IMPORTANCE: Accumulating evidence suggests that IL-17 A has broad pathogenic 
roles in multiple autoimmune and immune-mediated inflammatory diseases, 
including psoriasis and rheumatoid arthritis (RA). The development of new 
therapies that inhibit IL-17 pathway signaling is of clinical significance.
OBJECTIVES: This review aims to summarize the current preclinical evidence on 
the role of Th17 cells and IL-17 and related cytokines in immune-mediated 
disease pathophysiology, with a focus on psoriasis and rheumatoid arthritis, as 
well as to summarize recent clinical trials in these indications with newly 
developed IL-17 pathway inhibitors.
METHODS: A systematic literature search was conducted of PubMed using relevant 
keywords. Studies were assessed according to recent relevance to IL-17-mediated 
pathophysiology and clinical IL-17 inhibition. Experimental animal models of 
autoimmune disease and clinical studies that focused on IL-17 pathway inhibitors 
were included.
RESULTS: Preclinical studies suggest that IL-17A is an attractive therapeutic 
target. Several IL-17A inhibitors have advanced into clinical trials, including 
the anti-IL-17A monoclonal antibodies, secukinumab and ixekizumab, and the 
anti-17RA monoclonal antibody brodalumab. Each has shown variable and sometimes 
favorable results in proof-of-concept and phase II clinical trials and is 
currently undergoing further clinical evaluation in a range of immune-mediated 
diseases.
CONCLUSION: Targeting the IL-17 pathway shows promise as strategy to treat 
immune-mediated diseases ranging from skin to joints.