Retinoic-acid-orphan-receptor-C (RORC) is a master regulator of Th17 cells, which are pathogenic in several autoimmune diseases. Genetic Rorc deficiency in mice, while preventing autoimmunity, causes early lethality due to metastatic thymic T cell lymphomas. We sought to determine whether pharmacological RORC inhibition could be an effective and safe therapy for autoimmune diseases by evaluating its effects on Th17 cell functions and intrathymic T cell development. RORC inhibitors effectively inhibited Th17 differentiation and IL-17A production, and delayed-type hypersensitivity reactions. In vitro, RORC inhibitors induced apoptosis, as well as Bcl2l1 and BCL2L1 mRNA downregulation, in mouse and nonhuman primate thymocytes, respectively. Chronic, 13-week RORC inhibitor treatment in rats caused progressive thymic alterations in all analyzed rats similar to those in Rorc-deficient mice prior to T cell lymphoma development. One rat developed thymic cortical hyperplasia with preneoplastic features, including increased mitosis and reduced IKAROS expression, albeit without skewed T cell clonality. In summary, pharmacological inhibition of RORC not only blocks Th17 cell development and related cytokine production, but also recapitulates thymic aberrations seen in Rorc-deficient mice. While RORC inhibition may offer an effective therapeutic principle for Th17-mediated diseases, T cell lymphoma with chronic therapy remains an apparent risk.
Christine Guntermann, Alessandro Piaia, Marie-Laure Hamel, Diethilde Theil, Tina Rubic-Schneider, Alberto del Rio-Espinola, Linda Dong, Andreas Billich, Klemens Kaupmann, Janet Dawson, Klemens Hoegenauer, David Orain, Samuel Hintermann, Rowan Stringer, Dhavalkumar D. Patel, Arno Doelemeyer, Mark Deurinck, Jens Schümann
Histopathological analysis of thymic alterations in rats treated with retinoic-acid-orphan-receptor-C (RORC) inhibitor cpd 1 for 13 weeks compared with vehicle control.