Allergen-specific immunotherapy uses aqueous extracts of natural source materials as a basis for preparations to downregulate the allergic response. Recombinant DNA technology has enabled the cloning of many allergens, thus facilitating investigations aimed at improving efficacy and safety of immunotherapy.

To determine the effectiveness of a mixture of 5 recombinant grass pollen allergens in reducing symptoms and need for symptomatic medication in patients allergic to grass pollen.

A randomized, double-blind, placebo-controlled study of subcutaneous injection immunotherapy was performed in subjects with allergic rhinoconjunctivitis, with or without asthma. Primary endpoint was a symptom medication score compiled from separate symptom and medication scores. Secondary endpoints included a rhinitis quality of life questionnaire, conjunctival provocation, and specific antibody responses.

The symptom medication score showed significant improvements in subjects receiving recombinant allergens as opposed to placebo, with reductions in both symptoms and medication usage. The rhinitis quality of life questionnaire revealed clinically relevant significant improvements in overall assessment and in 5 of 7 separate domains, and conjunctival provocation showed a clear trend in favor of active treatment. All treated subjects developed strong allergen-specific IgG₁ and IgG₄ antibody responses. Some patients were not sensitized to Phl p 5 but nevertheless developed strong IgG antibody responses to that allergen.

A recombinant allergen vaccine can be a effective and safe treatment to ameliorate symptoms of allergic rhinitis. The clinical benefit is associated with modification of the specific immune response with promotion of IgG₄ and reduction of IgE antibodies consistent with the induction of IL-10–producing regulatory T cells.