AB0082 INHIBITION OF TGFβ SIGNALING USING SB-505124 BLOCKS TH17 DIFFERENTIATION AND RESTORES THE TH17/TREG BALANCE IN VIVO, BUT DOES NOT SUPPRESS EXPERIMENTAL ARTHRITIS. (2nd June 2020) - Aarts, J.
Abstract : Background: TGFβ is an important growth factor that promotes the differentiation of T helper 17 (Th17) as well as regulatory T-cells (Treg). Due to its dual role, the potential of TGFβ as therapeutic target is unclear. Objectives: In this study we aimed to investigate the effect of inhibition of TGFβ signaling with the ALK5 inhibitor SB-505124 on human Th17 differentiation in vitro, on cytokine production by human rheumatoid arthritis (RA) synovial explants, and study the effects of local SB-505124 treatment in vivo during innate immune and Th17-driven experimental arthritis models. Methods: Magnetic sorted naïve human T cells were differentiated into Th17 cells with CD3/CD28 activation beads, IL-2, TGFβ, IL-1β, IL-23, αIFNƳ and αIL-4 for 6 days. Human RA synovial biopsies were cultured for 24h w/o 5µM SB-505124, and supernatant was analyzed by Luminex. T cell-independent SCW arthritis and Th17-driven IL-1/mBSA arthritis were induced in C57Bl6, and mice were treated with SB-505124 by daily intra-articular injections from day 0-4. Results: SB-505124 potently reduced human Th17 differentiation in vitro by decreasing IL-17 and RORƳt gene expression and IL-17 protein production. SB-505124 significantly suppressed IL-6 and TNFα protein production by human RA synovial explants. In addition, SB-505124 did not affect acute joint inflammation during SCW-arthritis (T-cell independent model). Interestingly, SB-505124 reduced Th17 levels in draining lymph nodes (dLN) during IL-1/mBSA arthritis while increased levels of Tregs were observed. Surprisingly, despite this skewed Th17/Treg balance, this did not result in suppression of joint inflammation and destruction in this Th17-driven arthritis model, whereas anti-IL-17 antibody treatment showed significant therapeutic effects. Conclusion: We revealed suppressive effects of SB-505124 on human Th17 differentiation and the Th17/Treg balance in arthritic mice. However, SB-505124 did not suppress joint inflammation and destruction. This indicates that despite the importance of TGFβ in Th17 differentiation, targeting TGFβ signaling is not enough to suppress experimental arthritis. Disclosure of Interests: None declared