Single-Dose Lonvoguran Ziclumeran Cuts HAE Attacks by 87% in Phase 3 Trial

A single dose of lonvoguran ziclumeran (lonvo-z) reduced hereditary angioedema (HAE) attack rates by 87% compared with placebo in the phase 3 HAELO trial, according to topline 6-month efficacy data released by Intellia Therapeutics.¹

“The results we are seeing from lonvo-z demonstrate its potential to eliminate the need for chronic medication and related challenges,” said HAELO lead investigator Aleena Banerji, MD, professor at Harvard Medical School and director of clinical care at the Center for Drug and Vaccine Allergy at Massachusetts General Hospital, in a statement.1 “If approved as a one-time treatment, I would expect lonvo-z to be an appealing option for many patients.”

HAELO was a randomized, double-blind, placebo-controlled trial evaluating a single 50 mg intravenous dose of lonvo-z, an in vivo CRISPR-based gene editing therapy formerly known as NTLA-2002, in 80 patients aged ≥16 years with type I or II HAE.¹ A total of 52 patients received lonvo-z and 28 received placebo; 71% were receiving long-term prophylaxis (LTP) at baseline and discontinued these therapies before dosing.¹ The primary endpoint assessed the mean monthly attack rate during weeks 5 through 28.

During the 6-month efficacy period, the mean monthly attack rate was 0.26 in the lonvo-z arm compared with 2.10 in the placebo arm (P <.0001), meeting the primary endpoint.¹ All key secondary endpoints were also met, including a 62% rate of patients who were both attack-free and LTP-free, compared with 11% in the placebo group (P <.0001).¹ At data cutoff, all patients treated with lonvo-z, including those who crossed over after week 28, remained off prophylactic therapy.¹

Safety findings were consistent with earlier-stage data. The most common treatment-emergent adverse events, all reported as mild or moderate, included infusion-related reactions, headache, and fatigue. No serious adverse events were observed in the treatment arm during the primary observation period.¹

HAE, a condition characterized by recurrent, potentially life-threatening angioedema attacks driven by dysregulated bradykinin production, remains a rare genetic disorder affecting approximately 1 in 50,000 individuals.² Despite the availability of targeted therapies, including plasma kallikrein inhibitors such as lanadelumab and berotralstat, management often requires chronic administration and does not fully eliminate breakthrough attacks.³,⁴ The need for frequent injections or daily oral therapy contributes to treatment burden and adherence challenges.

Lonvo-z is designed to address this unmet need through in vivo gene editing. Using CRISPR/Cas9 technology, the therapy targets and inactivates the KLKB1 gene in hepatocytes, reducing kallikrein production and downstream bradykinin generation.¹ This mechanism builds on established clinical validation of kallikrein inhibition in HAE but introduces the possibility of sustained effect after a single administration.

The program has received multiple regulatory designations, including Orphan Drug and Regenerative Medicine Advanced Therapy (RMAT) designations from the US Food and Drug Administration, as well as PRIME designation in the European Union.¹ Intellia has initiated a rolling biologics license application (BLA) submission, with completion anticipated in the second half of 2026 and potential US launch in 2027 if approved.5

Although the magnitude of effect observed in HAELO is notable, interpretation remains constrained by the limited follow-up duration of 6 months for the primary endpoint. Longer-term durability, potential delayed adverse effects, and real-world generalizability remain key unanswered questions, particularly given the permanent genomic modification underlying the therapy. In addition, the trial required discontinuation of baseline prophylaxis before dosing, which may not fully reflect clinical practice patterns.1

If confirmed and approved, lonvo-z would represent a new therapeutic paradigm in HAE, shifting from chronic suppression of disease pathways to potentially durable modification of the underlying biology.1 However, clinicians will likely weigh efficacy against uncertainties related to long-term safety, reversibility, and patient selection in considering integration into practice.

“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,” said Intellia President and Chief Executive Officer John Leonard, MD, in the press release.1 “These data affirm lonvo-z’s potential, with one dose, to offer prolonged freedom from both attacks and the need for ongoing therapy.”

References

1. Intellia Therapeutics. Intellia Therapeutics reports positive phase 3 results in hereditary angioedema, marking a global first for in vivo gene editing. April 27, 2026. https://ir.intelliatx.com/news-releases/news-release-details/intellia-therapeutics-reports-positive-phase-3-results

2. Learn About Hereditary Angioedema. DiscoverHAE. https://www.discoverhae.com/what-is-hereditary-angioedema

3. Lanadelumab Cuts Monthly HAE Attack Rates in Real-World 3-Year Study. HCPLive. Published on July 22, 2025. Accessed April 27, 2026. https://www.hcplive.com/view/lanadelumab-cuts-monthly-hae-attack-rates-in-real-world-3-year-study

4. Derman C. FDA Approves Oral Berotralstat for Children Aged 2 – 11 Years with HAE. HCPLive. Published on December 12, 2026. Accessed April 27, 2026. https://www.hcplive.com/view/fda-approves-oral-berotralstat-children-aged-2-11-years-hae

5. Intellia Therapeutics Initiates Rolling Submission of Biologics License Application to FDA for Lonvoguran Ziclumeran (lonvo-z) as a One-Time Treatment for Hereditary Angioedema - Intellia Therapeutics. Intellia Therapeutics. Published on April 27, 2026. Accessed April 27, 2026. https://ir.intelliatx.com/news-releases/news-release-details/intellia-therapeutics-initiates-rolling-submission-biologics