CRISPR-Cas is a defense system that evolved in single-celled organisms to target and destroy viruses. Researchers have harnessed the precision-targeting nature of this exquisitely sensitive system to edit specific sections of DNA and RNA, from any organism, in a wide range of applications.1 From eradicating malaria through gene drives in wild mosquitoes,2 to engineering food crops resistant to disease and climate change,3 the possibilities seem endless—especially in therapeutic medical applications to cure diseases.