WEDNESDAY, Sept. 14, 2005 (HealthDayNews) -- Doctors have long used frozen pieces of ovary tissue to reconstruct ovaries damaged by chemotherapy or other ovarian failure, allowing affected women to conceive and have children.
But now, Israeli scientists say they have successfully transplanted whole frozen and thawed ovaries in sheep, produced eggs from these ovaries, and then triggered them in the laboratory into early embryonic development.
Moreover, tests showed that the transplanted ovaries in two of the five sheep were still functioning normally three years later.
The report appears in the September issue of Human Reproduction.
According to lead author Amir Arav, a senior scientist at the Institute of Animal Science, Agriculture Research Organization, these results show that it is possible to remove, freeze, thaw and replace ovaries, obtain eggs and maintain normal ovarian function.
"There is a lot of research still to be done, but we hope that it will not take more than a few years for this to become a practicable option for women, such as young cancer patients, who would otherwise be left infertile after their treatment," Yehudit Nathan, program manager at biotech company Core Dynamics, said in a prepared statement. The company funded the research.
The method is new because it used whole ovaries, along with their blood vessels, and showed that they were able to survive the freezing and thawing process. The key to the process is being able to control the formation of ice crystals during the freezing process. This reduces the damage caused to cells by usual freezing methods, according to the researchers.
Arav's team used sheep because their ovaries are similar to those of humans.
The approach offers new hope for using this method in women facing premature ovarian failure. In addition, freezing organs may be useful for other types of lifesaving human organ transplants, which are currently done using only fresh organs, the researchers noted.
"This approach could revolutionize the field of cryopreservation for diverse human applications, such as organ transplants, as well as helping women who face the loss of their fertility," Arav said in a statement.
Despite the success, fertility experts have reservations about how this new method might be used in women.
"This is an extremely encouraging report," said Dr. Kutluk Oktay, an associate professor of reproductive medicine at Weill Medical College of Cornell University in New York City. "If we can freeze a human ovary intact with its blood supply, a larger reserve of eggs can be preserved."
However, a human ovary is at least three to four times larger than a sheep ovary, and thus the outcome might be different in humans, Oktay said. "If the authors show that the sheep can actually have live births after this procedure, they must try this with human tissue to show its feasibility in patients," he said.
Another expert believes that, rather than freezing ovaries, freezing eggs is still a better alternative.
"The amount of surgical intervention required to use this technique is so much greater than what you would need to do with egg-freezing," said Dr. Jaime A. Grifo, the director of the Division of Reproductive Endocrinology at New York University Medical Center and a professor at NYU School of Medicine.
"Basically, patients would have to undergo two procedures for this to work," he said. Grifo said that this technique could be used for women who may have ovarian failure. "[But] the problem there is going to be that, in the patient who is a candidate for this, you will be freezing an ovary that is likely to develop ovarian failure anyway," Grifo said. "So are you really accomplishing anything?"
Another expert said other researchers have been using similar methods with similar results.
Researchers at Cornell have been doing this for some time, said Dr. Hugh Taylor, an assistant professor of reproductive endocrinology and infertility at Yale University School of Medicine. "It's an interesting technical feat, but whether it's going to be better than the alternative method of freezing pieces of ovarian tissue is not answered by this study," he said.
The American Society of Reproductive Medicine can tell you more about infertility.