Role of myeloid-derived suppressor cells in prediction of the effectiveness of biologics in children with psoriasis

Psoriasis is a chronic inflammatory skin disease characterized by increased proliferation of epidermal cells, impaired keratinization, and an inflammatory reaction in the dermis due to activation of T-lymphocytes and synthesis of proinflammatory cytokines. Pathophysiology of psoriasis is associated not only with activation of proinflammatory reactions, but also with decreased anti-inflammatory functions of immunosuppressive cells. It is known that Treg, Breg and MDSCs do not perform their classical homeostatic functions in psoriasis. In recent years, there have been more and more cases of developing resistance to ongoing therapy with genetically engineered biological drugs (GEBD) in childhood, requiring replacement or discontinuation of the drug. The aim of our work was to estimate the content of MDSCs subpopulations and their functional activity in the peripheral blood of children with psoriasis at different effectiveness of biotherapeutic drugs. We examined 110 children with psoriasis vulgaris before the appointment of biologics, at 16 and 52 weeks of therapy with adalimumab, etanercept and ustikinumab, aged 6 to 18 years. Сomparison group consisted of 34 healthy children. The effectiveness of therapy was assessed by the achievement of PASI 75 by one year of therapy. Contents of myeloid-derived suppressor cells (MDSCs) and their subpopulations, and the activity of arginase-1 were assessed by multicolor flow cytometry. An increased content of MDSCs was found in children with psoriasis against the comparison group (p = 0.000). Analysis of the effectiveness of biologics in children with psoriasis, according to PASI, showed a significant reduction in disease severity in the group of patients with good effect, both at week 16 of therapy (p = 0.000) and by one year (p = 0.017). In the group of patients with good effect of biological therapy, percentage of total MDSCs population was higher, both before start of treatment and by 52^nd week of therapy (p < 0.01). Children with psoriasis showed increased immunosuppressive function of MDSCs by arginase-1 activity versus the comparison group (p = 0.000). The arginase-1 activity in patients with psoriasis at the stage of disease regression (PASI < 10) was significantly increased relative to children in progressive stage of psoriasis (PASI≥10; p = 0.001). Thus, the content of MDSCs and their suppressive activity in children with psoriasis is an informative efficiency predictor of the biological drugs. Fading of biotherapy effect after the induction course is accompanied by decreased number of MDSCs and their functional activity.