Anti-IL17 mAb shows promising results in psoriasis treatment

Exciting – and surprising – results from a clinical trial for psoriasis are presented in this month’s issue by Krueger et al (J Allergy Clin Immunol 2012;130:145-154.e9). The authors report on a randomized trial of a new humanized IgG₄ monoclonal antibody, ixekizumab. It would be fair to say the results from their phase I trial are near astonishing.

Based on published evidence that psoriasis is a T_H17-mediated disease, the authors postulate that IL-17 acts as a “gatekeeping” cytokine in the pathogenesis of psoriasis, noting that much of the evidence from animal studies points to IL-22. They point out that IL-22 in humans is produced from a different T cell subset, T_H22 cells, unlike mice where T_H17 cell produce both.

Their speculation paid off. Krueger et al. report dose-dependent, significant improvement in both pathophysiology and clinical presentation of psoriasis subjects after only 2 weeks of ixekizumab treatment. Skin biopsies from subjects demonstrated rapid improvements in keratinocyte proliferation, hyperplasia, epidermal thickness, T cell and dendritic cell infiltration of the dermis and significantly suppressed expression of innate immunity peptides. After 6 weeks of treatment, the authors report that subjects’ skin appeared normal. Interestingly, 100% of subjects in the 150mg dosing group no longer presented clinically with psoriasis at 6 weeks of therapy. Krueger et al. comment that the effectiveness of ixekizumab at 2 and 6 weeks was surprising since other antibody therapies typically require 12 weeks to demonstrate efficacy. They also note that the adverse effects profile is agreeable and the drug well-tolerated.

Noting that many genes associated with psoriasis are co-regulated by IL-17 and TNF-α, Krueger et al. show that IL-17 blockade with ixekizumab is far more effective in suppressing the co-regulated genes than TNF-α blockade by etanercept. They suggest that their evidence shows that IL-17 is a pivotal cytokine in the pathology of psoriasis, affecting many effector functions of other T cell subsets.