Because the allergy desensitization process can cause severe reactions including anaphylaxis, a physician should supervise trained personnel.[3] The required training is[3]:

• Preparation of allergenic products
• Successful completion of a written test on aseptic technique and extract preparation and media-fill testing
• Knowledge of antiseptic hand cleaning and disinfection of mixing surfaces
• Ability to identify, measure, and mix ingredients

The prescribing physician should select allergen extracts. The physician should consider several important factors including the quality of allergen extracts, cross-reactivity, and degradation of allergens and immunotherapy doses, for example, the starting dose will be lower than the maintenance dose.[3]

Allergenic proteins from pollen, dander, dust mites, insects, mold, among others are the main ingredient of allergen extract. However, the final product is a mixture of diluents or solvents and preservatives. Different extracts including aqueous, glycerinated, lyophilized, acetone precipitated, alum-precipitated are available. Diluents will keep the allergen in liquid form; commonly used agents are glycerin, phenol saline, and HSA. The staff should use measures that include good personal hygiene, hand washing, and antiseptics to clean working areas. These include a water-based disinfectant followed by the application of alcohol on working surfaces for preparing allergen extracts. Alcohol kills organisms by dehydration. Sanitization will prevent bacterial contamination.[3]

Complications include systemic reactions like anaphylaxis and a local reaction at the injection site.[3]

Management of Complications[3]

• Topical corticosteroids, antihistamines, or cool compresses for local reaction
• Epinephrine is the mainstay treatment for anaphylaxis.

The physician should re-visit the benefit versus risk of continuing immunotherapy after systemic reactions.[3]

Asthma

Allergen immunotherapy can reduce short-term symptoms in allergic asthma; however, there is a moderate increase in the risk of systemic and local reactions based on meta-analysis.[6] A 3-year course of either sublingual or subcutaneous immunotherapy prevents asthma for up to 2 years in children and adolescents with grass/birch pollen that triggers moderate to severe allergic rhinitis; However, this still requires further research.[4]

Allergic Rhinitis

• Allergen immunotherapy is clinically effective, cost-effective, and disease-modifying in allergic rhinitis compared to standard drugs.[10][11]
• Sublingual immunotherapy for pediatric allergic rhinitis has shown improvement in symptomatic management and a decreased medication need based on a meta-analysis of the randomized controlled trials. More trials with a larger sample size are underway to assess safety in the pediatric population.[12]

Allergic Rhino-Conjunctivitis

Allergen immunotherapy has been found to be beneficial in improving rhino-conjunctivitis symptoms[13]. Some evidence suggests that there is a maintenance effect on reducing symptoms after discontinuation of immunotherapy.[14]

Current and Future Trends in Allergen Immunotherapy

There are different approaches to providing safety and overcoming the risk of severe adverse allergic reactions during immunotherapy. The data from the meta-analysis suggest new allergen preparations available are allergoids, recombinant allergens (recA) and modified-recombinant allergens (recA). Studies on virus-like-particles and CpG-motifs, adjuvants like MPL and aluminum hydroxide have been shown to increase immunological response and can improve safety and efficacy.[8] The latest approaches to allergen immunotherapy include the application of extract patches on the skin and/or inguinal lymph node injection. Recombinant technology or chemicals may alter allergen molecules that make them less reactive; this may be due to suppression of Th2 responses or stimulation of toll-like receptor (approval is pending).[15] The new advances in allergy immunotherapy not only provide disease-modifying treatments but are also cost-effective and improve the quality of life.[16] The major allergen Bet v 1 involved in birch pollen allergy may be the future of allergen immunotherapy for rhino conjunctivitis.[17]

Doses, Delivery, and Application of Immunotherapy 

• Comparison of pediatric and adult systemic reaction to subcutaneous immunotherapy shows significant grade 1 and Grade 2 systemic reactions that are higher in a pediatric population than adults. However, further studies are needed to evaluate the dosing strategy in children.[18]
• Subcutaneous allergen immunotherapy has shown that SCIT rarely causes any major clinical problems; there is a risk of less than 1.5% in patients who are HIV positive without AIDS, cancer (in remission), severe asthma, transplantation,  and during pregnancy, based on web-based survey.[19]
• Subcutaneous immunotherapy has the lowest risk of an allergic reaction ranking compared with 3 different methods of delivering immunotherapy; sublingual liquid (SLIT), sublingual tablets (AIT) and oral mucosal therapy (OMIT) using toothpaste. However, there are no significant differences between any of these delivery options. The most convenient factor for most patients is home immunotherapy administration.[20]