A Study of Tolerability and Safety of a New Cumulative Dose of Grass MATA MPL

This will be a placebo‐controlled study, using a 1:1 randomization and parallel‐group, single‐blind design, in patients with seasonal allergic rhino‐conjunctivitis to grass pollen conducted at multiple centres in the US. The study will be conducted outside the grass pollen season and is comprised of 3 periods. ‐ Period 1: Screening ‐ Period 2: Randomization and treatment ‐ Period 3: Post‐treatment safety follow‐up Period 1 consists of the screening visit (Visit 1) at which patient eligibility will be assessed. Blood samples will be taken for clinical safety laboratory assessments and for baseline transcriptomics analysis. Eligible patients will proceed to Period 2 for enrolment into study. Period 2 starts with the randomization visit (Visit 2: 3‐33 days after Visit 1), at which eligible patients will be randomly allocated to the Grass MATA MPL 35600 SU or placebo treatment groups and receive the first of 6 weekly injections of subcutaneous immunotherapy (SCIT). Injections 2 to 6 will be administered at Visits 3 to 7. After each injection, patients will be kept under observation at the site for at least 30 minutes by personnel qualified to observe for and manage local and systemic adverse events. This period may be extended by the investigator according to his/her judgment. The observation will be followed up by a telephone call approximately 24 hours after the time of injection. In the event of mild or moderate systemic adverse events judged by the investigator to be well‐tolerated by the patient and to show good recovery, the patient may continue treatment as scheduled. Period 3 (Visit 8 ‐ End of Study) will occur 6‐8 days after Visit 7 to review any AEs and to perform end‐of‐treatment assessments, which will include blood draws for safety laboratory tests and transcriptomics analysis.