Rescue In Vitro Maturation Using Ovarian Support Cells of Human Oocytes From Conventional Stimulation Cycles Yields Oocytes With Improved Nuclear Maturation and Transcriptomic Resemblance to In Vivo Matured Oocytes

Embryo development is orchestrated by several somatic types of ovarian cells, including stroma, theca, and granulosa cells that each send signals to oocytes; during oocyte maturation, oocytes rely on posttranscriptional modification, transcript degradation, and selective translation. There is little literature to date that has focused on transcriptome-wide changes in gene expression in oocytes after in vitro maturation (IVM), although the mechanisms of maturation may differ in vitro versus in vivo. There is theoretical promise in IVM for women who have contraindications to conventional ovarian stimulation (COS), but clinical utility so far has been low and difficult to validate, especially for rescue IVM solutions. Recently, a novel technology has demonstrated an ability to form ovarian support cells (OSCs) fromhuman-induced pluripotent stem cells (hiPSCs) through transcription factor-directed differentiation; these generated cells produce growth factor and are steroidogenic when in the presence of follicle-stimulating hormone. This study was a further exploration of this technology focusing on the potential of hiPSCderived OSCs to rescue immature oocytes that are retrieved in COS cycles. This study included oocytes donated for research purposes from 47 fertility patients between the ages of 25 and 45 years. Exclusion criteria were history of diabetes, thyroid disease, endometriosis, recurrent implantation failure, and oocyte maturation defect or chromosomal abnormality. Immature oocytes collected during a standard COS cycle were set aside for research purposes in a prematuration medium. Preparation of OSCs was previously described in earlier published studies.At the end of culture, oocytes were harvested and washed and subsequently evaluated for maturation using 3 criteria: germinal vesicle (GV), defined as the presence of aGV,which most often contained a single nucleolus;MI, defined as the absence of aGVand polar body; and MII, defined as the absence of a GV with the presence of a polar body. The oocytes that were matured using IVM were compared with controls that underwent spontaneous maturation without OSCs. There were significantly better maturation outcomes associated with OSCs (62% ± 5.57% vs 37% ± 8.96%, P = 0.0138). Investigating OSCs' reaction to culture with oocytes compared with culture inmedia alone, growth factors were significantlymore common in the presence of oocytes. Reciprocally, oocyte IVM is improved by the presence of OSCs, with the expression of CYP19A1 and MDK upregulated, both of which are integral to oocyte maturation. Careful examination also showed upregulation of IGF2, EGF, and IGFBP4 in the presence of oocytes and downregulation of EGFR and IGFBP2. When comparing oocytes that were matured in the presence of OSCs with those that were matured either spontaneously in vitro or in vivo, characteristics were similar; no significant differences were seen inmorphological properties, or in the spindle angle relative to the first polar body in the second stage of meiosis. Additionally, transcriptomic analysis showed that maturation state was well-predicted by transcriptional profile. This held true in several variations and states of maturation. Lastly, oocytes that were matured in the presence of OSCs showed a high molecular similarity to in vitro fertilization matured oocytes, more so than their media-matured controls. These results show that performing IVM by culturing oocytes with OSCs may be a way to rescue immature oocytes retrieved during COS cycles and stimulate maturation. This is the first study of its kind to explore this possibility, and thus future research opportunities are vast. Priorities for future studies include the clinical utility of this technology, as well as the potential ramifications and differences in embryos formed from rescued oocytes.