Some of the rats at a lab at the University of California, Irvine, used to walk funny. Their limp hind legs dragged behind them. and their tails, normally high in the air, sagged to the floor. Spinal cord injuries had paralyzed their back legs.
Then Hans Keirstead, Gabriel Nistor, and their colleagues at the lab inserted a crop of cells, called stem cells, into each rat's spinal cord. The cells repaired some of the damage, and a month later the rats began to move their rear legs and lift their tails. They can stand on their rear legs now and use them to hobble around.
Stem cells offer the promise of treating and even curing a large number of injuries and diseases in humans as well as rats. However, some people oppose certain types of stem cell research for ethical reasons, so the U.S. government has restricted funding for that type of work. Despite the restrictions, researchers are finding ways to study stem cells and develop them into treatments.
The scientists at the Irvine lab hope that similar stem cell implants will one day help paralyzed people regain some of their lost mobility. "This type of improvement would be a big help to patients with spinal cord injuries," Nistor told Current Science. "If we can promise them even a little bit of independence, they will be very glad."
So what, exactly, are stem cells? They are "mother" cells that can develop into different kinds of mature cells--blood cells, liver cells, brain cells, and many others. At the Irvine lab, stem cells were coaxed into becoming immature oligodendrocytes, which are cells that cover nerves with a fatty substance and enable them to efficiently relay messages to the body and the brain. Transplanted into the disabled rats' spinal cords, these stem cells matured completely into oligodendrocytes and helped repair some of the damage.
Elsewhere, researchers are investigating the ability of stem cells to rebuild damaged hearts, cure diabetes, and reverse Parkinson's disease, among many other conditions. Stem cells can also be used to study how the body develops and to better understand how that development can go wrong and lead to cancer.
Some of the most promising stem cell research, including the rat experiment, involves embryonic stem cells, which come from human embryos. A human embryo is a fertilized egg in the first three months of its development. Embryonic stem cells can mature into virtually any cell type and can be grown in large numbers. "The potential applications are unlimited," said Nistor.
Embryonic stem cells are usually harvested from leftover embryos developed at fertility clinics for women who have trouble conceiving babies. Although the extra embryos would otherwise be discarded, many Americans believe that experimenting with human embryos is morally wrong. For that reason, President George W. Bush announced on August 9, 2001, that the federal government would pay for research only on embryonic stem cell lines created before the August 9 date. A stem cell line is a batch of stem cells descended from a single embryo.
Only 22 embryonic stem cell lines are now eligible for federal research dollars. But those 22 are not enough, say many scientists. The 22 lines may degrade in time and lose their ability to reproduce or to develop into various body cells. Thousands of stem cell lines may be needed for research and treatment.
The U.S. government does not restrict funding for research on adult stem cells--stem cells that reside in the tissues of adults. Adult stem cells exist in the body's blood, bone marrow, brain, skin, liver, and muscles. However, unlike versatile embryonic stem cells, adult stem cells generally give rise only to the cells of a single organ: Stem cells from the liver give rise only to liver cells, stem cells from muscles give rise only to muscle cells, and so on. Adult stem cells are also relatively rare and difficult to work with. Today, the only stem cells used to treat diseases are the adult stem cells in human bone marrow that give rise to blood cells.
Some researchers have set up labs using money from private companies, not the federal government, so they are not restricted in their research. Others may soon receive state government funds not bound by federal rules. Last fall, California voters passed a $3 billion plan to invest in stem cell research. Earlier this year, New Jersey's governor proposed spending $380 million on stem cell studies. New York, Wisconsin, Illinois, and Connecticut lawmakers are also looking at ways of supporting stem cell work.
Even with such support, most stem cell therapies will take years to develop. Some adult stem cells have been tested as treatments for diabetes and kidney cancer, but only in a few patients. Embryonic stem cells may be tested for the first time in human patients starting next year.
That's when the Geron Corporation, the company that funds Keirstead's work, hopes to start a trial of stem cells in human patients who have spinal cord injuries. Critics say that implanting stem cells into human spinal cords is still too risky. But Tom Okarma, president of Geron, says that the cells are being carefully tested for safety in animals and that the tests will be completed before any human experiments begin.
"We think these cell types are going to revolutionize medicine," said Okarma.
Stem Cells: Promise and Problems
How embryonic stem cells could lead to new medical treatments and what the political debate is about:
1 Scientists collect "spare" embryos that are left over from fertility clinics and are slated for disposal.
2 Stem cells are removed from blastocysts, embryos that are about five days old and have taken shape as spheres. Stem cells are immature cells that can develop into any of the body's more than 200 tissues,
3 Stem cells are grown in a petri dish, As the cells divide, they become a line of stem cells that can then be used for research and possible treatments,
Potential medical uses Researchers hope to use stem cells t6 repair or replace cells damaged by diseases or injuries, such as:
* Parkinson's disease
* heart disease
* Alzheimer's disease
* spinal cord injury
* Opponents say the use of embryos is destroying human life.
* Proponents say stem cell research can save millions of lives and that fertility clinic embryos will be destroyed any way.
Cell Division (Page 10) Short Answer
1. What is a stem cell?
2. Why are adult stem cells less useful than embryonic stem cells?
3. What is a blastocyst?
4. What argument is put forth by opponents of human embryonic stem cell research?
5. What counterargument is made by proponents of human embryonic stem cell research?
1. A stem cell is a basic cell that can develop into different kinds of mature cells, such as blood cells, liver cells, brain cells, and many others.
2. Adults stem cells usually give rise only to the cells of a single organ, They are also relatively rare and difficult to work with.
3. A blastocyst is an embryo that is about five days old and has taken a spherical shape.
4. Opponents are against the research because they believe any experimentation with human embryos is morally wrong.
5. Proponents say that leftover embryos taken from fertility clinics would otherwise be destroyed, so they might as well be used in medical research.