Long-Term Effects of Sublingual Grass Therapy

Inclusion Criteria: * A clinical history of grass pollen-induced allergic rhinoconjunctivitis for at least 2 years with peak symptoms in May, June, or July; * A clinical history of moderate to severe rhinoconjunctivitis symptoms interfering with usual daily activities or with sleep as defined according to the Allergic Rhinitis and its Impact on Asthma (ARIA) classification of rhinitis; * A clinical history of rhinoconjunctivitis for at least 2 years requiring treatment with either antihistamines or nasal corticosteroids during the grass pollen season; * Positive skin prick test response, defined as wheal diameter greater than or equal to 3 mm, to Phleum pratense (e.g., Timothy grass); * Positive specific IgE, defined as greater than or equal to IgE class 2 (0.7 kU/L), against Phleum pratense; * A positive response to nasal allergen challenge with Phleum pretense, defined as an increase in TNSS greater than or equal to 7 points above baseline; * For women of childbearing age, a willingness to use an effective form of contraception for the duration of the trial; and * The ability to give informed consent and comply with study procedures. Exclusion Criteria: * Prebronchodilator forced expiratory volume at 1 second (FEV1) less than 70% of predicted value at either screening or baseline visit; * A clinical history of moderate to severe allergic rhinitis, according to the ARIA classification, due to tree pollen near or overlapping the grass pollen season; * A clinical history of persistent asthma and/or requiring regular inhaled corticosteroids for \> 4 weeks per year outside of the grass pollen season; * A clinical history of moderate- severe allergic rhinitis, according to the ARIA classification, caused by an allergen to which the participant is regularly exposed; * History of emergency visit or hospital admission for asthma in the previous 12 months; * History of chronic obstructive pulmonary disease; * History of significant recurrent acute sinusitis, defined as 2 episodes per year for the last 2 years, all of which required antibiotic treatment; * History of chronic sinusitis, defined as a sinus symptoms lasting greater than 12 weeks that includes 2 or more major factors or 1 major factor and 2 minor factors. Major factors are defined as facial pain or pressure, nasal obstruction or blockage, nasal discharge or purulence or discolored postnasal discharge, purulence in nasal cavity, or impaired or loss of smell. Minor factors are defined as headache, fever, halitosis, fatigue, dental pain, cough, and ear pain, pressure, or fullness. * At randomization, current symptoms of, or treatment for, upper respiratory tract infection, acute sinusitis, acute otitis media, or other relevant infectious process; serous otitis media is not an exclusion criterion. Participants may be re-evaluated for eligibility after symptoms resolve. * Any tobacco smoking within the last 6 months or a history of ≥ 10 pack years; * Previous treatment by immunotherapy with grass pollen allergen within the previous 5 years. * Any history of grade 4 anaphylaxis due to any cause as defined by the World Allergy Organization (WAO) grading criteria for immunotherapy; * History of bleeding disorders or treatment with anticoagulation therapy; * History of anti-IgE monoclonal antibody treatment; * Ongoing systemic immunosuppressive treatment; * History of intolerance to the study therapy, rescue medications, or their excipients; * For women of childbearing age a positive serum or urine pregnancy test with sensitivity of less than 50 mIU/mL within 72 hours before the start of study therapy; * The use of any investigational drug within 30 days of the screening visit; or * The presence of any medical condition that the investigator deems incompatible with participation in the trial.