Since the CRISPR genome editing technology was invented in 2012, it has shown great promise to treat a number of intractable diseases. However, scientists have struggled to identify potential off-target effects in therapeutically relevant cell types, which remains the main barrier to moving therapies to the clinic. Now, a group of scientists at the Gladstone Institutes and the Innovative Genomics Institute (IGI), with collaborators at AstraZeneca, have developed a reliable method to do just that.