Barcelona, 2 July 2018: Important steps in the development of an artificial ovary have been successfully completed by one of the world's leading groups in fertility preservation. Researchers from the Rigshospitalet in Copenhagen, Denmark, report today that they have for the first time isolated and grown human follicles to a point of "biofunctionality" on a bioengineered ovarian scaffold made of "decellularised" ovarian tissue. The early-stage follicles were isolated from patients having ovarian tissue frozen for fertility preservation ahead of other medical treatments likely to compromise ovarian function. 

The experiments are described today by Dr Susanne Pors from the Rigshospitalet's Laboratory of Reproductive Biology at the 34th Annual Meeting of ESHRE in Barcelona. The Danish group has by far Europe's greatest experience in ovarian tissue storage for fertility preservation, with ovarian tissue preserved over the past 20 years from 1100 patients and 115 thawed transplantations performed in 90 women.(1)

Pors said that developing an effective protocol of eliminating cells from ovarian tissue and the transfer of viable early-stage follicles would remove the possibility of reintroducing malignancies potentially present in the original tissue. Currently, most cases of fertility preservation by ovarian tissue freezing are performed ahead of cancer treatment, where radio- or chemotherapy are likely to destroy ovarian function. Thawing and regrafting the original cryopreserved tissue would thus run the risk of reintroducing any malignancy. "However," said Pors, "a bioengineered ovary would allow the growth and development of reseeded frozen-thawed early stage follicles in a tissue bed which is free of malignancies."(2)

The experiments were performed with ovarian tissue removed from women having fertility preservation ahead of cancer treatment. The inhabiting cells of the tissue were eliminated by a three-day chemical process, after which decellularisation was tested by DNA and collagen quantification. Removal of the inhabiting cells thus left an extracellular matrix scaffold of the original tissue. It was this bioengineered scaffold on which the isolated early-stage follicles were reseeded.

Tests on the functionality of the extracellular matrix showed that the tissues had been completely decellularised, with no native material evident. "We then found that ovarian cells and early-stage follicles were able to recellularise the decellularised tissue in vitro by successfully repopulating and migrating into the scaffold," explained Pors. Transplantation experiments (into mice) showed that the decellularised matrix was able to support survival and growth of early-stage follicles.

"This is the first time that isolated human follicles have survived in a decellularised human scaffold," said Pors, "and, as a proof-of-concept, it could offer a new strategy in fertility preservation without risk of malignant cell re-occurrence." The technique, she added, would be applicable to cancer patients having cryopreserved ovarian tissue transplanted for fertility restoration.(3)

Pors explained that the risk of recurring malignancy from frozen tissue is "real", especially for patients with leukaemia and cancers originating in the ovary. However, studies performed by the Copenhagen group and others show that the risk of transferring cancer cells from other malignancies appears to be very low.

Pors described this as a "proof-of-concept study" showing for the first time that human follicles can survive on a human decellularised scaffold. Further studies are planned to optimise the scaffold and reseeding procedure and to evaluate the quality of the follicles for further use.

In several countries, including Denmark, ovarian tissue cryopreservation has now moved beyond the experimental phase to be an established method of fertility preservation, with public reimbursement. "We have around 100 referrals a year," says Pors, "not only cancer patients but also those with other conditions demanding chemotherapy or radiation. We estimate that this represents around 80% of all patients in Denmark who could benefit from the procedure. In total we have frozen tissue from 1100 patients and have the highest rate of activity per citizen in Europe." One common complaint from many countries - in contrast to Denmark - is that referrals from oncologists for fertility preservation fall well below this level.