Prime Editing Enters a Wilson Disease Trial, With Human Results Still to Come

Prime editing has reached a new clinical milestone: the first patient in a trial for Wilson disease has received an infusion designed to alter DNA inside the body. The treatment, PM577a, aims to correct a disease causing mutation in liver cells. This is an early human study, so it has not yet shown whether the approach is safe or can control the disease. Results are expected next year.

The goal is a one-time treatment that lowers copper buildup before it causes lasting damage to the liver, nerves, or brain. That possibility remains a hypothesis. People with Wilson disease can manage it with lifelong medical treatment, and the new trial must establish whether editing liver cells can offer a safe, durable benefit.

Why prime editing is different

Prime editing is a CRISPR based method introduced in 2019. It uses a targeting molecule called pegRNA to guide the editor to a chosen stretch of DNA and provide a template for the intended change. The machinery makes a nick in one DNA strand, then copies the instructions into the genome. In laboratory tests, the approach has been used to replace DNA letters, add genetic code, and remove short sequences.

That range matters because different mutations require different repairs. Base editors can change certain DNA letters without deliberately cutting both strands, but they cannot make every possible letter swap. Prime editing may cover more types of small genetic changes, though the theoretical estimate that it could address up to 89 percent of disease associated variants is not evidence that it can treat that share of conditions in patients.

Conventional CRISPR-Cas9 usually cuts both strands of DNA. The cell then repairs the break, and that repair can create unintended changes. Researchers have reported cases where a single cut led to the loss of large chromosome sections. Prime editing and base editing were developed in part to avoid this kind of double strand break, but they still require careful testing for unintended edits and other harms.

Gene editing has already entered medical care through a different route. Casgevy, approved in 2024 for sickle cell disease and beta thalassemia, uses CRISPR-Cas9 on blood stem cells outside the body. Those edited cells are returned to the patient after treatment. PM577a instead packages its editor in lipid nanoparticles aimed at the liver and delivers it through an infusion.

Evidence behind the Wilson disease trial

Wilson disease results from mutations affecting a protein that moves copper out of liver cells. When that process fails, copper can accumulate and progressively injure the liver and nervous system. PM577a targets what Prime Medicine describes as the most common disease causing mutation in the United States and Europe. The company says correcting 20 to 30 percent of liver cells may be enough to produce a benefit, though that threshold has not been established in people receiving this treatment.

Animal findings offered a reason to proceed, but they are preliminary. In monkeys, one infusion edited about half of liver cells, with no notable changes reported in liver function, blood chemistry, or immune response. In mice modeling Wilson disease, the editor corrected 80 percent of cells with few off target edits. The company presented those results at a 2024 liver disease meeting; they have not been published in a peer reviewed journal. Animal results cannot establish how the treatment will behave in people.

The first patient’s infusion marks the start of testing in humans, not proof that the treatment works. Early trial results will need to show how participants tolerate the editor. Later evidence will need to establish whether it reduces excess copper, protects organs, and keeps its effects over time. A favorable safety profile in animals does not settle those questions.

What earlier editing studies add

Prime editing was previously tested in an approach for chronic granulomatous disease, a rare immune disorder. In one form of the disease, two DNA letters are missing. The edit aimed to restore them, a repair that conventional CRISPR-Cas9 and current base editing approaches cannot reliably make.

In an earlier study, researchers edited blood stem cells collected from two patients and returned the cells after chemotherapy cleared existing stem cells. Within a month, both patients had neutrophils capable of producing chemicals that kill pathogens. One patient’s reported benefit lasted at least six months. Most side effects were attributed to the chemotherapy, which is part of the cell transplant process. These results are encouraging but involve very few patients and edited cells outside the body.

Prime Medicine later stopped developing that treatment on its own and shifted attention toward editing genes directly inside the body. The company cited the cost of producing a custom batch of edited cells for each person as part of the reason. The Wilson disease trial tests whether delivery through the bloodstream can make that approach practical for a liver target.

For patients and families, the near term takeaway is that prime editing has moved from laboratory and animal work into an initial human test for Wilson disease. The next evidence to watch is whether PM577a is tolerated and whether copper levels and disease related measures improve over time. Researchers also say the delivery system may eventually be adapted to other Wilson disease mutations, including variants more common in other parts of the world. That broader use remains a possibility, not a result of the current trial.