Mechanisms of Allergen Immunotherapy

Overview

This study will examine how allergen immunotherapy (allergy shots) works to reduce or prevent reactions to allergens such as pollen, dust or cat dander. Certain T cells (types of white blood cells) called Th2 cells produce substances that generate allergies. Other T cells called Th1 cells produce substances that have opposite effects. This study will determine if allergy shots change the immune response to allergens by reducing the number of Th2 cells or by changing them into Th1 cells. A better understanding of how this treatment works may help scientists develop more effective allergy therapies. People between 18 and 50 years of age who have had allergic asthma for at least 1 year may participate in this study. Candidates' medical, allergy and medication histories will be reviewed, and they will have a physical examination, including routine blood tests, urinalysis, electrocardiogram (EKG), and lung function test. Blood will also be drawn to test T cell response to allergens, and 12 skin tests (similar to a tuberculosis skin test) will be done to test for sensitivity to various allergens. Participants will be admitted to the Clinical Center for 1 to 2 days for rush therapy (see below). They will have a brief history and physical examination. A heparin lock (thin plastic tube similar to an intravenous line) will be placed in an arm vein. They will then undergo the following procedures: * Rush/Cluster Immunotherapy - An allergen is given in increasing doses over 2 to 5 weeks. During rush therapy, the dose is increased rapidly over 1 to 2 days until a moderate level dose is reached. To reduce the chance of an allergic reaction, patients take prednisone, cetirizine (Zyrtec® (Registered Trademark)), ranitidine (Zantac® (Registered Trademark)) and montelukast (Singular® (Registered Trademark)) starting 24 hours before treatment begins until rush therapy ends. After discharge on the third day, patients return to the clinic once a week for the next 2 to 5 weeks for cluster therapy, in which the dose is increased more gradually to a maintenance level. * Maintenance Immunotherapy - Participants receive 12 weekly injections at the maintenance dose. Blood is drawn during one visit between weeks 2 and 7 of maintenance therapy. * Follow-up Visits - Patients return to the clinic 2 and 3 weeks after the last maintenance dose for blood draws and evaluations. In addition, a "late-phase" allergen skin test is done at the 3-week follow-up to compare reaction results with those from the test done at the screening visit. * End-of-Study Visit - 12 to 16 weeks after the last allergy shot, patients return for a final blood draw and brief evaluation.

Asthma is a major public health problem due to its high prevalence and significant impact on activities of daily living. Allergen immunotherapy or vaccination consists of the therapeutic administration of allergen extract. The efficacy of allergen immunotherapy in asthma is modest, however immunotherapy remains the only known disease modifying therapy for allergic asthma. Because the exact mechanism through which immunotherapy works is unclear, a greater understanding of the mechanism of action of allergen immunotherapy is needed before modern immunopharmacologic methods can be applied to increase its therapeutic efficacy. This goal of the study is to determine the effects of allergen immunotherapy on allergen specific T cell responses. This is an open label study in which allergen specific CD4+T lymphocyte responses will be monitored before, during and after 12 weekly injections of maintenance immunotherapy, allowing the study of both the induction as well as decay of these changes. Immunotherapy will be employed in a rush/cluster schedule consisting of the serial administration of rapidly increasing doses of allergen delivered subcutaneously over a 2 day period (rush), followed by more gradually increasing weekly injections over 2-6 weeks (cluster), during which time the subject is brought to a maintenance allergen dose, which will then be repeatedly administered on a weekly basis. Immunological endpoints will consist of the frequency and cytokine profile of allergen specific T cell responses as measured by intracellular cytokine staining and the measurement of in vitro induced T cell cytokines by real time RT-PCR. Ten allergic asthmatic subjects will be enrolled in the therapeutic arm of the study.