CRISPR Slashes Rare Swelling Attacks by 87%

Intellia's lonvo-z slashed hereditary angioedema attacks 87% in a landmark Phase 3 trial, becoming the first in vivo CRISPR therapy to succeed at scale

15 May 2026

Intellia Therapeutics has reported that its gene editing treatment, lonvo-z, cut the frequency of hereditary angioedema attacks by 87 per cent compared with a placebo in a global Phase 3 trial, meeting every primary and secondary endpoint the study set out to test.

The HAELO trial results, published on April 27, mark the first time an in vivo CRISPR therapy, one that edits genes inside the living body rather than in a laboratory, has succeeded at this scale.

Sixty-two per cent of patients who received the treatment remained entirely free of attacks and required no preventive medication during the six-month observation period.

Lonvo-z works by delivering genetic material to liver cells via a lipid nanoparticle, a microscopic fat-based carrier, where it permanently switches off the KLKB1 gene. That gene drives production of a protein that triggers the swelling episodes central to the disease. The therapy is administered as a single outpatient infusion.

Hereditary angioedema causes sudden, unpredictable swelling in the throat, abdomen, and face, and can be fatal. Existing treatments require ongoing injections or daily oral medication. A one-time intervention that removes that burden represents a substantially different option for patients, clinicians, and insurers.

Intellia has begun a rolling biologics licence application with the US Food and Drug Administration, with a potential US launch targeted for the first half of 2027. Approval would make lonvo-z the first in vivo CRISPR therapy cleared anywhere in the world, a regulatory outcome the broader gene medicine industry will monitor closely.

Safety data from HAELO were broadly favourable, with adverse events limited to mild infusion-related reactions. Regulators and investors will nonetheless watch liver enzyme readings over time, given earlier safety signals in Intellia's wider pipeline. The FDA review timeline and the agency's assessment of longer-term data remain the central uncertainties.