Phase 2 RCT: CRISPR-Based Therapy Reduces Attacks in Hereditary Angioedema

Background: Hereditary angioedema (HAE) is a rare autosomal dominant disorder characterized by unpredictable attacks of angioedema involving cutaneous tissues, the gastrointestinal tract, and, potentially, the larynx, posing a risk of asphyxiation. Current prophylactic treatments require frequent administration, often leading to suboptimal adherence and ongoing disease burden. NTLA-2002 is an in vivo CRISPR-Cas9–based therapy designed to permanently inactivate the KLKB1 gene in hepatocytes, thereby reducing plasma kallikrein levels and, hypothetically, lowering attack frequency in patients with HAE.

Objective: To evaluate whether a single intravenous infusion of NTLA-2002 (25 mg or 50 mg) would safely and effectively decrease HAE attack rates and reduce plasma kallikrein protein levels over a 16-week primary observation period, as compared with placebo.

Methods: This phase 2, randomized, double-blind, placebo-controlled trial included 27 adults with confirmed type 1 or type 2 HAE. Participants were assigned in a 2:2:1 ratio to receive a one-time dose of 25 mg or 50 mg of NTLA-2002 or placebo. The primary endpoint was the investigator-confirmed number of angioedema attacks per month from Week 1 through Week 16. Secondary endpoints included the number of moderate-to-severe attacks, use of on-demand therapy, adverse events, and changes in total plasma kallikrein protein levels (analyzed by immunoassays). Exploratory measures encompassed patient-reported outcomes using the Angioedema Quality of Life (AE-QoL) questionnaire.

Results: During the 16-week period, the mean monthly attack rate decreased by 75% in the 25 mg group and 77% in the 50 mg group relative to placebo (estimated rates of 0.70 vs. 0.65 vs. 2.82 attacks per month, respectively). Notably, 4 of 10 patients (40%) in the 25 mg group and 8 of 11 (73%) in the 50 mg group reported no attacks or further prophylaxis use after dosing. Placebo recipients showed only a 16% reduction from baseline. Adverse events were predominantly mild to moderate; headache, fatigue, and nasopharyngitis were most common. Infusion-related reactions occurred in a few patients but resolved without sequelae. A single transient grade 2 elevation in alanine aminotransferase was recorded in one participant given 25 mg of NTLA-2002. By Week 16, total plasma kallikrein levels decreased by 55% in the 25 mg group and 86% in the 50 mg group, with no meaningful changes in placebo.

Conclusions: A single intravenous infusion of NTLA-2002 significantly lowered attack frequency and reduced total plasma kallikrein levels in HAE. Most patients treated at 50 mg experienced no attacks, suggesting that long-term prophylaxis might be unnecessary for many. Longer observation supports durability, yet cost and potential long-term effects of gene editing warrant cautious interpretation.

Implications for Practice: If confirmed by larger phase 3 trials, this gene-editing approach could alter the management of HAE, reducing or eliminating the need for continuous prophylaxis. However, clinicians must weigh the high upfront cost, possible unpredictable immune responses, and the novelty of CRISPR-based therapies before integrating them into standard care.

Study Strengths and Limitations: Strengths include a placebo-controlled design, meaningful improvement in patient-reported outcomes, and robust plasma kallikrein protein reduction. Limitations are the small sample size, short primary observation period, and uncertain long-term safety in diverse populations.

Future Research: Ongoing phase 3 studies with larger cohorts and extended follow-up are essential to confirm safety, long-term efficacy, and cost-effectiveness.

Reference: Cohn DM, Gurugama P, Magerl M, et al. CRISPR-Based Therapy for Hereditary Angioedema. New England Journal of Medicine. 2024; DOI: http://doi.org/10.1056/NEJMoa2405734

• Editorial: Musunuru K. A Milestone for Gene-Editing Therapies. New England Journal of Medicine. 2024; DOI: http://doi.org/10.1056/NEJMe2412176