Introduction to Immunotherapy

• Immunotherapy, also known as desensitisation, is a treatment designed to reduce immune reactivity to specific allergens.
• It involves gradually increasing doses of allergen extracts to modify the immune response.
• Administration Types:
  • Subcutaneous Immunotherapy (SCIT): Delivered through injections.
  • Sublingual Immunotherapy (SLIT): Taken as drops or tablets under the tongue.

Who Might Benefit from Immunotherapy?

• Candidates for Immunotherapy:

  • Life-threatening Insect Sting Reactions: Effective for venom allergies, especially for those who’ve experienced anaphylactic reactions.
  • Severe Hay Fever (Allergic Rhinitis): Recommended when symptoms cannot be managed with standard medications.
  • Severe Animal Allergies: Useful when avoidance is impractical and medications are insufficient.
  • Allergic Asthma: Beneficial for patients with mild to moderate allergic asthma uncontrolled by other medications.

• Who Might Not Benefit:

  • Multiple Allergies: Immunotherapy is typically limited to one or two allergens and not suited for individuals with multiple severe allergies.
  • Allergic Rashes: Conditions like eczema and urticaria do not respond well to immunotherapy.
  • Severe Asthma: Not recommended due to the heightened risk of severe allergic reactions.

Types of Immunotherapy

1. Subcutaneous Immunotherapy (SCIT)

   • Administration: Injections of purified allergen extracts in the upper arm.
   • Schedule: Begins with frequent doses in the induction phase, followed by maintenance doses at longer intervals.
   • Rush Immunotherapy: A faster protocol with multiple injections daily; usually requires hospital observation.
   • Side Effects: Local reactions such as itching or swelling are common, and some may experience flu-like symptoms.

2. Sublingual Immunotherapy (SLIT)

   • Administration: Daily allergen extracts taken under the tongue.
   • Advantages: More convenient than injections and associated with milder allergic reactions.
   • Disadvantages: Requires consistent daily use.

Immunotherapy’s Effects on Asthma

• Subcutaneous Immunotherapy (SCIT):

  • Provides small improvements in quality of life and symptom control for allergic asthma.
  • Can reduce asthma medication needs and alleviate clinical symptoms in patients with specific sensitivities (e.g., dust mites).

• Sublingual Immunotherapy (SLIT):

  • HDM-SLIT (for house dust mite allergies) can lower asthma exacerbations and medication use.
  • JCP-SLIT (for Japanese cedar pollen allergies) reduces seasonal asthma exacerbations.
  • U.S. Recommendations: Not currently approved for allergic asthma due to limited evidence.

Safety of Immunotherapy

• SCIT:

  • There’s a risk of systemic reactions, including anaphylaxis, often within 30 minutes post-injection, requiring close monitoring.
  • Risk Mitigation: Pre-treatment with oral antihistamines may reduce the likelihood of severe reactions.

• SLIT:

  • Has a lower risk of systemic reactions than SCIT, making it generally safer for most patients.

Mechanisms of Action

• Antibody Production:
  • Immunotherapy promotes the production of IgG and IgA antibodies that compete with IgE, reducing allergic responses.
• Cellular Changes:
  • Th2 Suppression: Reduces Th2 cells and cytokines like IL-4 and IL-5, decreasing airway inflammation.
  • Regulatory T Cells (Tregs): Increases in Tregs help suppress allergic inflammation, enhancing tolerance to allergens.

Long-Term Effects of Immunotherapy

• Disease Modification: Unlike pharmacotherapies, immunotherapy can change the natural course of allergic disease.
• Sustained Benefits: Effects often persist for years post-treatment.
• New Sensitisation Prevention: Some evidence suggests immunotherapy reduces the likelihood of developing new allergies.
• Asthma Prevention: May lower the risk of asthma in children with allergic rhinitis.

Important Considerations for Immunotherapy

• Patient Selection:

  • Immunotherapy is not suitable for all patients, with careful evaluation of allergies, symptom severity, and overall health.
  • Conditions such as uncontrolled asthma or use of beta-blockers may exclude patients from treatment.

• Treatment Duration:

  • Typically requires 3–5 years, with consistent adherence necessary for optimal efficacy.

• Cost and Accessibility:

  • Immunotherapy can be expensive, with variable insurance coverage and specialist availability.

Conclusion

• Immunotherapy provides a promising option for individuals with severe allergic conditions, offering long-term symptom control and the potential to alter the course of allergic diseases.
• Ongoing research aims to refine treatment protocols, improve safety, and identify markers for predicting treatment success.

References

1. Galli, S. J., & Tsai, M. (2021). Mechanisms of immunotherapy in allergic diseases. Journal of Allergy and Clinical Immunology, 148(4), 897-911. PMC

2. Allergy UK. (n.d.). Immunotherapy Factsheet. Allergy UK

3. National Heart, Lung, and Blood Institute. (n.d.). Immunotherapy for Allergic Asthma. NHLBI