Prognostic significance of tumor-infiltrating immune cells and PD-L1 expression in esophageal squamous cell carcinoma

Abstract

Programmed death-1 receptor (PD-1) and its ligand (PD-L1) play an integral role in regulating the immune response against cancer. This study investigated the prognostic significance of PD-L1 expression on tumor cells and tumor-infiltrating immune cells (TILs) in the tumor microenvironment in Chinese patients with esophageal squamous cell carcinoma (ESCC). Archival formalin-fixed, paraffin-embedded ESCC samples from treatment-naïve patients with ESCC after surgery or by diagnostic endoscopic biopsy were collected between 2004 and 2014. Expression of PD-L1 in ESCC tumor specimens was assessed by immunohistochemistry (IHC), and the degree of TIL infiltration was evaluated by examining hematoxylin and eosin-stained (H&E) specimens. PD-L1+ as defined as ≥1% of tumor cell membranes showing ≥1+ intensity. In 428 patients, specimens from 341 (79.7%) were PD-L1+. In the definitive treatment group (patients who received curative esophagectomy or definitive [chemo-]radiation therapy), PD-L1 positivity was associated with a significantly shorter DFS and OS. In the palliative chemotherapy group exhibited, neither PFS nor OS correlated significantly with PD-L1 expression. PD-L1 expression was positively associated with TIL density. In 17 paired tumor tissues collected before and after treatment, an increase in PD-L1 expression was associated with disease progression, whereas a decrease in PD-L1 expression was associated with response to chemotherapy or disease control. So, PD-L1 expression was associated with a significantly worse prognosis in patients with ESCC. These observations suggest that PD-L1 may play a critical role in ESCC cancer progression and provide a rationale for developing PD-L1 inhibitors for treatment of a subset of ESCC patients.

Keywords: PD-L1; TILs; esophageal squamous cell carcinoma; prognostic factor; tumor microenvironment.

Figure 1. Tumor PD-L1 expressed at different levels in ESCC specimens

A. PD-L1 negative; B. ≥1% PD-L1-positive tumor cells with membrane staining of any intensity; C. ≥5% PD-L1-positive tumor cells with membrane staining of any intensity; D. ≥25% PD-L1-positive tumor cells with membrane staining of at least 2+ intensity.

Figure 2

A. PD-L1 mainly expresses on the membranes of the tumor cells; B. PD-L1 expresses on the membranes of tumor-infiltrating immune cells; C. PD-L1 expresses on stromal cells.

Figure 3. Different patterns of PD-L1 expression in ESCC specimens

A. Diffuse PD-L1 expression in the presence of TILs; B. Regional expression of PD-L1 colocalized with TILs; C. PD-L1 expression at the invasive front.

Figure 4. A & B: Correlation of PD-L1 expression and DFS/OS in the definitive treatment cohort

Figure 5. Kaplan–Meier survival curve for DFS and OS depending on TIL level: A & B: Correlation of TIL level and DFS/OS in the definitive treatment cohort

Figure 6. Changes in PD-L1 expression in paired specimens before and after different treatments: A-C: no treatment, H-score from 6 to 23; D-F: 2 cycles chemotherapy (just 1 sample showed an increase [red line]), H-score from 120 to 4; G-I: 4 or more cycles chemotherapy, H-score from 35 to 100

Figure 7. Changes of CD8+ A. and Foxp3+ B. lymphocytes in patients before and after chemotherapy (red line showed the decrease of CD8+ T cells and increase of Foxp3+ T cells)