In a milestone for gene-editing science, Prime Medicine has dosed the first human patient with an in vivo prime editing therapy, dubbed PM577a, earlier this month. This marks the first reported instance of prime editing—a next-generation DNA rewriting technique—being administered directly inside a living person’s body. The trial, now underway, targets Wilson disease, a genetic disorder that prevents the body from eliminating excess copper due to a mutation in the ATP7B gene.
How Prime Editing Differs from CRISPR
Traditional CRISPR–Cas9 gene editing is already famous for its ability to snip out faulty genetic code, but it cuts both strands of DNA, which can sometimes lead to unwanted changes. Prime editing, by contrast, makes a single nick in DNA and uses a specialized guide RNA to introduce precise corrections—effectively acting as a molecular word processor that can insert, delete, or rewrite DNA segments with high accuracy.
For this trial, Prime Medicine’s PM577a therapy was delivered through a one-time intravenous infusion. Lipid nanoparticles carried the editing machinery straight to the patient’s liver cells, where the therapy aimed to fix the H1069Q mutation in the ATP7B gene. The company has announced that public results from this Phase 1/2 study are expected in 2027.
What Makes This Trial a First?
Until now, prime editing in humans had only been attempted outside the body—in so-called ex vivo therapies, where cells are edited externally and then reinfused. The first ex vivo prime-edited treatment reached a patient in 2025. This new trial, however, involves editing DNA directly within the patient’s liver—a leap forward for the field.
No in vivo gene-editing therapy has yet won regulatory approval. However, the U.S. FDA is expected to rule early next year on an in-body CRISPR–Cas9 treatment for hereditary angioedema, another genetic disorder. If successful, Prime Medicine’s approach could pave the way for precise, one-time treatments for a range of inherited diseases.
So far, the company has not released data on whether the intended DNA correction occurred or if the patient benefited. However, the mere administration of in vivo prime editing represents a significant step in the quest to cure genetic diseases at their source.
