Human artificial oocytes from patients' somatic cells: past, present and future.

The first attempts at generating functional human oocytes by using the transfer of patients' somatic cell nuclei, as DNA source, into donor enucleated oocytes date back to the early 2000s. After initial attempts, that gave rather encouraging results, the technique was abandoned because of adverse results with this technique in the mouse model. Priority was then given to the use of induced pluripotent stem (iPS) cells, based on excellent results in the mouse, where mature oocytes and live healthy offspring were achieved. However, these results could not be reproduced in humans, and oogenesis with human iPS cells did not continue beyond the stage of oogonium. These data suggest that the use of enucleated donor oocytes will be necessary to achieve fertilizable human oocytes with somatic cell-derived DNA. The main problem of all these techniques is that they have to meet with two, sometimes contradictory, requirements: the haploidization of somatic cell-derived DNA, on the one hand, and the remodeling/reprogramming of DNA of somatic cell origin, so as to be capable of supporting all stages of preimplantation and postimplantation development and to give rise to all cell types of the future organism. Further research is needed to determine the optimal strategy to cope with these two requirements. LAY SUMMARY: The recourse to artificial oocytes, generated by using the patient's own DNA derived from cells of somatic origin, represents the ultimate opportunity for women who lack healthy oocytes of their own but yearn for genetically related offspring. Many different pathologies, such as ovarian cancer, premature ovarian failure, other ovarian diseases and natural, age-related ovarian decay can cause the absence of available oocytes. The demand for artificial oocytes is increasing continuously, mainly because of the tendency to postpone maternity to still more advanced ages, when the quantity and quality of oocytes is low. This minireview focuses on the generation of artificial oocytes using different strategies and scenarios, based on the accumulated experience in humans and experimental animals.