Upstream Bio is a clinical-stage biotechnology company developing a single drug candidate, verekitug, a monoclonal antibody that blocks the TSLP receptor to suppress inflammatory cascades in severe respiratory diseases. The initial target indications are severe asthma, chronic rhinosinusitis with nasal polyps (CRSwNP), and COPD. Verekitug is the only clinical-stage antibody known to target the TSLP receptor directly, as opposed to blocking the TSLP ligand like tezepelumab (Tezspire). Upstream Bio argues verekitug is differentiated by its potency, which supports quarterly (or less frequent) dosing versus monthly dosing for competing drugs, and by its potential to treat patients regardless of inflammatory biomarker status. Verekitug has reported positive Phase 2 results in both severe asthma and CRSwNP, and is currently in Phase 2 trials for COPD. Upstream Bio plans to initiate Phase 3 trials in severe asthma and CRSwNP in early 2027. The company has no revenue and funds operations through equity financing. It outsources all manufacturing to CDMOs and plans to commercialize verekitug, if approved, through a focused sales force targeting specialist physicians. Verekitug was acquired from Astellas in 2021, and Upstream Bio owes royalties to Regeneron and Lonza on any future net sales.