Follicle culture after ovarian cryostorage

Objectives: Cryostorage of ovarian cortical tissue, before devastating chem o- and/or radiotherapy for cancer, permits survival of primordial and early preantral follicles. This work aims for a system allowing the long-term ma turation in vitro (IVM) of small immature oocytes up to fertilisable metaph ase II oocytes. Methods: A culture system allowing follicle attachment perm itted the growth and maturation of isolated follicles (follicle diameter be tween 100 and 130 mu m) from 14-day-old (prepuberal) mice. Follicle and ooc yte development were observed under the inverted microscope and conditioned medium was used for biochemical analysis. Effects of recombinant gonadotro phins and oxygen tensions were studied for their specific effects on follic le development. Results: A 12-day culture period yielded full-grown oocytes which were able to complete meiosis (metaphase II). Live young were obtain ed after IVF and intra-uterine transfer of in vitro matured oocytes. Growth and maturation were only successful when recombinant gonadotropins were ad ded and when the incubator had a 20% oxygen tension. This system enabled th e growth of early preantral follicles after cryopreservation: 80% of frozen and thawed follicles survived up to culture-day 12 and yielded a comparabl e blastocyst formation rate as in controls. Conclusions: The mouse model su ggests that IVM is a valuable option after oocyte storage. The development of a comparable system for long-term culture of human follicles will imply the acquisition of non-invasive techniques to appreciate oocyte's maturity and developmental capacity. (C) 1998 Elsevier Science Ireland Ltd. All righ ts reserved.