A single infusion of Intellia Therapeutics' CRISPR therapy kept hereditary angioedema attacks down for as long as four years, according to integrated data the company presented at the ACAAI annual meeting on Friday.
The analysis covers 93 patients who received one 50 mg dose of lonvoguran ziclumeran, or lonvo-z, across the Phase 1/2 program and the Phase 3 HAELO trial. Attack rates fell 89% from baseline over follow-up of up to four years. Ninety-seven percent of patients never started long-term prophylaxis after treatment, and all 93 were free of it at their latest follow-up.
The presentation comes as the FDA reviews Intellia's biologics license application for the therapy. The agency accepted the filing with priority review and set a decision date of March 10, 2027. Intellia has said it is preparing for a U.S. launch in the first half of next year.
What HAE does to patients
Hereditary angioedema is a genetic condition caused by a deficiency or dysfunction of the C1 inhibitor protein. That imbalance leaves the kallikrein-kinin system overproducing bradykinin, which makes blood vessels leak fluid into tissue. The result is unpredictable swelling attacks, often in the hands, feet, face, abdomen, or throat. Swelling in the airway can be life-threatening.
Patients manage the disease in two ways. On-demand treatment stops an attack once it starts. Long-term prophylaxis is taken regularly to prevent attacks from happening. In the United States, about 35% of patients use on-demand treatment alone and about 65% use prophylaxis plus on-demand therapy, according to the company's presentation.
Prophylaxis has improved over the past decade, but it remains a chronic commitment. Some options are taken daily, some every few weeks, and some require injections or infusions. Patients cite the burden of lifetime dosing, insurance hurdles, and the fear of the next attack as persistent problems even when the drugs work.
The company's presentation cites a survey of 100 U.S. patients in which 34% reported at least one attack a month and 80% reported at least one in the past year. Fifty-four percent ranked mental health as one of the most burdensome parts of the disease, and 68% named the prospect of lifetime medication as a top concern. Among 89 patients on long-term prophylaxis, 80% said insurance changes had affected access to their medicine. Those figures come from a published patient survey that the company presented, not from the trial itself, but they describe the problem the therapy is meant to solve.
The Phase 3 result
HAELO randomized 52 patients to lonvo-z and 28 to placebo. The primary endpoint measured the mean monthly attack rate from week 5 to week 28. Lonvo-z reduced it 87% against placebo, to 0.26 attacks a month from 2.10, with a 95% confidence interval of 78% to 93% and a p value below 0.0001.
The key secondary endpoint was equally direct. Sixty-two percent of patients on lonvo-z were attack-free and off all prophylactic therapy during the six-month efficacy period, against 11% on placebo, an odds ratio of 12.8. The company also reported a 91% reduction in moderate-to-severe attacks and an 89% reduction in attacks that required on-demand treatment.
Among 35 patients who were taking long-term prophylaxis when they enrolled, the attack rate fell 81% after the switch to lonvo-z. Sixty-three percent achieved complete control, about three times their prior attack-free rate.
Those results were first announced in April and presented in full at the EAACI congress in June, with simultaneous publication in the New England Journal of Medicine. The filing rests on them.
What four years add
The new analysis is not a randomized comparison. It pools patients from the earlier Phase 1/2 studies with those from HAELO and follows them for as long as four years. That makes it the best available look at durability, which is the central question for any one-time therapy.
The numbers are consistent with the trial. Attack rates stayed 89% below baseline across the follow-up. In the 32 patients from the Phase 1/2 studies, mean plasma kallikrein fell 84% at four weeks and stayed reduced for up to four years. The company said 31 of 32 patients treated with the 50 mg dose remain in long-term follow-up.
The absence of a control group matters for interpretation. Patients in an open-label extension know they are receiving the therapy, and their reporting of attacks can change. The durability signal is strong, but it is not the same kind of evidence as the randomized trial. The company has said it plans to continue follow-up.
How the treatment works
Lonvo-z is an in vivo CRISPR therapy. It is given as a single intravenous infusion and uses CRISPR/Cas9 to inactivate the KLKB1 gene in the liver, which is the gene that produces prekallikrein, the precursor to plasma kallikrein. With less kallikrein, the cascade that produces bradykinin is dampened.
The infusion takes about four hours, with a median of 3.9 hours in HAELO and a range of 2.5 to 5.3 hours. Patients receive premedication with a corticosteroid and antihistamines to reduce infusion-related reactions. The company describes the setting as an outpatient clinic.
That delivery model is part of the commercial case. A one-time infusion could replace years of chronic prophylaxis, but it requires a treatment center, a half-day visit, and a monitoring period. It also concentrates the cost into a single event, which is the question payers will negotiate over.
HAE is an unusually clean target for gene editing. The disease is driven by a single pathway, the protein is made in the liver, and the edit can be delivered with a lipid nanoparticle that concentrates in that organ. The effect is measurable in the blood through kallikrein levels, and the clinical endpoint, attacks per month, is something patients can report. That combination explains why Intellia chose HAE for its first in vivo Phase 3 program, and why the readout carries weight beyond this one disease.
Safety
In HAELO, the company reported no serious adverse events in the lonvo-z arm and said treatment-emergent events were mild or moderate. Across the 93-patient integrated safety set, the most common events were infusion-related reactions, reported in 55%, followed by headache, fatigue, and nasopharyngitis.
The integrated table lists two serious adverse events among the 93 patients: a pulmonary embolism and a perforated gangrenous appendicitis. The company said no new long-term risks were identified with up to four years of follow-up. As with any gene-editing therapy, the long-term questions include whether the edit stays confined to the intended gene and whether the effect on the immune system or the liver changes over time.
The regulatory path
The FDA accepted the BLA for priority review in the fall. The agency told Intellia in September that it was not currently planning to hold an advisory committee meeting on the application. The PDUFA goal date is March 10, 2027.
If approved, lonvo-z would be the first in vivo CRISPR therapy on the U.S. market and the first one-time treatment for HAE. That would make the March 10 date a milestone for the field as much as for the company. Intellia has said it is building a commercial team and preparing for a launch in the first half of 2027. The company's presentation describes the therapy as a potential new modality rather than another chronic prophylactic.
The approval would not settle the access question. A one-time therapy with a large upfront price needs a payment model that health plans, pharmacy benefit managers, and Medicaid programs can accommodate. The company has not announced a price.
One-time therapies have produced a set of payment experiments: outcomes-based agreements that tie part of the price to how well the treatment works, warranties that require a refund if it fails, and installment arrangements that spread the cost over several years. None has become standard for gene therapies, and each adds administrative work for payers and providers. A therapy that replaces years of prophylaxis has to be priced against the cost of those years, which is a calculation each payer makes differently.
What the data do not answer
The trial followed patients for six months of controlled comparison and up to four years in extension. It did not answer how long the effect lasts beyond that window, whether re-dosing would be needed or possible, or how the therapy performs in patients with the most severe disease over a decade. The controlled comparison lasted six months; everything after that comes from an extension, not a second randomized trial. The FDA will weigh that structure when it reviews the application, without the public advisory committee that usually airs such questions.
It also did not compare lonvo-z with the newer oral prophylactics. The site covered one of those in September, when Pharvaris reported an 83% reduction in monthly attack rates with a once-daily pill. A pill taken every day and a single infusion that may last years are different products for different patients, and the choice will depend on how each performs outside the controlled setting.
The comparison that patients and doctors will make in practice is with the newest prophylactics, not with placebo. The past decade has produced lanadelumab and garadacimab, both injectable antibodies taken every few weeks; berotralstat, a daily oral pill; donidalorsen, an antisense therapy given every four to eight weeks; and deucrictibant, the oral candidate the site covered in September. Those drugs do not require a one-time infusion or a permanent edit. They also do not offer the possibility of stopping treatment entirely. The HAE market is crowded with options, and lonvo-z would enter it with a different claim rather than a better version of the same claim.
For now, the integrated data support the case Intellia is making to the FDA: one infusion, a deep and durable reduction in attacks, and most patients off chronic prophylaxis. For patients, the choice will come down to a single treatment with uncertain durability against a daily or monthly regimen with known effects. The agency's decision in March will determine whether that choice becomes available.
Primary sources
- Intellia Therapeutics, "Readying Lonvo-z for Patients with HAE," investor presentation, Exhibit 99.1 to Form 8-K, Nov. 12, 2026.
- Intellia Therapeutics, ACAAI 2026 integrated Phase 1/2/3 data presentation, Nov. 13, 2026.
- Clinical Trial Vanguard, "Intellia's Lonvoguran Ziclumeran Cuts HAE Attacks 87% in Phase 3 Trial," 2026.
- MedPath Trial, "Intellia's one-time CRISPR therapy lonvo-z cuts HAE attacks 89% and keeps 100% of patients off prophylaxis up to four years," Nov. 2026.