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Allergy immunotherapy: indications, efficacy, and safety: the clinical benefits usually last for years.

Article Excerpt
ABSTRACT: Although many effective pharmacological therapies are available for patients with allergies, only allergen-specific immunotherapy has been shown to have significant and long-lasting therapeutic and immunomodulatory effects in the management of allergic rhinitis, allergic asthma, and venom hypersensitivity. Standard allergen immunotherapy consists of subcutaneous injections of relevant allergens. It requires a buildup phase during which the dose of the vaccine is increased until a therapeutic (maintenance) level is achieved. This maintenance dose is usually continued for 3 to 5 years, and most patients continue to do well after injections are discontinued. Most patients tolerate immunotherapy well, but local reactions are not uncommon. Immunotherapy should be administered only in a physician's office, because some patients may experience systemic anaphylactic reactions requiring immediate therapy. Even with newer therapies on the horizon, allergen immunotherapy will continue to have an important role in the treatment of allergic diseases.

KEY WORDS: Immunotherapy, Allergy, Rhinitis, Insect hypersensitivity, Extrinsic asthma

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Allergic diseases have increased in prevalence over the past 20 years, affecting as many as 40 to 50 million persons in the United States. Since it was first described by Noon, (1) allergen immunotherapy has been used for nearly 100 years.

Allergen immunotherapy alters the course of allergic diseases through a series of injections of a mixture of extracts composed of clinically relevant allergens. The term "allergen extract" had been replaced by "allergen vaccine" by the World Health Organization until recently when the new term "allergen immunotherapy extract" was coined to define the mixture of extracts or the extract used for allergen immunotherapy. (2, 3) Allergen extract refers to the source material not yet integrated into the vaccine. Other terms used for allergen immunotherapy include hyposensitization, desensitization, allergy shots, and allergy injections.

In this article, I will review the indications and contraindications of allergen immunotherapy and how it is administered. I also will discuss its efficacy and safety.

Mechanisms

The exact mechanisms of how immunotherapy works are not fully understood, but they involve shifting a patient's immune response to an allergen from a predominantly "allergic" T-lymphocyte ([T.sub.H]2) response to a "nonallergic" T-lymphocyte ([T.sub.H]1) response. Lymphocytes of a [T.sub.H]2 phenotype typically produce interleukin (IL)-4 and IL-5, which are cytokines needed for IgE production and eosinophil survival, while [T.sub.H]1 lymphocytes produce interferon gamma.

Allergen immunotherapy causes regulatory T cells to produce increased levels of IL-10. (4) IL-10 causes a shift in allergen-specific IgE to allergen-specific IgG4, while the regulatory T cells down-regulate allergic immune responses in part through the release of IL-10 and transforming growth factor [beta].

When allergen immunotherapy is administered, the seasonal increase in allergen-specific IgE is blunted while protective allergen-specific IgG4 production is increased. The effectiveness of allergen immunotherapy is not dependent on the reduction in specific IgE levels. Periodic skin testing and in vitro IgE antibody measurements are not useful in evaluating responses to immunotherapy.

Indications

Allergen immunotherapy is used in the treatment of allergic rhinitis, allergic asthma, and stinging insect venom hypersensitivity. (5-8) The diagnosis of these diseases is based on the history and physical examination findings, supported by testing to confirm IgE sensitization. Skin testing by prick or intradermal method is the preferred diagnostic technique, but in vitro tests, such as CAP RASTs, are an alternative, especially when skin testing cannot be performed. Patients who have specific IgE--positive test results but no corresponding clinical findings are not candidates for allergen immunotherapy.

Candidates for venom or Hymenoptera immunotherapy include all patients who have experienced life-threatening allergic reactions or non--life-threatening systemic reactions to Hymenoptera stings. (3, 8) For a patient with...

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