Single-Cell Omics to Reveal Mechanisms of Response to Immunotherapy in Head and Neck Cancer

The body's natural defense system is designed to recognize and eliminate altered or foreign cells, including cancerous ones. However, cancer cells can occasionally evade this system, allowing them to develop and progress. Immunotherapy, particularly immune checkpoint blockade (ICB) therapy enhances the immune system's ability to detect and attack cancer cells by releasing the brakes on the immune response, including PD-(L)1 and CTLA4. While ICB therapy has significantly improved cancer treatment, the majority of patients still does not respond or experiences relapse. To address this challenge, combining different agents, such as anti-PD-(L)1 and anti-CTLA4, is considered crucial. However, these combinations are often used without a complete understanding of their mechanisms or which patients would benefit the most.

To investigate the contribution of anti-CTLA4 to anti-PD-L1 therapy, we conducted a neoadjuvant window-of-opportunity study in head and neck squamous cell carcinoma (HNSCC). Analysis of tumor biopsies before and after treatment using single-cell technologies revealed that T-cell expansion serves as an early response biomarker. Whereas anti-PD-L1 primarily expanded CD8+ T-cells, combination therapy expanded both CD4+ and CD8+ T-cells, with CD4+ T-cells exhibiting an activated T-helper 1 phenotype. Spatial profiling of CD4+ and CD8+ T-cells revealed that they were surrounded by dendritic cells expressing T-cell attracting factors or antibody-producing plasma cells.

We found that this environment existed already before treatment in patients who responded to anti-PD-L1 therapy, which was further augmented by the therapy. Conversely, combining anti-CTLA4 with anti-PD-L1 seems to trigger a de novo immune response by activating CD4+ T-cells in tumor-draining lymph nodes, which subsequently migrate to the tumor. This highlights the potential efficacy of combined anti-PD-L1/anti-CTLA4 therapy, especially for patients who initially failed to mount an anti-tumor immune response.

In conclusion, this research sheds light on the complexities of ICB therapies, offering valuable insights into their mechanisms and paving the way for informed advancements in the treatment of HNSCC and potentially other cancer types as well.