'Ripened eggs' used for cloning work
Immature human eggs could be a source of stem cells.
Researchers have managed to make the beginnings of a cloned human embryo using immature eggs incubated in the lab. If the technique can be perfected, they say it could provide a larger, more acceptable source of stem cells.
So far the cloned embryo cells have only been persuaded to divide once and so haven't developed enough to serve as a source of stem cells. But the researchers say they are convinced they can achieve this step within a few months.
At the moment, biologists rely on mature eggs when attempting to clone human embryos. These are often obtained from IVF clinics, where women may choose to donate some eggs for research. But since the majority of mature eggs are wanted for the IVF procedure, donation is relatively rare. "There's a shortage," explains Josiane Van der Elst of the University of Ghent in Belgium.
Van der Elst adds that 10-15% of the eggs produced by women for IVF are immature. In the rare instances where immature eggs are all that a woman can produce, researchers do attempt to mature them in the lab and use them in IVF procedures. But this has a very low success rate of about 10%, according to Bjorn Heindryckx, who worked on the study with Van der Elst.
If researchers could use these immature eggs, says Van der Elst, it would greatly increase the number of oocytes donated for stem cell work, while utilising a source that is usually simply discarded.
Researchers have only recently managed to clone a human embryo. A team of scientists led by Woo Suk Hwang of the Seoul National University achieved this feat last year by using 242 mature eggs harvested from 16 different female volunteers to produce one stem cell line. Researchers have since greatly improved the efficiency of this process. A second team, in the UK, has also managed to clone a human embryo from mature eggs.
The Belgian team attempted a similar cloning procedure with immature eggs. They placed the eggs in a solution that contained female reproductive hormones and allowed them to develop for about two days. They then removed the DNA from the eggs' nuclei and inserted genetic material from the subject they wished to clone. "It's a combination of two difficult things," says Van der Elst, who presented the findings at the annual meeting of the European Society for Human Reproduction and Embryology in Copenhagen this week.
In 8 of the 50 artificially matured eggs, the team was able to produce a two-cell embryo from this delicate procedure. Embryos need to grow to a clump of about 150 cells, called a blastocyst, before they can be harvested for stem cells.
"If we can use immature eggs there will be more sources of embryonic stem cells," says ethicist William Hurlbut of Stanford University in California. But ethical concerns remain. "Identifying ethically acceptable sources of oocytes is an important issue," says Kathy Hudson, director of the Genetics and Public Policy Center at Johns Hopkins University in Baltimore, Maryland. "But it is dwarfed by the challenge of bridging the ethical divide over destroying an embryo, irrespective of how it was created," she says.