Upstream Bio, Inc.

Upstream Bio, Inc. is a clinical-stage biotechnology company that develops treatments for inflammatory diseases, primarily focusing on severe respiratory disorders. The company is developing verekitug, a monoclonal antibody that is the only known antagonist in clinical development targeting the receptor for Thymic Stromal Lymphopoietin (TSLP). TSLP is a cytokine that drives inflammatory responses. Verekitug has demonstrated potent inhibition of the TSLP receptor in preclinical and clinical data. Upstream Bio has advanced verekitug into separate Phase 2 trials for severe asthma, including a long-term safety and efficacy extension study (Phase 2 LTE), chronic rhinosinusitis with nasal polyps (CRSwNP), and chronic obstructive pulmonary disease (COPD). The company reported positive top-line results in its CRSwNP Phase 2 trial in September 2025 and positive top-line results in its severe asthma Phase 2 trial in February 2026. The Phase 2 COPD trial was initiated in July 2025. Upstream Bio plans to initiate dosing in Phase 3 trials for both severe asthma and CRSwNP in the first quarter of 2027, with a strategy focused on maximizing efficacy without biomarker restriction, and quarterly at-home administration. In 2023, total estimated biologics sales for asthma in the United States, Europe, and Japan markets were approximately $7.5 billion. There are seven biologics approved for severe asthma, four of which are also approved for CRSwNP, and two are also approved for COPD. In December 2021, tezepelumab (Tezspire), a monoclonal antibody targeting the TSLP ligand, was approved by the U.S.