Second Chinese team reports gene editing in human embryos
Early-stage human embryos have been edited by scientists.
Researchers in China have reported editing the genes of human embryos to try to make them resistant to HIV infection. Their paper used CRISPR-editing tools in non-viable embryos that were destroyed after three days, and is only the second published claim of gene editing in human embryos.
According to the 6 April report in the Journal of Assisted Reproduction and Genetics, researchers at Guangzhou Medical University in China attempted—with limited success—to modify the CCR5 gene, which codes for a cell receptor that the HIV virus uses to enter T cells. Specifically the team 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. The 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 CCR5Δ32) 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 CCR5Δ32 mutation — some contained unmodified CCR5, whereas others had acquired different mutations.
In April 2015, a different China-based team announced that they had modified a gene linked to a blood disease in human embryos (which were also not viable, and so could not have resulted in a live birth). That report — a world first — touched off global deliberations over the ethics of modifying embryos and human reproductive cells, and led to calls for a moratorium on even such proof-of-principle research. However, an international scientific summit concluded in December 2015 that although gene-edited embryos should not be implanted in a woman’s uterus to establish a pregnancy, basic research in this area should continue. Exactly what research should take place is still controversial, however. U.K. officials have approved an embryo-editing study seeking to understand early human development.
Fan's work is establishing proof of principle for what would need to be done to generate an individual with resistance to HIV. This again fueled the worldwide debate on ethical and legal issues of germline modification. One thing for sure is that science is going forward before there’s been the general consensus after deliberation that such an approach is medically warranted.
Read more: Kang, X. et al. “Introducing precise genetic modifications into human 3PN embryos by CRISPR/Cas-mediated genome editing”, J. Assist. Reprod. Genet., April 2016
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