Danny M. Cohn, Padmalal Gurugama, Hilary J. Longhurst, Emel Aygören‐Pürsün, Timothy Craig, Henriette Farkas, J C Jacobs, William R. Lumry, Markus Magerl, Jonny Peter, Marc A. Riedl, David Maag, A. Golden, Mrinal Y. Shah, Andrea Sutherland, Catherine R. Miller, Ahmed M. Abdelhady, Yuanxin Xu, James S. Butler, David Lebwohl, John Leonard, Aleena Banerji
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.).