The Vitamin D Analogue Calcipotriol Reduces the Frequency of CD8+ IL-17+ T Cells in Psoriasis Lesions.

The vitamin D analogue calcipotriol is an immunomodulatory drug widely used to treat psoriasis; however, how calcipotriol affects the immune cells in psoriasis lesions is not fully understood. The aim of this study was to investigate the effect of calcipotriol on the frequency of CD4(+) and CD8(+) T cells and innate lymphoid cells (ILC) and their production of IL-17A, IFN-γ and IL-22 in psoriasis lesions in patients with chronic plaque psoriasis. Eighteen patients with psoriasis were included, and two similar psoriasis lesions were chosen for each patient. One lesion was treated with calcipotriol (50 μg/g) and the other with vehicle twice a day for 14 days. The clinical effect was measured by degree of erythema, scaling and induration in each lesion (SUM score). Skin biopsies were collected for histological and immunohistochemical analyses. Skin-derived cells were isolated and analysed by flow cytometry. After 14 days of treatment with calcipotriol, a significant clinical and histological effect was seen; however, we found no differences in the frequency of CD4(+) and CD8(+) T cells or ILC between calcipotriol- and vehicle-treated skin. The main finding was a significant decrease in CD8(+) IL-17(+) T cells in skin-derived cells from calcipotriol-treated skin, which was further supported by the absence of CD8(+) IL-17(+) T cells in immunohistochemical staining of calcipotriol-treated skin. No changes in the frequency of IL-22(+) or IFN-γ(+) cells were observed. Our findings show that the vitamin D analogue calcipotriol reduces the frequency of CD8(+) IL-17(+) T cells in psoriasis lesions concomitant with clinical improvement.