Intellia Therapeutics said its Crispr-based treatment for a rare swelling condition met its goals in a late-stage trial, marking a milestone for the field of gene editing and putting the company on track to seek approval from the U.S. Food and Drug Administration.

The company’s treatment uses Nobel Prize-winning technology Crispr to edit DNA and turn off the gene that controls production of a peptide that’s overactive in people with hereditary angioedema, causing them to experience potentially life-threatening swelling attacks. Intellia’s treatment is administered once through an hourslong infusion, making the edits directly in the liver.

Intellia said the one-time treatment reduced attacks by 87% compared with a placebo, meeting the study’s main goal. Six months after treatment, 62% of patients were free from attacks and weren’t using other therapies, Intellia said.

The company described the safety and tolerability of the treatment as “favorable,” reporting the most common side effects were infusion-related reactions, headaches and fatigue. Analysts were closely watching safety in the trial since a patient in a separate trial of a different treatment from Intellia died. That patient developed a liver injury and ultimately died from septic shock following an ulcer, according to the company.

“When you think about where we started with Crispr, just 12 years ago with some of the fundamental insights, I think there was a lot of talk about what might be possible, and we’ve had reports along the way in terms of milestones, but this is the first Phase 3 data in any indication with in vivo Crispr where you’re actually changing a gene that causes disease,” said Intellia CEO John Leonard.

The only FDA-approved Crispr-based medicine comes from Vertex Pharmaceuticals. Called Casgevy, the gene editing is done outside the body, or ex vivo. The process requires collecting a person’s blood cells, making the edits outside the body, then reinfusing them back into a patient. Intellia’s treatment, meanwhile, makes the edits inside the body, or in vivo.

Intellia said it has started a rolling application with the FDA and plans to complete the filing in the second half of this year. The company expects to launch the treatment in the U.S. in the first half of next year, if it’s approved.

If approved, Intellia’s treatment, lonvoguran ziclumeran, will compete with about a dozen other chronic drugs for HAE. Despite the allure of a one-time treatment, genetic medicines haven’t always been a commercial successes. BioMarin withdrew its gene therapy for Hemophilia A because of weak sales, for example.

Leonard said there are important differences between the two, like the fact that BioMarin’s therapy faced questions about how long the effects would last. In contrast, he said Intellia hasn’t seen a single case in almost six years where the effects diminished over time.

Despite the results, he’s reluctant to call Intellia’s treatment a functional cure.

“I think this is a tipping point for the disease and tipping point for Crispr-based in vivo therapy where you can make a change [and] it’s permanent,” Leonard said. “And, as far as we can tell, we don’t have a single patient in this program or other program where there’s been any waning of the effect of what we did to the gene or the effect of what we’ve seen with the clinical aspects of the disease itself. So it’s pretty exciting.”

Clarification: This story has been updated to clarify that a patient in a separate trial of a different treatment from Intellia developed acute liver injury and ultimately died from septic shock following an ulcer.