Lonvoguran Ziclumeran — In Vivo CRISPR Gene Editing in Hereditary Angioedema

BACKGROUND: Hereditary angioedema is a rare and potentially life-threatening genetic condition characterized by recurrent and debilitating swelling attacks. Lonvoguran ziclumeran (lonvo-z) - an investigational, in vivo gene-editing treatment based on clustered regularly interspaced short palindromic repeats (CRISPR) - is being developed as a single-dose treatment for hereditary angioedema. METHODS: In a phase 3, double-blind trial, we randomly assigned, in a 2:1 ratio, patients who were 16 years of age or older and had hereditary angioedema with C1 inhibitor deficiency to receive a single intravenous infusion of lonvo-z (at a dose of 50 mg) or placebo. The primary end point was the number of investigator-confirmed hereditary angioedema attacks per month (the monthly attack rate) from week 5 through week 28 after infusion. RESULTS: A total of 80 patients underwent randomization; 52 were assigned to receive lonvo-z and 28 to receive placebo. As of February 10, 2026, the median duration of follow-up was 7.5 months (range, 4.9 to 12.8). The least-squares mean monthly attack rate from weeks 5 through 28 was 0.26 (95% confidence interval [CI], 0.15 to 0.45) in the lonvo-z group and 2.10 (95% CI, 1.55 to 2.86) in the placebo group (relative difference, -87%; 95% CI, -93 to -78; P<0.001). Adverse events that occurred during or after infusion of lonvo-z or placebo were reported in 92% and 86% of the patients in the lonvo-z and placebo groups, respectively, from day 1 through week 28. Among the adverse events that occurred during or after infusion and more often in the lonvo-z group than in the placebo group, the most common (occurring in >10% of the patients in the lonvo-z group) included infusion-related reaction, headache, fatigue, back pain, and upper respiratory tract infection. No serious or grade 3 or higher adverse events were reported in the lonvo-z group. CONCLUSIONS: Among patients with hereditary angioedema, a single intravenous infusion of lonvo-z resulted in a significantly lower rate of hereditary angioedema attacks than placebo. (Funded by Intellia Therapeutics; HAELO ClinicalTrials.gov number, NCT06634420.).