• ZL-1503, a promising treatment for moderate-to-severe atopic dermatitis and other Type 2 helper T-cell (Th2)-driven diseases, strengthens Zai Lab’s growing global pipeline
• ZL-1503 originated from Zai Lab’s in-house discovery and development engine

SHANGHAI & CAMBRIDGE, Mass. / Dec 08, 2025 / Business Wire / Zai Lab Limited (NASDAQ: ZLAB; HKEX: 9688) today announced the dosing of the first participant in a global Phase 1/1b clinical trial evaluating the safety, tolerability, pharmacokinetics, and efficacy of ZL-1503, a potential first-in-class IL-13/IL-31R bispecific antibody for the treatment of atopic dermatitis (AD). ZL-1503, which was identified and advanced internally by Zai Lab’s discovery team, targets both IL-13 and IL-31 pathways with an extended serum half-life. The dual targeting potentially provides faster onset of action and superior efficacy.

In preclinical studies, ZL-1503 demonstrated the ability to simultaneously suppress inflammatory and pruritogenic (itch-causing) pathways implicated in AD. These findings, recently presented at the European Academy of Allergy and Clinical Immunology (EAACI) 2025 Congress, highlight ZL-1503’s potential as a novel therapeutic option for patients with moderate-to-severe AD.

“The progress of ZL-1503 is another strong example of our global development capabilities, underscoring the speed, scientific rigor and operational excellence of our team,” said Rafael G. Amado, M.D., President, Head of Global Research and Development, Zai Lab. “Importantly, ZL-1503 has the potential to provide patients with a novel and much-needed treatment option for managing their disease. We are encouraged by the preclinical data and look forward to evaluating its performance in the clinic.”

The Phase 1/1b study of ZL-1503 is a randomized, double-blind, placebo-controlled single-dose and multiple-ascending dose trial designed to evaluate the safety, tolerability, and pharmacokinetics of ZL-1503 in healthy volunteers and participants with moderate to severe AD.

About Zai Lab

Zai Lab (NASDAQ: ZLAB; HKEX: 9688) 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.

For additional information about Zai Lab, please visit www.zailaboratory.com or follow us at www.X.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 on the SEC’s website at www.sec.gov.