Tumor-associated antigen-reactive T cells and clinical outcomes in head and neck squamous cell carcinoma treated with pembrolizumab plus chemotherapy

Blood-based biomarkers associated with clinical outcomes in patients with head and neck squamous cell carcinoma (HNSCC) treated with pembrolizumab plus chemotherapy remain poorly defined. We investigated 38 patients with HNSCC treated with pembrolizumab plus 5-fluorouracil and platinum (FP). Baseline systemic inflammation and immune status were assessed using routine laboratory parameters. Peripheral blood mononuclear cells were analyzed by flow cytometry to assess exhaustion- and activation-associated markers on CD4⁺ and CD8⁺ T cells, including CD38, Tim-3, PD-1, and ICOS. Tumor-associated antigen (TAA)-reactive immune responses were evaluated by interferon-γ production following stimulation with epidermal growth factor receptor (EGFR)- and c-Met-derived peptides. PD-L1 CPS positivity, elevated neutrophil-to-lymphocyte ratio, and higher frequencies of CD8⁺CD38⁺ T cells were associated with clinical outcomes, with similar trends observed for selected inflammatory and peripheral T-cell activation/exhaustion-associated markers. Tumor-associated antigen-reactive immune responses were detected in a subset of patients and were associated with prolonged progression-free survival, while EGFR peptide reactivity was additionally associated with improved overall survival. In this exploratory study, immune reactivity to TAAs was associated with favorable clinical outcomes in patients receiving pembrolizumab plus FP. Together with systemic inflammation and peripheral T-cell activation/exhaustion markers, these findings support further evaluation of integrated blood-based immune profiling, including TAA-reactive immune responses, as candidate biomarkers in larger prospective cohorts.