Viable Eggs Harvested From Transplanted Sheep Ovaries

Israeli researchers have transplanted frozen, then thawed ovaries into sheep and then harvested functioning eggs.

Two human pregnancies have been reported after transplantation of frozen ovarian tissues but not intact ovaries. Both cases have been clouded by the possibility that the women’s damaged ovarian tissue had recovered and provided the eggs for the pregnancy.

A team headed by Amir Arav of the Agriculture Research Organization in Bet Dagan and Yehudit Nathan of the biotechnology company Core Dynamics in Nes Zyona reported Thursday in the journal Human Reproduction that the key to their success was a new technology for freezing organs that limits the number of damaging ice crystals formed in the process.

Cell damage caused by ice crystals has long been the leading problem in attempting to freeze tissues.

The team removed and froze the right ovaries from eight sheep, whose ovaries are similar to those of humans. The ovaries were re-implanted within two weeks. Five of the eight had normal blood flow, indicating that the transplant had succeeded.

The team harvested eggs from two of the sheep and activated them using chemicals that mimic fertilization. All went on to produce normal eight-cell embryos.

MRI studies 12 months after the transplant showed that the ovaries were functioning normally. The ovaries also produced normal hormonal cycles for at least three years.