The genome-editing tool CRISPR-Cas9 is revolutionizing the field of medicine. The technology, which took off in popularity among researchers about five years ago, can precisely edit DNA. The system includes two components: a DNA-cutting enzyme, called Cas9, and a piece of RNA, called guide RNA. A bit of guide RNA targets a specific chunk of DNA, directing Cas9 exactly where in the genome to snip. But slicing and dicing DNA isn’t without risks. Some researchers have been wary from the get-go, perhaps rightly so as details emerge about CRISPR’s sometimes-troubling safety record.
CRISPR’s Roller Coaster Safety Ride
The pro-CRISPR camp scored a win in March, when Nature Methods retracted a 2017 paper that had stirred controversy. The researchers originally said their CRISPR-edited mice had large numbers of so-called off-target mutations that resulted from Cas9 cutting at places other than the intended location. But the journal pulled the study because the authors couldn’t show if the changes came from gene editing or if they were pre-existing natural variations.
Over the summer, however, a series of papers looking at other aspects of CRISPR raised the specter of cancer. In June, two Nature Medicine studies reported a disturbing tendency. The gene editor was more difficult to use in healthy cells than in cells that lacked a key tumor-suppressing protein called p53. The findings suggest CRISPR might select for tumor-prone cells. “If you put this back into a patient, there’s a certain risk that these cells that have a p53 deficiency might cause cancer in the long term,” says Bernhard Schmierer, a researcher at the Karolinska Institute in Sweden, and a senior author of one of the studies.
