A research team in China has attempted to modify human embryos so that they harbor inactivated CCR5 genes and are resistant to HIV infection, Nature News reports. CCR5 encodes a protein that HIV relies on to enter and infect T cells, and people with naturally occurring CCR5Δ32 mutations are resistant to the virus.
As Yong Fan from Guangzhou Medical University and colleagues report in the Journal of Assisted Reproduction and Genetics, they collected more than 200 fertilized eggs with a second polar body donated by 87 patients. The researchers used the CRISPR/Cas9 genome editing approach to target and disrupt exon 4 of the CCR5 gene within some of these early human tripronuclear embryos. While the researchers were able to successfully introduce the CCR5Δ32 allele in four of 26 embryos, the efficiency of the approach was limited such that the edited embryos were mosaic. The embryos used were non-viable.
As Nature News notes, this is the second reported instance of genome editing of a human embryo. The first report, from researchers at Sun Yat-sen University, touched off a storm of ethical questions and discussions about the proper use of gene-editing technology.
Tetsuya Ishii, a bioethicist at Hokkaido University, tells Nature News that there appears to be no issues with how this study was conducted as it was approved by a local ethics committee and as the donors gave informed consent. But, he suspects that it might not have been necessary to use human embryos. "Introducing CCR5Δ32 and trying repair, even in non-viable embryos, is just playing with human embryos," Ishii tells Nature News.
The paper, adds Emory University's Xiao-Jiang Li, "just emphasizes that there are still a lot of technical difficulties to doing precision editing in human embryo cells." He says that those issues should be resolved using non-human primates, rather than human embryos.