Recent proteomic analyses have shown that a substantial number of key signal transduction components and transcription factors that regulate immune responses and inflammation are HDAC substrates.8, 9 Thus, HDAC inhibitors have been examined as promising anti-inflammatory agents.1, 8, 10 However, there are very few HDAC inhibitors that have been sufficiently developed to undergo clinical trials for RA treatment. Here, HDAC9 is linked to rheumatoid arthritis.