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Stem Cell Research

Stem Cell Research


Few topics in science and religion have been as hotly contested in recent years as stem cell research, largely because it involves the fate of, disposition of, and research on the human embryo. There are two basic types of stem cell researchthat involving adult cells (AS cells) and that involving human embryonic cells (ESCs or hES cells); only the latter is a source of controversy. In both cases, research is still at the early stages regarding the programming and uses of these cells, and there is comparatively little data about the efficacy of AS and hES cells for human therapies. That is why most scientists agree that, in the United States, government funding should be widely available for research on both types of stem cells, an issue that has been contested in the U.S. Congress.

Stem cells are unspecialized and so are able to renew indefinitely; they also have the capacity to differentiate into specialized cells. In humans, these cells are found in some adult organs, in blood, and in bone marrow (Mezey et al. 2000; Bjornson et al.1999); in the inner cell mass of the human embryo at the blastocyst stage (five to six days after fertilization) (Thomson et al. 1998); on the gonadal ridge of aborted or miscarried fetuses (Shamblott et al. 1998); and in the placenta and umbilical cord (hematopoetic stem cells).

Because stem cells have the capacity to regenerate, particularly ESCs, they have ushered in the era of "regenerative medicine," signaling that, in theory, these cells can be used to regenerate human tissues and cells, and ultimately increase quality of life and the human life span. Embryonic stem cells are the progenitor cells for the human body and at their earliest stage (the blastocyst stage) they are completely undifferentiated and can give rise to any cell type in the human body (totipotent, pluripotent, and multipotent are all terms that have been used to describe this phenomenon). At this stage the cells have not yet received their "marching orders" for what they will become; therefore, scientists have been experimenting with controlling the programming of ESCs in culture in order to direct their ends (controlled differentiation) to specialized cells such as blood, skin, and nerve cells.

In order to extract these embryonic stem cells, scientists must collapse the trophectoderm that surrounds the blastocyst in order to get the stem cells from the inner cell mass (ICM) where they reside within the blastocyst or pre-embryo. Such a technique destroys the pre-embryo and renders it incapable of implantation in the uteran wall. This is the crux of the ethical problem for those who oppose embryonic stem cell research.

Studies in 2001 and 2002 indicate the potential for primate parthenotes to form embryonic stem cells and to develop a variety of differentiated cell types in culture (Cibelli et al. 2001; Holden 2002). Parthenotes are embryos that grow from unfertilized eggs (chemically tricked into fertilizing and retaining the full choromosomal complement) that are, so far as is known, incapable of becoming viable fetuses in primates and humans. Thus, scientists hope that this may prove to be an ethically uncontroversial way to obtain stem cells, allowing researchers to avoid therapeutic cloning as means to this end.

The ethical and religious issues surrounding stem cell research concern not so much the therapeutic ends of the research (cures for Parkinson's disease, juvenile diabetes, Alzheimer's disease, heart disease, and a host of other degenerative diseases); rather, the controversy surrounds the status of the human embryo and points to larger issues about what it means to be human and when life begins.

The Roman Catholic Church and conservative Protestant churches have made the strongest opposition to embryonic stem cell research of all religious traditions in the United States. The Catholic position is that life begins at conception; thus the human embryo is accorded the full rights and dignity of a human person from the very moment that the sperm penetrates the egg. Therefore, it is a grave sin to destroy any human embryo since the act constitutes destruction of life itself, a responsibility belonging only to God. Moreover, the Catholic Church has opposed the creation of human embryos for research purposes (therapeutic cloning, for example) for two reasons: To do so would be to treat human life as a mere means to an end, which is a violation of human dignity and the sanctity of life; and embryos ought only to be created in conjunction with the conjugal act of love within the context of marriage (natural law). (Donum Vitae 1987). It is important to note, however, that there are a variety of dissenting Catholic positions on this issue.

Conservative Protestant churches such as the Southern Baptist Convention and fundamentalist independent Christian churches have tended to join the Catholic protest against ESC research and have emphasized prioritizing AS research as an acceptable means to the end of regenerative therapies. The rationale for such opposition does not emphasize a natural law approach to ethics and emphasizes instead a biblical approach. An argument that the Christian tradition has a mandate to protect the weakest and most vulnerable members of society (the embryo in this case) is advanced by Lutheran theologian Gilbert Meilaender in his essay "Some Protestant Reflections" (2001).

On the other hand, mainline Protestant denominations (United Church of Christ, Episcopal, Presbyterian, Methodist) tend to be supportive of all stem cell research so long as the human embryo is treated with respect. In 2001, the General Convention of the Presbyterian Church voted to endorse embryonic stem cell research. Mainline Protestantism has focused on the great amount of good that can come of this research and on concerns of distributive justice to ensure that the poor will receive the benefits of stem cell research equally with the rich. Moreover, most mainline Protestants (and many Catholics) support using excess embryos for stem cell research. These embryos have been frozen in fertility clinics and would be thawed and discarded eventually if they were not put to what many believe is a good endhuman healing. One Lutheran theologian who supports ESC research, in contrast to Meilaender's argument, is Ted Peters (Peters 2001).

Although there are three main branches of Judaism (Orthodox, Conservative, and Reform), and it is sometimes difficult to find agreement on bioethical issues, in this case most Jewish scholars are supportive of all stem cell research. This is due, primarily, to the fact that Judaism professes a strong mandate from God to heal and to reduce human suffering. Moreover, in Jewish law the embryo has no moral standing outside the womb; a developing embryo in laboratory culture is morally neutral until implantation. Therefore, the ends of all stem cell research appear to be morally coherent with Jewish ethics (Dorff).

Islam is also a diverse religious tradition. However, in general, Islam would be in favor of all forms of stem cell research since there appear to be no "recent rulings in Islamic bioethics regarding the moral status of the blastocyst from which the stem cells are isolated" (Sachedina). Islamic scholars have found that the Qur'han's focus is primarily on the developing fetus in the womb. Islam shares with Judaism a concern with human healing; thus, if ESCs hold real (not just speculative) potential for therapeutic healing, there would be no objection to proceeding with such research.


See also Biotechnology; Christianity, Roman Catholic, Issues in Science and Religion; Cloning; DNA; Gene Patenting; Gene Therapy; Genetic Engineering; Genetics; Judaism; Islam


Bibliography

bjornson, christopher r. r., et al. "turning brain into blood: a hematopoietic fate adopted by adult neural stem cells in vivo." science 283 (1999): 5347.

cibelli, jose b., et al. "parthenogenetic stem cells in nonhuman primates." science 295 (2002): 819.

chapman, audrey r.; frankel, mark s.; and garfinkel, michele s. "stem cell research and applications: monitoring the frontiers of biomedical research." in aaas science and technology policy yearbook, eds. albert h. teich, stephen d. nelson, ceilia mcenaney, and stephen j. lita. washington, d.c.: american association for the advancement of science, 2000. available from http://www.aaas.org/spp/yearbook/2000.

doerflinger, richard. "destructive stem-cell research on human embryos." origins 28 (1999): 769773.

congregation for the doctrine of the faith. "donum vitae (gift of life): instruction on respect for human life in its origins and on the dignity of procreation, replies to certain questions of the day." washington, d.c.: united states catholic conference, 1987.

dorff, elliot n. "stem cell research: a jewish perspective." in the human embryonic stem cell debate: science, ethics and public policy, ed. suzanne holland, karen lebacqz, and laurie zoloth. cambridge, mass.: the mit press, 2001.

farley, margaret a. "roman catholic views on research involving human embryonic stem cells." in the human embryonic stem cell debate: science, ethics and public policy, ed. suzanne holland, karen lebacqz, and laurie zoloth. cambridge, mass.: the mit press, 2001.

green, ronald m. "the stem cell conundrum." religion in the news 4 (2001): 1820, 25.

holland, suzanne; lebacqz, karen; and zoloth, laurie, eds. the human embryonic stem cell debate: science, ethics, and public policy. cambridge, mass.: mit press, 2001.

meilaender, gilbert. "some protestant reflections." in the human embryonic stem cell debate: science, ethics, and public policy, eds. suzanne holland, karen lebacqz, and laurie zoloth. cambridge, mass.: mit press, 2001.

mezey, Éva, et al. "turning blood into brain: cells bearing neuronal antigens generated in vivo from bone marrow." science 290 (2000): 177982.

national bioethics advisory commission. ethical issues in human stem cell research, 3 vols. rockville, md.: nbac, 19992000.

national research council committee on biological and biomedical applications of stem cell research; united states institute of medicine board on neuroscience and behavioral health; and national research council board on biology. stem cells and the future of regenerative medicine. washington, d.c.: national academy press, 2002.

peters, ted. "embryonic stem cells and the theology of dignity." in the human embryonic stem cell debate: science, ethics and public policy, eds. suzanne holland, karen lebacqz, and laurie zoloth. cambridge, mass.: mit press, 2001.

sachedina, abdulaziz. "islamic perspectives on research with human embryonic stem cells." in ethical issues in human stem cell research, vol. 3. rockville, md.: national bioethics advisory commission, 2000.

shamblott, michael j., et al. "derivation of pluripotent stem cells from cultured human primordial germ cells." proceedings of the national academy of sciences (usa) 95 (1998): 1372631.

thomson, james a., et al. "embryonic stem cell lines derived from human blastocysts." science 282 (1998): 11457.

suzanne holland

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stem cells

stem cells are ‘uncommitted’ cells, capable of dividing to make more stem cells, or, under appropriate conditions, to produce the kinds of specialized cells that make up the tissues and organs of the body.

A newly fertilized egg is the ultimate stem cell. It is totipotent – capable of generating all the different types of cells found in the body, and also the fetal part of the placenta and supporting tissues. The fertilized egg splits into two, and those into four, and so on. For the first few divisions, up to at least the 8-cell stage, all the cells of the tiny embryo are totipotent stem cells. Indeed, if these early cells separate, they can each continue to develop, making identical twins, triplets, quadruplets, etc.

About four days after fertilization, the route to commitment starts. Some cells form an outer layer, which becomes part of the placenta, while others make the inner mass, which is the beginning of the true embryo. Initially this consists entirely of pluripotent stem cells, which cannot give rise to placental tissue but can make any component of the fetus itself. As the embryo grows, and the parts of the body start to emerge, the individual stem cells within each future organ or tissue become further specialized so as to be capable of producing only a certain range of possible final cell types. These stem cells are then called multipotent. At a certain stage in the development of each ‘family tree’ of cells, one or both of the daughter cells produced by the division of a stem cell becomes ‘committed’, that is, incapable of further division. These committed daughters continue to differentiate and become the normal functional cells of the heart, skin, brain, kidney, and other organs.

Adult animals still have some multipotent stem cells, especially in tissues such as skin and blood, in which cells last only a short time and have to be replaced. Indeed, even in the adult brain, previously thought to be incapable of making new nerve cells, there are populations of stem cells, which are constantly producing relatively small numbers of new neurons.

We now stand at the threshold of a potential revolution in medical treatment for diseases and disorders in which organs stop working properly. At present, some such conditions, such as heart, kidney and liver disease, can be treated by transplantation of a replacement organ from another person. But demand for donor organs is far outstripping supply, and the failure rate of such surgery is quite high, mainly because of the problem of rejection. Many other disorders, such as stroke, diabetes and Alzheimer's disease, cannot presently be treated by transplantation. The great hope is that suitable stem cells, produced in large quantities through cell culture methods and injected into failing tissues and organs, will produce fresh, replacement cells to take over from lost or damaged ones.

Stem cells for such replacement therapy could be produced in a number of different ways. Ultimately, it might be possible to make them with the kind of methods used to produce the first cloned mammal, Dolly the sheep. An ordinary specialized adult cell from the patient could be used to produce a totipotent stem cell by removing the nucleus (with the DNA-containing chromosomes), and inserting it into a human egg from which the nucleus has been removed. But there are many problems with this approach, not least the fact that adult cells may have accumulated genetic errors, which will be transmitted to the stem cells produced. Everyone agrees that formidable technical obstacles must be overcome before the cloning of stem cells from adult cells becomes safe. There is also concern that the development of methods for therapeutic cloning would inevitably lead to the production of whole human beings, who, like Dolly, are genetic replicas of an adult. At present, the vast majority of scientists and clinicians, not to mention ethicists and politicians, are opposed to such reproductive cloning, but it must be said that resistance may decrease if the techniques involved can be made more reliable.

In principle, some of the patient's own stem cells could be harvested (most likely from bone marrow or certain parts of the brain), multi-plied in culture and injected into a diseased or damaged region to produce new cells. Stem cells derived from the patient's own body would have the great advantage that they would not be rejected. This approach has already been successful in experimental animals, with stem cells from bone marrow used to replace damaged heart muscle. It may soon be used in humans to treat heart disease, diabetes, and other such diseases. However, it would not be appropriate for the replacement of tissues that are diseased because of a genetic disorder (such as Huntington's disease or cystic fibrosis), since stem cells from the patient would have the same genetic mistake in their DNA. This strategy would also be inappropriate in acute conditions, demanding immediate treatment, because of the time needed for stem cells to multiply in culture.

The most immediately promising strategy is to isolate pluripotent stem cells from human embryos just a few days after fertilization, to culture them, and to inject them into the patient's diseased or damaged organ. Since such cells carry different DNA from that of the patient, they could be used to treat genetic disorders. On the other hand, this means that precautions would have to be taken to avoid rejection.

Transplantation of immature nerve cells and stem cells from the brains of aborted human embryos has been used for several years to treat the degenerative brain condition, Parkinson's disease, with reasonably encouraging results. Such treatment has not greatly alleviated the characteristic tremor of the hands, and some patients have developed disturbing unintended movements. But most have regained the ability to initiate and control their actions. It is probable that embryonic stem cell injection will soon be used in efforts to treat the degenerative diseases Huntington's disease and Alzheimer's, and even stroke, in which parts of the brain are destroyed becomes of interruption of the blood supply.

There is wide agreement among medical scientists that research on human embryonic stem cells is an important first step towards stem cell therapy, even though it may eventually be possible to use adult stem cells. Yet the prospect of harvesting cells from living human embryos smacks of Frankenstein or Brave New World, and ‘pro-life’ religious groups have mounted stout moral opposition. However, it would not be necessary to fertilize additional human eggs specifically for such research. Present methods for the production of ‘test-tube babies’ involve the production and storage (by freezing) of several fertilized eggs, the unwanted ones simply being destroyed or permanently stored. These surplus eggs could, with parental agreement, provide a ready source of embryos for stem cell collection. Moreover, as long as there are strict limits on the time for which the embryo is allowed to develop, it will have no nervous system or other organs, no possibility of feelings, and nothing approaching an independent life. Also, the indubitable suffering of the many people who might be helped by stem cell therapy ought to weigh heavily in the complex moral equation.

In 2001, the British government authorized stem cell research on human embryos up to 14 days post-conceptual age. Given the huge potential benefits of stem cell therapy, it is likely that other nations will follow suit.

Colin Blakemore

Bibliography

Further reading: Thomson, J. et al. (1998) Embryonic stem cell lines derived from human blastocysts. Science 282: 1145–1147.
US National Institutes of Health website. Stem cells: a primer. http://www.nih.gov/news/stemcell/primer.htm


See also: antenatal development; assisted reproduction; cloning; disease; gene therapy; genetics, human; organ donation; pregnancy; transplantation.

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Stem Cells

Stem Cells

BIBLIOGRAPHY

A stem cell has two special qualities: the ability to produce offspring of itself indefinitely, and the ability to differentiate into different types of specialized cells. Adult stem cells are found in various organs of fully formed organisms. For example, umbilical cord blood and bone marrow contain stem cells capable of producing the various cells found in the blood, such as red blood cells, white cells, and platelets.

Public debate about ethical, social, religious, and legal issues involving stem cells has centered on a different kind of stem cell, so-called embryonic stem cells, usually obtained from excess embryos created by in vitro fertilization (IVF), but sometimes created specifically for research or therapeutic purposes. These human embryonic stem cells (hESCs) have the capacity to form any tissue in the body; that is, they are totipotential.

HESCs are of scientific and medical interest for three reasons: (1) they provide an opportunity to do laboratory research on normal and abnormal differentiation; (2) they provide an opportunity to test experimental therapies, including drugs and genes, at a cellular level, without exposing living animals or humans to risk; (3) they present an opportunity to develop and transplant cell lines that can replace vital molecules such as insulin (for patients with diabetes mellitus) or dopamine (for patients with Parkinsons disease), or to replace damaged tissue in the heart, nervous system, or elsewhere.

HESCs from residual IVF embryos are unlikely to be sufficient for all research and therapeutic interests. If, for example, stem cells are to be useful in treating diabetes, it will be important to create a cell line that is genetically identical to the recipient, so that it will not be rejected after transplantation. This can be accomplished by removing the nucleus of an egg, replacing it with the nucleus from a cell obtained from the potential recipient, and allowing the egg to grow to a stage when stem cells can be removed. This is called somatic cell nuclear transfer (SCNT).

SCNT is also of interest for laboratory research on genetic disorders such as cystic fibrosis or Tay Sachs disease. An embryo is created using the nucleus from a somatic cell of a patient with the disorder being studied, and then stem cells with the abnormal gene are obtained from the early embryo. This is sometimes called research cloning. SCNT for the purpose of creating a cell line that would be used for treatment is sometimes called therapeutic cloning.

Objections to research involving hESCs involve several concerns. First, some believe that an embryo has the same moral status as a fully formed human and is entitled to the same protections. Destruction of an embryo, in this view, is morally equivalent to murder. Proponents of hESC research point out that residual embryos are used only when the parents intend to destroy them anyway, and are not destroyed because of the interest in stem cell research. They also point out that tens of thousands of residual IVF embryos are destroyed annually without similar objection.

Second, opponents also argue that there are alternative approaches to obtaining totipotential stem cells, such as using adult stem cells. Most experts believe adult stem cells are not totipotential and therefore should not divert research funds from the more promising embryonic stem cells.

Third, opponents object to SCNT combined with hESC research because of concerns that it is a critical technical step for reproductive cloning, the creation of genetically identical replicas of existing persons. Advocates of hESC research argue that reproductive cloning is nearly universally opposed at the present time, largely because of concerns about biologic safety, and that slippery slope arguments are insufficient to prohibit research that can help alleviate suffering, disability, and death from diseases affecting large numbers of existing persons.

Fourth, concerns have been raised that the transfer of human cells into the developing brain of laboratory animals could result in an animal capable of human experience and therefore with moral status comparable to a human. Although most neuroscientists consider this to be unlikely, some groups have proposed prohibiting full gestation of nonhuman primates if human stem cells have been implanted in their central nervous systems early in embryonic development.

Governmental policies reflect a range of approaches in different countries and states, and policies within any jurisdiction are often in flux, subject to the success of politicians with various views. Some prohibit human embryonic stem cell research; some permit it but have restrictions on use of public funds; some permit research using existing embryos but prohibit creation of embryos for research; and some restrict somatic nuclear cell transfer because of concerns that it may accelerate human reproductive cloning.

SEE ALSO Ethics in Experimentation; Medicine; Neuroscience; Public Policy; Reproductive Politics

BIBLIOGRAPHY

McHugh, Paul R. 2004. Zygote and ClonoteThe Ethical Use of Embryonic Stem Cells. New England Journal of Medicine 351 (3): 209211.

National Academy of Sciences. 2006. Understanding Stem Cells: An Overview of the Science and Issues from the National Academies. http://dels.nas.edu/bls/stemcells/booklet.shtml.

Sandel, Michael J. 2004. Embryo Ethics: The Moral Logic of Stem-Cell Research. New England Journal of Medicine 351 (3): 207209.

Walters, LeRoy. 2002. Human Embryonic Stem Cell Research: An Intercultural Perspective. Kennedy Institute of Ethics Journal 14 (1): 338.

Norman Fost

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stem cells

stem cells, unspecialized human or animal cells that can produce mature specialized body cells and at the same time replicate themselves. Embryonic stem cells are derived from a blastocyst (the blastula typical of placental mammals; see embryo), which is very young embryo that contains 200 to 250 cells and is shaped like a hollow sphere. The stem cells themselves are the cells in the blastocyst that ultimately would develop into a person or animal. "Adult" stem cells are derived from the umbilical cord and placenta or from blood, bone marrow, skin, and other tissues. The similar embryonic germ line cells come from a fetus that is 5 to 9 weeks old and are derived from tissue that would have developed into the ovaries or testes.

Medical researchers are interested in using stem cells to repair or replace damaged body tissues because stem cells are less likely than other foreign cells to be rejected by the immune system when they are implanted in the body. Embryonic stem cells have the capacity to develop into every type of tissue found in an adult; germ line cells and adult stem cells are less versatile. The processes that control such development, however, are not understood at present. Stem cells have been used experimentally to form the hematopoietic (blood-making) cells of the bone marrow; heart, blood vessel, muscle, tracheal, retinal, and insulin-producing tissue; bone; and sperm cells. Embryonic germ line cells have been used to help paralyzed mice regain some of the ability to move. Since the 1990s umbilical cord blood stem cells have sometimes been used to treat heart and other defects in children who have rare metabolic diseases and to treat children with certain anemias and leukemias. It has been shown that stem cells from this blood can migrate to damaged tissues and repair them.

Human stem cells have typically been extracted from surplus fertilized embryos produced during in vitro fertilization procedures. Some experimenters, however, have used embryos that were fertilized especially to produce stem cells. In so-called therapeutic cloning a nucleus from a patient's body cell, such as a skin cell, would be inserted into an egg that has had its nucleus removed to produce a blastocyst whose stem cells could be used to create tissue that would be compatible with that of the patient. Such a procedure was reported in 2005 to have been successfully undertaken in part by South Korean researchers who produced stem cell lines using genetic material from patients, but the data was subsequently shown to have been fabricated. (It was later determined, however, that the laboratory had produced stem cells using an egg that had developed through parthenogenesis, which does not involve fertilization or result in a viable human embryo.) In 2013, however, scientists at Oregon Health and Science Univ. reported that they had created such stem cells using genetic material from human skin cells and donated eggs.

Because extraction of embryonic stem cells destroys the embryo, the use of embryonic stem cells has been opposed by opponents of abortion. Japanese researchers led by Shinya Yamanaka used retroviruses in 2007 to transfer transcription factors to human skin cells and induce those cells to become stem cells (called induced pluripotent stem cells); Yamanaka's team had previously (2006) achieved similar results with mouse cells. In 2010 an American team announced that they had induced human skin cells to become stem cells using messenger RNA to reprogram the cells. Studies with mice have shown, however, that unlike embryonic stem cells induced stem cells are subject to attack by the recipient's immune system. Treatment with stem cells in humans is experimental and can have unexpected and damaging side-effects; some methods of producing mouse stem cells with retroviruses have led to significant rates of cancer when those cells have been transferred to mice.

The first embryonic stem cells to be isolated were extracted by British researchers from mouse blastocysts; the first human stem cells isolated and cultured were extracted by American scientists in 1998. In 1994 a National Institutes of Health (NIH) panel argued that creating human embryos for use in certain experiments might be justified, but Congress subsequently enacted (1995) a ban on federal financing for research involving human embryos in reaction to that report. The Dept. of Health and Human Services ruled in 1999, however, that that ban did not apply to financing work with stem cells, and guidelines for financing such research were issued by NIH the next year.

President George W. Bush, who had campaigned against financing embryonic stem cell research, announced in Aug., 2001, that he would support federal funding of research with embryonic stem cells, but only with the estimated 60 stem cell lines then existing. Some scientists challenged the assumption that these 60 stem cell lines would be sufficient for experimental and therapeutic needs, while others said the figure included some stem cell lines that had not yet been determined to be viable. In fact, in 2004, there were only 15 approved stem cell lines available to researchers funded by the U.S. government. The restrictions did not prevent other researchers, in the United States and elsewhere, from developing new embryonic stem cell lines and undertaking research with them using private funding, and California voted (2004) to create a $3 billion fund to underwrite embryonic stem cell research. A federal legislation that would have expanded the number of stem cell lines available for federally funded research was vetoed by the President Bush in July, 2006. The executive order issued by Bush was overturned in Mar., 2009, by President Barack Obama.

See also fetal tissue implant.

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stem cell

stem cell A cell that is not differentiated itself but can undergo unlimited division to form other cells, which either remain as stem cells or differentiate to form specialized cells. For example, stem cells in the bone marrow divide to produce daughter cells that differentiate into various types of immune cell (e.g. monocytes, lymphocytes, mast cells). Also, stem cells in the intestine continually divide to replace cells sloughed off the gut lining. Embryonic stem cells, such as those taken from an early human embryo, are capable of differentiating into many or all of the various tissue cells found in a fully developed individual – they are described as pluripotent. Cultures of such cells have the potential to provide replacement tissues and organs for medical use, including transplantation. However, ethical concerns have led to tight controls on research using human embryonic stem cells in many countries, including the USA and UK. See also haemopoietic tissue.

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stem cell

stem cell (stem) n. an undifferentiated cell that is able to renew itself and produce all the specialized cells within an organ. embryonic s. c. a cell of the blastocyst from which all the different cell types of the developing embryo are produced. haemopoietic s. c. a cell of the bone marrow from which all blood cells are derived.

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stem cell

stem cell A mitotically active cell that serves to replenish those that die during the life of a metazoan organism (somatic stem cell) or that produces a continuing supply of gametes (germinal stem cell).

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Stem Cell Research

STEM CELL RESEARCH

STEM CELL RESEARCH. SeeBioethics ; Genetic Engineering .

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