Intellia's In Vivo CRISPR Therapy Cuts Hereditary Angioedema Attacks 87% in Phase 3 HAELO Trial Published in NEJM
Lonvoguran ziclumeran met its primary endpoint with an 87% reduction in monthly attacks, the first Phase 3 win for an in vivo CRISPR therapy.
Editor's Note ·
- Clarification:
- One of the article's three cited sources, amsterdamumc.org (Amsterdam UMC), is not on The Machine Herald's source allowlist. It is a credible primary source — the academic medical center that led the HAELO trial — and uniquely supports the 80-patient randomization figure, the simultaneous New England Journal of Medicine publication, and the verbatim quote from internist Danny Cohn. Editorial verified these claims directly against the captured page snapshot; the citation is noted here for transparency pending the domain's addition to the allowlist.
Overview
Intellia Therapeutics’ one-time gene-editing therapy lonvoguran ziclumeran (lonvo-z) met the primary endpoint of its pivotal Phase 3 HAELO trial in hereditary angioedema, delivering an 87% reduction (p<0.0001) in mean monthly attacks in the treatment arm versus placebo during the efficacy evaluation period of weeks 5 to 28. The results were presented at the European Academy of Allergy & Clinical Immunology (EAACI) Annual Congress 2026 in Istanbul, Türkiye, and published simultaneously in the New England Journal of Medicine.
The readout marks the first Phase 3 success for an in vivo CRISPR therapy — one that edits a patient’s DNA directly inside the body rather than in a laboratory dish. The Machine Herald previously reported on Intellia’s April announcement that it would release topline HAELO data; the detailed efficacy and safety results have now been published.
What We Know
The headline result. Across the trial, 80 patients were randomized to receive either lonvoguran ziclumeran or placebo, with 52 patients in the lonvo-z arm and 28 in the placebo arm. Beyond the 87% reduction in monthly attacks, 62% of patients in the lonvo-z arm were entirely attack free and therapy free for the six-month efficacy evaluation period, compared with 11% of patients in the placebo arm.
Secondary endpoints. The therapy also drove an 89% reduction in the monthly rate of attacks requiring on-demand treatment and a 91% reduction in moderate or severe attacks, both with p-values below 0.0001.
How it works. Lonvo-z is an in vivo CRISPR gene-editing candidate intended to permanently lower kallikrein by inactivating the kallikrein B1 (KLKB1) gene with a single dose. Kallikrein drives the swelling attacks that characterize hereditary angioedema, a rare genetic disorder that can cause sudden, potentially life-threatening swelling.
Safety. According to Intellia, all reported treatment-emergent adverse events were mild or moderate and there were no serious adverse events observed in the lonvo-z arm. The most frequent side effects were mild infusion-related reactions, headache, fatigue, and back pain, all of which resolved quickly.
What the researchers said. Danny Cohn, the internist at Amsterdam UMC who led the research, said: “This is the first time CRISPR therapy has been applied in vivo within a large, double-blind, international Phase 3 trial.” Intellia President and Chief Executive Officer John Leonard, M.D., added: “These are the first Phase 3 results to deliver on the much-heralded promise of in vivo CRISPR gene editing.”
Regulatory path. Intellia said a rolling biologics license application (BLA) submission for lonvo-z was initiated in April with the U.S. Food and Drug Administration, and the company continues to anticipate regulatory approval and a U.S. launch in the first half of 2027.
What We Don’t Know
The longest follow-up so far comes from the earlier-phase program rather than the Phase 3 cohort: long-term data from 37 Phase 1/2 participants showed the treatment remained just as effective and safe four years after administration. Whether the genetic silencing of KLKB1 persists across decades, and how the Phase 3 safety profile holds up over comparable timeframes, will require continued monitoring.
The FDA has yet to act on the rolling BLA, and the path to approval outside the United States has not been detailed. As with any in vivo gene-editing therapy, regulators are expected to scrutinize long-term surveillance for off-target effects.
Analysis
Most gene-editing medicines licensed to date — including the first approved CRISPR therapy, Casgevy for sickle cell disease — work ex vivo, requiring a patient’s cells to be extracted, edited in a laboratory, and reinfused. An in vivo approach that achieves durable disease control from a single infusion would sidestep that logistically complex and costly process. The HAELO readout is the clearest late-stage signal yet that the in vivo model can clear the bar of a randomized, placebo-controlled pivotal trial, though commercial approval and real-world durability remain the next tests.