CRISPR's Most Precise Tool Just Rewrote Human DNA From the Inside Out

A Historic First in Gene Editing

Biotechnology company Prime Medicine has dosed the first human patient in a global Phase 1/2 clinical trial of PM577a, marking the first time a prime editing therapy has been administered directly inside a living body. The milestone, reached in October 2026, represents a new frontier for genetic medicine — one where doctors don't need to remove a patient's cells, fix them in a lab, and put them back. Instead, the editing machinery goes straight to the source.

In launching the trial, Prime Medicine joins a host of companies aiming to engineer cells directly in the body, rather than using the standard method of extracting a person's cells, editing their DNA in a laboratory and then reinjecting the altered cells. Rewriting DNA in the body, or *in vivo*, is appealing because manufacturing and administering the treatment might be much cheaper and faster than making a bespoke therapy for each person from their own cells.

What Is Wilson Disease — and Why Is It So Hard to Treat?

Wilson's disease is caused by mutations in a gene called *ATP7B*, which encodes a protein that transports excess copper out of the liver. If left untreated, the resulting build-up of copper can cause liver and nerve damage, as well as neurological disorders. Most patients currently manage the condition with lifelong copper-clearing medication — a burden that PM577a aims to eliminate with a single treatment.

PM577a is designed as a one-time therapy to correct the H1069Q mutation in ATP7B, which Prime Medicine described as the most prevalent Wilson disease-causing mutation in North America and Europe. The company is also developing a follow-on candidate for R778L, the most common Wilson mutation in East Asian populations. That means the program, if successful, could eventually reach patients across the globe.

How the Treatment Actually Works

PM577a is packaged in lipid nanoparticles — tiny fat-based particles that are taken up mainly by the liver after an intravenous infusion. The particles carry the editing instructions into liver cells, where the edit is made and the editing molecules are then broken down. The corrected gene stays, and it is passed on whenever an edited liver cell divides. That last point is crucial: this isn't a temporary fix. It's a permanent rewrite.

Another form of gene editing, called base editing, can rewrite individual DNA letters, but cannot make the particular corrections needed to fix the most common *ATP7B* mutations. That left prime editing, a more complex and versatile system that can insert, delete, and rewrite segments of DNA. Think of base editing as a pencil that can only erase certain marks — prime editing is the full toolkit.

What Comes Next

The open-label study will evaluate ascending doses of PM577a in adults and adolescents carrying at least one p.H1069Q allele, with efficacy assessments including copper efflux by 64Cu PET, serum ceruloplasmin, non-ceruloplasmin-bound copper, and 24-hour urinary copper excretion. The trial will also evaluate discontinuation of baseline standard-of-care therapies — meaning researchers want to know if patients can stop taking their daily medications entirely.

The FDA has granted Rare Pediatric Disease designation to the PM577 program , a status that could accelerate its path to approval. The trial must show that lipid nanoparticles deliver the editor efficiently enough in people, that editing is precise with minimal unintended changes, and that copper handling actually improves. As with any permanent edit, patients will need long-term follow-up. First results are expected in 2027 — and the gene-editing world will be watching closely.