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Stem cells are cells which are not terminally differentiated and are therefore able to produce cells of other types. Medical researchers hope they can be used to repair specific tissues or to grow organs from scratch. There are three types of stem cells: totipotent, pluripotent, and blood cells, or bone cells.
Blood from the placenta and umbilical cord that are left over after birth is a source of adult stem cells. Since 1988 these "cord blood" stem cells have been used to treat Gunther's disease, Hunter syndrome, Hurler syndrome, acute lymphocytic leukemia and many more problems occurring mostly in children. It is collected by removing the umbilical cord, cleansing it and withdrawing blood from the umbilical vein. This blood is then immediately analyzed for infectious agents and the tissue-type is determined. Cord blood is stored in liquid nitrogen for later use, when it is thawed and injected through a vein of the patient. This kind of treatment, where the stem cells are collected from another donor, is called allogenic treatment. When the cells are collected from the same patient they will be used on, it is called autologous.
In May of 2003, researchers announced that they had successfully used embryonic stem cells to produce human egg cells. Spokespersons stated that these egg cells could be used in turn to produce new stem cells. If research and testing proved that artificially created egg cells could be a viable source for embryonic stem cells, they noted, then this would remove the necessity of harvesting human embryos. Thus, the controversy over donating human egg cells and embryos would be largely dismissed.
Stem cells can be found in adult beings. Adult stem cells reproduce daily to provide certain specialized cells—for example 200 billion red blood cells are created each day in the body. Until recently it was thought that each of these cells could produce just one particular type of cell—this is called differentiation (see Morphogenesis). However in the past few years, evidence has been gathered of stem cells that can transform into several different forms. Bone marrow stem cells are known to be able to transform into liver, nerve, muscle and kidney cells.
Adult stem cells may be even more versatile than this. Researchers at the New York University School of Medicine have extracted stem cells from the bone-marrow of mice which they say are pluripotent. Turning one type of stem cell into another is called transdifferentiation.
In fact, useful sources of adult stem cells are being found in organs all over the body. Researchers at McGill University in Montreal have extracted stem cells from skin that are able to differentiate into many types of tissue, including neurons, smooth muscle cells and fat-cells. These were found in "dermis"—a layer of tissue beneath the skin.
In the same way that organs can be transplanted from cadavers, researchers at the Salk Institute in California have found that these could be used as a source of stem cells as well. Taking stem cells from the brains of corpses they were able to coax them into dividing into valuable neurons. However, whether they will function correctly when used in treatment has not yet been determined.
Stem cells which originate from embryos are seen to have the most potential because of their totipotent properties—they are able to grow into any of the 200 cell types in the body. Embryonic stem cells can be obtained from a cloned embryo, created by fusing a denucleated egg-cell with a patient's cell. The embryo produced is allowed to grow, and stem cells are then extracted. Because they are obtained from a clone, they are genetically compatible with the patient.
Although believed to have the largest medical potential, they are also the most controversial type of stem cells, because their utilization involves the destruction of human embryos. Some people believe that these embryos are human beings, and therefore destroying them for any reason is effectively murder. This belief is also the basis for the "Pro-life" opposition to abortion. On the other side of the debate, one scientist was quoted as saying that embryos contain only a few tens of cells and "the smallest insect is far more human in every respect except potential" . Some scientists also defend the use of embryos, citing the medical benefits that may one day be possible to achieve with them and the fact that many would have been destroyed, regardless. Pro-life groups respond that it would be possible to achieve the same benefits from the use of adult stem cells—although some scientists have placed greater hope in embryonic stem cell research instead.
Another controversy in the use of embryonic stem cells is the use of therapeutic cloning. This involves the cloning of early embryos from which stem cells are harvested, providing a larger source of the cells. Some see this as leading to reproductive human cloning, which they think is dangerous and unethical, and some believe any form of cloning is morally wrong.
For over 30 years, bone marrow stem cells have been used to treat cancer patients with conditions such as leukemia and lymphoma. These are destroyed in some chemotherapy treatments, but if they are removed before the process and then reinjected, the cells produce large amounts of red and white blood cells, to keep the body healthy and to help fight infections.
Since the 1980s stem cells have been taken from the blood instead of the bone-marrow, making the procedure safer for older people. Although normally scarce, the number of "peripheral blood cells" can be increased by a course of drugs, which release the stem cells from the bone-marrow. These are removed before chemotherapy, which kills most of them, and are re-injected afterwards.
Stem cells have been successfully used to treat paralysis due to spinal cord injuries, Parkinson's disease and other illnesses.
Research injecting neural (adult) stem cells into the brains of rats can be astonishingly successful in treating cancerous tumors. With traditional techniques brain cancer is almost impossible to treat because it spreads so rapidly. Researchers at the Harvard Medical School injected cells genetically engineered to convert a separately injected non-toxic substance into a cancer-killing agent. Within days the cells had migrated into the cancerous area and the injected substance was able to reduce tumor mass by 80 percent.
Stem cells are also apparently able to repair muscle damaged after heart attacks. Heart attacks are due to the coronary artery being blocked, starving tissue of oxygen and nutrients. Days after the attack is over, the cells try to "remodel" themselves in order to become able to pump harder. However, because of the decreased blood flow this attempt is futile and results in even more muscle cells to weaken and die. Researchers at Columbia-Presbyterian found that injecting bone-marrow stem cells into mice which had had heart attacks induced resulted in an improvement of 33 percent in the functioning of the heart. The damaged tissue had regrown by 68 percent. Clinical trials in humans are hoped for by 2003.
Working with critically ill heart patients, researchers in Vienna have successfully used Mesenchymal stem cells to regenerate healthy new heart tissue. The stem cells were harvested from the patient's own bone marrow and injected into the ventricle. The heart is stopped for approximately two minutes to allow the stem cells to attach to the existing heart tissue. The patient is only under local anesthesia so that the surgeons can monitor how the lack of cerebral oxygen is affecting the patient. The heart is then restarted and incisions closed. The procedure is minimally invasive, as far as heart surgeories are concerned.
All of the patients that received the new treatment experienced repaired scar tissue and most had nearly complete return of proper heart function. As stated previously in the article, autologous stem cell implants such as these could alleviate legal and moral issues revolving around stem cell therapies. Type 1 Juvenile Diabetes could be cured with stem cells in the future.
Due to the controversy surrounding embryonic stem cells, in November 2001 the U.S. National Institutes of Health announced a list of 72 approved human embryonic cell lines which researchers are to be allowed to work with. However some scientists declared problems they had with the list—that some cell lines are less useful to work with than others. Also other scientists are not convinced that the list actually contains 72 different lines—they think some are derivations of a single line.
Some ethicists, philosophers, theologians and clergy are very concerned with the ethical implications of stem cell research. In the U.S. many Christian groups have come out strongly against embyronic stem cell research as they view it as a form of abortion, which they see as murder (many of those opposing embryonic stem cell research advocate adult stem cell research as an alternative ). However, some proponents of research point out that stem cell research uses discarded embryos and that fertility clinics that routinely destroy thousands of embryos are not controversial at all, questioning the motivation of opponents of research . Jewish groups, of all denominations, have come out in favor of embyronic research, as they do not view an early stage embryo as a human being. Many Humanists, Unitarian Universalists, and many Muslim clerics have come out in favor of stem cell research.
After consulting with "scientists, scholars, bioethicists, religious leaders, doctors, researchers, members of Congress, [his] Cabinet, and [his] friends" and reading "heartfelt letters from many Americans," US President George W. Bush announced his executive decision on August 9, 2001 to prohibit the use of federal funding to work with embryonic cell lines created after that date, limiting research to a limited number of embryonic stem cell lines and adult stem cells. The decision does not prohibit the research itself, but only prohibits federal funding to be used for that particular research. In 2002, he appointed a Council on Bioethics formed from 18 doctors, legal and ethical scholars, scientists and a journalist. In February, 2004 President Bush removed from the council professors of ethics William May and biologist Elizabeth Blackburn. These two outspoken advocates of stem cell research were replaced with Benjamin Carson, Diana Schaub and Peter Lawler, all three of whom have expressed more conservative views on biotechnology.
As other countries, including South Korea (successfully cloning human embryos in early 2004 and extracting stem cells from them) and the United Kingdom (creating the world's first stem cell bank in May 2004) have moved forward with their stem cell research programs, some in the US have questioned the Bush Administration's policy severely restricting government-funded stem-cell research. In April 2004 206 members of Congress and some other prominent public figures signed a letter urging President Bush to reconsider the policy.
The 2004 Democratic presidential candidate, John Kerry, a self-professed Roman Catholic, has promised to support stem cell research if elected President of the United States.
A ballot initiative (November 2, 2004) in California to create a $3 billion state taxpayer-funded institute for embryonic stem cell research has received contributions from figures such as Bill Gates, venture capitalist John Doerr (an early backer of Internet search engine Google), and eBay founder Pierre Omidyar, as well as actors Michael J. Fox and Christopher Reeve, both suffering from conditions that might one day be helped by stem cell research.
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