How Does Allergy Immunotherapy Work?

Allergies of all kinds disrupt the lives of individuals worldwide and range in symptoms from mild discomfort to severe reactions. For those suffering from chronic and potentially life-threatening allergies, finding long-term relief can be challenging. While antihistamines and other medications may provide temporary relief, they don’t address the root cause which results in an allergic reaction. This is why allergy immunotherapy is a game-changer in the treatment of allergies – it is the only treatment that not only alleviates symptoms, but also alters the way the immune system responds to allergens. ⁵

Allergy immunotherapy, which includes both subcutaneous immunotherapy (SCIT) and sublingual immunotherapy (SLIT), is a method of treatment that gradually desensitizes the immune system to specific allergens. Over time, this leads to a significant reduction or even complete elimination of allergic reactivity. (HollisterStier products have not been authorized by the FDA for SLIT route of administration. Please refer to the full prescribing information for HollisterStier products.)

To understand how allergy immunotherapy works, it’s essential to grasp what allergies are and how they affect the body. Allergies occur when the immune system mistakenly identifies a harmless substance such as pollen, dust mites or pet dander, as a threat. In response, the immune system produces antibodies called Immunoglobulin E (IgE), which trigger the release of histamines and other biological chemicals, leading to the symptoms associated with allergies: sneezing, itching, swelling, and more.

Allergic reactions can vary in severity, ranging from mild seasonal allergies to life-threatening anaphylaxis. Common allergens include:

• Pollen
• Mold spores
• Pet dander
• Insect stings
• Certain foods (nuts, shellfish, dairy, etc.)

Alleriges can significantly impact quality of life, making daily activities uncomfortable or even dangerous for those with severe reactions.

The concept of allergy immunotherapy dates back to the early 20^th  century when Leonard Noon and John Freeman discovered that hay fever was caused by a sensitivity to grass pollen and that by introducing the same pollen in a distilled extract, patients would experience less severe symptoms. Today, immunotherapy is a well-established treatment used worldwide to manage a variety of allergies.¹

There are two main types of allergy immunotherapy: SCIT, commonly known as allergy shots, and SLIT, which involves placing drops or tablets under the tongue. Both methods aim to achieve the same goal, reducing the immune system’s overreaction to allergens, although they differ in their administration and treatment duration.

Allergy immunotherapy works by gradually exposing the immune system to increasing amounts of the allergen is allergic to, helping the body build tolerance over time. The treatment typically follows two phases⁵:

1. Desensitization (Build-Up) Phase: During this initial phase, the patient receives small doses of the allergen through a specific extract solution, either through injections or sublingual drops or tablets. These doses are gradually increased over several weeks or months, allowing the immune system to adapt without triggering a severe allergic reaction. The goal is to “train” the immune system to recognize the allergen as “harmless” so that an immune reaction is not triggered.
2. Maintenance Phase: Once the optimal dose is reached, the patient enters the maintenance phase, where the allergen extract dose remains consistent. By repeatedly exposing the body to the allergen, immunotherapy reduces the production of IgE antibodies and promotes the production of other antibodies, such as Immunoglobulin G (IcG), which block the allergen before it triggers an allergic response. Over time, this reprogramming of the immune system can lead to long-term tolerance, even after the treatment is ended.

As mentioned previously, there are two types of allergy immunotherapy, each with its unique approach and benefits:

• Subcutaneous Immunotherapy (SCIT):
  • Description and procedure: SCIT is the most common form of immunotherapy. It involves injecting small amounts of the allergen into the skin, usually in the upper arm. The injections start with a low dose and gradually increase over time.
  • Frequency and duration: SCIT typically requires weekly or bi-weekly visits to the allergist during the build-up phase, which lasts about 3-6 months. Once the maintenance dose is reached, injections are spaced out every 2-4 weeks for 3-5 years.
  • Benefits and potential side effects: SCIT is highly effective for a wide range of allergens including pollen, dust mites, and insect stings. Side effects are generally mild and may include redness or swelling at the injection site. Rarely, more severe reactions like anaphylaxis can occur, so treatments must be administered in a medical setting by a trained medical professional.
• Sublingual Immunotherapy (SLIT)*:
  • Description and procedure: SLIT involves placing allergen drops or tablets under the tongue, where the allergen is taken up by the immune system.
  • Frequency and duration: SLIT requires daily administration, which can be done at home.  Like SCIT, the treatment typically lasts 3-5 and must be prescribed by a medical provider.
  • Benefits and potential side effects: SLIT is a convenient option for those who prefer not to undergo regular injections or who might not have access to a medical provider every week. Side effects may include mild itching or swelling in the mouth. Serious reactions are rare, so certain patients may be advised to carry an epinephrine auto-injector as a precaution.

Both SCIT and SLIT are effective at reducing allergy symptoms and improving quality of life. The choice between the two depends on factors such as the type of allergy, patient preference, and convenience. SCIT is more versatile and treats a broader range of allergens. SCIT is currently the only effective treatment option for stinging insect venom allergies, including bee, wasp, yellowjacket, and hornet venom. The main benefit of SLIT is the lower likelihood of severe reactions which allows the treatment to be administered at home, reducing the amount of time a patient needs to spend in a medical office.

• Patients with moderate to severe allergies that are not well controlled with symptomatic medications
• Patients allergic to unavoidable allergens
• Patients known to have an anaphylactic reaction to an allergen in the past
• Patients older than five years old (or able to comply with treatment instructions and communicate any possible reactions)

Immunotherapy may not be suitable for patients with certain medical conditions, such as severe asthma or immune system disorders. A thorough evaluation by an allergist is essential to determine if immunotherapy is the right option.

Allergy immunotherapy offers a promising solution for those seeking long-term relief from allergies. By gradually desensitizing the immune system to specific allergens, immunotherapy reduces symptoms and addresses the root cause of the allergy. Whether administered through injections or sublingual drops⁶, immunotherapy can notably improve quality of life for allergy sufferers. With the potential to modify the course of allergic diseases and provide lasting relief, immunotherapy is a powerful tool in the fight against allergic reactions.

*HollisterStier products have not been authorized by the FDA for SLIT route of administration. Please refer to the full prescribing information for HollisterStier products.