Seeking to allay concerns, the researchers led by Junjiu Huang at Sun Yat-sen University in Guangzhou said the team used “non-viable” embryos, which cannot result in a live birth. He said they had been obtained from local fertility clinics.
But scientists expressed unease. George Daley, a stem-cell biologist at Harvard Medical School in Boston, told Nature “the study is a landmark, as well as a cautionary tale”.
The Chinese esearchers attempted to replace the gene responsible for a potentially fatal blood disorder called β-thalassaemia using a gene editing technique called CRISPR/Cas9.
The technique used by Huang’s team involves injecting embryos with the enzyme complex CRISPR/Cas9, which binds and splices DNA at specific locations. The complex can be programmed to target a problematic gene, which is then replaced or repaired by another molecule introduced at the same time. The system is well studied in human adult cell and in animal embryos. But there had been no published reports of its use in human embryos.
But Nature reports that procedure was successful in only a fraction of the 86 embryos. What’s more the CRISPR/Cas9 approach also introduced new mutations into other, unintended places in the genome.
“Their study should be a stern warning to any practitioner who thinks the technology is ready for testing to eradicate disease genes,” Daley said.
Huang agreed. “If you want to do it in normal embryos, you need to be close to 100%,” Huang says. “That’s why we stopped. We still think it’s too immature.”
Before the report, rumours of the study had already raised concerns about the practice. In an article in Nature last month, a group of eminent biomedical researchers warned against editing the DNA of human embryos.
“There are grave concerns regarding the ethical and safety implications of this research. There is also fear of the negative impact it could have on important work involving the use of genome-editing techniques in somatic (non-reproductive) cells,” they wrote.