Nuclear transfer involves the isolation and transfer of nuclear genetic material to the egg environment. One type of nuclear transfer is used in cloning research and regenerative medicine, called somatic cell nuclear transfer (SCNT). Other types of nuclear transfer techniques are applied in basic research, and in clinical research with applications in assisted reproductive technologies, namely: germinal vesicle transfer (GVT), spindle transfer (ST), pronuclear transfer (PNT) and polar body transfer (PBT) [21, 27-31].
PNT was shown to be applicable in human zygotes without adverse impact on pre-implantation embryonic development or rate of euploidy . However, PNT typically results in >20% carryover which is not acceptable for cytoplasm replacement therapy compared to <2% carryover of the ST technique . Using a nuclear transfer-membrane fusion system, ST has been shown to be applicable in human oocytes, however the method exerts an adverse impact on the rate of oocyte fertilization [13, 33, 34], warranting more research and development to optimize the ST protocol for human preimplantation development.
PB transfer [20, 21, 23, 35] is a similar technique, where the first polar body transfer is an alternative for ST and has been applied successfully in generating human blastocysts with no adverse impact on preimplantation development [27, 28], and the second polar body transfer is an alternative for PNT but it has not been successfully applied in human gametes . Furthermore, the PB transfer technique has nearly undetectable carryover levels . These nuclear transfer techniques all involve the transfer of chromosomes to eggs at different developmental stages.