The company is progressing with multiple Phase 2 trials for its investigational treatment targeting severe respiratory diseases.

Upstream Bio (UPB) shares saw an increase in after-hours trading on Friday following the company's presentation of pharmacology modeling data, which showed investigational antibody verekitug as potentially more potent than tezepelumab by targeting the TSLP receptor rather than its ligand.

Shares of the company finished at $11.36, down by 1.7%, but rose to $11.41 in after-hours trading with a 0.4% gain.

Results from the European Academy of Allergy & Clinical Immunology Congress demonstrated that verekitug produced lasting and thorough blockage of the TSLP/TSLPR complex, which drives critical inflammatory diseases, including severe asthma, as well as COPD and chronic rhinosinusitis with nasal polyps (CRSwNP).

The FDA-approved antibody Tezspire (tezepelumab), which targets severe asthma, operates through TSLP ligand inhibition and was developed jointly by AstraZeneca and Amgen.

The modeling study used a mechanistic PK/PD approach and incorporated clinical and published data. 

Simulations predicted that verekitug would lead to a greater reduction in fractional exhaled nitric oxide (FeNO)—a biomarker for airway inflammation—compared to tezepelumab.

The company is looking to assess top-line Phase 2 data in CRSwNP later this year, and in severe asthma in the first half of 2026.”

Verekitug is the only known monoclonal antibody in clinical development that directly targets the TSLP receptor, offering what the company describes as a more upstream and durable blockade of the inflammatory cascade.

The stock moved higher after the release, with investors responding positively to the strengthened differentiation case for verekitug as it advances through multiple Phase 2 trials. 

These include the Valiant study in severe asthma, the Vibrant trial in CRSwNP, and a planned trial in COPD.

Upstream Bio previously reported favorable tolerability, high subcutaneous bioavailability, and a consistent pharmacokinetic profile for verekitug in completed Phase 1 studies.

On Stocktwits, retail sentiment was ‘neutral’ amid ‘high’ message volume.

Upstream’s stock has declined 30.3% so far in 2025.

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