SAT0008 IL-23 DRIVES PATHOGENIC TH17 CELLS THROUGH EPIGENETIC REGULATION BY STAT3 IN SLE PATIENTS

Background Systemic lupus erythematosus (SLE) is a systemic autoimmune disease characterized by loss of self-tolerance and by broad immune dysregulation, which result in overproduction of autoantibody and cause severe inflammation in various organs(1). Although amplified mature Th17 cells are thought to be vital role in the development and progression of SLE, mechanism underlying their pathogenicity remain widely elusive in human(2). Objectives To elucidate the mechanism of pathogenic Th17 cells expansion, we probe the phenotype of Th17 cells in lupus patients and underlying epigenetic modification mediated by cytokine-induced signal transducer and activators of transcription (STAT) family factors in vitro. Methods Human naive CD4+ T cells were cultured by Th17 polarizing condition (TGF-β, IL-6, and IL-1β) for 5 days in vitro. To examine the role of specific cytokine in maturation of Th17 cells, we added various cytokines including IL-23 at the later time point (72hr). Expression of characteristic markers of pathogenic Th17 cell and STATs phosphorylation (p-STATs) were analyzed by flow cytometry and qPCR. The effect of baricitinib which is JAK1/JAK2 inhibitor on maturation of Th17 cell was investigated. Histone modifications were assessed by chromatin immunoprecipitation(ChIP)-PCR. To define the signals mediated by cytokine required for expansion of Th17 cell in SLE, Th17 phenotype and pSTATs were analyzed from blood samples of lupus patients by multi-color flow cytometry. Results In vitro, re-stimulation of Th17 cells with IL-23 markedly induced the characteristic markers of pathogenic Th17 cells such as RORγt and IL-17. IL-23 overwhelmingly activates the p-STAT3, not p-STAT4 for development of mature Th17 cells. IL-23-induced p-STAT3 was inhibited by baricitinib. In addition, proliferation of Th17 cells was suppressed by baricitinib in concentrate dependent manner. The loci of RORγt at STAT binding sites were marked by bivalent histone modifications. After IL-23 stimulation, STAT3 exclusively bound on RORγt gene loci supplemented by activating H3K4me3 and repressing H3K27me3 modifications. In memory Th17 cells, high proportion of IL-23R expression and STAT3/4 activation were identified from SLE patients compare with healthy individuals. Moreover, p-STAT3 was hypersensitively activated by IL-23 stimulation in memory Th17 cell only from lupus patients but not from healthy controls. Conclusion This study proves that IL-23 serves as a pivotal factor that drives expansion of pathogenic Th17 cells. IL-23-mediated STAT3 alter histone modification, resulting in inflammatory function of pathogenic Th17 cell that are characteristically expanded in patients with SLE. These findings could be one of the underlying mechanisms of pathogenesis of SLE and helpful evidence toward novel therapeutic targets for SLE. Reference [1] Tsokos GC. Systemic lupus erythematosus. N Engl J Med. 2011;365(22):2110-21. (2) Ma, J., et al., The imbalance between regulatory and IL-17-secreting CD4+ T cells in lupus patients. Clinical rheumatology, 2010. 29(11): p.1251-1258. Disclosure of Interests Seughyun Lee: None declared, Shingo Nakayamada Grant/research support from: Mitsubishi-Tanabe, Takeda, Novartis and MSD, Speakers bureau: Bristol-Myers, Sanofi, Abbvie, Eisai, Eli Lilly, Chugai, Asahi-kasei and Pfizer, Satoshi Kubo Speakers bureau: Bristol-Myers, Pfizer, Takeda, and Eli Lilly, Yamagata Kaoru: None declared, Kitanaga Yukihiro Employee of: Astellas, Yoshiya Tanaka Grant/research support from: Abbvie, Astellas, Bristol-Myers Squibb, Chugai, Daiichi-Sankyo, Eisai, Mitsubishi-Tanabe, MSD, Ono, Taisho-Toyama, Takeda, Speakers bureau: Abbvie, Asahi-kasei, Astellas, Bristol-Myers Squibb, Chugai, Daiichi-Sankyo, Eli Lilly, Eisai, Glaxo-Smithkline, Janssen, Mitsubishi-Tanabe, Novartis, Pfizer Japan Inc, Sanofi, Takeda, UCB, YL Biologics