Programmed Death Ligand-1 (PD-L1) Is an Independent Negative Prognosticator in Western-World Gallbladder Cancer

SIMPLE SUMMARY: Gallbladder cancer (GBC) is an aggressive malignancy with poor prognosis. Currently, therapeutic options are mostly limited to palliative chemotherapy. Considering the advances of immunotherapy, we assessed the expression of the programmed cell death ligand-1 (PD-L1) as the most widely used predictive marker for immunotherapy response in a large Western-world GBC cohort. Additionally, we quantified the expression of the T-cell immunoreceptor with Ig and ITIM domains TIGIT/CD155 axis as an emerging immune checkpoint. Our results indicate that PD-L1 is heterogeneously expressed in Western-world GBC and associated with distinct histomorphological tumor subtypes and increased immune cell densities. We show that a high tumoral PD-L1 expression is a significant negative prognosticator. In a subset of patients, we identified expression of TIGIT in scattered immune cells, which correlated with tumoral expression of its ligand CD155. Our results suggest a subset of GBC patients to be candidates for immunotherapy via (combined) PD-L1 and TIGIT/CD155 inhibition. ABSTRACT: Inhibition of the programmed cell death protein-1/ligand-1 (PD-1/PD-L1) axis has opened a new era in the treatment of solid cancers. However, there is no data on the expression and relevance of PD-L1 in Western gallbladder cancer (GBC). We assessed PD-L1 immunohistochemically in 131 GBC patients as Tumor Proportion Score (TPS), Immune Cell Score (IC) and Combined Positivity Score (CPS). Tumor cells expressed PD-L1 in a subset of 14.7% GBC patients at a TPS cut-off of 1%. Higher PD-L1 levels above 10% and 25% TPS were reached in 4.7% and 3.1% of GBC cases, respectively. At a 10% cut-off, TPS was associated with distinct histomorphological subtypes and correlated with poor tumor differentiation. Survival analysis revealed a TPS above 10% to be a highly significant and independent negative prognosticator in GBC. PD-L1 expression was associated with increased CD4(+), CD8(+) and PD-1(+) immune cell densities. In 14.8% of the cases, scattered immune cells expressed T-cell immunoreceptor with Ig and ITIM domains (TIGIT), which was correlated to tumoral expression of its ligand CD155. We here show that a high PD-L1 expression confers a negative prognostic value in Western-world GBC and highlight the TIGIT/CD155 immune checkpoint as a potential new target for GBC immunotherapy.