Pennsylvania Researchers Turn Stem Cells to Egg Cells

Use of such eggs might make therapeutic cloning * the idea of repairing patients' tissues by cloning their own body cells * ethically more acceptable to those who object to it. Further, the unfertilized eggs seem capable of developing parthenogenetically, or without the help of sperm, into embryos.

The research was by a team from Penn including Dr. Karin Hübner, Dr. Hans R. Schöler, and researchers elsewhere. They report in today's issue of Science that they developed a way to generate unfertilized eggs, known as oocytes, from mouse embryonic stem cells. They have not tried the same experiment with human embryonic stem cells, but the two species are generally very similar at the stem cell level.

If human oocytes could be generated in the same way from human embryonic stem cells, researchers would have a copious new source of oocytes, which are now obtained from patients through an uncomfortable procedure requiring strong drugs and surgery.

Dr. Schöler, a German citizen, said he was discussing with German parliamentarians whether generating human egg cells this way would be acceptable in Germany. If not, he said he would not undertake the experiment in his laboratory in the United States, even if it were legal here.

Dr. James Battey, chairman of a stem cell task force at the National Institutes of Health, said that researchers supported by the institutes should not undertake such experiments until there had been further ethical review and opinion sounding. He described the research as "a spectacular piece of science."

Human embryonic stem cells are obtained from the discarded human embryos generated in fertility clinics. The embryos, though only a few days past fertilization, are destroyed in the process. As a result, many opponents of abortion rights object to research that involves the cells. In August 2001, President Bush allowed federally financed researchers to start working with the human embryonic cell lines already established by that date, though not with any new ones. That research had long been barred by Congress.

The cells, which have the capacity to develop into all the tissues of the human body, are of great interest to researchers and physicians. Scientists have already discovered ways of inducing mouse and human embryonic stem cells to convert in the laboratory into brain, liver, pancreatic and other types of body cell. Dr. Schöler's team has added a new class of cell to this list * the germline cells which make the oocytes or sperm.

Human oocytes made in the laboratory this way could bring the idea of therapeutic cloning nearer to reality. This is the concept that physicians could generate new body tissues for a patient by taking a cell from the patient's skin, inserting the cell's nucleus into an oocyte whose own nucleus had been removed, and letting the oocyte develop into an early embryo. Stem cells could be taken from the embryo and induced to develop into heart muscle cells genetically identical to the patient's own.

But if the same embryo were put into a woman's womb, it might grow to term. This is reproductive cloning, the method used to make Dolly the sheep. There is wide opposition to using the technique in people.

Therapeutic cloning is seen by some as fraught with hazard because it could so easily lead to reproductive cloning, to the making of a baby instead of the generation of laboratory cell lines. Dr. Schöler said that oocytes made by his method could be genetically engineered so as to be inviable in the womb but still useful for therapeutic cloning, a procedure that might allay some objections to therapeutic cloning.

Opponents of stem cell research support legislation, passed by the House and pending in the Senate, that would outlaw both types of cloning. Dr. Arthur Caplan, an ethicist at Penn who has advised Dr. Schöler, said the new research showed such bans were premature because stem cell technology was moving so fast. "It's as if they were trying to regulate the aviation industry with only the Wright brothers' plane in front of them," Dr. Caplan said.

Besides the unaccustomed idea of generating human oocytes in the laboratory, Dr. Schöler's research points to another anomaly: the oocytes can develop in a dish into embryos, a process that involves a spontaneous doubling of their own genetic material instead of acquiring a second set of chromosomes from a sperm. Dr. Schöler said he has not yet had time to test whether the mouse oocytes and embryos are viable or whether human embryonic stem cells behave in the same way.

These developments have surprised theologians accustomed to defining human life as something that starts at conception with the union of oocyte and sperm. "This scientific research is like a cannon ball fired across the bow of Christian bioethics," Dr. Ted Peters of the Pacific Lutheran Theological Seminary in Berkeley said in a statement.

Dr. Peters added in an interview that ethicists in the past had thought human dignity could be seen to derive from the fertilization process. But mammalian cloning was the first shot at this argument and Dr. Scholer's generation of parthenogenetic embryos "is maybe the second shot," he said.

Thomas A. Shannon, an expert on Catholic teachings at the Worcester Polytechnic Institute, said the new research challenged the notion that conception signals the presumptive beginning of a human person, as argued in a Vatican document about the gift of life. "If fertilization is no longer a major marker for thinking of the beginning of a person, then where do you go next?" he said, suggesting a better definition might lie in when an embryo develops individuality and a nervous system.

A spokesman for the National Conference of Catholic Bishops did not return a telephone call.