CRISPR (clustered regularly interspaced short palindromic repeats)-related technologies are emerging therapeutic strategies to induce DNA modifications in humans. In this regard, gene editing of proprotein convertase subtilisin/kexin type 9 (PCSK9) might represent a promising approach for the prevention of coronary heart disease (CHD). The present study1 investigates the impact of a single-nucleotide PCSK9 loss-of-function mutation by CRISPR adenine base editors (ABE) on low-density lipoprotein cholesterol (LDL-C) levels in non-human primates.

• To introduce a precise single-nucleotide PCSK9 loss-of-function mutation, a CRISPR ABE was delivered in macaques using lipid nanoparticles (LNPs). Adenine base editors of PCSK9 was confirmed in primary human hepatocytes, primary monkey hepatocytes, and mice.

• In vivo CRISPR ABE delivery led to a near-complete knockdown of PCSK9 in the liver after a single infusion of LNPs, with concomitant reductions in blood levels of PCSK9 and LDL-C of 90% and 60%, respectively. These changes were sustained for at least 8 months after a single-dose treatment. No relevant side effects were observed in the animals treated with a CRISPR editor-based strategy.

• Off-target gene editing was found at only one site in macaque liver, whereas no off-target editing was found in human hepatocytes.

In vivo CRISPR base editing of PCSK9 durably lowers cholesterol in primates

Gene-editing technologies, which include the CRISPR–Cas nucleases1,2,3 and CRISPR base editors4,5, have the potential to permanently modify disease-causing genes in patients6. The demonstration of durable editing in target organs of nonhuman primates is a key step before in vivo administration of gene editors to patients in clinical trials. Here we demonstrate that CRISPR base editors that are delivered in vivo using lipid nanoparticles can efficiently and precisely modify disease-related genes in living cynomolgus monkeys (Macaca fascicularis).

We observed a near-complete knockdown of PCSK9 in the liver after a single infusion of lipid nanoparticles, with concomitant reductions in blood levels of PCSK9 and low-density lipoprotein cholesterol of approximately 90% and about 60%, respectively; all of these changes remained stable for at least 8 months after a single-dose treatment. In addition to supporting a ‘once-and-done’ approach to the reduction of low-density lipoprotein cholesterol and the treatment of atherosclerotic cardiovascular disease (the leading cause of death worldwide7), our results provide a proof-of-concept for how CRISPR base editors can be productively applied to make precise single-nucleotide changes in therapeutic target genes in the liver, and potentially in other organs.