This clinical trial is focused on studying the effects of a treatment for allergic rhinitis, commonly known as hay fever, which is an allergy to grass pollen. The study will explore the use of a treatment called intralymphatic immunotherapy (ILIT), which involves injecting small amounts of allergens directly into a lymph node to help the body build tolerance. This treatment will be combined with vitamin D to see if it enhances the effectiveness of the therapy. The study will also compare this combination treatment to another method called sublingual immunotherapy (SLIT), where the allergen is placed under the tongue.

Participants in the study will receive either the ILIT treatment with vitamin D, ILIT without vitamin D, or a placebo. The purpose of the study is to determine if the combination of ILIT and vitamin D leads to a significant improvement in symptoms during the grass pollen season compared to ILIT alone. The study will monitor participants over a period of time to assess changes in their symptoms and quality of life related to their allergy.

The study will involve several visits where participants will receive their assigned treatment and undergo assessments to track their progress. These assessments will include questionnaires about their symptoms and quality of life, as well as tests to measure immune responses. The goal is to find out if the combination of ILIT and vitamin D can provide better relief from hay fever symptoms compared to other treatments.