Allergen Immunotherapy Modalities

Subcutaneous immunotherapy (SCIT) has been the cornerstone of allergen desensitization since the early 1900s, with robust evidence for allergic rhinitis, asthma, and venom allergy. However, SCIT requires years of regular clinic visits, carries risk of systemic reactions (1-2 per million injections fatality rate), and has poor long-term adherence. The search for safer, more convenient delivery routes gained momentum in the 2000s with sublingual immunotherapy (SLIT) tablets emerging from European trials. Concurrently, the food allergy epidemic created demand for desensitization approaches to food allergens, particularly peanut, where avoidance was the only option and accidental exposures caused significant morbidity and mortality.

The GRASS trial was a pivotal study demonstrating that 3 years of grass pollen SLIT-tablet treatment provided sustained clinical benefit for 2 years after discontinuation, establishing durable disease modification comparable to SCIT. FDA approval of grass (Grastek), ragweed (Ragwitek), and dust mite (Odactra) SLIT tablets followed. For food allergy, the PALISADE trial of AR101 (Palforzia, a standardized peanut oral immunotherapy) demonstrated that 67% of peanut-allergic patients aged 4-17 could tolerate 600mg or more of peanut protein after treatment vs 4% with placebo. These results led to FDA approval of Palforzia in 2020, the first approved oral immunotherapy for any food allergy.

Epicutaneous immunotherapy (EPIT) via the Viaskin Peanut patch offered a potentially safer alternative to oral immunotherapy by delivering microgram doses of allergen through intact skin. The PEPITES trial showed that 35.3% of EPIT-treated children aged 4-11 met the responder criteria vs 13.6% with placebo, though efficacy was more modest than OIT. The patch approach had significantly fewer GI side effects and lower anaphylaxis rates, making it attractive for younger children and risk-averse families. Emerging approaches include modified allergens (hypoallergenic recombinant proteins), adjuvant-enhanced formulations, and epitope-based peptide vaccines that target T-cell responses while avoiding IgE cross-linking, potentially enabling safer and shorter treatment courses.

Current guidelines recognize both SCIT and SLIT as effective modalities for aeroallergen immunotherapy, with SLIT tablets offering comparable efficacy with improved safety for specific allergens (grass, ragweed, dust mite). The EAACI guidelines on allergen immunotherapy provide comprehensive recommendations for patient selection, route selection, and duration. For food allergy OIT, guidelines remain cautious, noting that while Palforzia is FDA-approved, it requires careful risk-benefit discussion given the side effect burden (GI symptoms, eosinophilic esophagitis risk) and the need for continued daily dosing to maintain desensitization.

The immunotherapy landscape is diversifying rapidly. SLIT tablets are established for grass, ragweed, and dust mite, with tree pollen tablets in development. Peanut OIT (Palforzia) is available but uptake has been limited by cost, side effects, and the requirement for in-clinic dosing escalation. Viaskin Peanut (EPIT) received a Complete Response Letter from the FDA but is being resubmitted with additional data. The most exciting frontier is multi-allergen immunotherapy and novel delivery platforms including intralymphatic injection, which may achieve tolerance with just 3 injections over 2 months. Biomarker-guided treatment selection and response prediction using component-resolved diagnostics and basophil activation testing are moving toward clinical implementation.