Prime Medicine receives FDA clearance to run first prime editing clinical trial

The FDA has OK’d the first-ever human trial of prime editing, Prime Medicine announced Monday, opening the door for testing a new technology that backers hope will widen the array of diseases that can be treated with gene editing.

Prime’s experimental therapy, PM359, is a treatment for chronic granulomatous disease (CGD), a rare genetic condition in which phagocytes — a white blood cell type important for fighting infections — don’t work properly. Typically diagnosed in early childhood, it can cause people to get seriously ill from bacteria or fungi that normally would cause few or no symptoms.

CGD is caused by mutations to the genes encoding for a key enzyme called the NADPH oxidase that the white blood cells need to fend off infections. Prime Medicine’s treatment is meant to correct the gene mutated in one of the variants of CGD.

The ex vivo therapy involves first extracting blood stem cells from the patient and then sending them to a lab, where prime editing would then be used with the goal of correcting the mutation. The cells would then be infused back into the patient, hopefully to restore long-term immune function.

David Liu

Prime editing is a newer type of gene editing that can rewrite short segments of DNA and doesn’t require double-stranded breaks, as with CRISPR/Cas9. It was developed by David Liu’s lab at the Broad Institute of MIT and Harvard, and was first described in a landmark 2019 paper. Liu and then-postdoc Andrew Anzalone founded Prime Medicine based on the technology.

The FDA has previously been cautious around clearing human studies of new gene editing treatments, leading some companies to begin their trials outside of the US. However, Prime’s trial was given the go-ahead without delay (the agency has a 30-day review window for new trials, after which companies can proceed if regulators don’t object).

“Clearance bucks the trend where first-of-its-kind technologies have faced setbacks (i.e., clinical hold) at the IND stage,” Stifel analyst Dae Gon Ha wrote in a note on Monday. Its shares $PRME rose 11% Monday morning.

Prime plans to run a Phase 1/2 study for PM359 beginning with a handful of adult participants with stable disease, before enrolling teenagers and children in the study. Initial data on the adult participants are expected in 2025, according to Prime.