Scientists Use Cloning Tech to Swap DNA in Human Eggs

Several research teams around the world including Conception, a California biotech company, and Katsuhiko Hayashi and colleagues at Osaka university are working on in vitro gametogenesis — creating eggs and sperm in the lab.

The others use a different technique that does not require donated eggs, making pluripotent stem cells from skin and then trying to convert them into eggs. This has succeeded with mice but not yet produced mature human eggs, said Mitalipov.

The success of OHSU’s cloning approach, transferring the nucleus between mature cells rather than using stem cells, depended on achieving a new type of cell division called mitomeiosis. “Nature gave us two methods of cell division and we just developed a third,” said Mitalipov.

So far the process is quite inefficient. The OHSU team produced 82 functional eggs that were fertilised with sperm through IVF but only 9 per cent developed to the blastocyst stage at which embryos would be transferred to establish a pregnancy in an IVF clinic. None was cultured beyond this point and there is no evidence that any would have grown into a healthy foetus. In natural reproduction about a third of new human embryos become blastocysts.

“We still have a lot of difficult work ahead to sort out the intricate process by which chromosomes pair and separate to create healthy embryos,” said Mitalipov.