TMP778, a selective inhibitor of RORγt, suppresses experimental autoimmune uveitis development, but affects both Th17 and Th1 cell populations

Experimental autoimmune uveitis (EAU), an animal model for severe intraocular inflammatory eye diseases, is mediated by both Th1 and Th17 cells. Here, we examined the capacity of TMP778, a selective inhibitor of RORγt, to inhibit the development of EAU, as well as the related immune responses. EAU was induced in B10.A mice by immunization with interphotoreceptor retinoid‐binding protein (IRBP). Treatment with TMP778 significantly inhibited the development of EAU, determined by histological examination. In addition, the treatment suppressed the cellular immune response to IRBP, determined by reduced production of IL‐17 and IFN‐γ, as well as lower percentages of lymphocytes expressing these cytokines, as compared to vehicle‐treated controls. The inhibition of IFN‐γ expression by TMP778 is unexpected in view of this compound being a selective inhibitor of RORγt. The observation was further confirmed by the finding of reduced expression of the T‐bet (Tbx21) gene, the transcription factor for IFN‐γ, by cells of TMP778‐treated mice. Thus, these data demonstrate the capacity of TMP778 to inhibit pathogenic autoimmunity in the eye and shed new light on its mode of action in vivo. Treatment of mice with TMP778, a selective inhibitor of RORgt inhibits the generation of both Th1 and Th17 cells. The unexpected inhibition of Th1 cells is explained by fewer Th17 cells being available for the switch to the Th1 phenotype.