Programmed Cell Death Ligand-1 (PD-L1) and CD8 Expression Profiling Identify an Immunologic Subtype of Pancreatic Ductal Adenocarcinomas with Favorable Survival

Immune-checkpoint therapy has failed to demonstrate meaningful clinical benefit in unselected cases of pancreatic adenocarcinoma (PDAC), but a subset of PDACs are known to upregulate pathways involved in acquired immune suppression. Further delineation of immunologic subtypes of PDAC is necessary to improve clinical trial designs and identify patients who might benefit from immune-checkpoint therapy. We used clinical survival and RNA expression data from The Cancer Genome Atlas (TCGA) to investigate the relationship between immune-modulating pathways and immune subset markers and their impact on survival in PDAC patients. Of the adaptive immune-resistance pathways, expression of PD-L1 and IDO1 was individually associated with poor survival. Although CD8 expression alone was not correlated with survival, the combination of PD-L1^- and high CD8 expression identified a subtype with favorable survival. We further extended these observations using an independent PDAC cohort from our institution via IHC, again observing that the PD-L1^-/CD8^high subtype was associated with positive prognosis. Although PDAC is regarded as a poorly immunogenic cancer type, these findings infer that T-cell infiltration in the absence of adaptive immune-resistance pathways is a feature of long-term survival in PDAC and imply the importance of developing future immunotherapeutic strategies based on data-supported biomarkers to refine patient selection.