Circulating naïve and effector memory T cells correlate with prognosis in head and neck squamous cell carcinoma

T-cell memory is an important mechanism for long-term protection against diverse pathogens. Generation and persistence of memory T cells are vital components of anti-tumor immunity, given their ability to persist for prolonged durations, as well as activate and migrate rapidly. In the present study, we investigated the clinical and prognostic significance of T-cell subsets in the peripheral circulation of patients with head and neck squamous cell carcinoma (HNSCC). Moreover, we calculated the enrichment scores of T-cell subsets in primary tumor tissues and compared their clinical characteristics using a public database. Multivariate survival analyses of circulating T-cell parameters revealed that clinical parameters, except M factor, were not independent prognostic factors, whereas proportions of CD8⁺ T cells, naïve T cells (T_N s), effector memory T cells (T_EM s), and CD38⁺ CD8⁺ T cells were independent prognostic factors, suggesting the importance of these peripheral T-cell parameters as independent prognostic biomarkers. Consistent with these results, the T-cell enrichment analysis indicated that enrichment of CD8⁺ T_N s in the tumor microenvironment was an independent prognostic factor. Moreover, an ex vivo experiment demonstrated significantly less cytotoxic activity in CD38⁺ T cells than in CD38^- T cells. These findings suggest that T-cell memory-related parameters in both systemic immunity and the tumor microenvironment could be used as prognostic biomarkers regardless of clinical characteristics. Further characterization of circulating T cells would lead to the development of novel biomarkers for patients with HNSCC.