Tyrosine Kinase 2 Signalling Drives Pathogenic T cells in Colitis

Abstract Background and Aims Tyrosine kinase 2 [TYK2] is required for the signalling of key cytokines in the pathogenesis of inflammatory bowel disease [IBD]. We assessed the efficacy of a novel selective TYK2 inhibitor [TYK2i] in experimental colitis, using pharmacological and genetic tools. Methods At onset of T cell transfer colitis, RAG1^{-/-} mice received vehicle or TYK2i daily by oral gavage. T cells lacking TYK2 kinase activity [TYK2^{KE}] were used to confirm selectivity of the inhibitor. To this end, RAG1^{-/-} or RAG1^{-/-}TYK2^{KE} animals were transferred with either wild type [WT] or TYK2^{KE}-CD45RB^{high} colitogenic T cells. Loss of body weight, endoscopic disease, the disease activity index [DAI], and histopathology scores were recorded. Tissues were analysed ex vivo for lymphocyte populations by flow cytometry. The impact of TYK2 inhibition on human DC-T cell interactions were studied using autologous Revaxis specific T cell assays. Results TYK2i [70 mg/kg] prevented weight loss and limited endoscopic activity during T cell transfer colitis. TYK2i [70 mg/kg] decreased DAI. Whereas transfer of WT T cells into RAG^{-/-}TYK2^{KE} hosts induced colitis, TYK2^{KE} T cells transferred into RAG1^{-/-}TYK2^{KE}recipients failed to do so. Ex vivo analysis showed a decrease in colon tissue Th1 cells and an increase in Th17 cells upon transfer of TYK2^{KE}-CD45RB^{high} cells. In human antigen-triggered T cells, TYK2i displayed reduced Th1 differentiation, similar to murine Th1 cells. Conclusions Oral administration of TYK2i, as well as transfer of T cells lacking TYK2 activity, reduced human Th1 differentiation and ameliorated the course of murine T cell transfer colitis. We conclude that TYK2 is a promising drug target for the treatment of IBD.