Asthma, a common problem among millions of people, is on the rise and so is the associated morbidity and mortality. This set of guidelines by EAACI (European Academy of Allergy and Clinical Immunology) can prove useful in taking decisions for prescribing AIT to patients of HDM-induced asthma.

EAACI recently developed a guideline for introducing Allergen Immunotherapy (AIT) as an add-on medicinal treatment for patients who suffer from house dust mite (HDM)-driven allergic asthma.

The guideline was formulated by a multi-disciplinary work group on the basis of the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. The evaluation for administration of subcutaneous (SCIT) and sublingual AIT (SLIT), drops and tablets was done for both, children and adults.

Note that the guideline does not address the following:

• Prevention of asthma caused due to allergy of HDM
• AIT alongside other allergen triggers
• The long-term benefit of AIT for HDM even after stopping AIT

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Allergen Immunotherapy (AIT)

AIT involves repeated administration of an allergen to induce tolerance in the patient. The generic treatment for the condition is mainly based on corticosteroids and other controllers, which help bring asthma under control and prevent exacerbations. However, because pharmacotherapy does not offer enough control over asthma and AIT has not been used to its full potential for either children or adults, it is being considered to fulfil the unmet need of controlling asthma triggered by HDM.

The reason for considering AIT is because it is possible to alter the underlying allergic disease mechanism, a trigger that creates a sustained clinical effect based on tolerance towards a specific allergen. Moreover, it seems to work for suppressing inflammation and bringing about multi-component improvement at a clinical level.

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Diagnosis of HDM-driven Asthma

Evaluating allergic sensitisation as a factor in asthma pathophysiology is important to understand how AIT can benefit when used alongside pharmacological asthma therapy. The same goes for endotypes, which play a significant role in asthma management at an individual level and the use of optimised AIT.

Currently, the diagnosis is based on the proof of HDM sensitisation combined with a detailed clinical history showing symptoms of HDM-driven asthma. Sequential longitudinal assessments over a period of one year can help confirm if HDM is the cause of asthma.

For accurate diagnosis of HDM‐driven allergic asthma:

• Evidence of allergic sensitization to HDM is needed
• Confirmation of HDM exposure and HDM as the main driver of asthma symptoms and control as per history needs to be proven
• A test to check allergen provocation (airway hyper-reactivity [AHR]) may be required

The conclusions to various trials are:

1. House dust mites, such as Dermatophagoides (D) pteronyssinus or D. farina are major triggers to asthma
2. These lead to the development of high‐titre allergen‐specific IgE
3. And there is substantial evidence, which correlates allergic conditions such as asthma, allergic rhinitis (AR) and atopic dermatitis (AD) with exposure to HDM or other indoor allergens

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Evidence-based Recommendations for AIT

Given below are the evidence-based recommendations for AIT applicable only to HDM-induced asthma:

HDM Subcutaneous Immunotherapy (SCIT)

1. HDM SCIT is recommended as an add-on treatment to regular therapy for children and adults with controlled HDM-driven allergic asthma. When used alongside regular therapy, HDM SCIT helps reduce symptoms and the use of medication.
2. HDM SCIT is recommended as an add-on treatment to regular therapy for adults with controlled HDM-induced asthma. This helps bring down allergen-specific AHR and improve quality of life.

The recommendations are conditional and based on low-quality evidence.

3. HDM-SCIT is recommended as an additional treatment, alongside regular asthma therapy for adults with controlled or partially controlled HDM‐driven allergic asthma.

Conditional recommendation based on moderate‐quality evidence.

Remarks:

• Asthma control and lung function should be assessed regularly
• Patients with moderate asthma may show better benefit (more safety data needed).
• The potential benefits in children could include the ICS sparing effect

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HDM Sublingual Immunotherapy (SLIT)

1. HDM SLIT drops are recommended for children with controlled HDM‐driven allergic asthma as an add‐on to regular asthma therapy. When used alongside regular therapy, the treatment is known to reduce symptoms and medication needs for HDM-induced asthma.

Conditional recommendation based on low‐quality evidence.

2. HDM SLIT‐tablets are recommended as a treatment in addition to the regular therapy, for adults with controlled and partially controlled, HDM‐induced allergic asthma. This can help bring down exacerbations and improve asthma control.

Conditional recommendation based on moderate‐quality evidence.

3. HDM SLIT (tablet) has showed a strong effect in adults for critical end points (exacerbations, asthma control, and safety). Thus, it is recommended as a treatment in addition to the regular asthma therapy for adults with controlled or partially controlled, HDM-induced allergic asthma.

Conditional recommendation based on moderate-quality evidence.

Remarks:

• Asthma control and lung function should be assessed regularly
• Patients with partially controlled asthma or with a history of severe asthma exacerbations over the past year should be carefully monitored

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Duration of AIT

There is evidence for efficacy after the first year of HDM AIT and currently, SCIT and SLIT are given for up to three years of treatment with an aim of achieving long-term efficacy. And there does not seem to be any additional benefit of giving therapy for five years.

The efficacy of HDM-induced asthma should be assessed after a year, using the same approach for asthma controller medication. If the assessment does not show efficacy after one year, a consideration must be given to stopping AIT.