Using genome editing to inactivate a protein called PCSK9 effectively reduces cholesterol levels in rhesus macaques, a species of monkey, according to researchers from the Perelman School of Medicine at the University of Pennsylvania. This is the first demonstration of a clinically relevant reduction of gene expression in a large animal model using genome editing. The team published their study this week in Nature Biotechnology, in which they describe a possible new approach for treating heart disease patients who do not tolerate PCSK9 inhibitors—drugs that are commonly used to combat high cholesterol.