This is a double-blind (masked) placebo-controlled trial in adults (N=108 subjects will be enrolled) with moderate to severe seasonal allergic rhinitis and allergic sensitization to grass pollen. Eligible participants who demonstrate a positive response defined by a Total Nasal Symptom Score [TNSS] ≥ 5 (Scale 0-12 in response to a Nasal Allergen Challenge [NAC] with grass pollen extract), will be randomized to one of the following 3 groups in a 1:1:1 ratio:~Grass allergen sublingual immunotherapy (SLIT) + dupilumab (n=36)~Grass allergen SLIT +dupilumab placebo (n=36)~Grass allergen SLIT placebo + dupilumab placebo (n=36)~Grazax® is a sublingual grass allergen immunotherapy product approved for clinical use in the United Kingdom and will be used as SLIT in this study. Grazax (and its matching placebo) will be self-administered daily by participants for a duration of two years.~Dupixent®is the brand name for dupilumab and is a monoclonal antibody against the interleukin 4 (IL-4) receptor. Dupilumab (and its matching placebo) will be administered every two weeks by subcutaneous injection through for a duration of two years, administered by study personnel. The treatment phase of two years will be followed by an observation phase of 1 year.
The primary objective of this study is to assess whether the combination of grass allergen sublingual immunotherapy (SLIT) and dupilumab for 2 years is more effective than double placebo in suppressing the nasal allergen challenge (NAC) response to grass pollen at 1 year after completion of study medication.