Scientists from Edinburgh (United Kingdom) and New York (USA) have achieved for the first time to grow out of the body immature human ovules until its last phase of development, the moment they are ready for fertilization with a sperm. The authors suggest that this technique could be used to preserve the fertility of girls before they receive treatments that could damage their eggs, such as chemotherapy or radiotherapy.

To develop a fertility preservation treatment, scientists will first have to demonstrate that mature ovules are viable and that when fertilized they produce healthy embryos, says Antonio Requena, the medical director general of the Valencian Institute of Infertility (IVI), who did not participate in the investigation. This has already been achieved in mice, but it will take several more years until the safety of the method in humans is demonstrated. In the study, which appears in the scientific journal Molecular Human Reproduction, 10 healthy women who had chosen to give birth by cesarean section participated. During the operation, the surgeons took biopsies of their ovaries that were used for the subsequent extraction of ovarian follicles-tissue envelopes that contain the ovules.

Cultivation is complicated, because the structures change a lot, explains Richard Anderson, one of the authors of the study at the University of Edinburgh. The primordial follicles only measure a few microns in diameter, while the mature follicle can measure two centimeters from side to side, says the biologist. To overcome these morphological changes, the researchers carried out the process in several phases: they started developing complete follicles, but when these became too large for culture techniques, they extracted the ovules and discarded the accessory tissue.

Previously, several research centers had managed to replicate parts of the development process, but this is the first time that it has been carried out completely. While in a healthy ovary the maturation of the ovum usually takes three months, in the laboratory it only took three weeks. Anderson argues that the fact that it happens faster in cultivation does not mean that something bad has happened, simply that development is possible in less time.

Requena warns that "we must be very cautious" before proceeding with fertility preservation techniques, but congratulates the researchers for the potential that their achievement has for the clinic. Normally, doctors can remove ovarian tissue from cancer patients to reimplant after treatment. However, this intervention carries the risk of reintroducing cancer cells to the body. With the new technique, the immature ovules that are extracted from the ovarian tissue can be developed and stored in the laboratory for later fertilization. Each isolated ovule would be free of contaminating cells: "we could fertilize them [in vitro] and obtain embryos, which is what would be implanted", explains the doctor.

Although they have shown that developing ovules in the laboratory is possible, the authors acknowledge that the process is not exactly efficient: of the 87 follicles that they cultivated, they managed to extract nine mature ovules. In addition, the cells that they obtained are not identical to those produced by the body. When the ovum matures completely, it must expel half of its genetic material in a secondary structure called the polar body. All laboratory ovules, whether mouse or human, show polar bodies larger than normal. "We do not know if the size of the polar body is relevant, but in mice the fertilization of laboratory eggs is not as efficient as when they grow in the body," says Anderson. Despite these limitations, the study has also clarified the development process of the human ovum in its different stages, which could facilitate the investigation of other infertility treatments and new techniques in regenerative medicine.

Source: El País