Upstream Bio, Inc. filed a Form 8-K with the SEC on September 1, 2026, disclosing its pivotal Phase 3 development plans for verekitug in severe asthma and chronic rhinosinusitis with nasal polyps (CRSwNP).

Key Highlights

  • Single dose regimen: The planned Phase 3 programs will evaluate a single high-dose subcutaneous regimen of 400mg administered every 12 weeks.
  • Patient enrollment: The company plans a single placebo-controlled study in each indication, enrolling approximately 1,500 patients across both trials combined.
  • Broad populations: Study populations are planned without restriction based on baseline biomarkers.
  • Primary endpoints: The asthma trial will measure annualized asthma exacerbation rates over 48 weeks; the CRSwNP trial will use co-primary endpoints of change from baseline in nasal polyp score and nasal congestion score, each at 48 weeks.
  • Phase 3 initiation timeline: The company stated it "remains on track to initiate Phase 3 clinical trials in severe asthma and CRSwNP in the first quarter of 2027."
  • Potential BLA submission: With supportive Phase 3 results, the company expects to submit a Biologics License Application to the FDA for both indications, which "could enable potential launch as early as 2030."

Upstream Bio's Verekitug Phase 3 Program Details

Upstream Bio, Inc. (NASDAQ:UPB), a Delaware-incorporated biopharmaceutical company headquartered in Waltham, Massachusetts, disclosed its pivotal Phase 3 development strategy for verekitug via an 8-K current report dated September 1, 2026. The disclosure was made under both Item 7.01 (Regulation FD) and Item 8.01 (Other Events), with an accompanying press release furnished as Exhibit 99.1.

According to the filing, the company plans to run a single placebo-controlled Phase 3 study in each of the two indications: severe asthma and CRSwNP. Both studies will evaluate a 400mg subcutaneous dose administered every 12 weeks. The filing states that study populations will be broad, with no restriction based on baseline biomarkers. For the asthma indication, the primary endpoint will be annualized asthma exacerbation rates measured over 48 weeks. For CRSwNP, the company disclosed co-primary endpoints consisting of change from baseline in nasal polyp score and change from baseline in nasal congestion score, each assessed at 48 weeks.

The filing notes that the company's forward-looking statements, including timelines for Phase 3 initiation, BLA submission, and potential launch, are subject to risks and uncertainties. These include the ability to advance verekitug through clinical development, dependence on third parties, regulatory interactions with the FDA, and the need for substantial additional funds, among other factors described in the company's most recent Annual Report on Form 10-K and Quarterly Report on Form 10-Q. The filing explicitly states that these forward-looking statements "represent the Company's views only as of today."

What Was Disclosed

Upstream Bio disclosed its Phase 3 clinical development plans for verekitug in severe asthma and CRSwNP, including dosing regimen, enrollment targets, study design, primary endpoints, and the company's stated timelines for trial initiation, BLA submission, and potential product launch.