The purpose of the study is to assess the efficacy and safety of 300 IR sublingual tablet of grass pollen allergen extract compared to placebo in adult patient with allergic rhinoconjunctivitis.

Allergy is one of the most common chronic disease in the world currently affecting between 10% and 25% of the general population.

Allergies to pollens characteristically result in seasonal rhinitis symptoms and allergic rhinoconjunctivitis is characterized by sneezing, congestion, rhinorrhea, nasal or palatal itching and itchy, watery, red and swollen eyes.

Even if several drugs effectively manage allergic rhinoconjunctivitis symptoms, immunotherapy is considered more appropriate for patients in whom these symptoms are not optimally controlled with relief medications.

In the study, each of the six rhinoconjunctivitis symptoms (sneezing, runny nose, itchy nose, nasal congestion, itchy eyes, watery eyes) will be evaluated daily and relief medication intake (oral antihistamines, eye drop antihistamine, nasal corticosteroid, oral corticosteroid) reported daily during the grass pollen season.

Efficacy and good safety profile of 300IR SLIT tablet administered once per day for approximately six months (starting 4 months before and over the season) will be demonstrated during the grass pollen season compared to placebo.

Inclusion Criteria:

1. Grass pollen-related allergic rhinoconjunctivitis for at least the last two pollen seasons.
2. Positive SPT to grasses
3. Total symptoms score for the previous pollen season more than 12 out of 18.
4. Patients with FEV1 ≥ 80% of the predicted value.

Exclusion Criteria:

1. Positive SPT to other grasses present during the grass pollen season and if endemic to the region
2. Patients with clinically significant confounding symptoms of allergy to other allergens potentially overlapping the grass pollen season
3. Asthma requiring treatment with medications other than beta-2 inhaled agonists.
4. Patients who have received any desensitization treatment for grass pollen in the past 5 years.
5. Ongoing immunotherapy with any other allergen.
6. Patients with any nasal or oral condition that could confound the efficacy or safety assessments
7. Patients with known history of hypersensitivity or intolerance to any of the excipients in the investigational product (such as lactose intolerance).
8. Patients with any past or current clinically significant condition which as judged by the investigator, may affect the patient's participation or the outcome of the study.
9. Patients treated with systemic or inhaled corticosteroids
10. Patients treated or under treatment with beta-blockers, continuous systemic corticotherapy or immunosuppressive drugs.
11. Pregnant, breastfeeding, or sexually active women who are not using a medically accepted contraceptive method as listed above.
12. Patients participating or having participated within 30 days before Screening in any clinical study.
13. Patients who are unlikely to complete the study for any reason, or patients who have to travel for extended periods of time during the grass pollen season which will compromise the data
14. Patients with history of drug or alcohol abuse.
15. Study staff, investigators, sub-investigators, as well as their children or spouses and family members of all study staff should not be enrolled in the study.
16. Patients will not be randomized in this study more than once.