Harbour BioMed’s WIN378 Shows Positive Phase 2 Asthma Data

Cambridge, Massachusetts, U.S.; Rotterdam, Netherlands; and Shanghai, China, September 8, 2026

WIN378 Shows Sustained Lung Function Improvement

The Phase 2 portion of POLARIS-1 enrolled 147 patients with uncontrolled, moderate-to-severe asthma, exceeding the initial target of 120 participants. The interim analysis included the first 98 patients and evaluated three dose levels of HBM9378/WIN378 against placebo. The study was designed to characterize pharmacokinetics, safety, immunogenicity and pharmacodynamic activity, while also assessing lung function and biomarkers of airway inflammation to guide dose selection for Phase 3. At Week 24 following a single dose, HBM9378/WIN378 demonstrated dose-dependent improvements in forced expiratory volume in one second (FEV1), an important measure of pulmonary function. Mean increases reached 174 mL, while placebo-adjusted mean increases reached 256 mL, with a reported p-value of 0.033. The effects emerged rapidly, with near-maximal responses observed as early as Week 2 and remaining sustained through Week 24. These results are particularly relevant to the company’s strategy of developing an antibody capable of providing extended treatment intervals.

TSLP Biomarkers Support Biological Activity

The interim analysis also demonstrated significant changes in key markers of airway inflammation. Mean fractional exhaled nitric oxide (FeNO) levels decreased by as much as 24 parts per billion, corresponding to a 43% reduction, with a reported p-value of 0.006. Mean blood eosinophil counts declined by as much as 200 cells/µL, or 51%, with a p-value below 0.0001. Both biomarkers are associated with inflammatory activity and can correlate with asthma exacerbations. HBM9378/WIN378 is a fully human, ultra-long-acting monoclonal antibody engineered to inhibit TSLP through a differentiated binding mechanism. The molecule binds to two distinct sites on TSLP, interfering with the interaction between TSLP and both of its co-receptors on epithelial cells. It was also engineered for increased potency, extended half-life and silenced effector function. The reported half-life of up to 75 days provides the pharmacokinetic rationale for investigating twice-yearly administration. The biomarker findings complement the observed lung-function improvements by providing evidence of pharmacodynamic activity following treatment. However, the Phase 2 findings remain interim, and the ongoing pivotal studies will be required to establish whether these biological effects translate into clinically meaningful reductions in asthma exacerbations.

Phase 3 Program Advances Twice-Yearly Dosing

The investigational therapy demonstrated a favorable interim safety and tolerability profile. As of the reported data cutoff, there were no treatment-related serious adverse events, withdrawals or discontinuations. Overall adverse events were balanced between treatment and placebo groups, while fewer than 1% of participants experienced injection-site reactions. Anti-drug antibodies were detected in 2% of participants, with no reported impact on the pharmacology of HBM9378/WIN378. The Phase 2 findings and population pharmacokinetic modeling supported advancement to the Phase 3 portion of POLARIS-1, which is evaluating two twice-yearly doses of HBM9378/WIN378 against placebo in patients with severe asthma. The primary endpoint is the annualized asthma exacerbation rate, alongside other efficacy measures. A second pivotal study, POLARIS-2, is planned to begin in the first half of 2027. The development program also extends beyond asthma. HBM9378/WIN378 is being evaluated in the Phase 2 SIRIUS study in chronic obstructive pulmonary disease (COPD), reflecting the broader potential of TSLP inhibition across respiratory diseases. For biopharmaceutical development, the Phase 2 results are notable for combining sustained FEV1 improvement, reductions in FeNO and eosinophils, favorable interim safety findings and pharmacokinetic support for twice-yearly dosing. The ongoing Phase 3 program will determine whether these findings can translate into reduced asthma exacerbations and support future regulatory development of this ultra-long-acting TSLP antibody.

Source: Harbour BioMed press release