In a world first, Chinese scientists have reported editing the genomes of human embryos. The results are published1 in the online journal Protein & Cell and confirm widespread rumours that such experiments had been conducted — rumours that sparked a high-profile debate last month2, 3about the ethical implications of such work.
In the paper, researchers led by Junjiu Huang, a gene-function researcher at Sun Yat-sen University in Guangzhou, tried to head off such concerns by using ‘non-viable’ embryos, which cannot result in a live birth, that were obtained from local fertility clinics. The team attempted to modify the gene responsible for β-thalassaemia, a potentially fatal blood disorder, using a gene-editing technique known as CRISPR/Cas9. The researchers say that their results reveal serious obstacles to using the method in medical applications.
“I believe this is the first report of CRISPR/Cas9 applied to human pre-implantation embryos and as such the study is a landmark, as well as a cautionary tale,” says George Daley, a stem-cell biologist at Harvard Medical School in Boston, Massachusetts. “Their study should be a stern warning to any practitioner who thinks the technology is ready for testing to eradicate disease genes.”
Some say that gene editing in embryos could have a bright future because it could eradicate devastating genetic diseases before a baby is born. Others say that such work crosses an ethical line: researchers warned in Nature2 in March that because the genetic changes to embryos, 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 on human embryos could be a slippery slope towards unsafe or unethical uses of the technique.
The paper by Huang’s team looks set to reignite the debate on human-embryo editing — and there are reports that other groups in China are also experimenting on human embryos.
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 cells and in animal embryos. But there had been no published reports of its use in human embryos.
Huang and his colleagues set out to see if the procedure could replace a gene in a single-cell fertilized human embryo; in principle, all cells produced as the embryo developed would then have the repaired gene. The embryos they obtained from the fertility clinics had been created for use inin vitro fertilization but had an extra set of chromosomes, following fertilization by two sperm. This prevents the embryos from resulting in a live birth, though they do undergo the first stages of development.
Huang’s group studied the ability of the CRISPR/Cas9 system to edit the gene called HBB, which encodes the human β-globin protein. Mutations in the gene are responsible for β-thalassaemia.