-Poster Presentation at the Thematic Poster Session

SHANGHAI, CHINA and NEW YORK, USA-June 8, 2026—Argo Biopharmaceutical Co., Ltd. (Argo Biopharma), a clinical-stage small interfering RNA (siRNA) therapeutics company, has been selected to present Phase II updated results for BW-20805 at the European Association of Allergy & Clinical Immunology (EAACI) 2026 Congress, being held on June 12-15, 2026 in Istanbul, Türkiye.

BW-20805 is an investigational siRNA therapy that targets and significantly inhibits prekallikrein (PKK), a well-validated target for hereditary angioedema (HAE) treatment, offering the possibility of prevention of HAE attacks with a long-term effect.

"We are pleased that the updated analysis from the ongoing Phase II data for BW-20805 has been selected for presentation at EAACI 2026. Following the presentation at AAAAI 2025, this reflects the continued strength and progress of the program. We look forward to sharing the latest findings and advancing our efforts to develop a potentially meaningful treatment option for patients," said Dr. Dongxu Shu, co-founder and Chief Executive Officer of Argo Biopharma.

The open-label study results, selected as a late breaking abstract presentation, titled "Long-Acting Prophylactic Injection BW-20805: Remarkable and Sustained HAE Attack Reduction — Updated Analysis from an Ongoing Phase 2 Study" (POSTER ID: D1.363), show that BW-20805 provides remarkable and sustained HAE attacks reductions, along with a consistent safety profile following repeated doses. The sustained and robust PKK suppression supports further evaluation of a Q6M dosing regimen.

Key Data Highlights:

• As of the cut-off, 18 participants were randomized and dosed (16 with post-dose data beyond Day 29). Time-normalized HAE attack rate was reduced by 99% in 600 mg Q24W with 83% (5/6) attack-free, 93% in 300 mg Q24W with 60% (3/5) attack-free, and 95% in 300 mg Q12W with 60% (3/5) attack-free.

• As of cut-off, 17 participants had post-dose PKK data available. Plasma PKK declined rapidly, with mean reductions exceeding 94% in pooled 300 mg groups and 96% in 600 mg Q24W on Day 85. Among participants completing 169 days, mean PKK reductions exceeded 90% across all three groups, with sustained robust suppression.

• BW-20805 was well tolerated among 18 patients across 3 treatment groups, There were no drug-related severe AEs or SAEs, No TEAE leading to study discontinuation or death were reported. Most common AE was injection site reaction, which was mild, and transient without medication.

About Hereditary Angioedema (HAE)

Hereditary angioedema (HAE) is a rare genetic condition that causes sudden and unpredictable swelling in different parts of the body. In severe cases, it can affect the throat and become life-threatening, with a mortality rate of up to 40% ¹. HAE affects about 1.5 people per 100,000 worldwide ². Current treatments require frequent dosing, highlighting the need for long-acting, preventive therapies. BW-20805 targets human hepatic PKK mRNA to inhibit PKK gene expression, offering the potential for effective prevention of HAE attacks with a significant and longer-lasting therapeutic effect.

About Argo Biopharma

Argo Biopharma is a clinical-stage biotechnology company committed to developing next-generation RNAi therapeutics to provide better treatment options for patients worldwide. The company has established a robust and diverse pipeline of RNAi molecule candidates targeting a wide range of indications, including cardiovascular diseases, viral infections, metabolic conditions, and specialty/rare diseases. Currently, Argo Biopharma has seven RNAi candidates in clinical development.

For more information, please visit www.argobiopharma.com .

INVESTOR & MEDIA INQUIRIES
Argot Partners
argobiopharma@argotpartners.com

References：

1. Pedro Giavina-Bianchi P, et al. (2011). CLINICS 66(9): 1627–1636.
2. Aygören-Pürsün, E, et al. (2018). Orphanet J Rare Dis 13(1): 73.