High-dimensional analysis reveals a novel signature for IL-17 producing CD8 T cells in inflammatory bowel disease

Abstract Background The pathogenesis of IBD has previously mainly been associated with a dysregulation of CD4 T-cell responses, and active disease is linked to induction of pathogenic IL-17 producing T helper cells. Importantly, CD8 T cells can also produce IL-17 and demonstrate a significant increase in active IBD. However, it remains unclear whether this is due to conventional or unconventional T-cell responses and whether these CD8 responses could play a role as novel biomarkers or therapeutic targets of active IBD. Methods We isolated lymphocytes from the peripheral blood and intestinal tissue of IBD patients (n = 56) and performed a detailed analysis of CD8 T-cell phenotype and function using high-parametric flow cytometry and mass cytometry in combination with algorithm-aided bioinformatic analysis. Results We observe a significant increase in IL-17 production by CD8 T cells in active IBD, primarily produced by conventional CD8 T cells. Unconventional T-cell subsets (e.g. MAIT cells, γδ T cells and NKT cells) represented only ~30% (peripheral blood) or ~25% (intestinal tissue) of IL-17 producing CD8 T cells (Tc17). The mass cytometric analysis identified Tc17 cells as a distinct cell population within the intestinal CD8 T-cell compartment that can be further subdivided into 3 subsets which share expression of phenotypic markers such as CD6, CD39, CD69 and PD1 and a low expression of CD27. This novel signature was validated in a separate cohort of IBD patients. Moreover, at initial IBD diagnosis, the IL-17 signature is associated with flare-free survival in a retrospective cohort analysis based on published transcriptome data. Conclusion Our data indicate that conventional IL-17 producing CD8 T cells are a very distinct cell population that is linked to IBD activity. The identification of a novel IL-17 CD8 signature may help guide treatment decisions as a biomarker and for immunotherapeutic approaches.