Determination of Grass Pollen Allergen Concentration Inducing Rhinoconjunctivitis Symptoms in Subjects Allergic to Grass Pollen in ALYATEC Allergen Exposure Chamber

Main Inclusion Criteria: * Subjects with symptoms of allergic rhinoconjunctivitis to grass pollen without associated asthma, requiring anti-allergic treatment for at least 2 consecutive pollen seasons; * Subjects with positive skin prick tests to grass pollen extracts (Phleum pratense): papule diameter ≥ 5 mm compared to the negative control (NaCl reaction \< 2 mm)); * Subjects with Phl p 5 specific recombinant Immunoglobulin E ≥ 0.70 kIU/L; * Forced expiratory volume in 1 second (FEV1) ≥ 70% of predicted value at screening and before allergenic exposures; * Women of childbearing age must have a negative pregnancy test at screening and before exposure visits; Main Exclusion Criteria: * Specific immunotherapy (SIT) to grass pollen allergens for more than one month in the 3 years preceding the screening visit; * Ongoing specific immunotherapy to another allergen * History of anaphylaxis following exposure to grass pollen or grass SITs; * Asthma * Ear, Nose \& Throat or ocular surgical intervention in the 6 months preceding inclusion;