Chinese researchers report this week that they have used the CRISPR gene-editing technique to modify the genome of a human embryo in an effort to make it resistant to HIV infection. The paper, reported on today by Nature News, is only the second-ever publication on the ethically fraught use 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. The researchers used flawed embryos that were not viable for fertility treatments and destroyed them after 3 days. A human embryo–editing paper from a different Chinese team published in April 2015 touched off a worldwide debate about the ethics of such experiments and led to calls for a research moratorium. 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. But according to the Nature News article, some experts question whether the CCR5-editing experiment needed to be done in human embryos.