US researchers have used the CRISPR gene-editing tool to alter a number of human embryos, according to MIT's Technology Review.
It reports that Oregon Health and Science University's Shoukhrat Mitalipov and his colleagues edited "many tens" of human embryos that were made through in vitro fertilization using sperm donated by men who carried inherited disease mutations. The embryos were not allowed to develop for more than a few days and were never going to be implanted, Tech Review says.
In 2015, researchers in China reported using CRISPR/Cas9 to modify the beta-globin gene, which is behind the blood disease beta-thalassemia, in non-viable human zygotes. This modification of the human germline led to a backlash in which others called the work immoral and premature. The following year another team in China reported editing the CCR5 gene in non-viable human embryos to make them resistant to HIV infection. And earlier this year, Chinese researchers also reported using CRISPR to repair mutations in three normal human embryos, as New Scientist notes.
Such earlier work had been plagued by mosaicism, Tech Review says, but it adds that Mitalipov and his colleagues worked around that by introducing the CRISPR system into the egg at the same time that it was fertilized.
Mitalipov declined to comment on the work to Tech Review, as it is under review for publication, but Tech Review says others have confirmed the embryos were edited using CRISPR.
"It is proof of principle that it can work. They significantly reduced mosaicism. I don't think it's the start of clinical trials yet, but it does take it further than anyone has before," a researcher with knowledge of the work tells Tech Review.
However, New Scientist adds that one of the problems with germline editing for genetic disease is "that there is actually little need for it." It notes that genetic diseases like cystic fibrosis can be prevented through screening and IVF.