For patients living with hereditary angioedema (HAE), the threat of sudden, unpredictable swelling is a constant, life-altering reality. With mortality rates for untreated throat swelling reaching as high as 40 percent, the search for a truly long-acting preventive treatment has been the primary goal of the field for years.

New data from Argo Biopharma suggests that goal may be within reach. At the European Association of Allergy & Clinical Immunology (EAACI) 2026 Congress in Istanbul, the company presented updated Phase II results for its investigational siRNA therapeutic, BW-20805. The study indicates that a single dose could potentially suppress HAE attacks for months at a time.

The Data Behind the Breakthrough

The open-label study, which tracked 18 participants, focused on the drug’s ability to target and inhibit prekallikrein (PKK)—a protein essential to the inflammatory cascade that triggers HAE swelling. By silencing the gene responsible for PKK production in the liver, the therapy aims to stop attacks before they begin.

The results, presented as a late-breaking abstract, showed a significant reduction in attack rates across three different dosing cohorts. Participants receiving a 600 mg dose every 24 weeks experienced a 99 percent reduction in HAE attacks, with 83 percent of those patients remaining entirely attack-free during the study period.

"The updated analysis from the ongoing Phase II data reflects the continued strength and progress of the program," said Dr. Dongxu Shu, co-founder and CEO of Argo Biopharma. The data also confirmed that the drug’s effect is durable. Plasma PKK levels remained suppressed by more than 90 percent across all treatment groups even after 169 days.

A Potential Shift in Dosing Regimens

Beyond the efficacy numbers, the most significant takeaway for clinicians is the potential for a Q6M (every six months) dosing schedule. Current HAE prophylactic treatments often require frequent administration, which can lead to treatment fatigue and inconsistent adherence.

If the six-month dosing interval holds up in larger, late-stage trials, it would represent a major shift in how HAE is managed. By moving from weekly or monthly injections to twice-yearly treatments, patients could see a dramatic improvement in their quality of life.

Safety data from the Phase II trial also appears consistent with earlier findings. There were no drug-related severe adverse events or deaths reported. The most common side effect was mild, transient injection site reactions, which resolved without medical intervention.

What Experts Say

While the results are promising, the medical community remains focused on the transition from open-label Phase II data to larger, randomized, placebo-controlled trials. The small sample size of 18 patients means that while the 99 percent reduction is statistically striking, it will need to be replicated in a broader, more diverse patient population to confirm long-term safety and efficacy.

Researchers are particularly interested in whether the robust PKK suppression observed in the 600 mg cohort will maintain its safety profile over years of repeated exposure. For now, the data provides a strong signal that targeting PKK via RNA interference is a viable, high-impact strategy for HAE prevention.

Key Takeaways

  • High Efficacy: The 600 mg Q24W dosing regimen demonstrated a 99% reduction in HAE attacks, with 83% of participants remaining attack-free.
  • Durable Suppression: Mean PKK protein levels remained suppressed by over 90% for at least 169 days, supporting the potential for a twice-yearly dosing schedule.
  • Safety Profile: The therapy was well-tolerated with no severe drug-related adverse events, with only mild, transient injection site reactions reported.

Argo Biopharma has not yet announced the timeline for Phase III trials, but the success at EAACI 2026 positions BW-20805 as a leading candidate in the next generation of HAE prophylaxis. The next major milestone will be the design and initiation of a pivotal study that could bring this long-acting option closer to regulatory review.

This article is for informational purposes only. Always consult a qualified healthcare professional before making any medical decisions.