by DAVID CYRANOSKI, SARA REARDON, and NATURE MAGAZINE
Human embryos are at the centre of a debate over the ethics of gene editing. IMAGE/Ed Uthman/Flickr
In a world first, Chinese scientists have reported that they have used powerful gene-editing techniques to modify human embryos. Their paper, published in the Beijing-based journal Protein & Cell on April 18, came as no surprise to the scientific community, but it has ignited a wide-ranging debate about what types of gene-editing research are ethical. The publication also raises questions about the appropriate way to publish such work.
In the paper, researchers led by Junjiu Huang, a gene-function researcher at Sun Yat-sen University in Guangzhou, describe how they used a system of molecules called CRISPR/Cas9, known for its ease of use, to cut DNA in human embryos and then attempted to repair it by introducing new DNA.
In a deliberate attempt to head off ethical concerns, the team used non-viable embryos obtained from fertility clinics, in which eggs had been fertilized by two sperm and so could not result in a live birth.
Gene-editing techniques such as those that rely on CRISPR/Cas9 had previously been used to modify DNA in adult human cells and animal embryos. Earlier this year, rumours were circulating that the methods were being applied in human embryos too, but the Huang paper is the first published report of this.
The team used CRISPR/Cas9 to modify a gene that can cause a potentially fatal blood disorder called ?-thalassaemia when it is mutated. Some researchers have suggested that such a procedure, if done in a viable embryo, could eradicate devastating genetic diseases before a baby is born. Others say that such work crosses an ethical line: in response to the rumours that the work was being carried out, researchers warned in Nature and Science in March that because the genetic changes to embryos—a procedure known as germline modification—are heritable, they could have an unpredictable effect on future generations.
Researchers have also expressed concerns that any gene-editing research in human embryos could be a slippery slope towards unsafe, unethical or non-medical uses of the technique.
Serious obstacles
Huang’s team says that its results reveal serious obstacles to using the method in a clinical setting. The team injected 86 embryos with CRISPR/Cas9, along with other molecules designed to add in new DNA. The researchers then waited 48 hours, by which time the embryos would have grown to about eight cells each. Of the 71 embryos that survived, 54 were genetically tested. This revealed that just 28 were successfully spliced, and that only 4 of those contained the genetic material designed to repair the cuts. “That’s why we stopped,” says Huang. “We still think it’s too immature.”
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