Entire frozen ovaries have been successfully thawed and transplanted for the first time. The experiment in rats offers hope to cancer patients whose treatment often leaves them sterile.
But critics point out that successfully transplanting a tiny thawed rat ovary is a far cry from successfully thawing and transplanting a much larger human ovary.
A team led by Roger Gosden at McGill University in Montreal bathed eight complete rat ovaries in a solution containing fructose and dimethylsulphoxide – chemicals designed to prevent large, destructive ice crystals forming between cells during freezing. The ovaries were then slowly frozen in liquid nitrogen.
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All eight ovaries survived defrosting and transplantation back into genetically identical rats. Four of the rats ovulated normally, and one became pregnant with two healthy foetuses.
In 2001, Gosden announced that he had successfully transplanted defrosted half ovaries in sheep, whose reproductive system is much more similar in size to a woman’s. These sheep went on to produce live offspring.
“Desperately disappointing”
But previous attempts to transplant thawed strips of ovary into women have had limited success. One woman did ovulate once, but this has not been repeated. Simon Fishel, an expert in reproductive medicine at the Park Hospital in Nottingham, has called the technique “desperately disappointing” in women.
Transplanting whole ovaries, instead of strips, into women might in theory extend the time period of ovulation and reduce the need for repeat transplants.
But Michael Taylor, at Organ Recovery Systems in Charleston, South Carolina, points out that rat ovaries are about the size of a baked bean. Larger organs are more susceptible to damage during freezing, he says.
“Size is key when considering extrapolation to larger organs that are totally refractory to successful cryopreservation,” he told Nature.
Journal reference: Nature (vol 415, p 385)