12 To investigate the clinical efficacy of the SQ tree SLIT‐tablet towards other species from the birch homologous group, subjects were exposed to white oak pollen ( Quercus alba Que a) in separate EEC sessions. 9, 10, 11 While in the EEC, birch allergic subjects are expected to experience rhinoconjunctivitis symptoms similar to what is normally experienced during the BPS. The present trial was conducted to confirm the optimal dose for clinical efficacy using an environmental exposure chamber (EEC) to eliminate variability of allergen exposure in different trial sites or seasons. However, clinical data and IgG 4 measurements suggested that the optimal dose for clinical efficacy was above 4 DU. 8 Consequently, the trial did not show a dose response for the primary endpoint (daily symptom score during the birch pollen season). 7 The tree pollen season, in which the phase II trial was conducted, was short and characterized by low birch pollen counts. 6 Efficacy of the SQ tree SLIT‐tablet (in doses from 0.5 to 12 DU) was evaluated in a phase II trial (EudraCT 2012‐000031‐59) which was a randomized, double‐blind, placebo‐controlled trial in 637 adults and adolescents with moderate to severe ARC induced by birch. Data from a phase I trial suggested that doses up to 12 development units (DU) have a tolerability profile suitable for at‐home administration. The SQ tree SLIT‐tablet is being developed as allergy immunotherapy (AIT) for treatment of ARC induced by pollen from the birch group. 4 Patients who are allergic to birch pollen may also experience symptoms in response to pollen from the other members of the birch group, which, due to successive seasons and geographical distribution of the birch group species, increases the burden of tree pollen allergy in terms of relevant seasons and regions. 3 The relevance of birch pollen as a representative allergen source has been confirmed by in vitro IgE inhibition studies in which birch pollen extract almost completely inhibited human IgE binding to alder, hazel, hornbeam, and oak allergen extracts. An additional two species (beech and chestnut) have been suggested as members of the birch homologous group. 1 Based on amino acid sequence homology of the major allergens and IgE cross‐reactivity, five tree species (birch, alder, hornbeam, hazel, and oak) have been assigned to the same homologous group 2 termed the “birch homologous group”, with birch as the representative species. The prevalence of birch pollen sensitization in adults has been estimated to be more than 20% in some areas of central Europe, with a mean prevalence of 8% of the population in 13 developed countries worldwide. In Europe and North America, exposure to pollen from birch and other related trees may lead to development of respiratory allergic diseases such as allergic rhinoconjunctivitis (ARC).
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