Differential and lasting gene expression changes in circulating CD8 T cells in chronic HCV infection with cirrhosis and related insights on the role of Hedgehog signaling

The impact of chronic hepatic infection on antigen non-specific immune cells in circulation is not well understood and may influence long term health. We reported lasting global hyperfunction of circulating CD8 T cells in HCV-infected individuals with cirrhosis. Whether gene expression patterns in bulk CD8 T cells are associated with the severity of liver fibrosis in HCV infection is not known. RNA sequencing of blood CD8 T cells from treatment-naïve, HCV-infected individuals with minimal (Metavir F0-1 ≤ 7.0 kPa) or advanced fibrosis or cirrhosis (F4 ≥ 12.5 kPa), before and after direct-acting antiviral therapy, was performed. Principal component analyses determined robust differences in over 350 genes expressed by CD8 T cells from HCV-infected individuals with minimal or advanced fibrosis and data suggests this remains relatively stable after viral clearance. Gene ontology analyses identified disaggregated gene expression related to cellular metabolism, including upregulated phospholipase, phosphatidyl-choline/inositol activity and second-messenger-mediated signaling, while genes in pathways associated with nuclear processes, RNA transport and cytoskeletal dynamics were reduced. Gene Set Enrichment Analysis identified decreased expression of genes regulated by the cMyc and E2f transcription factors in cirrhotics, compared to the minimal fibrosis group, as well as reduced expression of genes linked to oxidative phosphorylation, mTOR signaling, and more. Upregulated gene sets in cirrhotics included IFN-α, -γ, TGF-β response genes, apoptosis and apical surface pathways, among others. The hedgehog (Hh) signaling pathway was the top featured gene set upregulated in cirrhotics. Inhibition of Hh signaling with cyclopamine ablated CD8 T cell IFN-γ production, suggesting its involvement in hyperfunction. This is the first analysis of bulk CD8 T cell gene expression profiles in HCV infection in the context of liver fibrosis severity, and suggests cirrhosis significantly reprograms the CD8 T cell pool. The novel finding of increased Hh signaling in cirrhosis may contribute to generalized CD8 T cell hyperfunction observed in chronic HCV infection. Understanding the lasting nature of immune cell dysfunction may help mitigate remaining clinical challenges after HCV clearance and more generally, improve long term outcomes for individuals with severe liver disease. ### Competing Interest Statement The authors have declared no competing interest.