At meeting on guardrails for gene editing of human embryos, some call for a dead end

WASHINGTON — Keith Joung knows better than a lot of people what, exactly, it might require to prove to regulators and patients that CRISPR could be safely used to alter the genome of a human embryo. If, of course, society decided that was a good idea. Joung, an early pioneer of the gene-editing technology, was the first to show CRISPR could target and cut DNA inside an embryo — in zebrafish — back in 2013.

Not long after, his group was among the earliest to discover that CRISPR could get a bit sloppy — inadvertently slicing up unintended regions of the genome in all sorts of cells — complicating hopes it might be used to cure illnesses from cancer to muscular dystrophy. A pathologist by training, Joung has spent much of the intervening decade designing ever-more sensitive methods for detecting these so-called off-target effects and finding ways to minimize the chances they occur.

Such methods have, in the last two years, proved pivotal in the decisions by regulators to approve the first CRISPR-based medicine — an infusion of gene-edited blood...