Windward Bio’s WIN378 Delivers Positive Phase 2 Asthma Data as Twice-Yearly Anti-TSLP Antibody Moves Into Phase 3
Windward Bio has reported positive interim Phase 2 results for WIN378, also known as HBM9378 or SKB378, showing sustained improvements in lung function and key inflammatory biomarkers after a single dose in patients with uncontrolled asthma. With a half-life reaching 75 days and pharmacologic effects maintained through Week 24, the findings support the drug’s central proposition: controlling severe asthma with just two injections a year.
Windward has now initiated the Phase 3 portion of the global POLARIS-1 study, moving the ultra-long-acting anti-TSLP antibody into pivotal development. Windward Bio’s Phase 2 announcement
The advancement is also an important milestone for the drug’s original developers, Harbour BioMed and Kelun-Biotech, which jointly developed the molecule and originally shared its global rights equally. Windward subsequently licensed rights outside Greater China and several Southeast and West Asian markets. (PR Newswire)
A single dose produces effects lasting through six months
POLARIS-1 (NCT07120503) is an operationally seamless global Phase 2/3 study evaluating WIN378 in adults with uncontrolled asthma.
The Phase 2 portion is a 48-week, randomized, double-blind study comparing three subcutaneous dose levels of WIN378 with placebo. It was designed to characterize pharmacokinetics, safety, immunogenicity and pharmacodynamic activity, while examining lung function and airway inflammation and helping select doses for Phase 3.
Enrollment reached 147 patients, exceeding the original target of 120. The newly reported interim analysis covers the first 98 patients. (GlobeNewswire)
The results at Week 24 after a single dose were encouraging across several measures.
FEV1, a standard measure of lung function, increased in a dose-dependent manner by as much as 174 mL, with a placebo-adjusted improvement reaching 256 mL (p=0.033).
WIN378 also produced substantial reductions in two biomarkers closely associated with Type 2 airway inflammation. Fractional exhaled nitric oxide (FeNO) declined by as much as 24 ppb, or 43% (p=0.006), while blood eosinophils fell by as much as 200 cells/µL, or 51% (p<0.0001). (GlobeNewswire)
Perhaps more important for the drug’s differentiation, the effects appeared quickly and persisted. Near-maximal effects were observed as early as Week 2 and remained through Week 24, despite patients having received only a single dose.
WIN378’s observed half-life reached 75 days, and Windward said the interim clinical results and population pharmacokinetic modeling support the potential for twice-yearly administration. (GlobeNewswire)
Why twice-yearly dosing could matter
TSLP, or thymic stromal lymphopoietin, sits relatively high in the inflammatory cascade that drives asthma. Released largely by epithelial cells in response to environmental and inflammatory triggers, the cytokine can activate multiple downstream immune pathways.
The target has already been clinically validated in asthma, but Windward is attempting to differentiate WIN378 through duration of action and its binding characteristics.
WIN378 is a fully human monoclonal antibody engineered for increased potency, extended half-life and silenced effector function. According to Windward, it has a distinctive binding mechanism that blocks TSLP signaling by binding two different sites on TSLP and interfering with its interaction with both co-receptors on epithelial cells. (GlobeNewswire)
The molecule’s pharmacokinetic profile could be especially important commercially.
Long-term asthma biologics can be highly effective, but treatment requires patients to remain on regular dosing schedules. Reducing treatment to two doses per year could potentially lessen treatment burden and improve convenience—provided WIN378 ultimately demonstrates durable protection against asthma exacerbations.
That last point is now the critical question for Phase 3.
Phase 3 shifts the focus to asthma exacerbations
Based on the Phase 2 findings, Windward has selected two twice-yearly dose levels for the Phase 3 portion of POLARIS-1.
Unlike the interim analysis, which focused heavily on pharmacodynamics, lung function and biomarkers, the pivotal portion is designed to test whether those biological effects translate into meaningful clinical outcomes.
The primary endpoint is annualized asthma exacerbation rate in patients with severe asthma, alongside other key efficacy measures. (GlobeNewswire)
Windward has already initiated this Phase 3 portion and plans to start a second pivotal trial, POLARIS-2, during the first half of 2027.
The company also plans to present more complete Phase 2 POLARIS-1 data at an upcoming medical congress. (GlobeNewswire)
Clean safety profile so far
Safety did not raise obvious concerns in the interim analysis.
As of the data cutoff, Windward reported no treatment-related serious adverse events, withdrawals or treatment discontinuations. Overall adverse-event rates were balanced between WIN378 and placebo groups.
Injection-site reactions occurred in less than 1% of participants, while approximately 2% developed anti-drug antibodies. Windward said those antibodies had no observed impact on WIN378’s pharmacology. (GlobeNewswire)
The findings build on an earlier first-in-human Phase 1 study in 50 healthy adults, in which HBM9378 showed a mean half-life ranging from roughly 55 to 66 days across tested doses and was generally well tolerated. (Harbour Biomed)
The longer half-life of up to 75 days now observed in POLARIS-1 strengthens the rationale for the six-month dosing interval being taken into Phase 3.
A Harbour BioMed–Kelun asset now being developed globally by Windward
WIN378 has an unusually interesting development history.
Originally known as HBM9378 at Harbour BioMed and SKB378 at Kelun-Biotech, the antibody began as a co-development program between the two Chinese biopharma companies, which equally shared global rights. (PR Newswire)
In January 2025, the companies licensed WIN378 to Windward Bio for research, development, manufacturing and commercialization outside Greater China and several Southeast and West Asian countries.
The agreement included $45 million in upfront and near-term milestone payments, comprising cash and equity in Windward’s parent company, with total potential payments of up to $970 million, plus tiered royalties ranging from single digits to double digits on net sales. (Harbour Biomed)
For Harbour BioMed in particular, the program also serves as external validation of its antibody discovery technology. HBM9378 originated from the company’s H2L2 Harbour Mice platform, which generates conventional fully human antibodies. (Harbour Biomed)
WIN378 is expanding beyond asthma
Asthma is not the only opportunity being pursued.
Windward has also begun the Phase 2 SIRIUS study in chronic obstructive pulmonary disease (COPD), with the first patients dosed in June 2026. The expansion reflects the broader biological role of TSLP across inflammatory respiratory diseases. (Harbour Biomed)
That gives Windward two major respiratory indications in which to test whether WIN378’s ultra-long-acting profile can translate into a meaningful clinical advantage.
The Phase 2 POLARIS-1 results provide an encouraging first signal. A single dose produced sustained improvements in lung function and substantial reductions in inflammatory biomarkers through six months, while maintaining a clean safety profile.
But the pivotal test is still ahead.
For an asthma biologic designed around twice-yearly administration, the most important question is not simply whether it suppresses eosinophils or FeNO for six months. It is whether that sustained pharmacology can prevent clinically meaningful asthma exacerbations across the same interval.
Phase 3 POLARIS-1 is now positioned to answer that question. If the exacerbation data ultimately match the durability seen in the Phase 2 biomarkers and lung-function results, WIN378 could emerge as a differentiated entrant in the increasingly competitive asthma biologics market.
References
- Windward Bio — September 8, 2026. Positive Phase 2 results of WIN378 in asthma and initiation of Phase 3.
Windward Bio Phase 2/3 announcement - Harbour BioMed — September 8, 2026. HBM9378/WIN378 achieves positive Phase 2 results and enters Phase 3.
Harbour BioMed announcement - Kelun-Biotech — September 8, 2026. Positive Phase 2 results for SKB378/WIN378 and Phase 3 initiation.
Kelun-Biotech announcement - ClinicalTrials.gov. POLARIS-1 Phase 2/3 study, NCT07120503.
POLARIS-1 clinical trial record - Harbour BioMed — March 22, 2026. Phase 1 results for HBM9378/SKB378/WIN378.
HBM9378 Phase 1 results - Harbour BioMed — January 2025. License agreement with Windward Bio for HBM9378/SKB378.
HBM9378/WIN378 licensing agreement - Harbour BioMed — June 9, 2026. First patients dosed in the Phase 2 SIRIUS COPD study.
WIN378 SIRIUS COPD study announcement
