Prospects of Germline Nuclear Transfer in Women With Diminished Ovarian Reserve

Abstract

Diminished ovarian reserve (DOR) is associated with a reduced quantity and quality of the retrieved oocytes, usually leading to poor reproductive outcomes which remain a great challenge for assisted reproduction technology (ART). Women with DOR often have to seek for oocyte donation, precluding genetically related offspring. Germline nuclear transfer (NT) is a novel technology in ART that involves the transfer of the nuclear genome from an affected oocyte/zygote of the patient to the cytoplast of an enucleated donor oocyte/zygote. Therefore, it offers opportunities for the generation of genetically related embryos. Currently, although NT is clinically applied only in women with serious mitochondrial DNA disorders, this technology has also been proposed to overcome certain forms of female infertility, such as advanced maternal age and embryo developmental arrest. In this review, we are proposing the NT technology as a future treatment option for DOR patients. Strikingly, the application of different NT strategies will result in an increase of the total number of available reconstituted embryos for DOR patients.

Keywords: diminished ovarian reserve; germline nuclear transfer; oocyte quality; polar body transfer; poor ovarian response; spindle transfer.

Figure 1

Different nuclear transfer (NT) techniques can occur at the oocyte or the zygote stage. Reconstruction at the oocyte stage: Germinal vesicle transfer (GVT): the nucleus is transferred in an enucleated GV oocyte. Following in vitro maturation, the reconstructed oocyte can be fertilized by the patient’s partner sperm. Spindle transfer (ST): The spindle from a mature oocyte (MII) is transferred to the enucleated MII donor oocyte. Polar body 1 transfer (PB1T): The first polar body from an MII oocyte is transferred to an enucleated MII oocyte of a donor. Reconstruction at the zygote stage: Pronuclear transfer (PNT): the pronuclei from a fertilized oocyte are transferred to the enucleated donor zygote. Polar body 2 transfer (PB2T): The second polar body of a fertilized oocyte is transferred to a zygote containing the male pronucleus of the patient’s partner. The paternal pronucleus can occur in two ways: (a) by fertilization of a donor’s oocyte. Following fertilization, the male and female pronuclei form. The female pronucleus of the donor can be removed and replaced by the second polar body of the patient’s MII oocyte. (b) The donor’s MII oocyte is enucleated and injected with the partner’s sperm. Following the formation of the male pronucleus, the second polar body from a patient’s zygote can be transferred.

Figure 2

(A) Polar body 1 transfer (PB1T): The first polar body of a mature oocyte is transferred to a donor mature oocyte from which the spindle has been removed. Following reconstruction, the oocyte is fertilized, extruding the second polar body. (B) Spindle transfer (ST): The spindle of the patient’s oocyte can be transferred into an enucleated donor metaphase II (MII) oocyte. The reconstructed oocyte can be fertilized with the patient’s sperm and extrude the second polar body. (C) Polar body 2 transfer (PB2T): An oocyte of the donor is enucleated and fertilized with the sperm of the patient’s partner. A single pronucleus is being formed, containing only the genetic material of the partner. Polar body 2 resulting from PB1T or ST can be transferred to the zygote, including now the genetic material of the patient and the correct genetic load.