WALTHAM, Mass., Sept. 1, 2026
Upstream Bio, Inc. has announced its pivotal Phase 3 development plans for verekitug in severe asthma and chronic rhinosinusitis with nasal polyps (CRSwNP), following productive End-of-Phase 2 discussions with the U.S. Food and Drug Administration (FDA). The company plans to conduct one placebo-controlled Phase 3 trial in each indication, evaluating a single high-dose regimen of 400 mg verekitug administered every 12 weeks. Upstream Bio said the Phase 3 strategy is designed to evaluate the therapy in broad patient populations without restricting enrollment based on baseline biomarkers. The company remains on track to initiate both Phase 3 trials in the first quarter of 2027, advancing verekitug into late-stage development for two severe inflammatory respiratory diseases with substantial unmet medical needs.
Upstream Bio Advances Quarterly Verekitug Program
Upstream Bio’s Phase 3 strategy centers on quarterly dosing of verekitug, with approximately 1,500 patients expected to be enrolled across the two pivotal trials. The company intends to evaluate a single 400 mg subcutaneous dose administered every 12 weeks against placebo. In severe asthma, the primary endpoint will be annualized asthma exacerbation rate (AAER) over 48 weeks. In CRSwNP, the study will use co-primary endpoints measuring changes from baseline in nasal polyp score (NPS) and nasal congestion score (NCS) at 48 weeks. By using broad study populations, Upstream Bio aims to assess the potential efficacy of verekitug across patients irrespective of biomarker status. The company said the streamlined development strategy is intended to efficiently establish the therapy’s efficacy and safety while evaluating a convenient quarterly administration schedule for patients.
Verekitug Targets the TSLP Receptor
Verekitug is a fully human IgG1 monoclonal antibody designed to target and inhibit the thymic stromal lymphopoietin (TSLP) receptor, a signaling pathway involved early in inflammatory responses. According to Upstream Bio, TSLP activation can initiate downstream inflammatory pathways involving targets including IL-4, IL-5, IL-13, IL-17 and IgE. By targeting the TSLP receptor, verekitug is being developed to interfere with inflammatory signaling upstream of several downstream pathways. The company describes verekitug as the only known antagonist currently in clinical development that directly targets and inhibits the TSLP receptor. More than 500 participants have received verekitug across its clinical development programs, with positive Phase 2 results reported in severe asthma and CRSwNP. The candidate is also being evaluated in an ongoing Phase 2 trial for chronic obstructive pulmonary disease (COPD).
Advertisement
Phase 3 Trials Planned for First Quarter 2027
Upstream Bio expects both pivotal Phase 3 trials to begin in Q1 2027, marking the next major development milestone for verekitug. The company said that, if supported by successful Phase 3 results, it expects to submit a Biologics License Application (BLA) to the FDA for both indications, potentially supporting a commercial launch as early as 2030. The development strategy follows FDA discussions on the Phase 3 design and reflects the company’s focus on a high-dose, every-12-week regimen intended to combine sustained treatment exposure with less frequent administration. With verekitug moving toward pivotal testing in both severe asthma and CRSwNP, the company is positioning the program around its differentiated TSLP receptor mechanism, broad patient population strategy and potential for quarterly at-home treatment.
Source: Upstream Bio,, press relese
