Parthenogenesis — when eggs develop into embryos without being fertilized by sperm — occurs in some insects and reptiles. There is a persistent report that a virgin birth once took place in humans, but this should be regarded as mythical.
Very rarely, eggs do develop parthenogenetically in humans, but the resulting embryo either dies or turns into an ovarian tumor. It is precisely this aspect of parthenogenetic human embryos that makes them interesting to many biologists, because their inviability frees them from the legal problems and pro-life controversies that surround the cloning of human embryos.
All embryos are special because they contain stem cells: cells that are “pluripotent,” or able to become any of the body’s varied cell types — muscle, nerve, skin, heart — you name it. Stem cells from your own body would, in theory, enable you to develop any new organ or repair any damaged one. Their use, say some researchers, would be a more effective treatment for many diseases than all other forms of therapy combined: They could potentially revolutionize medicine.
One big question was whether stem cells could be harvested from parthenogenetically derived embryos. Previous attempts had been unsuccessful, but now Jose Cibelli and colleagues at Advanced Cell Technology in Worcester, Mass. — famous for producing last year what was apparently the first cloned human embryo — have done it. The paper describing their technique is published today in Science.
Starting with 77 monkey eggs, the researchers managed to get 28 of them to metaphase, the point at which the chromosomes in each cell move apart prior to the first cell division. These were then “parthenogenetically activated,” and four out of the 28 formed blastocysts, the stage at which an embryo consists of a hollow ball of 50-200 cells. From one of these, they derived a cell line (a stable supply of cells from a single source), which has been growing continuously for the past 10 months.
The cells were induced to develop into neural cells, smooth muscle cells, fat cells, spontaneously beating heart-like cells and others. The researchers had achieved their goal, saying that they had demonstrated the “broad differentiation capabilities of primate stem cells derived from parthenogenesis” — and guaranteed a paper in Science.
Stem cells have already achieved medical success. Last year, a 46-year-old German had stem cells from bone marrow in his pelvis injected into arteries near his heart. He had suffered a heart attack, and the oxygen deprivation to his cardiac tissue had killed off a quarter of his heart muscle. The bone marrow stem cells would (if they had stayed in the bone) have developed into blood, but instead they migrated to areas of damaged heart tissue and developed into muscle, which began to beat.
“The potential clinical applications include treatment of diseases where specific celltypes have become dysfunctional. These diseases include a broad array of medical problems, such as Parkinson’s and Huntington’s diseases, heart disease and diabetes,” said Michael West, co-author of the Science paper and a researcher at Advanced Cell Technology (their address, appropriately, is 1 Innovation Drive).
“We believe this technique will work on humans,” said West in an e-mail interview.
The German success was broadly welcomed by observers, as it used stem cells from the adult patient himself, thereby avoiding the need to create or clone an embryo. But bone-marrow stem cells are less flexible and harder to culture than those from embryos. Will the new parthenogenetic technique likewise escape the media frenzy and pro-life protests that greeted the cloning of human embryos?
“It is hard to say,” said West. “We have laid out our case as to why we believe a pre-implantation blastocyst is not an individualized human, that is, it has not yet started to form a human being, and therefore why its use in saving a living, breathing human being is the morally correct solution.
“Some are not likely to agree with us on this for some time. The Roman Catholic Church, for instance, is still opposed to most forms of birth control and is still opposed to in vitro fertilization. These groups may prefer we use parthenogenesis, but I suggest that all these alternatives are ethically advisable, and which we use needs to be a decision based on what can save a human life.”
The medical potential of stem cells is matched only by their financial potential, which is why the area is one of the most active research fields in biology.
For example, researchers at Kyoto University’s Institute for Frontier Medical Studies also have a paper published this week, in the journal Proceedings of the National Academy of Sciences. In it, Yoshiki Sasai and colleagues demonstrate a highly efficient technique for coaxing primate embryonic stem cells into becoming mature brain cells. The method could be used in research and transplantation in a variety of neurodegenerative diseases, such as Parkinson’s.
Both West and Sasai emphasize that most clinical applications of stem-cell technology are a few years off. And before then, we can expect intense debate over the ethics of its use.
For West, the issue is clear-cut. The most compelling argument for the use of stem cells, he says, is “the suffering of our fellow human beings that cannot be rescued using any technology currently in medical practice. Embryonic stem cells are striking in their potential for new therapies to treat many currently untreatable conditions. They will form any cell type in the human body and even self-assemble into complex tissues. Combined with cloning, they could change medicine as we know it today.”