Why the Controversy?
IN THE hands of a skilled craftsman, a lump of soft clay can be fashioned into practically any shape. Embryonic stem cells are the living equivalent of that piece of moist clay; they have the potential to give rise to virtually all of the over 200 cell types making up the human body. How do they do this? Consider what happens to a newly fertilized egg cell.
Soon after fertilization an egg cell begins to divide. In humans about five days of cell division results in a minute ball of cells called a blastocyst. It is essentially a hollow sphere that is composed of a shell-like outer cell layer and a small cluster of about 30 cells called the inner cell mass, which is attached to the inside wall of the sphere. The outer cell layer becomes the placenta; the inner cell mass, the human embryo.
At the blastocyst stage, though, the cells of the inner cell mass have not yet begun to specialize into specific cell types, such as nerve, kidney, or muscle cells. Hence, they are designated stem cells. And because they give rise to virtually all the different cell types in the body, they are said to be pluripotent. To make sense of the excitement and controversy surrounding stem cells, let us see what researchers have done thus far and what their goals are, beginning with embryonic stem cells.
Embryonic Stem Cells
The report Stem Cells and the Future of Regenerative Medicine states: “In the last 3 years, it has become possible to remove these [human embryonic] stem cells from the blastocyst and maintain them in an undifferentiated state in cell culture lines in the laboratory.” * Simply put, embryonic stem cells can be cultured so as to produce an unlimited number of identical copies of themselves. Embryonic stem cells extracted from mice, first cultured in 1981, have produced billions of duplicate cells in the laboratory!
Because all these cells remain undifferentiated, scientists hope that with the right biochemical triggers, stem cells could be directed to develop into virtually all the cell kinds that may be needed for tissue replacement therapy. Simply put, stem cells are seen as a potential source of unlimited ‘spare parts.’
In two animal studies, researchers coaxed embryonic stem cells into becoming insulin-producing cells, which were then transplanted into diabetic mice. In one study the symptoms of diabetes were reversed, but in the other the new cells failed to produce enough insulin. In similar studies, scientists have had partial success in restoring neural function in spinal-cord injuries and in correcting Parkinson’s disease symptoms. “Those studies provide promise,” says the National Academy of Sciences, “but not definitive evidence, that similar treatments could be effective in humans.” But why is research on human embryonic stem cells so controversial?
Why the Concern?
The main focus of concern is that the process of extracting embryonic stem cells essentially destroys the embryo. This, explains the National Academy of Sciences, “deprives a human embryo of any further potential to develop into a complete human being. For those who believe that the life of a human being begins at the moment of conception, ESC [embryonic stem cell] research violates tenets that prohibit the destruction of human life and the treatment of human life as a means to some other end, no matter how noble that end might be.”
Where do laboratories get the embryos from which stem cells are extracted? Generally from in vitro fertilization clinics, where women have provided eggs for in vitro fertilization. Leftover embryos are usually either frozen or discarded. One clinic in India discards over 1,000 human embryos each year.
While research on embryonic stem cells continues, some investigators are focusing their efforts on a much less controversial form of stem cell—the adult stem cell.
Adult Stem Cells
“The adult stem cell,” says the National Institutes of Health (NIH) in the United States, “is an undifferentiated (unspecialized) cell that is found in a differentiated (specialized) tissue,” such as bone marrow, blood and blood vessels, the skin, the spinal cord, the liver, the gastrointestinal tract, and the pancreas. Initial research suggested that adult stem cells were much more limited in scope than their embryonic counterparts. However, later findings in animal studies suggest that certain kinds of adult stem cells may be able to differentiate into tissues other than those from which they came.
Adult stem cells isolated from blood and bone marrow, called hematopoietic stem cells (HSCs), have the ability to “self-renew continuously in the marrow and to differentiate into the full complement of cell types found in blood,” says the National Academy of Sciences. This type of stem cell has already been used to treat leukemia and a number of other blood disorders. * Now some scientists also claim that HSCs appear to give rise to nonblood cells such as liver cells and cells that resemble neurons and other cell types found in the brain.
Using another type of stem cell derived from the bone marrow of mice, researchers in the United States appear to have made another significant advance. Their study, published in the journal Nature, showed that these cells seem to have “all the versatility of embryonic stem cells,” according to The New York Times. “In principle,” the article adds, these adult stem cells could “do everything expected of embryonic stem cells.” Nevertheless, researchers working with adult stem cells still face major hurdles. These cells are rare and difficult to identify. On the other hand, any medical benefits they may yield will not involve the destruction of human embryos.
Health Risks and Regenerative Medicine
Whatever form of stem cell is used, therapies will still have serious drawbacks—even if scientists master the processes that yield tissues for transplantation. One major obstacle is the rejection of foreign tissue by the recipient’s immune system. The present solution is to administer potent drugs that suppress the immune system, but such drugs carry serious side effects. Genetic engineering may circumvent this problem if stem cells can be altered so that tissues derived from them do not appear foreign to their new host.
Another possibility might be to use stem cells taken from the patient’s own tissues. In early clinical trials, hematopoietic stem cells have already been used in this way to treat lupus. Diabetes may yield to similar therapies, as long as the new tissue is not susceptible to the same autoimmune attack that may have caused the disease in the first place. People with certain heart diseases may also benefit from stem cell therapies. One proposal is that at-risk patients donate their own stem cells in advance so that these could be cultured and later used to replace diseased cardiac tissue.
In wrestling with the problem of immune rejection, some scientists have even proposed cloning patients but allowing the clones to develop only to the blastocyst stage, when embryonic stem cells can be harvested. (See the box “How a Clone Can Be Made.”) Tissues cultured from these stem cells would be genetically identical to the donor-recipient and so would not trigger an immune response. But besides being morally repugnant to many people, such cloning may be futile if the intent is to cure a genetically based disease. Summing up the immune problem, the National Academy of Sciences stated: “An understanding of how to prevent rejection of transplanted cells is fundamental to their becoming useful for regenerative medicine and represents one of the greatest challenges for research in this field.”
Embryonic stem cell transplantation also carries the risk of tumor formation, in particular a tumor called a teratoma, meaning “monster tumor.” This growth may comprise a variety of tissues, such as skin, hair, muscle, cartilage, and bone. During normal growth, cell division and specialization follow a strict genetic program. But these processes can run awry when stem cells are severed from the blastocyst, cultured in vitro, and later injected into a living creature. Learning to master artificially the enormously complex processes of cell division and specialization is yet another major hurdle facing researchers.
No Imminent Cures
The report Stem Cells and the Future of Regenerative Medicine states: “Because of a misunderstanding of the state of knowledge, there may be an unwarranted impression that widespread clinical application of new therapies is certain and imminent. In fact, stem cell research is in its infancy, and there are substantial gaps in knowledge that pose obstacles to the realization of new therapies from either adult or embryo-derived stem cells.” Clearly, there are more questions than answers. Some scientists are even “bracing themselves for a backlash when treatments fail to materialize,” says a New York Times report.
Stem cell science aside, medicine has made great strides in many areas in recent decades. Yet, as we have seen, some of these advances raise complex moral and ethical questions. So where can we turn for sound guidance on such matters? What is more, as research becomes more sophisticated and expensive, therapies and medications often reflect that cost. Some researchers have already estimated that stem cell therapies may cost hundreds of thousands of dollars per patient. Yet, even now millions of people are unable to keep up with escalating medical costs and insurance premiums. So who really will benefit if and when the stem cell revolution arrives at the clinic? Only time will tell.
What we can be sure of, however, is that no therapy conceived by man will eliminate sickness and death. (Psalm 146:3, 4) Only our Creator has the power to do that. But does he purpose to do so? The following article shows the Bible’s answer to that question. It also discusses how the Bible can guide us through the increasingly complex maze of moral and ethical questions that arise today, even those of a medical nature.
^ par. 6 The report was prepared in 2001 by various committees and boards for the National Academy of Sciences in the United States.
^ par. 15 For a discussion of Scriptural and other issues related to bone-marrow transplantation, please see The Watchtower, May 15, 1984, page 31.
[Box/Picture on page 6]
Another Source of Stem Cells
Besides adult and embryonic stem cells, embryonic germ cells have also been isolated. Embryonic germ cells are derived from the cells in the gonadal ridge of an embryo or a fetus, which give rise to eggs or sperm. (The gonadal ridge becomes the ovaries or testes.) Although embryonic germ cells are different in many ways from embryonic stem cells, both are pluripotent, or able to give rise to virtually all cell types. This potential makes pluripotent cells very attractive candidates for the development of unprecedented medical treatments. However, the excitement over such potential therapies is tempered by the controversy centering on the source of these cells. They are derived either from aborted fetuses or from embryos. Thus, obtaining these cells involves fetal and embryo destruction.
[Box/Pictures on page 8, 9]
How a Clone Can Be Made
In recent years scientists have cloned a variety of animals. In 2001 a laboratory in the United States even attempted, albeit unsuccessfully, to clone a human. One way that scientists make clones is through a process called nuclear transfer.
First, they extract an unfertilized egg cell from a female (1) and enucleate the cell, or remove its nucleus (2), which contains the DNA. From the body of the animal to be cloned, they obtain a suitable cell, such as a skin cell (3), the nucleus of which contains its owner’s genetic blueprint. They insert this cell (or just its nucleus) into the enucleated egg and pass an electric current through it (4). This fuses the cell with the egg cytoplasm (5). With its new nucleus, the egg now divides and grows as if it were fertilized (6), and a clone of the creature from which the body cell was taken begins to develop. *
The embryo can then be implanted in the womb of a surrogate mother (7), where, in the rare instance that all goes well, it will grow to term. Alternatively, the embryo may be kept only until the inner cell mass can be used to obtain embryonic stem cells that can be kept in culture. Scientists believe that this basic process should work with humans. In fact, the above-mentioned attempt to clone a human was performed with a view to acquiring embryonic stem cells. Cloning for this purpose is called therapeutic cloning.
^ par. 35 Dolly the sheep was the first mammal cloned from an adult cell. Scientists implanted the nucleus of a cell from the mammary gland of an adult sheep into an enucleated egg cell.
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1 → 2 → 3 → 4 → 5 → 6 → 7
[Diagram on page 7]
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Embryonic Stem Cells (Simplified)
Fertilized egg (day 1)
Four cells (day 3)
Blastocyst with its inner stem cell mass (day 5)
Cultured stem cells
Over 200 different types of cells in the human body
→ Thyroid cells
→ Pancreatic cell (could help cure diabetes)
→ Pigment cells
→ Red blood cells
→ Kidney cells
→ Skeletal muscle cells
→ Cardiac muscle cells (could repair a damaged heart)
→ Lung cell
→ Nerve cell (could treat Alzheimer’s and Parkinson’s and repair spinal cord injuries)
→ Skin cells
Blastocyst and cultured stem cells: University of Wisconsin Communications; all other art: © 2001 Terese Winslow, assisted by Lydia Kibiuk and Caitlin Duckwall
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Adult Stem Cells (Simplified)
Stem cell found in bone marrow
→ Red blood cells
→ Potentially, many other cells
→ Nerve cell
© 2001 Terese Winslow, assisted by Lydia Kibiuk and Caitlin Duckwall