In-vivo allergen extract potency is maintained in a sublingual immunotherapy maintenance vial of pollens and mites.

Background

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.

Objective

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.

Methods

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.

Results

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.

Conclusion

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.