Researchers seeking alternate ways to clone tissue for medical purposes have created a monkey embryo without the use of sperm to make stem cells that then turned into heart, brain and other specialized material.
Dr. Michael West, who heads Advanced Cell Technology in Worcester, Mass., said he and his colleagues used chemicals to cause a monkey egg to turn into an embryo, a process called parthenogenesis, and then extracted stem cells from that embryo to make the specialized tissues.
“These were fully developed cells that could have been used medically,” he said.
Advanced Cell Technology announced in November that it had cloned a human embryo that was allowed to grow to six cells.
Dr. West said although the new study used only monkey eggs, it demonstrates that it may be possible to make human embryonic stem cells through parthenogenesis. Other experts, however, said such a technique would have a medical application limited to women of reproductive age and would not benefit males.
A report on the study appears today in the journal Science.
Dr. West said he believes making embryos through parthenogenesis may bypass ethical objections raised by many toward therapeutic cloning a technique aimed at making specialized cells to treat ailing hearts, diseased brains or to cure conditions such as diabetes.
In contrast to reproductive cloning, which could produce a whole person, therapeutic cloning involves growing embryos for only a few days in order to produce specialized cells for medical treatment of a specific patient.
However, President Bush and some members of Congress are opposed to all forms of human cloning. A bill to ban all human cloning has passed the House, and the Senate is expected to take up the issue this year. The National Academy of Sciences, in a recent report, opposed reproductive cloning, which would make a whole person, but said therapeutic cloning, which would make only special cells, has a potential in medicine.
Dr. West said the study using monkey cells mimicked parthenogenesis in nature, though it is not considered a normal process.
“Parthenogenesis occurs naturally in some women, forming a mass of cells from an egg in the ovary,” he said. This group of cells is called a teratoma, a benign mass that may contain fully developed cells, Dr. West said. Teratomas form on the ovary and are usually removed surgically.
In the study, Dr. West and his team exposed 77 monkey eggs to chemicals that can cause the eggs to develop into embryos. “The chemicals cause the egg to believe it has contacted a sperm” and to change into an embryo, Dr. West said.