Overexpression and gene amplification of PD-L1 in cancer cells and PD-L1+ immune cells in Epstein–Barr virus-associated gastric cancer: the prognostic implications

Abstract

Cancer cells use PD-L1 to evade antitumor immunity through interaction with programmed cell death protein 1 (PD-1) on T cells. Recent whole-genome sequence studies revealed frequent gene amplification of PD-L1 in Epstein-Barr virus-associated gastric cancer (EBVaGC). To investigate the significance of PD-L1 in cancer cells and their microenvironment in EBVaGC, we studied PD-L1 expression by analysis of the public database and immunohistochemistry with fluorescent in situ hybridization (FISH) of the PD-L1 gene. Analysis of the database from The Cancer Genome Atlas also disclosed high expression of PD-L1 in EBVaGC compared with other molecular subtypes of GC. Expression of PD-L1 was frequently detected in cancer cells of EBVaGC (33/96; 34%), with infiltration of PD-L1 immune cells in its stroma (43/96; 45%). Both expression of PD-L1 in cancer cells and PD-L1 immune cell infiltration in EBVaGC were significantly correlated with diffuse histology according to Lauren's classification and tumor invasion (pT1b or more). As a prognostic indicator, PD-L1 expression in cancer cells correlated with poor outcomes in both overall survival and disease-specific survival (P=0.0498, 0.007). PD-L1-positive cancers had dense infiltration of PD-L1 immune cells as well as CD8 and PD-1 cells in EBVaGC. FISH analysis of representative samples of the tumor demonstrated gene amplification of PD-L1 in 11% of cases. PD-L1-amplified cells corresponded to PD-L1-positive cells showing high-intensity immunohistochemical staining among cancer cells showing weak or moderate intensities. Taken together, PD-L1 expression in cancer cells and their microenvironment may contribute to the progression of EBVaGC, and gene amplification occurs as clonal evolution during progression. This specific subtype of GC infected with EBV is potentially a good candidate for immunotherapy targeting of the PD-L1/PD-1 axis.

Gastric cancer: Basic aspects

“…Further IHC analysis of a large series of 232 GCs from Japan showed that EBVaGC (42% of the series) had higher PD‐L1 expression in tumor cells (34%) and in immune cells from the tumor stroma (45%) than non‐EBVaGC. In EBVaGC, PD‐L1 expression in tumor and immune cells was associated with the diffuse histologic type, tumor invasion depth, and poor patient prognosis . Also corroborating the TCGA results, 11% of EBVaGC had PD‐L1 gene amplification.…”

“…Similarly, Saito et al . analyzed the TCGA database and showed that EBVaGC express higher levels of PD‐L1 mRNA than the other TCGA GC subtypes.…”

Multiparametric immune profiling in HPV– oral squamous cell cancer

“…In contrast to our data, an inverse correlation between tumor PD-L1 expression and outcome of HNSCC patients has recently been shown in a Chinese cohort (42), which might be at least partially explained by the lack of distinction of the HPV status and/or a distinct pathogenesis among ethnic groups. This might be of great impact, as high PD-L1 expression levels can be mediated by external stimuli, including cytokines secreted from immune cells, or intrinsic constitutive expression due to gene amplification (43), utilization of an ectopic promoter by translocation (44), disruption of the 3′ untranslated region of PD-L1 (45), or aberrant signaling pathways (46). Based on our previous data in melanoma (32), we investigated the ratios as well as the spatial relationship between CD8 + T cells and immune suppressors.…”

CD8 T‐cell regulation by T regulatory cells and the programmed cell death protein 1 pathway

“…In fact, high PD‐L1 levels on retrovirus‐infected cells result in evasion of cytotoxic killing, demonstrating that PD‐L1 expression by target cells can ultimately determine their elimination . Moreover, various cancers can override cytotoxic elimination by a mechanism dependent on tumour PD‐L1 over‐expression, which can be the result of aberrant PD‐L1 gene amplification . Therefore, effective cytotoxic control is not only determined by CD8 T‐cell numbers and their intrinsic function and killing potential, but also by the susceptibility of the target cells themselves, which is greatly influenced by the expression of inhibitory ligands.…”

“…27 Moreover, various cancers can override cytotoxic elimination by a mechanism dependent on tumour PD-L1 over-expression, which can be the result of aberrant PD-L1 gene amplification. [28][29][30][31] Therefore, effective cytotoxic control is not only determined by CD8 T-cell numbers and their intrinsic function and killing potential, but also by the susceptibility of the target cells themselves, which is greatly influenced by the expression of inhibitory ligands.…”