The aim of this study is to determine the optimal concentration of grass pollen allergens inducing rhinoconjunctivitis in subjects allergic to grass pollen in ALYATEC allergen exposure chamber.

Four concentrations of grass pollen allergen (Phl p 5) are tested during 3-hour exposures: 0, 30, 60 and 90 ng/m3.

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;

The grass pollen allergen (Phl p 5) concentrations corresponding to concentrations A, B, C and D are assigned randomly by the technician and the pharmacist of the exposure chamber so that neither the investigator, the participants nor the clinical and medical staff are aware of the exposure doses.