1Executive summary: Embryonic stem cells are the inner cell mass taken from a fertilized embryo. A clone is the result of an artificially created embryo made in a laboratory. Both have the potential of developing into a live birth. Because no proof of concept has adequately demonstrated that embryonic stem cells or cloning can be used to cure disease or replace injured or diseased organs or tissue in humans, and because a controversy exists over the ethics of using human embryonic stem (hES) cells and human cloning in research, namely, that such research is immoral because it destroys nascent human life, a moratorium should be put in place banning this research until it can clearly demonstrate its potential for clinical use. Experiments involving mice and small animals are not sufficiently predictive in this regard. This means demonstrating at the primate level that embryonic stem cells and cloning can achieve the results hoped for in humans. This has not been done. Until research involving primate stem cells and cloning can reach the level that would clear the way for human trials, no experimentation with human embryonic stem cells or human cloning, either at the therapeutic or reproductive level, should be allowed.
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Monkey XO47 sits on an operating table at the Biomedical Research Foundation at Bourryeau Estate on St. Kitts, a small island nation in the West Indies in the Caribbean Sea. The research facility is housed in a remodeled sugar cane mill, a remnant of the days when the island was dotted by sugar plantations planted by wealthy Europeans in the 1700s. In fact, the chimney stack that was employed in the sugar refining process still stands beside the building and Bourreay Estate still has working sugar farms. The towering smoke stacks have an eerie resemblance to the chimneys that rose up by the extermination centers during the Holocaust.
The green vervet monkey weighs 12 pounds and measures 34 inches from the tip of his tail to the shaved portion on the top of his head. His fur is a mélange of black, yellow, and olive, with white under parts and a coal-black face. Before being brought to the table, he was staggering about an open-air enclosure on the grounds of the stem-cell research facility, stumbling because he has a form of experimentally induced Parkinson's disease.
The monkey is among thousands that now populate the island, some estimating that the monkey population outnumbers the human population by three to one. They were brought here from Africa as pets for the European settlers and eventually over-ran the country. Farmers have tried for years to eliminate these feral animals, who sometimes pull up their crops of onions and other vegetables, but they have not been successful.
2So the research facility is welcomed by the inhabitants of St. Kitts because of its potential to control its unwanted monkey tribe. And the tropical island serves as an ideal setting for the biomedical research firm because it is cost-effective. While climate controlled cages and captive breeding and feeding are required in United States facilities, they are not necessary here.
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| Dr. Eugene Redmond outside the St. Kitts Biomedical Research Foundation |
Dressed in blue surgical scrubs in the operating room, Dr. Eugene Redmond of Yale University, a soft-spoken, 65-year-old psychiatrist and neurosurgeon, administers anesthesia to the monkey to sedate it, then after waiting for it to take effect, places a clamp on the monkey's head. The clamp is a special head holder that holds the brain in a fixed position in space. He then takes micro calipers to measure a target within that space, the target being the dopamine producing region of the monkey's mid-brain.
The monkey has been previously treated with the drug MPTP that destroys dopamine cells, inducing a disease that mimics most of the signs and symptoms of Parkinson's disease. Like a person with Parkinson's disease, it has difficulty walking and moving, has lost its appetite and is suffering from tremors.
He positions a surgical drill over the bald spot and bores a small hole in the skull, then drops a long needle down and injects three million human brain cells into its cranium, then pulls out the needle, sutures up the incision and places him in a cage shared with a half dozen other experimental monkeys, all of whom have identical incisions in their scalps.
The neural stem cells injected into the monkey's brain were derived from fetal brain tissue taken from human cadavers, the product of abortions. Judging from other experiments, the human neural stem cells will soon take hold and begin to grow, their fibers reaching out to bind with their monkey counterparts (Bearden, 2005).
3As a result of the injection of the fetal cells into the monkey's brain, over a course of time, monkeys like XO47 and his cage mates were able to walk, move and eat better, and had diminished tremors, a research team from Yale, Harvard, the University of Colorado, and the Burnham Institute reported June 11 in Proceedings of the National Academy of Sciences (Study shows stem cells curb Parkinson's disease in primate, 2007).
Human therapeutic value not established
While these results are promising, it will be years before it is known whether a similar procedure would have therapeutic value for humans, Redmond explains.
A cure for Parkinson disease has been attempted experimentally in other primates. Writing in the Journal of Clinical Investigation, January 2005, Yashushi Takagi and his research team from the Kyoto University in Japan successfully generated dopaminergic (DA) neurons (nerves that transmit dopamine, a chemical substance that is involved with brain functions such as movement, memory, attention, and problem-solving) from cultured monkey embryonic stem (ES) cells. The loss of DA neurons is associated with the neurodegenerative disorder Parkinson disease. They then transplanted the DA neurons into the brains of several monkeys with Parkinson disease (PD). Analysis of the brain tissue, behavioral studies, and functional imaging revealed that the transplanted cells functioned as DA neurons and diminished the symptoms of Parkinson disease (Takagi, 2005).
However, this experiment did not involve all the neural systems associated with Parkinson disease, but just the substantia nigra, a portion of the brain whose destruction is associated with Parkinson disease. In this experiment, monkeys were treated with the chemical MPTP to destroy the nigra. The reported noted that:
The results of this study remain in keeping with observations made in human patients, suggesting that ES cells are a promising candidate for a donor source for cell transplantation treatment of PD. It should be noted, however, that the MPTP-treated monkey is a model of acute selective nigral [nerve cells that produce dopamine] destruction whereas human PD patients also experience progressive deterioration and pathological changes of other neural systems.
The report concluded that:
Although the results presented here encourage the development of strategies involving ES cell-derived neurons for treatment of neurological diseases, further studies will be needed to address the long-term efficacy and safety of using these cells. For instance, the low survival rate of the grafted cells or neurons is comparable to that noted in previous reports.
In this experiment, the transplanted neurons did not last long. This experiment, as well as the prior one, do not represent a cure of Parkinson disease but hint at how investigators might proceed.
Primates are being studied because they are more similar biologically than other, smaller animals. However, while the scientific literature contains numerous studies involving embryonic stem cells derived from small animals, research involving primate stem cells is sparse.
Proof of concept needed
Such studies are called "proof of concept." As the New York Times explains:
In theory, stem cells isolated from an early human embryo can transform themselves into virtually any kind of cell in the body, kindling hope that one day they may be transplanted into human patients to provide new tissue wherever it is needed--heart muscle for cardiac patients, insulin-producing cells for diabetics, nerve cells to repair crushed spinal cords and so on. But there are serious hurdles to overcome before this dream can be realized, including figuring out what controls the differentiation of stem cells and combating their tendency to form tumors. Clearly it is unethical to study the unknown actions of stem cells in human subjects. One obvious solution is to insert the cells into animals and watch how they develop. Depending on what kind of stem cells are used and where they are put in the animal, it may also be possible to pluck some particular human biological feature or disease trait out of its natural context and recreate it in an animal model, where it can be examined and manipulated at will (Shreeve, 2005).
4Regarding the term "proof of concept," the "concept" is that embryonic stem cells or cloning can be used to cure disease and repair organs, while the "proof" is a demonstration of these concepts carried out in an experimental animal.
To obtain funding, scientists studying embryonic stem cells and other types of stem cells--such as Dr. James A. Thomson of the University of Wisconsin in Madison, the person who established the first line of stem cells in 1998--are making claims that their investigations will, indeed, provide the cures cited above.
There is a big problem, however. Since Thomson's discovery, no scientist in regenerative medicine has demonstrated that there is a reasonable expectation that in the foreseeable future such therapies will result in healing human patients. Instead, their claims lack scientifically credible proofs that their concept of cures using embryonic stem cells or cloning actually will work clinically.
At present, research involving embryonic stem cells and human cloning is being heatedly debated on ethical grounds, with those in opposition to the research claiming that such experimentation results in the taking of human life, while others say that taking a life at the embryonic stage doesn't matter, for such research has the potential to save lives. Because of this controversy and because of the lack of evidence that ES cells potentially can cure disease or heal injury, a moratorium should be established on all research involving human embryonic stem cells and human cloning, including therapeutic and reproductive cloning, until the scientific community can prove that their claims are based on scientifically valid proofs of concept.
Where are the cures?
Leading scientists have said they worry that as the issue becomes increasingly politicized, advocates of stem-cell research are promising the public quick cures for diseases, raising expectations that may not be fulfilled.
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Biochemist and Nobel laureate Thomas Cech, president of the Howard Hughes Medical Institute (HHMI) and James Battey, Jr., director of the National Institute on Deafness and Other Communication Disorders and chairman of the NIH Stem Cell Task Force, outlined their concerns in an article titled "Stem Cell Politics" in the October 19, 2006 New England Journal of Medicine:
"People get pushed into making outrageous statements on both sides. . . . Ultimately, it could come back to haunt the scientific community if the research under a future administration is allowed to go forward and people very reasonably say, `Where are the cures?'"
5"Everything gets polarized, and it has to be either black or white, no shades of gray allowed," Cech said. "People get pushed into making outrageous statements on both sides. . . . Ultimately, it could come back to haunt the scientific community if the research under a future administration is allowed to go forward and people very reasonably say, `Where are the cures?'" (Okie, 2006)
Yet, 12 years after Thomson incubated the first line of embryonic stem cells, scooping out the nucleus from left-over embryos from fertility clinics and growing them in Petri dishes, and over a year after President Barak Obama relaxed restriction on the federal funding of embryonic stem cells research, not one cure has been achieved.
This call for a moratorium is not demanding human cures, however, but simply a demonstration that cures using embryonic stem cells are realistically possible in humans. As mentioned, such a demonstration in the scientific community is normally based on performing an experiment that provides proof that the concept will work, that is, that the idea is feasible, and this is usually done in medicine by showing that such an envisioned therapy for humans works in laboratory animals.
Scientists have conducted experiments on mice and rats, helping to restore function in damaged hearts and spines by means of differentiating in the laboratory embryonic stem cells into tissues that have been transplanted. However, when it comes to stem cells, mice are poor examples of what will work in humans. Instead, primates should be used.
Two parts to proof of concept
The proof of concept, also called proof of principle, should be in two parts: first, that differentiation into tissue at the primate level can be achieved and that it can be transplanted to restore function, say of a diseased heart or a damaged spine, and secondly, that such tissue can be transplanted without being rejected because of the immune response.
For example, at the clinical level for a patient with a spinal cord injury, the realization of a dream of regenerative medicine would be that new sheeting around the nerve cord could be regrown by means of stem cell therapy, restoring function. Or say a patient has a heart attack and part of that person's heart dies. By means of stem cell therapy, a new section is regrown, transplanted, and function is restored to that person's heart.
A major drawback of conventional organ transplants is that the body attempts to destroy the new graft because it senses that the transplant is not of the same genetic makeup and treats that new tissue like it was invading bacteria. This means medical providers must administer immunotherapy to combat this response, which can compromise the patient's immune system and lead to complications, including death.
Preventing organ rejection
Stem cell therapy is envisioned as providing an opportunity to defeat the immune response.
There are two basic concepts that in theory would provide healthy tissue or organs for transplantation, while avoiding organ rejection.
One is a new method of obtaining stem cells that mimic embryonic stem cells called induced pluripotent stem cell (iPSC) technology. As explained earlier in this series, it involves reprogramming somatic, that is, body cells, into stem cells. Because the body cells would be taken from a patient needing treatment, no immune rejection would occur since the cells would have the same DNA as the patient. However, so far scientists have not been able to get these cells to differentiate into tissue that will have therapeutic value at the human level.
The other method involves using a process called somatic cell nuclear transfer (SCNT), that is, cloning. Researchers would take body cells from a patient and convert those cells into cloned stem cells, which have the potential to grow into any of the 200-plus tissue types of the human body. This would be done by first scooping out the nucleus of an egg and replacing it with body cells from a patient, switching them back to the blank slate of stem cells. Researchers would then allow the cells to grow within the newly created embryonic environment to obtain differentiated tissue and organs. At some point, these differentiated cells would be harvested for use as a graft, either unaltered or subjected to genetic or chemical modification. Immune rejection would be avoided because the cells, now tissue or organs, came from the patient being treated.
6Theoretically, the process would involve growing tissue or a whole organ in the laboratory, directing growth toward the type of organ needed, say nerve, heart, retina or bone tissue. If the process was limited to an injury, appropriate tissue would simply be regrown. However, if the malfunction was due to a disease or genetic error, the process could include correcting the disease or genetic error present in the patient's harvested cells. In essence, the disease would be cured in the laboratory. The repaired and now healthy tissue would be transplanted back into the patient, curing that patient and at the same time, avoiding immune rejection.
While this process has been used to produce the clone Dolly the sheep and other animal clones, no live clonal births have been achieved at the primate level and no clone beyond a few cells has been achieved at the human level.
That is a brief overview. Now let us look at the subject in more detail.
The promise of embryonic stem cells
With Thomson's discovery of how to culture the stem cells found inside a human embryo, he wrote in a research paper published by Science titled "Embryonic Stem Cell Lines Derived from Human Blastocysts" that: "These cell lines should be useful in human developmental biology, drug discovery, and transplantation medicine (Thomson, 1998)."
7Terry Devitt, Director of Research Communications, University of Wisconsin Stem Cell and Regenerative Medicine Center (UW-SCRMC), Nov. 6, 1998 announced the achievement in "Wisconsin scientists culture elusive embryonic stem cells." The news release will be quoted in full, as it describes the hoped-for promises of stem cell research and maps out the battle plan of using this new weapon against injury and disease:
Wisconsin scientists culture elusive embryonic stem cells
The dream of one day being able to grow in the laboratory an unlimited amount of human tissues for transplantation is one step closer to reality.
Writing in the journal Science, a team of scientists from UW-Madison report the successful derivation and prolonged culture of human embryonic stem cells--cells that are the parent cells of all tissues in the body.
The achievement has profound implications for transplant medicine, drug discovery and basic developmental biology. It opens the door to growing from scratch everything from heart muscle to bone marrow and brain tissue.
The work "shows you can derive and culture these cells, and it opens the possibility for some dramatic new transplantation therapies," said James A. Thomson, a UW-Madison developmental biologist and the lead author of the report published Nov. 6 in the nation's leading scientific journal. "Although a great deal of basic research needs to be done before these cells can lead to human therapies, I believe that in the long run they will revolutionize many aspects of transplantation medicine."
James Thomson in his lab
The work, which was supported by the Menlo Park, Calif.-based biotechnology company Geron Corp., caps a 17-year international race to be the first to capture and sustainably culture human embryonic stem cells. By providing the raw material for virtually every kind of human tissue, new customized strategies for treating a wide range of human diseases including diabetes, heart disease, some forms of cancer, and Parkinson's disease can now be developed.
8For example, many diseases, such as Parkinson's and juvenile onset diabetes mellitus, occur because of the death or dysfunction of just one of a few cell types. The replacement of those cells would offer lifelong treatment. To treat heart disease, heart muscle cells could be injected directly to shore up failing heart tissue.
Such clinical applications are years--perhaps more than a decade--away.
The embryonic stem cells were derived from the inner cell masses of donated human blastocysts. A blastocyst is a hollow ball of about 140 cells that develops several days after fertilization. The embryos from which the blastocysts developed were produced in a laboratory dish for clinical purposes, prepared to assist couples having difficulty achieving pregnancy. They were left over after successful clinical procedures to treat infertility, and in cooperation with the UW-Madison Medical School's department of obstetrics and gynecology, were donated specifically for this project with the informed, written consent of the patients.
The hope for pluripotent stem cells.
8aThomson's team established five independent cell lines and has been able to grow them indefinitely in culture. They have observed the cells to differentiate into the three primary germ lines that make up the body--endoderm, ectoderm and mesoderm--and subsequently into arrays of tissue cells such as cartilage, bone, muscle, neural and gut cells.
For biologists, these cell lines offer insights into developmental events that cannot be studied directly in the human embryo, but which have important clinical consequences for birth defects, infertility and pregnancy loss, said Thomson. Moreover, a more complete understanding of normal development will ultimately allow the prevention or treatment of abnormal human development.
The most likely immediate application of human embryonic stem cell technology, according to Thomson, would be strategies to quickly screen hundreds of thousands of chemicals for effective medicines. By measuring how pure populations of specific differentiated cells respond to potential drugs, it would be possible to sort out drugs that may be both useful or problematic in human medicine.
The Wisconsin Alumni Research Foundation (WARF), an independent, not-for-profit corporation that manages patents on behalf of UW-Madison, has applied for a patent on the human embryonic stem cell technologies described in today's Science article and Geron Corp. has a license to develop the technology. The company has invested significantly in the long quest for human embryonic stem cells. In addition to supporting the efforts at Wisconsin, it has funded other groups doing similar work at Johns Hopkins University and at the University of California at San Francisco.
Because there is a prohibition on the use of federal money for such research, federal funds were not used to support the stem cell work at Wisconsin.
"Our hope is that these cells could be grown in the laboratory and then used to regenerate failing tissue," said Thomas Okarma, Geron vice president for research and development. "Because these cells do not age, they could be used to generate virtually a limitless supply of cells and tissue for transplantation."
While the Wisconsin scientists have been able to capture and culture undifferentiated human embryonic stem cells, their transformation into different types of cells cannot yet be directed. Under certain culture conditions the embryonic stem cells differentiate, but the differentiation is to a random, mixed population of cells.
Finding ways to direct the human embryonic stem cells to become specific cells of clinical importance is an important next step required before new therapies can be developed.
Ways to prevent the immune system from rejecting transplanted cells also need to be developed. However, banking embryonic stem cells with records of genetic compatibility, or genetically altering cells to reduce or combat immune rejection, are two potential strategies for overcoming the problem, said Thomson.
Thomson's group is now actively pursuing collaborations with clinical scientists and transplant surgeons to perform the basic research needed to ultimately develop human embryonic cell-based therapies. Among those is Jon Odorico, a UW-Madison transplant surgeon, who cited the potential of human embryonic stem cells to be used in very focused ways to repair or replace damaged or diseased tissues or organs.
8b"The principal theoretical advantages of this type of treatment for organ replacement over current organ transplantation is the fact that the cells can be grown in large quantities, helping to negate the problem of the limited supply of donor organs, and can be genetically engineered outside the body to escape immune attack," Odorico said.
These "experiments have opened up some exciting new areas of research for transplant surgeons," he added.
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Biology-Online.org, a resource for biology related information, outlined the promise of stem cell research as follows:
Today's most urgent problem in transplantation medicine is the lack of suitable donor organs and tissues...treatments to replace, repair, or enhance the biological function of damaged tissue through cell transplantation/replacement therapy have until recently been limited to a few systems...it is to be anticipated that human (embryonic and adult) stem cell research may help millions of people who are affected by a wide range of intractable human ailments (Parkinson's disease, spinal cord injuries, heart failure, and diabetes).
Proof of this potential has been claimed to have been demonstrated in animals, according to the authors of Biology-Online.org:
The in vitro developmental potential and the success of ES cells in animal models demonstrate the principle of using hES-derived cells as a regenerative source for transplantation therapies of human diseases.
However, research scientists admit that stem cell research is not there yet when it come to human application:
Before therapeutically applicable, any ES-based treatment must, however, show limited potentials for toxicity, immunological rejection, or tumor formation, and at present, human ES cell research has not reached this threshold (Requirements of stem cell-based therapies--embryonic stem cells: prospects for developmental biology and cell therapy, 2010).
Such are the claims and caveats.
Thomson said that success might take a decade, yet as mentioned, a dozen years have passed and still no clinical trials and no cures have been achieved. Plus, to base the possibilities of such cures on experiments with small animals is dubious.
Safety
A major hurdle in any new medical procedure is the safety of the therapy. A crucial element in assessing stem cell safety is to answer this question: do the cells act as they are intended once transplanted? Stem cells have the potential to cure, damage or even to kill, that is, stem cell tissue upon transplant in theory may help heal a spinal cord injury or generate a disease state, such as cancer. Scientists test the theoritical capabilities by applying it to laboratory animals.
Using a number of methods, researchers do this testing by inducing conditions in such animals that mimic human injury or disease. Then, using the envisioned new medical procedure involving stem cells, they go about trying to cure that experimentally created condition. According to a National Institute of Health's report (Assessing human stem cell safety, 2010):
A critical element of the safety net is the transplantation of human stem cells into animals to demonstrate that the therapy does what it is supposed to do ("proof of concept") and to assess toxicity. Admittedly, animal models of human disease are imperfect because most human maladies do not spontaneously occur in animals. Chemical, surgical, and immunologic methods are used to damage neurons; induce diabetes; simulate heart attacks, stroke, and hypertension; or compromise organ function. In situations when focal genetic lesions are known to cause disease, the creation of transgenic mouse colonies in which the culpable gene is either eliminated or over-expressed results in disease models that are capable of faithfully reproducing human-disease-specific pathologies.
What must be demonstrated is evidence of cures in the animal models, such as improved function. According to the NIH:
Human stem cells must be transplanted into animal models of human disease. Transplantation of neural stem cells should demonstrate measurable evidence of efficacy in models of neurodegenerative disease, such as Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis (ALS), Alzheimer's disease, as well as spinal cord injury and stroke. Improved liver function after transplantation of hepatocyte precursors should be observed in an animal model of hepatic failure. Normalization of blood insulin concentrations and amelioration of diabetic disease symptoms should result from the transplantation of pancreatic islet progenitors in a mouse model of diabetes. It is likely that in all cases, immunosuppression will be required due to immunologic incompatibility between humans and the animal model species (usually mouse or rat).
Note however, that the NIH says that the animal model species usually involved is the "mouse or rat."
9Small animal "proofs" questioned
As mentioned, by means of experiments with small animals, stem cell researchers have attempted to demonstrate that the regenerative therapies they dream of are in deed feasible at the clinical level for humans and are safe. However, it turns out that mice and small animals do not furnish the best examples of how a cure might be effectively and safely carried out in humans.
Pioneer stem cell researchers Junying Yu and Thomson of the University of Wisconsin at Madison reviewed the state of stem cell research in an on-line paper for the National Institute of Health titled "Embryonic Stem Cells." They noted that:
Although scientists have gained more insights into the biology of human ES cells since 2001, many key questions remain to be addressed before the full potential of these unique cells can be realized. It is surprising, for example, that mouse and human ES cells appear to be so different with respect to the molecules that mediate their self-renewal, and perhaps even in their developmental potentials.
They explain that:
... human and mouse embryos differ significantly, particularly in the formation, structure, and function of the fetal membranes and placenta, and the formation of an embryonic disc instead of an egg cylinder...
Thus, mice can serve in a limited capacity as a model system for understanding the developmental events that support the initiation and maintenance of human pregnancy (Yu, 2009).
In a review summarizes the current state of ES cell-derived heart therapy titled "Differentiation of Pluripotent Embryonic Stem Cells Into Cardiomyocytes," sponsored in part by the National Institutes of Health and the National Institute on Aging, the report called into question the reliability of extrapolating the potential of human embryonic stem cells from studies on mice and whether such ES-derived heart cells would be functional in humans. It stated:
However, it remains unclear whether hES cells will be as versatile as their mouse counterparts regarding self-renewal, genetic manipulation, or developmental capacity. Clinically, it is also unclear whether pure cell populations of hES cell-derived cardiomyocytes can be readily isolated in sufficient quantities for therapy or whether these cardiomyocytes can integrate and function appropriately in the heart after transplantation (Boheler, 2002).
However, mouse and human ES cells differ in a number of significant ways, raising the very real possibility that breakthroughs in mouse stem cell science simply won't be reproducible with human stem cells.
A research study by the Whitehead Institute for Biomedical Research observed in a news release that what one demonstrates in mice may not work in humans (Scientists create more pluripotent human embryonic stem cell, 2010). It stated that:
However, mouse and human ES cells differ in a number of significant ways, raising the very real possibility that breakthroughs in mouse stem cell science simply won't be reproducible with human stem cells.
10Despite the fact that proof of concept in small animals has been called into question regarding the efficacy of stem cell research at the human level, it is still being used to validate the application of such research for humans.
If it can work for mice it can work for humans?
According to Guidelines for Human Embryonic Stem Cell Research (2005) by the National Academies Press, research with mouse embryonic stem (mES) cells helps prove the concept that embryonic stem cells have the potential of being useful in regenerative medicine. The report notes that:
Developmentally relevant signaling factors [chemical substances, such as proteins and growth factors, involved in orchestrating the stem cell driven repair process] can also be used to induce mES [mouse embryonic stem] cells to differentiate into specific cell types in vitro, including hematopoietic stem cells, beating cardiac muscle cells, neuronal progenitors, endothelial cells, and bone cells. In some cases, those differentiated cell types can be transplanted into animals to form functional tissues. Such work engenders excitement about regenerative medicine using hES [human embryonic stem] cells (Lanza et al., 2004).
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| Mouse and human: a difference |
That above quote is a proof of concept statement. It is a claim that embryonic stem cells, because they supposedly work to restore function in mice, can also do so in humans, that is, that they can serve to cure disease and replace failed organs. Many of these "proof of concept" studies are reported in Handbook of stem cells, vol. 1 embryonic stem cells, 2004, edited by leaders in the field, namely, Robert Lanza, John Gearhart, Bridig Hogan, Douglas Melton, Roger Pederson, James Thomson and Michael West.
For instance, in chapter 70, "Use of embryonic stem cells to treat heart disease," by Joshua D. Dowell, et al, the introduction states the following:
It is now well established that cardiomyocytes [cells of muscular tissue in the heart] can be stably transplanted into normal or injured adult hearts. Recent studies have demonstrated that transplanted donor cells can form a functional syncytium [network of cardiac muscle cells] with the host myocardium [muscular tissue of the heart]. It is also well established that embryonic stem (ES) cells can differentiate into functional cardiomyocytes in vitro and that these ES cell-derived cardiomyocytes form stable intracardiac grafts when transplanted into the myocardium. ES cells might thus be a suitable source of donor cardiomyocytes for cell transplantation therapies aimed at restoring lost myocardial mass in diseased hearts.
11One of the major studies cited was by a team from the Charles A. Dana Research Institute and the Harvard-Thorndike Laboratory, Cardiovascular Division, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston. In "Transplantation of embryonic stem cells improves cardiac function in postinfarcted rats" the team lead by Jiang-Yong Min stated that:
Massive loss of cardiac myocytes [heart muscle tissue] after myocardial infarction (MI) [heart attack] is a common cause of heart failure. The present study was designed to investigate the improvement of cardiac function in MI rats after embryonic stem (ES) cell transplantation. MI in rats was induced by ligation [surgically tying off] of the left anterior descending coronary artery...Animals in the treated group received intramyocardial injection of ES cells in injured myocardium.
Min and team concluded that:
...this study demonstrates the feasibility of transplanting ES cells into injured myocardium in rats. Transplanted ES cells were able to form stable intramyocardial grafts and to improve cardiac function in postinfarcted failing hearts. Our results raise the possibility that ES cell transplantation may provide a new and novel approach to improve cardiac function after a massive MI (Min, 2002).
In the summary of the review of several studies in Handbook on Stem Cells, including the one above, the authors state:
The data summarized above indicated that donor cardiomyocytes were stable following transplantation into normal or injured recipient hearts; furthermore, they were capable of forming a functional syncytium with the host myocardium. In addition, the data demonstrated that highly differentiated cardiomyocytes could be derived from ES cells and that these cells could be stably transplanted into recipient hearts (p. 718).
Human trials put on hold
However, as noted above, just because these procedures appear to work for mice do not mean they will work for humans. As mentioned in Part I, one of the most promising application of stem cell research is the generation of nerve tissue.
Early in 2009, the Federal Drug Administation gave Geron Corporation--the company that helped fund the pioneering development of stem cell research--the green light to go ahead with clinical trials. This was a first. The goal of the trial was to restore function to patients with injured spinal cords (Geron Receives FDA Clearance to Begin World's First Human Clinical Trial of Embryonic Stem Cell-Based Therapy, 2009).
However, the trial was put on hold later in the summer of that year, awaiting further data from animal experiments.
Evan Snyder, a neuroscientist who heads up the stem cell research center at the Burnham Institute for Medical Research in San Diego, commented that the research may not be ready for humans, saying that pre-human trials, which involved mice, should have been performed on larger animals.
"There's a lot of debate among spinal cord researchers that the pre-clinical data itself doesn't justify the clinical trial," said Snyder, who is working on using neural stem cells himself (Ertelt 2009).
Disease not cured
And the reasoning of regenerative scientists gets even cloudier. Not only can one not dependably conclude that what will work in mice will work in humans, but the experiments involving experimental mice do not necessarily validate the cures claimed.
While "many diseases, such as Parkinson's and juvenile onset diabetes mellitus, occur because of the death or dysfunction of just one of a few cell types," as stated in "Wisconsin scientists culture elusive embryonic stem cells", it does not necessarily follow that "The replacement of those cells would offer lifelong treatment." Experiments that supposedly demonstrate the efficacy of stem cell therapy often, in fact, do not.
For instance, that transplanted tissue derived from ES cells can restore function to "normal or injured recipient hearts" does not necessarily demonstrate the likelihood that, as stated above, "ES cells might thus be a suitable source of donor cardiomyocytes for cell transplantation therapies aimed at restoring lost myocardial mass in diseased hearts."
The experimental mice did not have diseased hearts, but instead, "normal or injured hearts." Recall that the injury to the mouse heart was surgically caused by restricting blood flow to the heart by means of tying it off with a ligature, that is, a tourniquet. Let us suppose that a portion of a heart damaged by heart disease was replaced successfully using ES cells. This would not cure the disease, say narrowing of the blood vessels due to plaque buildup or blockage due to a blood clot, but would merely replace the injured tissue. Thus such ES cell therapy would be at best a temporary solution to a systemic problem, i.e., on-going heart disease. While damaged tissue might be restored, heart disease would not be cured by the transplant.
12Thus, these proofs that stem cells can be used to cure disease in humans are flawed at two level. First, mice and small animals are not good examples of the possibilities for cures in humans and secondly, in the experiments cited, stem cells do not cure, but at best, replace diseased or damaged tissue.
How realistic are such cure claims?
Exaggerated claims of curative potential are wide spread. While embryonic stem cells are often cited in the scientific community as being potentially useful in treating, by means of transplantation, such conditions as Parkinson's disease, Alzheimer's disease, heart disease and diabetes, just how realistic is it to think that stem cells could achieve this?
"...what are you going to do--replace the brain? So we are looking at a very simplistic approach here to treat people..."
I have an interest in a number of these things that are thrown around in the press, particularly things like Alzheimer's, diabetes and Parkinson's. These are very complex disorders. To say that you will cure them by putting in a few cells is a joke. We do not even know the genetic basis. We know that there are environmental factors. We know that Alzheimer's is a global [involving the total organ] disease; what are you going to do--replace the brain? So we are looking at a very simplistic approach here to treat people... There is a genetic basis to many of these conditions. If you go putting in cells derived from whatever source you might think, they are going to be subject to exactly the same processes, so you have problems on your hands there (Fact Sheet: There is no proof of concept that embryonic stem cells can cure the many diseases claimed, 2002).
Conceptually, replacing tissue when it comes to curing something as complex as brain disease is most likely unrealistic. For instance, as Rowe noted, Alzheimer's is a disease involving the total brain and is caused by genetic, environmental, and lifestyle factors. While one can envision replacing a damaged heart, how does one replace a damaged brain? Obviously, medical science will never be able to do that, for the brain is physically who we are.
Replacing tissue that has been damaged or destroyed by a disease process with tissue generated from stem cells, such as new brain cells for Parkinson's disease, or new heart cells for a heart attack patient, will represent at best a patch-up job, but not a cure. And the same difficulty would apply to whole organ replacement, if stem cell therapy can ever reach that level.
Just what is "pluripotent"?
But the dream of regenerative medicine gets even more elusive. Taken from the grab-bag of the blastocyst, embryonic stem cells are supposedly the answer to tissue and organ regeneration. But just what are embryonic stem cells? Do they really have the ability to generate the 200-plus tissue-types as the regenerative medicine gurus claim?
Stem cells that have the ability to develop into all these tissue types have been called "pluripotent."
According to the Harvard Stem Cell Institute (HSCI), self-described as "A scientific collaborative established to fulfill the promise of stem cell biology," pluripotent stem cells are:
Stem cells that can become all the cell types that are found in an organism, but not the embryonic components of the trophoblast and placenta (these are usually called extra-embryonic tissues). Isolated human embryonic stem cells are pluripotent, and although they can generate any cell in the body, they would not be able to generate the placenta (Glossary--pluripotent stem cells, 2010).
In nature, these extra-embryonic tissues of the embryo, consisting of the trophoblast and the placenta, are what organize the stem cells into all tissues of the body. The pluripotentality of the stem cells is dependant on the extra-embryonic tissues. What stem cell biologists are trying to do is mimic the function of the trophoblast and the placenta in the laboratory, creating tissue directly out of stem cells without the mediating function of the extra-embryonic tissue.
13According to the Handbook on Stem Cells:
...a widely adopted convention is to describe ES cells as pluripotent stem cells to distinguish them from cells like those of the haematopoietic [blood] system, which have a narrower but nevertheless impressive range of differentiation potential (Lanza, et al, 2004, p. 16).
So, what is potential or potency?
Potency can be defined as the range of developmental capabilities of a cell that is in a permissive or supportive environment. A unipotent cell can just make one type of cell, whereas an oligopotent cell, such as a hematopoietic stem cell, can make several cell types. A mulitpotent cell can be considered as having the potential to generate multiple cell types, such as the derivatives of one germ layer. Finally, a cell is considered to be totipotent if it displays the full range of developmental capabilities when it is placed in a permissive environment (Cibelli, Principles of Cloning, p. 110).
Pluripotency is between multipotency and totipotency. The definition of pluripotency found in the National Institute of Health's glossary on stem cell information is similar to the definition by the HSCI, but adds how pluripotency is demonstrated (Glossary--pluripotent, 2010):
Pluripotent--Having the ability to give rise to all of the various cell types of the body. Pluripotent cells cannot make extra-embryonic tissues such as the amnion, chorion, and other components of the placenta. Scientists demonstrate pluripotency by providing evidence of stable developmental potential, even after prolonged culture, to form derivatives of all three embryonic germ layers from the progeny of a single cell and to generate a teratoma after injection into an immunosuppressed mouse.
Thus, human ES cells are defined as being able to differentiate at the pluripotent level, namely, to have the potential of developing into all tissue types with the exception of going to the final step of producing a living being, that is, they are not totipotent.
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And how is this capability assessed? That is, how is the ability to differentiate defined for human ES cells? What would be the proof of the concept that such stem cells can, in fact, differentiate and are pluripotent?
Incredibly, the NIH defines the capability of pluripotency to be demonstrated by forming a teratoma, that is, a tumor when injected into mouse tissue. This is a widely accepted view among regenerative scientists.
In an article in Handbook of Stem Cells by editors Lanza, et al, Richard L. Gardner in Chapter 2, "Pluripotential stem cells from vertebrate embryos: present perspective and future challenges," maps out the parameters of an ES cell. He states that:
14The basic characteristics of an ES cell include self-renewal, multilineage differentiation in vitro and in vivo, clonogenicity, a normal karyotype [chromosomes of cells], extensive proliferation in vitro under well defined culture conditions, and the ability to be frozen and thawed. In animal species, in vivo differentiation can be assessed rigorously by the ability of ES cells to contribute to all somatic lineages and produce germ line chimerism. These criteria are not appropriate for human ES cells; consequently, these cells must generate embryoid bodies and teratomas containing differentiated cells of all three germ layers.
In stating that "These criteria are not appropriate for human ES cells," he is pointing out that ethically it would not be appropriate to prove the concept that such ES cells are capable of differentiating in vivo, because this would mean introducing the stem cells into a human embryo or egg and allowing it to come to term, that is, be born.
Therefore, because "These criteria are not appropriate for human ES cells," to assess the ability to differentiate, Gardner posits the following definition, echoing the definition by the NIH:
...consequently, these cells must generate embryoid bodies and teratomas containing differentiated cells of all three germ layers (Lanza et al, 2004, p. xxix).
But, does this make sense?
According to the National Institute of Health, embryoid bodies are rounded collections of cells that arise when embryonic stem cells are cultured in suspension, that is, in vitro. Embryoid bodies contain cell types derived from all 3 germ layers (Glossary--embroid bodies, 2010). However, the differentiation within the embryoid bodies, although occurring in a three dimensional manner is largely disorganized relative to the carefully orchestrated events of normal embryonic development (Embryoid body, 2010).
A "teratoma" is defined as follows:
A teratoma is an encapsulated tumor with tissue or organ components resembling normal derivatives of all three germ layers... The tissues of a teratoma, although normal in themselves, may be quite different from surrounding tissues, and may be highly disparate; teratomas have been reported to contain hair, teeth, bone and very rarely more complex organs such as eye, torso, and hands, feet, or other limbs (Teratoma, 2010).
15According to the National Institute of Health's glossary on stem cell information, a "teratoma" is:
A multi-layered benign tumor that grows from pluripotent cells injected into mice with a dysfunctional immune system. Scientists test whether they have established a human embryonic stem cell (hESC) line by injecting putative stem cells into such mice and verifying that the resulting teratomas contain cells derived from all three embryonic germ layers (Glossary--teratoma, 2010).
Definition of "pluripotent" wishful thinking
So, folks, the way we know that we can get pluripotent embryonic stem cells to produce all the tissues comprising the human body is because such stem cells can produce a disorganized collection of cells in vitro or tumors upon being injected into mice in vivo. Sorry, these proof-of-concepts prove stem cells can produce balls of disorganized cells or tumors, and at best, non-functioning differentiation at the first stages. Wishful thinking should not enter into proving a concept.
To define pluripotency and differentiation in humans by the ability of embryonic stem cells to produce an embryoid body or teratoma is patently absurd. If this definition were to be used to support obtaining funding of research projects, claiming that embryonic stem cells are therefore capable of differentiating into tissue for regenerative therapies, that would be fraud.
"This marks an important biological difference between embryos and ES cells; the former generate a body plan and the latter cannot."
According to Martin F. Pera, writing for Hematology, "Stem cells: hype and reality," while differentiated cells can be recognized in the teratoma, they are disorganize and follow no body plan. He stated in chapter 2 on "Embryonic stem cells" the following:
For obvious ethical reasons it will never be possible to demonstrate that human ES cells can colonize all the tissues of a newborn baby following introduction into a host embryo. The developmental potential of human ES cells is, however, easy to demonstrate by inoculating the cells into an immunodeficient animal host. Under these conditions, ES cells form benign teratomas consisting of an incredible range of differentiated cells. The differentiated cells are often organized histotypically into complex structures such as ganglia. It is important to note that certain phenomena are never observed in teratomas. For example, no axis formation or segmentation into a body plan is ever observed in a teratoma. This marks an important biological difference between embryos and ES cells; the former generate a body plan and the latter cannot (Verfaillie, 2002).
Of particular importance is the statement that:
It is important to note that certain phenomena are never observed in teratomas. For example, no axis formation or segmentation into a body plan is ever observed in a teratoma. This marks an important biological difference between embryos and ES cells; the former generate a body plan and the latter cannot.
If a group of people applied for funding to build a duplicate of the San Francisco Golden Gate Bridge and were asked by the investors what proof they could offer to demonstrate they had the capabilities to build such a bridge, what do you suppose would be their answer if the following exchange occurred:
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| But can you drape the cables? |
Investors: can you build this bridge?
16Group: Yes, we can build a span made up of suspension cables and steel struts because we know how to make the cables and the struts.
Investors: Can you put them together in an organized span so that they will support the structure of the bridge? That is, using these parts, do you have a plan for the body of the bridge? Can you drape the cables to support the roadway?
Group: We don't have a clue on how to do that, but we are working on that. So, when can we expect funding for this project?
Of course, no sensible investor would buy that line of reasoning, nor would they provide funding, yet researchers in regenerative medicine are expecting the public to support research based on wishful and illogical thinking regarding the pluripotent features of embryonic stem cells. A body plan is essential. Without being able to organize parts into a functioning whole, a structure such as a bridge or a human being does not work and is not viable.
Potential flows only from totipotency
However, the error in thinking may be even worse than this. Pera states that:
We can define a totipotent cell as one that can give rise to a new individual if provided with appropriate maternal support. Pluripotent cells can give rise to all tissues of the body plus many of the cells that support the pregnancy but are unable to produce a new individual on their own (Verfaillie, 2002).
But wait a minute. Is that really so? Do, in fact, pluripotent cells can give rise to all tissues of the body? And if so, how does Pera know this? He knows this because pluripotent cells inside the complete embryo do this, that is how. But, can we make this inference for the environment outside the complete embryo? That is, can pluripotent cells "give rise to all tissues of the body" without producing a new individual first? This is a critical question.
Recall, that we are not talking about a totipotent environment, but merely pluripotent cells deprived of the trophoblast and the cytoplasm, that is, deprived of the microenvironment of a totipotent cell. We are talking about stem cells in a laboratory environment, not an embryonic one.
Pera assumes that pluripotent cells can differentiate based on evidence in the in vivo world and is applying this known potentiality to the in vitro world. He is assuming that since it can be done with a full embryo with maternal support, then given the right chemicals and the right manipulations, it can be done in a laboratory environment, as well.
Healthy cells or tumor cells?
But, just what in reality does the proof of concept prove embryonic stem cells are, absent the microenvironment of the complete embryo? As mentioned, when injected into an adult cell environment, that is, the wrong environment, they are not healthy cells, but tumorigenic. Further, an embryonic stem cell line resembles the characteristics of cancer.
Concerning embryonic stem cells capacity to generate tumors and mimic cancer:
17It is well established that undifferentiated, early embryonic cells commonly generate teratomas or teratocarcinomas when transplanted to extrauterine sites. This is not surprising, because ES cells display many features characteristic of cancer cells including unlimited proliferative capacity, clonal propagation, and a lack of both contact inhibition and anchorage dependence (Requirements of stem cell-based therapies, 2010).
In fact, as reported in Principles of Cloning "...stem cells that are out of biological control in the adult may be one source for tumorigenesis (p. 113)"
What controls development, what governs differentiation, is the totipotent embryo at the blastocyst stage, which includes the trophoblast, cytoplasm and the nucleus (stem cells). Scoop out the stem cells and you may not be getting pluripotent cells, but instead tumor cells.
In short, pluripotency may be inextricably linked with totipotency. That is, without the complete embryo, the nucleus cells may actually not be pluripotent, but instead have the characteristic of a disease process since they are out of control.
That totipotency, rather than just pluripotency, is necessary for differentiation can be demonstrated by the fact that a unipotent skin cell can be turned into a stem cell by means of somatic cell nuclear transfer and that, if left in the embryonic environment and implanted in a maternal host, can differentiate into a living creature upon birth, as was accomplished with Dolly the sheep.
Further, the embryonal carcinoma (EC) cell, as the stem cell of teratocarcinomas has come to be know, has been characterized as a pluripotential cell. EC cells injected into an adult grow progressively and kill it. However, these vary same cancerous cells, if introduced into the blastocyst were able to participate in normal development and were found to be able to contribute to most if not all organs and tissue of the resulting offspring (Lanza et al, 2004 p. 15).
Cancer and stem cells have similar properties as reported in the Proceedings of the National Academy of Science by a team led by Lynne-Marie Postovit in "Human embryonic stem cell microenvironment suppresses the tumorigenic phenotype of aggressive cancer cells," Program in Cancer Biology and Epigenomics, Children’s Memorial Research Center, Feinberg School of Medicine, Northwestern University:
Metastatic cancer cells resemble stem cells in their ability to self-renew and to derive a diverse progeny. Moreover, the phenotype of stem cells and cancer cells is profoundly influenced by the microenvironment. During embryogenesis, precursor cells are specified to particular fates through the delivery of signaling molecules, and malignant cells similarly release and receive cues that promote tumor growth and metastasis. There also is a convergence between cancer cells and stem cells in the molecular messengers they implement to regulate self-renewal and cell fate.
On the other hand, the environment of the embryo inhibits, that is, controls, tumorigenicity so that normal tissue results.
The multipotent phenotype of metastatic cancer cells permits them to respond to cues normally restricted to developmental processes. Hence, we hypothesized that embryonic microenvironments, which are inherently permissive to normal stem cell differentiation, may be used to reprogram (i.e., redifferentiate) cancer cells toward a benign phenotype. Indeed, embryonic microenvironments have been shown to inhibit the tumorigenicity of a variety of cancer cell lines. For example, the mouse embryonic microenvironment can reprogram teratocarcinoma cells to a nontumorigenic phenotype capable of differentiating into normal tissues (Postovit, 2008)...
Embryonal carcinoma cells are pluripotent stem cells derived from teratocarcinomas and are considered the malignant counterparts of human embryonic stem cells (Przyborski, 2004).
18What does this tell us? That the normal development of pluripotent stem cells depends on environment, namely, the embryonic microenvironment of the totipotent blastocyst, which includes the trophoblast and cytoplasm. It governs the development of the pluripotent stem cells into normal tissue. Pluripotency has the ability to differentiate into the various organs of the body only in the context of totipotency. Without the regulatory environment provided by a totipotent cell, stem cells are not functionally pluripotent, but out of control, that is, in an adult cell environment tumorigenic or cancerous.
The pluripotent stem cell has two sides to its coin: normal or malignant. Both ES cells and EC cells are capable of producing tissues from all three primary germ layers. Inject either ES or EC cells into a de-nucleated egg and you get life. Inject ES cells into a mouse and you get a teratoma. Inject EC cells into a mouse and it is lethal.
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| Stem cell scientists modern day alchemists? |
Alchemy
Stem cell researchers are participating in a form of alchemy. "Alchemy" is defined as 1. a form of chemistry and speculative philosophy of the Middle Ages that attempted to discover an elixir of life and a method for transmuting base metals into gold. and 2. any seemingly magical process of transmuting ordinary materials into something of true merit.
Pluripotency in effect can be either lead (a tumor or cancer), or gold (capable of producing all 200-plus tissue types of the body). Defining lead to be gold would not in reality turn lead into gold. Nor does defining pluripotency as the ability to create a tumor, as researchers have done, give stem cells in the laboratory the ability to differentiate into clinically useful tissue.
In the hands of regenerative scientists--biological science's modern day counterpart to the alchemists--to date pluripotent stem cells have remained lead. However, in the hands of nature, the full embryo can even turn biological lead into gold, that is, the embryo can turn a cancer cell into a live born mouse by means of somatic cell nuclear transfer, i.e. cloning. Thus, we see the importance of the full embryo, which includes the trophoblast and cytoplasm, for allowing pluripotent stem cells to grow into viable tissue.
And it is this very environment, the mircoenvironment of the blastocyst from which the stem cells have been sucked, that the embryonic stem cell scientists are trying to replace with laboratory voodoo.
Cancer lines
Moreover, the longer embryonic stem cells are cultured in these laboratories, the more cancer-like they become. P.W. Andrews, et al, writing in Biochemical Society Transactions, noted in "Embryonic stem (ES) cells and embryonal carcinoma (EC) cells: opposite sides of the same coin," that "embryonic stem cells may develop in culture in ways that mimic changes that occur in embryonic carcinoma cells during tumor progression (Andrews, 2005).
"The results suggest that ES cells may develop in culture in ways that mimic changes occurring in EC cells during tumour progression."
In this study, the team led by Andews made the following observations:
Embryonal carcinoma (EC) cells are the stem cells of teratocarcinomas, and the malignant counterparts of embryonic stem (ES) cells derived from the inner cell mass of blastocyst-stage embryos, whether human or mouse. On prolonged culture in vitro, human ES cells acquire karyotypic changes that are also seen in human EC cells. They also ‘adapt’, proliferating faster and becoming easier to maintain with time in culture. Furthermore, when cells from such an ‘adapted’ culture were inoculated into a SCID (severe combined immunodeficient) mouse, we obtained a teratocarcinoma containing histologically recognizable stem cells, which grew out when the tumour was explanted into culture and exhibited properties of the starting ES cells. In these features, the ‘adapted’ ES cells resembled malignant EC cells. The results suggest that ES cells may develop in culture in ways that mimic changes occurring in EC cells during tumour progression.
Prolonged culture of human ES cells acquire changes that make them like human EC cells, and in fact, produce teratocarcinoma, that is, are cancerous, when injected into mice.
The long and the short of the issue is that pluripotency may or may not be a good thing. In a blastocyst, stem cells are the stuff out off which life is made, but in the laboratory, they tend to produce tumors. The potential of pluripotent cells can be to generate tissue that is normal or tumorous, with tumors being either benign or malignant. Some exeriments have coaxed stem cells to differentiate, but not to the point where they can be used clinically to repair injured or diseased tissue.
Possibly, the human embryonic stem cell lines being cultured in laboratories around the world are just sprawling collections of tumors in Petri dishes. At least, that concept is what is proven when such cells are injected into mice--they produce teratomas. And what is the proof of concept when cells from prolonged cultures of ES lines are injected into mice? They produce cancer.
Regenerative scientists pride themselves in being able to maintain prolonged cultures of these cells and ship them around the world for study. It would take more than alchemy to produce healthy tissue in the laboratory out of collections of tumorigenic and cancerous cells .
But what about immune rejection?
You think it is bad, now? There is yet another problem. Even if scientists could get embryonic stem cells to differentiate to produce tissue that could be transplanted, this tissue would still be rejected because an embryo is from a person different than the patient, being that it is the beginnings of a totally separate and totally genetically different human being with completely unique DNA. That is, such tissue would be rejected just a readily as a transplant of, say, a heart from a deceased individual donated to a patient needing a heart transplant, because of the patient's immune response.
So, as asked earlier in this series, what is a poor regenerative scientist supposed to do?
How can one achieve differentiation and avoid immune rejection?
Answer: clone. As explained above, take a somatic cell from a patient, plop it into an human egg and presto, you have converted those cells to stem cells that have the same DNA as the patient. This is a form of nuclear reprogramming whereby a skin cell is switched into a stem cell by using an egg.
19But, it is not that simple.
As explained earlier in this series, while this can be done for numerous animal species, it can not be done for humans. And it has only been partially successful at the primate level, and was achieve with considerable difficulty and involved numerous attempts.
Reporting in Neurology Today on a study in Nature, investigators coaxed primate skin cells back in time to an embryonic stem cell state, using somatic cell nuclear transfer.
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James A. Byrne, PhD, a postdoctoral fellow at the Stanford University Institute for Stem Cell Biology and Regenerative Medicine and the lead author of a new study in Nature, said that the findings are a proof of concept that could one day lead to cellular treatments for all sorts of diseases. He performed the research at the Oregon National Primate Research Center in Portland in collaboration with Shoukhrat Mitalipov, MD.
No one has been able to get a primate somatic cell, in this case a skin fibroblast, to program back into an embryonic stem cell, Dr. Byrne noted. As explained earlier, it is the hope of regenerative scientists that such embryonic stem cell lines could in theory become any cell in the body.
20To test that theory, the Oregon scientists coaxed the fibroblasts, or skin cells, from a 9-year-old rhesus monkey and merged the skin cells with unfertilized monkey eggs that had the DNA removed. The eggs now contained DNA from the skin cells, and gave way to embryonic stem cells. Then, the scientists let the stem cells differentiate for three weeks. They found markers of neuronal stem cells. They also identified heart cells, and tested them to see if they did what nature intended them to do. In a test tube, the stem cells that became heart cells started beating (Talan, 2008).
Commenting on the achievement, researchers said it was therefore likely that this could be done at the human level. According to J. B. Gurdon, Wellcome Trust/Cancer Research UK Gurdon Institute and Department of Zoology, University of Cambridge and D. A. Melton, Molecular and Cellular Biology, Harvard/Howard Hughes Medical Institute (HHMI), in the Science December 19, 2008 issue of Science "Nuclear Reprogramming in Cells (Gurdon, 2008):
These proliferation- and differentiation-competent cells were derived from blastocysts grown after transplanting nuclei from adult monkey cells to enucleated monkey eggs. It is therefore likely that human eggs contain the components required to reverse the differentiation of adult human somatic cells.
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| Semos, the monkey whose skin cells were used to create the cloned embryos |
But, does this proof of concept prove it will work for humans? It took 304 monkey eggs to obtain the two embryonic stem cell lines. Of the Oregon team's attempts at creating a monkey clone, 213 resulted in embryos and just 35 of those became blastocysts and only two of those yielded stem cells. According to Mitalipov, the team's leader, 77 embryos had been implanted in a dozen surrogates, but no embryo made it day 25 (Cyranoski, 2007).
Because the embryos did not result in any live births, the safety of using this method for humans has been questioned, for the only way to test if this would work clinically for humans is a proof of concept result in monkeys that demonstrated that such stem cells were indeed viable. And viability, that is, the ability of stem cells to develop and to function safely and properly, can only be demonstrated by a live birth involving those cells, such as the clone Dolly did.
But, this can not be done for monkeys, thereby calling into doubt this particular "proof of concept" experiment, and therefore the entire idea of somatic cell nuclear transfer for human application, since primate demonstration of this concept is a critical step toward clinical trials in humans.
"The gold standard for the completeness of reprogramming by eggs has been described as the formation of a fertile adult animal containing functional cells of every kind (termed totipotency)," said researchers Gurdon and Melton (Gurdon, 2008).
As Josephine Quintavalle, director of the campaign group Comment on Reproductive Ethics (Core) told BBC News: "Bringing a clone to term is the only way to show that the cloned tissue is safe." (Breakthrough in primate cloning, 2007)
Further, using human eggs in an attempt to create an embryo by means of somatic cell nuclear transfer, research teams around the world, including those from Harvard University and Advanced Cell Technology, have failed to clone a human being. A few divisions of cells is the best they can do.
Cloning is inefficient
Even if cloning could be achieved for human beings so as to avoid immune rejection, the efficiency of somatic cell nuclear transfer is so low that it most likely would not be practical clinically.
In the foreword to Principles of Cloning, Robert M. Moor of the Development and Differentiation Laboratory, Babraham Institute, Cambridge, United Kingdom, called into question the utility of cloning altogether. He said:
21Many investigators have reported that fully differentiated cells in amphibia and mammals revert to a totipotent state when exposed to the cytoplasm of oocytes and eggs. Although widely acclaimed, this important advance is still beset by major difficulties and uncertainties arising from the exceedingly small percentage of differentiated nuclei that develop into viable young after transplantation. The current emphasis on cloning an ever-increasing range of mammals has demonstrated the universality of the problem; irrespective of the species studied, only 1 to 2% of cloned embryos survive to birth. In my view, the repetitious and disappointing nature of these results argues strongly for a redirection of effort. Would it not be more rewarding to move away from the cloning of ever more animals and focus heavily instead on the molecular and cellular events associated with nuclear reprogramming.
In fact, stem cell pioneer Thomson himself doubts if therapeutic cloning will ever be efficient enough to be commercially viable. "It would be astronomically expensive," he said.
In fact, stem cell pioneer Thomson himself doubts if therapeutic cloning will ever be efficient enough to be commercially viable. "It would be astronomically expensive," he said.
And he had further discouraging words:
Clearly...the generation of human embryos by nuclear reprogramming to create novel human ES cell lines would be exceptionally controversial. Furthermore, the poor availability of human oocytes, the low efficiency of the nuclear transfer procedure, and the long population-doubling time of human ES cells make it difficult to envision this becoming a routine clinical procedure even if ethical considerations were not a significant point of contention. By studying how oocyte cytoplasm mediates nuclear reprogramming in these animal models, it might be likely that nuclear reprogramming could be achieved by other methods, thereby obviating the need for human oocytes (Practical obstacles to "therapeutic" cloning, 2006).
Regenerative scientists such as Thomson and Moor agree that there are better methods of nuclear reprogramming than cloning.
One such alternative method of nuclear reprogramming is induced pluripotency stem cell technology. Cells taken from patients and subjected to iPSC technology would solve the problem of immune rejection. But, then we are left with the problem of achieving differentiation--and this has not been accomplished clinically--and thus are back to square one.
Obstacle after obstacle pop up at every turn for researchers trying to apply stem cells for therapeutic use in humans. Differentiation can not be achieved in a test tube for clinical use in humans. Cloning would theoretically achieve differentiation as well as prevent immune rejection. However, human egg cells can't make a clone and monkey egg cells just barely, and not a viable clone. Further, cloning is inefficient and expensive, plus, even if it could be done, human egg cells are difficult, costly, and risky to harvest from a woman's ovaries.
So, once again, what, oh what is a poor regenerative scientist to do?
Maybe rabbit mothers would work
Well, how about transferring human stem cells into an animal cell, such as a rabbit egg cell, to get what you want? And that is just what they are doing in the Alice-in-Wonderland world of regenerative science.
22In "Is a Woman Interchangeable with a Rabbit?" David Kotter reported that:
A research team at Shanghai Second Medical University has created hybrid embryos that contain a mix of DNA from both humans and rabbits. Cells from the foreskins of two 5 year old boys and two men were fused with rabbit eggs from which the majority of rabbit DNA had been removed. More than 100 of those new entities grew into early part-human, part-rabbit embryos before they were destroyed for stem cell research. Nevertheless, scientists wondered what, exactly, such a creature would be if it were transferred to a human or animal womb to develop to term.
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| Photo of two women at an art museum illustrating article "Is a woman interchangeable with a rabbit?" |
Douglas Melton, the Harvard University cell biologist and cloning expert, noted that although this is the first creation of a human "Chimeric" embryo--a reference to the fabulist Chimera of Greek mythology, which had a lion's head, a goat's body, and a serpent's tail--it is not the first time scientists have blended human cells in the lab animals. Some mice, for example have been endowed with human brain cells for research purposes (Kotter, 2008).
And human brain cells have been mixed with the cells of monkeys, as noted above.
The process used to fuse the human stem cells with a rabbit egg is somatic cell nuclear transfer, the process used to create Dolly the sheep. However, the utility of such a chimeric process has been called into question. Interviewed by Mark Henderson, science correspondent of the London Times, regarding the rabbit-human cells, Melton said:
23I'm convinced that the cells do have the capacity to differentiate into different cell types, but it is unclear how long the cells can grow in culture. It would be very surprising if the cell lines were stable (Henderson, 2003).
Commenting on this procedure in "Nuclear Reprogramming in Cells," Gurdon and Melton observed:
Because of the ethical concerns about obtaining human unfertilized eggs, animal eggs such as those of cows, mice, or rabbits might be used to generate ES cells from transplanted human somatic nuclei. Nuclear transfers between different strains or subspecies are just as successful as those within a species; however, eggs produced by transfers between very different species such as human and mouse, cow, or pig generally die before the 32-cell stage. So far, there is no confirmed evidence that proliferating ES cells can be obtained from such distant combinations, including human nuclei in monkey cytoplasm (Gurdon, 2008).
This chimeric experiment involving rabbit and human fusion is just another failed proof of concept regarding embryonic stem cell research.
The Nuremberg Code
Stemming from the trials at Nuremberg following World War II, a set of 10 medical research ethics principles for human experimentation were established called the Nuremberg Code. The ten points include that:
- The voluntary consent of the human subject is absolutely essential.
- The experiment should be so designed and based on the results of animal experimentation and a knowledge of the natural history of the disease or other problem under study that the anticipated results will justify the performance of the experiment.
- The experiment should be so conducted as to avoid all unnecessary physical and mental suffering and injury.
- No experiment should be conducted where there is an a priori reason to believe that death or disabling injury will occur.
As pointed out in Part II, embryonic stem cell research fails on all these points. However, let us just concentrate on the ethical principle that human experiments should be "based on the results of animal experimentation and a knowledge of the natural history of the disease or other problem under study that the anticipated results will justify the performance of the experiment."
If human embryonic stem cell therapies may not be extrapolated from mouse embryonic stem cells experiments because of the significant differences between human and mouse embryonic stem cells, then possibly it would be more reasonable and more ethical to stop using human embryos for experimentation subjects until the efficacy of primate embryonic stem cells experimentation could be demonstrated.
And so far, primate experiments have not been able to demonstrate a proof of the concept that stem cells will work at the clinical level for the treatment of disease or injury in humans.
Further, pluripotency may not be capable without a totipotent environment. That is, you can't get stem cells to develop into functioning adult cells without the use of the full embryo. To prevent immune rejection and to achieve differentiation, cloning is the most logical option.
However, experiments with the full embryo demonstrate that at the primate level, stem cells from such clones may not be safe, because the clones have not resulted in live births. Worse yet, at the human level, cloning to date is impossible.
24And even if cloning could be achieved, it is inefficient and would be "astronomically" expensive.
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In fact, leading regenerative scientists recommend abandoning cloning altogether, recommending other methods of nuclear reprogramming. However, no scientist to date using nuclear reprogramming, such as induced pluripotent stem cells technology, has been able to differentiate stems cells to the point that they could be used in clinical trials. Even with iPSC technology, cloning most likely would have to be employed to achieve differentiation, which would entail embryonic involvement.
Thus, embryonic stem cell scientists end up like the proverbial dog chasing its own tail.
The big error
The big error that these new alchemists may be making is that the creation of life may be dependant on sequential steps that produce a unified, whole organism, not just parts. That is, to get the parts, one needs to first create a separate, whole organism--what scientists call an embryo and at term an "adult."
In nature, the development of pluripotent stem cells into a living organism is dependent on a totipotent environment. The environment of the totipotent blastocyst, which includes the trophoblast and cytoplasm, provides the scaffold or matrix that enables the stem cells inside to assemble themselves, as mentioned in Part I. Plus, growth is sequential. It starts out small and step by step develops into a living organism with arms, hands, legs, feet, heart, brain, eyes, and on and on. Each body part induces the development of another other part, as explained in Part I. What is produced is a unified, functioning whole that working together--not separately--creates life.
Integration is essential to life. To think that one can grow separately in different laboratory gardens a foot, a toe, an eyelid, a brain or a tongue maybe the height of wishful thinking. It may be like a farmer thinking he can grow the parts of a corn crop separately--stalks in one field, leaves in another field, a field of tassels over here and just ears over there. For obvious reasons, that would not be possible. To grow, means to build step by step together, not part by part separately.
The stated dream of stem cells scientist to make tissues and organs "growing from scratch" may be like a cook trying to bake a cake "starting from scratch," using flour, baking powder, salt, sugar, butter and eggs, but leaving out the milk and not using a mixing bowl or a baking pan. In this example, the dry ingredients would be the stem cells, the milk would be the cytoplasm and the containing trophoblast would be the mixing bowl and baking pan. Without all the elements working together, baking such a cake would not make a very good dessert.
25And let us say that we could create an artificial trophoblast and artificial cytoplasm. What would be the point? You would still be creating life to destroy it so as to save it, which would not only be immoral, but irrational.
In the case of regenerative medical scientists' exploitation of the human embryo, the opium is hubris and the hope for money and fame, all creating the illusion of human cures.
The idea that you can pipette out the nucleus of an embryo and grow those stem cells into human organ parts or perhaps pipette out the nucleus of an egg and replace it with somatic cells to grow human organ parts may be not only alchemy, but a pipe dream. A pipe dream is a fantastic hope or plan that is generally regarded as being nearly impossible to achieve, originating in the 19th century as an allusion to the dreams experienced by smokers of opium pipes.
In the case of regenerative medical scientists' exploitation of the human embryo, the opium is hubris and the hope for money and fame, all creating the illusion of human cures.
Conclusion
Conclusion? Forget it. Scientists are knocking on the wrong door in thinking that embryonic stem cells or cloning will provide clinical therapies for humans.
Because experimentation with embryonic stem cells and cloning have not demonstrated proof that the envisioned concept will work at the human level and because it is highly controversial in that many claim it involves the destruction of nascent human life, a moratorium should be declared.
A better way
Instead, other non-embryonic stem cell avenues should be explored, such as adult stem cell treatments.
Such scientists as Melton himself think this might be a better choice, that is, forget the avenues of totipotency, such as cloning, and pluripotency, such as differentiation in a test tube. He and his colleague Gurdon noted:
However, as far as therapy is concerned, we do not regard totipotency or even pluripotency (the formation of many but not all cell types) as a necessary attribute. It would not, for example, be therapeutically useful to supply a patient with spinal cord injury with replacement cells of every kind.
What do Gurdon and Melton think would be a better way? They recommend exploring ways to grow replacement tissue from cells that have less differentiation potential, such as oligopotent and unipotent stem cells--and these come from the adult human body itself, not the embryo. Oligopotent stem cells can differentiate into only a few kinds of cells, such as lymphoid or myeloid cells. Unipotent stem cells, such as muscle stem cells, produce only one cell type, their own, but have the property of self-renewal, which distinguishes them from non-stem cells. Gurdon and Melton observed that:
It may also be increasingly fruitful to find populations of naturally dividing cells in adult organs so that these cells in their naturally less-specialized state can be expanded and differentiated in culture before implantation. A future objective, in our view, is to aim for unipotency and oligopotency (the generation of only one or a few cell types) rather than pluripotency (the potential to differentiate into any of the three germ layers) and certainly not totipotency (the potential to differentiate into all embryonic and extraembryonic cell types). Likewise, we would much prefer to be able to create new cells by switching normal cells from a closely related lineage than by going back to totipotency and then narrowing down the differentiation options from a wide range. For replacement therapy, totipotency and germline transmission are not desirable criteria or objectives. An oligopotent state with limited differentiation potential is likely to be much safer and more useful from a therapeutic point of view (Gurdon, 2008).
Since therapy is the stated goal of regenerative medicine, possibly researchers should redirect their efforts to more realistic pursuits, that is, research on stem cells from adult cell environments, not embryonic. And for those who don't get the message, embryonic stem cell research and human cloning should be banned, since it involves the destruction of human life.
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