February 3, 2009

Human Clones Can’t Come from Animal Eggs

According to a report appearing in the journal Cloning and Stem Cells, animal eggs cannot be used to create human clones.

Dr. Robert Lanza of Advanced Cell Technology and his colleagues failed in an effort to use mouse, cow, and rabbit eggs to produce workable human embryos.

Lanza reported that his team was able to make a viable embryo using human cells, and believes that human cloning appears to be possible in principle.

Researchers in the past have tried using animal eggs as a source for embryonic stem cells.  Currently human eggs have to be used, but harvesting the eggs requires a surgical procedure to get them from a woman.

The technique used by researchers, called somatic cell nuclear transfer, attempts to replace the nucleus of an egg cell with the nucleus from a donor cell.

If the process is successful, the egg will start dividing as if it had been fertilized.  The resulting embryo takes most of its DNA from the donor cell.

"The idea was to simply to plunk a patient's DNA into an empty cow or rabbit egg -- and presto -- you reprogram the DNA back into a stem cell," Lanza told Reuters News.

Researchers have yet to be successful attempting this theory.

"For the last decade, we've carried out literally hundreds of experiments trying to create patient-specific stem cells using animal eggs," Lanza said.  "We got beautiful little hybrid embryos, but it didn't work no matter how hard we tried."

Often a hybrid embryo would be created, but would fizzle out after one, or many divisions.

According to Lanza, using the egg of another species appears to turn off the genes needed to make an embryo.  Researchers had hoped it would turn the genes on.

The human-human clone seemed the most successful, but still stopped before producing stem cells, said Lanza.

"We see exactly the same genes turned on in a normal embryo are actually turned on in a human clone," added.

Ian Wilmut, who cloned Dolly the sheep, the first cloned mammal, said the results of the study were disappointing.

"This very important paper suggests that livestock oocytes (egg cells) are extremely unlikely to be suitable as recipients for use in human nuclear transfer," said Wilmut.

Lanza believes it could be possible to create "banks" of stem cells for the many types of tissue found in humans.

This could be achieved through a new method called induced pluripotent stem cells, in which skin cells are reprogrammed to act like stem cells, said Lanza.


On The Net:

journal Cloning and Stem Cells