Randomized, Double-Blind, Placebo-Controlled Trial of Vitamin D Supplementation in the Build-up Phase of House Dust Mite-Specific Immunotherapy.

Purpose: Vitamin D (VitD) is an immunomodulatory molecule capable of alleviating allergic symptoms. However, the effectiveness of allergen-specific immunotherapy (AIT) is not commonly evidenced in the early build-up phase. The aim of the study was to determine the potential of VitD supplementation in this treatment phase.

Methods: Thirty-four house dust mite (HDM)-allergic adult patients treated with subcutaneous AIT were randomized to receive VitD2 60,000 IU/week or placebo for 10 weeks and followed up for 10 weeks. The primary endpoints were the symptom-medication score (SMS) and the treatment response rate. The secondary endpoints were eosinophil count and levels of plasma IL-10, Der p 2-specific IgG4, and dysfunctional regulatory T (CRTH2⁺ Treg) cells.

Results: Of 34 patients, 15 in each group completed the study. Patients with VitD deficiency receiving a VitD supplement showed significantly lower mean change SMS than the placebo group in weeks 10 (mean difference -54.54%, P = 0.007) and 20 (mean difference -42.69%, P = 0.04). The percentage of treatment responders reached 78% and 50% in the VitD and placebo groups, respectively, and the effect remained in week 20 (89% and 60%). No significant difference was observed for the tested immunological read-outs, with the exception of the frequency of CRTH2⁺ Treg cells, which was remarkably reduced in the VitD-treated patients. Moreover, improvement in SMS was correlated to the number of CRTH2⁺ Treg cells. Our in vitro experiment indicated that VitD downregulated activation markers, whereas it improved the function of CRTH2⁺ Treg cells.

Conclusions: VitD supplementation in the build-up phase of AIT could relieve symptoms and decrease Treg cell dysfunction, especially in patients with VitD deficiency.