Intellia Therapeutics has reported positive Phase 3 results for lonvoguran ziclumeran in hereditary angioedema, marking what it said is the first successful late-stage trial for an in vivo CRISPR gene editing therapy.

The US biotech said its Haelo study met the primary endpoint and all key secondary endpoints, while it also began a rolling biologics license application submission to FDA seeking approval for the one-time treatment.

Hereditary angioedema is a rare genetic disease that causes recurrent swelling attacks which can become life-threatening when they affect the airway. Many patients require long-term preventative treatment and can still experience breakthrough attacks.

Lonvoguran ziclumeran, also known as lonvo-z and previously NTLA-2002, is designed as a one-time outpatient infusion. It uses in vivo CRISPR gene editing to inactivate the KLKB1 gene, aiming to permanently reduce kallikrein activity and lower bradykinin levels linked to attacks.

In the placebo-controlled Phase 3 trial, 80 patients were enrolled, with 52 receiving lonvo-z and 28 receiving placebo. Intellia said 71% of participants were using long-term prophylaxis at study entry and had to stop treatment before dosing.

During the six-month efficacy evaluation period from weeks five to 28, Intellia said a single dose of lonvo-z reduced attacks by 87% versus placebo. Mean monthly attack rate was 0.26 in the treatment arm compared with 2.10 in the placebo group.

The company added that 62% of patients receiving lonvo-z were completely attack free and therapy free during the same period, compared with 11% in the placebo arm.

Safety data released by the company showed the most common treatment emergent adverse events were infusion-related reactions, headache and fatigue. Intellia said all adverse events reported up to the February 10 2026 data cutoff were mild or moderate, with no serious adverse events observed in the lonvo-z arm.

John Leonard, president and chief executive officer of Intellia, said: “As the first Phase 3 data reported for an in vivo gene editing therapy, today’s HAELO results represent a profound milestone for Intellia, the broader CRISPR and precision medicine fields and, most importantly, the HAE community.”

He added: “For those patients who have spent years battling unpredictable breakthrough swelling attacks, anxiety about their next attack or the many burdens associated with chronic prophylactic treatment, lonvo-z represents a potential paradigm shift in treatment.”

The company expects to complete the rolling BLA submission in the second half of 2026. If approved, Intellia said it anticipates a US launch in the first half of 2027.

Additional data from the Haelo trial are due to be presented at the European Academy of Allergy and Clinical Immunology Congress in Istanbul in June.

The results could be closely watched across the sector as developers seek to prove that one-time gene editing medicines can move beyond rare blood disorders into broader commercial markets.