Circulating CD137 T Cell Levels Are Correlated with Response to Pembrolizumab Treatment in Advanced Head and Neck Cancer Patients.

Pembrolizumab, an anti-PD-1 antibody, has been approved as first-line treatment for recurrent or metastatic head and neck squamous cell carcinoma ((R/M) HNSCC). However, only a minority of patients benefit from immunotherapy, which highlights the need to identify novel biomarkers to optimize treatment strategies. CD137 T cells have been identified as tumour-specific T cells correlated with immunotherapy responses in several solid tumours. In this study, we investigated the role of circulating CD137 T cells in (R/M) HNSCC patients undergoing pembrolizumab treatment. PBMCs obtained from 40 (R/M) HNSCC patients with a PD-L1 combined positive score (CPS) ≥1 were analysed at baseline via cytofluorimetry for the expression of CD137, and it was found that the percentage of CD3CD137 cells is correlated with the clinical benefit rate (CBR), PFS, and OS. The results show that levels of circulating CD137 T cells are significantly higher in responder patients than in non-responders ( = 0.03). Moreover, patients with CD3CD137 percentage ≥1.65% had prolonged OS ( = 0.02) and PFS ( = 0.02). Multivariate analysis, on a combination of biological and clinical parameters, showed that high levels of CD3CD137 cells (≥1.65%) and performance status (PS) = 0 are independent prognostic factors of PFS (CD137 T cells, = 0.007; PS, = 0.002) and OS (CD137 T cells, = 0.006; PS, = 0.001). Our results suggest that levels of circulating CD137 T cells could serve as biomarkers for predicting the response of (R/M) HNSCC patients to pembrolizumab treatment, thus contributing to the success of anti-cancer treatment.