Cytokines as Therapeutic Targets in Rheumatoid Arthritis and Other Inflammatory Diseases

The human immune system involves highly complex and coordinated processes in which small proteins named cytokines play a key role. Cytokines have been implicated in the pathogenesis of a number of inflammatory and autoimmune diseases. Cytokines are therefore attractive therapeutic targets in these conditions. Anticytokine therapy for inflammatory diseases became a clinical reality with the introduction of tumor necrosis factor (TNF) inhibitors for the treatment of severe rheumatoid arthritis. Although these therapies have transformed the treatment of patients with severe inflammatory arthritis, there remain significant limiting factors: treatment failure is commonly seen in the clinic; safety concerns remain; there is uncertainty regarding the relevance of immunogenicity; the absence of biomarkers to direct therapy decisions and high drug costs limit availability in some healthcare systems. In this article, we provide an overview of the key efficacy and safety trials for currently approved treatments in rheumatoid arthritis and review the major lessons learned from a decade of use in clinical practice, focusing mainly on anti-TNF and anti-interleukin (IL)-6 agents. We also describe the clinical application of anticytokine therapies for other inflammatory diseases, particularly within the spondyloarthritis spectrum, and highlight differential responses across diseases. Finally, we report on the current state of trials for newer therapeutic targets, focusing mainly on the IL-17 and IL-23 pathways.