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- In The Media -
New Work May Provide Stem Cells While Taking Baby From Equation
By Andrew Pollack
The New York Times
Tuesday, November 06, 2001
LOS ANGELES, Nov. 5 -- In a development that may sidestep some of the ethical issues surrounding stem cell research, a scientist here says he has created stem cells that can turn into nerve cells using a kind of embryo that cannot develop into a baby.
The work, done in mice, is one of several recent experiments that explore the usefulness of asexual reproduction in deriving stem cells.
The researcher, Dr. Jerry L. Hall, uses chemicals to coax an egg to grow into an embryo of sorts without being fertilized by a male's sperm. Such embryos, even if implanted into a womb, would not grow to become viable babies, Dr. Hall and other experts said. But the embryos can be grown in a laboratory for a few days, long enough to become a source of stem cells.
Embryonic stem cells can turn into virtually all types of the body's cells, potentially providing replacement cells that can be transplanted into patients to cure diseases. But opponents say such research is immoral because deriving stem cells involves destroying embryos, which they see as nascent human life.
Dr. Hall argues that if an ''embryo'' were not formed by conception and would not be able to turn into a child, that might make stem cell work more acceptable.
''We feel that this really could circumvent a lot of ethical concerns,'' said Dr. Hall, an embryologist at the Institute for Reproductive Medicine and Genetic Testing, a fertility clinic here. He presented his work at the annual meeting of the American Society for Reproductive Medicine in Orlando, Fla., late last month.
But Richard M. Doerflinger of the United States Conference of Catholic Bishops, said the technique was unlikely to end the opposition the Roman Catholic Church has to embryonic stem cell work.
The real question, he said, is whether these are really embryos. If they are, ''the fact that these beings would not survive to birth does not answer the question,'' he said. ''Our teaching about the embryo does not rely on it having been created by fertilization.''
Numerous scientific questions remain as well about the work, which has not been published in a scientific journal. Dr. Hall, who did the research with Dr. Yan-Ling Feng of the Center for Reproductive Research and Testing in Rockville, Md., said they had not determined whether the stem cells could turn into other types of cells, or even whether the nerve cells were normal.
Dr. Hall said he had not yet tried to derive human stem cells this way. But others are getting closer to that. The University of Massachusetts has applied for a patent on using the technique to derive stem cells from primates, including humans. The work was done with Advanced Cell Technology, a stem cell and cloning company in Worcester, Mass.
Scientists at the university and the company derived a line of stem cells from monkeys that could be maintained for months and that spontaneously differentiated into many types of cells including beating heart cells, according to the patent application, which has been published in Europe but not yet granted.
Dr. Michael West, chief executive of Advanced Cell Technology, would not comment when asked if the company had tried this in humans. He also would not discuss the company's work in detail, saying he did not want to jeopardize an upcoming publication in a scientific journal.
The work takes advantage of a phenomenon known as parthenogenesis. It is known that some species of flowers, insects, lizards and snakes can reproduce asexually, with the female's egg growing into a baby without being fertilized by a male..
Parthenogenesis, which is from the Greek for virgin birth, does not occur naturally in mammals. But for decades scientists have known how to trick the eggs of mice, rabbits and other mammals into developing as if they had been fertilized by subjecting the eggs to various chemicals or to temperature changes, needle pricks or electrical shocks. The resulting embryos are called parthenotes. It has not been reported that this has ever been done with human eggs, however, and it would raise ethical questions.
An egg has a full number of chromosomes right up until fertilization, when it ejects half of them and receives a half set from the sperm. So if this ejection is suppressed, an egg will have the full number of chromosomes.
The embryos created this way would not be clones of the woman, Dr. Hall said, because the chromosomes in an egg are somewhat different from the woman's set. Still, he said, the tissues derived from stem cells from such embryos would be close enough to a woman's own tissues that they would not be rejected if transplanted back into the woman.
Another possible way to develop such compatible tissues is to use stem cells made by cloning the patient's own cells. The idea, known as therapeutic cloning, is to take genetic material from a patient's cell and fuse it with an egg that is missing its own nucleus, creating an embryo that is a genetic copy of the patient. But because an embryo made through that method would in theory be able to develop into a person, Roman Catholic authorities and other abortion opponents have objected.
To create the parthenotes, Dr. Hall and Dr. Feng bathed the mouse egg cells in alcohol and then exposed them to a chemical called cytochalasin D. About 30 percent of the eggs were activated and 40 percent of those went on to form a blastocyst, a several-day-old embryo from which stem cells can be taken. The stem cells were treated with retinoic acid to turn them into nerve cells.
Dr. Azim Surani, a professor of biology at Cambridge University, said the work was not surprising since he and others had derived parthenogenetic stem cells more than a decade ago and saw evidence that they would turn into nerve cells. But he said it was unclear how many other types of cells could be created this way. ''They don't form muscle cells very easily,'' he said.
Dr. Surani also said the parthenotes and any tissues derived from them might be abnormal. That is because in normal embryo development, certain genes from the father but not the mother, or vice versa, are turned on. But parthenotes don't have genes from the father, so this process, called imprinting, would go awry. Lack of imprinting is also probably the reason that parthenotes do not develop into babies, he said.
Still, Dr. West said it might be possible one day to produce human babies through parthenogenesis. Male parthenotes could be created, too, he said, by replacing the DNA in an egg with the DNA from two of a male's sperm cells.
But male and female parthenotes have shown differences, said Dr. Jose Cibelli, vice president for research at Advanced Cell Technology. Stem cells derived from male par thenotes tend to turn into muscle cells, while stem cells from female parthenotes turned more often into brain and nerve cells, he said.
Dr. West said that if this process could be used to produce live offspring it would open up vast new reproductive possibilities. A woman could give birth by herself. Or two men may be able to each contribute one sperm to have a baby together.
Copyright 2002 The New York Times Company
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