Upstream Bio, Inc.

Upstream Bio, Inc. is a clinical-stage biotechnology company headquartered in Waltham, Massachusetts, focused on developing treatments for inflammatory diseases, with an initial emphasis on severe respiratory disorders. Founded in April 2021, the company's mission is to identify and address the upstream drivers of inflammation to alleviate the burden of these conditions on patients.

The company's lead product candidate is verekitug (also known as UPB-101), a clinical-stage monoclonal antibody. Verekitug functions by antagonizing the thymic stromal lymphopoietin (TSLP) receptor, thereby inhibiting TSLP-driven inflammation, a pathway implicated in various immune-mediated diseases. This therapeutic approach targets severe respiratory indications, including severe asthma, chronic rhinosinusitis with nasal polyps (CRSwNP), and chronic obstructive pulmonary disease (COPD). Verekitug is currently undergoing Phase 2 clinical trials across these indications.

Upstream Bio became a publicly traded company in October 2024, listing on Nasdaq under the ticker symbol UPB, following an upsized initial public offering that raised approximately $293 million. Dr. E. Rand Sutherland serves as the Chief Executive Officer, with Mike Gray as CFO and COO. In February 2026, the company reported positive top-line Phase 2 VALIANT results for verekitug in severe asthma, demonstrating a 56% reduction in annualized asthma exacerbation rate (AAER) at a 100 mg every 12-week dosing schedule. However, the stock experienced a significant drop following these results, as investors expressed concerns about the efficacy of a twice-yearly dose compared to existing competitors. Upstream Bio also presented additional Phase 2 VIBRANT data for verekitug in CRSwNP in March 2026, showing significant reductions in nasal polyp score and nasal congestion. The company plans to initiate Phase 3 dosing for verekitug in severe asthma and CRSwNP in the first quarter of 2027.