CD8A and head and neck squamous cell carcinoma: Patients harboring higher level of PD-1 expression showed a significantly improved OS (Fig. 7B, P = 0.032), Based on the prognostic value of activated CD8+ T cells, we calculated ssGSEA score of activated CD8+ T cells in HNSCC patient samples and divided them into high activated CD8+ T cells group and low activated CD8+ T cells group with the median cutoff.