Expression of PD-L1 and CD4+ tumor-infiltrating lymphocytes predict survival in head and neck squamous cell carcinoma

Abstract

The clinical efficacy of immune checkpoint blockade has been recently demonstrated in a variety of cancer types. The aim of the present study was to characterize the expression profile of tumor-infiltrating lymphocytes (TILs) and programmed death-ligand 1 (PD-L1) in head and neck squamous carcinoma (HNSCC). A total of 63 patients with HNSCC were enrolled in the present study. CD3⁺ and CD4⁺ TILs and the expression of PD-L1 were detected by immunohistochemistry. PD-L1 mRNA levels were evaluated by reverse transcription-quantitative PCR analysis. The association of TILs and PD-L1 with patient clinicopathological characteristics was also assessed. CD3⁺ and CD4⁺ TILs were detected in 100% of the samples. CD3⁺ was the predominant subset of TILs. PD-L1 was expressed in 53 of 61 (86%) patients when a score of ≥1 on tumor cells was considered positive and in 28 patients (45.2%) when a score of >5 on tumor cells was considered positive. PD-L1 mRNA levels were determined to be significantly correlated with PD-L1 protein expression. Survival analysis demonstrated that high CD4⁺ TILs were associated with improved overall survival (OS) and disease-free survival (DFS), and furthermore, the association of high PD-L1 expression with unfavorable OS and DFS was statistically significant. Multivariate analysis identified CD4⁺ TILs and PD-L1 as prognostic markers for HNSCC. The results of the present study suggested that increased CD4⁺ TILs in HNSCC may be associated with improved outcomes, while high expression of PD-L1 may indicate unfavorable OS and DFS; thus, these factors may serve as predictors of the response to immune checkpoint therapy.

Keywords: PD-L1; head and neck squamous cell carcinoma; prognostic value; tumor-infiltrating lymphocytes.

Figure 1

Immunohistochemistry for tumor-infiltrating lymphocytes and PD-L1 staining in head and neck squamous cell carcinoma. Representative images and quantification of PD-L1, CD3⁺ and CD4⁺ cells (magnification, x200). ^**P<0.001. PD-L1, programmed death ligand 1.

Figure 2

Evaluation of PD-L1 mRNA expression in patients with HNSCC. (A) Bar plot representing the relative fold change of PD-L1 mRNA levels in HNSCC compared with adjacent normal tissues. (B) Correlation analysis of PD-L1 protein levels with PD-L1 mRNA levels (P<0.001). R, Spearman correlation coefficient; HNSCC, head and neck squamous cell carcinoma; PD-L1, programmed death ligand 1.

Figure 3

Prognostic significance of CD4⁺ TILs and PD-L1 protein expression in patients with head and neck squamous cell carcinoma. (A and B) Kaplan-Meier curves indicated that the number of CD4⁺ TILs was associated with (A) OS (P=0.0042) and (B) DFS (P=0.0037). (C and D) Association of PD-L1 expression with (C) OS and (D) DFS. The P-value was calculated by using the log-rank test. PD-L1, programmed death ligand 1; OS, overall survival; DFS, disease-free survival; TIL, tumor-infiltrating lymphocyte.