Slide 1: Top-line Results for the Phase 2 VALIANT Trial in Severe Asthma
Top-line Results for the Phase 2 VALIANT Trial in Severe Asthma February 11, 2026 © 2026 Upstream Bio, Inc. Exhibit 99.1
Slide 2: Forward-looking statements
This presentation contains “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934, each as amended. These statements may be identified by words such as “aims,” “anticipates,” “believes,” “continue,” “could,”
Slide 3: Agenda
Agenda Introduction Rand Sutherland, MD Chief Executive Officer VALIANT Phase 2 Top-line Results Aaron Deykin, MD Chief Medical Officer and Head of R&D Path Forward Rand Sutherland, MD Analyst Q&A Rand Sutherland, MD Aaron Deykin, MD © 2026 Upstream Bio, Inc.
Slide 4: Phase 2 VALIANT study met primary endpoint in reduction of AAER
Phase 2 VALIANT study met primary endpoint in reduction of AAER © 2026 Upstream Bio, Inc. AAER, annualized asthma exacerbation rates * Placebo-corrected 400mg q24w 39% reduction in AAER (p<0.02) 139mL improvement in FEV1 26.3ppb* reduction in FeNO 44.9% * reduction vs baseline Verekitug was generall
Slide 5: About Upstream Bio
About Upstream Bio Clinical-stage immunology company focused on severe respiratory diseases © 2026 Upstream Bio, Inc. Developing the only known clinical-stage antagonist of the TSLP receptor Verekitug’s pharmacology is unique and characterized by rapid, complete and sustained occupancy of the TSLP r
Slide 6: Large and growing commercial opportunity in core indications
Large and growing commercial opportunity in core indications, with asthma and COPD alone expected to be a $35B+ global biologics market in 2033 Biologic eligible severe asthma patients in the US1 of biologic sales are in the US2 Severe Asthma 2023: $7.5B2 2032e: $12.6B2 CRSwNP 2025: >$1.5B5,6* COPD
Slide 7: Phase 2 VALIANT Trial in Severe Asthma
Phase 2 VALIANT Trial in Severe Asthma Aaron Deykin, MD Chief Medical Officer and Head of R&D © 2026 Upstream Bio, Inc.
Slide 8: VALIANT Phase 2 trial design
VALIANT phase 2 trial design Enrolled 478 patients with severe asthma across 15 countries1-3 Global, randomized, placebo-controlled phase 2 trial with up to 60-week treatment period (NCT06196879) © 2026 Upstream Bio, Inc. Follow-up Verekitug 400 mg SC q24w (Medium dose) Placebo SC q12w 1:1:1:1 N = 4
Slide 9: VALIANT ITT population disposition
VALIANT ITT population disposition 433 (91%) of participants completed treatment © 2026 Upstream Bio, Inc. *Including one participant who was not dosed due to AE. AE, adverse event; ITT, intent-to-treat; q×w, every × weeks. Data on file. Table 14.1.1.1. 478 participants randomized Placebo n=119 Vere
Slide 10: Baseline characteristics were balanced across treatment groups
Baseline characteristics were balanced across treatment groups Reflect an uncontrolled, severe asthma population Verekitug (n=) Age, mean (SD), years1 54.6 (12.15) 53.8 (11.74) 51.7 (15.37) 54.0 (13.06) Female sex, n (%)1 73 (60.3) 79 (66.9) 72 (60.0) 81 (68.1) Race, n (%)1 White Black/African Ameri
Slide 11: Verekitug was generally well tolerated across treatment groups
AE category, % of participants1 Any TEAE Any grade 3-5 TEAEs Any TEAEs with outcome of death Any serious TEAEs Any TEAEs leading to study drug discontinuation/interruption Most common TEAE, any grade (≥5% in any cohort)2 Nasopharyngitis Bronchitis Headache Urinary tract infection Back pain Influenza
Slide 12: Secondary endpoints
Secondary endpoints† AAER over 60 weeks (95% CI)1* 0.66 (0.47, 0.94) 0.92 (0.67, 1.27) 0.78 (0.55, 1.08) 1.52 (1.13, 2.03) Rate ratio vs placebo (95% CI) P value 0.44 (0.28, 0.69) 0.0003 0.61 (0.40, 0.93) 0.0227 0.51 (0.33, 0.79) 0.0028 – Prebronchodilator FEV1 (mL) change from baseline at 60 weeks,
Slide 13: Verekitug doses led to numerical improvements in lung function and FeNO
© 2026 Upstream Bio, Inc. Verekitug 100 mg q12w and 400 mg q24w doses led to numerical improvements in lung function and FeNO as early as week 2 and sustained over 60 weeks No. of participants Secondary endpoints were not powered for statistical significance. FeNO, fractionated exhaled nitric oxide;
Slide 14: Clinically meaningful improvements in secondary endpoints and biomarkers at 24 weeks
Verekitug led to clinically meaningful improvements in all secondary endpoints and biomarkers at 24 weeks © 2026 Upstream Bio, Inc. P values for secondary endpoints are nominal and not adjusted for multiple comparisons. ACQ-6, Asthma Control Questionnaire; FeNO, fractional exhaled nitric oxide; FEV1
Slide 15: AAER subgroup analysis
Verekitug Placebo Rate ratio (95% CI) Subgroups n AAER n AAER Overall 121 0.66 119 1.52 0.44 (0.28, 0.69) Age, years < 65 91 0.58 91 1.45 0.40 (0.23, 0.68) ≥ 65 30 0.87 28 1.67 0.52 (0.22, 1.22) Sex Male 48 0.47 38 2.09 0.23 (0.09, 0.57) Female 73 0.80 81 1.24 0.65 (0.39, 1.07) Region North America
Slide 16: Phase 2 VALIANT study met primary endpoint in reduction of AAER
Phase 2 VALIANT study met primary endpoint in reduction of AAER © 2026 Upstream Bio, Inc. AAER, annualized asthma exacerbation rates * Placebo-corrected 400mg q24w 39% reduction in AAER (p<0.02) 139mL improvement in FEV1 26.3ppb* reduction in FeNO 44.9% * reduction vs baseline Verekitug was generall
Slide 17: Path Forward
Path Forward Rand Sutherland, MD Chief Executive Officer © 2026 Upstream Bio, Inc.
Slide 18: Focused on data-driven decision-making and rapid execution
Focused on data-driven decision-making and rapid execution © 2026 Upstream Bio, Inc. Immediate next steps 2027 Conduct integrated analyses of Phase 2 data sets in CRSwNP and severe asthma to enable dose optimization and selection for Phase 3 trials in both indications Continue strong execution of Ph
Slide 19: Thank you Q&A
Thank you Q&A © 2026 Upstream Bio, Inc.