Unfertilized Monkey Eggs Yield Stem Cells, Study Shows

Sep. 23–In a finding that could reshape the ethical debate over stem cells, scientists have shown that cells extracted from the embryo of an unfertilized monkey egg are similar to their fertilized counterparts in almost every respect.

“Except that they don’t carry the same ethical baggage,” said Kent Vrana, a neurobiologist at Wake Forest University School of Medicine in Winston-Salem, N.C. The study appears in today’s online edition of Proceedings of the National Academy of Sciences.

Embryonic stem cells are the basic material from which virtually all organs, cells and other body tissues are formed. With the right coaxing and conditions, these cells can produce neurons, blood cells, hair, eggs and sperm. Scientists hope one day to unleash the cells’ transformative powers to treat and replace damaged or diseased tissue.

“There are more than a hundred million incurably diseased people in this country right now who could benefit from this kind of research,” said Eve Herold, the public education manager of the Stem Cell Research Foundation, an organization based in Clarksburg, Md., whose mission is to educate the public and fund stem cell research.

However, ethical objections surround the use of embryonic stem cells in human medicine, and federal laws limit research because the procedure used to acquire stem cells requires that an embryo be grown for a few days and then harvested.

For abortion opponents, this is unacceptable, said Richard Doerflinger, spokesman for the U.S. Conference of Catholic Bishops.

Now researchers believe that if an unfertilized human embryo can be created via parthenogenesis — the process in which an egg is finessed into developing without the help of sperm — the ethical objections might be alleviated.

“So far there have been no reports that you can create an individual animal by parthenogenesis,” said Jose Cibelli, a professor of animal biotechnology at Michigan State University in East Lansing and author on the paper.

“But we’re still debating what a being produced by parthenogenesis is,” Doerflinger said. Until it’s proved that a parthenogenetic embryo is not human, the bishops are against destroying them.

“This points to how difficult it is to define humanhood,” said Robyn Shapiro, director of the Bioethics Center at the Medical College of Wisconsin.

In light of this study, if you use two common criteria to define the beginnings of human life — the human genome and the potential to develop into a human being — then “does that mean one should ascribe moral status to an egg?” she asked.

Federal law now prohibits federal funding for research in which human embryos are harmed or placed at risk. That includes any human embryo derived by fertilization, parthenogensis, cloning or any other means.

“So, until that is changed, we’re unable to do this with human eggs,” Vrana said.

The study is an extension of earlier research conducted by a team of scientists from the Mayo Clinic in Rochester Minn., Sloan Kettering Cancer Center in New York and Advanced Cell Technology in Worcester, Mass. The earlier research was published in the journal Science last year.

At that time, the scientists were able to show they could create an embryo from an unfertilized monkey egg.

The new research demonstrates that the stem cells extracted from the “single-parent” embryos — or parthenotes — can be converted into mature cells such as nerve cells, heart cells and smooth muscle. It also shows that they can be kept indefinitely.

Eventually, researchers would like to demonstrate that these stem cells could be used to treat degenerative diseases such as Parkinson’s disease and juvenile diabetes.

The idea, said Cibelli, is that a woman could produce a handful of eggs and preserve a line of her own self-replicating stem cells, which she could use whenever she needed.

Unfortunately, this research will only benefit pre-menopausal women who are still producing eggs. Older women would not be helped. Nor would men.

Despite the promise of the research, there are concerns about the feasibility of using the cells. Because the cells have not yet been transplanted back into the monkey donor, it is not yet known if her body will accept or reject them, Cibelli said.

“The DNA of those eggs is not exactly the same as the donors,” said Cibelli, explaining the process of recombination in which the DNA of eggs and sperm are shuffled a bit so that they don’t come out as carbon copies.

“That’s why you are not exactly like your siblings,” said Cibelli, “if your mom and dad’s gametes didn’t go through recombination, you’d look exactly like your sisters and brothers.”

There’s also a concern that imprinting — a process in which genes remain dormant — could make some cells useless, said Neal First, a retired professor of reproductive biology and animal technology at the University of Wisconsin-Madison. He was not an author of the paper.

First explained that every human has two copies of genes: one from their mother and one from their father. At any one time, only one of these copies is active. Early in the process of development that produces eggs and sperm, a gene from one parent is “imprinted” to be inactive in the offspring.

In a cell derived from parthenogenesis, a gene may have been inactivated before it became an egg and thus would not be expressed. If the gene for cardiomyocyte cell development were inactivated by imprinting, for example, those cells could not be used to repair a damaged heart.

Su-Chun Zhang, a professor of anatomy and neurology at UW-Madison’s Waisman Center, said that even if these issues don’t prove problematic, the potential for the research to provide therapeutic application is limited.

Not only could it be applied to only a limited portion of the population — fertile women — but he said that it was an inefficient process.

“They started with 77 eggs,” he said, and only one produced a viable line.

Still, Vrana, believes the work so far is promising.

“We have every reason to believe that this will be successful,” he said.

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