When is allergen immunotherapy effective?

Allergen immunotherapy is used to treat allergic symptoms such as rhinitis and itchy eyes in Japanese patients with cedar pollen allergy (JCPA). Administration of small amounts of pollen over several years may suppress severe allergic symptoms when these patients are later exposed to large amounts of pollen in the environment. Herein, we developed a simple mathematical model to identify conditions in which allergen immunotherapy is effective. We considered the dynamics of type 2 T helper cells (Th2) and regulatory T cells (Treg), both of which differentiate from naive T cells. Therapy was considered successful under the following three conditions: (1) Without therapy patients develop allergic symptoms upon exposure to environmental pollen, (2) with therapy patients do not develop symptoms upon exposure, and (3) patients do not develop allergic symptoms to the therapy itself. We defined scores for therapeutic success and identified ranges of parameters in which allergen immunotherapy is likely to be successful. Treg cells have a longer lifespan than Th2 cells, allowing accumulation over many years. In accordance, therapy with linear dose increases (rather than constant doses) reduced the risk of allergies to the therapy itself, and led to stronger accumulation of resistance to pollen exposure.