Longitudinal liver sampling in patients with chronic hepatitis B starting antiviral therapy reveals hepatotoxic CD8+ T cells

Abstract

Accumulation of activated immune cells results in nonspecific hepatocyte killing in chronic hepatitis B (CHB), leading to fibrosis and cirrhosis. This study aims to understand the underlying mechanisms in humans and to define whether these are driven by widespread activation or a subpopulation of immune cells. We enrolled CHB patients with active liver damage to receive antiviral therapy and performed longitudinal liver sampling using fine-needle aspiration to investigate mechanisms of CHB pathogenesis in the human liver. Single-cell sequencing of total liver cells revealed a distinct liver-resident, polyclonal CD8 + T cell population that was enriched at baseline and displayed a highly activated immune signature during liver damage. Cytokine combinations, identified by in silico prediction of ligand-receptor interaction, induced the activated phenotype in healthy liver CD8 + T cells, resulting in nonspecific Fas ligand–mediated killing of target cells. These results define a CD8 + T cell population in the human liver that can drive pathogenesis and a key pathway involved in their function in CHB patients.

Liver-resident CD8+ T cells in viral hepatitis: not always good guys

“…It is important to note that the two populations of liver-resident CD8 + T cells in chronic HBV infection described by Pallett et al ( 12 ) and Nkongolo et al ( 13 ) may look similar at first sight, since they both express tissue-residency markers, such as CD69 and CXCR6, activation markers, such as CD38 and HLA-DR, and exhaustion markers, such as PD-1. Of note, PD-1 expression may indicate activation and/or serve as an optimal adaption to the liver’s immune landscape, allowing cell survival despite having only limited help from other cell types, such as CD4 + T cells.…”

“…They are thus associated with viral control in chronic HBV infection and also persist after viral clearance ( Figure 1B ) ( 12 ). The hepatotoxic liver-resident CD8 + T cells identified by Nkongolo et al ( 13 ), however, are non–HBV-specific bystander CD8 + T cells, are induced by IL-2 and IL-12, and not only express IFN-γ, but also FAS-L, which contributes to hepatocyte apoptosis and thus liver damage. Importantly, these hepatotoxic liver-resident CD8 + T cells are primarily found in patients with HBV replication and liver inflammation, while their quantity and activation signature substantially decreased with reduced viral replication and liver inflammation during antiviral therapy ( Figure 1B ).…”

“…In contrast to protective HBV-specific CD8 + T cells, the exact nature and pathogenic mechanisms of nonspecific bystander CD8 + T cells have obtained little attention during the last twenty years. In this issue of the JCI , Nkongolo et al ( 13 ) now focus on bystander CD8 + T cells in chronic HBV infection by taking advantage of two methodological advances: liver cell sampling by fine-needle aspiration (FNA) and in-depth cell characterization by single-cell RNA sequencing (scRNA-Seq) ( 13 ). FNA has minimal risks and causes little discomfort, allowing repeated application, and is able to provide a comprehensive picture of the intrahepatic immune landscape ( 14 ).…”

“…FNA has minimal risks and causes little discomfort, allowing repeated application, and is able to provide a comprehensive picture of the intrahepatic immune landscape ( 14 ). Nkongolo et al ( 13 ) performed scRNA-Seq in longitudinal FNAs from patients with chronic HBV infection, high viral load, and liver inflammation who were starting antiviral therapy with tenofovir. By comparing the frequencies of cell populations before antiviral treatment when liver inflammation was pronounced and at 24 weeks on treatment when liver inflammation had resolved, they identified a distinct CD8 + T cell population that was associated with inflammation and fibrosis.…”

“…Importantly, these hepatotoxic liver-resident CD8 + T cells are primarily found in patients with HBV replication and liver inflammation, while their quantity and activation signature substantially decreased with reduced viral replication and liver inflammation during antiviral therapy ( Figure 1B ). In consequence, flow cytometry analysis can identify the hepatotoxic CD8 + T cell population only in patients with active disease before therapy, not in patients undergoing antiviral treatment ( 13 ).…”