Zai Lab Presents New Preclinical Data Suggesting ZL-1503, an IL-13/IL-31Rα Bispecific Antibody, Provides Rapid Itch Relief and Reduction in Inflammation in Atopic Diseases

-Efficacy and safety data shared at IMMUNOLOGY2026 reinforce potential of ZL-1503 as a first-in-class treatment for moderate-to-severe atopic dermatitis and other IL-13 and IL-31-driven diseases

-Strong inhibition of both inflammatory and pruritic pathways over 112 days following a single dose of ZL-1503, together with a favorable preclinical safety profile, supports potential for less frequent dosing than current biologics

-Zai Lab initiated first-in-human Phase 1/1b studies of ZL-1503 in December 2025; clinical data expected in 2H 2026

SHANGHAI & CAMBRIDGE, Mass., April 18, 2026--(BUSINESS WIRE)--Zai Lab Limited (NASDAQ: ZLAB; HKEX: 9688) today announced new data from a preclinical study of ZL-1503, demonstrating that the company’s internally developed IL-13/IL-31Rα bispecific antibody may lead to sustained suppression of intense pruritus (itch) and inflammation caused by atopic diseases. The findings, featured in a poster presentation at the IMMUNOLOGY2026 conference in Boston, MA, reinforce the potential of ZL-1503 to be a first-in-class treatment option for moderate-to-severe atopic dermatitis and other IL-13 and IL-31-driven diseases.

IL-13 and IL-31 are key mediators in atopic disease. IL-13 promotes Type 2 inflammation and tissue changes, while IL-31 drives itch and amplifies local immune responses. Together, these cytokines perpetuate the itch-scratch-inflammation cycle that underlies the development and persistence of atopic dermatitis and related conditions, highlighting the need for therapies that effectively target both pathways simultaneously. ZL-1503 was engineered to disrupt this cycle by blocking both IL-13 and IL-31Rα-mediated signaling concurrently.

"The breadth of activity across pruritus and atopic disease models in this study, including sustained suppression of symptoms from a single dose over 112 days, reinforces our belief that dual targeting of IL-13 and IL-31 pathways represents a compelling therapeutic approach," said Rafael G. Amado, M.D., President, Head of Global Research and Development at Zai Lab. "These data support our conviction that ZL-1503 has the potential to make a meaningful difference for patients and collectively support its clinical advancement."

In the preclinical study presented today, researchers evaluated the ability of ZL-1503 to inhibit IL-31-induced scratching and IL-13-dependent signaling (pSTAT6), and its efficacy in models of asthma, allergic conjunctivitis, and rhinitis triggered by a controlled allergen challenge.

Key study results presented at IMMUNOLOGY2026 include:

Efficacy

• A single intravenous dose of ZL-1503 (0.3, 3, 10 mg/kg) produced sustained, dose-dependent inhibition of both IL-31-induced scratching and IL-13-dependent pSTAT6 signaling over a 112-day observation period, demonstrating durable pathway suppression.

• A single dose of 10 mg/kg also significantly improved lung function, reduced airway inflammation in asthma, and alleviated symptoms of allergic rhinitis and conjunctivitis.

• Transcriptomic and histopathological analyses further demonstrated broad suppression of T helper 2 (TH2)-related inflammatory pathways, immune cell infiltration, and mast-cell activation across lung, nasal mucosa, and conjunctival tissues, providing mechanistic evidence of ZL-1503’s effects at the site of inflammation.

Safety: ZL-1503 demonstrated a favorable nonclinical safety profile across all studies, supporting its advancement into human clinical trials.

In December 2025, Zai Lab initiated Phase 1/1b first-in-human studies of ZL-1503 in healthy volunteers and adult patients with moderate-to-severe atopic dermatitis in Australia, New Zealand, and China.

Details of the ZL-1503 poster presentations at IMMUNOLOGY2026:

Title: ZL-1503: A Bispecific Antibody Targeting IL-13 and IL-31Rα Sustains Suppression of Pruritus and Atopic Disease in Non-Human Primates
Presenter: Henry Wu
Session Title: Immediate and Delayed Hypersensitivity Exhibit Hall
Date/Time: Saturday, April 18, 2026, from 2:30 p.m. – 3:30 p.m. ET
Location: Thomas M. Menino Convention & Exhibition Center, Boston, MA
Poster Board Number: 194

About ZL-1503

ZL-1503 is a potential first-in-class bispecific antibody targeting IL-13 and IL-31Rα engineered by Zai Lab’s in-house discovery engine to simultaneously suppress both inflammatory and pruritogenic (itch-causing) pathways implicated in AD and other IL-13 and IL-31-driven diseases, potentially offering faster onset of action and superior efficacy compared to single-pathway inhibition.

ZL-1503 is currently being evaluated in the ongoing global Phase 1/1b clinical trial evaluating its safety, tolerability, pharmacokinetics, and efficacy. This clinical advancement is supported by preclinical studies in which ZL-1503 demonstrated the ability to simultaneously suppress inflammatory and pruritogenic pathways implicated in AD.

About Zai Lab

Zai Lab Limited (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 https://x.com/ZaiLab_Global.

Zai Lab Forward-Looking Statements

This press release contains forward-looking statements relating to our future expectations, plans, and prospects, for Zai Lab, including, without limitation, statements relating to our prospects and plans for developing and commercializing ZL-1503, the potential benefits of ZL-1503, and the potential treatment of atopic dermatitis and other type 2 helper T-cell (TH2)-driven diseases. 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 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 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.

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