Abundant PD-L1 expression in Epstein-Barr Virus-infected gastric cancers

Abstract

Gastric cancer (GC) is a deadly disease with limited treatment options. Recent studies with PD-1 inhibition have shown promising results in GC, but key questions remain regarding which GC subclass may respond best. In other cancers, expression of the PD-1 ligand PD-L1 has been shown to identify cancers with greater likelihood of response to PD-1 blockade. We here show with immunohistochemistry that Epstein-Barr Virus (EBV)+ GCs (n = 32) have robust PD-L1 expression not seen in other GCs. In EBV+ GC, we observed PD-L1 staining in tumor cells in 50% (16/32) and immune cells in 94% (30/32) of cases. Among EBV-negative GCs, PD-L1 expression within tumors cells was observed only in cases with microsatellite instability (MSI), although 35% of EBV-/MSS GCs possessed PD-L1 expression of inflammatory cells. Moreover, distinct classes of GC showed different patterns of PD-L1+ immune cell infiltrations. In both EBV+ and MSI tumors, PD-L1+ inflammatory cells were observed to infiltrate the tumor. By contrast, such cells remained at the tumor border of EBV-/MSS GCs. Consistent with these findings, we utilized gene expression profiling of GCs from The Cancer Genome Atlas study to demonstrate that an interferon-γ driven gene signature, an additional proposed marker of sensitivity to PD-1 therapy, were enriched in EBV+ and MSI GC. These data suggest that patients with EBV+ and MSI GC may have greater likelihood of response to PD-1 blockade and that EBV and MSI status should be evaluated as variables in clinical trials of these emerging inhibitors.

Keywords: EBV-infected gastric cancers; MSI gastric cancer; PD-1 inhibitors; PD-L1.

Conflict of interest statement

SD, XL, XX, MCC, AMC, ES, FS, TF, SJR, CSR and AJB: no conflicts of interest. GJF receives patent licensing fees on the PD-1 pathway from Bristol-Myers-Squibb, Roche, Merck, EMD-Serrono, Boehringer-Ingelheim, Amplimmune/AstraZeneca, and Novartis. GJF has served on scientific advisory boards for CoStim, Novartis, Roche, and Bristol-Myers-Squibb.

Figures

Figure 1. PD-L1 expression (IHC) staining of whole tissues slides of FFPE EBV+ GC and MSI GCs

(A) EBV+ GC with 9p24.1 amplification (amp) has abundant PD-L1 expression of tumor cells. (B) EBV+ GC and MSI GC (C) with PD-L1+ immune cells with a tumor infiltrating infiltration pattern (TI). (D) MSI GCs with PD-L1+ immune cells exclusively at the invasive margin (IM) (D). Magnification 20×, insert indicates area of higher magnification. Associations between EBV status and PD-L1 expression in TCGA study (E) and validation series (F).

Figure 2

Supervised hierarchical cluster analyses (A) and gene set enrichment analyses (GSEA) (B) shows enrichment of IFN-γ response genes in EBV+ GCs. (C) Single sample gene set enrichment (GSE) analyses shows IFN-γ GSE in EBV+ and MSI GCs (left), IFN-γ GSE in GCs with and without 9p24.1 amplification (middle, cases with 9p24.1 amplification indicated in red) and absence of an association between IFN-γ GSE and mutational load in genomic stable (GS) and chromosomal instable (CIN) GCs (right).