"Waste" follicular aspirate from fertility treatment--a potential source of human germline stem cells?

Fertility clinics worldwide routinely produce a large volume of 'waste' follicular aspirate, which is potentially an abundant source of immature ovarian follicles. Current attempts to cultivate these further in vitro to yield viable mature oocytes for fertility treatment have not yet achieved much success. Instead, recent lines of evidence have emerged that are suggestive of a potential stem cell niche within such immature ovarian follicles. The recent discovery of follicular renewal and putative germ-line stem cells within the postnatal mammalian ovary shook the foundations of reproductive biology by challenging the established dogma that mammalian females lose the capacity for germ cell renewal during fetal life, such that a fixed reserve of germ cells (oocytes) enclosed within follicles is endowed at birth. More intriguingly, another recent study in the Drosophila model provided compelling evidence that somatic progenies (nurse cells) of germ-line stem cells had the ability to revert back to the stem-cell-like state. This introduces the exciting possibility that within the mammalian ovarian follicle, similar somatic progenies of germ-line stem cells may also possess a greater intrinsic ability to revert back into functional stem cells. If this is the case, then a favored candidate would be the cumulus/granulosa of immature ovarian follicles, since such cells are true homologues of nurse cells found within the Drosophila ovary. The successful elucidation of a human germ-line stem cell niche within immature ovarian follicles is likely to have huge ramifications in stem cell biology and regenerative medicine.

The cryopreservation of human embryonic stem cells.

hES (human embryonic stem) cells hold tremendous potential in the newly emerging field of regenerative medicine, in addition to being a useful tool in basic scientific research and for pharmacological and cytotoxicity screening. However, an essential prerequisite for the future widespread application of hES cells are the development of efficient cryopreservation protocols to facilitate their storage and transportation. This review summarizes the current state of progress in the field of hES cell cryopreservation, by critically examining and comparing the various cryopreservation protocols that have been developed. These can be classified into two categories: (1) conventional slow-cooling protocols and (2) vitrification protocols. Previously, the application of slow-cooling cryopreservation protocols to freely-suspended hES cell clumps yielded extremely dismal results. However, a recent study demonstrated that post-thaw survivability was markedly improved when slow-cooling protocols were applied instead to adherent hES colonies. Vitrification protocols have been shown to be much better than the standard slow-cooling protocol for the cryopreservation of freely suspended hES cell clumps. However, no study has yet attempted to apply vitrification protocols to adherent hES colonies. It must be noted that vitrification protocols are extremely labour-intensive and tedious to perform manually. Additionally, the use of cryostraws in vitrification protocols is unsuited for handling bulk quantities of hES cells, in addition to posing serious technical difficulties in developing machine automation for cryopreservation. These are some of the major challenges that have to be overcome if further progress is to be made in this field.