Scientists working have for the first time developed embryos from whole ovaries which were transplanted after being frozen and then thawed.
The journal Human Production reported that eggs obtained from two ovaries produced early sheep embryos.
And researchers at Israel's Institute of Animal Science believe the procedure could one day work with humans.
Scientists have been seeking ways to preserve the fertility of women undergoing aggressive cancer treatment.
One option is to harvest, fertilise and then freeze a woman's eggs, but the rate of successful pregnancies following this method is low.
Another option is to freeze and transplant thawed strips of ovarian tissue. There have been reports of two babies born following this technique, reports BBC.
Dr. Arav and his team were then able to retrieve eggs from the transplanted ovaries, which were chemically induced to begin cell-division — the process triggered naturally by sperm fertilization that turns them into embryos.
“What was most surprising was that when we opened the animals and collected the oocytes (eggs), they looked fine and we were able to activate them and produce embryos from these eggs,” said Dr. Arav, lead author of a paper published Thursday in Human Reproduction.
“We really wanted to know if these eggs that we have are able to become embryos. Probably next time we'll do fertilization as well (to produce a lamb).”
The scientists removed one ovary from each of eight sheep in 2001. The reproductive organs were then frozen for different periods of time — from a week to a month — then transplanted back into the animals.
In five of the animals, blood began to circulate to the ovary immediately after the operation. Two of the sheep who resumed hormone production are still “cyclic” after four years, Dr. Arav said by phone from near Tel Aviv.
“The method of freezing is a new technique, a new concept in thermodynamics, where we can control the ice crystal propagation and we can freeze very, very slowly,” he said. “This is what makes all the (ovarian) cells survive,” informs Globe and Mail.