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

Abstract

<i>Background and objectives:</i> 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. <i>Materials and methods</i>: 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. <i>Results:</i> Tumor invasion (pT) was significantly correlated with intratumoral (<i>p</i> = 0.011) and peritumoral (<i>p</i> = 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 <i>p</i> = 0.007; peritumoral <i>p</i> = 0.037, T-test). Lymph node metastasis (pN) and TNM stage were significantly correlated with PD-L1 expression in CRC cells (<i>p</i> = 0.015, <i>p</i> = 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; <i>p</i> = 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; <i>p</i> = 0.001; multivariate HR 0.48; 95% CI 0.28-0.82; <i>p</i> = 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; <i>p</i> < 0.001) and multivariate analysis (HR 3.42; 95% CI: 1.95-6.01; <i>p</i> < 0.001). <i>Conclusion</i>: The CD8+ CTL density and PD-L1 expression are prognostic biomarkers for the survival of patients with CRC.