Intratumoral Cytotoxic T-Lymphocyte Density and PD-L1 Expression Are Prognostic Biomarkers for Patients with Colorectal Cancer

Abstract

Background and objectives: Cytotoxic T-lymphocyte (CTL)-mediated inflammatory response to tumors plays a crucial role in preventing the progression of some cancers. Programmed cell death ligand 1 (PD-L1), a cell-surface glycoprotein, has been reported to repress T-cell-mediated immune responses against tumors. However, the clinical significance of PD-L1 in colorectal cancer (CRC) remains unclear. Our aim was to elucidate the prognostic significance of PD-L1 expression and CD8+ CTL density in CRC. Materials and methods: CD8 and PD-L1 immunostaining was conducted on 157 pathologic specimens from patients with CRC. The CD8+ CTL density and PD-L1 expression within the tumor microenvironment were assessed by immunohistochemistry. Results: Tumor invasion (pT) was significantly correlated with intratumoral (p = 0.011) and peritumoral (p = 0.016) CD8+ CTLs density in the tumor microenvironment. In addition, there was a significant difference in the intensity of CD8+ CTLs between patients with and without distant metastases (intratumoral p = 0.007; peritumoral p = 0.037, T-test). Lymph node metastasis (pN) and TNM stage were significantly correlated with PD-L1 expression in CRC cells (p = 0.015, p = 0.029, respectively). Multivariate analysis revealed a statistically significant relationship between the intratumoral CD8+ CTL density and disease-free survival (DFS) (hazard ratio [HR] 2.06; 95% confidence interval [CI]: 1.01-4.23; p = 0.043). The DFS was considerably shorter in patients with a high expression of PD-L1 in cancer cells than those with a low expression (univariate HR 2.55; 95% CI 1.50-4.34; p = 0.001; multivariate HR 0.48; 95% CI 0.28-0.82; p = 0.007). Conversely, patients with high PD-L1 expression in tumor-infiltrating lymphocytes had a longer DFS in both univariate analysis (HR 0.25; 95% CI: 0.14-0.44; p < 0.001) and multivariate analysis (HR 3.42; 95% CI: 1.95-6.01; p < 0.001). Conclusion: The CD8+ CTL density and PD-L1 expression are prognostic biomarkers for the survival of patients with CRC.

Keywords: PD-L1 expression; colorectal cancer; cytotoxic T lymphocytes; prognosis; tumor microenvironment.

Figure 1

Representative images showing low density of intratumoral CD8+ (I-CD8+) cytotoxic T lymphocytes (CTLs) (red arrows) (A), high density of I-CD8+ CTLs (black arrows) (B), low density of peritumoral CD-8+ (P-CD8+) CTLs (black arrows) (C), and high density of P-CD8+ CTLs (red arrows) (D) in colorectal cancer (×400).

Figure 2

Kaplan–Meier curves of overall survival (OS) versus CD8+ cytotoxic T lymphocytes (CTLs) density in patients with colorectal cancer. Kaplan–Meier curves demonstrating an association between high intratumoral CD8+ (I-CD8+) (A) and peritumoral CD8+ (P-CD8+) CTLs density (B) versus five-year OS (p = 0.002, p = 0.011, respectively).

Figure 3

Expression patterns of PD-L1 within the tumor microenvironment of colorectal carcinoma. PD-L1 expression in normal colorectal mucosa (red arrows) (A,B). Low (black arrows) (C) and high (red arrows) (D) PD-L1 expression in cancer cells (CCs). Low (red arrows) (E) and high (black arrows) (F) PD-L1 expression on tumor-infiltrating lymphocytes (TILs).

Figure 4

Kaplan–Meier curves of overall survival (OS) versus PD-L1 expression in patients with colorectal cancer. Kaplan–Meier curves demonstrating an association between PD-L1 expression by cancer cells (CCs) (A) and by tumor-infiltrating lymphocytes (TILs) (B) versus five-year OS (p < 0.001).