Survival analysis with regard to PD-L1 and CD155 expression in human small cell lung cancer and a comparison with associated receptors

Abstract

Immune checkpoints expressed on tumor cells may suppress the cytotoxicity of tumor-infiltrating lymphocytes (TILs) via interaction with their ligands. In the present study, checkpoint proteins and ligands, including programmed death-1 (PD-1), programmed death ligand-1 (PD-L1), cluster of differentiation (CD)155 and T cell immunoreceptor with immunoglobulin and ITIM domains (TIGIT) were systematically analyzed in patients with small cell lung cancer (SCLC). Furthermore their clinicopathological features and survival rates were investigated. Immunohistochemistry was performed in order to analyze the expression of PD-L1, CD155, PD-1 and TIGIT in 60 patients with SCLC, and survival analyses were performed using the Kaplan-Meier method and Cox proportional hazards model. It was reported that CD155/TIGIT and PD-L1/PD-1 were highly expressed on tissues of surgically resected SCLC. High expression levels of PD-L1, CD155 or PD-L1+CD155 were significantly associated with shorter survival. However, high expression levels of PD-1 or TIGIT exhibited no obvious association with shorter survival time. Moreover, patients with SCLC in whom PD-L1 and CD155 levels were highly expressed had the shortest survival rate. Multivariate survival analysis revealed that highly expressed PD-L1 [hazard ratio (HR)=2.55, 95% confidence interval (CI)=1.18-5.51, P=0.017] and CD155 (HR=2.40, 95% CI=1.05-5.50, P=0.038) were independent prognostic factors for overall survival (OS) time in SCLC. In addition, it was reported that TIGIT and PD-1, the receptors of CD155 and PD-L1, respectively, were also constitutively expressed on CD8⁺ TILs and tumor cells in SCLC. High expression levels of PD-L1 and CD155 were independent prognostic factors for OS time in patients with SCLC.

Keywords: cancer immunotherapy; cluster of differentiation 155; immune checkpoint; programmed death ligand-1; small cell lung cancer.

Figure 1.

Association between co-stimulatory (CD226) and co-inhibitory (PD-1, TIGIT, CD96 and CD112R) molecules and their ligands (PD-L1, CD112 and CD155) in the tumor microenvironment. CD, cluster of differentiation; PD, programmed death; PD-L, programmed death ligand; TIGIT, T cell immunoreceptor with immunoglobulin and ITIM domains; MHC, major histocompatibility complex; NK, natural killer; TCR, T cell receptor.

Figure 2.

Expression of PD-L1, PD-1, CD155 and TIGIT in SCLC detected by immunohistochemistry (left panels, magnification, ×200; right panels, magnification, ×400). CD, cluster of differentiation; PD, programmed death; PD-L, programmed death ligand; TIGIT, T cell immunoreceptor with immunoglobulin and ITIM domains.

Figure 3.

Kaplan-Meier curves comparing OS rates between the high and low expression groups of PD-L1, PD-1, CD155 and TIGIT. SCLC patients with higher PD-L1 expression (PD-L1-high group) tended to have a shorter OS (16.26±2.91 months) compared with the PD-L1-low group (36.43±6.46 months; P=0.001). SCLC patients with higher CD155 expression (CD155-high group) tended to have a shorter OS (16.20±2.42 months) compared with the CD155-low group (29.87±3.66 months; P=0.002). Furthermore, patients were divided into three groups based on the expression levels of CD155 and PD-L1. The OS of SCLC patients with PD-L1 or CD155 overexpression (26.70±6.99 months) tended to be shorter compared with patients with low expression levels of both (38.82±2.67 months), and the OS of patients who had high expression levels of PD-L1 and CD155 was poorest (13.13±2.53 months) (P<0.001). In the PD-1 and TIGIT high or low expression groups, there were no significant associations with survival time. Low or high-censored indicates censored data in the low/high expression groups. These censored data represent patients with SCLC who were lost to follow-up or still alive at the end of the follow-up time. CD, cluster of differentiation; PD, programmed death; PD-L, programmed death ligand; TIGIT, T cell immunoreceptor with immunoglobulin and ITIM domains; SCLC, small cell lung cancer; OS, overall survival.

Figure 4.

Immunofluorescence double staining of PD-1/TIGIT and CD8 in small cell lung cancer. Nuclear staining with DAPI (blue); CD8 staining with TRITC-goat anti-rabbit second antibody (red) or FITC-donkey anti-rabbit second antibody (green); PD-1 staining with FITC-goat anti-mouse second antibody (green); TIGIT staining with TRITC-donkey anti-goat second antibody (red). Sections were photographed at magnification, ×400. CD, cluster of differentiation; PD, programmed death; TIGIT, T cell immunoreceptor with immunoglobulin and ITIM domains; FITC, fluorescein isothiocyanate; TRITC, tetramethylrhodamine; TILs, tumor-infiltrating lymphocytes.