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Allergen immunotherapy

Allergen immunotherapy is the only treatment option that not only treats the symptoms but also the causes of allergies. It is well established for respiratory allergies since the 1920ies.

Allergen immunotherapy is particularly useful for allergies to insect bites and asthma. For food allergies, allergen immunotherapy is only used since two decades and remains an experimental treatment option.

The principle of desensitisation

Allergen immunotherapy is also called desensitisation or hypo-sensitisation. The principle of allergen immunotherapy is to desensitise the immune system by introducing very low doses of the allergen. Afterwards, increasing doses of allergen are administered.

In the course of a successful desensitisation the (mis-)response of the allergic immune system decreases and allergy improves. Patients who do not respond after an entire year of allergen immunotherapy are unlikely to improve with further treatment. In these patients allergen immunotherapy should be discontinued.

Treatment risks

During allergen immunotherapy, adverse systemic reactions are uncommon. However, because of the risk of severe allergic reactions (anaphylaxis) – especially after injections – allergen immunotherapy should only be administered by trained healthcare providers and emergency medications (antihistamine, corticosteroids and epinephrine) and equipment should be immediately available. Therefore, hospitalisation might be necessary.

Allergen immunotherapy in clinical practice

There are three types of administering the allergen:

• Subcutaneous immunotherapy – allergy shots, high risk of systemic anaphylactic reactions
• Sublingual immunotherapy – drops or tablets under the tongue, efficacy low
• Oral immunotherapy – traces in food or tablets, only recently used for food allergies

Subcutaneous and sublingual immunotherapy

Subcutaneous and sublingual immunotherapies are used since decades for the treatment of various allergies, especially for respiratory allergies, like asthma, and for allergies to insect bites. In experimental settings, sublingual immunotherapy is used as a causative treatment for food allergies in children. For more information please consider public information on the internet and excellent scientific reviews on this topic.

Oral immunotherapy

Beside sublingual immunotherapy, oral immunotherapy is the only causative treatment for food allergies. Although oral immunotherapy is used since two decades, clinical trials are scarce. Oral immunotherapy is mainly used in clinical studies for food allergies to peanuts, milk, and eggs. Oral immunotherapy showed promising results in reducing sensitivity to these food allergens. However, it is not ready for routine clinical practice and remains an experimental therapy.

A notable exception is the ingestion of heated milk and egg. This type of oral immunotherapy appears to be safe and effective – especially for children – and might soon enter into clinical practice.

Protocols for oral immunotherapy vary considerably. They typically include an initial rapid dose escalation day, followed by a build-up phase, and then a maintenance phase, similar to inhalant subcutaneous immunotherapy. It seems that for patients with extreme food allergy, a slower, more cautious version of the treatment protocol is needed. Treatment efficacy is generally tested using oral food challenges and skin-prick tests.

Successful oral immunotherapy is used for treating food allergies and decreases the IgE-dominated response. Furthermore, it increases allergen-specific IgG4 and IgA antibodies and reduces the reactivity of mast cells and basophils, which both largely contribute to allergic reactions.

“Oral immunotherapy remains an experimental therapy”

Although some health providers offer oral immunotherapy in their practice, there are many questions to be answered until oral immunotherapy will become broadly available. These questions include:

• The optimal dosing for all stages of oral immunotherapy needs to be clarified.
  • Same applies to the duration and frequency of optimal dosing
• It is currently unknown if oral immunotherapy can induce permanent allergen tolerance
• Most clinical studies have excluded people with severe allergic reactions (anaphylaxis)

Because oral immunotherapy is experimental, there are also completely new treatment strategies under investigation. One such novel treatment strategy in oral immunotherapy is to use peanut proteins that are attached to white blood cells. For patients with extreme food allergy the use of Omalizumab – an anti-IgE monoclonal antibody – greatly increases safety and tolerability of oral immunotherapy, without interfering with an effective desensitisation.

Outcomes of allergen immunotherapy

The aim of allergen immunotherapy is to help your body get used to the allergen so it doesn’t react to it so severely. Allergen immunotherapy might not cure your allergy entirely, but may greatly improve your allergic symptoms.

Successful allergen immunotherapy has been demonstrated to provide long-term clinical benefits, including symptom reduction even more than 3 years after end of treatment. Thus, allergen immunotherapy can greatly improve your quality of life. Successful allergen immunotherapy results in a long-term reduction in serum allergen-specific IgE levels and greatly reduces the early immune response.

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