IL-17A is essential for cell activation and inflammatory gene circuits in subjects with psoriasis

Abstract

Background: In subjects with psoriasis, inflammation and epidermal hyperplasia are thought to be controlled by T cell-derived cytokines. Evidence suggests that the T(H)17 cell cytokine IL-17A (IL-17) might play a role in disease pathogenesis.

Objective: We sought to understand the effect that neutralization of IL-17 has on the clinical features of psoriasis and to understand the role that IL-17 has in inflammatory pathways underlying psoriasis in human subjects.

Methods: We examined skin lesions obtained from 40 subjects participating in a phase I, randomized, double-blind, placebo-controlled trial of the anti-IL-17 mAb ixekizumab (previously LY2439821) in which subjects received 5, 15, 50, or 150 mg of subcutaneous ixekizumab or placebo at weeks 0, 2, and 4.

Results: There were significant dose-dependent reductions from baseline in keratinocyte proliferation, hyperplasia, epidermal thickness, infiltration into the dermis and epidermis by T cells and dendritic cells, and keratinocyte expression of innate defense peptides at 2 weeks. By week 6, the skin appeared normal. Quantitative RT-PCR and microarrays revealed an ablation of the disease-defining mRNA expression profile by 2 weeks after the first dose of study drug. The effect of IL-17 blockade on expression of genes synergistically regulated by IL-17 and TNF-α was of higher magnitude at 2 weeks than in prior studies with TNF-α antagonism.

Conclusion: Our data suggest that IL-17 is a key "driver" cytokine that activates pathogenic inflammation in subjects with psoriasis. Neutralizing IL-17 with ixekizumab might be a successful therapeutic strategy in psoriasis.

Figure 1. IL-17 neutralization results in decreased keratinocyte proliferation and differentiation, leukocyte infiltration and keratinocyte release of inflammatory cytokines

A representative example of serial skin biopsies from a subject treated with 150 mg ixekizumab is presented. Histological analysis included H&E staining. Immunohistochemical analysis included staining for Keratin 16 (K16), Ki67, CD3, CD11c, LL37/cathelicidin, S100A7, S100A8, BD 2 and DC-LAMP. Scale bar is 50 microns.

Figure 2. IL-17 neutralization results in decreased expression of cytokines from multiple T cell subsets

At baseline and weeks 2 and 6, mRNA expression for Keratin 16 (k16) and LCN, a IL-17 target gene, were analyzed as well as mRNA expression levels for T-cell cytokines: IFN-γ, IL-17 A and F, IL-22, and DC cytokine IL-23. *p<0.05 vs baseline. Data are shown as mean ± SEM.

Figure 3. Identification of genes modulated >6 fold by IL-17 neutralization

A. Differentially expressed genes that had a >6 fold change compared to baseline in the 150 mg group were identified and clustered. mRNA expression of these genes is presented for the placebo group for comparison. B. Gene expression data for untreated lesional skin biopsies (LS) and nonlesional skin biopsies (NS) from a previous experiment (28). The genes are ordered according to the clustering results in A. Asterisks represent those genes that are synergistically regulated by TNF and IL-17. Plus signs indicate those that are additively coregulated by TNF and IL-17.

Figure 4. Comparison of treatment effect at week 2 for ixekizumab, etanercept, and placebo

A-B. Mean (95% CI)I for fold change from baseline for each treatment for A) RT-PCR and B) histological variables. C. Venn-diagram summarizing the number of genes among those in the psoriasis transcriptome with improvement of at least 75%. D. Estimated density distribution of the treatment effect multiplied by the sign of the lesional (LS) vs. nonlesional (NL) direction to show only the magnitude of the change towards resolution. The insert graph has the density distribution of the difference in effect between ixekizumab and etanercept for all genes and the genes in the psoriasis transcriptome. For all genes, one can see a 0-centered distribution (equal effects) but for the psoriasis genes, there is a shift to the right, indicating larger changes with ixekizumab treatment among psoriasis genes. E. Proportion of psoriasis genes improved by more than 75% in each gene-set. F. Average improvement in each gene-set.