Results are expected in the second half of 2018, following which Allergy will expect to start work on the parameters for the Phase III trial.
The year-long study, which will involve 440 patients across Germany, Austria and Poland, is designed to identify the optimal effective dose and will adopt the challenge testing method used recently in a birch pollen allergy study.
If approved, the product will be the first registered subcutaneous (injected under the skin) immunotherapy product in the US for allergy.
The US allergy immunotherapy market might be worth as much as US$2bn currently with grass vaccine sales of US$300-400mln per annum.
Manuel Llobet, Allergy’s chief executive, said: "The start of treatment in this important Phase II trial marks an exciting and critical period of trials for the group's research and development pipeline.
"This trial aims to strengthen the Group's portfolio in Europe and the US and takes us another step closer to treating patients in the major US market."