Enhancement of Tumor Antigen-specific T-cell Responses by Immune Checkpoint Blockade in Human Papillomavirus-related Head and Neck Squamous Cell Carcinoma

Background/Aim: Human papillomavirus (HPV)positive head and neck squamous cell carcinoma (HNSCC) is clinically and immunologically distinct from HPV-negative HNSCC. Herein, we investigated the presence of tumor antigens HPV E6/E7 and wild-type p53-specific T-cell responses, and the impact of immune checkpoint blockade in patients with HPV-positive HNSCC. Materials and Methods: Peripheral blood mononuclear cells (PBMCs) from patients with HPV-positive HNSCC were stimulated with HPV E6/E7 or wild-type p53-derived peptide mixture and evaluated using the interferon-gamma enzyme-linked immunosorbent spot assay. Flow cytometry was performed to analyze the proportion of T-cell subsets and T cells expressing immune checkpoint molecules. Results: HPV E6/E7-specific T cells were detected in 22 (95.7%) of 23 patients, whereas wildtype p53-specific T cells were detected in 3 (15.0%) of 20 patients. Seven (43.8%) of 16 patients exhibited wild-type p53-specific T-cell responses, as determined using whole proteins instead of peptides. Immune checkpoint blockade enhanced wild-type p53-specific T-cell responses in 9 (45.0%) of 20 patients. Flow cytometric analysis of PBMCs revealed that responders exhibiting enhanced wild-type p53specific T-cell responses following immune checkpoint blockade had a significantly higher proportion of Ki 67+CD4+ T cells, Ki-67+CD8+ T cells, regulatory T cells, PD-1+CD4+ T cells, and TIM-3+CD4+ T cells than nonresponders. Conclusion: Our findings indicate that tumor antigen-specific T cells are present in the peripheral blood of patients with HPV-positive HNSCC. Blockade of checkpoint pathways can enhance T-cell responses in certain patients, probably via activated T cells, Tregs, and/or exhausted CD4+ T cells.