The new technique could remove the need to deliberately destroy embryos for stem cells.Punchstock

Researchers have succeeded in developing a human embryonic stem-cell line from an embryo that had died naturally.

The development may offer a non-problematic source of embryonic cells in countries such as Germany and the United States where the law does not allow the use of cell lines whose creation caused the destruction of embryos.

If the work bears fruit, researchers could instead create stem-cell lines from embryos that had naturally stopped developing during in vitro fertilization procedures.

"Fewer than half of human eggs fertilized in vitro do not develop to the 'blastocyst' stage, which is required for implantation," says Miodrag Stojkovic, who led the project at the University of Newcastle in the UK. He is now deputy director of the Principe Felipe Research Centre in Valencia, Spain. "There are many different reasons why they don't survive."

Arrested development

Stojkovic used 161 donated embryos in his study, which is scheduled to be published in Stem Cells¹. The embryos came from two local in vitro fertilization clinics. Of these, 29 were developing, 119 'arrested' (stopped dividing) 3 to 5 days after fertilization, and 13 arrested 6 to 7 days after fertilization.

Arrested embryos were monitored for up to two days to make sure they would not revive, thus meeting the standard embryologists' criteria for being dead.

Stojkovic's team derived healthy embryonic stem-cell lines from one of the 13 late-arrested embryos, along with eight of the normally developing embryos. They had no success using embryos that arrested early.

Only a few of the cells, called blastomeres, in the arrested embryos had remained healthy — many had distorted shapes or damaged chromosomes. "But there were enough undamaged blastomeres to allow us some limited success," says Stojkovic.

The efficiency of the process is very low at the moment, but scientists may be able to improve on this in the future, he says.

Maximum potential

Stojkovic says he did not set out to find ways to address the concerns of politicians, but rather to maximize the use of donated material. "I think that if you are given donated human embryos for research, you have a moral duty to use as much of the material as possible — and we have now found that we don't have to discard half of the embryos immediately, as we used to."

Nevertheless, stem-cell scientists in countries with restrictive embryo-protection laws are excited by the potential of Stojkovic's achievement. "There is no destruction of an embryo," says Hans Schöler, a director of the Max Planck Institute for Molecular Biomedicine in Münster, Germany. "If everything is confirmed, I don't see how anyone could attack such cell lines as unethical."

Schöler has been critical of another recent paper on 'ethically acceptable' embryonic stem cells. That paper, by Robert Lanza and his colleagues from Advanced Cell Technologies in Worcester, Massachusetts, proved in principle the idea that human embryonic stem-cell lines can be created without destroying embryos, but did not actually do it (see ''Ethical' stem-cell paper under attack'). This method, which Lanza is pursuing, could theoretically be used to create an embryonic stem-cell line from an embryo that grows into a healthy baby.

So why have researchers not done this before? Stojkovic says the procedure is difficult, and puts his success down to the methodology. "We had to try a lot of tricks to coax the blastomeres to grow," he says, including removing the sheath of the embryo and using very specific culture conditions.

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Max Planck Institute for Molecular Biomedicine in Münster, Germany

• References

  1. Zhang X., et al. Stem Cells Express, (in the press) (2006).