Allergen-specific immunotherapy (SIT) is the only disease-modifying treatment for allergies. It interferes with the pathological immunologic mechanisms that lead to the development of allergy. SIT significantly alleviates allergic symptoms, thereby decreasing the need for symptomatic medication, and it also offers long-term protection and prevents the development of asthma in people who already have allergic rhinoconjunctivitis. The main route of administration has been subcutaneous (SCIT), but recently sublingual immunotherapy (SLIT) has been gaining considerable interest. It is recommended to administer SIT for at least 3 to 5 years, in order to induce a strong immune response against allergens and to ensure long-term protection. Recent studies revealed that compliance to SCIT is significantly higher than for SLIT (Egert-Schmidt et al, 2014).
- SCIT involves the administration of a course of injections, starting with a very low dose of allergen and building up gradually until a plateau or maintenance dose is achieved. Maintenance injections are then given at 4- to 6-week intervals for 3 to 5 years.
- SLIT involves daily sublingual administration of allergen drops or tablets (available since 2014), for a period of 3 to 5 years.
Currently, most SIT products are still prepared from poorly defined allergen extracts (Valenta et al, 2012). However, as more allergen molecules are being structurally characterized, it has become possible to produce well-defined recombinant and synthetic molecules, coupled allergens, and genetic vaccines. Other SIT improvements include the addition of omalizumab or adjuvants (with toll-like receptor agonist activity), cell-based approaches (allergen-expressing stem cells, engineered T regulatory cells, engineered Th1 cells), the use of different administration routes (intralymphatic, epicutaneous), and passive immunization with allergen-specific antibodies. So far, SIT has not been developed as prophylactic vaccination with the aim of preventing allergic sensitization. This challenging new approach is still in early research phases, and it could represent a significant advancement (Fig. 1). The prophylactic treatment would obviously be a major step forward because it would not be limited to the treatment of allergic patients, but would also prevent allergies and, hence, stop the currently exploding allergy epidemic.