Alternative sources of gametes: reality or science fiction?

Although great progress has been made in both the investigation and treatme nt of infertility, a considerable number of patients still fail to conceive . Spermatogenic failure and/or oocyte ageing appear to be responsible for a large proportion of cases. The use of donor gametes may bring legal, ethic al and even social problems of acceptance that can discourage infertile cou ples from the donor route. Fortunately, emerging reproductive technologies and preliminary results from animal experiments provide some hope for alter native sources of gametes through which these infertile patients can finall y conceive their own genetic child. In conjunction with intracytoplasmic sp erm injection (ICSI), fertilization of human oocytes with immature sperm pr ecursors, e.g, spermatids and even secondary spermatocytes, has resulted in healthy babies, Pregnancies have also resulted from the use of spermatids derived from in-vitro spermatogenesis. In the mouse, even primary spermatoc ytes appear able to participate in normal embryogenesis. In view of the pos sibility for transplantation and even xenotransplantation of spermatogonia to a host testis in animals, a similar use of human male stem cells might p rovide an attractive source for the treatment of males with arrested sperma togenesis, as well as male cancer patients. Transplantation of somatic cell nuclei and their haploidization within oocytes may prove to be a practical way of eradicating age-related aneuploidy and so constitute an innovative source of healthy oocytes. Most importantly, however, the safety of the pro cedures described here needs to be proven before their application to the h uman arena. Finally, we discuss the implications of cytoplasmic quality and of genetic imprinting in the context of these manipulations.