Nature has more on the (non-viable) human embryos that were modified to resist HIV before being destroyed:
Researchers in China have reported editing the genes of human embryos to try to make them resistant to HIV infection. Their paper — which used CRISPR-editing tools in non-viable embryos that were destroyed after three days — is only the second published claim of gene editing in human embryos.
In the paper, Fan, who works at Guangzhou Medical University in China, and his team say that they collected a total of 213 fertilized human eggs between April and September 2014. The fertilized eggs, donated by 87 patients, were unsuitable for implantation as part of in vitro fertility therapy, because they contained an extra set of chromosomes.
Fan’s team used CRISPR–Cas9 genome editing to introduce into some of the embryos a mutation that cripples an immune-cell gene called CCR5. Some humans naturally carry this mutation (known as CCR5?32) and they are resistant to HIV, because the mutation alters the CCR5 protein in a way that prevents the virus from entering the T cells it tries to infect.
Genetic analysis showed that 4 of 26 human embryos targeted were successfully modified. But not all the embryos’ chromosomes harboured the CCR5?32 mutation — some contained unmodified CCR5, whereas others had acquired different mutations.
George Daley, a stem-cell biologist at Children’s Hospital Boston in Massachusetts, says that the paper’s main advance is the use of CRISPR to introduce a precise genetic modification successfully.