The cutting edge can be slippery

Talk about repairing the airplane while in flight.

When Beam Therapeutics debuted last May, it had been just two years since co-founder David Liu of Harvard reported a new and possibly better way to CRISPR genomes, called base editing. Since then the Cambridge, Mass., company has hired up a storm (70 employees), raised boatloads of money ($135 million in Series B), and eyed ever-more diseases (10, undisclosed) that it will try to cure with base editing, which changes single nucleotides like an A to a G.

On Wednesday, though, Liu and his colleagues reported that one of Beam's best base editors, called ABEmax, edits RNA, not just the DNA it's supposed to. Liu called that "unanticipated," since even the 0.2% rate of RNA editing they found might cause cells to produce dysfunctional proteins. Beam thinks it has a fix, creating next-gen ABEs with lower RNA editing, but along with reports that base editors sometimes make off-target DNA edits, the surprises underline just how exciting it can be to launch a company based on brand new, barely tested technology.