-Data highlights potential of ZL-1503 as a promising treatment for moderate-to-severe atopic dermatitis and other IL-13 and IL-31-driven diseases

-Favorable preclinical safety profile, prolonged half-life and durable suppression of both inflammatory and pruritogenic pathways support advancement of ZL-1503 to IND-enabling studies

-Zai Lab plans to file an IND for ZL-1503 for moderate-to-severe atopic dermatitis by the end of 2025

Zai Lab Limited (NASDAQ: ZLAB; HKEX: 9688) today announced new data from its preclinical study of ZL-1503, the Company’s promising IL-13/IL-31R bispecific antibody, demonstrating its ability to simultaneously suppress the inflammatory and pruritogenic (itch-causing) pathways in atopic dermatitis (AD). The findings, featured during a poster presentation at the European Academy of Allergy and Clinical Immunology (EAACI) Congress 2025 in Glasgow, Scotland, highlight the potential of ZL-1503 as a novel treatment option for moderate-to-severe AD.

Medications that inhibit IL-4/IL-13 signaling have markedly improved the therapeutic landscape for AD. Certain AD symptoms are mediated by IL-31; however, they are only partially alleviated by IL-4/IL-13 inhibition. As a result, many patients experience slow and modest clinical responses to currently available medications.

ZL-1503 was evaluated in a pilot preclinical study in non-human primates to assess its long-term effects on IL-31-mediated scratching and IL-13-induced signaling (pSTAT6). Key study results presented at the EAACI Congress 2025 include:

• An intravenous single dose of ZL-1503 (10 mg/kg, iv) completely inhibited IL-13-mediated pSTAT6 and IL-31-induced scratching for at least 76 days in all preclinical subjects.
• Two out of three subjects exhibited prolonged IL-13-mediated pSTAT6 inhibition for over 118 days, and one out of three subjects sustained IL-31-induced scratching inhibition for over 133 days.
• Pharmacokinetic (PK) analysis of serum samples collected during the study revealed that ZL-1503 exhibited slow clearance, correlating closely pharmacodynamic (PD) responses, demonstrating strong PK/PD relationships in blocking IL-13 and IL-31 pathways in the preclinical model.
• ZL-1503 was well tolerated following weekly IV dosing up to 150 mg/kg.
• Additionally, in vitro studies showed that binding to one target did not affect ZL-1503’s blocking effects on the other target.

Details regarding the ZL-1503 poster presentation at EAACI Congress 2025 are as follows:

Title: ZL-1503: A Bispecific Antibody Targeting Inflammatory and Pruritogenic Pathways with a Prolonged Serum Half-life and Sustained Activity in Non-human Primates

Presenter: Linda Liu, Ph.D., Senior Vice President, Biologics Discovery, Zai Lab

Session Title: Thematic Poster Session 18 (TPS18), Biologicals 01

Date/Time: Friday, June 13, 2025, from 12:00 - 13:00 BST

Abstract Number and Location: n°000625 & Poster Prefix D1.365, Poster Zone

About Zai Lab

Zai Lab is an innovative, research-based, commercial-stage biopharmaceutical company based in China and the United States. We are focused on discovering, developing, and commercializing innovative products that address medical conditions with significant unmet needs in the areas of oncology, immunology, neuroscience, and infectious disease. Our goal is to leverage our competencies and resources to positively impact human health worldwide.

For additional information about Zai Lab, please visit www.zailaboratory.com or follow us at www.X.com/ZaiLab_Global, www.twitter.com/ZaiLab_Global.

Zai Lab Forward-Looking Statements

This press release contains forward-looking statements relating to our future expectations, plans, and prospects, including, without limitation, statements regarding product candidates in our pipeline including ZL-1503 and related preclinical studies; the potential benefits of ZL-1503; and the potential treatment of atopic dermatitis and other diseases involving the IL-13 and IL-31 pathways. All statements, other than statements of historical fact, included in this press release are forward-looking statements, and can be identified by words such as “aim,” “anticipate,” “believe,” “could,” “estimate,” “expect,” “forecast,” “goal,” “intend,” “may,” “plan,” “possible,” “potential,” “will,” “would,” and other similar expressions. Such statements constitute forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Forward-looking statements are not statements of historical fact or guarantees or assurances of future performance. Forward-looking statements are based on our expectations and assumptions as of the date of this press release and are subject to inherent uncertainties, risks, and changes in circumstances that may differ materially from those contemplated by the forward-looking statements. We may not actually achieve the plans, carry out the intentions, or meet the expectations or projections disclosed in our forward-looking statements, and you should not place undue reliance on these forward-looking statements. Actual results may differ materially from those indicated by such forward-looking statements as a result of various important factors, including but not limited to (1) our ability to successfully commercialize and generate revenue from our approved products, (2) our ability to obtain funding for our operations and business initiatives, (3) the results of our clinical and pre-clinical development of our product candidates, (4) the content and timing of decisions made by the relevant regulatory authorities regarding regulatory approvals of our product candidates, (5) risks related to doing business in China, and (6) other factors identified in our most recent annual and quarterly reports and in other reports we have filed with the U.S. Securities and Exchange Commission (SEC). We anticipate that subsequent events and developments will cause our expectations and assumptions to change, and we undertake no obligation to update or revise any forward-looking statements, whether as a result of new information, future events, or otherwise, except as may be required by law. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date of this press release.

Our SEC filings can be found on our website at www.zailaboratory.com and the SEC’s website at www.sec.gov.

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