IL-17A is an essential cytokine to sustain pathogenic cell activation and inflammatory gene circuits in psoriasis vulgaris

In psoriasis, inflammation and epidermal hyperplasia are thought to be controlled by T cell-derived cytokines. Evidence now suggests that Th17 and Th22 cells infiltrate psoriasis lesions and by secreting IL-17 and IL-22, respectively, may drive disease-specific gene or cell responses. While studies in model systems indicate that IL-22 has a dominant pathogenic role, there is evolving evidence that IL-17 contributes to features of psoriasis. To more fully understand the role of IL-17 in human disease pathogenesis, we examined psoriatic skin lesions obtained from patients treated with an anti-IL-17 (IL-17 A) monoclonal antibody, LY2439821. In a phase 1, randomized, double-blind, placebo-controlled dose escalation trial, patients with chronic psoriasis were randomized to receive 3 doses of subcutaneous LY2439821 at 5 mg (n=8), 15 mg (n=8), 50 mg (n=8), 150 mg (n=8) or placebo (n=8) at weeks 0, 2 and 4. Repeat biopsies were taken from the same lesional area at baseline, week 2 and 6. At week 6, a PASI75 was observed in 0/8, 2/8, 5/7 and 8/8 patients receiving 5 mg, 15 mg, 50 mg or 150 mg LY2439821 respectively and 0/8 patients receiving placebo. The antibody was well-tolerated. In patients receiving the two highest doses, histological and immunohistochemical analyses of biopsies revealed significant reductions from baseline in keratinocyte proliferation, hyperplasia and epidermal thickness after 2 weeks, as well as reduced infiltration into the dermis and epidermis by T-cells (CD3+) and dendritic cells (CD11c and DC-LAMP). Keratinocyte expression of innate defense proteins, S100A7, S100A8, beta-defensin2 and LL37/cathelicidin was also reduced. By week 6, the skin appeared normal with a reversal of disease defining pathological features. Quantitative RT-PCR revealed decreased expression of interferon gamma (IFN-gamma), IL-22 and IL-17, key cytokines from T cell subsets Th1, Th22 and Th17, respectively. In order to explore the extent to which IL-17 blockade influences an even broader set of inflammatory or psoriatic disease related genes, mRNA levels from skin biopsy samples were evaluated using whole genome microarrays. At week 2, the highest dose of LY2439821 modulated over 1500 genes significantly (>1.5 fold change [FC], p<0.05). Of these, 51 genes were strongly suppressed (>7-fold) including IL-19, lipocalin, amphiregulin, granzyme B, and several chemokines. In a separate analysis, those genes known to be synergistically regulated by both IL-17 and TNF-alpha showed the greatest normalization in expression compared to genes known to be regulated by TNF-alpha alone, IFN-gamma or Interferon alpha. Our data suggest that Th17 cells, through the expression of IL-17, mediate psoriasis pathogenesis, and that neutralization of IL-17 with LY2439821 suppresses signaling through multiple inflammatory circuits by inhibiting expression of cytokines from multiple T cell subsets, as well as chemokines, and antimicrobial proteins from keratinocytes.

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Krueger JG, Fretzin S, Suárez-Fariñas M, Haslett PA, Phipps KM, Cameron GS, McColm J, Katcherian A, Cueto I, White T, Banerjee S, Hoffman RW