Hepatoma-intrinsic CCRK inhibition diminishes myeloid-derived suppressor cell immunosuppression and enhances immune-checkpoint blockade efficacy

Gut. 2018 May;67(5):931-944. doi: 10.1136/gutjnl-2017-314032. Epub 2017 Sep 22.

Abstract

Objective: Myeloid-derived suppressor cells (MDSCs) contribute to tumour immunosuppressive microenvironment and immune-checkpoint blockade resistance. Emerging evidence highlights the pivotal functions of cyclin-dependent kinases (CDKs) in tumour immunity. Here we elucidated the role of tumour-intrinsic CDK20, or cell cycle-related kinase (CCRK) on immunosuppression in hepatocellular carcinoma (HCC).

Design: Immunosuppression of MDSCs derived from patients with HCC and relationship with CCRK were determined by flow cytometry, expression analyses and co-culture systems. Mechanistic studies were also conducted in liver-specific CCRK-inducible transgenic (TG) mice and Hepa1-6 orthotopic HCC models using CRISPR/Cas9-mediated Ccrk depletion and liver-targeted nanoparticles for interleukin (IL) 6 trapping. Tumorigenicity and immunophenotype were assessed on single or combined antiprogrammed death-1-ligand 1 (PD-L1) therapy.

Results: Tumour-infiltrating CD11b+CD33+HLA-DR- MDSCs from patients with HCC potently inhibited autologous CD8+T cell proliferation. Concordant overexpression of CCRK and MDSC markers (CD11b/CD33) positively correlated with poorer survival rates. Hepatocellular CCRK stimulated immunosuppressive CD11b+CD33+HLA-DR- MDSC expansion from human peripheral blood mononuclear cells through upregulating IL-6. Mechanistically, CCRK activated nuclear factor-κB (NF-κB) via enhancer of zeste homolog 2 (EZH2) and facilitated NF-κB-EZH2 co-binding to IL-6 promoter. Hepatic CCRK induction in TG mice activated the EZH2/NF-κB/IL-6 cascade, leading to accumulation of polymorphonuclear (PMN) MDSCs with potent T cell suppressive activity. In contrast, inhibiting tumorous Ccrk or hepatic IL-6 increased interferon γ+tumour necrosis factor-α+CD8+ T cell infiltration and impaired tumorigenicity, which was rescued by restoring PMN-MDSCs. Notably, tumorous Ccrk depletion upregulated PD-L1 expression and increased intratumorous CD8+ T cells, thus enhancing PD-L1 blockade efficacy to eradicate HCC.

Conclusion: Our results delineate an immunosuppressive mechanism of the hepatoma-intrinsic CCRK signalling and highlight an overexpressed kinase target whose inhibition might empower HCC immunotherapy.

Keywords: Cellular Immunology; Hepatocellular Carcinoma; Immunotherapy.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blotting, Western
  • Carcinoma, Hepatocellular / immunology*
  • Carcinoma, Hepatocellular / metabolism
  • Cell Culture Techniques
  • Cyclin-Dependent Kinases / metabolism*
  • Cytokines / metabolism
  • Female
  • Flow Cytometry
  • Gene Expression Regulation, Neoplastic
  • Humans
  • Immunohistochemistry
  • Immunoprecipitation
  • Immunosuppression
  • Liver / pathology
  • Liver Neoplasms / immunology*
  • Liver Neoplasms / metabolism
  • Male
  • Mice
  • Mice, Transgenic
  • Myeloid-Derived Suppressor Cells / immunology*
  • Real-Time Polymerase Chain Reaction
  • Signal Transduction

Substances

  • Cytokines
  • Cyclin-Dependent Kinases
  • cyclin-dependent kinase-activating kinase