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Stem Cell History, Politics and Scientific Background

Stem Cell History and Scientific Background

How and why we age has always been a topic of general human interest. The exact mechanisms by which particular cells age, die, and either are or are not replaced by new cells is of increasing scientific interest as well. Dr. Leonard Hayflick, the renowned cell biologist and founder of “molecular gerontology”, played a key role in our understanding of these cellular mechanisms. By his discovery of the built-in limitations of cellular longevity, he established the fact that there exists a limit to the number of times that normal (noncancerous) cells can divide. This limit is known as the “Hayflick limit”.

While employed in cell biology and mycoplasmology at Wistar in the 1950s, Dr. Hayflick noticed that each cultured human and animal stem cell has a predetermined number of times that it can replicate in order to create another stem cell. Prior to his discovery of this, it had been commonly believed for at least sixty years, since the turn of the previous century, that cells would continue to divide indefinitely. Dr. Hayflick discovered that cells stop growing after about 50 divisions, or population doublings. As he described,

“They continued to eat, excrete waste, and perform all the metabolic housekeeping necessary to stay alive. They just didn’t replicate anymore. Eventually, debris attached to them, and they ultimately suffered ‘degeneration’.” (From Stephen S. Hall, “Merchants of Immortality”, 2003).

It is now commonly understood that normal cells in culture have a finite limit to the number of times they can divide. (This is unlike cancer cells, which are the only “immortal” cells). But the discovery was initially a startling one. Together with Paul Moorhead, Dr. Hayflick published his revolutionary findings, which contradicted current dogma, first in Experimental Cell Research in 1961, and again in an updated version in Experimental Research, in 1965. Entitled, “The limited in vitro time of human diploid cell strains,” this paper introduced the new idea that the number of times a human cell is capable of dividing is innately limited. The paper had previously been rejected by the Journal of Experimental Medicine, and Dr. Hayflick still possesses the now famous rejection letter, in which the journal’s editor wrote, “The largest fact to have come out from tissue culture in the last fifty years is that cells inherently capable of multiplying will do so indefinitely if supplied with the right milieu in vitro.” (Ibid.) Time will tell exactly how many other dogmatic pillars shall be overturned by future discoveries.

Dr. Hayflick’s discovery not only shattered conventional “wisdom”, but it also focused attention on the cell as the fundamental location of aging. Dr. Hayflick was able to demonstrate for the first time that both mortal and immortal mammalian cells exist. Much of modern cancer and stem cell research today is based upon this distinction.

The cellular senescence (from the Latin, “senex”, meaning “old man” or “old age”), or cellular death, discovered by Dr. Hayflick is now known to involve the successive shortening of chromosomal telomeres with each cell cycle as cells repeatedly divide. This feature of replicative cell senescence has become an established principle in biogerontology, the field of aging, although the exact mechanisms behind this process are still not yet fully understood. In addition to the successive shortening of telomeres, other factors in the process of DNA replication during cell division all contribute to “aging”, such as cumulative DNA damage and mutation, as well as cross linkage.

Despite the “Hayflick limit”, it has also been shown that cells may be immortalized, “crashing right through the Hayflick limit and continuing for dozens more cell doublings”, by the extension of telomeres with telomerase. (“Hayflick Unlimited: Extension of Life Span by Introduction of Telomerase into Normal Human Cells.” Science, 1997). In 1998, the Geron Corporation developed techniques for extending telomeres, thereby demonstrating the ability of lengthened telomeres to prevent cellular senescence. Clearly, more work in this field will no doubt impact clinical applications of cancer and stem cell therapies.


Politics & Government Regulations

Ethical considerations aside, the field of embryonic stem cell research is highly regulated, with numerous restrictions on the donation of embryonic materials, and these restrictions apply to all research, whether federally or privately funded. In other words, even privately funded research is subject to complex restrictions and “guidelines” (recently drafted by the President’s Council on Bioethics), which are necessary in order to oversee the quality of the materials. A case in point is Proposition 71 in California, which allows for the privately funded California Institute of Regenerative Medicine, which was proposed in order to bypass the Presidential Executive Order, issued on August 9th, 2001, which banned federal funding for any embryonic stem cell lines established after that date. Even privately funded embryonic stem cell research conducted at this Institute, however, will still be very tightly regulated, and still subject to numerous restrictions. Such “red tape” does not apply to research conducted on adult stem cells, in which only informed consent of the participants is required.

Since none of the embryonic stem cell lines already in existence have any genetic diseases, it has been pointed out by Dr. Irving Weissman of Stanford University, among other researchers, that embryonic stem cell lines with genetic diseases should be established. This would allow the production of human pluripotent stem cell lines for the treatment of people with specific genetic diseases, but it would also require the transfer of genetic information from an adult stem cell into an unferlized egg in order to establish the genetic cell line. Among the risks involved in such procedures is the possibility of creating a (genetically diseased) blastocyst capable of producing gametes. Such controversial procedures shall be addressed in further detail in the section on “Therapeutic Cloning.”

A blastocyst contains approximately 200 cells, and even for an expert in developmental biology it is difficult to distinguish a human blastocyst from that of any other species. In establishing a stem cell line from human embryonic stem cells, the culturing of the human embryo occurs for no longer than 14 days, at which point the “primitive streak” forms: this is the stage at which the embryo ceases to be an undifferentiated ball of cells but now has a front and a back, with an early formation of the nervous system and other physiological attributes characteristic of the human species.

In order to obtain the stem cells that are needed to establish an embryonic cell line, the developing embryo is then destroyed. For this reason, President George W. Bush banned the federal funding of research on embryonic and fetal stem cell lines established after August 9th, 2001, the date on which he announced his Presidential Executive Order. Prior to his administration, however, Congress had passed, and President Clinton had signed, legislation prohibiting the use of federal money for the destruction of embryos for research purposes. By the time President Bush inherited the dilemma, he responded by restricting federal funding for research to the limited set of stem cell lines that had already been established. Although more than sixty cell lines were listed as having already been in existence on this date, August 9th, 2001, many were later shown not to be viable, due to contamination or other problems. Today, only 17 of these cell lines are available for distribution.

The NIH Stem Cell Registry was then created to document existing cell lines and their availability, and to carry out initial tests to assess the quality of these lines.

Some organizations have pointed out the risk of cross transfer of animal viruses and other disease agents in these cell lines. As the London based Institute of Science in Society has written,

“All existing lines have been cultured on feeder layers of mouse cells, and are hence unsuitable for transplant, because it risks transferring mouse viruses and other disease agents to human patients and creating an epidemic.” (From www.i-sis.org.uk).

In response to the scarce availability of human embryonic stem cell (hESC) lines, some researchers have begun to create their own hESC lines, even though research with such cells is barred from federal funding. A case in point is the Harvard biologist Doug Melton, who, in March of 2004, created 17 new hESC lines. Since researchers who wish to work with these particular cell lines are prohibited from using federal money to do so, the cell lines are available for privately funded research only. However, as researchers are discovering, private dollars are even more scarce than cell lines. Furthermore, as with the existing hESC lines, even these new hESCs are all still grown on mouse feeder cells, and therefore,

“their usefulness in clinical applications will be limited. There have been attempts to develop alternative feeder or feeder free culture systems, but these were not optimal for deriving and growing clinical grade hES cells, as they all use animal products of one kind or another, and carry the risk of cross transfer of animal viruses and other disease causing agents.” (From www.i-sis.org.uk).

Regardless of their ultimate safety or viability, such cell lines have been characterized as “embryonic” by the detection of surface antigen markers specific to embryonic stem cells, and by determining if the cells are pluripotent, and by demonstrating that the cells are undifferentiated. In order to qualify for federal funding, all cells are required to have been removed from the embryo prior to August 9th, 2001, the date on which the President announced his policy. To ensure that all criteria are met, all stem cell lines are listed in NIH’s Stem Cell Registry. Stem cells that are not listed in this registry have not met the criteria established by President Bush on August 9th, 2001, and therefore may not be supported by federal research funding.

Organizations currently addressing the ethical questions surrounding embryonic stem cells include:

  • The President’s Council on Bioethics
  • The Kennedy Institute of Ethics at Georgetown University
  • The American Association for the Advancement of Science & the Institute for Civil Society, which together issued the publication, “Stem Cell Research & Applications; Monitoring the Frontiers of Biomedical Research”
  • The International Society for Stem Cell Research, which issued the publication, “The Ethics of Human Embryonic Stem Cell Research”
  • The European Union, which issued the publication entitled, “Report On Human Embryonic Stem Cell Research”

Ethically, morally, and politically, human embryonic stem cells are a charged and sensitive topic, not only in the U.S. but internationally as well. However, even disregarding the ethical dilemmas presented by embryonic stem cells, the scientific reasons alone are sufficient to classify such cells as undesirable. Due to the risk of teratoma (tumor) formation from such cells, both Germany and Norway have prohibited research on fertilized eggs, with Norway banning both the derivation of and the use of embryonic stem cell lines altogether.

It is not commonly known, but there have been no scientific studies which were able to successfully demonstrate any ability of embryonic stem cells to treat disease. In other words, there remains no concrete proof that embryonic stem cells are useful in treating disease, although this is not widely advertised. As we shall see in a forthcoming section, this lack of evidence is dramatically different from placental, umbilical cord and other types of adult stem cells, where there is ample scientific proof demonstrating the efficacy of such cells in treating a wide range of disease.

In response to the question, “Have human embryonic stem cells been used successfully to treat any human diseases yet?”, the National Institutes of Health (NIH) has posted the following answer on their website:

“Scientists have only been able to do experiments with human embryonic stem cells (hESC), since 1998 when a group led by Dr. James Thomson at the University of Wisconsin developed a technique to isolate and grow the cells.”

In other words, human embryonic stem cells have not yet actually been used to treat any human diseases. hESCs are still in the laboratory, experimental phase.

The NIH then points out:

“Adult stem cells such as blood-forming stem cells in bone marrow (called hematopoietic stem cells, or HSCs) are currently the only type of stem cell commonly used to treat human diseases. Doctors have been transferring HSCs in bone marrow transplants for over 40 years. More advanced techniques of collecting, or ‘harvesting’, HSCs are now used in order to treat leukemia, lymphoma and several inherited blood disorders. The clinical potential of adult stem cells has also been demonstrated in the treatment of other human diseases that include diabetes and advanced kidney cancer. However, these newer uses have involved studies with a very limited number of patients.” (From http://stemcells.nih.gov).

The NIH continues:

“Pluripotent stem cells offer the greatest therapeutic potential, yet formidable technical challenges still need to be overcome. First of all, scientists must learn how to control their development into all the different types of cells in the body. Second, the cells now available for research are likely to be rejected by a patient’s immune system. Another serious consideration is that the idea of using stem cells from human embryos or human fetal tissue troubles many people on ethical grounds.”

As previously mentioned, adult stem cells, typically considered to be multipotent or monopotent rather than pluripotent, have been thought to offer less flexibility. Now, however, it has been repeatedly shown that some adult stem cells exhibit strong pluripotency, yet as recently as 2001 even the NIH subscribed to this previous, now outdated view:

“Adult stem cells that could give rise to all cell and tissue types have not yet been found. Adult stem cells are often present in only minute quantities and can therefore be difficult to isolate and purify. There is also evidence that they may not have the same capacity to multiply as embryonic stem cells do. Finally, adult stem cells may contain more DNA abnormalities – caused, for example, by sunlight, toxins, and errors in making more DNA copies during the course of a lifetime.” (From http://stemcells.nih.gov).

The NIH has not yet issued an updated publication on stem cells, incorporating recent discoveries. Nevertheless, in describing the overall importance of stem cell research, the NIH adds:

“The development of stem cell lines that can produce many tissues of the human body is an important scientific breakthrough. This research has the potential to revolutionize the practice of medicine and improve the quality and length of life.”

They continue, however,

“Human embryonic stem cells are thought to have much greater developmental potential than adult stem cells.”

More specifically, the key concept is that pluripotent stem cells have much greater developmental potential than do multipotent or monopotent stem cells. To reiterate, the important question is not so much a matter of embryonic versus adult stem cells, but rather, it is a matter of pluripotent versus multipotent and monopotent stem cells.

The policies of other countries regarding stem cell and cloning (please see the section on “therapeutic cloning”) research include:

  • In the United Kingdom: Research on embryos is allowed up to 14 days after conception, using embryos that were created for reproduction or solely for research purposes. Therapeutic cloning has been approved, although it is currently on hold under judicial review. The first human embryonic stem cell bank in the UK opened in May of 2004, by which time the House of Lords had recommended human embryonic stem cell research exclusively for the treatment of patients with organ failure. New evidence was then introduced in which adult stem cells are shown to exhibit as much transdifferentiation capability and flexibility as do embryonic stem cells. The debate is still ongoing.
  • In France, Australia, and Canada, debates are also ongoing. The use of human embryonic stem cells has been permitted, along with the derivation of stem cells from embryos which are no longer needed by their genetic parents for reproduction. However, the creation of new embryos purely for research is not allowed. A ban on cloning has been proposed in France and Canada, and the proposal has been passed in Australia.
  • In Germany, the derivation of human embryonic stem cells for research is banned, although the importation of such cells is allowed, within limits. There is also a ban on cloning.

Other countries, as well as the European Union and the United Nations, are still debating both the scientific and the ethical issues of stem cell research and cloning.

Therapeutic Cloning: An Unnecessary Risk

Characteristics, and a Comparison with Adult Stem Cell Research

Proponents of therapeutic cloning claim that this technique may offer a new mode of treatment in the repair and regeneration of tissue and organs. Especially in the field of organ transplantation, where immune rejection is common, therapeutic cloning is often seen as a way of eliminating this problem of immune rejection. Critics, however, claim that this view is incorrect, and that immune rejection still exists in therapeutic cloning, along with a myriad of other complexities and problems.

In therapeutic cloning, stem cells are created from a donor for the main purpose of providing tissue (such as for organ repair), in the event that the donor might need such treatment at a future date. The way in which this is done is as follows.

A somatic (adult) cell from the donor is transferred into an enucleated egg (an egg from which the nucleus has been removed), yielding a single celled cloned embryo. When the egg has developed into a blastocyst, the inner cell mass is then removed and cultured into embryonic stem cells, which are grown to produce the desired, healthy, “therapeutic” cells (such as nerve cells, muscle cells, organ tissue, etc.). These new cells are then transplanted back into the patient (who is presumed to be the same as the donor of the original somatic cell, in order to avoid immune rejection).

A single cell, cultured in a dish by itself, will divide to form a population of identical cells, known as cell clones. The resulting cloned embryo is therefore genetically identical to the donor. Until very recently, this characteristic of identical genetic matching has been considered the primary advantage of “therapeutic” cloning. Now, however, there is evidence to prove otherwise.

Other names for therapeutic cloning include Somatic Cell Nuclear Transfer (SCNT, which gave rise to Dolly the sheep), and Cell Replacement through Nuclear Transfer (CRNT). Whichever name is used, therapeutic cloning requires the deliberate creation and disaggregation (destruction, in other words) of a human embryo.

It is possible, however, that the cloning may be used for reproductive purposes instead of for “therapeutic” purposes. For example, from an adult female, the DNA may be removed from a harvested egg (thus “enucleating” the egg). Skin cells may then be removed from an adult male, and the DNA of these cells may be transferred into the nucleus of the woman’s unfertilized egg, to produce an early stage embryo with the donor’s DNA. From this cloned embryo, human embryonic stem cells (hESCs) may be grown in the laboratory, and then implanted into a surrogate woman who ultimately gives birth to a clone of the man from whom the skin cells were derived. This is how Dolly the sheep was produced. Although “reproductive cloning” and “therapeutic cloning” have different objectives, the means by which they are conducted, and the controversies surrounding such means, are inseparably linked.

According to Dr. Robert Lanza, “It is true that the techniques developed in CRNT research can prepare the way scientifically and technically for efforts at reproductive cloning.” (Robert Lanza et al., “The ethical validity of using nuclear transfer in human transplantation”, JAMA, 284, 3175 – 3179, 12/27/2000). Needless to say, reproductive cloning is already widely recognized to be an ethical can of worms.

Ethical controversies aside, however, David A. Prentice, Ph.D., of the Department of Life Sciences at Indiana State University, adds that cloning is unsafe both for the clone and for the surrogate mother. He points out that even apparently healthy clones have abnormalities in gene expression. “A review of all the world’s cloned animals suggests that every one of them is genetically and physically defective,” he says. He also cites Ian Wilmut, who points out that, “There is abundant evidence that cloning can and does go wrong and there is no justification for believing that this will not happen in humans.” (Quoted in “Gene defects emerge in all animal clones”, Sunday Times of London, 4/28/02).

The success rate of reproductive cloning is extremely low, as 277 nuclear transfers were required to enucleated the eggs from which Dolly the sheep was created. It has been pointed out that even when animals are successfully cloned, every one of them, without exception, suffers from numerous genetic abnormalities. Even Dolly the sheep was “born” with incomplete epigenetic reprogramming (the heritable erasure and remarking of genes that determines either normal or abnormal development). Currently, the highest efficiency rate of SCNT cloning in any species is 7% (with pigs), and in most species the success rate is below 1%. However, even when successful, from 10,000 genes that were analyzed in cloned mice, approximately 400 of these genes were found to express genetic abnormalities.

Dr. Prentice offers some further alarming statistics on the success rates (or the lack thereof) of cloning in animals:

  • Dolly the sheep, the first cloned animal: 1 live birth out of 277 cloned embryos. Success rate = 0.4%.
  • Cloned mice: 5 live births out of 613. Success rate = 0.8%
  • Cloned pigs: 5 live births out of 72 cloned embryos implanted. Success rate = 7%.
  • Cloned goats: 3 live births out of 85 cloned embryos implanted. Success rate = 3.5%.
  • Cloned cattle: 30 live births out of 496 cloned embryos implanted. Success rate = 6%.
  • Cloned cat: 1 live birth out of 188 cloned embryos. Success rate = 0.5%.
  • Cloned gaur: 1 live birth out of 692 cloned embryos. Success rate = 0.1%.
  • Cloned rabbits: 6 live births out of 1852 cloned embryos. Success rate = 0.3%.

One of the risks for the surrogate mother presented by cloning is what is known as “large offspring syndrome”, in which the cloned embryo develops into an abnormally, and dangerously, large fetus by the time of birth. But there are also many other ways in which cloning places women at risk. For example, in order to treat all of the 17 million people in the U.S. who suffer from diabetes, Dr. Prentice has made some sobering calculations. Allowing for 10 eggs harvested per donor, and allowing for a generous 20% cloning efficiency to achieve the blastocyst stage, as well as a generous 10% efficiency at initiating the embryonic stem cell culture, a minimum of 850 million eggs would be required, which translates into 85 million women of childbearing age who would be required as donors. This would be more than one-third the population of the United States, who would be needed as egg donors for the treatment of a group of people roughly one-sixteenth as large in population size.

While high dose hormone therapy and surgery have been developed to obtain eggs in large numbers, such techniques nevertheless pose significant health risks by jeopardizing the donor’s immediate health and future reproductive success. Additionally, the possibility for commercial exploitation puts economically disadvantaged women in particular jeopardy.

Overall, Dr. Prentice concludes, therapeutic cloning may be judged as unsuccessful. Transplantation remains one of its many problems, and Dr. Prentice cites W.M. Rideout as having stated, “Our results raise the provocative possibility that even genetically matched cells derived by therapeutic cloning may still face barriers to effective transplantation for some disorders.” (W.M. Rideout et al., “Correction of a genetic defect by nuclear transplantation and combined cell and gene therapy,” an online publication in Cell, 3/8/2002).

It has been proposed by a number of researchers that cloning is not able to provide the claimed medical treatments, and Drs. James Thomson and Alan Trounson add that there is a very low chance of success in the clinical use of therapeutic cloning. (Dr. James Thomson, “Multilineage differentiation from human embryonic stem cell lines”, Stem Cells, 2001; Dr. Alan Trounson, “The derivation and potential use of human embryonic stem cells”, Reproduction, Fertility and Development, 2001). Additionally, Dr. Irving Weissman of Stanford University, and Dr. John Gearhart have both stated before the President’s Council on Bioethics that transplant rejection will still occur, even though the cells from the cloned embryos are considered “genetically identical” to the donor. (Dr. Irving Weissman, 2/13/2002, before the President’s Council on Bioethics; Dr. John Gearhart, 4/25/2002, before the President’s Council on Bioethics). Dr. Thomas Okarma, CEO of Geron Corporation, has pointed out that cloning is not commercially viable, stating that, “The odds favoring success are vanishingly small, and the costs are daunting. It would take thousands of [human] eggs on an assembly line to produce a custom therapy for a single person. The process is a nonstarter, commercially.” (Quoted by Denise Gellene in, “Clone Profit? Unlikely”, Los Angeles Times, 5/10/2002). Corroborating such a view, Drs. Odorico, Kaufman and Thomas have written, “The poor availability of human oocytes, the low efficiency of the nuclear transfer procedure, and the long population doubling time of human embryonic stem cells make it difficult to envision this becoming a routine clinical procedure.” (Odorico JS, Kaufman DS, Thomson JA, “Multilineage differentiation from human embryonic stem cell lines,” Stem Cells, 2001).

Dr. Prentice adds, however, that it is unlikely that large numbers of mature human oocytes would actually be available for the production of embryonic stem cells, particularly if hundreds are required to produce each embryonic stem cell line. “The technical capability for nuclear transfer would also need to be widely available, and this is unlikely,” he says. Dr. Alan Trounson adds,

“In addition, epigenetic remnants of the somatic cell used as the nuclear donor can cause major functional problems in development, which must remain a concern for embryonic stem cells derived by nuclear transfer. Although it is possible to customize embryonic stem cells by therapeutic cloning or cytoplasmic transfer, it would appear unlikely that these strategies will be used extensively for producing embryonic stem cells compatible for transplantation.” (Alan O. Trounson, “The derivation and potential use of human embryonic stem cells,” Reproduction, Fertility and Development, 2001).

As Dr. Irving Weissman of Stanford University stated in his testimony before the President’s Council on Bioethics,

“I should say that when you put the nucleus in from a somatic cell, the mitochondria still come from the host. And in mouse studies it is clear that those genetic differences can lead to a mild but certainly effective transplant rejection, and so immunosuppression, mild though it is, will be required for that.” (Dr. Irving Weissman, 2/13/02, before the President’s Council on Bioethics).

Dr. Alan Trounson, the Australian embryonic stem cell expert and a globally recognized leader in the field, has stated that cloning has now become “unnecessary and obsolete”. He says that stem cell research has advanced so rapidly, just in the past few months alone, that therapeutic cloning is now unnecessary. “My view,” he states, “is that there are at least three or four other alternatives that are more attractive already.” In light of this realization, he has abandoned his own work in therapeutic cloning, turning his attention instead to the more promising field of stem cell research.

Emphasizing the point that therapeutic cloning faces too many “logistical problems,” and that other techniques show “greater promise” and offer “better options,” Dr. Trounson adds, “I can’t see why, then, you would argue for therapeutic cloning in the long term, because it is so difficult to get eggs and you’ve got this issue of [destroying] embryos as well.” (“Stem cell cloning not needed, says scientist”, The Age [Melbourne], 7/29/2002; “Stem cell research outpaces cloning”, The Australian, 7/29/2002; “Therapeutic cloning no longer necessary: expert”, AAP Newsfeed, 7/29/2002).

Many experts are now extolling the promise of regenerative medicine through stem cells, instead of through therapeutic cloning. Even the previously assumed multipotency and monopotency of adult stem cells is now being challenged by more recent data, which have demonstrated that some adult stem cells are capable of exhibiting pluripotency. The versatility of adult stem cells is thus much greater than originally thought.

Arguments against human cloning include:

  • There is no evidence that cloning is necessary or useful for medical treatments.
  • Cloning research will divert resources away from other, more worthy areas of research, and delay cures.
  • Banning only implantation (reproductive cloning) is unenforceable.
  • Cloning creates a class of human beings who exist only as a means to achieve the ends of others.
  • Cloning risks the health, safety and possible exploitation of women.
  • Cloning may possibly lead to the commodification and commercialization of human life.
  • Cloning is the “gateway” to genetic manipulation and control of human beings.

Additionally, a report issued in February of 2004 from South Korea highlights the difficult logistics of human cloning. The report describes the first successful attempt to create a hES cell line by SCNT. Researchers at the South Korea Seoul National University, in a study led by Dr. Hwang Woo Suk, were the first to successfully clone a human embryo, for purposes of growing “customized” stem cells for replacement tissue in the treatment of disease. Sixteen (unpaid) women voluneteers had been recruited for participation in the study, and they were then given hormone injections to induce superovulation, which resulted in the production of 242 eggs that were used to produce the single hES cell line. Each volunteer also donated some cells directly from one of her ovaries. From the cumulus cells surrounding the developing oocyte (the immature egg cell), the nuclei were transplanted to the egg of the same individual, using the same process as that used in the cloning of animals. Donor and recipient were therefore the same, presumably eliminating the risk of immunological rejection. However, only one-fourth of the SCNT eggs successfully reached the blastocyst stage (at which point the inner cell mass was harvested to create hES cells), despite the fact that additional chemicals were used to “jump start” the cellular division. From a total of 30 blastocysts, 20 inner cell masses were harvested, but only one ES cell line was successfully obtained. The cells in this ES cell line are genetically identical to the donor, and began forming muscle, bone and other tissues in test tubes and when implanted into mice. The results were published in the U.S. Journal Science.

Citizen’s rights activists and bioethicists complained of the lack of transparency surrounding the recruitment of the egg donors, and they raised questions over how rigorously Hwang and his colleagues had followed the ethical guidelines imposed upon their research. A further complication is the fact that it is not yet fully understood how to control the direction of hESC growth, so researchers are still trying to determine the specific types of tissue into which the cells will grow, a goal which continues to remain elusive.

Even Alan Colman, one of the experts on Dolly the sheep, was quoted as saying, “I do not welcome this.” Cloned embryos, if transferred into a woman’s uterus, could, theoretically, grow into cloned babies. The bioethics of such research has triggered debate among scientists and politicians worldwide.

It was noted, however, that attempts by the South Koreans to clone male cells failed. Even beyond the ethical questions, there still remain concerns that therapeutic cloning is too inefficient and too expensive.

In summary, therapeutic cloning may correctly be viewed as unsafe, unethical, and unnecessary.

The greatest hope for clinical regenerative medicine may therefore be found in postnatal and adult stem cell research.

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