Jasper Therapeutics Inc. (JSPR) released preliminary data Tuesday from its ETESIAN Phase 1b study that should make asthma researchers sit up and take notice. The company tested subcutaneous briquilimab in adult patients with allergic asthma, and the results tell a compelling story about what happens when you can effectively target the underlying mechanisms of the disease.
Here's what stood out: a single 180mg subcutaneous dose of briquilimab produced substantial reductions in sputum eosinophils at both six and twelve weeks. For context, eosinophils are white blood cells that play a starring role in allergic asthma, and getting those numbers down matters. The drug also delivered improvements over baseline in FEV1, which is essentially the gold standard for measuring how well someone's lungs are functioning. These improvements showed up in both Early Asthmatic Response and Late Asthmatic Response measurements.
The company also saw significant reductions in serum tryptase, mirroring what other briquilimab studies have shown at the 180mg dose level. And importantly, patients tolerated the treatment well, with a favorable safety profile throughout.
Breaking Down the Eosinophil Results
Treatment with briquilimab decreased sputum eosinophil levels before and after allergen challenge, which is exactly what you want to see in asthma studies. Patients in the briquilimab group showed reduced mean sputum eosinophil levels at pre-allergen challenge timepoints, dropping from 1.88% at baseline down to 0.44% at day 41 and 0.38% at day 83. The drug also reduced mean sputum eosinophil levels 24 hours following allergen challenge.
On the safety front, briquilimab performed well in the study with no dose-limiting toxicities observed. Safety observations potentially related to KIT blockade were infrequent and generally limited to low-grade events. None resulted in discontinuations or dose delays, and most resolved during repeat dosing.
Mystery Solved: What Went Wrong in Earlier Trial Cohorts
Jasper also addressed the elephant in the room. The company completed its internal investigation into some puzzling results from July 2025, when cohort 8 and cohort 9 in the BEACON trial showed an anomalous lack of clinical response. In those cohorts testing 240mg doses, not a single U.S. patient out of ten achieved Complete Response or Well Controlled UAS7 by week 12, which was obviously concerning.
After completing their investigation, reviewing additional data from subsequent dosing, and consulting with a panel of chronic spontaneous urticaria experts, Jasper concluded the unexpected results weren't caused by problems with the drug product itself. Instead, it appears to have been a patient selection issue. According to the company, nine of the ten patients in question likely didn't actually have chronic spontaneous urticaria, as their symptoms weren't mast cell-driven.
JSPR Price Action: Jasper Therapeutics shares were up 8.72% at $1.87 at the time of publication on Tuesday. The stock is trading near its 52-week low of $1.56.
