Allergen immunotherapy or desensitization involves treatment with increasing doses of an allergen extract either given by injection into the skin or by a dissolvable tablet or drops under the tongue (sub-lingual immunotherapy). Unlike drug treatments for allergic disease which mask or suppress allergic reactions, immunotherapy "resets" the immune system to prevent allergic reactions. It was first used in the early 1900s.
Injection Allergen Immunotherapy
Injection under the skin was the first route used to give immunotherapy and remains the most effective form of this treatment. It involves injections of gradually increasing doses of allergen extract (which contains a carefully controlled mix of the allergen proteins of say, grass pollen) over time. For example treatment of grass pollen hay-fever might involve a series of increasing weekly doses over 12-16 weeks followed by monthly maintenance "shots".
The risk of immunotherapy is that injection of an allergen to a sensitised patient can cause a severe allergic reaction or anaphylaxis. For this reason such treatment should be given in expert centres with full support facilities, and a wait period of one hour after each injection is recommended.
What is immunotherapy used to treat?
In the UK injection immunotherapy is generally restricted to severe reactions to bee or wasp stings, or for severe summer hay fever that does not respond to other treatments. It can also be used or severe allergies to animals such as cats, dogs or horses, or in some cases for house dust mite allergy.
Injection immunotherapy is NOT used in the UK for patients with uncontrolled asthma or for multiple allergies. Similarly some other illnesses may prevent the use of immunotherapy.
How effective is injection immunotherapy?
In clinical trials one year of treatment resulted in up to 65% reduction in symptoms and medication requirement for severe hayfever: these were carefully selected patients. For bee and wasp venom there is a 90% or more reduction in the risk for anaphylaxis if stung.
If you are interested in finding out more ask your GP to refer you: the first step is a history and skin or blood tests to confirm IgE sensitisation to the allergen.
Recently an oral/sub-lingual (under the tongue) form of immunotherapy for grass pollen allergy was licensed in the UK. This preparation termed Grazax (TM ALK Ltd) is a tablet taken under the tongue then swallowed and is used every day for at least three months before the grass season then throughout the pollen season. It was effective in clinical trials with 40-60% reductions in symptom scores and requirement for medication. Side effects were minor, with no reported severe reactions or anaphylaxis although it is recommended that the first dose be given in the clinic, it can be used at home thereafter. Side effects include oral itching and mild swelling.
Other sub-lingual preparations are available but are not yet licensed in the UK.
Attempts have been made to reduce the number of injections needed for effective immunotherapy. These include modified allergens such as Pollinex Quatro (Allergy Therapeutics PLC) which can be given as four pre-seasonal injections with significant reduction of symptoms and requirement for medication in published trials (20-30%). These vaccines are available for grass, birch pollen and some other allergens.