First pilot study of maternal spindle transfer for the treatment of repeated in vitro fertilization failures in couples with idiopathic infertility.

Objectives: To gain insights into the technical feasibility of maternal spindle transfer (MST) applied in the context of repeated in vitro fertilization (IVF) failures for the treatment of idiopathic infertility.

Design: A prospective pilot study.

Setting: IVF center.

Patient(s): Twenty-five infertile couples with multiple previous unsuccessful IVF cycles (range, 3-11), no previous pregnancy, and no history of mitochondrial DNA (mtDNA) disease participated. The study focused on women <40 years, with previous IVF attempts characterized by a pattern of low fertilization rates and/or impaired embryo development. Couples with severe male-factor infertility were not eligible. Oocyte donors with previous successful IVF outcomes were matched with patients according to standard practice.

Intervention(s): We performed MST by transferring metaphase II spindles from the patients' oocytes into the previously enucleated donor oocytes, followed by intracytoplasmic sperm injection, in vitro embryo culture, blastocyst biopsy, and vitrification. Only euploid blastocysts were considered for embryo transfer.

Main Outcome Measure(s): Outcome measures included oocyte fertilization, blastocyst development, clinical pregnancy and live birth, incidence of mitochondrial carryover and potential mtDNA reversal, as well as general health of the children born.

Result(s): Twenty-eight MST cycles produced 6 children (19 embryo transfers, 7 clinical pregnancies). Pediatric follow-up of the children, performed at intervals from birth to 12-24 months of age, revealed their development to be unremarkable. DNA fingerprinting confirmed that the nuclear DNA of MST children was inherited from both parents, without any contribution from the oocyte donor. For 5 of the children, mtDNA was derived almost exclusively (>99%) from the donor. However, 1 child, who had similarly low mtDNA carryover (0.8%) at the blastocyst stage, showed an increase in the maternal mtDNA haplotype, accounting for 30% to 60% of the total at birth.

Conclusion(s): This pilot study provides the first insights into the feasibility of applying MST for patients with idiopathic infertility and repeated IVF failures. Reconstructed oocytes produced embryos capable of implanting, developing to term and producing apparently healthy newborns/children. However, claims concerning the efficacy of MST with respect to infertility treatment would be premature considering the limitations of this study. Importantly, mtDNA reversal was detected in one child born after MST, a finding with possible implications for mitochondrial replacement therapies.

Clinical Trial Registration Number: Pilot trial registry number, ISRCTN11455145. The date of registration: 20/02/2018. The date of enrolment of the first patients: 18/03/2018.