Intellia Therapeutics to Release World's First In Vivo CRISPR Phase 3 Data on April 27
Intellia Therapeutics will report topline Phase 3 results for lonvoguran ziclumeran in hereditary angioedema on April 27, 2026 — the first Phase 3 readout for any in vivo CRISPR candidate.
Overview
On April 24, 2026, Intellia Therapeutics announced it will release topline data from the global Phase 3 HAELO clinical trial of lonvoguran ziclumeran (lonvo-z) on April 27, 2026. The announcement marks a landmark moment in genomic medicine: HAELO’s readout will be the world’s first Phase 3 data from any in vivo CRISPR gene editing candidate — meaning a therapy that rewrites a patient’s DNA directly inside the body rather than in a laboratory dish.
Lonvo-z targets hereditary angioedema (HAE), a rare and potentially life-threatening genetic disorder characterized by sudden, severe swelling episodes in the skin, gastrointestinal tract, and airways. If the Phase 3 results hold, Intellia plans to submit a biologics license application (BLA) to the FDA in the second half of 2026, targeting a U.S. commercial launch in the first half of 2027.
What We Know
The mechanism. Lonvo-z uses lipid nanoparticles (LNPs) — the same delivery platform proven in mRNA COVID-19 vaccines — to ferry two components into liver cells: messenger RNA encoding the CRISPR-Cas9 enzyme and a guide RNA targeting the KLKB1 gene. Once inside hepatocytes, Cas9 creates a permanent double-strand break at the KLKB1 locus; the cell’s own imprecise repair machinery then introduces small insertions or deletions that permanently silence the gene. KLKB1 encodes prekallikrein, the precursor to plasma kallikrein — the enzyme that drives bradykinin production and, in turn, HAE attacks. Silencing the gene with a single infusion is intended to prevent attacks indefinitely without repeated dosing.
Early clinical data is compelling. A pooled Phase 1/2 analysis in 32 patients given a one-time 50 mg dose of lonvo-z demonstrated deep, stable, and durable reductions in plasma kallikrein across all participants with up to three years of follow-up. The mean reduction in monthly HAE attack rate was 98% compared to pre-treatment baseline. In the Phase 1 cohort of ten patients followed for three full years, all participants achieved complete freedom from inflammatory attacks, with a median attack-free, treatment-free duration of 23 months at data cutoff.
Phase 3 trial design. HAELO is a randomized, double-blind, placebo-controlled global study enrolling at least 60 adults and adolescents aged 16 and older with Type I or Type II HAE. Participants are randomized 2:1 to receive a single 50 mg intravenous infusion of lonvo-z or placebo. The primary endpoint measures the change in HAE attack frequency between weeks 5 and 28 post-dose. Patients in the placebo arm become eligible for optional crossover to lonvo-z at week 28. Enrollment in the HAELO study was completed ahead of the April 27 data announcement.
Safety profile to date. In Phase 1/2 data, the most frequently reported adverse events were infusion-related reactions, predominantly mild (Grade 1), and all resolved. Investigators reported no treatment-emergent serious adverse events and no treatment-related adverse events beyond 28 days post-dosing — a notable finding given that CRISPR therapies could in principle cause off-target edits.
Regulatory and competitive context. The only CRISPR-based therapy currently approved by the FDA is Casgevy (exagamglogene autotemcel), developed by CRISPR Therapeutics and Vertex Pharmaceuticals for sickle cell disease and beta-thalassemia. Casgevy is an ex vivo therapy — patient cells are extracted, edited in the laboratory, and reinfused. Lonvo-z would be the first in vivo CRISPR therapy to reach Phase 3 and, if approved, the first such treatment licensed for clinical use. The distinction matters: in vivo approaches eliminate the logistically complex and expensive process of harvesting and re-engineering a patient’s own cells.
What We Don’t Know
The most critical unknown is whether the Phase 3 HAELO readout will replicate the near-complete attack suppression seen in the smaller Phase 1/2 cohorts. Phase 3 studies routinely enroll more diverse patient populations across multiple geographic sites, conditions that can dilute efficacy signals observed in tightly controlled early trials. The trial enrolled a minimum of 60 participants — a modest number by regulatory standards for any pivotal study — which means the confidence intervals around the primary endpoint could be wide.
The durability question also remains partially open. While Phase 1 data shows sustained responses at three years, it is drawn from only ten patients. Whether the genetic silencing of KLKB1 persists across decades, or whether hepatocyte turnover gradually restores gene expression, is not yet established at scale.
Finally, the path to approval beyond the U.S. is undefined. Intellia has signaled a BLA submission in the second half of 2026, but comparable filings with the European Medicines Agency and other regulators have not been announced. The safety picture for in vivo CRISPR — including long-term monitoring for off-target edits at non-target genomic loci — will be scrutinized by regulators in every jurisdiction.