P-798 A feasible clinical model to generate genotyped oocytes for infertile women
Authors: Tsai S , XIe P , Rosenwaks Z , Palermo G 
Published: July 2024

Abstract

Study question
Is it possible to generate genotyped oocytes by utilizing accessible somatic cells in a somatic cell nuclear transfer model?

Summary answer
Genotyped oocytes generated through haploidization of endometrial somatic cells exhibited reliably completed embryo development and yielded healthy offspring.

What is known already
The generation of genotyped oocytes through neogametogensis or somatic cell nuclear transfer (SCNT) would be the ultimate solution to treat female infertility due to primary ovarian insufficiency or agonadism. Among the various approaches, somatic cell haploidization appears more feasible (Lee, et al 2022). Unfortunately, this approach has only been successful in a murine model using cumulus cells. However, this donor cell type is not ideal when translated into clinical setting, due to the absence of cumulus cells in patients who are void of oocytes, which arguably is the patient population that would potentially benefit the most from this technique.

Study design, size, duration
In a mouse SCNT model, endometrial stromal cells (EMSCs) were injected into enucleated oocytes. Cumulus cells (CCs) were used as another source of nuclear donor. Intact MII oocytes were used as control. Post-SCNT oocytes and controls were inseminated by spermatozoa from B6-EGFP mice to monitor paternal genome presence through embryo development and offspring. Embryos were cultured in a time-lapse microscope. To prove gamete competence, blastocysts were transferred into pseudo-pregnant recipients and offspring health was assessed.

Participants/materials, setting, methods
Endometrial stromal cells were cultured for 4 days and exposed to aphidicolin overnight to synchronize at G1 phase of cell cycle. Cumulus cells were collected after denudation. Oocytes from B6D2F1 mice were enucleated under polarized light microscope. SCNT was performed with CCs or EMSCs by lipofectamine-mediate fusion. Oocytes were inseminated with spermatozoa from GFP-positive transgenic mice. Embryos morphokinesis were assessed by a time-lapse system. Blastocysts were transferred into 2.5-dpc surrogate CD1 mice.

Main results and the role of chance
Control oocytes(n = 75) fertilized at 93.3%(70/75) and progressed to 2-cell stage at 93.3%(70/75), 8-cell at 93.3%(70/75) and blastocyst at 89.3%(67/75). The control embryos started syngamy at 14.4±1h, reaching the 4-cell stage at 37.3±3h and blastulation at 80.6±8h.
A total of 484 oocytes were enucleated, 470(97.1%) survived and underwent SCNT using CCs(n = 85) or EMSCs(n = 385). Fusion rate was 95.5% for CC with a haploidization rate of 70.9%(56/79) that led to a fertilization rate of 64.3%(36/56). The CC cohort developed to 2-cell, 8-cell, and morula at 47.4%, 35.4%, and 22.8%, with a delay in development at syngamy at 19.0±8h(P&lt;0.0001).
In the EMSC cohort, fusion rate was 96.0%(361/376). Haploidization rate was 65.4%(236/361), comparable to the CC cohort(P = 0.35). Fertilization was lower in the EMSC cohort at 47.0%(P&lt;0.01) compared to the CC cohort. Subsequently, EMSC cohort yielded similar cleavage rates to 2-cell stage at 30.7%, 8-cell stage at 29.4%, and morula stage at 28.5%. The blastocyst rate was higher in the EMSC cohort at 28.0%(P&lt;0.05). The EMSC cohort yielded similar developmental timing comparing to controls from pronuclear appearance to 4-cell cleavage but a delay manifested afterward at 37.3±3h(P&lt;0.0001). In the EMSC cohort, 42 blastocysts were transferred, yielding 3 healthy pups(2 male,1 female).

Limitations, reasons for caution
While we generated consistent haploidization and satisfactory fertilization, full pre-implantation development remained low. Even more limited was the live birth rate, which probably related to subtle factors such as an imprinting issue due to insufficient reprogramming of the somatic cell donor.

Wider implications of the findings
The SCNT model described to generate genotyped oocytes, although still with limited efficiency, represents a feasible reproductive option for women with agonadism and compromised ovarian reserve. This model is still a better approach to complete neogametogenesis.

Trial registration number
not applicable