The research team, led by Dr Yong Fan of the Guangzhou Medical University in China, used CRISPR/Cas9 to introduce a particular mutation into the CCR5 gene. People with this mutation are known to be resistant to HIV infection because the altered CCR5 protein prevents the virus from entering T cells.
The study, published in the Journal of Assisted Reproduction and Genetics, involved 213 human embryos donated by patients undergoing IVF. The embryos could not be used for fertility treatment as they each had extra set of chromosomes and so were not viable.
Dr Fan and this team performed the CRISPR technique on 26 embryos but found that this resulted in only four containing the intended CCR5 mutation. Even in those cases, the mutation was not found in all the embryo's cells. The researchers also detected 'off-target' effects, with unintended mutations being picked up in other locations in the genome.
The embryos were all destroyed after three days.
The researchers acknowledge the ethical issues involved, but argue that this type of proof-of-principle research should continue while these are debated. 'We believe that any attempt to generate genetically modified humans through the modification of early embryos needs to be strictly prohibited until we can resolve both ethical and scientific issues,' they write.
'This paper doesn't look like it offers much more than anecdotal evidence that it works in human embryos, which we already knew. It's certainly a long way from realising the intended potential [of a human embryo with all its copies of CCR5 inactivated],' Professor George Daley, a stem-cell biologist at Children's Hospital Boston in Massachusetts, told Nature News.
In January, Dr Kathy Niakan of the Francis Crick Institute was given permission by the HFEA to use CRISPR to begin genetically editing human embryos in order to research the mechanisms of early miscarriage (see BioNews 837). But Professor Daley says that Dr Niakan's research is intrinsically different because it's about answering fundamental questions of embryology, whereas Dr Fan's is about generating an individual with resistance to HIV. 'That means the science is going forward before there's been the general consensus after deliberation that such an approach is medically warranted,' said Professor Daley.