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Background:  

The SQ tree SLIT-tablet (containing birch extract) proved clinically sig-nificant effects during the pollen season for birch as well as alder/hazel.

Immune outcomes of this treatment for allergens from multiple birch homologous trees need further investigation. 

We hypothesize that birch pollen extract AIT modulates a highly cross-reactive immune response and that this may be the basis for the ob-served clinical cross-protection.

Methods:

Blood samples were collected from 397 birch allergic patients during SQ tree SLIT-tablet or placebo treatment (1:1) for up to 40 weeks.

 Serum IgE and IgG4specific to birch, and birch homologous tree pollens from alder, hazel, hornbeam, beech and chestnut were measured by ImmunoCAP.

IgE-Blocking Factor (IgE-BF) for alder, birch and hazel during treatment was measured by Advia Centaur and blocking effects for birch and all these birch homologous tree pollens were further investi-gated by basophil activation (BAT).

Antibody readouts were investigated in patient subsets. 

T-cell responses (proliferation) to allergen extracts and peptide pools (group 1 allergens) were investigated in T-cell lines from 29 untreated birch pollen-allergic individuals.

Results: 

Significant Pearson correlations between serum IgE towards birch, alder, hazel, hornbeam and beech were observed (r-values    > .86). 

T-cell reactivity was ob-served throughout the birch homologous group. Almost identical kinetics for changes in IgE towards birch, alder and hazel were observed during treatment and similar species-specific changes were seen for serum-IgG4. IgG4 reactivity towards birch and alder, hazel, hornbeam and beech correlated significantly at end-of-treatment (r-values    > .72). 

Treatment resulted in similar IgE-BF kinetics for alder, birch, and hazel and blocking of BAT for multiple trees in most actively treated patients investigated.

Conclusions: 

Systematic analyses of T-cell and antibody cross-reactivities before and during birch pollen extract AIT provide the immunological basis for the observed clin-ical effect of SQ tree SLIT-tablet treatment of tree pollen allergy induced by multiple trees in the birch homologous group.