PD-L1 expression correlates with tumor-infiltrating lymphocytes and better prognosis in patients with HPV-negative head and neck squamous cell carcinomas

Introduction The importance of immune tumor microenvironment in the prognosis of patients with head and neck squamous carcinomas (HNSCC) is increasingly recognized. We analyzed the prognostic relevance of PD-L1 and PD-1 expressions in relation to the infiltration by CD8(+) and FOXP3(+) tumor-infiltrating lymphocytes (TILs). Methods Samples from 372 surgically treated HPV-negative HNSCC patients were evaluated by immunohistochemistry for PD-L1 expression [both tumor proportion score (TPS) and combined proportion score (CPS)], PD-1 expression in immune cells, and density of infiltrating CD8(+) and FOXP3(+) TILs. PD-L1 expression and CD8(+) TIL density were combined to establish the type of tumor microenvironment. Results 29.5% cases exhibited PD-L1 TPS positivity (>= 1%), whereas PD-L1 CPS positivity (>= 1%) was observed in 40% cases. 47.5% cases showed positive PD-1 expression (>= 1%). PD-L1 and PD-1 positivity correlated with a high density of both CD8(+) and FOXP3(+) TILs. In univariate analysis, PD-L1 TPS positivity (P = 0.026), PD-L1 CPS positivity (P = 0.004), high density of CD8(+) TIL (P = 0.001), and high density of FOXP3(+) TIL (P = 0.004) were associated with a better disease-specific survival (DSS). However, in multivariate analysis, only high density of CD8(+) TIL was associated with a better DSS (P = 0.002). The type of tumor microenvironment correlated with DSS (P = .008), with the better DSS observed in cases with type I (PD-L1 CPS positivity and high density of CD8(+) TIL). Conclusions High infiltration by CD8(+) TIL is associated with better survival outcomes. Positive PD-L1 expression correlates with a high infiltration by TILs, explaining its association with better prognosis.