Zai Lab Limited (NASDAQ: ZLAB; HKEX: 9688), an innovation-driven, global biopharma company, today announced positive preliminary, first-in-human results from the single-ascending-dose portion of its global Phase 1/1b trial of ZL-1503, an internally discovered, long-acting IL-13/IL-31 receptor alpha (Rα) bispecific antibody. Findings from the study will be presented at the American College of Allergy, Asthma & Immunology (ACAAI) 2026 Annual Scientific Meeting.

The Phase 1 data from healthy volunteers demonstrated rapid and sustained inhibition of the IL-13 pathway, with at least 90% inhibition of phosphorylated STAT6 (pSTAT6), an atopic dermatitis- (AD) related signaling biomarker, through Week 12 following a single dose of 200 mg or higher. Treatment also resulted in reductions in downstream inflammatory biomarkers, including TARC and CCL26, supporting broad modulation of type 2 inflammatory signaling.

Pharmacokinetic results demonstrated dose-proportional exposure and an extended half-life of approximately 40 to 50 days, nearly twice as long as that of several approved anti-IL-13 and anti-IL-31 biologics. These findings support further evaluation of extended maintenance dosing intervals, with a target of once every 12 weeks. ZL-1503 was well tolerated across all evaluated dose levels, with no serious adverse events, dose-limiting toxicities, or detectable anti-drug antibodies.

“These first-in-human findings reinforce the potential of ZL-1503 as a differentiated, first-in-class treatment option for patients with atopic dermatitis,” said Rafael G. Amado, M.D., President and Head of Global Research and Development at Zai Lab. “By combining two clinically validated mechanisms in a single, half-life-extended bispecific, ZL-1503 has the potential to control inflammation, deliver rapid and durable itch relief, and enable less frequent dosing. We have already initiated the next phases of this global study, which is evaluating the pharmacokinetics, safety, and initial efficacy of repeated doses of ZL-1503 in patients with moderate-to-severe atopic dermatitis and a subcutaneous formulation.”

ZL-1503 is a novel, long-acting, investigational bispecific antibody being developed for moderate-to-severe atopic dermatitis and other IL-13- and IL-31-driven diseases. IL-13 and IL-31 are key mediators of AD pathogenesis. IL-13 promotes type 2 inflammation and tissue remodeling, while IL-31 drives pruritus (itch) and amplifies local immune responses. Together, these cytokines perpetuate the itch-scratch-inflammation cycle that contributes to the development and persistence of AD and related conditions. ZL-1503 disrupts this cycle, and it incorporates serum half-life extension technology to prolong systemic exposure, potentially enabling less frequent dosing. Preclinical data presented earlier this year demonstrated that ZL-1503 provided rapid itch relief and significantly reduced inflammation in animal models of atopic diseases.

The ongoing randomized, double-blind, placebo-controlled Phase 1/1b trial (NCT07235384) is evaluating single ascending doses of ZL-1503 in healthy volunteers and multiple ascending doses in adults with moderate-to-severe atopic dermatitis. The findings presented at ACAAI 2026 include pharmacokinetic (PK) data following single-dose administration, pharmacodynamic (PD) assessment of AD-related biomarkers across ZL-1503 dose levels ranging from 50 to 1,000 mg or placebo, and preliminary safety and immunogenicity data from a total of 48 healthy volunteers.

Key results include:

  • Sustained pharmacodynamic activity: At Week 12, ZL-1503 achieved at least 90% inhibition of pSTAT6 at doses ranging from 200 to 1,000 mg. Reductions were also observed in circulating type 2 inflammatory biomarkers associated with AD, including TARC, CCL26, and IgE.

  • Favorable pharmacokinetic and immunogenicity profiles: ZL-1503 demonstrated dose-proportional exposure. As of the data cut-off, no anti-drug antibodies were detected in participants who received ZL-1503.

  • Encouraging safety and tolerability: ZL-1503 was well tolerated at all evaluated dose levels, with no dose-limiting toxicities, treatment-emergent adverse events (TEAEs) leading to study drug interruption, or serious adverse events (SAEs) reported. Most TEAEs were mild and were associated with study procedures or intercurrent illnesses.

Data from the Part B trial cohort evaluating multiple ascending doses of ZL-1503 in patients with moderate-to-severe atopic dermatitis are expected in the first half of 2027. Zai Lab has also completed enrollment in an intravenous-to-subcutaneous bioavailability bridging study of ZL-1503. Initial data from this Phase 1 trial are expected in 2027.

ACAAI 2026 ZL-1503 poster details:

Title: Preliminary Results From The First-In-Human, Single Ascending Dose Study Of ZL-1503, A Half-Life-Extended Anti-IL-13/IL-31Rα Bispecific Antibody, In Healthy Volunteers

Presenter: Henry Wu, Zai Lab

Date/Time: Friday, November 13, 2026; 2:50 p.m. Mountain Time

ePoster ID: R376

Abstract Number: 8201

Details regarding the webcast and conference call are as follows:

Date/Time: Friday, November 13, 2026, at 5:00 a.m. PT / 8:00 a.m. ET / 9:00 p.m. HKT

Registration available at:

Webcast presentation (preferred): https://edge.media-server.com/mmc/p/a7xzskym

Dial-in: https://register-conf.media-server.com/register/BI3cdc6b1d6502458aaafbca52f735d28d

Presenter: Rafael G. Amado, M.D., President, Head of Global Research and Development, Zai Lab

About ZL-1503

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

ZL-1503 is currently being evaluated in an ongoing global Phase 1/1b clinical trial evaluating its safety, tolerability, pharmacokinetics, and preliminary efficacy. This clinical advancement is supported by preclinical studies demonstrating the ability of ZL-1503 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 www.linkedin.com/company/zai-lab or 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 and the potential treatment of atopic dermatitis and other immune-mediated inflammatory 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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