At a recent genome-editing meeting in Hong Kong, Dr. He Jiankui of the South University of Science and Technology in Shenzhen, China reported that he used CRISPR-based gene editing to create HIV-resistant humans by disabling copies of the CCR5 gene, whose product enables HIV to establish an infection. However, evidence supporting his claim is lacking, and data presented at the conference suggests that the twin sisters that were modified could still remain susceptible to HIV and other types of viral infection. In response, leaders of the U.S. National Academy of Sciences (NAS), U.S. National Academy of Medicine (NAM), and the Chinese Academy of Sciences (CAS) joined to author an editorial denouncing the work and calling for experts worldwide to define very clearly the types of genome-editing research that should be deemed off-limits. There is no questioning the potential power of gene-editing technologies to treat and possibly cure human disease. But scientists worldwide are united in the need for careful ethical and scientific oversight as these technological capabilities advance.