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

Abstract

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.

Figure 1.. Gene expression of adaptive immune resistance markers in PDAC patients.

A heatmap of gene expression of adaptive immune resistance markers in PDAC patients from TCGA (n=152). Please also see Supplementary Fig. S2, Supplementary Table S1). Genes included in the heatmap are PD-L1 (CD274), IDO1, CTLA4, LAG3, CD276 (B7-H3), V-set domain containing T-cell activation inhibitor 1 (VTCN1; also known as B7-H4), CD70, Hepatitis A virus cellular receptor 2 (HAVCR2; also known as T-cell immunoglobulin and mucin-domain containing-3 (TIM-3)), CD40, CD47, tumor necrosis factor receptor superfamily member 18 (TNFRSF18I; also known as glucocorticoid-induced TNFR-related protein (GITR)), TIGIT, or LIGHT (also known as tumor necrosis factor superfamily member 14 (TNFSF14)). Each column is a sample.

Figure 2.. Five year survival based on gene expression in TCGA cohort (n = 152).

Kaplan-Meier plots of 5-year survival based on (A) PD-L1 (CD274) and IDO1 expression and (B) expression of other adaptive immune resistance markers in PDAC patients. Number of patients per group indicated in panel legend. Red curves correspond to marker-positive samples, and blue curves correspond to marker-negative samples. P-value and hazard ratio (HR) with corresponding confidence interval in the parentheses calculated by log-rank test. The p-value cutoff was 0.05.

Figure 3.. Pairwise Pearson’s correlation between immune markers in TCGA cohort (n=152).

(A-I) Scatter plots of pairwise expression between immune markers. The Pearson’s correlation coefficient (r) and corresponding p-value are shown at the top of each plot. The p-value cutoff is 0.05.

Figure 4.. The correlation of PD-L1 (CD274) and IDO1 with a Th1/IFNγ gene signature in TCGA cohort (n=152).

Heat map demonstrating the relationship of PD-L1/IDO1 and CD8A expression with markers of a Th1/IFNγ gene signature (beyond just IFNγ), such as IL12Rβ2 (IL12RB2), JAK2, and STAT1. Positive Pearson’s correlation coefficients are represented by red, and negative correlations are represented by blue in the figure.

Figure 5.. Five-year survival stratified by a combined analysis of immunomodulatory pathways and CD8A expression in TCGA cohort (n=152).

Survival is stratified by a combined analysis of immunomodulatory pathways and CD8A expression. (A) Survival based on high/low PD-L1 (CD274) expression and high/low CD8A expression. (B) Survival based on high/low IDO1 and high/low CD8A expression. Number of patients per group indicated in panel legend. P-value and hazard ratio (HR) with corresponding confidence interval in the parentheses calculated by log-rank test. The p-value cutoff is 0.05.

Figure 6.. Parallel analysis in an independent cohort of PDACs (n=33) using immunohistochemistry.

(A) Survival stratified by PD-L1 (CD274) and (B) IDO1 expression. (C) Survival based on PD-L1 (CD274) expression and IDO1 expression. (D) Survival based on PD-L1 (CD274) expression and high/low CD8A expression. (E) Survival based on IDO1 and high/low CD8A expression. Representative PD-L1 and IDO1 staining is shown in Supplementary Fig. S1. Number of patients per group indicated in panel legend. P-value and hazard ratio (HR) with corresponding confidence interval in the parentheses calculated by log-rank test. The p-value cutoff is 0.05.