<i>In-vivo</i> allergen extract potency is maintained in a sublingual immunotherapy maintenance vial of pollens and mites

<b>Background:</b> Allergen immunotherapy (IT) in Europe is generally administered as monoallergen IT. However, in some patients and in other parts of the world, multiallergen IT is common practice. A key question is whether allergens in a mixture retain their allergenicity over time. <b>Objective:</b> To demonstrate if allergenicity, as measured by skin-prick testing (SPT), is maintained after 6 months in a sublingual immunotherapy (SLIT) maintenance vial with three allergen extracts in a single individual vaccine, including two pollens and Dermatophagoides. <b>Methods:</b> We prepared two maintenance SLIT vials that contained mixed Dermatophagoides species (2000 AU/mL), ash tree and Bermuda grass pollens (1:50 w/v), one 6 months before SPT and the second 0-2 weeks before SPT, and three fresh vials (0-2 weeks before SPT) for each individual allergen. Duplicate SPTs were conducted with all five vials, diluent and positive (histamine 1 mg/mL) controls. Wheals were measured at 10 minutes (controls) and 20 minutes (allergen vaccines). The mean wheal diameter was calculated as the average of the longest and orthogonal diameters, i.e., (D₁ + D₂)/2. For each allergen extract, two replicate wheals were obtained per participant; their mean diameters were averaged to yield a patient-level mean wheal diameter. These patient-level means were then averaged across all the participants. The paired t-test was used to calculate statistically significant differences between the mean wheal diameters of the extracts, with significance at p < 0.05. <b>Results:</b> The mean ± standard deviation wheal diameter produced by the 6-month-old and the fresh extracts were 8.7 ± 3.3 mm and 8.4 ± 2.87 mm, respectively. This difference was not significant. Moreover, the potency of both pollen extracts was conserved when mixed with house-dust mite extracts. <b>Conclusion:</b> In our pilot study, allergenicity of tree and grass pollen allergens in an allergen mix with Dermatophagoides in a SLIT maintenance vial was maintained over 6 months. Replication in a larger population would consolidate our findings.