NIH is deeply concerned about the work just presented at the Second International Summit on Human Genome Editing in Hong Kong by Dr. He Jiankui, who described his effort using CRISPR-Cas9 on human embryos to disable the CCR5 gene. The need for development of binding international consensus on setting limits for this kind of research, now being debated in Hong Kong, has never been more apparent. Without such limits, the world will face the serious risk of a deluge of similarly ill-considered and unethical projects. Lest there be any doubt, and as we have stated previously, NIH does not support the use of gene-editing technologies in human embryos.