. "Human Cloning." Biotechnology: In Context. Ed. Brenda Wilmoth Lerner and K. Lee Lerner. Detroit: Gale, In Context Series. Student Resources in Context. Web. 12 Nov Document URL OverType=&query=&prodId=SUIC&windowstate=normal&contentModules=& amp;mode=view&displaygroupname=reference&limiter=&currpage=&disa blehighlighting=false&displaygroups=&sortby=&search_within_results=& amp;p=suic&action=e&catid=&activitytype=&scanid=&documentid= GALE%7CTTGGVK &source=Bookmark&u=ever24551&jsid=bb4d51765 e91 f806e6f68b46b4aa436c Gale Document Number: GALE TTGGVK