A Single Infusion Rewrites Liver Cells as In Vivo CRISPR Therapy Clears the Phase 3 Trial Threshold

For patients with hereditary angioedema, the challenge is not only recurrent swelling, but also the uncertainty that the next attack could suddenly obstruct the airway. The in vivo CRISPR therapy lonvoguran ziclumeran (lonvo-z), developed by Intellia Therapeutics, has now significantly reduced attacks in a Phase 3 trial, moving the concept of “one treatment, long-term freedom from medication” another step from an early idea toward regulatory review.

HAELO is a randomized, double-blind, placebo-controlled trial that enrolled 80 patients aged 16 or older with type 1 or type 2 hereditary angioedema; 52 received a single 50 mg infusion of lonvo-z, while 28 received placebo. From week 5 through week 28, the treatment group’s mean monthly attack rate was 87% lower than that of the placebo group; 62% of patients in the treatment group had no attacks during this period and did not require prophylactic maintenance treatment, compared with 11% in the placebo group.

More detailed results showed an 89% reduction in attacks requiring on-demand rescue medication and a 91% reduction in moderate or severe attacks. The patient-reported Angioedema Quality of Life score improved by 17.04 points versus placebo, exceeding the 6-point threshold generally considered clinically meaningful for the scale. The full results were presented at the 2026 annual meeting of the European Academy of Allergy and Clinical Immunology and simultaneously published in The New England Journal of Medicine.

Lonvo-z differs from ex vivo gene-editing therapies already on the market: rather than first removing a patient’s cells, it delivers CRISPR/Cas9 editing components directly into the body, targeting the KLKB1 gene in liver cells. Disabling this gene can durably reduce plasma kallikrein, thereby suppressing the bradykinin signaling that drives swelling. This pathway has already been validated by existing preventive medicines, but lonvo-z seeks to replace the continuous suppression required by daily oral medication or regular injections with a single permanent edit.

As of the primary analysis cutoff date, all adverse events reported in the treatment group were mild or moderate, and no serious adverse events occurred; the more common events included infusion reactions, headache, fatigue, back pain, and upper respiratory tract infection. However, the primary efficacy observation period was only six months, and median follow-up was also just 7.5 months. For irreversible gene editing that may remain with patients for many years, rare toxicities, off-target changes, effects on the liver, and how long efficacy can be maintained still require larger-scale and longer-term follow-up to answer.

The significance of this trial therefore extends beyond a therapy for a rare disease: it marks the first time in vivo CRISPR editing has reached Phase 3 clinical testing and will directly test how regulators weigh the short-term benefits of one-time permanent editing against lifelong risks. Intellia initiated a rolling biologics license application submission to the U.S. Food and Drug Administration in April 2026 and plans to complete the submission in the second half of the year; the company’s stated possibility of approval and launch in the first half of 2027 still depends on data review, manufacturing quality, and long-term safety monitoring requirements.