IL21 and rheumatoid arthritis: However, clinical trials of approved biological agents for RA including TNF-α inhibitors, IL-6 receptor inhibitor, T cell co-stimulation blocker, B cell eliminator, and intracellular signal inhibitors of JAK pathway showed similar response with limited efficacy of 30~ 40% in ACR70 improvement rates, whereas therapeutic failure appeared in the blockage of other targets such as IL-1, IL-12, IL-17, IL-20, IL-21, IL-23, anti-CD4, anti-BAFF, and inhibitors of intracellular signal molecular of p38-MAPK and SYK [1].