|10-08-2002, 07:40 AM||#1|
Join Date: Jul 2001
Why Clone Humans? (Hushing adult stem cells and hyping ES cells)
Why Clone Humans?
Why is human cloning contemplated at all? To help infertile couples have children? To provide cells and tissues for transplant? Dr. Mae-Wan Ho and Prof. Joe Cummins reveal how the scientific establishment is manipulating public opinion to support research that's both morally and scientifically indefensible.
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The first human clone
An international team of fertility scientists made news last year by announcing they will clone human beings mainly to help infertile couples, despite strong opposition from religious groups and from scientists cloning animals. Earlier this year, a member of the team, Italian physician Severino Antinori, claimed they have produced the first cloned humans. But this was contradicted by his US counterpart, Panayiotis Zavos, who nevertheless reaffirmed their determination to make cloned human beings a reality.
Human cloning has been contemplated at least as far back as five years ago when Dolly the cloned sheep was unveiled. A clone is an identical copy of an individual. There are natural clones, produced when the fertilised egg splits up into two or more cells, each of which develops into a foetus, resulting in identical twins or triplet.
The process that produced Dolly is different. It is somatic cell nuclear transplant (SCNT), and involves taking a nucleus from an ordinary cell and transferring it into an unfertilised egg that has had its nucleus removed. The egg with the cell nucleus is then stimulated to develop into an embryo.
The company Advanced Cell Technology, based in Massachusetts, laid claim to the "first cloned human embryo" on Thanksgiving 2001. But it has other uses in mind for the human embryo. Michael West, the company's founder and president, explained that the cloned human embryo will bring "a whole new era of medicine", providing replacement cells and tissues, "like the way we repair a car when it's broken".
Instead of allowing the embryo to develop further, the mass of cells inside the hollow sphere - which would have developed into a fetus - is harvested to produce embryonic stem (ES) cells (see Box 1). The ES cells can be grown in culture and multiplied indefinitely, to differentiate into every tissue and cell type in the body for replacing damaged body parts. Human cloning for this purpose is euphemistically called, 'therapeutic' human cloning, to distinguish it from cloning to produce babies or 'reproductive cloning'.
What are stem cells?
Stems cells are cells in mammals including human beings that have the ability to divide indefinitely and give rise to differentiated cells. The fertilised egg cell possesses this ability to the highest degree, for it has the potential to divide and develop into the entire organism with the full complement of cell types. The fertilised egg cell is totipotent.
Totipotency is retained as the egg divides into two and even four cells, so that each cell, when separated, is capable of developing into a complete foetus. That's how twins, triplets and quadruplets come about; they are natural human clones with identical genetic and cytoplasmic makeup.
When the embryo is four to six days old, and after several rounds of cell division, a hollow sphere is formed, called a blastocyst, within which is a cluster of cells, the inner cell mass. The outer layer will form the placenta and other supporting tissues for the development of the foetus in the womb. The inner cell mass will go on to form all the tissues of the foetus' body. These cells are no longer totipotent, but pluripotent, ie, they can give rise to many types of cells, but not all of the ones required for foetal development.
As development proceeds, the inner cell mass divides further and become more restricted in the range of cells they will become. For example, blood stem cells will eventually give rise to red blood cells, white blood cells and platelets, and skin stem cells will give rise to all the various types of skin cells. These more specialised stem cells in the body are said to be multipotent.
Pluripotent stem cells isolated from the blastocyst embryo came to be known as embryonic stem cells or ES cells.
Stem cells are also found in children and adults, these are known as adult stem cells. Blood stem cells, for example, are found in the bone marrow of every child and adult, and also in the blood stream; they continually replace the supply of blood cells throughout life. But the most surprising recent discovery is that adult stem cells also exist in the brain as well as in muscle, liver, skin and other tissues.
Both embryonic and adult stem cells can potentially be used in cell and tissue replacement, hence the intense interest from biotech companies and the biomedical community.
Although human ES cells have been obtained from 'spare' human embryos from in vitro fertilisation clinics and aborted foetuses under 'informed consent', the most controversial route is via 'therapeutic' human cloning (see main text).
Proponents argue that, by taking the nucleus for cloning from the patient, it would overcome immune rejection of the transplanted tissues and cells. But adult stem cells can equally be taken from the transplant patient without the risks of immune rejection.
Another argument put forward in favour of 'therapeutic' human embryo cloning is that adult stem cells are much more restricted in their potential to become different cell types than ES cells. But this argument, too, is no longer tenable (see main text).
The announcement from the company coincided with widespread press coverage and a cover article in the mainstream publication, Scientific American. But the work itself was published in an obscure electronic journal.
The same company had transferred nuclei from human somatic cells into cow eggs in 1998. President Clinton had asked the National Bioethics Advisory Commission to consider the implications of the work. "[The] creation of an embryonic stem cell that is part human and part cow raises the most serious of ethical, medical and legal concerns", Clinton wrote, "I am deeply troubled by this news of experiments involving the mingling of human and non-human species." Undaunted, the company transferred human nuclei into sow's eggs two years later.
In fact, the company has not produced anything resembling a 'human embryo'. The furthest any egg developed was to the six-cell stage. Unfertilized eggs chemically stimulated to develop passed well beyond that stage before arresting, so the experiment was a complete failure.
Scientists delivering the brave new world
Condemnation came swiftly from the scientific establishment, not because they disagree with 'therapeutic' human cloning, but because the experiment was shoddy and the way it was hyped could jeopardize the chances of 'therapeutic' human cloning gaining public acceptance.
Robert Winston, Professor of Fertility Studies at Imperial College, London, is a supporter not only of 'therapeutic' but also of reproductive human cloning, so is Nobel Laureate Francis Crick of the DNA double-helix fame along with a list of other establishment scientists. Winston says "it is difficult to argue that there is anything wrong with producing a human clone" for they are just like twins produced naturally. His worry about people like Severino Antinori, is that, again, through their incompetence, they might "bring valuable DNA science into public disrepute".
Winston could have mentioned that there are fundamental, insurmountable technical problems with cloning that has nothing to do with incompetence of the scientists. Abnormalities cannot be avoided on account of a combination of ill-understood factors, among them genetic instability of the cells, and failure of epigenetic reprogramming of the cell nucleus by the egg. Dolly was one success out of 277 nuclear transplants, but is now suffering from arthritis, which, her creator Ian Wilmut is blaming on the cloning process. Similar abnormalities are turning up in all species of cloned animals, and even the surrogate mothers often get ill.
'Therapeutic' human cloning and embryonic stem cell research turn human embryos directly into commodities and nothing else. Almost no one mentioned the women who provided the eggs for the company's cloned embryos. They underwent a battery of physical and psychological tests and tests for infectious diseases before they were chosen as donors. They were injected with hormones to make them over-ovulate and the eggs collected for an unspecified number of days. There will be no shortage of women, especially the poor and needy, who will be forced into selling their eggs on the open global market. Advertisements for egg donors have already appeared on the internet.
Hushing adult stem cells and hyping ES cells
That is not all; the scientists supporting 'therapeutic' human cloning are trying to hush up and discredit adult stem cells that are showing much more promise in terms of health benefits than ES cells. At the same time, they are hyping the promise of ES cells and down-playing the risks of cancer and uncontrollable growth.
Science published an article last year showing that mice cloned from ES cells suffered many genetic defects due to the genetic instability of the cells. A key phrase referring to the genetic instability of the embryonic stem cells that might "limit their use in clinical application", was removed days before the paper appeared in print.
The US National Bioethics Advisory Commission (NBAC) recommended to Clinton to support embryonic stem cell research, with an important caveat that it is "justifiable only if no less morally problematic alternatives are available for advancing the research."
It is now clear that such morally less problematic alternatives do exist.
Science and technology of adult stem cells streets ahead of ES cells
Many excellent peer-reviewed publications have documented that adult stem cells are developmentally just as flexible as embryonic stem cells, that they are much more promising for repairing damaged tissues and treatment of other diseases, and established cell lines already exists. Furthermore, they can easily be isolated from patients requiring treatment, thus avoiding all problems of immune rejection and the need for immune suppressive drugs that carry their own risks.
The developmental potential of adult stem cells has been documented in numerous publications. Bone marrow cells enriched for haematopoietic stem cells (HSC) differentiate into mature liver cells in the liver of rodents and humans. Mouse bone marrow cells can generate skeletal muscle cells in the body, and skeletal muscle cells can give bone marrow cells. Bone marrow could be reconstituted from cultured brain, and glial and neurons cells were obtained from bone marrow.
A 'pluripotent neural stem cell' was isolated from adult mouse brain. It not only gave rise to all types of cells in the brain, but when co-cultured with muscle cell line, developed into muscle cells. These neural stem cells can be grown indefinitely in culture.
More remarkably, researchers in Yale University, New York University and John Hopkins School of Medicine, provided definitive proof that one single adult stem cell can generate cells of many types. One single stem cell from the bone marrow of mice can reconstitute the bone marrow of a mouse destroyed by irradiation, as well as develop into practically all the tissues of the body.
These results were confirmed and extended by a second group from the Stem Cell Institute, Department of Medicine, and Cancer Center, University of Minnesota Medical School, Minneapolis. They isolated stem cells from the bone marrow of human subjects, and showed that the cells can be expanded extensively in culture, some for more than 80 cell doublings. And some of the expanded individual cells could be expanded further to 107 cells to differentiate into bone forming cells, cartilage forming cells, fat cells, skeletal muscle cells and endothelial cells, simply by changing the culture conditions and adding the appropriate cytokines (locally acting cellular hormones).
Similar stem cells were found in mouse and rat bone marrow, which can be expanded for more than 100 cell doublings in culture. When injected into an early blastocyst mouse embryo, single cells can contribute to most, if not all somatic cell types. On transplanting into non-irradiated or minimally irradiated adult host, the cells engraft and differentiate into haematopoietic cells, and the epithelium of liver, lung and gut. Furthemore, these cells exhibit a high degree of genetic stability in culture as well as regulated growth characteristics.
Another source of readily available adult stem cells turns out to be skin. Skin stem cells can make neurons, glia, smooth muscle and fat cells. Again, cell lines have been established that kept their pluripotency for at least one year.
In summary, adult stem cells are readily available from bone marrow and from skin and other sources (see later) of both human and other species. These cells are developmentally just as flexible as embryonic stem cells; there appears to be no developmental boundaries that they cannot cross. Established adult human stem cell lines already exist and, unlike ES cells, they exhibit high degrees of genetic stability.
ES cells are promoted on ground that they are developmentally more flexible. But too much flexibility may not be desirable. Transplant of embryonic cells into the brains of Parkinson's patients turned into an irredeemable nightmare because the cells grew uncontrollably. Embryonic stem cells also show genetic instability and carry considerable risks of cancer. When injected under the skin of certain mice, they grow into teratomas, tumors consisting of a jumble of tissue types, from gut to skin to teeth, and the same happens when injected into the brain.
Another problem is that, up to now, there are no human ES cell lines that could be used for therapeutic purposes. The reason is that ES cell lines require a feeder layer of cells, and all the human ES cell lines that have been established required a feeder layer of mouse fibroblasts, and risk transferring mouse viruses to human beings.
Still, the campaign to discredit adult stem cells continues. Two articles appeared as 'advance online publications' in May 2002 in the top British journal Nature, accompanied by a news report that begins, "The hyped ability of adult stem cells to sprout replacement tissue types is being called into question.
They may instead be fusing with existing cells, creating genetically mixed-up tissues with unknown health effects".
That was untrue. The papers reported the fusion of adult stem cells with other cells, which occurs at very low frequencies, unless a drug known to enhance cell fusion added. Consequently, neither paper actually questioned the existence of adult stem cells at all.
This anti-publicity on adult stem cells came on the heels of a paper announcing 'success' in ES cell transplant in a Parkinson rat model published in the house journal of the United States National Academy of Sciences. Actually, five out of 25 rats receiving the transplant died with "teratoma-like tumors" in their brains, a well-known hazard of ES cells. In a further six rats, the graft "did not survive". Five rats that "did not receive full behavioral testing was analysed histologically". The behavioural improvement was a modest 40% in the remaining rats that were tested.
Another opportunity to promote ES cells presented itself in June, in two advanced online papers published by Nature. One described the use of embryonic stem (ES) cells to reverse the symptoms of Parkinson's disease, the other, the isolation of adult stem cells from bone marrow that can produce all cell types in the body referred to earlier.
The accompanying news report entitled, "Stem cell hopes double" opines that both ES and adult stem cell research could yield promising therapies, different cells for different therapies, "so most scientists advocate supporting both types of research".
But this judgement not only brushes ethical considerations aside, it misrepresents the science and ignores good therapeutic practice.
On reading the papers carefully, one discovers that the ES cells need to be genetically modified and extensively manipulated in vitro before they can be transplanted safely. It involves using the cytomegalovirus promoter to drive over-expression of a transcription factor, the risks of which are undetermined.
By contrast, the report on adult stem cells - the latest in a series of similar publication - confirm that the cells could be transplanted directly without genetic modification or pre-treatments. They differentiate according to cues from the surrounding tissues and do not give uncontrollable growth or tumours.
The adult stem cells also show high degrees of genomic stability during culture.
Nature and Science have both been slow to mention the many publications documenting the record of safe effective therapy based on adult stem cells, as well as the careful research revealing their further therapeutic potentials.
* Bone marrow cells were successfully used to repair the heart of a patient who had
sustained an acute myocardial infarction in Dusseldorf University Cardiac Clinic. Mononuclear bone marrow cells of the patient were prepared and 6 days after infarction 1.2¥107 cells were transplanted into the artery supplying the heart. Ten weeks later, the infarcted area had been reduced from 24.6 % to 15.7 % of left
ventricular circumference, while pumping activity of the heart has also improved by 20-30 %.
* Physicians in the Netherlands (Utrecht and Leiden) treated four children, aged 6 to 11 with juvenile chronic arthritis (JCA), who did not respond to the usual treatments available. Bone marrow was taken from the patients one month before chemotherapy and irradiation depleted the T (thymus) cells, and the patients' own bone marrow were transplanted back. The children were followed for 6 to 18 months afterwards when they were maintained free of immune-suppressive drugs. There was rapid reconstitution of the immune system in 3 out of the four children. All showed marked decrease in joint swelling, pain and morning stiffness, as well as improvements in other indicators.
* Researchers in North Western University, Chicago had been selecting patients with severe systemic lupus erythematosus for treatment with bone marrow transplants since 1996. These patients did not respond to the usual treatment with cyclosphosphamide (an immune suppressive drug). Nine patients underwent drug treatment to mobilise their stem cells, two of them were excluded because of infection. The remaining seven underwent the chemotherapy to knock out their immune cells before being transplanted back with their own hematopoietic cells. They were followed up between 12 to 40 months (median 25 mos). All were free from lupus since; and their renal, cardiac, pulmonary and blood markers remained normal.
* A patient with Crohn's disease, an autoimmune disorder affecting the digestive system, was successfully treated with a similar procedure using bone marrow cells.
* White blood cells from a daughter provided immune 'killer cells' that were tolerated by her mother, thereby ridding the mother of an otherwise untreatable cancer. Cells of the foetus are known to persist in mothers for many years. Mothers might therefore be tolerant to cells from their offspring. A 52-year-old Asian woman suffering from carcinoma of the thymus received 1010 white blood cells from her 32-old daughter. The cells were collected after the daughter was given granulocyte macrophage colony stimulating factor for 5 days to boost her white blood cells. No immune suppressive drugs were given, and they were not needed. Within three days of transfusion, the patient stopped coughing and her appetite returned. Her clinical status continued to improve thereafter. By day 210, she had regained her lost weight and resumed a normal active lifestyle. Her tumour had regressed.
* Human umbilical cord cells can be expanded indefinitely in culture when epidermal growth factor is applied. By selecting out sub-populations that are blood stem cells, clones are obtained that differentiate into nerve cells of the central nervous system in the presence of special media, or when co-cultured with rat brain cells. This offers potential for replacing brain cells in neuro-degenerative disorders such as Parkinson's.
Adult stem cells beat embryonic stem cells by every important criterion (see Box 2).
Adult versus embryonic stem cells
Both have the same potential to give rise to a wide range of differentiated cells
Both have the same potential for growth, but only adult stem cells have given established cell lines in humans that can be used for cell and tissue replacement therapy
Controllability Growth and differentiation of adult stem cells are much easier to control than ES cells, both in vitro and in vivo
Risks ES cells have a tendency to develop into teratomas on being transplanted or to grow uncontrollably.
Adult stem cells show a high degree of genomic stability in long term culture, while ES cells are unstable.
Ease of isolation
Adult stem cells can easily be isolated from human subjects, while ES cells have to be isolated by destroying human embryos.
Ease of use
Adult stem cells have been used directly after isolation or after expansion in culture, the transplanted cells simply differentiate according to cues from surrounding tissues. ES cells, on the other hand, require extensive treatments and even genetic modification, before they can be safely used.
To avoid immune rejection, ES cells have to be tissue-matched from a bank of stem cells created from 'spare' human embryos. Otherwise, a special human embryo has to be created for the purpose, by transferring the patient's genetic material into an empty egg. In contrast, there is no problem of immune rejection with adult stem cells because the cells can readily be isolated from the patients requiring transplant.
The use of adult stem cells raises no moral issue; ES stem cells on the other hand, requires the destruction of human embryos and is morally unacceptable to many.
Adult stem cells already have a record of safe effective therapy, while ES cells are still at experimental stage with animal models.
Commercial imperatives are the major impetus for ES cell research, much more so than for adult stem cells research. There are more opportunities for patenting cells and cell lines as well as isolation procedures. The risks of cancer, uncontrollable growth, genome instability and other hurdles make ES cells a bad investment in terms of finance as well as health benefits. In contrast, the most widely used adult stem cells, such as bone marrow cells and cord blood cells, cannot be patented, and are hence more likely to generate affordable therapies that can benefit everyone.
Therapies based on minimum intervention also minimise side-effects and costs. Research on adult stem cells can easily go down this route, to stimulate stem cells to regenerate in situ, as some reseachers have already suggested. Another approach is to regenerate organs in culture, by seeding artificial scaffolds with adult stem cells isolated from the patients.
Scientists should stop manipulating public opinion to promote research that's both morally and scientifically indefensible. At the same time, governments need to invest our tax money in scientific research that can genuinely benefit the health of the nation, and not be misled by false promises of the next economic boom.
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