Study of the immunomodulatory effects of irradiation on human papillomavirus-driven vs. carcinogen-driven head and neck squamous cell carcinoma

PhD thesis defended by Christoph SCHIFFLERS (Prof. Carine MICHIELS & PD Angelika RIEMER) - 15/09/2023

Prof. Carine MICHIELS, UNamur, Department of biology, Laboratory of Cellular and Molecular Biology (URBC) 

PD Angelika Riemer, German Cancer Research Center (DKFZ), Immunotherapy and Immunoprevention

  • Prof. Carine Michiels, UNamur (supervisor)
  • PD Angelika Riemer, DKFZ (co-supervisor)
  • Prof. Nicolas Gillet, UNamur (president of the jury)
  • Prof. Sophie Lucas, UCLouvain (external member)
  • Prof. Maria Oliveira, University of Porto (external member)
  • Dr. Anne-Catherine Wéra, CHU UCL Namur (external member)

Infections with high-risk human papilloma viruses (HPV) cause an increasing rate of head and neck cancers. These HPV-driven (HPV+) cancers are associated with better outcome and treatment responses compared to their carcinogen-induced HPV- counterparts. However, high rates of tumor relapse and diagnosis at late stages limit the therapeutic outcome. Despite significant differences between HPV+ and HPV- head and neck squamous cell carcinomas (HNSCC), their treatments are the similar and most frequently involve radiation therapy (RT). In addition to cause cancer cell death and tumor shrinkage, RT modulates a plethora of biological processes that affects tumor control. Most notably, RT can induce an immunogenic form of cell death triggering an innate and subsequently adaptive anti-tumor immune response. While this can lead to systemic cancer cell eradication via CD8+ T cells, this phenomenon is rare and relies on multiple factors such as the immunogenicity of cancer cell death and tumor antigen presentation. It is also influenced by immunosuppressive mechanisms, such as the expression of inhibitory immune-checkpoint ligands. These processes can be altered in response to RT and thereby affect anti-tumor immunity. Whether they are regulated by the HPV remains unknown.

Therefore, this project aimed to assess the role of the HPV-status on the alterations of immunogenic and immune-suppressive mechanisms in response to head and neck cancer radiotherapy. We showed that RT promotes the induction of immunogenic cell death, regardless of the HPV-status. In addition, multiple immune-checkpoints and other immune-modulatory molecules at the surface of cancer cells can be overexpressed in response to irradiation. Particularly, our results evidenced that the induction of DNA double-strand breaks promotes the expression of PD-L1 in HPV- as well as metastatic/recurrent but not primary HNSCC cell lines, via DNA damage response signaling. In primary HNSCC cell lines, HPV was shown to interfere epigenetically with PD-L1 expression. Finally, to assess the therapeutic relevance of these observations, a new HPV-driven base of tongue tumor model was developed in immunocompetent MHC-humanized mice. Taken together, this study identified that the regulation of PD-L1 expression by HPV might be used as biomarker to identify HNSCC that could be candidates for combined radio-immunotherapy treatment. Further investigation is required to determine the therapeutic relevance of the regulation of PD-L1 expression by irradiation for the optimal design of radio-immunotherapy sequences for the treatment of head and neck cancer.