Human embryos cloned using immature eggs
Dr. Kirsty Horsey
Progress Educational Trust27 June 2005
BioNews reporting from ESHRE conference, Copenhagen: A team of Belgian scientists has managed to clone human embryos using egg cells matured in the laboratory. The achievement, reported at the annual conference of the European Society of Human Reproduction and Embryology (ESHRE), could help overcome the shortage of donated eggs available for 'therapeutic cloning' research. The researchers, based Ghent University, say their work could eventually lead to new infertility treatments using artificial eggs and sperm.
Many scientists think that research on ES cells obtained from cloned human embryos could lead to new therapies for a range of disorders. But such research requires a supply of mature human eggs, of which there is a shortage since nearly all those retrieved are currently used in fertility treatments. However, immature eggs are not routinely used for treating infertility patients, and so can be donated for research purposes.
Bjorn Heindryckx and his colleagues grew immature human egg cells in the laboratory for 44 hours, after which time 85 per cent had developed into mature eggs. They then removed the genetic material from these cells and replaced it with the nuclei of cumulus cells (egg-nurturing cells) taken from another individual, before activating cell division. Eighteen of the 25 matured egg cells survived this nuclear transfer process, of which five grew to the two-cell stage. Three of these embryos grew to the six-ten cell stage, one of which continued growing to the 'compacted' stage, where individual cells start to flatten and increase their contact with each other.
The team say that to their knowledge, it is the first time that cloned embryos have been created using eggs matured in the laboratory. 'Our final goal is to use human therapeutic cloning for infertility treatment by creating artificial eggs and sperm for patients who are infertile because of absence or premature loss of eggs or sperm', said Heindryckx. However, he warned that there were still many problems to overcome before this goal could be reached, not least the fact that none of these embryos developed to the blastocyst stage (around five days), when embryonic stem (ES) cells can be isolated.
Another study presented at the meeting could potentially help overcome this problem. US scientists have managed to obtain ES cells from mouse embryos that had not reached the blastocyst stage of development. Researchers based at Weill Medical College of Cornell University in New York took individual cells from mouse embryos that had reached the eight-cell stage, two days after fertilisation. Of 46 such cells, 43 started to grow and divide in the laboratory. After two days, 22 formed an 'inner cell mass' - the structure in which ES cells are found, from which the team managed to grow one ES cell line.
Team member Ameeta Bahia told delegates that if the technique could be replicated in humans, it would 'reduce wastage of precious material'. The scientists plan to test their method on single cells removed from embryos during preimplantation genetic diagnosis treatment.
Reproduced with permission from BioNews, an email and online sources of news, information and comment on assisted reproduction and genetics.